Physical education as a means of improving brain activity

Rhythms of bioelectric activity

Brain neurons have their own electrical waves, which can be recorded using an electroencephalogram. This procedure allows you to learn a lot about a person’s health status.

Bioelectric rhythms are divided into several types according to frequency and amplitude:

1. Alpha waves. This type of waves appears when a person dreams. They are associated with imaginative thinking. This state appears in a person when he is relaxed, doing yoga or meditation. During these periods, the pictures in your head become much brighter and the boundaries become clearer. In this state, the brain is able to quickly perceive new information. The frequency of alpha waves is 8-13 Hz.
2. Beta waves. This type of waves predominates while a person is awake. It is characterized by motor activity. During this period, the left hemisphere of the brain is activated. An excess of beta waves can be seen in people's behavior. In this case, it is characterized by increased emotionality and overexcitation. Depression and apathy indicate a lack of beta waves in the brain. People with a predominance of the rhythm of these waves are often dependent on a variety of bad habits, such as alcohol, smoking and drugs. By evening, wave activity decreases. The frequency of beta waves is 14-20 Hz.
3. Gamma waves. The predominance of these bioelectrical rhythms causes a state of hyperconsciousness. Ordinary reason fades into the background. This state is popularly called inspiration. The rhythm frequency of these waves is 21 -30 Hz.
4. Delta waves. This rhythm has the lowest frequency, which is 1-4 Hz. People whose brains activate delta waves most frequently are highly intuitive. Their presence also helps people better navigate space. An excess of delta waves makes a person feel guilty, even if he was not involved in the incident.
5. Theta waves. A similar rhythm is recorded in a state of meditation or in sleep with dreams. It is in this state that some representatives of humanity see prophetic dreams. The pictures that appear in your head are more blurry and carry a deeper meaning. A large number of people are deprived of this type of wave activity. The rhythm frequency is 4-8 Hz.

High brain frequencies

High-frequency brain activity primarily includes beta rhythms. The range of beta rhythms is quite wide, so in neurofeedback it is usually divided into 3 components: lower beta (12-15 Hz), beta (15-22 Hz) and upper beta (23-35 Hz).

Low Beta (12-15 Hz)

Low beta is one of the most interesting rhythms because it includes the sensorimotor rhythm (SMR), if this activity is recorded in the area of ​​the sensorimotor cortex (between C3 and C4). Low beta is based on the same mechanism of signal transmission in the thalamocortical loop that produces alpha rhythm. Those. low beta is also the frequency of relative brain inactivity.

Sensorimotor rhythm became a source of considerable interest to scientists more than 30 years ago when Dr. Barry Sterman, studying SMR in cats, accidentally discovered that cats that had been additionally trained to produce SMR were much more resistant to the effects of the toxin methylhydrazine. Sterman identified SMR as the rhythm of inactivity of the brain's motor system and characterized it as an indicator of the intention to remain still.

In experiments examining the toxic effects of aviation fuel, cats that received SMR training showed significantly less susceptibility to seizures caused by the toxin. This led to further research into CMR training as a means of reducing epileptic seizures in children. In addition to the anticonvulsant effect, CMR training has shown significant benefits in solving a large number of problems, such as insomnia, tics, tremors, and has generally established itself as a method of significantly increasing the body’s resistance to any type of stress.

Thanks to these properties, over the past decades, CMR training has increasingly found use in clinical practice. Essentially, this type of training allows doctors to influence the psychophysiological state of patients at the most fundamental level, rather than focusing on working with symptoms.

In adults, the SMR is typically found in the frequency range between 12 and 15 Hz. Sometimes this range can be shifted up or down. For example, in 8-year-old children, the alpha range may be closer to 6.5 - 9.5 Hz, and the SMR is correspondingly shifted to 9-12 Hz.

The best way to establish the SMR range is empirical. If the SMR range is chosen correctly, then when training it, you usually experience relaxation of the body, a significant decrease in muscle tone and often drowsiness. If there is no response to SMR training, then it is necessary to gradually change the trained range until the desired response is obtained.

The sensorimotor rhythm is also called “sleep spindles.” It appears during the initial stages of slow-wave sleep, which immediately follows drowsiness. The brain's ability to stay out of beta, produce synchronous rest frequencies, and, if necessary, desynchronize again into beta, also ensures the ability to sleep soundly and wake up rested. In the case of insomnia, SMR training often results in falling asleep during the training session. However, even while asleep, SMR training continues to have beneficial effects.

