Sensed signal strength for stimulation electrode selection

Abstract

Systems, devices, and techniques are configured to determine an electrode combination for delivering electrical stimulation. In one example, an IMD includes stimulation circuitry configured to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes and sensing circuitry configured to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes. The IMD may also include processing circuitry configured to determine that the signal satisfies a threshold, responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes, and control the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

Description

SENSED SIGNAL STRENGTH FOR STIMULATION ELECTRODE SELECTIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 712,070 filed October 25, 2024 which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This disclosure generally relates to electrode selection for an implantable medical device.BACKGROUND

[0003] Medical devices may be external or implanted, and may be configured to sense neural signals (e.g., central and peripheral nerves) and / or deliver electrical stimulation therapy to various tissue sites of a patient to treat a variety of symptoms or conditions such as, for example, one or more of chronic pain, tremor, Parkinson’s disease, other movement disorders, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, gastroparesis, sleep apnea, neural control of prosthetic devices, or stimulation to provide peripheral sensation. A medical device delivers electrical stimulation therapy via one or more leads that include electrodes located proximate to target locations associated with the brain, the spinal cord, pelvic nerves, peripheral nerves, or the gastrointestinal tract of a patient. For bipolar stimulation, the electrodes used for stimulation may be on one or more leads. For unipolar stimulation, the electrodes may include one or more leads and an electrode on a stimulator housing located remotely from the target site (e.g., near clavicle or near upper gluteus maximus). It may be possible to use leadless stimulation using electrodes mounted on the stimulator housing. Hence, electrical stimulation is used in different therapeutic applications, such as deep brain stimulation (DBS), spinal cord stimulation (SCS), pelvic floor stimulation, gastric stimulation, or peripheral nerve field stimulation (PNFS).

[0004] A clinician or processing circuitry may select one or more electrodes of the electrodes of the leads as stimulation electrodes wherein the electrical stimulation is delivered through the stimulation electrodes. The clinician or processing circuitry may additionally or alternatively select one or more electrodes of the electrodes of the leads as sensing electrodes wherein a response of the nerve or nearby tissue is recorded through the sensing electrodes.The electrodes on the leads may include one or more electrodes per lead and each electrode may be segmented into a smaller lead.SUMMARY

[0005] This disclosure describes example techniques for determining, or selecting, an electrode combination for delivering electrical stimulation. In some examples, one or more electrodes are closer (i.e., proximate) to a nerve of a patient, and selecting or recommending the electrodes closest to the nerve of the patient for stimulation electrodes may be beneficial for therapy. When implanting a lead, a clinician may attempt to place the lead parallel to the nerve, nerve bundle, or other tissue which they are trying to stimulate or otherwise modulate. In some examples, due to the local anatomy of a patient the lead is placed in a non-parallel orientation. With a non-parallel orientation, the lead may not be parallel to the nerve and some electrodes along the length of the lead may be closer to the nerve (or other target tissue) than the other electrodes of the lead. Identifying the electrodes which are closer than the other electrodes of the one or more electrodes may enable the clinician to select desired electrodes and / or perform other programming or lead selection for therapy delivery via the implanted lead and associated implantable medical device (IMD).

[0006] In one example, an implantable medical device (IMD) may be configured to deliver stimulation through one or more electrodes of one or more leads. The IMD may generate and deliver electrical stimulation through one or more electrodes of the electrodes of the lead and sense a response. The response, such as an evoked response, may be sensed via a different electrode combination (e.g., sensing electrodes), than the stimulation electrodes. The IMD, external programmer, or other device, may analyze the signal of the response to the test stimulation and determine which electrodes of the one or more electrodes are the closest (i.e., proximal / proximate) to the nerve (or otherwise the desired electrodes for delivering therapy). Selecting the electrodes which are closest to the nerve may decrease a stimulation magnitude needed to activate the nerve, may decrease a delay between stimulation and nerve activation, may decrease the power consumption of the IMD, and / or may increase a longevity of the electrodes and leads.

[0007] In one example, an implantable medical device includes: stimulation circuitry configured to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; sensing circuitry configured to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; and processing circuitry configured to: determine that the signalsatisfies a threshold; responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes; and control the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0008] In another example, a method includes: controlling, by processing circuitry, stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; controlling, by the processing circuitry, sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; determining, by the processing circuitry, that the signal satisfies a threshold; selecting, by the processing circuitry and responsive to determining that the signal satisfies the threshold, the set of sensing electrodes as a second set of stimulation electrodes; and controlling, by the processing circuitry, the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0009] In another example, a non-transitory computer-readable storage medium comprising instructions that, when executed by processing circuitry, cause the processing circuitry to: control stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; control sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; determine that the signal satisfies a threshold; responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes; and control the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0010] The details of one or more examples of the techniques of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. l is a conceptual diagram illustrating an example system that includes an implantable medical device (IMD) configured to deliver electrical stimulation to a patient according to an example of the techniques of the disclosure.

[0012] FIG. 2 is a block diagram of the example IMD of FIG. 1 for delivering electrical stimulation according to an example of the techniques of the disclosure.

[0013] FIG. 3 is a block diagram of the external device of FIG. 1 for communicating with a medical device according to an example of the techniques of the disclosure.

[0014] FIG. 4A is a conceptual diagram illustrating an example parallel sacral nerve lead placement.

[0015] FIG. 4B is a conceptual diagram illustrating an example non-parallel sacral nerve lead placement.

[0016] FIG. 5 is a flowchart illustrating an example method of selecting stimulation electrodes based on an evoked signal.

[0017] FIG. 6 is a flowchart illustrating an example operation of a medical device configured to adjust the stimulation electrodes, stimulation magnitude, stimulation parameters, and contacts based on electrode proximity and a magnitude of a response.

[0018] FIG. 7 is a flowchart illustrating an example technique for selecting electrodes based on a threshold from hyperpolarizing then depolarizing a nerve.

[0019] FIG. 8 is a flowchart illustrating an example technique for selecting electrodes based on a threshold for a nerve using short stimulation pulse widths.

[0020] FIG. 9 is a flowchart illustrating an example technique for selecting electrodes based on a threshold of a stimulus configured to elicit an evoked compound action potential (ECAP).

[0021] FIG. 10 is a flowchart illustrating an example technique for determining electrodes based on a threshold from unipolar stimulation.DETAILED DESCRIPTION

[0022] This disclosure describes example devices, systems, and techniques related to selecting electrodes of a medical device for electrical stimulation therapy (e.g., neuromodulation such as deep brain stimulation (DBS), spinal cord stimulation (SCS), sacral nerve stimulation (SNS), or peripheral nerve stimulation therapy). The electrical stimulation therapy may be delivered via multiple electrodes of one or more leads (e.g., cylindrical or paddle leads) implanted to provide stimulation in the brain, in the spinal cord, in the sacral nerve, or the tibial nerve of a patient. In some examples, electrical stimulation therapy is delivered via a leadless device. When implanting a lead, a clinician may attempt to place the lead parallel to the nerve or nerve bundle which they are trying to stimulate. Due to the local anatomy of a patient or other surgery complexities, the lead may be placed such that the lead is not parallel (i.e., non-parallel) with the nerve. If the lead is non-parallel to the desired nerve or other target tissue, then one or more electrodes of the one or more electrodes may be closerto the nerve than the other electrodes of the lead. Electrodes which are closer to the nerve may have a lower stimulation threshold while electrodes which are further from the nerve may have higher stimulation thresholds. Lower stimulation thresholds may decrease a stimulation magnitude to activate the nerve, may decrease a delay between stimulation and nerve activation, may decrease the power consumption of the IMD, and may improve a longevity of the leads and / or devices.

[0023] To select which electrodes to use as stimulation electrodes, the system may be configured to stimulate a nerve from a first electrode, or set of electrodes, and measure a first response of the nerve, a muscle near or innervated by the nerve, and / or the region surrounding the nerve. The system may then stimulate the nerve from a second electrode, or set of electrodes, and / or with a different electrical stimulation, and measure a second response of the nerve and / or the region surrounding the nerve. Based on a comparison between the first response and the second response or a comparison of either the first response or the second response to a threshold, the system may determine one or more electrodes which are closer to the nerve than one or more other electrodes. The one or more closer electrodes may be selected as the stimulation electrodes through which therapy is delivered, thereby potentially decreasing a stimulation magnitude to activate the nerve, decreasing a delay between stimulation and nerve activation, decreasing the power consumption of the IMD, and improving a longevity of the leads. Electrical stimulation therapy may additionally or alternatively be adaptively adjusted to continuously, or intermittently, perform the analysis to select the one or more electrodes closer to the nerve. The adaptive adjustments may be based on a posture or movement of the patient, the stimulation waveform or amplitude, and / or the sensing electrodes.

[0024] Determining which one or more electrodes are closer to the nerve than the other electrodes of the plurality of electrodes may include determining that a signal evoked by the electrical stimulation delivered by a first set of stimulation electrodes and sensed by sensing circuitry via a set of sensing electrodes selected from the plurality of electrodes, satisfies a threshold. If the threshold is satisfied, the first set of stimulation electrodes may be swapped with the set of sensing electrodes such that the first set of stimulation electrodes become sensing electrodes and the sensing electrodes become a second set of stimulation electrodes. Swapping the electrodes enables closer electrodes to be used as stimulation electrodes. Using closer electrodes as the stimulation electrodes decreases the thresholds for stimulation and may thereby increase longevity of the device and the leads.

[0025] Determining if the threshold is satisfied may be based on any potential combination of individual thresholds or processes which determine which electrodes of the plurality of electrodes are closest to the nerve. Determining which electrodes of the plurality of electrodes are closest to the nerve is complicated by the fact that for any individual combination of electrodes if the stimulation electrode is close but the sensing electrode is far away the signal may look small even though the stimulation electrode is close because the signal is attenuated before reaching the sensing electrode. Vice versa, if the sensing electrode is close but the stimulation electrode is far away the signal may look small because the stimulation signal is attenuated even though the sensing electrode is close to the neve.Therefore, for any individual combination of electrodes it can be difficult to know whether the signal is small because the sensing electrode is far away or because the stimulation electrode is far away, or both. To differentiate which electrode is closer, any potential combination of individual thresholds or processes may determine which electrodes of the plurality of electrodes are closest to the nerve.

[0026] In one example, the process involves hyperpolarizing a nerve, depolarizing the nerve, and then sensing a response. The stimulation electrodes are then changed (e.g., they may be flipped with the sensing electrodes) and the process of hyperpolarizing a nerve, depolarizing the nerve, and then sensing the response may be repeated. Such a process may reveal which electrodes are closer to the nerve because stimulation of the nerve via electrodes which are closer to the nerve may produce a greater amplitude of a response or greater magnitude of a difference. In some examples, an electrode proximal to the nerve may be desired as compared to an electrode distal to the nerve at hyperpolarizing the nerve. In some examples, the stimulation is a stimulation waveform configured to induce an ECAP. Such a stimulation waveform may reveal which electrodes are closer to nerve because stimulation electrodes which are closer may produce a greater amplitude of a response or greater magnitude of a difference. The process may additionally or alternatively involve delivering shorter pulses (e.g., <100ps pulses) via the stimulation electrodes. An electrical field elicited by stimulation from any one or more electrodes decreases with distance from one or more electrodes. The strength duration relationship for activation of any one or more nerves of the target nerve and / or neural tissue means that higher amplitudes may be needed to activate neurons using shorter pulse widths. The strength-duration relationship of neurons describes how the intensity of a stimulus and the length of time it is applied interact in whether a neuron triggers an action potential. This occurs because a neuron's membrane potential integrates inputs (e.g., charge) over time until it reaches an activation threshold needed to firean action potential. A higher amplitude stimulus may bring the membrane potential of the neuron to the activation threshold in less time, while a lower amplitude stimulus may bring the membrane potential to the activation threshold over a longer duration. Therefore, decreasing pulse width of a stimulation thereby increases an amplitude required to activate a neuron. In some examples, one or more electrodes sequentially or simultaneously deliver unipolar stimulation. Unipolar stimulation which is between an electrode and the can enables a single electrode to be tested at a time, whereas bipolar stimulation may have two electrodes. Since a single electrode may be tested at a time, unipolar stimulation enables the effects of an individual electrode to be isolated, and therefore the proximity of each electrode to be isolated. As such, two or more electrodes could individually, i.e., sequentially, deliver stimulation via unipolar stimulation and the responses to the stimulation could be ranked. Additionally or alternatively, every combination of electrodes could be tested and ranked to determine the best combination of stimulation and sensing electrodes.

[0027] FIG. 1 is a conceptual diagram illustrating an example system 100 that includes implantable medical device (IMD) 106 which may deliver therapy to and / or sense physiological signals from target tissue. The target tissue may include or be near spinal cord 128 and / or pelvic nerves 120 (e.g., a pudendal nerve or a sacral nerve), or any other nervous or muscle tissue that may be stimulated or from which physiological signals may be sensed of patient 112 through lead 114 (coupled to IMD 106 via connector 108). Lead 114 may carry a plurality of electrodes 116 at the distal end of lead 114. IMD 106 may provide neurostimulation to treat symptoms of patient 112, such as pain, fecal or urinary incontinence, erectile dysfunction, or other sexual dysfunction. IMD 106 may thus be configured to provide sacral nerve stimulation in one example.

[0028] In other examples, IMD 106 may be configured to deliver electrical stimulation to other nerves that may alleviate symptoms related to pelvic floor disorders. In one example, IMD 106 may be configured to deliver electrical stimulation to the tibial nerve (e.g., tibial nerve stimulation). Electrodes 116 may be implanted near a suitable portion of the tibial nerve, which may be located in a leg and / or ankle of patient 112. In some examples, some of electrodes 116 are configured to sense signals and others of electrodes 116 may be configured to deliver adaptive electrical stimulation to the target tissue. In other examples, all of electrodes 116 are configured to both sense signals and deliver adaptive electrical stimulation to nerve 120. In some examples, unipolar stimulation is possible where one electrode is a housing or otherwise on the housing (i.e., a can) of IMD 106.

