JP7401046B2 - Brain function measurement device and brain function measurement method - Google Patents

Description

The present invention relates to a brain function measuring device and a brain function measuring method using magnetic field generating means such as a magnet, and means for detecting magnetic lines of force returning in a loop-shaped path of the magnetic field generating means.

In recent years, for example, functional near-infrared spectroscopy (NIRS) has been proposed as a method for non-invasively measuring brain function. This method calculates the amount of oxygenated hemoglobin flowing through the brain's capillaries by controlling the information transmission function of nerve cells, which converts visual and auditory information taken in from sensory organs such as the eyes and ears into electrical signals and propagates them to the brain. This method uses near-infrared light to measure changes in

Patent Documents 1 and 2 disclose non-invasive brain function measurement devices that measure brain activity in the cerebral cortex using functional near-infrared spectroscopy. This measurement device irradiates the brain with near-infrared light from a light source placed on the subject's scalp (hereinafter sometimes abbreviated as scalp), and the reflected and scattered light generated by this irradiation is also reflected onto the scalp. This invention measures the state of brain activity as changes in blood flow in the brain's capillaries by receiving light with a light receiver placed in the brain.

Furthermore, as a non-invasive brain function measurement method by measuring near-infrared light transmitted through the brain, an invention according to Patent Document 3 has been disclosed, in which a near-infrared light source is placed in the oral cavity and the base of the brain is By emitting near-infrared light from the head toward the scalp and receiving the transmitted light with a receiver placed on the scalp, brain activity is measured as changes in blood flow in the brain's capillaries. In this case, near-infrared light passes through deep parts of the brain, making it possible to measure brain function that reflects internal brain activity.

Furthermore, an invention related to Patent Document 4 is disclosed as a non-invasive brain function measuring device using a magnetic field generating means, in which a magnetic field generating source such as a magnet is placed in the oral cavity, and the magnetic field is applied from the base of the brain toward the scalp. By generating a magnetic field and measuring the transmitted magnetic field using magnetic field detection means placed on the scalp, brain activity can be measured as changes in the magnetic field.

Furthermore, an invention according to Non-Patent Document 1 has been disclosed as a non-invasive brain function measuring device using a magnet, in which a static magnetic field is irradiated inside the head from a magnetic field generating means installed on the scalp, and the outermost part of the brain is By measuring the strength of the magnetic field lines that return to the scalp via the cerebral cortex (hereinafter sometimes referred to as magnetic field strength) using a magnetic field detection means installed in the scalp, brain activity can be determined by measuring the magnetic field strength. It is measured as a change in

Japanese Patent Application Publication No. 57-115232 Japanese Unexamined Patent Publication No. 63-275323 Japanese Patent Application Publication No. 2010-082370 JP 2018-122019 Publication

Osamu Hiwaki, Development of non-invasive brain signal measurement technology using static magnetic fields that penetrate the cerebral cortex, NEURO2019 (42nd Japan Neuroscience Congress, 62nd Japan Neurochemistry Society Joint Meeting) Abstracts, 1O-08a1 -3, July 25-28, 2019, Niigata

In the measuring devices disclosed in Patent Documents 1 and 2, the near-infrared light source is located on the same scalp as the light receiver that receives the reflected light and scattered light, so the distance is, for example, several centimeters. , their spatial resolution is low and they can only measure brain activity in shallow parts of the brain, making it impossible to measure brain function inside the brain with high precision.
Furthermore, changes in the absorbance of oxygenated hemoglobin and deoxygenated hemoglobin can only be measured on the order of several seconds at most, and the temporal resolution is also low.

In the brain function measuring device disclosed in Patent Document 3, the near-infrared light emitting source is placed in the oral cavity, so power must be supplied to the light emitting source. For example, lead wires and signal lines are connected to the oral cavity. It is necessary to pull the battery into the mouth or place the battery in the oral cavity, which causes discomfort to the subject and complicates the measurement work. Furthermore, since near-infrared light is located at the base of the brain, there is concern that it may have an adverse effect on sensory organs near the base of the brain, such as the retina of the eye. Furthermore, the light receiver must be brought into close contact with the scalp, and if hair or the like gets caught between the light receiver and the scalp, measurement sensitivity will decrease.

