I introduced one invasive neuromodulation method before, which is DBS
However, current technology is not mature enough, so invasive technique is a very dangerous way to stimulate brains.
If we want to stimulate the cranial nerves in a non-invasive way, can we do it? The answer is yes!
TMS is a noninvasive brain stimulation technique that we are introducing today.
The full name of TMS is Transcranial Magnetic Stimulation, which is a very common way to stimulate brain nerves noninvasively.
Transcranial magnetic stimulation TMS. Image Credit: Rumruay / Shutterstock R By
How does TMS work?
TMS is simply an annular metal ring with electrical currents, which generates a corresponding magnetic field.
The magnetic field can pass through the skull without being disturbed basically, forming a corresponding induced current in the brain
The current in the brain will stimulate the surrounding nerves, so as long as the position is calculated accurately, the nerves in a specific position in the brain can be stimulated, and then the purpose of non-invasive neuromodulation can be achieved.
Method
The researcher will take the TMS instrument and use a rack to fix it in place. Because the experiment time may be long, holding by hand will lose accuracy over time.
The instrument would be close to the subject's head, and brain tomography is usually done before the whole experiment to help the researcher determine the location of the stimulus in the subject’s brain.
A set of optical detectors and a display screen are often used to visualize the location. When in use, the researcher will look at the display screen to locate the direction of the TMS coil.
The purpose of the process is usually to stimulate some parts of the brain, thereby curing depression and other symptoms caused by inactive parts of the brain
Of course, stimulating a specific location, such as the sensory-motor reign of the brain, can also cause some specific muscles to contract involuntarily.
The way of stimulation is to generate magnetic fields of different frequencies by passing currents of different frequencies through the coil to achieve stimulation of different frequencies.
Sometimes you will see the word rTMS, which refers to repetitive TMS, the same technique but use repetitive electrical current to create repetitive stimuli.
Structure of TMS Device
As mentioned earlier, the TMS instrument consists of a set of coils, a position detection device, and a display screen.
Sometimes the position detection device will not be used, instead, the 10-20 position mentioned in the previous EEG is used to locate the stimulation positions
If you are interested, you can go back and review
The thing that is worth mentioning here is the shape of the coil.
In fact, other than the O-shaped coil, there are many variations. I will talk about two different types here because the others are basically the same with some adjusted angles.
Udupa K. Transcranial magnetic stimulation in exploring neurophysiology of cortical circuits and potential clinical implications. Indian J Physiol Pharmacol 2020;64(4):244-57.
On the left, it is a circular coil, we can see that the shape of its magnetic field is also a circle, and on the right is what we call it a figure 8 coil
With the current in different directions for the top and the bottom of figure 8, some magnetic fields can cancel each other, and some can strengthen each other, at the end it generates a concentrated and stronger magnetic field, which is very suitable for single-point stimulation.
The most commonly used TMS is the figure-8 coil, after all, its stimulation area is small, and therefore, more precise. It has better control of the position of the stimulation.
Other Research
I've seen research that moves coils to map functional locations throughout the whole brain
For example, when a finger moves while an area is under stimulation, we can mark the position as the motor movement of the finger.
Moreover, in some stroke patients, when they were repeatedly stimulated by TMS, the functional position changed. That means after constant stimulation, the brain will reconnect itself and bypass the damaged area
Perhaps this technology can be used to treat brain-related injuries in the future.
The speech is attached here, in case you are interested
Reminder
Although this technology is certified by the FDA, the United States Food and Drug Administration, it is still dangerous, because it is related to the brain after all.
For medical use, make sure to discuss with your doctor before the treatment
My Point of View
TMS is often used in medical treatment and research. Although I have not personally experienced research, I'm sure the current technology is not going to achieve the level that allows people to feel they actually touch things with their normal hands. However, by pulsing the TMS signal to the brain at different frequencies, we are able to speed up the reconnection of the brain, which would be very useful in the future if it could be applied to the treatment of many brain injuries. Although such an application is not the same as the original intention of the use of the brain-computer interface, it is not a bad thing to see a big step forward in medical treatment.
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