[0029] Although the examples described in this disclosure are generally applicable to a variety of medical devices including external devices and IMDs, application of such techniques to IMDs and, more particularly, implantable electrical stimulators (e.g., neurostimulators) are described for purposes of illustration. More particularly, the disclosure will refer to a sacral nerve stimulation (SNS) for purposes of illustration, but without limitation as to other types of medical devices or other therapeutic applications of stimulation. System 100 may be configured to deliver one or more of deep brain stimulation (DBS), spinal cord stimulation (SCS), sacral nerve stimulation (SNS), tibial nerve stimulation (TNS), targeted drug delivery (TDD), pelvic stimulation, gastric stimulation, or peripheral nerve field stimulation (PNFS), or any other stimulation therapy capable of treating a condition of patient 112. Patient 112 ordinarily is a human patient. In some cases, however, therapy system 100 may be applied to other mammalian, non-mammalian, or non-human patients.

[0030] SNS, or other therapies such as DBS or TNS, may operate open loop or, alternatively, adaptive in the sense that IMD 106 may adjust, increase, or decrease the magnitude of one or more parameters of the SNS in response to changes in patient activity or movement, a severity of one or more symptoms of a disease of patient 112, a presence of one or more side effects due to the SNS, or one or more sensed signals of patient 112. For example, one example of system 100 is an SNS system with capabilities to both deliver stimulation and sense intrinsic neuronal signals. System 100 may provide for “closed-loop” therapy where IMD 106 may continuously monitor the state of certain biomarker signals and deliver stimulation according to pre-programmed routines based on the biomarker signals.

[0031] Therapy system 100 may be implanted into other regions or otherwise provide therapy to manage symptoms or provide treatment of other patient conditions, such as, but not limited to, seizure disorders (e.g., epilepsy) or mood (or psychological) disorders (e.g., major depressive disorder (MDD), bipolar disorder, anxiety disorders, post-traumatic stress disorder, dysthymic disorder, and obsessive-compulsive disorder (OCD)) as well as, for example, neural control of prosthetic devices or stimulation to provide sensory feedback to patient 112. At least some of these disorders may be manifested in one or more patient movement behaviors. A movement disorder or other neurodegenerative impairment may include symptoms such as, for example, muscle control impairment, motion impairment or other movement problems, such as rigidity, spasticity, bradykinesia, rhythmic hyperkinesia, nonrhythmic hyperkinesia, and akinesia. In some cases, the movement disorder may be asymptom of Parkinson’s disease. However, the movement disorder may be attributable to other patient conditions.

[0032] IMD 106 includes a therapy module (e.g., which may include processing circuitry, signal generation circuitry, or other electrical circuitry configured to perform the functions attributed to IMD 106) that includes a stimulation generator configured to generate and deliver electrical stimulation therapy to patient 112 via a subset of electrodes 116 of lead 114. The subset of electrodes 116 that are used to deliver electrical stimulation to patient 112, and, in some cases, the polarity of the subset of electrodes 116 may be referred to as a stimulation electrode combination. The stimulation electrode combination may be selected for a particular patient 112 and target tissue site (e.g., selected based on the patient condition or selected based on the lead orientation with respect to nerve 120). The group of electrodes 116 includes at least one electrode and may include a plurality of electrodes. In some examples, the plurality of electrodes 116 have a complex electrode geometry such that two or more electrodes are located at different positions around the perimeter of the respective lead.

[0033] In some examples, sensed signals reflect changes in electrical current produced by the sum of electrical potential differences among nerves, such as nerve 120, in the region. Examples of neurological signals include, but are not limited to, bioelectric signals generated from local field potentials (LFP) sensed within one or more regions near nerve 120. In some examples, IMD 106 employ electroneurogram (ENG) to measure a response of the muscles near nerve 120 or innervated by nerve 120. An electroneurogram may record the electrical activity of neurons of the central nervous system (brain and spinal cord) or the peripheral nervous system (nerves and ganglions). An ENG may include involves placing electrodes in or proximate neural tissue to record the electrical signals generated by neural tissue. In other examples, IMD 106 may sense evoked signals, such as evoked compound action potentials (ECAPs), evoked resonant neural activity (ERNA), electromyogram (EMG), etc.

[0034] Electrical stimulation generated by IMD 106 may be configured to manage a variety of disorders and conditions. In some examples, the stimulation generator of IMD 106 is configured to generate and deliver electrical stimulation pulses to patient 112 via electrodes of a selected stimulation electrode combination. However, in other examples, the stimulation generator of IMD 106 may be configured to generate and deliver a continuous wave signal, e.g., a sine wave or triangle wave. In either case, a stimulation generator within IMD 106 may generate the electrical stimulation therapy for SNS according to a selected therapy program. In examples in which IMD 106 delivers electrical stimulation in the form of stimulation pulses, a therapy program may include a set of therapy parameter values (e.g.,stimulation parameters), such as a stimulation electrode combination for delivering stimulation to patient 112, pulse frequency, pulse width, and a current or voltage amplitude of the pulses. As previously indicated, the electrode combination may indicate the specific electrodes 116 that are selected to deliver stimulation signals to tissue of patient 112 and the respective polarities of the selected electrodes. The electrical stimulation generated by IMD 106 may generate, for example, burst pulses, interleaved pulses, or concurrent pulses.

[0035] In some examples, electrodes 116 are radially-segmented electrodes. Radially-segmented electrodes refer to electrodes that are segmented radially along the lead. As one example, lead 114 may include a first set of electrodes 116 arranged circumferentially around lead 114 that are all at the same height level on lead 114. Each of electrodes 116 in the first set of electrodes 116 is a separate segmented electrode and form a level of radially-segmented array of electrodes. Lead 114 may include a second set of electrodes arranged circumferentially around lead 114 that are all at the same height level on lead 114. Each of the electrodes 116 in the first set of electrodes is a separate segmented electrode and form a level of radially-segmented array of electrodes. Segmented electrodes 116 may be beneficial for directional stimulation and sensing.

[0036] IMD 106 may be implanted within a subcutaneous pocket, or at any other suitable site within patient 112. Generally, IMD 106 is constructed of a biocompatible material that resists corrosion and degradation from bodily fluids. IMD 106 may include a hermetic housing to substantially enclose components, such as a processor, therapy module, and memory.

[0037] System 100 may additionally include an implanted lead extension coupled to IMD 106 via connector 108 (also referred to as a connector block or a header of IMD 106). In the example shown in FIG. 1, lead 114 is implanted near a sacral region of the spinal cord of patient 112 in order to deliver electrical stimulation to one or more regions of nerve 120, which may be selected based on the patient condition or disorder controlled by therapy system 100. The specific target tissue site and the stimulation electrodes used to deliver stimulation to the target tissue site, however, may be selected, e.g., according to the identified patient behaviors and / or other sensed patient parameters. For example, the target tissue site may be the location of bioelectric signals includes a signal component of interest. The stimulation electrodes used to deliver stimulation to the target tissue site may be those that are most proximal to a source of the signal component of interest, e.g., using the example techniques described in this disclosure. Other lead 114 and IMD 106 implant sites are suitable depending on clinical application or target tissue / nerve.

[0038] Existing lead sets include axial leads carrying ring electrodes disposed at different axial positions and so-called “paddle” leads carrying planar arrays of electrodes. In some examples, lead 114 includes electrode combinations within an axial lead, a paddle lead, or among two or more different leads. Alternatively, more complex lead array geometries may be used. Electrodes 116 may additionally or alternatively be cuff electrodes wrapped around the sacral (or other pelvic) nerve.

[0039] Lead 114 may be coupled to a common lead extension (not shown) wherein the common lead extension extends from connector 108 to any point closer to the implant site or region of interest, wherein one or more leads 114 may be connected to the common lead extension. The common lead extension enables IMD 106 to be implanted at a site distal to the region of interest while enabling the one or more leads 114 to extend a shorter distance than they would otherwise extend. In other examples, one or more leads 114 may be coupled to IMD 106 via separate lead extensions or directly to connector 108. Lead 114 may be positioned to deliver electrical stimulation to one or more target tissue sites within nerve 120 to manage patient symptoms associated with a movement disorder of patient 112. Lead 114 may be implanted to position electrodes 116 at suitable locations of nerve 120 through respective holes in hip 124. Leads 114 may be placed at any location along nerve 120 such that electrodes 116 are capable of providing electrical stimulation to target tissue sites along nerve 120 during treatment. For example, electrodes 116 may be surgically implanted by inserting lead 114 through sacral foramina 126 of hip 124 of patient 112. Specifically, lead 114 may be inserted from a dorsal side of hip 124 through a sacral foramen to a ventral side of hip 124. Lead 114 may be inserted into the S3 sacral foramen such that electrodes extend along nerve 120 without manipulation of lead 114 on a ventral side of hip 124. Electrodes 116 may be electrically coupled to IMD 106 via one or more leads 114. In some examples, lead 114 may be inserted into other foramen, such as S2 or S4.

[0040] In the example shown in FIG. 1, electrodes 116 of leads 114 are shown as ring electrodes. Ring electrodes may be used in SNS applications because ring electrodes are relatively simple to program and are capable of delivering an electrical field to any tissue adjacent to electrodes 116. In other examples, electrodes 116 may have different configurations. For example, at least some of electrodes 116 of leads 114 may have a complex electrode array geometry that is capable of producing shaped electrical fields. The complex electrode array geometry may include multiple electrodes (e.g., partial ring or segmented electrodes) around the outer perimeter of each lead 114, rather than one ring electrode. In this manner, electrical stimulation may be directed in a specific direction fromleads 114 to enhance therapy efficacy and reduce possible adverse side effects from stimulating a large volume of tissue.

[0041] In some examples, a housing of IMD 106 includes one or more stimulation and / or sensing electrodes. The housing of IMD 106 may additionally or alternatively be referred to as a can and the can itself may operate as an electrode, such that it may provide stimulation and / or sensing through the surface of the device itself. In some examples, leads 114 have shapes other than elongated cylinders as shown in FIG. 1. For example, lead 114 may be paddle leads, spherical leads, bendable leads, or any other type of shape effective in treating patient 112 and / or minimizing invasiveness of lead 114.

[0042] IMD 106 includes a memory to store a plurality of therapy programs that each define a set of therapy parameter values. In some examples, IMD 106 selects a therapy program from the memory based on various parameters, such as sensed patient parameters and the identified patient behaviors. IMD 106 may generate electrical stimulation based on the parameters of the selected therapy program to manage the patient symptoms associated with a movement disorder.

[0043] External device 104 wirelessly communicates with IMD 106 as needed to provide or retrieve therapy information. External device 104 is an external computing device that the user, e.g., a clinician and / or patient 112, may use to communicate with IMD 106. For example, external device 104 may be a clinician programmer that the clinician (e.g., doctor, physician, nurse) uses to communicate with IMD 106 and program one or more therapy programs for IMD 106. Alternatively, external device 104 may be a patient programmer that allows patient 112 to select programs and / or view and modify therapy parameters. The clinician programmer may include more programming features than the patient programmer. In other words, more complex or sensitive tasks may only be allowed by the clinician programmer to reduce or limit an untrained patient from making changes to IMD 106.External device 104 may be any type of computing device, such as a proprietary device, a cellular phone, a smartphone, a tablet computing device, a laptop, or any other type of computing device. Generally, external device 104 includes a user interface that may provide and / or receive information from a user. In some examples, external device 104 is configured to pass information between IMD 106 and a different external device, but external device 104 may or may not have a user interface for programming. Instead, external device 104 may receive programming commands from the different external device (e.g., a server or other computing device that includes a user interface) and transmit those programming commandsto IMD 106 and / or receive information from IMD 106 and send that information to the different external device.

[0044] When external device 104 is configured for use by the clinician, external device 104 is configured to transmit initial programming information to IMD 106. This initial information may include hardware information, such as the type of leads 114 and the electrode arrangement, the position of leads 114 within nerve 120, the configuration of electrode array 116, initial programs defining therapy parameter values, and any other information the clinician suitably programs into IMD 106. External device 104 may also be capable of completing functional tests (e.g., measuring the impedance of electrodes 116 of leads 114). External device 104 may additionally be capable of testing differences between electrodes 116 such that external device may determine a proximity of each electrode 116 to nerve 120 or region of interest. Additionally, the differences between the electrodes 116 may inform external device 104 of which electrodes to use for stimulation electrodes and which electrodes to use for sensing electrodes.

[0045] The clinician may also store therapy programs within IMD 106 with the aid of external device 104. During a programming session, the clinician may determine one or more therapy programs that may provide efficacious therapy to patient 112 to address symptoms associated with the patient condition, and, in some cases, specific to one or more different patient states, such as a sleep state, movement state or rest state. For example, the clinician may select one or more stimulation electrode combinations with which stimulation is delivered to nerve 120 and such stimulation electrode combinations may change based on the one or more different patient states and additionally may be continuously or intermittently updated by IMD 106. During the programming session, the clinician may evaluate the efficacy of the specific program being evaluated based on feedback provided by patient 112 or based on one or more physiological parameters of patient 112. External device 104 may assist the clinician in the creation / identification of therapy programs by providing a methodical system for identifying potentially beneficial therapy parameter values and / or identifying which electrodes 116 to deliver stimulation from and / or which electrodes 116 to sense signals.

