Relief of electrical sensations associated with treatment of a subject with an alternating electric field by deactivating selected electrode elements

Abstract

When an alternating current electric field is applied to a subject's body using an array of electrode elements, the subject may experience an electric sensation. This electric sensation can be improved by selectively deactivating (or reducing the current through) different electrode elements for different periods of time and receiving feedback indicating whether or not the electric sensation is occurring during each of the different periods. If deactivating (or reducing the current through) one of the particular electrode elements improves the electric sensation, the subject can be treated with the alternating current electric field while the particular electrode element remains deactivated (or is driven with less current).

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Application No. 63 / 411,939, filed September 30, 2022, the entirety of which is incorporated herein by reference. [Technical field] The present invention relates to the reduction of electrical sensations associated with treating a subject with an alternating electric field by deactivating selected electrode elements. [Background technology]

[0002] Tumor treating field (TT field) therapy is a proven approach to treating tumors using alternating current (AC) electric fields at frequencies between 50 kHz and 1 MHz (e.g., 150–200 kHz). In the conventional Optune® system, TT fields are delivered to the patient via four transducer arrays placed on the patient's skin adjacent to the tumor (e.g., the front, back, left, and right sides of the head in the case of glioblastoma). The transducer arrays are arranged in pairs, and each transducer array is connected to an AC signal generator via a multiwire cable. The AC signal generator (a) sends an AC current to the anterior / posterior pair of transducer arrays for 1 second to induce an electric field in the tumor in a first direction. Then, (b) sends an AC current to the left / right pair of arrays for 1 second to induce an electric field in the tumor in a second direction. Steps (a) and (b) are then repeated for the duration of the treatment. Each transducer array contains multiple (e.g., 9–20) electrode elements, all wired in parallel.

[0003] Alternating current electric fields can also be used to treat conditions other than tumors. For example, as described in U.S. Patent No. 10,967,167 (incorporated herein by reference in its entirety), alternating current electric fields can be used to increase the permeability of the blood-brain barrier (BBB), allowing, for example, chemotherapy drugs to reach the brain. Summary of the Invention [Means for solving the problem]

[0004] One aspect of the present invention relates to a first method for improving electrosensation in a subject receiving treatment with an alternating current electric field, the first method comprising selectively deactivating one or more different electrode elements during different time periods while an alternating current electric field is applied, receiving feedback indicating whether electrosensation occurs during the different time periods, and determining whether deactivating the particular electrode element or elements improves electrosensation.

[0005] Some examples of the first method further include treating the subject using an alternating electric field while the predetermined electrode element or elements are deactivated.

[0006] In some examples of the first method, accepting feedback is performed by accepting input from the subject. In some examples of the first method, accepting feedback is performed by processing electrical signals representing the subject's neural activity from a set of ECAP electrodes. In some examples of the first method, accepting feedback is performed by processing electrical signals representing measurements of the subject's neural or muscle activity. In some examples of the first method, accepting feedback is performed by processing electrical signals representing measurements of electromyogram signals for measuring muscle activity. In some examples of the first method, accepting feedback is performed by processing electrical signals representing measurements of accelerometers for measuring muscle activity.

[0007] Another aspect of the invention relates to a second method for improving electrosensation in a subject treated with an alternating current electric field, the second method comprising selectively reducing current through one or more different electrode elements during different time periods while an alternating current electric field is applied, receiving feedback indicating whether electrosensation is occurring during the different time periods, and determining whether reducing the current through a particular electrode element or elements improves electrosensation.

[0008] Some examples of the second method further include treating the subject using an alternating electric field while a given electrode element or elements are operating at a lower current than the other electrode elements.

[0009] In some examples of the second method, accepting feedback is performed by accepting input from the subject. In some examples of the second method, accepting feedback is performed by processing electrical signals representing the subject's neural activity from a set of ECAP electrodes. In some examples of the second method, accepting feedback is performed by processing electrical signals representing measurements of the subject's neural or muscle activity. In some examples of the second method, accepting feedback is performed by processing electrical signals representing measurements of electromyogram signals for measuring muscle activity. In some examples of the second method, accepting feedback is performed by processing electrical signals representing measurements of accelerometers for measuring muscle activity.

[0010] Another aspect of the present invention relates to a third method for applying an electrical signal to a first set of at least four first electrode elements and a second set of at least four second electrode elements positioned on opposite sides of a target region on a subject's body, the third method including: (a) applying an alternating current signal between the second set of at least four second electrode elements and a majority of the first electrode elements, wherein one or more different elements of the first set of at least four first electrode elements are not used or operate using a reduced current during different time periods, respectively; receiving first feedback indicating whether the subject is experiencing or about to experience electrical sensations during the different time periods; and determining, at least in part based on the received first feedback, whether electrical sensations are improved when one or more predetermined elements of the first set of at least four first electrode elements are not used or operate using a reduced current.

[0011] Some examples of the third method further include applying the alternating current electric field to the target region using a second set of at least four second electrode elements and all of the first electrode elements except one or more predetermined elements of the first set of at least four first electrode elements. Some examples of the third method further include applying the alternating current electric field to the target region while one or more predetermined elements of the first set of at least four first electrode elements are operating at a lower current than other elements of the first set.

[0012] In some examples of the third method, the step of accepting the first feedback is performed by accepting input from the subject. In some examples of the third method, the step of accepting the first feedback is performed by processing electrical signals representing neural activity of the subject from the set of ECAP electrodes.

[0013] Some examples of the third method further include controlling the amplitude of the alternating current signal. Optionally, these examples may further include increasing the amplitude of the alternating current signal until the determination indicates that the subject is experiencing or is about to experience an electric sensation.

[0014] In some examples of the third method, before step (a), the method further includes applying an alternating current signal between a second set of at least four second electrode elements and all of the first electrode elements during a first period of time, and receiving feedback indicating whether the subject is experiencing or about to experience an electrical sensation during the first period of time.

[0015] Some examples of the third method further include applying a second alternating current signal between a first set of at least four first electrode elements and a majority of the second electrode elements, wherein one or more different elements of the second set of at least four second electrode elements are not used or operate using a reduced current during different respective time periods, receiving second feedback during the application of the second alternating current signal indicating whether the subject is experiencing or about to experience electrosensation, and determining, based at least in part on the received second feedback, whether electrosensation is improved when one or more predetermined elements of the second set of at least four second electrode elements are not used or operate using a reduced current. Optionally, these examples may further include applying an alternating current electric field to the target region using the first set of at least four first electrode elements and all second electrode elements except for certain elements of the second set of at least four second electrode elements.