Beta rhythm (15-22 Hz)

Beta waves are commonly associated with conscious thinking and inherently indicate brain activation and interaction between different areas of the cerebral cortex. Because this interaction typically occurs between closely spaced cortical areas, beta activity is more localized than low-frequency brain activity.

Beta training is quite widely used in neurofeedback to train the activation of different areas of the brain. In cases where a lack of beta activity is obvious and the existing problems are related to underactivation of the brain, beta training can be effective in activating problem areas and normalizing thinking and behavior. Beta is also used in peak performance training, which can be used even in the absence of any problems, to improve mental speed and concentration.

At its core, the beta rhythm is an antagonist of the alpha rhythm. The more beta rhythm activity in any area of ​​the brain, the less able the brain is to generate alpha rhythm in that area. This is why alpha training with eyes closed usually also involves beta suppression.

For most people, a useful beta frequency range is 15-22 Hz. Predominant activity in the higher range may be experienced as arousal and anxiety. Also, anxiety and restlessness can be felt if the beta level in the right hemisphere is higher than in the left. If the beta level significantly exceeds the theta level, this is an indicator that the brain is trying to shield the conscious mind from subconscious material.

High beta (23-35 Hz)

When a person is worried about something and cannot stop the thought process, this is usually manifested on the EEG by an increase in activity in the upper beta range. Activity in this range can only be trained in the direction of decrease and not vice versa. Normally, the brain does not produce much upper beta, since it is extremely energy-consuming and can only be useful if some dangerous situation arises that requires quick decisions and actions.

The presence of high levels of upper beta in the left temporal lobe is often the result of emotional neglect and lack of attention from parents during childhood. Under the influence of these factors, or any psychotraumatic events, the brain often develops the ability to activate emotional and declarative memory independently of each other. As a result, even when remembering positive events, only the left temporal lobe, responsible for narrative detailed memory, is activated, and the right temporal lobe, responsible for emotional and sensory memory, remains inactive. On the other hand, when faced with painful memories, such people may activate only the right temporal lobe, causing severe emotional pain, even in the absence of an intellectual context for understanding these memories. But this situation applies specifically to the case of significant asymmetry in the activity of the temporal lobes in the upper beta range.

Gamma rhythm

In addition to beta frequencies, high-frequency brain activity also includes gamma rhythm, which includes brain activity at frequencies from 35 to 100 Hz. Some sources indicate the upper limit of the gamma rhythm range as 170 Hz and above. In neurofeedback, only the lower part of the range from 35 to 45 Hz is usually considered.

According to the most widespread theory, synchronization between neural elements at the frequency of the gamma rhythm is a special mechanism of neural cooperation that allows the integration of various features of the same image into a single object of perception. As a result of this process, the brain collects and integrates information that comes from various senses, linking them into a single whole. According to research, the gamma rhythm plays an important role in the process of conscious information processing and is observed when solving problems that require maximum concentrated attention.

Recent studies with Tibetan monks have shown a connection between the gamma rhythm and the state of meditation. The researchers compared the brain activity of a group of meditating monks with the brain activity of a group of novice meditators. And if in a state of ordinary meditation the brain activity of both groups did not differ much, then during traditional Buddhist compassion meditation, the neural structures in the monks’ brains began to produce a synchronous high-amplitude gamma rhythm. In the group of beginner meditators, such brain activity was not observed. In light of the existing theory about the role of the gamma rhythm, it can be assumed that in a state of meditation, monks are able to transfer the brain to a much higher level of perception than is available to an ordinary person.

Training the gamma rhythm in neurofeedback requires a particularly careful approach, since the recorded activity at gamma frequencies may actually be electromyographic activity of the muscles of the head and neck. Gamma rhythm training is usually done in terms of increasing coherence and synchrony.

Disorganization of bioelectrical activity

In some cases, diffuse changes in brain BEA may be observed, which can affect the overall health of the person.

The causes of brain disorders can be:

1. Concussions and brain injuries. With moderate severity, no special treatment is required to restore wave rhythms.
2. Inflammation of the spinal cord and brain. As a rule, diffuse changes in BEA occur with meningitis.
3. Radiation exposure causes moderate changes in the bioelectrical activity of the brain.
4. Toxic poisoning. Long-term treatment will be required to restore the wave rhythm.
5. Atherosclerosis. In the initial stage of the disease, changes in the wave rhythm are not very noticeable, but if the disease progresses, then massive death of brain cells occurs, and neural conduction noticeably deteriorates.
6. General changes in the structure of the brain caused by weak immunity.