[0046] However, in some examples, IMD 106 or external device 104 (e.g., a clinician programmer, a patient programmer, a recharger, a programmer fob, etc.), alone or in combination, may automatically determine electrode configuration and therapy parameters. For example, the medical device may determine which electrodes to use for stimulation based on which electrodes are most proximal to target tissue such as nerve 120. In some examples,external device 104 outputs information indicating the selected electrode configuration for stimulation and the determined stimulation amplitude or other therapy parameter for the clinician (e.g., a clinician or a physician) to review and confirm before IMD 106 delivers therapy via the selected electrode configuration with the determined stimulation amplitude. External device 104 or IMD 106 may additionally or alternatively automatically adjust the stimulation electrodes and / or the sensing electrodes based on one or more criteria. The one or more criteria may be preset by a clinician.

[0047] External device 104 may also be configured for use by patient 112. When configured as a patient programmer, external device 104 may have limited functionality (compared to a clinician programmer) in order to reduce or limit patient 112 from altering critical functions of IMD 106 or applications that may be detrimental to patient 112. In this manner, external device 104 may only allow patient 112 to adjust values for certain therapy parameters or set an available range of values for a particular therapy parameter. For example, external device 104 may only allow patient 112 to adjust an amplitude or an intensity (by combination or amplitude, pulse width and / or pulse rate).

[0048] External device 104 may also provide an indication to patient 112 when therapy is being delivered, when patient input has triggered a change in therapy or when the power source within external device 104 or IMD 106 needs to be replaced or recharged. For example, external device 104 may include an alert LED and / or a touchscreen, may flash a message to patient 112 via a programmer display, generate an audible sound or somatosensory cue to confirm patient input was received, e.g., to indicate a patient state or to manually modify a therapy parameter.

[0049] Therapy system 100 may be implemented to provide chronic stimulation therapy to patient 112 over the course of several months or years. However, system 100 may also be employed on a trial basis to evaluate therapy before committing to full implantation. If implemented temporarily, some components of system 100 may not be implanted within patient 112. For example, patient 112 may be fitted with an external medical device, such as a trial stimulator, rather than IMD 106. The external medical device may be coupled to percutaneous leads or to implanted leads via a percutaneous extension. If the trial stimulator indicates SNS system 100 provides effective treatment to patient 112, the clinician may implant a chronic stimulator within patient 112 for relatively long-term treatment.

[0050] In some examples, IMD 106 is configured to provide electrical stimulation for treatment of a patient condition supplemental to medication provided to patient 112.Although some examples are described with the use of IMD 106 that provides stimulation,the techniques are not limited and the techniques may apply to examples where no stimulation is provided. For example, IMD 106 may not provide stimulation and treatment of a patient condition of patient 112 may be provided by medication or by medication with other techniques. For example, IMD 106 may use LFP to determine medication for one disorder of patient 112 and may apply stimulation for another disorder of patient 112. A single IMD 106 may listen / monitor to different LFP bands to look at various medication or disease states via the same lead / same hemisphere or different hemispheres.

[0051] FIG. 2 is a block diagram of the example IMD 106 of FIG. 1 for delivering electrical stimulation according to an example of the techniques of the disclosure. In the example shown in FIG. 2, IMD 106 includes stimulation generation circuitry 202, sensing circuitry 204, telemetry circuitry 208, processing circuitry 210, memory 212, and power source 220. Each of these circuits may be or otherwise include electrical circuitry configured to perform the functions attributed to each respective circuit. Memory 212 may include any volatile or non-volatile media, such as a random-access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), ferroelectric RAM (FRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. Memory 212 may store computer-readable instructions (e.g., electrical stimulation information 214 and electrode selection program 216) that when executed by processing circuitry 210, cause IMD 106 to perform various functions. Memory 212 may be a storage device or other non-transitory medium.

[0052] Stimulation generation circuitry 202 may be a single channel or multi-channel stimulation generator. In particular, stimulation generation circuitry 202 may be capable of delivering a single stimulation pulse, multiple stimulation pulses, or a continuous signal at a given time via a single electrode combination or multiple stimulation pulses at a given time via multiple electrode combinations. For example, as mentioned above, stimulation generation circuitry 202 may include multiple voltage or current sources and sinks that are coupled to respective electrodes to drive the electrodes as cathodes or anodes simultaneously or at different times. In this example, IMD 106 may or may not utilize switch circuitry for time-interleaved multiplexing of stimulation via different electrodes. Switch circuity may enable stimulation generation circuitry 202 to be configured to deliver multiple channels on a time-interleaved basis. For example, switch circuitry may serve to time divide the output of stimulation generation circuitry 202 across different electrode combinations at different times to deliver multiple programs or channels of stimulation energy to patient 112.

[0053] Processing circuitry 210 of IMD 106 may control sensing circuitry 204 to sense, via electrodes 116 interposed along leads 114, one or more bioelectric signals of nerve 120 of patient 112. Processing circuitry 210 of IMD 106 may deliver, via electrodes 116 (and stimulation generation circuitry 202), electrical stimulation therapy to patient 112 based on the sensed one or more bioelectric signals of nerve 120. Processing circuitry 210 of IMD 106 may select which electrodes of electrodes 116 to connect to stimulation circuitry 202 and which electrodes of electrodes 116 to connect to sensing circuitry 204 based on the sensed one or more bioelectric signals of nerve 120. The selection of which electrodes of electrodes 116 to connect to sensing circuitry 204 may additionally be informed by the electrode selection program 216 stored on memory 212.

[0054] Telemetry circuitry 208 supports wireless communication using one or more communication protocols (e.g., using Bluetooth™, Wi-Fi™, Near-Field Communication (NFC), Near Field Magnetic Induction (NFMI), Long Term Evolution, 5th generation (LTE / 5G), or MedRadio (MICS: Medical Implant Communication Service, MEDS: Medical External Device Service, MB AD: Medical Body Area Network)) between IMD 106 and an external device 104 or another computing device under the control of processing circuitry 210. In some examples, telemetry circuitry 208 supports a telemetry frequency that corresponds to a high frequency or radio frequency, which may be a radio frequency established via Bluetooth, Wi-Fi, Near-Field Communication (NFC), 175KHz inductive telemetry, or MICS, for example. Telemetry circuitry 208 may be configured to receive an inductive sting. Processing circuitry 210 of IMD 106 may receive, as updates to programs (e.g., at least one program parameter), values for various stimulation parameters such as magnitude and electrode combination, from external device 104 via telemetry circuitry 208. The updates to the therapy programs may be stored within therapy programs 214 portion of memory 212. Telemetry circuitry 208 in IMD 106, as well as telemetry modules in other devices and systems described herein, such as external device 104, may accomplish communication by radiofrequency (RF) communication techniques (e.g., Bluetooth, Wi-Fi, Near-Field Communication (NFC), or MICS). In addition, telemetry circuitry 208 may communicate with external medical device external device 104 via proximal inductive interaction of IMD 106 with external device 104. Accordingly, telemetry circuitry 208 may send information to external device 104 on a continuous basis, at periodic intervals, or upon request from IMD 106 or external device 104.

[0055] Telemetry circuitry 208 may periodically output an advertisement packet for a connection at an advertising interval. The advertisement packet may include information onhow to connect with the advertising device, such as, for example, one or more of: (1) media access control (MAC) addresses for the medical device and external device; (2) a real timepoint in time for the transfer to start; (3) an indication of a starting frequency; (4) an indication of a hop set; (5) a connection interval; or (6) a connection latency. Telemetry circuitry 208 may be configured to output an advertisement packet, such as, an advertisement for a wireless communication session or advertisement compliant with another protocol.

[0056] Processing circuitry 210 may include fixed function processing circuitry and / or programmable processing circuitry, and may include, for example, any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or any other processing circuitry configured to provide the functions attributed to processing circuitry 210 herein may be embodied as firmware, hardware, software or any combination thereof. Processing circuitry 210 may control stimulation generation circuitry 202 according to therapy programs 214 stored in memory 212 to apply particular stimulation parameter values specified by one or more of programs, such as voltage amplitude or current amplitude, pulse width, and / or pulse rate.

[0057] In the example shown in FIG. 2, the set of electrodes 116 includes electrodes 116A, 116B, 116C, 116D, 116E, 116F, 116G, and 116H. Processing circuitry 210 may control individual voltage or current sources and sinks coupled to respective electrodes 116, functioning as cathodes or anodes, to deliver stimulation signals to tissue of a patient, such as patient 112. In other examples, processing circuitry may control switch circuitry to apply the stimulation signals generated by stimulation generation circuitry 202 to selected combinations of electrodes 116.

[0058] Power source 220 delivers operating power to various components of IMD 106. Power source 220 may include a small rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD 106. In some examples, power consumption is small enough to allow IMD 106 to utilize patient motion and implement a kinetic energy-scavenging device to trickle charge a rechargeable battery. In other examples, traditional batteries may be used for a limited period of time.

[0059] In some examples, processing circuitry 210 continuously measures the one or more bioelectric signals in real time. In other examples, processing circuitry 210 may periodically sample the one or more bioelectric signals according to a predeterminedfrequency, external triggering event, or after a predetermined amount of time. In some examples, processing circuitry 210 periodically samples the signal at a frequency of approximately 2-4 Kilohertz (kHz). In some examples, processing circuitry 210 periodically samples the waveform at a frequency of approximately 10-20Hz. In some examples, processing circuitry 210 periodically samples the waveform at a frequency of approximately 130 Hz. In some examples, processing circuitry 210 may sample the signal and / or the waveform at any frequency suitable to determine the waveform.

[0060] In the example shown in FIG. 2, memory 212 stores electrical stimulation information 214. Electrical stimulation information 214 may include program parameters (e.g., a therapy parameter set), such as a stimulation electrode combination, electrode polarity, current or voltage amplitude, pulse width, and pulse rate. In some examples, individual therapy programs are stored as a therapy group, which defines a set of therapy programs with which stimulation may be generated during a therapy session in which stimulation therapy is delivered. The stimulation signals defined by the therapy programs of the therapy group may be delivered together on an overlapping or non-overlapping (e.g., time-interleaved) basis.

[0061] Accordingly, in some examples, stimulation generation circuitry 202 generates electrical stimulation signals in accordance with the electrode stimulation information 214 stored in memory 212. Electrode stimulation information 214 may include the electrical stimulation parameters (e.g., program parameters) noted above. Other ranges of therapy parameter values may also be useful and may depend on the target stimulation site within patient 112. While stimulation pulses are described, stimulation signals may be of any form, such as continuous-time signals (e.g., sine waves) or the like. Stimulation generation circuitry 202 is an example of therapy circuitry configured to deliver a therapy from IMD 106. Other types of therapies may additionally, or alternatively, be delivered using therapy circuitry and IMD 106.

[0062] The adaptive SNS therapy is defined by electrical stimulation information 214. For example, electrical stimulation information 214 may include a current amplitude (for a current-controlled system) or a voltage amplitude (for a voltage-controlled system), a pulse rate or frequency, and a pulse width, or a number of pulses per cycle. In examples where the electrical stimulation is delivered according to a “burst” of pulses, or a series of electrical pulses defined by an “on-time” and an “off-time,” the one or more parameters may define one or more of a number of pulses per burst, an on-time, and an off-time. Processing circuitry 210, via electrodes 116, delivers to patient 112 adaptive SNS and may adjust one or moreparameters defining the electrical stimulation based on corresponding parameters of the sensed one or more bioelectric signals of nerve 120.

[0063] In accordance with the techniques of the disclosure, processing circuitry 210 of IMD 106 may implement electrode selection program 216 stored on memory 212 to determine which electrodes of electrodes 116 to select as stimulation electrodes and which electrodes of electrodes 116 to select as sensing electrodes. Techniques described herein may enable IMD 106 to select one or more proximate electrodes 116 of leads 114, wherein selecting electrodes 116 which are closer electrodes as stimulation electrodes may decrease the thresholds for stimulation and may thereby increase longevity of the device and the leads. Increasing a battery longevity or lead longevity may reduce the risk of replacement surgeries to replace primary batteries or reduce recharge burden on patients with rechargeable batteries in IMD 106.

[0064] FIG. 3 is a block diagram of the external device 104 of FIG. 1. Although external device 104 may generally be described as a hand-held device, external device 104 may be a larger portable device or a stationary device. In addition, in other examples, external device 104 may be included as part of an external charging device or include the functionality of an external charging device. As illustrated in FIG. 3, external device 104 may include processing circuitry 310, memory 312, user interface 302, telemetry circuitry 308, and power source 320. Memory 312 may store instructions that, when executed by processing circuitry 310, cause processing circuitry 310 and external device 104 to provide the functionality ascribed to external device 104 throughout this disclosure. Each of these components, or modules, may include electrical circuitry that is configured to perform some or all of the functionality described herein. For example, processing circuitry 310 may include processing circuitry configured to perform the processes discussed with respect to processing circuitry.

[0065] In general, external device 104 includes any suitable arrangement of hardware, alone or in combination with software and / or firmware, to perform the techniques attributed to external device 104, and processing circuitry 310, user interface 302, and telemetry circuitry 208 of IMD 106. In various examples, external device 104 may include one or more processors, which may include fixed function processing circuitry and / or programmable processing circuitry, as formed by, for example, one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. External device 104 also, in various examples, may include a memory 312, such as RAM, ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, a CD-ROM, comprising executable instructions for causing the one or moreprocessors to perform the actions attributed to them. Moreover, although processing circuitry 310 and telemetry circuitry 308 are described as separate modules, in some examples, processing circuitry 310 and telemetry circuitry 308 are functionally integrated with one another. In some examples, processing circuitry 310 and telemetry circuitry 308 correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units. While telemetry circuitry 308 is described as being arranged within external device 104, in some examples, aspects of telemetry circuitry 308 (e.g., configuring a medical device to advertise at an advertising interval or initiating a communication session) may be performed by telemetry circuitry 308 external to external device 104 (e.g., in an intermediate device).