[0016] In some examples of the third method, the step of receiving the first feedback is performed by processing electrical signals representing measurements of nerve or muscle activity of the subject. In some examples of the third method, the step of receiving the first feedback is performed by processing electrical signals representing measurements of electromyogram signals for measuring muscle activity. In some examples of the third method, the step of receiving the first feedback is performed by processing electrical signals representing measurements of accelerometer signals for measuring muscle activity.

[0017] In some examples of the third method, during application, at least two different elements of the first set of at least four first electrode elements are not used or operate using a reduced current during different respective time periods, and in these examples, determining includes determining whether the electrical sensation is improved when at least two predetermined elements of the first set of at least four first electrode elements are not used or operate using a reduced current.

[0018] Another aspect of the present invention relates to a first device for applying electrical signals to a first set of at least four first electrode elements and a second set of at least four second electrode elements positioned on opposite sides of a subject's body. The first device includes an AC signal source, a first set of at least four first electrically controlled switches, and a controller. The AC signal sources have at least one amplitude control input. Each first switch is configured, depending on the state of its respective first control input, to either (i) close to allow current to flow between the AC signal source and its respective first electrode element, or (ii) open to prevent current from flowing between the AC signal source and its respective first electrode element. The controller is configured to control the state of the first control input of each of the first switches, and is further configured to (a) apply a first control signal to the first control input causing a selected one of the first switches to open for a respective time period; (b) accept a plurality of first feedback signals indicating whether the subject is experiencing or about to experience an electric sensation while the selected one of the first switches is open for the respective time period; and (c) determine, based at least in part on the accepted plurality of first feedback signals, whether the electric sensation is improved when a particular one of the first switches is open.

[0019] In some embodiments of the first device, the controller is further configured to control application of the electrical signal to the first set of at least four first electrode elements and the second set of at least four second electrode elements such that a predetermined one of the first switches is open while the subject is being treated with the alternating electric field.

[0020] Some embodiments of the first device further include a user interface configured to generate a plurality of first feedback signals based on input received from the subject. Some embodiments of the first device further include an ECAP measurement system configured to accept signals representative of neural activity from the set of ECAP electrodes, the ECAP measurement system generating the plurality of first feedback signals.

[0021] In some embodiments of the first device, the controller is further configured to control the amplitude control input. Optionally, in these embodiments, the controller may be further configured, prior to step (a), to apply a first control signal to the first control input that causes all of the first switches to close, control the amplitude control input to increase the amplitude, and accept a third signal indicative of whether the subject is experiencing or about to experience an electrosensation.

[0022] Some embodiments of the first device further include a second set of at least four second electrically controlled switches, each second switch configured to (i) close to allow current to flow between the AC signal source and a respective second electrode element or (ii) open to prevent current from flowing between the AC signal source and a respective second electrode element, depending on the state of a respective second control input. In these embodiments, the controller is further configured to control the state of the second control input of each second switch, and the controller is further configured to (x) apply second control signals to the second control inputs to cause selected ones of the second switches to open for respective time periods, (y) accept a plurality of second feedback signals indicating whether the subject is experiencing or about to experience electrosensation while selected ones of the second switches are open for respective time periods, and (z) determine whether electrosensation is improved when a particular one of the second switches is open, based at least in part on the received plurality of second feedback signals.

[0023] Optionally, in the embodiment of the first device described in the previous paragraph, the controller is further configured to control application of the electrical signals to the first set of at least four first electrode elements and the second set of at least four second electrode elements such that a predetermined one of the second switches is open while the subject is being treated with the alternating electric field. Optionally, the embodiment described in the previous paragraph may further include a user interface, the user interface configured to generate a plurality of first feedback signals and a plurality of second feedback signals based on input received from the subject. Optionally, the embodiment described in the previous paragraph may further include an ECAP measurement system configured to accept signals representing neural activity from the set of ECAP electrodes, the ECAP measurement system generating a plurality of first feedback signals and a plurality of second feedback signals.

[0024] Some embodiments of the first device further include a second set of at least four second electrically controlled switches, each configured to (i) close to allow current to flow between the AC signal source and a respective second electrode element, or (ii) open to prevent current from flowing between the AC signal source and a respective second electrode element, depending on the state of a respective second control input. In these embodiments, the controller is further configured to control the state of the second control input of each second switch, and the controller is further configured to (x) apply second control signals to the second control inputs to cause selected ones of the second switches to open for respective time periods, (y) accept a plurality of second feedback signals indicating whether the subject is experiencing or about to experience electrosensation while selected ones of the second switches are open for respective time periods, and (z) determine whether electrosensation is improved when a particular one of the second switches is open based at least in part on the received plurality of second feedback signals. The controller is further configured to control the amplitude control input.

[0025] Optionally, in the embodiment of the first device described in the previous paragraph, the controller is further configured, before step (a), to apply a first control signal to the first control input that closes all of the first switches, control the amplitude control input to increase in amplitude, and accept a third signal indicating whether the subject is experiencing or about to experience an electric sensation. [Brief explanation of the drawings]

[0026] [Figure 1] 1 shows how a transducer array can be positioned on a subject's head to treat glioblastoma using alternating electric fields. [Figure 2] FIG. 1 is a block diagram of an embodiment of treating a subject using an alternating electric field with one or more electrode elements deactivated to improve electrosensation. [Figure 3] 1 is a flowchart of an approach for determining which transducer array contributes most to electrosensation. [Figure 4] 1 is a flowchart of an approach for determining which electrode elements in a particular transducer array contribute most to electrosensation. [Figure 5] FIG. 10 is a block diagram of another embodiment of treating a subject using an alternating electric field with one or more electrode elements deactivated to improve electrosensation. DETAILED DESCRIPTION OF THE INVENTION

[0027] Various embodiments will now be described in detail with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0028] When treating a subject with an AC electric field, the greater the amplitude, the greater the therapeutic effect. However, as the amplitude of the AC electric field increases or the frequency of the AC electric field decreases (e.g., to around 100 kHz), some subjects experience an electrosensory effect when the AC electric field switches direction. This electrosensation can be, for example, a vibratory sensation, paresthesia, a sensation of muscle fiber twitching or contraction, or a flickering sensation of light in the eyes. These sensations can deter some subjects from continuing treatment with the AC electric field. The electrosensation is believed to arise from the interaction of the AC electric field with nerve cells or fibers (neurons or axons) located near or adjacent to the transducer array. Disclosed herein are devices and methods for reducing electrosensation while treating a subject with an AC electric field by deactivating one or more electrode elements.

[0029] 1 shows an example in which four transducer arrays 21, 22, 23, and 24 are positioned on the front, back, left, and right sides of a subject's head. As the amplitude of the AC electric field increases and / or the frequency of the AC electric field decreases, the subject may begin to experience electrical sensations beneath or near one or more of the transducer arrays 21-24.

