Transcranial magnetic stimulation coil

Abstract

The present invention provides a transcranial magnetic stimulation coil capable of generating an electric field in the deep part of the brain. A wearable device 2 is configured in a substantially spherical shape having an inner accommodation space capable of accommodating the head of a subject. A part of the wearable device 2 is an opening portion 21 through which the head can pass, so that the wearable device can be worn on the head via the opening portion 21. A first winding portion 11 is disposed on a right side surface portion 23, and a second winding portion 12 is disposed on a left side surface portion 24. Conducting wires constituting the first winding portion 11 and conducting wires constituting the second winding portion 12 are disposed on a top surface portion 22 and a back surface portion 25 as well. The conducting wires disposed on the top surface 22 are parallel to each other.

Description

Transcranial Magnetic Stimulation Coil

[0001] The present invention relates to a transcranial magnetic stimulation coil.

[0002] Transcranial magnetic stimulation (TMS) is a treatment that stimulates brain neurons by passing an electric current through a coil placed near the subject's brain to induce an electric field (see Patent Document 1 below). It has recently become clear that TMS is effective for many neurological disorders that are resistant to drug treatment.

[0003] TMS is also used to treat depression in patients for whom medication is ineffective. Approximately 30% of all depression patients are drug-resistant. However, among patients who undergo TMS treatment, only about 30% achieve remission, and there is a need to improve this remission rate. One of the reasons for the low remission rate with TMS treatment is thought to be the inability to generate an electric field deep within the brain.

[0004] Patent No. 6628340

[0005] The present inventors have discovered that by using an inverse problem analysis technique, it is possible to stimulate neurons deep within the brain by configuring the coil in a specific manner.

[0006] The present invention has been made based on the above findings, and a main object of the present invention is to provide a transcranial magnetic stimulation coil capable of generating an electric field deep in the brain.

[0007] The means for solving the above problems can be described as follows:

[0008] (Item 1) A coil device includes a coil body formed by winding a conductor around it, and a wearing device that supports the conductor and is detachably attached to the head of a subject, the wearing device being configured in a substantially spherical shape with a storage space capable of storing the head therein, and a portion of the wearing device being an opening through which the head can pass, thereby enabling the wearing device to be attached to the head via the opening, the wearing device having a top surface portion disposed in a position covering the top of the head, a right side surface portion disposed in a position covering the right side of the head, a left side surface portion disposed in a position covering the left side of the head, and a back surface portion disposed in a position covering the occipital region of the head, the coil body having a first winding portion formed by winding the conductor around a virtual first winding axis, and a second winding portion formed by winding the conductor around a virtual second winding axis, the first winding portion being disposed on the right side surface portion, and the second winding portion being disposed on the left side surface portion, A transcranial magnetic stimulation coil, wherein the conductor constituting the first winding portion and the conductor constituting the second winding portion are also arranged on the upper surface portion and the back surface portion, and the conductors arranged on the upper surface portion are parallel to each other.

[0009] (Item 2) The transcranial magnetic stimulation coil according to Item 1, wherein the conductors arranged on the upper surface portion are equally spaced apart.

[0010] (Item 3) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the spacing between the conductors arranged on the top surface portion is closer than the spacing between the conductors arranged on the right side surface portion and the spacing between the conductors arranged on the left side surface portion.

[0011] (Item 4) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the conductor constituting the first winding portion and the conductor constituting the second winding portion are spaced apart from each other so as not to overlap each other above the head.

[0012] (Item 5) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the first winding axis and the second winding axis are at the same position.

[0013] (Item 6) A transcranial magnetic stimulation device comprising: the transcranial magnetic stimulation coil according to item 1 or 2; and a power supply that supplies an alternating current or a current with a predetermined waveform to the transcranial magnetic stimulation coil.

[0014] (Item 7) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the coil body is configured by winding around one of the conductor wires.

[0015] (Item 8) The transcranial magnetic stimulation coil according to Item 1 or 2, further comprising a second coil body, the second coil body being configured by winding a second conductor in a direction different from the conductor constituting the coil body, and the second coil body being positioned so as to overlap with the coil body.

[0016] (Item 9) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the wearing device is a helmet type.