Symptoms of diffuse changes may include:

• frequent headaches;
• dizziness;
• neurosis;
• apathy;
• depression;
• absent-mindedness;
• loss of interest in everything that is happening;
• sudden mood swings;
• fast fatiguability;
• low self-esteem;
• slow response;
• sudden changes in blood pressure.

Consequences of diffuse changes

If the symptoms of disorders were noticed at an early stage and the correct treatment was prescribed on time, then there will be no health problems in the future. However, if a person has ignored the signs of diffuse changes for a long time, then in the future this may be reflected in the form of:

• psycho-emotional diseases;
• seizures;
• formation of tissue edema;
• motor impairment;
• developmental delay;
• low level of immune defense.

Ignoring symptoms and lack of treatment can trigger the onset of epilepsy.

Diagnostic methods

If a person notices signs of disorganization of brain activity, then he needs to see a doctor and undergo examinations that will help identify abnormalities, as well as consult with him on how to increase brain activity.

The main methods for diagnosing diffuse changes in the bioelectrical activity of the brain are:

1. Inspection. The first examination must be carried out by a specialist. Examination of external symptoms can reveal many abnormalities.
2. Magnetic resonance imaging. Thanks to this examination, it is possible to detect neoplasms that are the cause of disorganization of the BEA of the brain. When a special drug is administered intravenously, the image can be used to track the general condition of the blood vessels, which can also lead to diffuse changes in the brain.
3. Electroencephalography. This type of diagnosis allows you to fully track wave rhythms in the brain and identify many abnormalities.

The main type of diagnosing disorders of bioelectrical activity is electroencephalography. Special sensors are connected to the patient’s head, which record the brain’s reaction to various external stimuli. All indicators are reflected on paper in the form of waves. Based on the EEG results, it is possible to determine the area of ​​the brain in which diffuse changes in the BEA are detected and the degree of its damage.

Loads that are performed during EEG:

• exposure to light;
• slow opening or closing of the eyes;
• special breathing technique;
• sound impulses.

EEG does not require special preparation. Before the examination you must:

• do not drink alcohol for 2 days before the EEG;
• do not have acute respiratory diseases;
• do not take large amounts of food;
• do not smoke 2 hours before the start of the examination;
• stop taking certain medications.

Despite the fact that the procedure may look very dangerous due to the large number of wires and sensors, you need to know that EEG is completely safe for human health.

Physical activity and the brain

Why do we do running, aerobics, swimming? To look better, to lose excess weight, to keep blood vessels and heart in order... And hardly anyone goes to a fitness club to improve memory or attention. But it has long been known: physical exercise has a beneficial effect not only on the body, but also on the psyche. It would seem that everything is obvious: if a person does not abuse a sedentary lifestyle, he gets sick less, and this only benefits the brain. But the connection between physical exercise and mental function, as research has shown in recent years, may be closer and more immediate.

Photo: Syda_Productions/ ru.depositphotos.com.

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There is a lot of research here. For example, a review paper published in the British Journal of Sports Medicine a few months ago suggested that age-related decline in cognitive function in people over fifty years of age can be slowed down by systematic physical activity. Older adults who do aerobic exercise combined with resistance exercise perform better on psychological tests that require quick switching from one task to another, tactical thinking, concentration, and active use of working memory (the so-called part of memory that deals with relevant information; more details). about what working memory is and how it works, see “Science and Life” No. 7, 2021). Older people are attracted to such studies for obvious reasons: the brain naturally weakens with age, and therefore it becomes easier to assess the factors that inhibit this process. However, there are similar data for young people and even children. Thus, an article in the journal “Medicine & Science in Sports & Exercise” (April 2021) states that in children aged 9 to 11 years, physical fitness and good working memory go hand in hand: if a child has developed muscles, then and he will perform well on memory tests and, importantly, demonstrate academic success. (All this, of course, is very different from the usual idea of ​​a stupid school strongman and a smart but frail “nerd.”)