[0066] Memory 312 (e.g., a storage device) may store instructions that, when executed by processing circuitry 310, cause processing circuitry 310 and external device 104 to provide the functionality ascribed to external device 104 throughout this disclosure. For example, memory 312 may include instructions that cause processing circuitry 310 to obtain a parameter set from memory or receive a user input and send a corresponding command to IMD 106, or instructions for any other functionality. In addition, memory 312 may include a plurality of programs, where each program includes a parameter set that defines stimulation therapy.

[0067] User interface 302 may include a button or keypad, lights, a speaker for voice commands, a display, such as a liquid crystal (LCD), light-emitting diode (LED), or organic light-emitting diode (OLED). In some examples the display is a touch screen. User interface 302 may be configured to display any information related to the delivery of stimulation therapy, identified patient behaviors, sensed patient parameter values, patient behavior criteria, or any other such information. User interface 302 may also receive user input. The input may be, for example, in the form of pressing a button on a keypad or selecting an icon from a touch screen.

[0068] One or more sensors 301 may include one or more accelerometers 340, a light sensor 342, and a microphone 344. For example, one or more accelerometers 340 may be configured to determine information indicating a movement of external device 104.Information may include one or more of an acceleration in an x-direction, acceleration in a y-direction, or an acceleration in a z-direction. The x-direction may be perpendicular to both the y-direction and the z-direction. External device 104 may additionally, or alternatively, include a gyroscope that may detect the movement and / or generate motion information. Light sensor 342 may be configured to determine light information (e.g., an ambient light level of an environment detected by light sensor 342). Microphone 344 may be configured todetermine sound information (e.g., an ambient sound level of an environment detected by microphone 344). For example, microphone 344 may detect speech (e.g., from patient 112 or a caretaker of patient 112).

[0069] Telemetry circuitry 308 may support wireless communication between IMD 106 and external device 104 under the control of processing circuitry 310. Telemetry circuitry 308 may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired connection. In some examples, telemetry circuitry 308 provides wireless communication via an RF or proximal inductive medium. In some examples, telemetry circuitry 308 includes an antenna (e.g., an internal or external antenna).

[0070] Examples of local wireless communication techniques that may be employed to facilitate communication between external device 104 and IMD 106 include RF communication according to the 802.11 or Bluetooth specification sets (e.g., Classic Bluetooth, Bluetooth high speed and Bluetooth Low Energy (BLE) protocols) or other standard or proprietary telemetry protocols. In this manner, other external devices may be capable of communicating with external device 104 without needing to establish a secure wireless connection. While examples described herein may refer to connections as using the Bluetooth protocol for establishing a connection and using advertisements compliant with the Bluetooth protocol other known and future protocols may be used. For example, techniques described herein for establishing a connection between IMD 106 and external device 104 may be compliant with any RF communication protocol and / or may use any telemetry frequency.

[0071] Telemetry circuitry 308 may receive the advertisement packet from IMD 106, for example, and connect with another device (e.g., IMD 106) using the received advertisement packet. The advertisement packet may include information on how to connect with the advertising device, such as, for example, one or more of: (1) media access control (MAC) addresses for the medical device and external device; (2) a real time-point in time for the transfer to start; (3) an indication of a starting frequency; (4) an indication of a hop set; (5) a connection interval; or (6) a connection latency.

[0072] In some examples, processing circuitry 310 defines the parameters of electrical stimulation therapy, stored in memory 312, for delivering adaptive SNS to patient 112. In one example, processing circuitry 310 of external device 104, via telemetry circuitry 308, issues commands to IMD 106 causing IMD 106 to deliver electrical stimulation therapy via electrodes 116 via leads 114.

[0073] FIG. 4A is a conceptual diagram illustrating an example parallel sacral nerve lead placement 400. FIG. 4B is a conceptual diagram illustrating an example non-parallel sacral nerve lead placement 450. FIGS. 4A and 4B are discussed together for simplicity.

[0074] Lead 114 may be inserted through an opening in a sacrum of a hip a patient, such as sacral foramina 126 of hip 124 of patient 112 of FIG. 1. There may be one or more openings through hip 124 of patient 112. One of the openings through the sacrum of patient 112 may be sacral foramina 126. Sacral foramina 126 are small openings in the sacrum, which is a triangular bone at the base of your spine. There are typically four pairs of sacral foramina 126, wherein each sacral vertebrae, S1-S4 has one pair. Each foramen serves as a passageway for the sacral nerves and blood vessels, allowing them to travel from the spinal cord to the pelvis and lower limbs. The anterior foramina are generally wider than the posterior foramina. Lead 114 may be inserted through any sacral foramina 126. The clinician may select which sacral foramina 126 to insert each of the one or more leads 114 therethrough based on individual characteristics. The clinician may choose to insert the lead 114 through sacral foramina 126 of the S3 vertebrae as one or more branches of the sacral nerve may enter therethrough. In the example shown in FIGS. 4A-4B, S3 sacral foramina 126 may have one or more nerves 120, such as the sacral nerve, crossing through.

[0075] As shown in the example of FIG. 4A, in a parallel lead placement 400, lead 114 runs parallel along nerve 120. In parallel lead placement 400, each electrode 116 of lead 114 is equidistant to nerve 120. Parallel lead placement 400 may be the result of careful and skilled placement by the clinician to ensure that lead 114 follows nerve 120. With parallel lead placement 400 any electrode of electrodes 116 may be selected as stimulation electrodes and any electrode of electrodes 116 may be selected as sensing electrodes because no electrode is closer or further from nerve 120 and therefore each electrode has the same stimulation and sensing impedance.

[0076] As shown in the example of FIG. 4B, in a non-parallel lead placement 450, lead 114 does not run parallel along nerve 120. In non-parallel lead placement 450, one or more electrodes 116 of lead 114 are a different distance from nerve 120 than another electrode of electrodes 116 of lead 114. In some examples, such as the example shown in FIG. 4B, each electrode of electrodes 116 is a different distance from nerve 120. Non-parallel lead placement 450 may be the result of other nearby nerves, tissue, or blood vessels displacing lead 114 from nerve 120. Additionally or alternatively non-parallel lead placement 450 may be the result of patient 112 moving wherein as patient 112 moves spinal cord 128 likewise shifts thereby moving nerve 120. With non-parallel lead placement 450 one electrode ofelectrodes 116 is the closest electrode of electrodes 116 to nerve 120 and thereby has the lowest impedance. Typically, the electrode of electrodes 116 which is the closest to nerve 120 has the lowest stimulation threshold. Lower stimulation thresholds may improve battery longevity, lead longevity, and may improve patient outcomes. Non-parallel lead placement 450 is exaggerated in FIG. 4B for descriptive and illustrative purposes wherein lead 114 is nearly touching nerve 120 proximate to sacral foramina 126 but is multiple nerve widths away at a point distal to sacral foramina 126. In some examples, lead 114 is 5% farther away, 10% farther away, 15% farther away, or any other percent farther away at a distal end versus a proximate end, or vice versa. In some examples, medial electrodes of electrodes 116, electrodes which are in between (e.g., equidistant) the proximate end near sacral foramina 126 and distal end may be farther away than electrodes at either the proximate end near sacral foramina 126 or the distal end. In such an example, lead 114 would bow out and away from nerve 120.

[0077] FIG. 5 is a flowchart illustrating an example method of selecting stimulation electrodes based on an evoked signal. The example method includes controlling stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes (500), controlling sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes (505), determining that the signal satisfies a threshold (510), selecting the set of sensing electrodes as a second set of stimulation electrodes (515), and controlling the stimulation circuitry to deliver electrical stimulation to the second set of stimulation electrodes (520).

[0078] Controlling stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes (500) may include selecting the first set of stimulation electrodes from a plurality of electrodes and driving one or more components of IMD 106 to deliver the stimulation. The plurality of electrodes may include electrodes 116 on lead 114. The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The first set of stimulation electrodes may be selected by a clinician, may be selected randomly, or may be selected heuristically by processing circuitry of IMD 106. Processing circuitry 210 may drive or otherwise control stimulation generation circuitry 202 of IMD 106 to deliver stimulation to nerve 120 or surrounding tissue.

[0079] Controlling sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes (505) may include selecting the sensing electrodes from the plurality of electrodes and sensing the response evoked by the electrical stimulation. Theplurality of electrodes may include electrodes 116 on lead 114. The response may include a neural response of nerve 120. In some examples, the response may include a neural response of nearby neurons and / or neural tissue, thereby the response may include an electroneurogram (ENG). In some examples, the response may include a muscular response of muscle nearby or innervated by nerve 120, thereby the response may include electromyogram (EMG). The sensing electrodes may be selected by a clinician, may be selected randomly, or may be selected heuristically by processing circuitry of IMD 106. Processing circuitry 210 may control sensing circuitry 204 of IMD 106 to sense the stimulation response from nerve 120 or surrounding tissue. Processing circuitry 210 may read an electrode selection program 216 and thereafter electrically couple sensing circuitry 204 to one or more electrodes 116 of lead 114 based on the electrode

[0080] Determining that the signal satisfies a threshold (510) may include processing circuitry 210 comparing the signal to or via any number of algorithms, thresholds, threshold ranges, or other processes to determine which electrodes of the electrodes 116 are proximate nerve 120 and which electrodes of the electrodes 116 are distal nerve 120. Based on the determination of which electrodes of the electrodes 116 are proximate nerve 120 and which electrodes of the electrodes 116 are distal nerve 120, the processing circuitry may select the set of sensing electrodes as a second set of stimulation electrodes (515).

[0081] The threshold may include a depolarization process which may include delivering stimulation configured to hyperpolarize nerve 120 then delivering stimulation configured to depolarize nerve 120 from a first set of electrodes selected from a plurality of electrodes 116. Subsequently the process may include delivering stimulation configured to hyperpolarize nerve 120 then delivering stimulation configured to depolarize nerve 120 from the first set of electrodes selected from a plurality of electrodes 116. The signals from first set of electrodes evoked by the stimulation without hyperpolarization first may be compared to the signals from first set of electrodes evoked by the stimulation with hyperpolarization first and then depolarization afterwards to determine which electrodes are proximate nerve 120 or have a lower activation threshold. The threshold may additionally or alternatively include a short stim process which may include delivering stimulation to nerve 120 with stimulation pulses of I OO s or shorter from a first set of electrodes selected from a plurality of electrodes 116 and subsequently delivering stimulation to nerve 120 with stimulation pulses of I OO s or shorter from a second set of electrodes selected from a plurality of electrodes 116. The signals evoked by the stimulation from the first set of electrodes may be compared to the signals evoked by the stimulation from the second set of electrodes to determine whichelectrodes are proximate nerve 120 or have a lower activation threshold. The threshold may additionally or alternatively include an ECAP process which may include delivering stimulation to nerve 120 with a stimulus magnitude sufficient to elicit an ECAP from a first set of electrodes selected from a plurality of electrodes 116 and subsequently delivering stimulation to nerve 120 with a stimulus magnitude sufficient to elicit an ECAP from a second set of electrodes selected from a plurality of electrodes 116. The signals evoked by the stimulation from the first set of electrodes may be compared to the signals evoked by the stimulation from the second set of electrodes to determine which electrodes are proximate the nerve or have a lower activation threshold.

[0082] The threshold may additionally or alternatively include a unipolar stimulation process which may include sequentially delivering unipolar stimulation from each electrode of a first set of electrodes selected from a plurality of electrodes 116 to nerve 120 and sensing via a can of IMD 106 the signal evoked by the unipolar stimulation. Processing circuitry 210 and / or processing circuitry 310 may rank the signal evoked by each unipolar stimulation based on magnitude, response rate, a derivative of the magnitude with respect to time, a time duration of a neural response, or any other factor of the signal evoked by the unipolar stimulation. The threshold may additionally or alternatively include a signal to noise ratio. Processing circuitry 210 and / or processing circuitry 310 may calculate a signal to noise ratio of any signal recorded and thereafter may compare the signal to noise ratio to any other signal to noise ratio calculated. The signal may be the stimulation result of any stimulation parameters. An increase in noise level may indicate that the stimulation electrode is farther from nerve 120 and therefore may have a higher stimulation threshold. The threshold may additionally or alternatively include a timing-based process, wherein a time between a stimulation and a signal evoked by the stimulation is compared. The timing-based determination may additionally or alternatively include analyzing a slope (such as the first derivative of the magnitude of the signal with respect to time) of the signal evoked by the stimulation or any other derivative or time-domain mathematical transformations.

[0083] The hyperpolarization to depolarization process may include delivering stimulation configured to depolarize nerve 120 from a first set of electrodes selected from a plurality of electrodes 116. Subsequently the process may include delivering stimulation configured to hyperpolarize nerve 120 then delivering stimulation configured to depolarize nerve 120 from the first set of electrodes selected from a plurality of electrodes 116. The process may be repeated from a second set of electrodes and thereafter the responses from the first set of electrodes and the second set of electrodes may be compared to determine whichset of electrodes among the first set of electrodes, the second set of electrodes, the sensing electrodes, and any subset thereof are closest to the nerve.

[0084] Hyperpolarizing nerve 120 may include making the inside of nerve 120 more negative relative to the outside. Hyperpolarization may be achieved through an application of a negative electrical current to nerve 120 which may increase the negative charge in the cell. Hyperpolarization may decrease an excitability of nerve 120, thereby making it harder (e.g., increases the minimum stimulation amplitude or duration) to subsequently depolarize nerve 120. As such, pairing a hyperpolarization with a subsequent depolarization increases a signal to noise ratio because the magnitude or duration of stimulation required to achieve depolarization is greater than if the cell was not initially hyperpolarized.