[0030] As the amplitude of the AC electric field increases and / or the frequency of the AC electric field decreases, the subject may begin to experience electrical sensations under or near one or more of the transducer arrays 21-24. However, it is also possible that the onset of electrical sensations occurs only under one, two, or three of these transducer arrays. For ease of explanation, assume that once the amplitude of the AC electric field reaches a predetermined value, a given subject begins to experience electrical sensations only under the left transducer array 23. This electrical sensation limits the amplitude of the AC electric field that can be comfortably applied to the subject, thereby limiting the effectiveness of the treatment.

[0031] In the illustrated example, each transducer array 21-24 (including the left transducer array 23) includes nine electrode elements. However, in alternative examples, each transducer array 21-24 can include a different number of electrode elements (e.g., from 4 to 50 electrode elements). Each transducer array 21-24 is similar in many respects to a conventional Optune® transducer array. However, unlike Optune® transducer arrays, the electrode elements in any transducer array of FIG. 1 are not all wired in parallel. Instead, each electrode element in any transducer array 21-24 is provided with an independent conductor, allowing each electrode element in any transducer array to be independently activated or deactivated. One example of a suitable approach for implementing a transducer array with independently activatable and independently deactivatable electrode elements is disclosed in U.S. Pat. No. 11,395,916 (Wasserman et al., hereinafter the “916 patent”), the entire contents of which are incorporated herein by reference.

[0032] Due to the arrangement of nerve fibers within a subject's body, the presence of sweat, or other factors, electrosensation may result from only a few (e.g., one or two) of the nine electrode elements in a particular transducer array. In this situation, electrosensation can be improved by selectively deactivating one or more different electrode elements during different time periods while applying an AC electric field, receiving feedback indicating whether electrosensation occurs during each of the different time periods, and determining whether deactivating a particular electrode element(s) improves electrosensation. The subject is then treated with an AC electric field while the selected electrode element(s) is / are inactive. This allows the amplitude of the AC electric field to be increased without causing discomfort to the subject.

[0033] 2-4 illustrate a first approach for determining which electrode elements within a transducer array are responsible for electrosensation in a particular subject and then deactivating those electrode elements when using the transducer array to treat the subject with alternating current electric field therapy (e.g., a TT field). More specifically, FIG. 2 is a block diagram of one embodiment for treating a subject using an alternating current electric field with one or more electrode elements deactivated to improve electrosensation, FIG. 3 is a flowchart of an approach for determining which transducer array elements are most contributing to electrosensation, and FIG. 4 is a flowchart of an approach for determining which electrode elements within a particular transducer array are most contributing to electrosensation.

[0034] FIG. 2 illustrates an apparatus for treating a target region of a subject's body with an AC electric field that avoids or mitigates electrical sensations based on user feedback received via a user interface 80. The embodiment of FIG. 2 includes an AC voltage generator 40 that generates an AC output at a frequency between 50 kHz and 1 MHz (e.g., 50-500 kHz, 75-300 kHz, or 150-250 kHz). The AC voltage generator 40 has at least one control input that can be used, for example, to control the output amplitude of the AC voltage generator 40. The frequency of the AC voltage generator 40 varies depending on the type of treatment. For example, when using a TT field to treat tumors, the frequency would be between 150 and 200 kHz. Alternatively, the frequency could be between 50 kHz and 200 kHz (e.g., 100 kHz) to increase the permeability of the subject's blood-brain barrier.

[0035] In the example shown in FIG. 2 , a transducer array 23 including a set of first electrode elements 45L is positioned to the left of a target area on the subject's body (e.g., shaved skin), and a transducer array 24 including a set of second electrode elements 45R is positioned to the right of the target area on the subject's body. In another embodiment, the first set of electrode elements 45L / 45R and the second set of electrode elements 45L / 45R can be implanted in the subject's body (e.g., just beneath the skin) to the left and right of the target area, respectively. When an AC voltage generator 40 applies a voltage between electrode elements 45L and 45R, an AC electric field is induced in the target area with electric field lines running generally from right to left. The frequency of the AC electric field matches the frequency of the AC voltage generator 40. Electrode elements 45L / 45R may be capacitively coupled or conductive electrode elements.

[0036] Notably, the electrode elements in any of the transducer arrays 23-24 are not all wired in parallel. Instead, each electrode element in any of the transducer arrays 23-24 is provided with an independent conductor, allowing each electrode element in any of the transducer arrays to be independently activated or deactivated. This can be accomplished using an electronic switch bank 60 that includes a dedicated switch for each electrode element 45R in the right transducer array 24 and a dedicated switch for each electrode element 45L in the left transducer array 23 (e.g., as described in the '916 patent). Thus, in the example shown in FIG. 2 (where the left and right transducer arrays 23 and 24 each include nine electrode elements), the electronic switch bank 60 includes 9 × 2 = 18 switches.

[0037] The AC voltage generator 40 has one output pin for powering the left electrode element 45L and another output pin for powering the right electrode element 45R. Nine switches in bank 60 either (a) allow the signal from the left output pin of AC voltage generator 40 to reach each of the electrode elements 45L in transducer array 23 or (b) block the signal from the left output pin of AC voltage generator 40 from reaching each of the electrode elements, depending on the state of control signals arriving from controller 30. Additionally, nine additional switches in bank 60 either (a) allow the signal from the right output pin of AC voltage generator 40 to reach each of the electrode elements 45R in transducer array 24 or (b) block the signal from the right output pin of AC voltage generator 40 from reaching each of the electrode elements, depending on the state of control signals arriving from controller 30. This allows the controller 30 to independently activate or deactivate each electrode element 45L in the left transducer array 23, and also allows the controller 30 to independently activate or deactivate each electrode element 45R in the right transducer array 24.

[0038] User interface 80 accepts input from a user indicating whether the subject is experiencing electrical sensations, which may be implemented using, for example, a touch screen, a keyboard, dedicated push buttons, voice recognition, or any of a variety of other approaches apparent to those skilled in the relevant art.

[0039] Assume a situation in which a subject is experiencing electrical sensations. Using the flowcharts of Figures 3 and 4, it can be determined which electrode elements of which transducer arrays are most contributing to the electrical sensations. Once this information is confirmed, the controller 30 can deactivate the identified electrode elements. Treatment of the patient with an alternating electric field (e.g., a TT field) can then proceed.