In the brain function measurement device disclosed in Patent Document 4, a magnetic field generation source such as a magnet is placed in the oral cavity to generate a magnetic field from the base of the brain toward the scalp, and a magnetic field detector placed on the scalp detects the transmitted magnetic field. By measuring, some of the problems of the brain function measuring device disclosed in Patent Document 3 are solved. However, as is well known, the static magnetic field from a magnet etc. returns from the north pole to the south pole in a loop-like path, which causes a misalignment between the active area of the brain and the measurement point on the scalp, causing the magnet and magnetic field to be detected. There is a problem in that it becomes difficult to identify areas of the cerebral cortex near the straight line connecting the organs as active areas.

In the brain function measuring device disclosed in Non-Patent Document 1, a magnetic field is irradiated into the head from a magnetic field generating means made of a permanent magnet placed on the scalp, and is applied to the scalp via the cerebral cortex at the outermost part of the brain. Some of the problems of the brain function measuring device disclosed in Patent Document 4 are solved by measuring the returned magnetic field strength using a magnetic field detection means installed in the scalp. However, it is necessary to install the magnetic field generating means and the magnetic field detecting means as a set on the scalp with a predetermined distance apart, which makes it difficult to increase the density of the magnetic field detecting means. There is a problem in that the strength and direction of the magnetic field applied to the inside of the part cannot be easily changed.

In view of the above-mentioned problems, an object of the present invention is to provide a brain function measuring device and a brain function measuring method that enable highly accurate measurement that can accurately and easily identify active areas of the brain.
More specifically, a magnetic field is applied to the inside of the head from an electromagnet placed on the scalp, and by utilizing the phenomenon in which the magnetic field lines from the electromagnet return in a loop-like path, the magnetic field is transmitted via the cerebral cortex, the outermost part of the brain. By measuring the intensity of the magnetic field lines that return to the scalp with a magnetic field detector placed directly above the electromagnet, the active areas and state of the brain are measured.

The brain function measuring device of the present invention for achieving the above object includes a magnetic field generating means placed on the scalp, and a magnetic field detection device placed directly above the magnetic field generating means to detect the magnetic field generated by the magnetic field generating means. A brain function measuring device comprising means for irradiating a magnetic field from the magnetic field generating means to the outermost cerebral cortex of the brain, and utilizing a phenomenon in which lines of magnetic force from the magnetic field generating means return in a loop-shaped path. The present invention is characterized in that brain function is measured non-invasively by detecting with the magnetic field detection means the intensity of magnetic lines of force that return as a signal reflecting the activity state of the cerebral cortex.

The magnetic field generating means may be an electromagnet consisting of a plurality of coils configured and arranged so that a current in a predetermined direction is applied to each coil in order to irradiate a magnetic field to a localized position of the brain.

The electromagnet constituting the magnetic field generating means may be capable of changing the direction and intensity of magnetic lines of force generated from the plurality of coils by changing the direction and intensity of current application.

The magnetic field detection means for detecting a magnetic field returned as a signal reflecting the activity state of neurons in the cerebral cortex is a single-axis magnetic field detector or a two-axis magnetic field detector disposed directly above the magnetic field generation means. , or a three-axis magnetic field detector.

The magnetic field generation means and the magnetic field detection means are used as a set (hereinafter sometimes abbreviated as a detection end) to avoid interference with other magnetic field generation means or magnetic fields such as terrestrial magnetism existing in the measurement environment. Therefore, it may be installed inside a magnetically shielded container.

The method for measuring brain function of the present invention to achieve the above object irradiates a magnetic field to the outermost part of the brain, the cerebral cortex, using a magnetic field generating means placed on the scalp, and causes lines of magnetic force from the magnetic field generating means to loop. Brain function is measured non-invasively by using a magnetic field detection means to detect the strength of the magnetic field lines that return as a signal reflecting the activity state of neurons in the cerebral cortex by utilizing the phenomenon of returning along a path like this. It is characterized by

As the magnetic field generating means, an electromagnet consisting of a plurality of coils can be used.

As the electromagnet constituting the magnetic field generating means, it is possible to use an electromagnet that can change the direction and intensity of magnetic lines of force generated from a plurality of coils by changing the direction and intensity of current application.

The magnetic field detection means for detecting a magnetic field returned as a signal reflecting the activity state of neurons in the cerebral cortex may be a single-axis magnetic field detector or a two-axis magnetic field detector disposed directly above the magnetic field generating means. A magnetic field detector or a three-axis magnetic field detector can be used.