A 2021 article in the journal Neurology noted that the difference in biological brain age between those who regularly exercise and those who are not physically active can be as much as ten years. At the same time, what exactly a person does is important. Several years ago, researchers from the University of Pittsburgh (USA) compared how the state of the brain changed over the course of a year in older people who either went for a brisk walk three times a week (quite long - from 30 to 45 minutes) or performed exercises stretching. It turned out that in those who walked, some areas of the prefrontal cortex and hippocampus, responsible for planning and memory, increased in size. The increase was small, only 2-3%, but it was still enough to overcome the age-related “shrinking” of the brain. The walking participants also showed good results in tests of spatial memory. In those who did stretching for a year, the hippocampus continued to shrink, as usually happens in old age.

There is evidence that physical activity helps reduce cognitive impairment in schizophrenia and Parkinson's disease; in particular, in patients with schizophrenia, after several months of quite moderate exercise, the hippocampus increased by 12%. Finally, those who play sports know very well that exercise relieves stress and gives a feeling of mild euphoria.

But why is all this happening? Why does physical activity help relieve stress, improve memory, and enlarge certain areas of the brain? There are several explanations here. Let's start with emotions and stress.

It is believed that the feeling of euphoria that occurs after prolonged physical activity appears due to endocannabinoids - neurotransmitter molecules that are synthesized in the brain and act on neurons in various nerve centers. Endocannabinoids have many functions: they are involved in the regulation of appetite, influence memory, learning and emotions, and, in addition, serve as a kind of internal pain reliever, which the brain resorts to in a variety of cases. Exercise stimulates the release of neurotransmitters, which reduce anxiety and cause a slight feeling of joy.

But there are other anti-stress mechanisms that are activated when playing sports. It is known that stress and depression cause atrophy of neurons and synapses: connections between nerve cells weaken and break, and new ones are not formed. The nerve cell becomes “non-contact” and unnecessary, the overall diversity of nerve circuits decreases, and the decrease in the number of nerve circuits in turn affects cognitive abilities and the ability to find a way out of difficult situations. Two years ago, researchers from the University of Georgia (USA) showed that in rats that lead an active lifestyle, neurons successfully resist the stress effect, maintaining the ability to form more and more new cellular contacts. And this happens thanks to the neuropeptide galanin, the level of which increases noticeably after exercise and increases precisely in the areas of the brain responsible for fighting stress. The anti-stress effect of “fitness” provided by galanin was also manifested in the behavior of rats: the animals, despite the unpleasant circumstances that were arranged for them in the experiment, were active and curious - in other words, they were not very worried about the troubles and did not drown in stress.

If we talk about cognitive functions and the increase in certain areas of the brain, then one explanation suggests itself: exercise makes the heart beat faster, therefore, the blood supply to the brain improves and it begins to work better. This hypothesis is supported by the results of researchers from the University of Texas at Dallas (USA): in 2013, they published a paper in the journal “Frontiers in Aging Neuroscience” in which they stated that physical exercise stimulates blood flow to the posterior cingulate cortex and hippocampus. In both cases, metabolism increased and neuron activity increased. Participants in the experiment who regularly exercised at the gym performed better on memory tests, and the changes occurred in exactly the following order: first, blood flow improved, then cognitive performance.

But blood isn't everything. Cells in our body do not grow by themselves; they need molecular signals - special proteins that act on cellular receptors, pushing the cells to certain actions. Proteins that stimulate the growth and development of neurons are called neurotrophins, and the most active among them is BDNF (brain-derived neurotrophic factor, neurotrophic, or neurotropic, brain factor). BDNF includes genes that control the growth of nerve cells and the formation of new synapses, and therefore nerve circuits, and it is especially active in the hippocampus and cortex, that is, in areas responsible for learning and memory. It has been observed that in both animals and humans, the level of BDNF increases sharply with physical exercise, and that with a jump in BDNF, hippocampal growth and improvement in cognitive functions occur. Experiments on mice have shown that the level of the signaling protein remains high for several days after “fitness”. In 2013, an article was published in the journal Cell Metabolism, the authors of which described the chain of signals from muscles to the brain. Researchers were able to identify a protein released from working muscles, which, acting through several intermediaries, gives a signal to special brain cells to synthesize this same BDNF. That is, the muscles themselves give the brain a stimulating signal.