[0017] (Item 10) The transcranial magnetic stimulation coil according to Item 1 or 2, wherein the wearing device is configured to cover at least a portion of the user's face and a position below the user's eyes, and at least a portion of the first winding portion or the second winding portion is disposed at a position below the user's eyes.

[0018] According to the present invention, it is possible to provide a transcranial magnetic stimulation coil capable of generating an electric field deep in the brain, thereby making it possible to stimulate neurons deep in the brain.

[0019] 6A is a schematic explanatory diagram of a transcranial magnetic stimulation coil according to one embodiment of the present invention. It is an explanatory diagram schematically showing the position and current direction of the conductor in the magnetic stimulation coil of FIG. 1. It is a schematic plan view of FIG. 1. The bottom of the figure is the forward direction of the head (i.e., the direction of the face). It is an enlarged cross-sectional view of a main part taken along line A-A in FIG. 3. It is an explanatory diagram schematically showing an example of actual wiring of the magnetic stimulation coil of FIG. 1. It is a diagram showing the results of a simulation of the electric field strength generated in the brain using the magnetic stimulation coil of FIG. 1. It is a diagram showing the coil shape that is the premise of the simulation of FIG. 6A. It is a diagram showing the cross-sectional position that is the premise of the simulation result of FIG. 6A. It is a graph showing the results of a simulation of the electric field strength generated in the brain using the magnetic stimulation coil (helmet coil) of FIG. 1 and the electric field strength generated by a conventional figure 8 coil, in which the vertical axis represents the electric field strength and the horizontal axis represents the distance from the center of the head, i.e., depth (mm). It is an explanatory diagram schematically showing the position and current direction of the second conductor in the second coil body used in the transcranial magnetic stimulation coil according to Variation 1 of the present invention. 15 is an explanatory diagram showing the coil (conductor) of FIG. 2 as viewed from a different direction. FIG. 16 is an explanatory diagram showing the coil of FIG. 8 superimposed above the coil of FIG. 9. FIG. 17 is a graph showing the waveform of a current applied to two coils used in Modification 1, with the vertical axis representing the current value (I) and the horizontal axis representing time (t). FIG. 18 is a graph showing the waveform of a current applied to two coils used in Modification 1, with the vertical axis representing the current value (I) and the horizontal axis representing time (t). FIG. 19 is a graph showing the waveform of a current applied to two coils used in Modification 1, with the vertical axis representing the current value (I) and the horizontal axis representing time (t). FIG. 19 is a graph for explaining how an electric field having a beat frequency is generated by the overlap of two electric fields, with the vertical axis representing the electric field strength and the horizontal axis representing time (t). FIG. 19 is an explanatory diagram showing a full-face type wearing device in Modification 2 of the present invention as viewed from diagonally above the front. FIG. 19 is an explanatory diagram showing the wearing device of FIG. 15 as viewed from the front. FIG. 19 is an explanatory diagram showing the wearing device of FIG. 15 as viewed from above. FIG. 19 is an explanatory diagram showing the wearing device of FIG. 15 as viewed from the rear. FIG. 20 is an explanatory diagram showing a coil main body in Modification 2 of the present invention as viewed from diagonally above the front. 20 is an explanatory diagram of the coil body of Fig. 19 as seen from the front, an explanatory diagram of the coil body of Fig. 19 as seen from above, and an explanatory diagram of the coil body of Fig. 19 as seen from the rear.23 is an explanatory diagram of a transcranial magnetic stimulation coil with the coil main body of FIG. 19 attached to the wearing device of FIG. 15. FIG. 24 is an explanatory diagram of the magnetic stimulation coil of FIG. 23 viewed from the front. FIG. 25 is an explanatory diagram of the magnetic stimulation coil of FIG. 23 viewed from above. FIG. 26 is an explanatory diagram of the magnetic stimulation coil of FIG. 23 viewed from the rear. FIG. 27 is a graph showing the results of simulation of the electric field intensity produced by the magnetic stimulation coil (helmet coil) of FIG. 1, the electric field intensity produced by a conventional figure 8 coil, and the electric field intensity produced by the magnetic stimulation coil (full face coil), in which the vertical axis represents the electric field intensity and the horizontal axis represents the distance from the center of the head, i.e., the depth (mm).