The magnetic field generation means and the magnetic field detection means are used as a set (hereinafter sometimes abbreviated as a detection end) to avoid interference with other magnetic field generation means or magnetic fields such as terrestrial magnetism existing in the measurement environment. Therefore, it can be installed and used inside a magnetically shielded container.

By changing the direction and intensity of the current applied to the magnetic field generating means, the direction and intensity of the magnetic lines of force may be changed and selected to detect the activation state of the cerebral cortex.

Alternatively, the depth of the magnetic field applied to the inside of the living body may be adjusted by changing the length of the coil in the magnetic field direction, and different activation states may be detected depending on the depth position of the cerebral cortex.

According to the brain function measuring device and the brain function measuring method of the present invention, the activation state of neurons in the cerebral cortex can be measured non-invasively with a relatively simple device configuration, and by using magnetic field signals, the activation state of neurons can be measured non-invasively. Even when hair or the like is caught between the ends and the scalp, highly accurate measurement is possible without being affected by it. Furthermore, there is no need to treat the hair or the like to improve contact with the scalp, unlike measurement methods that use electricity or light.
In addition, by using an electromagnet consisting of multiple coils configured and arranged so that a current is applied to each coil in a predetermined direction as a magnetic field generating means, local It becomes possible to irradiate a magnetic field to a certain position.
Furthermore, by adjusting the direction and intensity of the current applied to the coil, it is possible to change the direction and intensity of the magnetic lines of force, making it possible to change the direction and intensity of the magnetic lines of force irradiated with a single detection end, making it possible to change the direction and intensity of the magnetic lines of force. The activation status of nerve fibers in the cortex can be understood in detail.

FIG. 2 is a diagram illustrating the concept of a brain function measuring device and a brain function measuring method of the present invention, taking as an example the case of an electromagnet consisting of two coils. FIG. 3 is a diagram illustrating the concept of measurement using a magnetically shielded detection end, taking as an example the case of an electromagnet consisting of two coils. This is a diagram illustrating the concept of measurement in which the polarity of the magnetic field generating means is changed, taking as an example an electromagnet consisting of two coils. (b) is one in which a magnetic field is generated from a coil close to the magnetic field detection means in the opposite direction to the direction toward the scalp. FIG. 3 is a diagram showing the state of a brain activity measurement experiment. Figures illustrating the brain activity measurement method and measurement results during right wrist median nerve stimulation; (a) shows the arrangement of 16 detection ends on the scalp, and (b) shows the measurement with each detection end. This shows the time-series signal.

Since the present invention uses a method that uses magnetic fields, electroencephalography (EEG) is used to solve the inverse problem of evaluating which parts of the brain are activated from the measurement results at multiple points on the scalp. :EEG) has the following advantages.
1. Since the magnetic permeability of the head is approximately uniform, the permittivity of the substances intervening between nerve cells and the scalp (cerebrospinal fluid, dura mater, bone, etc., hereinafter sometimes abbreviated as intervening substances) is different. Compared to the electroencephalogram method, which is easily influenced by various factors, highly accurate measurement values can be obtained.
2. There is no need to consider intervening substances when finding a solution to the above inverse problem, and the algorithm can be simplified.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, parts having the same functions are given the same numbers and explanations may be omitted.

Figure 1 shows the concept of the brain function measuring device and brain function measuring method of the present invention, taking as an example the case of an electromagnet consisting of two coils. A magnetic field 4 is irradiated onto the cerebral cortex 3, which is the target of brain activity measurement, by a magnetic field generating means 2 consisting of an electromagnet configured and arranged so that a directional current is applied.
At this time, as shown in the figure, the magnetic field is applied to a local position approximately below the midpoint between the two coils.
The activation state of the cerebral cortex 3 is measured by measuring the magnetic field 4 that returns to the scalp 1 after undergoing changes due to interaction with brain activity using the magnetic field detection means 5.
The signal indicating the activation state of the cerebral cortex 3 measured by the magnetic field detection means 5 is transmitted as a time-series signal via an analog/digital converter (not shown), etc., to a personal computer (not shown). The signal is stored in the device, and signal processing, calculations, etc. are performed as necessary.
Although FIG. 1 only shows the measurement state using one set of magnetic field generating means 2 and magnetic field detecting means 5, if necessary, multiple sets of magnetic field generating means 2 and magnetic field detecting means 5 may be connected to the upper part of the subject's scalp 1. Of course, it is possible to measure the activity state of the cerebral cortex 3 at a plurality of points at the same time.