Interestingly, according to one hypothesis, the human brain evolved as people became physically more resilient. It is known that more hardy animals have larger brains than less hardy animals (of course, if we compare animals of approximately the same size). On the other hand, there are experiments on the reproduction of rodent “athletes”. Individuals that ran tirelessly in the squirrel wheel were repeatedly crossed with each other, and as a result, curious molecular features appeared in the offspring - they had increased levels of various growth factors, including BDNF. In 2012, an article appeared in the journal Proceedings of the Royal Society Biology B describing the following scenario. When our ancestors began to hunt, the luckiest were those who could run long and hard, chasing wounded prey. Obviously, the hardiest individuals received an evolutionary advantage: they ate better, brought prey to the group, were popular with the opposite sex, etc. Their genes passed from generation to generation, including the gene that provides high levels of BDNF. The protein initially worked in the muscles, helping the nerves in them grow (following the strengthening of muscle tissue, its innervation should also increase). However, then the excess BDNF reached the brain, and it sharply began to grow. Of course, there were other important evolutionary factors that made humans “brainy,” but the muscle-brain connection through BDNF may well have played a role.

Over time, new variants began to appear in the gene encoding BDNF, and now the effect of the neurotropic factor will most likely depend on the form in which the BDNF gene was acquired by an individual. This gene has a special variant that can be found in about 30% of people - its carriers have smaller areas of the brain than others, and the person himself is more predisposed to neuropsychiatric and neurodegenerative diseases. Researchers from the University of Milan found that if there is such a special BDNF gene in the genome, then exercise does not work against stress and anxiety. (Given the role of the protein BDNF in the brain, it is not surprising that it also influences the stress response.) However, exercise affects the activity of a number of genes in the brain, many of which are not directly related to synapses and the transmission of neural impulses. So we'll have to wait until researchers get a full picture of how muscles act on the brain, although you can start exercising right now.

Dictionary

A synapse is a connection between two neurons or between a neuron and some other cell, where the transmission of a nerve impulse occurs using neurotransmitter substances of different natures.

The hippocampus is the area of ​​the brain responsible for short-term memory and its transformation into long-term memory. In addition, the hippocampus provides spatial orientation and is involved in the formation of emotions.

The prefrontal cortex is a section of the cerebral cortex that is the anterior part of the frontal lobes. The prefrontal cortex is extremely closely connected with most brain structures, and its main function is to control thinking in general and regulate behavior in accordance with internal motives and plans.

Effect of nutrition on brain BEA

To increase brain activity, the body needs vitamins and minerals such as:

• iodine;
• zinc;
• copper;
• manganese;
• B vitamins;
• vitamin C;
• calcium, etc.

To replenish the reserves of these substances, you can drink vitamin complexes or dietary supplements, but these compounds are also found in various foods:

• sea ​​and river fish;
• cauliflower;
• eggs;
• milk, cottage cheese and cheese;
• avocado;
• sunflower seeds;
• oatmeal;
• nuts;
• dietary meat;
• bananas and grapes;
• herring;
• potato;
• sesame;
• mango;
• apples;
• liver;
• seaweed;
• butter.

In addition to these foods, it is necessary to provide the body with the required amount of water. It is recommended to drink 1.5-2.5 liters of pure still water per day.

How to increase

Every person should think about how to increase brain activity, since his standard of living depends on this. The brain, like the entire body as a whole, needs constant training. In their absence, a sharp decline in strength is observed.

You can increase brain activity by doing the following exercises:

1. In childhood, everyone was often forced to learn poems by heart and for good reason, because this is the optimal load for the brain. To get a positive result, it is enough to learn one quatrain once a day.
2. Solving crosswords and various puzzles. Solving Sudoku can also be included in this category. During the day you need to solve 2-3 Sudoku or one large crossword puzzle.
3. Play boardgames.
4. When shopping, use your brain; to do this, it is enough to mentally calculate the total cost of your purchases. The number does not need to be exact. She should be close.
5. Any unusual action for the body puts a strain on the brain. So, for example, while brushing your teeth, you can change your hand, put on your shoes on the other foot, or stir sugar in tea with your left hand.
6. While walking, you need to concentrate your attention on a person or some object. When he disappears from sight, you need to completely reproduce his image in your head and think about him.

In addition to mental exercises, it is necessary to perform physical ones. They allow the body to relax and relieve nervous tension, and also supply the brain with the right amount of oxygen. An evening jog will improve the general condition of the body and help keep your brain “light.” This type of physical activity is recommended if you have an important meeting scheduled for the next day.

What is an EEG and why is it needed?