[0040] 3, the controller 30 sends control signals to the switch bank 60 so that the signal from the left terminal of the AC voltage generator 40 is applied to all electrode elements 45L of the left transducer array 23, and the signal from the right terminal of the AC voltage generator 40 is applied to all electrode elements 45R of the right transducer array 24. The controller 30 also sends control signals to the AC voltage generators to control the amplitude of the AC voltages.

[0041] Next, in S30, the controller 30 determines whether an electric sensation is occurring. This determination is made based on input received from the user interface 80. If an electric sensation is not occurring, the process proceeds to S40, where the controller determines whether a temperature limit (e.g., 41°C) has been reached. If the temperature limit has not been reached, the process proceeds to S42, where the controller 30 issues a command to the AC voltage generator to increase its amplitude. The process then returns to S30, and the S30 / S40 / S42 loop continues until either an electric sensation occurs or the temperature limit is reached.

[0042] If the temperature limit is reached (which can be determined, for example, based on input from a temperature sensor incorporated into the transducer array), processing proceeds to S60, where controller 30 outputs an indication that temperature was the limiting factor.

[0043] If an electrical sensation occurs (this is determined based on input from the user interface 80 informing the controller 30 which transducer array 23 / 24 caused the electrical sensation), processing proceeds to S50, where the controller 30 stores information indicating which transducer array (i.e., the left array 23 or the right array 24) was responsible for the electrical sensation, and the amplitude setting A1 of the AC signal generator 40 at which the electrical sensation began.

[0044] Once the controller 30 identifies which transducer array is responsible for electrosensation (i.e., the left array 23 or the right array 24), it coordinates the application of electrical signals to a first set of at least four first electrode elements and a second set of at least four second electrode elements located on opposite sides of the subject's body. (Note that in this paragraph and the paragraph describing FIG. 4 below, the electrode elements on the side responsible for electrosensation are referred to as the first set of first electrode elements, and the electrode elements on the opposite side are referred to as the second set of second electrode elements.) The controller 30 then configures the switches in the bank 60 to apply alternating current signals between the second set of at least four second electrode elements and a majority of the first electrode elements, where different elements in the first set of at least four first electrode elements are not used during different time periods. The controller 30 then receives first feedback (via the user interface 80) indicating whether the subject is experiencing or about to experience electrosensation during different time periods. Based at least in part on the received first feedback, the controller determines whether improved electrosensation occurs when certain elements in the first set of at least four first electrode elements are not used.

[0045] One example of how the controller 30 may perform the steps described in the previous paragraph is to implement the flowchart of FIG. 4 to determine whether a particular electrode element in an identified transducer array contributes more to electrical sensation than other electrode elements in that transducer array. Specifically, a loop is initialized in S120, and in S130-S150, the loop is implemented to set switches in the bank 60, apply an AC signal of amplitude A1 to all but one of the first electrode elements, and receive feedback from the user via the user interface 80 to determine whether electrical sensation is occurring. Each time through the loop, a different one of the first electrode elements is deactivated. If no electrical sensation occurs during a pass through the loop, the process jumps from S140 to S170, where an AC electric field ("AEF") is applied to a target region of the subject's body using a second set of second electrode elements and all but one of the first electrode elements of a given first set of electrode elements. In this way, the electrode elements that contribute most to the electrical sensation are deactivated and the amplitude of the AC signal generated by the AC voltage generator 40 can be increased to a level above A1.

[0046] If there is no electrical sensation at all when passing through the loop (as reported via the user interface 80), the process jumps from S150 to S160 and applies an alternating electric field to the subject's body with an amplitude less than A1 using all electrode elements in the first set and the second set of electrode elements.

[0047] It should be noted that instead of isolating the electrosensation problem to a particular electrode element within a particular transducer array using the steps shown in FIG. 3 and then using the steps shown in FIG. 4 to deactivate one electrode element at a time until the electrosensation disappears, an alternative approach can be used. In this alternative approach, the steps shown in FIG. 3 (which isolate the electrosensation problem to a particular transducer array) are omitted. Instead, the process begins by performing the steps shown in FIG. 4 for a particular one of the transducer arrays, deactivating one electrode element at a time and determining whether the electrosensation disappears when one of the electrode elements is deactivated. If deactivating any of the particular transducer arrays does not eliminate the electrosensation, the controller 30 performs the steps shown in FIG. 4 for the next transducer array, deactivating one electrode element at a time and determining whether the electrosensation disappears when one of the electrode elements of the second transducer array is deactivated. If deactivating an electrode element on the second transducer array eliminates the electrical sensation, the controller 30 can identify the electrode element causing the problem and continue treating the subject while leaving that electrode element deactivated.

[0048] The operation of the embodiment of FIG. 2 is not limited to the specific situation described above in connection with FIGS. 3 and 4, where only a single electrode element on any transducer array is responsible for electrosensing. Conversely, two or more electrode elements on a particular transducer array may be responsible for electrosensation. In this situation, multiple electrode elements may be turned off for different periods of time, and feedback is received indicating whether the subject is experiencing or about to experience electrosensation during each of the different periods. Finally, the system determines, at least in part, whether electrosensation is improved when two or more electrode elements are not being used.

[0049] Returning to Figure 2, instead of using a switch bank 60 to individually turn on and off current through each electrode element 45L, 45R, a circuit bank may be used that can individually block current through each electrode element. Activation of any circuit in the bank reduces the current through each of the electrode elements 45L, 45R, rather than completely blocking the current. These embodiments are otherwise similar to the embodiments described above in connection with Figures 2-4.

[0050] Additional situations are also contemplated in which two or more electrode elements on a particular transducer array cause electrical sensations. In one example, the electrode elements are organized into groups, and the groups are arranged so that all elements within a particular group are simultaneously switched on or off. For example, a 3 × 3 electrode element array is divided into three groups, each containing three electrode elements. In this situation, rather than turning off each electrode element individually to determine whether the subject experiences (or is about to experience) electrical sensations, as described above in connection with FIG. 4, the electrode elements in each group are turned off collectively to determine whether the subject experiences electrical sensations when that group is turned off. If any group is found to be causing electrical sensations, that group can be disabled or the current to that group can be reduced to improve electrical sensations.

[0051] In another situation, electrode elements are arranged in groups of two or more closely spaced electrode elements, with individual elements within the group being switched on or off to deliver different levels of current to specific areas of the subject's body. For example, 18 electrode elements can be arranged in a 3x3 array of electrode element pairs. When both elements in any pair are on, a certain level of current is delivered to the spot under that pair. However, if only one element in a particular pair is on, only 50% of the specified level of current is delivered to that location. Again, the current delivered to each pair of electrode elements can be reduced in turn to determine whether the subject is experiencing (or is about to experience) electrical sensations. If any group is found to be the cause of the electrical sensation, that group can be operated at a lower current to improve the electrical sensation.