FIG. 2 takes as an example the case of an electromagnet consisting of two coils. In order to avoid interference with other magnetic field generating means 2 or magnetic fields such as the earth's magnetism existing in the measurement environment, a hollow cylindrical magnetic shielding container 8 is used. The detection end (magnetic field generation means 2 and magnetic field detection means 5) is shown in the figure, and the detection end is placed on the bottom of the magnetically shielded container 8 and placed on the scalp 1 via the mounting board 6 . has been done. By covering the detection end with the magnetic shield container 8 , it is possible to perform highly accurate measurement while suppressing the influence of the magnetic field that causes noise during measurement.
Note that, in order to enable magnetic field irradiation and magnetic field detection, the bottom portion of the magnetic shielding container 8 is of course made of a material that does not have a magnetic shielding effect.

FIG. 3 shows an example of an electromagnet consisting of two coils. By changing the direction of the current applied to the two coils constituting the electromagnet, the magnetic field 4 irradiated from the magnetic field generating means 2 to the cerebral cortex 3 can be increased. This figure shows a detection end structure with changed polarity. In the figure, (a) shows the magnetic field 4 generated in the direction from the coil close to the magnetic field detection means 5 toward the scalp 1, and (b) shows the magnetic field 4 generated in the opposite direction from the coil close to the magnetic field detection means 5 toward the scalp 1. A magnetic field 4 is generated in this direction.
Since the interaction between the magnetic field 4 and the activity of the cerebral cortex changes depending on their relative direction, by using methods (a) and (b) separately as necessary, the direction of the activity of nerve fibers in the cerebral cortex can be determined. It becomes possible to obtain a measured value by the magnetic field detection means 5 corresponding to the above.
Furthermore, by changing the intensity of the current applied to the electromagnet, the intensity of the magnetic field 4 irradiated from the magnetic field generating means 2 to the cerebral cortex 3 can be changed, and the activity of nerve fibers in the cerebral cortex can be controlled by the magnetic field 4. It becomes possible to measure the strength of

Furthermore, by changing the length of the coil in the magnetic field direction, it is possible to adjust the depth of the magnetic field irradiated inside the living body, and to detect different activation states depending on the depth position of the cerebral cortex.

1 to 3 show an example in which an electromagnet consisting of two coils with different applied current directions is used as a magnetic field generating means, but one of the coils is omitted and an electromagnet consisting of one coil is used as a magnetic field generating means. Of course, it can also be used as

Furthermore, instead of an electromagnet, it is also possible to use earth's magnetism existing in the environment as the magnetic field generating means.

An example of the brain function measuring device and the brain function measuring method of the present invention and its results will be described with reference to the drawings. In the drawings, parts having the same functions are given the same numbers and explanations may be omitted.

FIG. 4 shows an experimental state in which signals induced in the cerebral cortex 3 were measured in response to an electrical stimulation test of the median nerve of the left wrist using 16 detection terminals.
The magnetic field generating means 2 uses a figure-8 coil electromagnet with a diameter of 10 mm and 30 turns that generates a magnetic field in a localized area of the brain, and the magnetic field detecting means 5 uses a high-sensitivity sensor MI manufactured by Aichi Micro Intelligent. -CB-1DH was used. Furthermore, the mounting board 6 was made of a plastic disc with a diameter of 13 mm.
In the experiment, the magnetic field generating means 2 and the magnetic field detecting means 5 were placed close to the scalp. The magnetic field generating means 2 was installed so that the direction of the magnetic field 4 passing through the brain was in the front-back direction of the subject's head, and the magnetic field detecting means 5 was placed near the central axis of the front coil. A current of 200 mA was passed through the coil serving as the magnetic field generating means 2 so that the magnetic field generated by the magnetic field generating means 2 was directed forward in the brain.
The electrical stimulation was applied to the median nerve with a pulse width of 300's and an intensity of 3.6 mA using a surface stimulation electrode. The stimulation interval was set to 0.8 s, the signal was measured from 100 ms before stimulation to 500 ms after stimulation, and the somatosensory evoked signal was obtained by calculating the average of the 500 measurement data.