[0020] A transcranial magnetic stimulation coil (hereinafter sometimes simply referred to as a "magnetic stimulation coil" or "coil") according to one embodiment of the present invention will be described below.

[0021] (Configuration of this embodiment) The coil of this embodiment is composed of a coil body 1 formed by winding a single conductor wire, and a helmet-type wearing device 2 that supports the conductor wire and is detachably worn on the subject's head (not shown) (see FIGS. 1 and 2). Note that FIG. 2 is intended to show the position of the conductor wire and the direction of current flow (see the arrows along the conductor wire in FIG. 2), and the actual coil body 1 is formed by winding a single conductor wire. A specific configuration example of the coil body 1 will be described later.

[0022] The wearing device 2 is configured in a roughly spherical shape with a storage space inside that can store the subject's head (see Figures 1 and 3). A part of the wearing device 2 (on the left side in Figure 1) is an opening 21 through which the head can pass, so that the wearing device 2 can be attached by placing it over the head through the opening 21.

[0023] The wearing device 2 has an upper surface part 22 positioned to cover the top of the head, a right side surface part 23 positioned to cover the right side of the head, a left side surface part 24 positioned to cover the left side of the head, and a back surface part 25 positioned to cover the back of the head (see Figures 1 and 3). These parts 22 to 25 of the wearing device 2 are configured to form an integrated, approximately spherical shape as a whole.

[0024] The coil body 1 has a first winding section 11 formed by winding a conductor around a virtual first winding axis (not shown) and a second winding section 12 formed by winding the conductor around a virtual second winding axis (not shown) (see FIG. 2). The first winding axis passes through approximately the center of the conductor wound with the smallest diameter in the first winding section 11 and is set at a position that passes near the frontal lobe of the brain inside the head when worn. The second winding axis passes through approximately the center of the conductor wound with the smallest diameter in the second winding section 12 and is set at a position that passes near the frontal lobe of the brain inside the head when worn. Preferably, the first winding axis and the second winding axis are in the same position (i.e., they overlap when extended).

[0025] The first winding portion 11 is disposed on the right side surface 23, and the second winding portion 12 is disposed on the left side surface 24. The conductors constituting the first winding portion 11 and the second winding portion 12 are also disposed on the top surface 22 and the back surface 25 (see FIG. 3). The conductors constituting the first winding portion 11 and the second winding portion 12 are disposed apart so that they do not overlap above the head.

[0026] The conductors arranged on the top surface 22 are parallel to each other. Furthermore, the conductors arranged on the top surface 22 are equally spaced apart. The spacing between the conductors arranged on the top surface 22 is closer than the spacing between the conductors arranged on the right side surface 23 and the spacing between the conductors arranged on the left side surface 24 (see FIGS. 1 to 3 ). In other words, the spacing between the conductors arranged on the top surface 22 is narrower than the maximum spacing between the conductors arranged on the right side surface 23 and the maximum spacing between the conductors arranged on the left side surface 24.

[0027] Here, the mounting fixture 2 has a groove 3 formed therein to match the wiring shape of the coil body 1, and by storing the conductor wire in this groove 3, it is possible to form the coil body 1 in a predetermined shape (see Figure 4).

[0028] (Specific Wiring Example) Figure 5 shows a specific example in which the coil body 1 is configured by winding a single conductor. In this example, the conductor is wound around starting from position P1 and passing sequentially through positions P2 to P10. The conductors may cross each other here, but appropriate insulation measures can be taken. Also, in Figure 5, at the intersection of the wires, one conductor passes through the inside of the wearing device 2. The conductor that passes through position P10 is extended to the opposite side of the wearing device 2 (the right side surface 23 in the illustrated example) and wound around again so as to be arranged in a substantially symmetrical manner (i.e., plane symmetry with respect to the left and right sides of the head).

[0029] A transcranial magnetic stimulation device can be configured with the transcranial magnetic stimulation coil of this embodiment and a power supply (not shown) that supplies an alternating current or a current of a predetermined waveform (e.g., pulsed) to the transcranial magnetic stimulation coil. The configuration of the power supply may be the same as that of a conventional transcranial magnetic stimulation device, and therefore a detailed description thereof will be omitted.

[0030] (Operation of this embodiment) Next, the operation of the magnetic stimulation coil of this embodiment will be described.