[0052] In many anatomical locations, it is desirable to use an electric field whose orientation alternates between different directions. In these locations, additional transducer arrays, each including a set of at least four electrode elements 45 (not shown in FIG. 2 ), may be placed on other sides (e.g., anterior and posterior) of the target region. In these embodiments, the AC voltage generator 40 is preferably configured to repeatedly alternate between (a) applying a voltage between the left electrode element 45L and the right electrode element 45R and (b) applying a voltage between the anterior electrode element and the posterior electrode element. The AC voltage generator 40 can switch between these two states every second or at different intervals (e.g., between 50 milliseconds and 10 seconds). Thus, the direction of the electric field in these embodiments repeatedly alternates between the left / right and anterior / posterior directions.

[0053] In these bidirectional embodiments, the electronic switch bank 60 includes a dedicated switch for each electrode element in each additional array. Thus, in an example where each transducer array includes nine electrode elements, the electronic switch bank 60 includes 9 x 4 = 36 switches. This allows the controller 30 to individually activate or deactivate each electrode element in the additional transducer arrays. The additional transducer arrays (i.e., the front and rear transducer arrays 21-22) are treated in a manner similar to the left and right transducer arrays 23-24 described above.

[0054] 2-4, the controller 30 determines that an electrical sensation is occurring (S30 and S140) based on feedback from the subject received via the user interface 80. However, in an alternative embodiment, instead of relying on the user interface to notify the system that an electrical sensation is occurring, the system can automatically detect that the subject is experiencing (or about to experience) an electrical sensation using hardware that measures electrically evoked compound action potentials (ECAPs).

[0055] During certain types of electrical stimulation of biological tissue, electrically evoked compound action potentials (ECAPs) represent the nearly synchronized firing of a population of electrically stimulated nerve fibers. When an electrical signal of sufficient energy to activate nerve fibers is applied, fibers of different diameters and in different locations are activated nearly simultaneously (e.g., within a few milliseconds), and their action potentials (APs) propagate at different velocities near the recording electrode. Furthermore, different nerve fibers of different diameters have different activation thresholds and conduction velocities, conveying different signals for, for example, types of sensation (e.g., vibration, temperature, hair movement, muscle contraction, joint position).

[0056] It turns out that ECAPs, which are related to electrosensation, can be measured using a series of electrodes placed on a subject's skin. These electrodes detect the combined sum of individual APs arriving at approximately the same time, which are displayed as a curve of predetermined amplitude and duration. The signals from these electrodes can be used to detect or predict whether a subject is likely experiencing, or is about to experience, electrosensation.

[0057] 5 illustrates embodiments that rely on ECAP signals received using such electrodes to detect or predict whether a subject may be experiencing or is about to experience electrosensation. In these embodiments, the ECAP signals provide feedback to controller 30 (instead of user interface 80 in the embodiment of FIG. 2).

[0058] The AC voltage generator 40, switch bank 60, and electrode elements 45L, 45R in this embodiment of Figure 5 are similar to the corresponding elements in the embodiment of Figure 2 above. The operation of the controller 30 is also similar to that of the controller in the embodiment of Figure 2, with one important exception. More specifically, whereas the approach of Figure 2 receives feedback from a user interface indicating that the subject is experiencing electrosensation, in this embodiment of Figure 5, the controller 30 receives feedback from the ECAP system 50 indicating whether the subject is experiencing or about to experience electrosensation.

[0059] 5, in addition to the electrode elements 45L / 45R used to induce an AC electric field in the target region, separate electrode sets 55L, 55R are also provided for determining whether the subject is likely experiencing or about to experience electrosensation. More specifically, a first ECAP electrode set 55L configured to detect ECAP signals is positioned near the first electrode set 45L, and a second ECAP electrode set 55R configured to detect ECAP signals is positioned near the second electrode set 45R. The first and second ECAP electrode sets 55L, 55R, positioned on the left and right sides, respectively, may each be passive electrode arrays.

[0060] Signals (e.g., about 0.2 to 2 mV) from these ECAP electrodes 55L, 55R are received by the ECAP measurement system 50, which measures the ECAP on the left and right sides of the subject's body based on the signals arriving from the ECAP electrodes 55L, 55R positioned on the left and right sides, respectively. The ECAP measurement system 50 processes these signals (e.g., using an amplifier and an analog-to-digital converter) and transfers the resulting data to the controller 30. In this manner, the ECAP generated on each side of the subject's body in response to the application of an AC electric field is measured.

[0061] ECAP associated electrosensation is measured using ECAP electrodes 55L, 55R and ECAP measurement system 50, and those measurements are reported to controller 30 so that controller 30 can determine whether the subject is likely experiencing electrosensation or is about to experience electrosensation. Thus, controller 30 in this FIG. 5 embodiment can perform steps similar to those described above in connection with FIGS. 3-4, except that instead of receiving feedback from a user interface that electrosensation is occurring (S30 and S140), controller 30 in this FIG. 5 embodiment receives feedback from ECAP system 50 indicating whether the subject is experiencing electrosensation or is about to experience electrosensation.

[0062] As explained above, at some anatomical locations, it may be desirable to use electric fields that alternate in different directions. In these locations, additional transducer arrays may be provided, located on other sides of the target region (e.g., anterior and posterior). In this situation, each set of electrode elements 45 preferably has its own associated set of ECAP electrodes 55x that is used to determine whether the subject is likely experiencing or about to experience electrosensation. Controller 30 responds to signals arriving from these additional sets of ECAP electrodes 55x (preprocessed by ECAP system 50) as explained above for signals arriving from the left and right sets of ECAP electrodes 55L, 55R (also preprocessed by ECAP system 50).

[0063] The embodiment of FIG. 5 relies on a passive array of ECAP electrodes to measure neural activity, based on the theory that neural activity can be used to determine whether electrosensation is occurring or imminent. However, various alternative approaches for automatically determining whether electrosensation is occurring or imminent can be used in place of the ECAP-based techniques described above. One example of an alternative approach is to measure muscle activity using electromyography signals, based on the theory that muscle activity (e.g., twitching) can indicate the occurrence of electrosensation. In these embodiments, electromyography (EMG) signals are acquired using a set of EMG electrodes, preprocessed by an EMG system, and forwarded to a controller (similar to controller 30 described above, but programmed to interpret EMG signals rather than ECAP signals). Another example of an alternative approach is to measure muscle activity using mechanical sensors (e.g., accelerometers), based on the theory that muscle activity (e.g., twitching) is an indication that electrosensation is occurring. In these embodiments, vibration or acceleration signals are captured using mechanical sensors, preprocessed by an appropriate front end, and forwarded to a controller (similar to controller 30 above, but programmed to interpret mechanical events rather than ECAP signals). Other approaches based on measured nerve or muscle activity can also be used.