[0085] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulation generation circuitry 202 may be configured to deliver the depolarizing stimulation to nerve 120 through the first set of electrodes. Stimulation generation circuitry 202 may additionally be configured to deliver the hyperpolarizing stimulation and subsequently deliver the depolarizing stimulation to nerve 120 through the first set of electrodes. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120. Sensing circuitry 204 may record how hyperpolarized nerve 120 becomes and how quickly nerve 120 hyperpolarizes through the set of sensing electrodes. Sensing circuitry may then record how depolarized nerve 120 becomes and how quickly nerve 120 depolarizes through the set of sensing electrodes. Subsequently, one or more electrodes which are capable of stimulating a nerve 120 may be selected as a second set of electrodes. Stimulation generation circuitry 202 may deliver the hyperpolarizing stimulation and subsequently deliver the depolarizing stimulation to nerve 120 via the second set of electrodes. The second set of electrodes may include different electrodes than the first set of electrodes or one or more electrodes may be in both sets. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120.

[0086] The set of sensing electrodes for the first set of stimulation electrodes and the set of sensing electrodes may be the same or different sensing electrodes. Using the same sensing electrodes may improve a comparison reliability. Using different sensing electrodes, such as using the second set of stimulation electrodes as recording electrodes for the first set of stimulation electrodes and using the first set of stimulation electrodes as recording electrodes for the second set of stimulation electrodes may enable a direct comparison between those two sets of electrodes. Sensing circuitry 204 may record how hyperpolarized nerve 120 becomes and how quickly nerve 120 hyperpolarizes through the set of sensing electrodes.Sensing circuitry 204 may then record how depolarized nerve 120 becomes and how quickly nerve 120 depolarizes through the set of sensing electrodes.

[0087] Processing circuitry 210 and / or processing circuitry 310 may compare the signals evoked by the stimulation delivered via first set of electrodes to the signals evoked by the stimulation delivered via the second set of electrodes to determine which electrodes are proximate the nerve or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved may be compared to the hyperpolarization then depolarization of nerve 120 achieved through the first set of electrodes. Additionally, processing circuitry 210 and / or processing circuitry 310 may compare the time to depolarization and / or the amplitude of stimulation required to elicit depolarization with and without the hyperpolarization. The depolarization of nerve 120 achieved compared to the depolarization stimulus applied by the first set of electrodes may be compared to the depolarization of nerve 120 achieved compared to the depolarization stimulus applied by the second set of electrodes. Additionally, processing circuitry 210 and / or processing circuitry 310 may compare the time to depolarization between the signals evoked by the stimulation delivered via the first set of electrodes to the signals evoked by the stimulation delivered via the second set of electrodes.

[0088] The short stim process may include a technique in which processing circuitry 210 and / or processing circuitry 310 selects a stimulation waveform which may be selected from electrical stimulation information 214 of memory 212 with short pulse widths. Stimulation generation circuitry 202 may deliver the stimulation waveform from a first set of electrodes selected from a plurality of electrodes 116 and stimulation generation circuitry 202 may subsequently deliver a stimulation waveform with short pulse widths from second set of electrodes selected from a plurality of electrodes 116. An electrical field elicited by stimulation from any one or more electrodes decreases with distance from one or more electrodes. The strength duration relationship for activation of any one or more nerves of the target nerve and / or neural tissue means that higher amplitudes may be needed to activate neurons using shorter pulse widths. Therefore, decreasing pulse width of a stimulation thereby requires an increase to amplitude in order to activate a neuron. Higher amplitudes of stimulation occur closer to an electrode. As such, if an electrode is farther away from nerve 120 which is being excited, the short pulses stimulate nerve 120 less, but an electrode is closer to nerve 120, the short pulses stimulate nerve 120 more and therefore for the same amplitude of input, the output may be significantly, and non-linearly, lower for the electrode which is farther away.

[0089] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulation generation circuitry 202 may deliver the stimulation waveform with short pulse widths to nerve 120 via the first set of electrodes. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120. Sensing circuitry 204 may record a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via the set of sensing electrodes. Subsequently, one or more electrodes which are capable of stimulating a nerve 120 may be selected as a second set of electrodes. Stimulation generation circuitry 202 may deliver the stimulation waveform with short pulse widths to nerve 120 via the second set of electrodes. The second set of electrodes may include different electrodes than the first set of electrodes or one or more electrodes may be in both sets. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120.

[0090] The stimulation waveform may include tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse width and an amplitude. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps) whereas amplitude is the strength or intensity of the electrical pulse and typically ranges from 0.2 to 8 milliamps (mA). A short pulse width may be less than lOOps. In other examples, a short pulse width may be less than 250ps, less than 175ps, less than 75ps, or less than 50ps.

[0091] The set of sensing electrodes for the first set of stimulation electrodes and the set of sensing electrodes may be the same or different sensing electrodes. Using the same sensing electrodes may improve a comparison reliability. Using different sensing electrodes, such as using the second set of stimulation electrodes as recording electrodes for the first set of stimulation electrodes and using the first set of stimulation electrodes as recording electrodes for the second set of stimulation electrodes may enable a direct comparison between those two sets of electrodes. The set of sensing electrodes may record a response to the stimulation waveform.

[0092] Processing circuitry 210 and / or processing circuitry 310 may compare the signals evoked by the stimulation delivered via the first set of electrodes to the signals evoked by thestimulation delivered via the second set of electrodes to determine which electrodes are proximate the nerve or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved by the stimulus applied by the first set of electrodes may be compared to the depolarization of nerve 120 achieved by the stimulus applied by the second set of electrodes. Processing circuitry 210 and / or processing circuitry 310 may compare the time to depolarization between the signals evoked by the stimulation delivered via the first set of electrodes to the signals evoked by the stimulation delivered via the second set of electrodes.

[0093] The ECAP process may include processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform which may be selected from electrical stimulation information 214 of memory 212 to be delivered from a first set of electrodes selected from a plurality of electrodes 116 and subsequently may include processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform which may be selected from electrical stimulation information 214 of memory 212 to be delivered from second set of electrodes selected from a plurality of electrodes 116. The stimulation waveform may be any waveform which elicits an evoked compound action potential (ECAP). ECAPs are the synchronous firing of a population of electrically stimulated nerve fibers. ECAPs may correlate with SCS-induced sensations in humans and provides effective analgesia but may be associated with paresthesia as well. Since an ECAP is a measure of the synchrony of firing of a population of nerve fibers, such as nerve 120, a ratio of an amplitude of the ECAP to the stimulation amplitude and / or an amplitude or a slope of the ECAP itself may inform how much of nerve 120 is activated and how quickly that quantity of nerve 120 is activated. Due to attenuation caused by tissue, electrodes which are farther from nerve 120 may cause an ECAP which has a smaller amplitude relative to the stimulation amplitude, the ECAP may have a smaller amplitude, and / or the slope (e.g., a derivative of the amplitude) of the ECAP may be lower.

[0094] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulation generation circuitry 202 may be configured to deliver the stimulation waveform configured to elicit an ECAP to nerve 120 via the first set of electrodes. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120. Sensing circuitry 204 may record a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via the set of sensing electrodes.Subsequently, one or more electrodes which are capable of stimulating a nerve 120 may be selected as a second set of electrodes. Stimulation generation circuitry 202 may deliver thestimulation waveform configured to elicit an ECAP to nerve 120 via the second set of electrodes. The second set of electrodes may include different electrodes than the first set of electrodes or one or more electrodes may be in both sets. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120.

[0095] The stimulation waveform may include any of tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse shape, pulse width (i.e., duration), an amplitude, a frequency, and a polarity. Pulse shape describes how the stimulation waveform rises and falls with respect to time. The pulse shape may be biphasic or triphasic (i.e., includes two or three phases), which may minimize tissue damage and charge buildup. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps). Amplitude is the strength or intensity of the electrical pulse and typically ranges from 2 to 8 milliamps (mA). The frequency of pulses is how many times a second a pules is delivered and may range from 20 to 100 Hz. Polarity is whether the waveform is either cathodic-first or anodic-first. Cathodic-first pulses may effectively depolarize the nerve membrane. Each parameter is adjusted by a clinician or patient 112 until patient 112 feels paresthesia which indicates that nerve 120 is being activated.

[0096] The set of sensing electrodes for the first set of stimulation electrodes and the set of sensing electrodes may be the same or different sensing electrodes. Using the same sensing electrodes may improve a comparison reliability. Using different sensing electrodes, such as using the second set of stimulation electrodes as recording electrodes for the first set of stimulation electrodes and using the first set of stimulation electrodes as recording electrodes for the second set of stimulation electrodes may enable a direct comparison between those two sets of electrodes. The set of sensing electrodes may record a response to the stimulation waveform.

[0097] Processing circuitry 210 and / or processing circuitry 310 may compare the signals evoked by the stimulation delivered via the first set of electrodes to the signals evoked by the stimulation delivered via the second set of electrodes to determine which electrodes are proximate the nerve or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved by the stimulus applied by the first set of electrodes may be compared to the depolarization of nerve 120 achieved by the stimulus applied by the second set ofelectrodes. Processing circuitry 210 and / or processing circuitry 310 may compare the time to depolarization between the signals evoked by the stimulation delivered via the first set of electrodes to the signals evoked by the stimulation delivered via the second set of electrodes.

[0098] The unipolar stimulation process may include processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform which may be selected from electrical stimulation information 214 of memory 212. The stimulation waveform may be delivered sequentially from each of a first set of electrodes selected from a plurality of electrodes 116 in a unipolar format. Unipolar stimulation is a format of electrical stimulation where one electrode is placed on or within the tissue being stimulated, while the other electrode is positioned at a point different than the electrodes or tissue being stimulated. In unipolar stimulation, the electrical current flows from the internal electrode through the tissue to the external electrode. For example, an electrode of electrodes 116 may be chosen and stimulation delivered through the electrode with a can of an implantable medical device, such as IMD 106 of FIG. 1, as the other electrode. Unipolar stimulation allows for another way to compare the effects of stimulation from each electrode to determine which electrode is most proximate the nerve. Specifically, the effect of an individual stimulation electrode may be separated from the effects of one or more stimulation electrodes as the can of IMD 106 may act as an anode or cathode to a single stimulation electrode of the one or more electrodes. Sensing electrodes may still be provided on the lead to be relatively close to the nerve for detecting signals.

[0099] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulation generation circuitry 202 may be configured to deliver the stimulation waveform to nerve 120 via the first set of electrodes. The sensing electrode may be selected as the can of IMD 106. Sensing circuitry 204 may record a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via the sensing electrode. This process may be repeated sequentially for each electrode of the first set of electrodes such that each electrode stimulates nerve 120 with the stimulation waveform sequentially.Alternatively, each electrode of the first set of electrodes may stimulate nerve 120 in any order which may be selected by the clinician, randomly selected, or heuristically selected based on previous results.

[0100] The stimulation waveform may include any of tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse shape, pulse width (i.e., duration), an amplitude, a frequency, and a polarity. Pulse shape describes how the stimulation waveform rises and falls with respect to time. The pulse shape may be biphasic or triphasic (i.e., includes two or three phases), which may minimize tissue damage and charge buildup. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps). Amplitude is the strength or intensity of the electrical pulse and typically ranges from 2 to 8 milliamps (mA). The frequency of pulses is how many times a second a pules is delivered and may range from 20 to 100 Hz. Polarity is whether the waveform is either cathodic-first or anodic-first. Cathodic-first pulses may effectively depolarize the nerve membrane. Each parameter is adjusted by a clinician or patient 112 until patient 112 feels paresthesia which indicates that nerve 120 is being activated.

[0101] Processing circuitry 210 and / or processing circuitry 310 may rank the signals evoked by each electrode of the first set of electrodes among each other to determine which electrodes are proximate the nerve or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved by the stimulus applied by each electrode of the first set of electrodes may be compared to the depolarization of nerve 120 achieved by each other electrode of the first set of electrodes. Additionally, the time to depolarization may be compared between each electrode of the first set of electrodes.

[0102] The signal to noise ratio may be applied to any process or threshold. A signal to noise ratio includes comparing the level of a signal to the level of background noise. The signal to noise ratio is defined as the ratio of signal power to noise power and is often expressed in decibels (dB). A higher SNR indicates a clearer signal, while a lower SNR means the signal is more obscured by noise. In some examples, the SNR is calculated by taking an amplitude of the signal component, which may take the form of an ECAP or other depolarization spike of nerve 120, and comparing that amplitude to the amplitude of background noise (e.g., noise caused by movement or other environmental noise). A higher SNR may indicate that the electrode used for stimulation is close, thereby producing a large signal or that the electrode used for sensing is farther away, such that the noise is higher. The SNR may provide additional information, or a check on whether the other process was correct.

[0103] The timing-based process may be applied to any process or threshold. A signal (e.g., an ECAP or other depolarization spike) of nerve 120, may be compared in the time-domain to the response from any other response. The time domain comparison may compare a temporal difference between the stimulation and the response. The temporal difference may be related to the distance between the stimulation electrode and the nerve 120. For example, an electrode which is farther from a nerve 120 may have a longer delay between stimulation and response and therefore a time between stimulation and response may be correlated to approximate the distance between nerve 120 and the electrode, or electrodes, which transmit the stimulation.

[0104] Controlling the stimulation circuitry to deliver electrical stimulation to the second set of stimulation electrodes (520) based on determination that the second set of stimulation electrodes satisfy the threshold. As discussed throughout above with regard to determining that the signal satisfies a threshold (510) and selecting the set of sensing electrodes as a second set of stimulation electrodes (515), the threshold may be based, at least in part, on the processes discussed above. Alternatively, if the second set of stimulation electrodes does not satisfy the threshold, then the first set of stimulation electrodes may be selected to deliver the electrical stimulation.