[0031] First, when wearing the device, the wearing device 2 with the coil main body 1 attached is placed over the subject's head. This allows the coil main body 1 to be placed in a position facing the required areas (in this embodiment, the parietal region, left and right temporal regions, and the occipital region of the subject's head). In TMS, the coil main body 1 must be placed in an accurate position relative to the head. In this embodiment, accurate positioning can be achieved simply by placing the wearing device 2 over the subject's head, which has the advantage of making it possible to perform TMS in clinics or homes with limited equipment.

[0032] Next, a current is passed from a predetermined power source through the coil body 1. This current is an alternating current or a pulsed current with a predetermined waveform. This generates an electric field at a predetermined position in the user's brain, thereby enabling TMS therapy.

[0033] (Simulation Results) A simulation was performed on the electric field generated by the magnetic stimulation coil configured according to this embodiment. The results are shown in FIG. 6A. FIG. 6A shows the electric field strength in a cross section (vertical cross section) in the longitudinal direction (vertical direction) of the magnetic stimulation coil. In this figure, the darker the density, the stronger the electric field strength. The coil shape used in the simulation (substantially the same as the coil in FIG. 2) is shown in FIG. 6B, and the vertical cross section in FIG. 6A is shown by the gray surface in FIG. 6C.

[0034] These results demonstrate that the magnetic stimulation coil of this embodiment can generate an electric field deep within the brain.

[0035] Figure 7 shows the results of a simulation of the electric field strength generated in the brain using the magnetic stimulation coil of this embodiment and the electric field strength generated by a conventional figure-eight coil (P / N 9925, 3190, Magstim). With the coil of this embodiment, the decrease in electric field strength is small even with increasing depth. This result also demonstrates that the magnetic stimulation coil of this embodiment can generate an electric field deep within the brain.

[0036] Considering the simulation results shown in Figures 6A and 7, it is believed that the coil of this embodiment can form a relatively localized (localized) electric field within the brain. This is expected to enable deep stimulation within the brain while relatively reducing stimulation to the surrounding area of ​​the target area. Therefore, the coil of this embodiment is expected to effectively stimulate the dorsolateral prefrontal cortex (DLPFC) or anterior cingulate cortex (ACC) with an electric field while reducing the possibility of side effects such as convulsions and headaches. Direct stimulation of the anterior cingulate cortex (ACC) with an electric field is believed to be effective in TMS treatment.

[0037] (Other Embodiments) (Modification 1) Next, another embodiment of the present invention (hereinafter referred to as "Modification 1") will be described with reference to Figures 8 to 10. In the description of Modification 1, components that are basically common to the above-described embodiment will be designated by the same reference numerals to avoid complication of description.

[0038] The magnetic stimulation coil of this first modification example includes a second coil body 210 in addition to the coil body 1. The second coil body 210 is formed by winding a single second conductor in a direction different from the winding direction of the conductor constituting the coil body 1. Specifically, the second conductor in the second coil body 210 of this embodiment is wound in a substantially horizontal direction. This winding direction can be referred to as horizontal winding if the winding direction of the coil body 1 is considered vertical winding. Note that FIG. 8 shows the position and current direction of the second conductor, and the actual second coil body 210 is formed by winding a single second conductor. For reference, FIG. 9 also shows the winding direction of the coil body 1.

[0039] The second coil body 210 is disposed in a position overlapping the upper side of the coil body 1 (see FIG. 10). Note that in FIGS. 8 to 10, the mounting fixture 2 is omitted to make the winding direction easier to see, but the second coil body 210 is also attached to the mounting fixture 2 by forming an appropriate groove (not shown) in the mounting fixture 2 or by other appropriate mounting means. Also, the second coil body 210 is naturally insulated from the coil body 1. Note that it is possible to overlap the second coil body 210 below the coil body 1.

[0040] 11 to 13 show examples of patterns of current applied to each coil in Modification 1. In these figures, vertical winding refers to the coil body 1, and horizontal winding refers to the second coil body 210.

[0041] In the example of Figure 11, a current is applied for one cycle, with the direction of the current reversing forward and backward. The phases of the currents applied to the coil body 1 and the second coil body 210 are shifted by a quarter of a cycle. This allows electric fields to be generated at different positions and with different timing, which can lead to even greater therapeutic effects. Actual treatment is performed by applying such a current (i.e., pulses) a predetermined number of times at predetermined intervals.