Figure 5 shows an overview of the experimental results, with (a) showing the locations where the 16 detection ends were placed on the subject's scalp, and (b) showing the actual time series obtained from the 16 magnetic detection means 5. This shows the signal waveform.
The location of the detection end is CFz, CF2, CF4, CF6, Cz, C2, C4, C6, CPz, CP2, CP4, CP6, Pz, P2 in the electrode placement of the expanded international 10-20 method used for electroencephalogram measurement. , P4, and P6.

The part of the cerebral cortex that is activated in response to median nerve stimulation of the right hand is the area that controls the hand in the primary somatosensory cortex of the left cerebral hemisphere, but the location of the extended international 10-20 method closest to this part is It is CP4. As a result of measurement using the prototype brain function measurement device and brain function measurement method, as shown in Figure 5(b), a large amplitude signal was observed localized to this CP4 region, confirming the effectiveness of the present invention. .

According to the present invention, it is possible to measure the activation state of the brain with high accuracy both temporally and spatially using a simple device configuration and a simple procedure, and it can be applied to non-invasive brain function measurement. can.

1 Scalp of the subject 2 Magnetic field generating means 3 Cerebral cortex 4 Magnetic field 5 Magnetic field detecting means 6 Mounting board 7 Direction of current flowing through the coil which is the magnetic field generating means 8 Magnetic shielding container

Claims (12)

A magnetic field generating means is placed on the scalp of the subject and is composed of an electromagnet that can change the direction and intensity of the generated magnetic lines of force ; A brain function measuring device comprising magnetic field detection means for detecting the intensity of magnetic lines of force returning via the cerebral cortex in a loop-like path as a signal reflecting an activity state . The brain function measuring device according to claim 1, wherein the electromagnet is a coil that generates a loop-shaped magnetic field in a localized region of the brain. 3. The brain function measuring device according to claim 2, wherein the electromagnet is an electromagnet that can change the direction and intensity of magnetic lines of force by changing the direction and intensity of current applied to a plurality of coils. 2. The magnetic field detector according to claim 1, wherein the magnetic field detection means is a 1-axis magnetic field detector, a 2-axis magnetic field detector, or a 3-axis magnetic field detector arranged directly above the magnetic field generating means. Brain function measurement device. The brain function measuring device according to claim 1, wherein the magnetic field generating means and the magnetic field detecting means are installed in a magnetically shielded container. A magnetic field generating means consisting of an electromagnet placed on the scalp of the subject and capable of changing the direction and intensity of the generated magnetic lines of force is used to irradiate a magnetic field to the cerebral cortex at the outermost part of the brain, and from the magnetic field generating means. Utilizing the phenomenon that magnetic lines of force return in a loop-like path, a magnetic field placed on the scalp detects the strength of the magnetic lines of force that return via the cerebral cortex as a signal reflecting the activity state of the cerebral cortex. A brain function measurement method characterized by non-invasively measuring brain function by detecting it using a means. 7. The brain function measuring method according to claim 6, wherein a plurality of coils are used as the electromagnets to generate a loop-shaped magnetic field in a local region of the brain. 8. The brain function measuring method according to claim 7, wherein the electromagnet is an electromagnet whose direction and intensity of magnetic lines of force can be changed by changing the direction and intensity of current applied to a plurality of coils. 7. The magnetic field detector according to claim 6, wherein a 1-axis magnetic field detector, a 2-axis magnetic field detector, or a 3-axis magnetic field detector arranged directly above the magnetic field generating means is used as the magnetic field detection means. Brain function measurement method. 7. The brain function measuring method according to claim 6, wherein the magnetic field generating means and the magnetic field detecting means are installed and used in a magnetically shielded container. The magnetic field is detected by the magnetic field detection means by changing the direction and intensity of the current applied to the plurality of coils constituting the electromagnet to change and select the direction and intensity of the magnetic lines of force . The method for measuring brain function according to any one of claims 7 to 10 . Claims 7 to 11, characterized in that the depth of the magnetic field applied to the inside of the living body is adjusted by changing the length of the magnetic field generating means in the magnetic field direction, and the magnetic field is detected by the magnetic field detecting means. The method for measuring brain function according to any one of these methods .

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