[0105] FIG. 6 is a flowchart illustrating an example operation of a medical device configured to adjust the stimulation electrodes based on electrode proximity. The example operation includes selecting an electrode set (600), stimulating the selected stimulation electrode set (605), analyzing whether the response is large enough (610), altering stimulation waveform if the response is not large enough (615), testing whether the stimulation electrodes satisfy a threshold if the response is large enough (620), setting the sense electrodes as the new stimulation electrodes if the threshold is met (625), and keeping the stimulation electrodes as the new stimulation electrodes and / or using a different programing method if the threshold is not met (630).

[0106] Selecting an electrode set (600) may include processing circuitry 210 and / or processing circuitry 310 selecting the first set of stimulation electrodes from a plurality of electrodes. The plurality of electrodes may include electrodes 116 on lead 114. The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The first set of stimulation electrodes may be selected by a clinician, may be selected randomly, or may be selected heuristically by processing circuitry of IMD 106. Heuristic selection of the first set of stimulation electrodes may be based on a previous selection, may be based on a selection by the clinician, or may be based on any other factor which informs electrode selection.

[0107] Stimulating the selected stimulation electrode set (605) may include processing circuitry such as processing circuitry 210 driving one or more components of IMD 106, such as stimulation generation circuitry 202 to deliver the stimulation. Processing circuitry 210 may drive or otherwise control stimulation generation circuitry 202 of IMD 106 to deliver stimulation to nerve 120 or surrounding tissue. The stimulation which is delivered may be any stimulation waveform. The stimulation waveform may be configured to treat any disease or relieve any symptoms which are experienced or otherwise afflict a patient such as patient 112.

[0108] Analyzing whether the response is large enough (610) may include sensing circuitry, such as sensing circuitry 204, which senses a response to the stimulating the selected electrode set (605). Sensing the response may be similar to controlling sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes (505). Sensing may include processing circuitry 210 selecting the sensing electrodes from the plurality of electrodes and coupling sensing circuitry 204 to the sensing electrodes to sense the response from one or more components of IMD 106. The plurality of electrodes may include electrodes 116 on lead 114. The response may include a neural response of nerve 120 or a muscular response of muscle nearby to nerve 120. The sensing electrodes may be selected by a clinician, may be selected randomly, or may be selected heuristically by processing circuitry of IMD 106. Processing circuitry 210 may control sensing circuitry 204 of IMD 106 to sense the stimulation response from nerve 120 or surrounding tissue. The sensed signal may be compared to a threshold. The threshold may be a threshold magnitude, a threshold time duration, or a threshold which combines these factors and any other factors.

[0109] Altering stimulation waveform if the response is not large enough (615) may include increasing a stimulation magnitude, a stimulation duration, or any other factor of the stimulation waveform which would thereby increase a response to the stimulation. The stimulation may be iteratively increased where the stimulation waveform is marginally changed, and the process of step 605 and 610 are repeated. Alternatively, the stimulation may be increased based on a magnitude of the response and / or a magnitude of the stimulation.

[0110] Testing whether the stimulation electrodes satisfy a threshold if the response is large enough (620) may include processing circuitry 210 and / or processing circuitry 310 selecting the threshold criteria. The threshold criteria were discussed above with respect to determining that the signal satisfies a threshold (510) which may include any number of algorithms, thresholds, threshold ranges, or other processes to determine which electrodes of the electrodes 116 are proximate nerve 120 and which electrodes of the electrodes 116 aredistal nerve 120. The processes as discussed above may include a hyperpolarization to depolarization process, a short stim process, an ECAP process, a unipolar stimulation process, a SNR ratio, and / or a timing-based process.[OHl] If the stimulation electrodes satisfy (e.g., greater than or meets) a threshold (“YES” branch of block 620) IMD 106 may set the sense electrodes as the new stimulation electrodes (625). If the stimulation electrodes do not satisfy (e.g., less than) a threshold (“NO” branch of block 620) IMD 106 may keep the stimulation electrodes as the stimulation electrodes and / or using a different programming method (630). Additionally or alternatively, the stimulation magnitude and other stimulation parameters may be adjusted based on the testing whether the stimulation electrodes satisfy a threshold if the response is large enough (620). In some examples, IMD 106 may select the new stimulation electrodes from all of the electrodes of the one or more of the sensing electrodes and one or more stimulation electrodes (e.g., setting the sense electrodes as the new stimulation electrodes if the threshold is met) (625). In some examples, IMD 106 may select the new stimulation electrodes from the stimulation electrodes (e.g., keeping the stimulation electrodes as the new stimulation electrodes if the threshold is not met (630)). Based on the selection, IMD 106 may notify a clinician and / or IMD 106 may indicate through any method to clinician which electrodes are determined to be proximate electrodes (e.g., a notification or indication to or at a clinician programmer, or any other suitable notification to a clinician). Additionally or alternatively, IMD 106 may notify patient 112 and / or IMD 106 may indicate to patient 112 which electrodes are determined to be proximate electrodes. In some examples, IMD 106 may use different programming methods, the different programming methods may include altering the selection of the electrode set 600 and repeating steps 600-620, may include changing a different attribute of the stimulation waveform at step 615 and repeating steps 600-620, or any other different programming method which a clinician may employ to select which electrodes to stimulate from initially.

[0112] FIG. 7 is a flowchart illustrating an example technique for determining electrodes for stimulation based on a threshold using a process of hyperpolarizing and then depolarizing a nerve. The example technique includes stimulating with a first set of electrodes to depolarize the nerve (700), sensing the response at sensing electrodes (705), stimulating with the first set of electrodes to hyperpolarize the nerve (710), stimulating with the second set of electrodes to depolarize the nerve (715), sensing the response at the sensing electrodes (720), comparing the responses (725), determining and selecting proximate electrodes (730), and confirming the responses (735).

[0113] The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The hyperpolarization to depolarization process may include IMD 106 delivering stimulation through one or more electrodes 116 configured to hyperpolarize nerve 120 then IMD 106 may deliver stimulation through one or more electrodes 116, which may be the same or different one or more electrodes which delivered the hyperpolarization stimulation, configured to depolarize nerve 120 from a first set of electrodes selected from a plurality of electrodes 116. Subsequently the process may include delivering stimulation configured to hyperpolarize nerve 120 then delivering stimulation configured to depolarize nerve 120 from a second set of electrodes selected from a plurality of electrodes 116. Hyperpolarizing nerve 120 may include making the inside of nerve 120 more negative relative to the outside. Hyperpolarization may be achieved through an application of a negative electrical current to nerve 120 which may increase the negative charge in the cell. Hyperpolarization may decrease an excitability of nerve 120, thereby making it harder (e.g., increases the minimum stimulation amplitude or duration) to subsequently depolarize nerve 120. As such, pairing a hyperpolarization with a subsequent depolarization increases a signal to noise ratio because the magnitude or duration of the depolarizing pulse is greater than if the cell was not initially hyperpolarized.

[0114] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulating with the first set of electrodes to depolarize nerve 120 (700) may include stimulation generation circuitry 202 delivering depolarizing stimulation to nerve 120 via a first set of electrodes. A set of sensing electrodes may be one or more electrodes which are capable of sensing a response of nerve 120. The one or more electrodes of the sensing electrodes may include the first set of electrodes and / or any other set of electrodes capable of sensing a response of the nerve. Sensing the response at sensing electrodes (705) may include sensing circuitry 204 recording how depolarized nerve 120 becomes and how quickly nerve 120 depolarizes via the set of sensing electrodes.Subsequently, the first set of electrodes may include one or more electrodes which are capable of stimulating nerve 120. Stimulating with the first set of electrodes to hyperpolarize nerve (710) may include stimulation generation circuitry 202 configured to deliver the hyperpolarizing stimulation via the first set of electrodes. Stimulating with the first set of electrodes to depolarize nerve (715) may include, subsequent to delivering the hyperpolarizing stimulation in 710, stimulation generation circuitry 202 delivering the depolarizing stimulation to nerve 120 via the second set of electrodes. Sensing the response atthe sensing electrodes (720) may include sensing circuitry 204 recording how hyperpolarized nerve 120 becomes and how quickly nerve 120 hyperpolarizes via the first set of electrodes. Sensing the response at the sensing electrodes (720) may additionally include the sensing electrodes recording how depolarized nerve 120 becomes and how quickly nerve depolarizes. The first set of electrodes may include a subset or all of the sensing electrodes. The set of sensing electrodes may include one or more electrodes, which are capable of sensing a response of nerve 120 (720).

[0115] Comparing the responses (725) and determining and selecting proximate electrodes (730) may include processing circuitry 210 and / or processing circuitry 310 comparing the signals evoked by the first set of electrodes after only depolarizing the nerves to the signals evoked by the first set of electrodes after hyperpolarizing and depolarizing the nerve to determine whether the first electrode set is proximate nerve 120 or has a suitable activation threshold. Specifically, the first electrode set may be proximate nerve 120 if the difference between the signals sensed at 705 and the signals sensed at 720 are small and the signal is strong. Alternatively, the first electrode set may be distal nerve 120 if the difference between the signals sensed at 705 and the signals sensed at 720 are large and / or the signal is weak. The difference in depolarization of nerve 120 achieved between the signals sensed at 705 and the signals sensed at 720 may be compared. Additionally, the time to depolarization may be compared between the signals sensed at 705 and the signals sensed at 720. Based on the comparison, the first set of electrodes, and / or one or more electrodes of the first set of electrodes may be determined to be proximate electrodes and thereafter those electrodes may be selected as the stimulation electrodes. Additionally or alternatively, a clinician may be notified and / or it may otherwise be indicated to the clinician which electrodes are determined to be proximate electrodes. Such indication may include a notification or indication to or at a clinician programmer. Additionally or alternatively, the patient may be notified and / or it may otherwise be indicated to the patient which electrodes are determined to be proximate electrodes.

[0116] IMD 106 may confirm the responses (735) by repeating steps 700-720 with a second set of electrodes in place of the first set of electrodes. In this manner, the confirmation in step 735 may be optional in some examples. The second set of electrodes may be selected from the electrodes and may include any subset of the first set of electrodes and / or any subset of the sensing electrodes. Confirming the responses (735) may further include repeating step 725. Additionally, when repeating step 725 with the data recorded for the second set of electrodes, the comparison may be between the data sensed at 705, the datasensed at 720, as well as the data sensed in the repetitions of 705 and 720 with the second set of electrodes. The comparison may confirm that electrode set 1 is closer to nerve 120 and / or may determine that electrode set 1 is not closer to nerve 120 than either the sensing electrodes and / or the second set of electrodes.

[0117] In some examples, processing circuitry of IMD 106 may deliver, via electrical stimulation from a first set of stimulation electrodes, a stimulus configured to depolarize the nerve, as a first electrical stimulation and sense via a set of sensing electrodes, the signal evoked by the first electrical stimulation. Processing circuitry of IMD 106 may deliver via second electrical stimulation from the first set of stimulation electrodes a stimulus configured to hyperpolarize the nerve followed in time by a stimulus configured to depolarize the nerve, and then sense via the sensing electrodes, the signal evoked by the second electrical stimulation. The processing circuitry of IMD 106 may then compare the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation to determine a proximity of the first set of stimulation electrodes to the nerve. In some examples, processing circuitry of IMD 106 may additionally or alternatively deliver from a second set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a third electrical stimulation, sense via the set of sensing electrodes, the signal evoked by the third electrical stimulation. Processing circuitry of IMD 106 may deliver a fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve followed in time by a stimulus configured to depolarize the nerve, and then sense via the sensing electrodes, the signal evoked by the fourth electrical stimulation. IMD 106 may then compare the signal evoked by the first electrical stimulation, the second electrical stimulation, the third electrical stimulation, and the fourth electrical stimulation. Based on the comparison, IMD 106 may determine whether the first set of electrodes, the second set of electrodes, the sensing electrodes, and / or any subset thereof are closest to the nerve. The third electrical stimulation and fourth electrical stimulation may be additional or optional confirmation steps as noted by step 735.

[0118] FIG. 8 is a flowchart illustrating an example technique for determining electrodes for stimulation based on a threshold for a nerve based on stimulation that has short pulse widths. The example operation includes stimulating with a first set of electrodes with a lOOps (or less) pulse (800), sensing the response at sensing electrodes (805), stimulating with a second set of electrodes with a lOOps (or less) pulse (810), sensing the response at the first set of electrodes (815), comparing the responses (820), and determining and selecting proximate electrodes (825).

[0119] The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The short stim process may include selecting a stimulation waveform with short pulse widths to be delivered from a first set of electrodes selected from a plurality of electrodes 116 and subsequently selecting a stimulation waveform with short pulse widths to be delivered from second set of electrodes selected from a plurality of electrodes 116. The electrical field elicited by stimulation from any one or more electrodes decreases with distance from one or more electrodes. The strength duration relationship for activation of any one or more nerves of the target nerve and / or neural tissue means that higher amplitudes may be needed to activate neurons using shorter pulse widths. The strength-duration relationship of neurons describes how the intensity of a stimulus and the length of time it is applied interact in whether a neuron triggers an action potential. This occurs because a neuron's membrane potential integrates inputs over time until it reaches an activation threshold needed to fire an action potential. A higher amplitude stimulus may bring the membrane potential of the neuron to the activation threshold in less time, while a lower amplitude stimulus may bring the membrane potential to the activation threshold over a longer duration. Therefore, decreasing pulse width of a stimulation thereby increases an amplitude required to activate a neuron. Furthermore, this impedance is non-linear such that the impedance does not vary linearly with the distance or the voltage. As such, if an electrode is farther away from nerve 120 which is being excited, the short pulses would be attenuated before reaching nerve 120, but an electrode is closer to nerve 120, the short pulses are less attenuated before reaching nerve 120 and therefore for the same amplitude of input, the output may be significantly, and non-linearly, lower for the electrode which is farther away.