[0064] Illustrative Embodiments

[0065] Embodiment 1 is a method of improving electrosensation in a subject receiving treatment with an alternating current electric field, the method comprising selectively deactivating one or more different electrode elements during different time periods while the alternating current electric field is being applied; receiving feedback indicating whether electrosensation is occurring during the different time periods; and determining whether deactivating the particular electrode element or elements improves electrosensation.

[0066] Embodiment 2 is the method of embodiment 1, further comprising treating the subject using an alternating electric field while the predetermined electrode element or elements are deactivated.

[0067] Embodiment 3 is the method of embodiment 1, wherein the step of accepting feedback is performed by accepting input from the subject.

[0068] Example 4 is the method of Example 1, wherein the step of receiving feedback is performed by processing electrical signals representative of the subject's neural activity from the set of ECAP electrodes.

[0069] Embodiment 5 is the method of embodiment 1, wherein the step of receiving feedback is performed by processing electrical signals representing a measure of the subject's nerve or muscle activity.

[0070] Example 6 is the method of Example 1, wherein the step of receiving feedback is performed by processing an electrical signal representing a measurement of an electromyogram signal for measuring muscle activity.

[0071] Embodiment 7 is the method of embodiment 1, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of an accelerometer for measuring muscle activity.

[0072] Embodiment 8 is a method of improving electrosensation in a subject treated with an alternating current electric field, the method comprising selectively reducing current through one or more different electrode elements during different time periods while the alternating current electric field is applied; receiving feedback indicating whether electrosensation is occurring during the different time periods; and determining whether reducing the current through a particular electrode element or elements improves electrosensation.

[0073] Example 9 is the method of Example 8, further comprising treating the subject using an alternating electric field while a given electrode element or elements are operating at a lower current than other electrode elements.

[0074] Embodiment 10 is the method of embodiment 8, wherein the step of accepting feedback is performed by accepting input from the subject.

[0075] Example 11 is the method of Example 8, wherein the step of receiving feedback is performed by processing electrical signals representing the subject's neural activity from the set of ECAP electrodes.

[0076] Example 12 is the method of Example 8, wherein the step of receiving feedback is performed by processing electrical signals representing a measure of the subject's nerve or muscle activity.

[0077] Embodiment 13 is the method of embodiment 8, wherein the step of receiving feedback is performed by processing an electrical signal representing a measurement of an electromyogram signal for measuring muscle activity.

[0078] Example 14 is the method of Example 8, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of an accelerometer for measuring muscle activity.

[0079] Embodiment 15 is a method for applying an electrical signal to a first set of at least four first electrode elements and a second set of at least four second electrode elements positioned on opposite sides of a target region on a subject's body, the method comprising: (a) applying an alternating current signal between the second set of at least four second electrode elements and a majority of the first electrode elements, wherein one or more different elements of the first set of at least four electrode elements are not used or operate using a reduced current during respective different time periods; receiving first feedback indicating whether the subject is experiencing or about to experience electrical sensations during respective different time periods; and determining, at least in part based on the received first feedback, whether electrical sensations are improved when one or more particular elements of the first set of at least four electrode elements are not used or operate using a reduced current.

[0080] Example 16 is the method of Example 15, further comprising applying an alternating electric field to the target area using a second set of at least four second electrode elements and all of the first electrode elements except for one or more predetermined elements of the first set of at least four first electrode elements.

[0081] Embodiment 17 is the method of embodiment 15, further comprising a step in which one or more predetermined elements of the first set of at least four electrode elements are operated at a lower current than other elements of the first set to apply an alternating electric field to the target area.

[0082] Embodiment 18 is the method of embodiment 15, wherein the step of accepting the first feedback is performed by accepting input from the subject.

[0083] Embodiment 19 is the method of embodiment 15, wherein the step of receiving the first feedback is performed by processing electrical signals representing the subject's neural activity from the set of ECAP electrodes.

[0084] Embodiment 20 is the method of embodiment 15, further comprising the step of controlling the amplitude of the AC signal.

[0085] Embodiment 21 is the method of embodiment 20, further comprising a step of increasing the amplitude of the alternating current signal until the determination indicates that the subject is experiencing or is about to experience an electric sensation.

[0086] Embodiment 22 is the method of embodiment 15, further comprising, before step (a), applying an alternating current signal between a second set of at least four second electrode elements and all of the first electrode elements during a first period, and receiving feedback indicating whether the subject is experiencing or about to experience an electrical sensation during the first period.

[0087] Embodiment 23 is the method of embodiment 15, further comprising the steps of applying a second alternating current signal between a first set of at least four first electrode elements and a majority of the second electrode elements, wherein one or more different elements of the second set of at least four second electrode elements are not used or operate using a reduced current during different periods of time; receiving second feedback indicating whether the subject is experiencing or about to experience electrical sensations during the application of the second alternating current signal; and determining, at least in part based on the received second feedback, whether electrical sensations are improved when one or more predetermined elements of the second set of at least four electrode elements are not used or operate using a reduced current.

[0088] Embodiment 24 is the method of embodiment 23, further comprising applying an alternating electric field to the target area using a first set of at least four first electrode elements and all but certain elements of a second set of at least four second electrode elements.

[0089] Embodiment 25 is the method of embodiment 15, wherein the step of receiving the first feedback is performed by processing an electrical signal representing a measure of the subject's nerve or muscle activity.

[0090] Embodiment 26 is the method of embodiment 15, wherein the step of receiving the first feedback is performed by processing an electrical signal representing a measurement of an electromyogram signal for measuring muscle activity.

[0091] Embodiment 27 is the method of embodiment 15, wherein the step of receiving the first feedback is performed by processing an electrical signal representing a measurement of an accelerometer for measuring muscle activity.

[0092] Example 28 is the method of example 15, wherein during application, at least two different elements of the first set of at least four first electrode elements are not used or operate using a reduced current during respective different periods, and determining includes determining whether the electrical sensation is improved when at least two predetermined elements of the first set of at least four first electrode elements are not used or operate using a reduced current.