Scientists love to look for the first mention of their science. For example, I saw an article that seriously stated that the first experiments on electrical stimulation of the brain were carried out in Ancient Rome, when someone was shocked by an electric eel. One way or another, usually, the history of electrophysiology is usually counted approximately from the experiments of Luigi Galvani (XVIII century). In this series of articles we will try to tell a small part of what science has learned over the last 300 years about the electrical activity of the human brain, about what profits can be derived from all this.

Where does electrical activity in the brain come from?

The brain consists of neurons and glia. Neurons exhibit electrical activity, glia can also do this, but in a different way [], [], and we will not pay attention to it today.

The electrical activity of neurons involves pumping sodium, potassium and chlorine ions between the cell and the environment. Signals are transmitted between neurons using chemical mediators. When a transmitter released by one neuron hits a suitable receptor on another neuron, it can open chemically activated ion channels, allowing small amounts of ions into the cell. As a result, the cell changes its charge slightly. If enough ions enter the cell (for example, a signal arrives simultaneously at several synapses), other voltage-dependent ion channels open (there are more of them), and the cell is activated entirely in a matter of milliseconds according to the “all or nothing” principle, after which it returns to previous condition. This process is called an action potential.

How can I register it?

The best way to record the activity of individual cells is to stick an electrode into the cortex. It could be one wire, it could be a matrix with several dozen channels, it could be a pin with several hundred, or it could be a flexible board with several thousand (what do you think, Elon Musk).

This has been done on animals for a long time. Sometimes for health reasons (epilepsy, Parkinson's disease, complete paralysis) they do it on humans. Patients with implants are able to type text with the power of thought, control exoskeletons, and even control all degrees of freedom of an industrial manipulator.

It looks impressive, but in the near future such methods will not come to every district clinic, and, especially, to healthy people. Firstly, it is very expensive - the cost of the procedure for each patient is measured in hundreds of thousands of dollars. Secondly, implantation of electrodes into the cortex is still a serious neurosurgical operation with all possible complications and damage to the nervous tissue around the implant. Thirdly, the technology itself is imperfect - it is not clear what to do with the tissue compatibility of implants, and how to prevent them from becoming overgrown with glia, as a result of which the desired signal ceases to be registered over time. In addition, training each patient to use the implant can take more than a year of daily training.

You can not stick the wires deep into the cortex, but carefully place them on it - you will get an electrocorticogram. Here the signal of individual neurons can no longer be recorded, but the activity of very small areas can be seen (the general rule is that the farther from the neurons, the worse the spatial resolution of the method). The level of invasiveness is lower, but the skull still needs to be opened, so this method is used mainly for monitoring during operations.

You can put the wires not even on the cortex, but on the dura mater (the thin skull that is located between the brain and the real skull). Here the level of invasiveness and possible complications is even lower, but the signal is still quite high quality. An epidural EEG will be obtained. The method is good for everyone, however, surgery is still needed.

Finally, a minimally invasive method for studying the electrical activity of the brain is an electroencephalogram, namely, recording using electrodes that are located on the surface of the head. The method is the most widespread, relatively cheap (top devices cost no more than several tens of thousands of dollars, and most are several times cheaper, consumables are practically free), and has the highest time resolution of non-invasive methods - you can study perception processes that take a few milliseconds. Disadvantages are low spatial resolution and a noisy signal, which, however, contains a sufficient amount of information for some medical and neural interface purposes.

In the picture of an action potential, you can see that the curve has two main parts - the action potential itself (the large peak) and the synaptic potential (the small change in amplitude before the large peak). It would be logical to assume that what we record on the surface of the head is the sum of the action potentials of individual neurons. However, in reality, everything works the other way around - the action potential takes about 1 millisecond and, despite its high amplitude, does not pass through the skull and soft tissues, but synaptic potentials, due to their longer duration, are well summed up and recorded on the surface of the skull. This was proven using simultaneous recordings using invasive and non-invasive methods. It is also important that the activity of not every neuron can be recorded using EEG (more details here).

It is important that there are about 86 billion nerve cells in the brain (read about how this can be calculated with such accuracy), and it is impossible to count the activity of one neuron in such noise. However, some information can still be extracted. Imagine that you are standing in the center of a football stadium. While the fans are just making noise and talking to each other, you hear a steady hum, but as soon as even a small part of those present start chanting the chant, it can already be heard quite clearly. It’s the same with neurons—a meaningful signal can be seen on the surface of the skull only if a large number of neurons simultaneously exhibit synchronous activity. For non-invasive EEG, this is approximately 50 thousand synchronously working neurons.