[0120] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulating with a first set of electrodes with a lOOps pulse (800) may include stimulation generation circuitry 202 delivering the stimulation waveform with short pulse widths to nerve 120 via the first set of electrodes. Although a pulse width of lOOps may be used in one example, other pulse widths may be used in other examples.Sensing the response at sensing electrodes (805) may include sensing circuitry 204 recording a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via a set of sensing electrodes. The set of sensing electrodes may include one or more electrodes which are capable of sensing a response of a nerve 120. Stimulating with a second set of electrodes with a lOOps pulse (810) may include generation circuitry 202 subsequently delivering thestimulation waveform with short pulse widths to nerve 120 via a second set of electrodes stimulation. The second set of electrodes may include one or more electrodes which are capable of stimulating a nerve 120. The second set of electrodes may include different electrodes than the first set of electrodes or one or more electrodes may be in both sets.Sensing the response at the first set of electrodes (815) may include sensing circuitry 204 recording a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via the first set of electrodes. The first set of electrodes may be one or more electrodes which are capable of sensing a response of a nerve 120.

[0121] The stimulation waveform may include any of tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse width and an amplitude. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps) whereas amplitude is the strength or intensity of the electrical pulse and typically ranges from 2 to 8 milliamps (mA). A short pulse width may be less than lOOps. In other examples, a short pulse width may be less than 250ps, less than 175ps, less than 75ps, or less than 50ps.

[0122] The set of sensing electrodes for the first set of stimulation electrodes and the set of sensing electrodes may be the same or different sensing electrodes. Using the same sensing electrodes may improve a comparison reliability. Using different sensing electrodes, such as using the second set of stimulation electrodes as recording electrodes for the first set of stimulation electrodes and using the first set of stimulation electrodes as recording electrodes for the second set of stimulation electrodes may enable a direct comparison between those two sets of electrodes. The set of sensing electrodes may record a response to the stimulation waveform.

[0123] Comparing the responses (820) and determining and selecting proximate electrodes (825) may include processing circuitry 210 and / or processing circuitry 310 comparing the responses to the stimulation delivered by the first set of electrodes to responses to the stimulation delivered the second set of electrodes to determine which electrodes are proximate nerve 120 or have a lower activation threshold. Specifically, the magnitude of stimulation required to elicit depolarization of nerve 120 by the stimulus applied by the firstset of electrodes and / or the depolarization of nerve 120 achieved by the stimulus applied by the first set of electrodes after hyperpolarization may be compared to magnitude of stimulation required to elicit the depolarization of nerve 120 by the stimulus applied by the second set of electrodes and / or the depolarization of nerve 120 achieved by the stimulus applied by the second set of electrodes after hyperpolarization. Additionally, the time to depolarization may be compared between the first set of electrodes and the second set of electrodes. Based on the comparison, one or more electrodes may be determined to be proximate electrodes and thereafter those electrodes may be selected as the stimulation electrodes. Additionally or alternatively, processing circuitry 210 may control telemetry circuitry 208 to notify and / or indicate to a clinician which electrodes are determined to be proximate electrodes. Such indication may include a notification or indication to or at a clinician programmer such as external device 104. Additionally or alternatively, the patient may be notified and / or it may otherwise be indicated to the patient which electrodes are determined to be proximate electrodes.

[0124] FIG. 9 is a flowchart illustrating an example technique for selecting electrodes based on a threshold for a stimulus configured to elicit an ECAP. The example operation includes stimulating with a first set of electrodes with an ECAP inducing waveform (900), sensing the response at sensing electrodes (905), stimulating with a second set of electrodes with an ECAP inducing waveform (910), sensing the response at the first set of electrodes (915), comparing the responses (920), and determining and selecting proximate electrodes (925).

[0125] The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The ECAP process may include processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform to be delivered from a first set of electrodes selected from a plurality of electrodes 116 and subsequently processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform to be delivered from second set of electrodes selected from a plurality of electrodes 116. The stimulation waveform may be any waveform which elicits an evoked compound action potential (ECAP). ECAPs are the synchronous firing of a population of electrically stimulated nerve fibers. ECAPs may correlate with SCS-induced sensations in humans and provides effective analgesia but may be associated with paresthesia as well. Since an ECAP is a measure of the synchrony of firing of a population of nerve fibers, such as nerve 120, a ratio of an amplitude of the ECAP to the stimulation amplitude and / or an amplitude or a slope of the ECAP itselfmay inform how much of nerve 120 is activated and how quickly that quantity of nerve 120 is activated. Due to attenuation caused by tissue, electrodes which are farther from nerve 120 may cause an ECAP which has a smaller amplitude relative to the stimulation amplitude, the ECAP may have a smaller amplitude, and / or the slope (e.g., a derivative of the amplitude) of the ECAP may be lower.

[0126] The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. Stimulating with a first set of electrodes with an ECAP inducing waveform (900) may include stimulation generation circuitry 202 delivering the stimulation waveform configured to elicit an ECAP to nerve 120 via the first set of electrodes. Sensing the response at sensing electrodes (905) may include sensing circuitry 204 recording a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform via the set of sensing electrodes. The set of sensing electrodes may be one or more electrodes which are capable of sensing a response of nerve 120. Stimulating with a second set of electrodes with an ECAP inducing waveform (910) may include stimulation generation circuitry 202 delivering the stimulation waveform configured to elicit an ECAP to nerve 120 via a second set of electrodes. The second set of electrodes may be selected may include one or more electrodes which are capable of stimulating nerve 120. The second set of electrodes may include different electrodes than the first set of electrodes or one or more electrodes may be in both sets. Sensing the response at the first set of electrodes (915) may include sensing circuitry 204 recording a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform, via the first set of electrodes.

[0127] The stimulation waveform may include any of tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse shape, pulse width (i.e., duration), an amplitude, a frequency, and a polarity. Pulse shape describes how the stimulation waveform rises and falls with respect to time. The pulse shape may be biphasic or triphasic (i.e., includes two or three phases), which may minimize tissue damage and charge buildup. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps). Amplitude is the strength or intensity of the electrical pulse andtypically ranges from 2 to 8 milliamps (mA). The frequency of pulses is how many times a second a pules is delivered and may range from 20 to 100 Hz. Polarity is whether the waveform is either cathodic-first or anodic-first. Cathodic-first pulses may effectively depolarize the nerve membrane. Each parameter is adjusted by a clinician or patient 112 until patient 112 feels paresthesia which indicates that nerve 120 is being activated.

[0128] The set of sensing electrodes for the first set of stimulation electrodes and the set of sensing electrodes may be the same or different sensing electrodes. Using the same sensing electrodes may improve a comparison reliability. Using different sensing electrodes, such as using the second set of stimulation electrodes as recording electrodes for the first set of stimulation electrodes and using the first set of stimulation electrodes as recording electrodes for the second set of stimulation electrodes may enable a direct comparison between those two sets of electrodes. The set of sensing electrodes may record a response to the stimulation waveform.

[0129] Comparing the responses (920) and determining and selecting proximate electrodes (925) may include processing circuitry 210 and / or processing circuitry 310 comparing the response recorded by the first set of electrodes to the responses recorded by the second set of electrodes to determine which electrodes are proximate nerve 120 or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved by the stimulus applied by the first set of electrodes may be compared to the depolarization of nerve 120 achieved by the stimulus applied by the second set of electrodes. Additionally, the time to depolarization may be compared between the first set of electrodes and the second set of electrodes. Based on the comparison, one or more electrodes may be determined to be proximate electrodes and thereafter those electrodes may be selected as the stimulation electrodes. Additionally or alternatively, processing circuitry 210 may control telemetry circuitry 208 to notify and / or indicate to a clinician which electrodes are determined to be proximate electrodes. Such indication may include a notification or indication to or at a clinician programmer. Additionally or alternatively, the patient may be notified and / or it may otherwise be indicated to the patient which electrodes are determined to be proximate electrodes.

[0130] FIG. 10 is a flowchart illustrating an example technique for selecting electrodes based a threshold using unipolar stimulation. The example operation includes stimulating with an electrode of the first set of stimulation electrodes via unipolar stimulation (1000), sensing the response at a sensing electrode combination (1005), determining if all electrodes of the first set were tested (1010) and selecting the next electrode of the first set if needed(1012), ranking the electrodes of the first set of stimulation electrodes based on the sensed response (1015), and determining and selecting proximate electrodes (1020).

[0131] The target tissue may include any nerves or any tissue surrounding any of the nerves. The nerves are discussed with respect to nerve 120 of FIG. 1, but may be any nerve, nerve cluster, or other tissue of the body. The unipolar stimulation process may include processing circuitry 210 and / or processing circuitry 310 selecting a stimulation waveform of electrical stimulation information 214 stored in memory 212 which may be delivered sequentially from each of a first set of electrodes selected from a plurality of electrodes 116 in a unipolar format. Unipolar stimulation is a type of electrical stimulation where one electrode is placed on or within the tissue being stimulated, while the other electrode is positioned at a point different than the electrodes or tissue being stimulated. In unipolar stimulation, the electrical current flows from the internal electrode through the tissue to the external electrode. For example, an electrode of electrodes 116 may be chosen and stimulation delivered through the electrode with a can of IMD 106 as the other electrode. Unipolar stimulation allows for an effect of an individual stimulation electrode to be separated from the effects of a sensing electrode because the sensing electrode would be the can of IMD 106 at a separate location and therefore a proximity of a sensing electrode to nerve 120 would not affect the results for any individual stimulation electrode.

[0132] Stimulating with an electrode of the first set of stimulation electrodes via unipolar stimulation (1000) may include processing circuitry 210 and / or processing circuitry 310 selecting an electrode from a first set of electrodes and stimulation generation circuitry 202 delivering stimulation through the electrode and grounding the response with a can of IMD 106 or some other electrode that is remote from the stimulus electrode. The first set of electrodes may be one or more electrodes which are capable of stimulating a nerve 120. The first set of electrodes may deliver the stimulation waveform to nerve 120. Sensing the response at a sensing electrode combination (1005) may include sensing circuitry 204 recording a response of nerve 120 to the stimulation waveform, including how depolarized nerve 120 becomes and how quickly nerve 120 responds to the stimulation waveform. In some examples, the sensing electrode combination may include the can of IMD 106, an electrode at the can, or some other electrode remote from another electrode on the lead. In some examples, the sensing electrode combination is formed by two electrodes on the lead. Determining if all electrodes of the first set were tested (1010) may include processing circuitry 210 and / or processing circuitry 310 comparing the number of electrodes which have been tested to the number of electrodes in the first set of electrodes. This process may berepeated sequentially for each electrode of the first set of electrodes such that each electrode stimulates nerve 120 with the stimulation waveform sequentially. Instead of stimulating the nerves sequentially, each electrode of the first set of electrodes may stimulate nerve 120 in any order which may be selected by the clinician, randomly selected, or heuristically selected based on previous results.

[0133] The stimulation waveform may include any of tonic stimulation which includes delivering continuous pulses at a constant frequency and amplitude, burst stimulation which includes groups of pulses at a high frequency, separated by intervals of no stimulation, high-frequency stimulation which includes delivering pulses at a very high frequency (e.g., 10 kHz) or multiphasic stimulation which delivers high-frequency, charge-neutral pulse energy to multiple electrodes. Each pulse includes a pulse shape, pulse width (i.e., duration), an amplitude, a frequency, and a polarity. Pulse shape describes how the stimulation waveform rises and falls with respect to time. The pulse shape may be biphasic or triphasic (i.e., includes two or three phases), which may minimize tissue damage and charge buildup. Pulse width describes a duration of each electrical pulse delivered and typically ranges from 100 to 500 microseconds (ps). Amplitude is the strength or intensity of the electrical pulse and typically ranges from 2 to 8 milliamps (mA). The frequency of pulses is how many times a second a pules is delivered and may range from 20 to 100 Hz. Polarity is whether the waveform is either cathodic-first or anodic-first. Cathodic-first pulses may effectively depolarize the nerve membrane. Each parameter is adjusted by a clinician or patient 112 until patient 112 feels paresthesia which indicates that nerve 120 is being activated.

[0134] Ranking the first set of stimulation electrodes (1015) and determining and selecting proximate electrodes (1020) may include processing circuitry 210 and / or processing circuitry 310 ranking the responses by each electrode of the first set of electrodes among each other to determine which electrodes are proximate nerve 120 or have a lower activation threshold. Specifically, the depolarization of nerve 120 achieved by the stimulus applied by each electrode of the first set of electrodes may be compared by processing circuitry 210 and / or processing circuitry 310 to the depolarization of nerve 120 achieved by each other electrode of the first set of electrodes. Additionally, the time to depolarization may be compared by processing circuitry 210 and / or processing circuitry 310 between each electrode of the first set of electrodes. Based on the ranking, one or more electrodes may be determined to be proximate electrodes and thereafter those electrodes may be selected as the stimulation electrodes. Additionally or alternatively, a clinician may be notified and / or it may otherwise be indicated to the clinician which electrodes are determined to be proximate electrodes. Suchindication may include a notification or indication to or at a clinician programmer.Additionally or alternatively, the patient may be notified and / or it may otherwise be indicated to the patient which electrodes are determined to be proximate electrodes.

[0135] The following examples are a non-limiting list of examples in accordance with one or more techniques of this disclosure.

[0136] Example 1. An implantable medical device comprising: stimulation circuitry configured to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; sensing circuitry configured to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; and processing circuitry configured to: determine that the signal satisfies a threshold; responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes; and control the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0137] Example 2. The implantable medical device of example 1, wherein the processing circuitry is further configured to: control the stimulation circuitry to increase a magnitude of the electrical stimulation until the signal evoked by the electrical stimulation satisfies a magnitude threshold; and responsive to satisfying the magnitude threshold, updating the magnitude of the subsequent electrical stimulation.