[0093]

[0013] Example 29 is an apparatus for applying electrical signals to a first set of at least four first electrode elements and a second set of at least four second electrode elements disposed on opposite sides of a subject's body, the apparatus including: an alternating current signal source having at least one amplitude control input; a first set of at least four first electrically controlled switches, each first switch configured to (i) close to allow current to flow between the alternating current signal source and a respective first electrode element or (ii) open to prevent current from flowing between the alternating current signal source and a respective first electrode element depending on a state of a respective first control input; and a controller configured to control the state of the first control input of each first switch. The controller is further configured to (a) apply a first control signal to the first control input to open selected first switches for respective time periods, (b) accept a plurality of first feedback signals indicating whether the subject is experiencing or about to experience electrical sensations while the selected first switches are open for the respective time periods, and (c) determine whether electrical sensations are improved when a given first switch is open based at least in part on the accepted plurality of first feedback signals.

[0094] Embodiment 30 is the device of embodiment 29, wherein the controller is further configured to control the application of electrical signals to a first set of at least four electrode elements and a second set of at least four electrode elements so that a predetermined one of the first switches opens while the subject is being treated with the alternating electric field.

[0095] Embodiment 31 is the device of embodiment 29, further including a user interface, wherein the user interface is configured to generate a plurality of first feedback signals based on input received from the subject.

[0096] Embodiment 32 is the device of embodiment 29, further including an ECAP measurement system configured to receive signals representing neural activity from the set of ECAP electrodes, the ECAP measurement system generating a plurality of first feedback signals.

[0097] Example 33 is the apparatus of example 29, wherein the controller is further configured to control the amplitude control input.

[0098] Embodiment 34 is the device of embodiment 33, wherein the controller is further configured, before step (a), to apply a first control signal to the first control input that causes all of the first switches to be closed, to control the amplitude control input to increase in amplitude, and to accept a third signal indicating whether the subject is experiencing or about to experience an electrical sensation.

[0099] Example 35 is the device of Example 29, further including a second set of at least four second electrically controlled switches, each second switch configured to (i) close to allow current to flow between the AC signal source and a respective second electrode element or (ii) open to prevent current from flowing between the AC signal source and a respective second electrode element in response to a state of a respective second control input, the controller being further configured to control the state of the second control input of each second switch, the controller being further configured to (x) apply second control signals to the second control inputs to cause selected second switches to open for respective time periods, (y) accept a plurality of second feedback signals indicating whether the subject is experiencing or about to experience electrosensation while the selected second switches are open for the respective time periods, and (z) determine whether electrosensation is improved when a given second switch is open based at least in part on the received plurality of second feedback signals.

[0100] Embodiment 36 is the device of embodiment 35, wherein the controller is further configured to control the application of electrical signals to the first set of at least four electrode elements and the second set of at least four electrode elements so that a predetermined one of the second switches is open while the subject is being treated with the alternating electric field.

[0101] Embodiment 37 is an apparatus of embodiment 35, further including a user interface, wherein the user interface is configured to generate a plurality of first feedback signals and a plurality of second feedback signals based on input received from the subject.

[0102] Embodiment 38 is an apparatus of embodiment 35, further including an ECAP measurement system configured to receive signals representing neural activity from a set of ECAP electrodes, the ECAP measurement system generating a plurality of first feedback signals and a plurality of second feedback signals.

[0103] Example 39 is the apparatus of example 35, wherein the controller is further configured to control the amplitude control input.

[0104] Embodiment 40 is the device of embodiment 39, wherein the controller is further configured, before step (a), to apply a first control signal to the first control input causing all of the first switches to close, control the amplitude control input to increase the amplitude, and accept a third signal indicating whether the subject is experiencing or about to experience an electrical sensation.

[0105] Headings are provided for convenience only and should not be construed as limiting the invention in any way. Embodiments described under any heading or in any portion of this disclosure may be combined with embodiments described under the same heading or other headings or other portions of this disclosure. Unless otherwise specified herein or clearly contradicted by context, any combination of elements described herein in all possible variations is encompassed by the invention.

[0106] Although the present invention has been disclosed with reference to particular embodiments, numerous modifications, changes, and variations can be made to the described embodiments without departing from the scope of the invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but rather have the full scope defined by the language of the following claims and equivalents thereof. [Explanation of symbols]

[0107] 30 Controllers 40 AC voltage generator 45L, 45R electrode element 50 ECAP measurement system 55L, 55R electrode set 60 Switch Bank 80 User Interface

Claims

1. An apparatus for applying an electrical signal to a first set of at least four first electrode elements and a second set of at least four second electrode elements positioned on the opposite side of the subject's body, An AC signal source having at least one amplitude control input, A first set of at least four first electrical control switches, each of which is configured to either (i) close so that current flows between the AC signal source and each of the first electrode elements, or (ii) open so that current does not flow between the AC signal source and each of the first electrode elements, depending on the state of the respective first control input, The system includes a controller configured to control the state of each of the first control inputs of the first electrical control switch, The aforementioned controller further, (a) Apply a first control signal to the first control input and open the selected switch from the first electrical control switches during the respective periods. (b) While the selected first electrical control switch is open during each period, the subject receives a plurality of first feedback signals indicating whether or not he is experiencing or about to experience electrosensation, (c) A device configured to determine, at least in part, whether electrical sensation has improved when a particular one of the first electrical control switches is open, based on the plurality of accepted first feedback signals.

2. The apparatus according to claim 1, wherein the controller is further configured to control the application of electrical signals to a first set of at least four of the first electrode elements and a second set of at least four of the second electrode elements, so that a particular one of the first electrical control switches is opened while a subject is being treated in an alternating electric field.

3. The apparatus according to claim 1, further comprising a user interface, the user interface configured to generate the plurality of first feedback signals based on input received from a subject.

4. The apparatus according to claim 1, further comprising an ECAP measurement system configured to receive signals representing neural activity from a set of ECAP electrodes, wherein the ECAP measurement system generates the plurality of first feedback signals.

5. The apparatus according to claim 1, wherein the controller is further configured to control the amplitude control input.

6. The controller further, before step (a), A first control signal is applied to the first control input that closes all of the first electrical control switches. The amplitude control input is controlled to increase the amplitude, and, The apparatus according to claim 5, configured to receive a third signal indicating whether a subject is experiencing or about to experience electrosensation.

7. A second set of at least four second electrical control switches, Each of the second electrical control switches is configured to either (i) close so that current flows between the AC signal source and each of the second electrode elements, or (ii) open so that current does not flow between the AC signal source and each of the second electrode elements, depending on the state of the respective second control input, and further comprises a second set of the second electrical control switches. The controller is further configured to control the state of each of the second control inputs of the second electrical control switch. The aforementioned controller further, (x) Apply a second control signal to the second control input and open the selected switch from the second electrical control switches during the respective periods. (y) While the selected second electrical control switch is open for each period, the subject receives a plurality of second feedback signals indicating whether or not he is experiencing or about to experience an electrical sensation, (z) The apparatus according to claim 1, configured to determine, at least in part, whether electrical sensation has improved when a particular one of the second electrical control switches is open, based on the plurality of accepted second feedback signals.