[0042] In the example of Fig. 12, a pulse current whose direction is constant and not reversed is applied for one period. Except for the phase shift amount being half a period, the other operations are the same as in the example of Fig. 11.

[0043] In the example shown in Figure 13, currents are applied to the coil body 1 and the second coil body 210 at slightly different frequencies. As a result, the intensity of the electric field formed by these currents has a "beat" that oscillates with a period equal to the difference between the two frequencies (see Figure 14). This corresponds to the envelope of the electric field intensity obtained by superposing the two electric fields. TMS treatment can be performed using an electric field with this beat frequency. This has the advantage that the frequencies of the magnetic and electric fields generated by each coil can be increased, which can be expected to generate electric fields at deeper locations, while also allowing electric fields to be generated at a frequency low enough for treatment.

[0044] Other configurations and advantages of the first modification are basically the same as those of the first embodiment, so further detailed explanation will be omitted.

[0045] (Modification 2) Next, yet another embodiment of the present invention (hereinafter referred to as "Modification 2") will be described with reference to Figures 19 to 26. In the description of Modification 2, components that are basically common to the above-described embodiment will be designated by the same reference numerals to avoid complication of description.

[0046] As shown in FIGS. 15 to 18 , the magnetic stimulation coil according to the second modification uses a wearing device 2 shaped like a full-face helmet. This wearing device 2 has a front portion 26 that covers the front of the face. An eye opening 261, which is a through-hole for exposing the eyes, is formed in the front portion 26 at a position corresponding to the user's eyes. That is, the wearing device 2 of the second modification is configured to cover at least a portion of the user's face, and a position below the user's eyes. The opening 21 of the second modification is formed in the lower part of the wearing device 2. In addition, in FIGS. 15 to 18 and 23 to 26 , hidden lines are appropriately indicated by dashed lines.

[0047] In Modification 2, a portion of the first winding portion 11 and the second winding portion 12 of the main body 1 is arranged in a position below the user's eyes (see FIGS. 19 to 26). In this embodiment, the conductors constituting the first winding portion 11 and the second winding portion 12 are arranged around the eye-opening portion 261. However, as shown in FIGS. 23 and 24, the conductors constituting the main body 1 are not arranged at the position of the eye-opening portion 261, thereby ensuring the safety of the user.

[0048] In the second modification, the mounting fixture 2 is also provided with a groove 3 for mounting the coil body 1, but the groove 3 is not shown in Figures 15 to 18 and 23 to 26. Note that it is possible to use other appropriate mounting means instead of the groove 3.

[0049] 1, the first winding portion 11 and the second winding portion 12 are partially crowded together near the temporal region, which can make it difficult to attach the conductors. In contrast, in Modification 2, the coil body 1 is arranged up to the front of the face, which has the advantage of being able to increase the electric field strength in the brain without having to crowd the first winding portion 11 and the second winding portion 12 near the temporal region.

[0050] Fig. 27 shows the results (full face coil) of a simulation of the electric field strength generated in the brain using the magnetic stimulation coil of Modification 2, in addition to the results shown in Fig. 7. According to Modification 2, the decrease in electric field strength with increasing depth is even less. This result shows that the magnetic stimulation coil of Modification 2 can generate an electric field at even deeper positions in the brain.

[0051] Other configurations and advantages of the second modification are basically the same as those of the first embodiment, so further detailed explanation will be omitted.

[0052] The present invention is not limited to the above-described embodiments, and various modifications may be made to the specific configuration of the present invention within the scope of the claims.

[0053] In the above-described embodiment, the coil body 1 is configured from a single conductor wire, but it is also possible to configure the coil body 1 from multiple conductor wires. In this case, current can be passed through each conductor wire individually. The pattern of current flow through each conductor wire can also be selected arbitrarily. It is also possible to configure the coil body 1 from multiple conductor wires and control the current pattern, etc., so that the same electric field can be generated as in the case of a single conductor wire. The same applies to the second coil body 210. The conductor wire may be at least one or more selected from the group consisting of a solid wire, a wire consisting of multiple single wires (e.g., stranded wire, Litz wire), and a solid or hollow pipe.