[0138] Example 3. The implantable medical device of any of examples 1 and 2, wherein the signal further comprises an electroneurogram (ENG) signal evoked by the electrical stimulation near the target tissue.

[0139] Example 4. The implantable medical device of any of examples 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least: delivering, via the electrical stimulation from the first set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering, via a second electrical stimulation from the first set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve; delivering, via the second electrical stimulation from the first set of stimulation electrodes, a stimulus configured to depolarize the nerve; sensing, via the sensing electrodes, the signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0140] Example 5. The implantable medical device of any of examples 1 through 4, wherein the processing circuitry is further configured to determine that the signal satisfies the threshold by at least: delivering, via the electrical stimulation from a second set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a third electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the third electrical stimulation; delivering, via a fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve; delivering, via the fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to depolarize the nerve; sensing, via the sensing electrodes, the signal evoked by the fourth electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation, the second electrical stimulation, the third electrical stimulation, and the fourth electrical stimulation.

[0141] Example 6. The implantable medical device of any of examples 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least: delivering the electrical stimulation via the first set of stimulation electrodes, wherein the electrical stimulation has a pulse width less than or equal to 100 microseconds ( / / s), and wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering a second electrical stimulation via the second set of stimulation electrodes, wherein the second electrical stimulation has a pulse width less than or equal to 100 s; sensing, via the first set of stimulation electrodes, a second signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0142] Example 7. The implantable medical device of any of examples 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least: delivering, via the electrical stimulation from the first set of stimulation electrodes, a stimulus configured to elicit an ECAP, wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering, via a second electrical stimulation from the second set of stimulation electrodes, a stimulus configured to elicit an ECAP; sensing, via the first set of stimulation electrodes, the signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, thesignal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0143] Example 8. The implantable medical device of any of examples 1 through 7, wherein the processing circuitry is configured to determine that the signal satisfies the threshold further by at least: sequentially delivering, via electrical stimulation from each of the first set of stimulation electrodes, unipolar stimulation; sensing, via the set of sensing electrodes, signals evoked by the electrical stimulation from respective electrodes of the first set of stimulation electrodes; and ranking the signals evoked by the electrical stimulation from two or more of the first set of stimulation electrodes.

[0144] Example 9. The implantable medical device of any of examples 1 through 8, wherein the threshold is based on a signal to noise ratio.

[0145] Example 10. The implantable medical device of any of examples 1 through 9, wherein the threshold is based on a timing of the signal evoked by the electrical stimulation.

[0146] Example 11. A method comprising: controlling, by processing circuitry, stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; controlling, by the processing circuitry, sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; determining, by the processing circuitry, that the signal satisfies a threshold; selecting, by the processing circuitry and responsive to determining that the signal satisfies the threshold, the set of sensing electrodes as a second set of stimulation electrodes; and controlling, by the processing circuitry, the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0147] Example 12. The method of example 11, further comprising: controlling, by the processing circuitry, the stimulation circuitry to increase a magnitude of the electrical stimulation until the signal evoked by the electrical stimulation satisfies a magnitude threshold; and responsive to satisfying the magnitude threshold, updating, by the processing circuitry, the magnitude of the subsequent electrical stimulation.

[0148] Example 13. The method of any of examples 11 and 12, wherein the determining that the signal satisfies a threshold comprises measuring an electroneurogram (ENG) signal evoked by the electrical stimulation near the target tissue.

[0149] Example 14. The method of any of examples 11 through 13, wherein the target tissue comprises a nerve and wherein the determining that the signal satisfies a threshold comprises: delivering, via the electrical stimulation from the first set of stimulationelectrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering, via a second electrical stimulation from the second set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve; delivering, via the second electrical stimulation from the second set of stimulation electrodes, a stimulus configured to depolarize the nerve; sensing, via the first set of stimulation electrodes, the signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0150] Example 15. The method of any of examples 11 through 14, wherein the target tissue comprises a nerve, and wherein determining that the signal satisfies a threshold comprises: delivering, via the electrical stimulation from a second set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a third electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the third electrical stimulation; delivering, via a fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve; delivering, via the fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to depolarize the nerve; sensing, via the sensing electrodes, the signal evoked by the fourth electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation, the second electrical stimulation, the third electrical stimulation, and the fourth electrical stimulation.

[0151] Example 16. The method of any of examples 11 through 13, wherein the target tissue comprises a nerve and wherein the determining that the signal satisfies a threshold comprises: delivering the electrical stimulation via the first set of stimulation electrodes, wherein the electrical stimulation has a pulse width less than or equal to 100 / is, and wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering a second electrical stimulation via the second set of stimulation electrodes, wherein the second electrical stimulation has a pulse width less than or equal to 100 s; sensing, via the first set of stimulation electrodes, a second signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0152] Example 17. The method of any of examples 11 through 13, wherein the target tissue comprises a nerve, and wherein determining that the signal satisfies a thresholdcomprises: delivering, via the electrical stimulation from the first set of stimulation electrodes, a stimulus configured to elicit an ECAP, wherein the electrical stimulation is a first electrical stimulation; sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation; delivering, via a second electrical stimulation from the second set of stimulation electrodes, a stimulus configured to elicit an ECAP; sensing, via the first set of stimulation electrodes, the signal evoked by the second electrical stimulation; and comparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

[0153] Example 18. The method of any of examples 11 through 17, wherein determining that the signal satisfies a threshold further comprises: delivering, via the electrical stimulation from the first set of stimulation electrodes, unipolar stimulation; sensing, via the set of sensing electrodes, signals evoked by the electrical stimulation; and ranking the signals evoked by the electrical stimulation from two or more of the first set of stimulation electrodes.

[0154] Example 19. The method of any of examples 11 through 18, wherein the threshold is based on a signal to noise ratio.

[0155] Example 20. The method of any of examples 10 through 19, wherein the threshold is based on a timing of the signal evoked by the electrical stimulation.

[0156] Example 21. The method of any of examples 10 through 19, wherein determining that the signal satisfies a threshold comprises comparing the signal evoked by the electrical stimulation to the electrical stimulation.

[0157] Example 22. The method of any of examples 10 through 20, further comprising: controlling communication circuitry to notify a clinician whether the first set of stimulation electrodes or the second set of stimulation electrodes are configured to deliver the electrical stimulation.

[0158] Example 23. The method of any of examples 10 through 21, wherein: the first set of stimulation electrodes comprises a first electrode and a second electrode, the second set of stimulation electrodes comprises a third electrode and a fourth electrode, the target tissue comprises a nerve; and determining that the signal satisfies a threshold comprises: stimulating, via the electrical stimulation from the first electrode and the second electrode, the nerve, wherein the electrical stimulation is a first electrical stimulation; sensing a first signal evoked by the electrical stimulation to the first electrical stimulation at the third electrode and the fourth electrode; stimulating, via a second electrical stimulation from the third electrode and the fourth electrode, the nerve; sensing a second signal evoked by thesecond electrical stimulation at the first electrode and the second electrode; comparing the first signal evoked by the first electrical stimulation to the second signal evoked by the second electrical stimulation; and selecting the first electrode and the second electrode as the first set of stimulation electrodes based on the first signal evoked by the electrical stimulation being greater that the second signal evoked by the electrical stimulation or selecting the third electrode and the fourth electrode as the second set of stimulation electrodes based on the first signal evoked by the electrical stimulation being less than the second signal evoked by the electrical stimulation.

[0159] Example 24. A non-transitory computer-readable storage medium comprising instructions that, when executed by processing circuitry, cause the processing circuitry to: control stimulation circuitry to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes; control sensing circuitry to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; determine that the signal satisfies a threshold; responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes; and control the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

[0160] The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit comprising hardware may also perform one or more of the techniques of this disclosure.

[0161] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or unitsmay be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0162] The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

[0163] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An implantable medical device comprising:stimulation circuitry configured to deliver electrical stimulation to a target tissue via a first set of stimulation electrodes selected from a plurality of electrodes;sensing circuitry configured to sense a signal evoked by the electrical stimulation via a set of sensing electrodes selected from the plurality of electrodes; andprocessing circuitry configured to:determine that the signal satisfies a threshold;responsive to determining that the signal satisfies the threshold, select the set of sensing electrodes as a second set of stimulation electrodes; andcontrol the stimulation circuitry to deliver subsequent electrical stimulation via the second set of stimulation electrodes.

2. The implantable medical device of claim 1, wherein the processing circuitry is further configured to:control the stimulation circuitry to increase a magnitude of the electrical stimulation until the signal evoked by the electrical stimulation satisfies a magnitude threshold; and responsive to satisfying the magnitude threshold, updating the magnitude of the subsequent electrical stimulation.

3. The implantable medical device of any of claims 1 and 2, wherein the signal further comprises an electroneurogram (ENG) signal evoked by the electrical stimulation near the target tissue.

4. The implantable medical device of any of claims 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least:delivering, via the electrical stimulation from the first set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a first electrical stimulation;sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation;delivering, via a second electrical stimulation from the first set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve;delivering, via the second electrical stimulation from the first set of stimulation electrodes, a stimulus configured to depolarize the nerve;sensing, via the sensing electrodes, the signal evoked by the second electrical stimulation; andcomparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

5. The implantable medical device of any of claims 1 through 4, wherein the processing circuitry is further configured to determine that the signal satisfies the threshold by at least:delivering, via the electrical stimulation from a second set of stimulation electrodes, a stimulus configured to depolarize the nerve, wherein the electrical stimulation is a third electrical stimulation;sensing, via the set of sensing electrodes, the signal evoked by the third electrical stimulation;delivering, via a fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to hyperpolarize the nerve;delivering, via the fourth electrical stimulation from the second set of stimulation electrodes, a stimulus configured to depolarize the nerve;sensing, via the sensing electrodes, the signal evoked by the fourth electrical stimulation; andcomparing, via the processing circuitry, the signal evoked by the first electrical stimulation, the second electrical stimulation, the third electrical stimulation, and the fourth electrical stimulation.

6. The implantable medical device of any of claims 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least:delivering the electrical stimulation via the first set of stimulation electrodes, wherein the electrical stimulation has a pulse width less than or equal to 100 microseconds ( / / s), and wherein the electrical stimulation is a first electrical stimulation;sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation;delivering a second electrical stimulation via the second set of stimulation electrodes, wherein the second electrical stimulation has a pulse width less than or equal to 100 s; sensing, via the first set of stimulation electrodes, a second signal evoked by the second electrical stimulation; andcomparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

7. The implantable medical device of any of claims 1 through 3, wherein the target tissue comprises a nerve, and wherein the processing circuitry is configured to determine that the signal satisfies the threshold by at least:delivering, via the electrical stimulation from the first set of stimulation electrodes, a stimulus configured to elicit an ECAP, wherein the electrical stimulation is a first electrical stimulation;sensing, via the set of sensing electrodes, the signal evoked by the first electrical stimulation;delivering, via a second electrical stimulation from the second set of stimulation electrodes, a stimulus configured to elicit an ECAP;sensing, via the first set of stimulation electrodes, the signal evoked by the second electrical stimulation; andcomparing, via the processing circuitry, the signal evoked by the first electrical stimulation and the signal evoked by the second electrical stimulation.

8. The implantable medical device of any of claims 1 through 7, wherein the processing circuitry is configured to determine that the signal satisfies the threshold further by at least:sequentially delivering, via electrical stimulation from each of the first set of stimulation electrodes, unipolar stimulation;sensing, via the set of sensing electrodes, signals evoked by the electrical stimulation from respective electrodes of the first set of stimulation electrodes; andranking the signals evoked by the electrical stimulation from two or more of the first set of stimulation electrodes.

9. The implantable medical device of any of claims 1 through 8, wherein the threshold is based on a signal to noise ratio.

10. The implantable medical device of any of claims 1 through 9, wherein the threshold is based on a timing of the signal evoked by the electrical stimulation.

11. The implantable medical device of any of claims 1 through 10, wherein the processing circuitry is configured to determine that the signal satisfies a threshold by at least comparing the signal evoked by the electrical stimulation to the electrical stimulation.

12. The implantable medical device of any of claims 1 through 11, wherein the processing circuitry is configured to control communication circuitry to notify a clinician whether the first set of stimulation electrodes or the second set of stimulation electrodes are configured to deliver the electrical stimulation.

13. The implantable medical device of any of claims 1 through 12, wherein:the first set of stimulation electrodes comprises a first electrode and a second electrode,the second set of stimulation electrodes comprises a third electrode and a fourth electrode,the target tissue comprises a nerve; andthe processing circuitry is configured to determine that the signal satisfies a threshold by at least:controlling the stimulation circuitry to stimulate, via the electrical stimulation from the first electrode and the second electrode, the nerve, wherein the electrical stimulation is a first electrical stimulation;controlling the sensing circuitry to sense a first signal evoked by the electrical stimulation to the first electrical stimulation at the third electrode and the fourth electrode;controlling the stimulation circuitry to stimulate, via a second electrical stimulation from the third electrode and the fourth electrode, the nerve;controlling the sensing circuitry to sense a second signal evoked by the second electrical stimulation at the first electrode and the second electrode;comparing the first signal evoked by the first electrical stimulation to the second signal evoked by the second electrical stimulation; andselecting the first electrode and the second electrode as the first set of stimulation electrodes based on the first signal evoked by the electrical stimulationbeing greater that the second signal evoked by the electrical stimulation or selecting the third electrode and the fourth electrode as the second set of stimulation electrodes based on the first signal evoked by the electrical stimulation being less than the second signal evoked by the electrical stimulation.

14. A non-transitory computer-readable storage medium comprising instructions that, when executed by the processing circuitry, cause the processing circuitry to perform the function of any of claims 1 through 13.

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