8. The apparatus according to claim 7, wherein the controller is further configured to control the application of electrical signals to a first set of at least four of the first electrode elements and a second set of at least four of the second electrode elements, so that a particular one of the second electrical control switches is opened while a subject is being treated in an alternating electric field.

9. The apparatus according to claim 7, further comprising a user interface, the user interface configured to generate a plurality of first feedback signals and a plurality of second feedback signals based on input received from a subject.

10. The apparatus according to claim 7, further comprising an ECAP measurement system configured to receive signals representing neural activity from a set of ECAP electrodes, wherein the ECAP measurement system generates a plurality of first feedback signals and a plurality of second feedback signals.

11. The apparatus according to claim 7, wherein the controller is further configured to control the amplitude control input.

12. The controller further, before step (a), A first control signal is applied to the first control input that closes all of the first electrical control switches. The amplitude is increased by controlling the amplitude control input, and, The apparatus according to claim 11, configured to receive a third signal indicating whether a subject is experiencing or about to experience electrosensation.

13. A method for improving electrical sensation in subjects receiving treatment using an alternating electric field, A controller configured to control each electrode element while an alternating electric field is applied selectively deactivates one or more different electrode elements during different periods of time. The controller receives feedback indicating whether or not electrical sensations are occurring during each different period, A method comprising the step of determining whether the electrosensory sensation is improved when the controller deactivates one or more specific electrode elements.

14. The method according to claim 13, further comprising the step of the controller treating a subject using the alternating electric field while a particular one or more electrode elements are deactivated.

15. The method according to claim 13, wherein the step of receiving feedback is performed by receiving input from a subject.

16. The method according to claim 13, wherein the step of receiving feedback is performed by processing electrical signals representing the activity of a subject's nerves from a set of ECAP electrodes.

17. The method according to claim 13, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of nerve or muscle activity of the subject.

18. The method according to claim 13, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of electromyographic signals for measuring muscle activity.

19. The method according to claim 13, wherein the step of receiving feedback is performed by processing an electrical signal representing an accelerometer measurement for measuring muscle activity.

20. A method for improving electrical sensation in subjects receiving treatment using an alternating electric field, A controller configured to control each electrode element while an alternating electric field is applied selectively reduces the current flowing through one or more different electrode elements during different periods. The controller receives feedback indicating whether or not electrical sensations are occurring during each different period, A method comprising the step of determining whether the controller improves electrosensory perception by reducing the current flowing through one or more specific electrode elements.

21. The method according to claim 20, further comprising the step of the controller treating a subject using the alternating electric field while a particular one or more electrode elements are operating at a lower current than other electrode elements.

22. The method according to claim 20, wherein the step of receiving feedback is performed by receiving input from a subject.

23. The method according to claim 20, wherein the step of receiving feedback is performed by processing electrical signals representing the activity of a subject's nerves from a set of ECAP electrodes.

24. The method according to claim 20, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of nerve or muscle activity of the subject.

25. The method according to claim 20, wherein the step of receiving feedback is performed by processing electrical signals representing measurements of electromyographic signals for measuring muscle activity.

26. The method according to claim 20, wherein the step of receiving feedback is performed by processing an electrical signal representing an accelerometer measurement for measuring muscle activity.

27. ​​A method for applying an electrical signal to a first set of at least four first electrode elements and a second set of at least four second electrode elements positioned opposite a target region of a subject's body, (a) A controller configured to control the first electrode elements and the second electrode elements applies an AC signal between a second set of at least four of the second electrode elements and a majority of the first electrode elements, wherein one or more different elements of the first set of at least four of the first electrode elements are not used for different periods or operate with reduced current; The controller receives a first feedback indicating whether the subject is experiencing or attempting to experience electrosensation during each different period, A method comprising the step of determining, at least in part, based on the accepted first feedback, whether the electrosensory perception has improved when one or more specific elements of a first set of at least four first electrode elements are not used or are operating with a reduced current.

28. The method according to claim 27, further comprising the step of the controller applying an alternating electric field to a target region using a second set of at least four of the second electrode elements and all first electrode elements of a first set of at least four of the first electrode elements except for one or more specific elements.

29. The method of claim 27, further comprising the step of applying an alternating electric field to a target region, wherein the controller applies an alternating electric field to a target region, with one or more specific elements of a first set of at least four first electrode elements operating at a lower current than the other elements of the first set.

30. The method according to claim 27, wherein the step of receiving first feedback is performed by receiving input from a subject.

31. The method according to claim 27, wherein the step of receiving first feedback is performed by processing electrical signals representing the activity of a subject's nerves from a set of ECAP electrodes.

32. The method according to claim 27, further comprising the step of the controller controlling the amplitude of the AC signal.

33. The method of claim 32, further comprising the step of increasing the amplitude of the AC signal until a determination indicates that the subject is experiencing or about to experience an electrosensation.

34. Before step (a), During the first period, the controller applies an AC signal between at least four second electrode elements and all first electrode elements. The method according to claim 27, further comprising the step of the controller receiving feedback indicating whether the subject is experiencing or about to experience an electrosensation during the first period.

35. The controller applies a second AC signal between a first set of at least four of the first electrode elements and a majority of the second electrode elements, The step of having one or more different elements of the second set of at least four of the second electrode elements either not being used for different periods or operating with reduced current, The controller receives a second feedback indicating whether the subject is experiencing or attempting to experience an electrical sensation while the second AC signal is being applied, The method according to claim 27, further comprising the step of determining whether the electrical sensation has been improved when one or more specific elements of the second set of at least four second electrode elements are not used or are operating with a reduced current, based at least in part on the accepted second feedback.

36. The method of claim 35, further comprising the step of the controller applying an alternating electric field to the target region using a first set of at least four of the first electrode elements and all second electrode elements of a second set of at least four of the second electrode elements except for a specific element.

37. The method according to claim 27, wherein the step of receiving first feedback is performed by processing electrical signals representing a measurement of nerve or muscle activity of the subject.

38. The method according to claim 27, wherein the step of receiving first feedback is performed by processing an electrical signal representing a measurement of an electromyographic signal for measuring muscle activity.

39. The method according to claim 27, wherein the step of receiving first feedback is performed by processing an electrical signal representing an accelerometer measurement for measuring muscle activity.

40. During the application step, at least two different elements of the first set of the at least four first electrode elements are either not used or operate with reduced current during their respective different periods. The method according to claim 27, wherein the determining step includes determining whether electrical sensation has improved when at least two specific elements of the first set of at least four first electrode elements are not used or are operating with a reduced current.

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