[0054] Furthermore, in the above-described embodiments, "parallel" and "equally spaced" do not need to be strict, and some deviation is permissible as long as it does not cause practical problems.

[0055] Furthermore, the current waveform applied to the coil body 1 and the second coil body 210 may be any waveform suitable for generating an electric field, and may be any waveform other than a sine wave, such as a square wave, a triangular wave, a sawtooth wave, etc. Here, the sine wave may be a sine wave with time decay.

[0056] The magnitude (absolute value) of the current and voltage applied to the coil may be determined within the range usable for the conductor that constitutes the coil. For example, the current may be 50 A or more, preferably 200 A or more, and more preferably 500 A or more, and may be 20,000 A or less, preferably 8,000 A or less, and more preferably 5,000 A or less. The voltage may be 10 V or more, preferably 50 V or more, and more preferably 200 V or more, and may be 10,000 V or less, preferably 5,000 V or less, and more preferably 2,000 V or less.

[0057] Furthermore, when a pulse current is applied to the coil, the pulse width (half-width of the pulse) may be 1 μs or more, preferably 10 μs or more, and more preferably 100 μs or more, or may be 100 ms or less, preferably 10 ms or less, and more preferably 1 ms or less.

[0058] REFERENCE SIGNS LIST 1 coil body 11 first winding portion 12 second winding portion 2 mounting fixture 21 opening 22 upper surface portion 23 right side surface portion 24 left side surface portion 25 rear surface portion 26 front surface portion 261 eyelet portion 3 groove 210 second coil body

Claims

1. A coil device comprising a coil body formed by winding a conductor around it, and a wearing device that supports the conductor and is detachably attached to the head of a subject, wherein the wearing device is configured in a substantially spherical shape with a storage space capable of storing the head inside, and a part of the wearing device has an opening through which the head can pass, thereby allowing the wearing device to be attached to the head via the opening, the wearing device has a top surface portion positioned to cover the top of the head, a right side surface portion positioned to cover the right side of the head, a left side surface portion positioned to cover the left side of the head, and a back surface portion positioned to cover the occipital region of the head, the coil body has a first winding portion formed by winding the conductor around an imaginary first winding axis, and a second winding portion formed by winding the conductor around an imaginary second winding axis, the first winding portion being positioned on the right side surface portion, and the second winding portion being positioned on the left side surface portion, A transcranial magnetic stimulation coil, wherein the conductor constituting the first winding portion and the conductor constituting the second winding portion are also arranged on the upper surface portion and the back surface portion, and the conductors arranged on the upper surface portion are parallel to each other.

2. The transcranial magnetic stimulation coil according to claim 1, wherein the conductors arranged on the upper surface are equally spaced apart.

3. A transcranial magnetic stimulation coil as described in claim 1 or 2, wherein the spacing between the conductors arranged on the top surface portion is closer than the spacing between the conductors arranged on the right side surface portion and the spacing between the conductors arranged on the left side surface portion.

4. A transcranial magnetic stimulation coil as described in claim 1 or 2, wherein the conductor constituting the first winding section and the conductor constituting the second winding section are spaced apart so that there is no overlapping portion above the head.

5. A transcranial magnetic stimulation coil according to claim 1 or 2, wherein the first winding axis and the second winding axis are in the same position.

6. A transcranial magnetic stimulation device comprising the transcranial magnetic stimulation coil according to claim 1 or 2 and a power supply that supplies an alternating current or a current of a predetermined waveform to the transcranial magnetic stimulation coil.

7. The transcranial magnetic stimulation coil according to claim 1 or 2, wherein the coil body is formed by winding a single conductor around the coil body.

8. A transcranial magnetic stimulation coil according to claim 1 or 2, further comprising a second coil body, the second coil body being formed by winding a second conductor in a direction different from the conductor constituting the coil body, and the second coil body being positioned so as to overlap with the coil body.

9. The transcranial magnetic stimulation coil according to claim 1 or 2, wherein the wearing device is a helmet type.

10. A transcranial magnetic stimulation coil as described in claim 1 or 2, wherein the wearing device is configured to cover at least a portion of the user's face and a position below the user's eyes, and at least a portion of the first winding portion or the second winding portion is positioned below the user's eyes.

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