The idea of ​​measuring tension on a person’s head was first implemented in 1924 by a rather interesting person. The first EEG recording looked like this:

It is difficult to understand what this signal means, but it is immediately clear that it does not look like white noise - it contains spindles of oscillations of high amplitude and different frequencies. This is the alpha rhythm - the most noticeable rhythm of the brain that can be seen with the naked eye.

Now, of course, EEG rhythms are analyzed not by eye, but by mathematical methods, the simplest of which are spectral.

Fourier spectrum of an electroencephalogram divided into stripes (source)

There are several bands in which rhythmic EEG activity is usually analyzed, here are the most popular:

8-14 Hz - Alpha rhythm. Presented mainly in the occipital areas. Increases greatly when closing the eyes, is also suppressed during mental stress and increases during relaxation. This rhythm is produced when excitation circulates between the cortex and thalamus. The thalamus is a kind of router that decides how to redirect incoming information to the cortex. When a person closes his eyes, he has nothing to do, he begins to generate background activity, which causes the alpha rhythm in the cortex. In addition, the default mode network plays an important role - a network of structures that are active during quiet wakefulness, but this is a topic for a separate article.

A type of alpha rhythm with which it can easily be confused is the mu rhythm. It has similar characteristics, but is recorded in the central areas of the head, where the motor cortex is located. An important feature is that its power decreases when a person moves his limbs, or even thinks about doing so.

14-30 Hz - Beta rhythm. More pronounced in the frontal lobes of the brain. Increases with mental stress.

30+ Hz - Gamma rhythm. It may be somewhere inside the brain, but most of what can be recorded from the surface comes from the muscles. We found this out as follows:

It is necessary to somehow remove muscle activity from the head in order to record an EEG with and without muscles. Unfortunately, there is no easy way to turn off the muscles in your head without turning them off throughout your body. We take a scientist (no one else would agree to this), pump him up with a muscle relaxant, as a result of which all his muscles turn off. The problem is that if all the muscles are turned off, including the diaphragm and intercostal muscles, he will not be able to breathe. The solution is to put him on a ventilator. The problem is that he also cannot speak without muscles. The solution is to put a tourniquet on his hand so that the muscle relaxant does not get there, then he can give signals with this hand. The problem is that if you drag out the experiment, the hand will fall off. The solution is to stop the experiment when the scientist stops feeling his hand, and hope that everything will end well. The result is that the proportion in the spectrum of EEG frequencies greater than 20 Hz against the background of a muscle relaxant becomes 10-200 times smaller; the higher the frequency, the higher the drop.

1-4 Hz - Delta rhythm. Expressed during the phase, suddenly, delta sleep (deepest sleep), also increases under stress.

In addition to rhythmic activity, the EEG also contains evoked activity. If we know exactly at what moment we show a person a stimulus (this could be a picture, sound, tactile sensation, or even smell), we can see what the reaction was to this particular stimulus. The signal-to-noise ratio of such a response in relation to the background EEG is quite low, but if we show the stimulus, for example, 10 times, cut the EEG relative to the moment of presentation and average, then we can obtain fairly detailed curves, which are called evoked potentials (not to be confused with potentials actions).

This is the evoked potential for sound. We’ll leave the details to psychophysiologists - here it’s enough for us to understand that every extreme means something. With sufficient averaging, the responses of structures ranging from the auditory nerve (I) to the associative cortex (P2) will be visible.

What can you do with it?

There are many things that can be done, but today we will focus on brain-computer interfaces. These are real-time EEG analysis systems that allow you to issue commands to a computer or robot without the use of muscles—the closest thing to telekinesis that modern science can provide.

The most obvious thing that comes to mind is to make an interface based on rhythmic activity. We remember that there is little alpha rhythm when a person is tense, and a lot when he is relaxed? So relax. We write an EEG, do a Fourier transform, when the power in the window around 10 hertz has become above a certain threshold, light a light bulb - that’s control of the computer with the power of thought. The same principle can make it possible to control other rhythms. Due to the simplicity and undemanding requirements for equipment, quite a lot of toys have appeared that work on this principle - Neurosky, Emotiv, thousands of them. In principle, if you try hard, a person can learn to come to the desired state, which will be correctly classified. The problem with consumer devices is that they often write a low-quality signal, and most of them do not know how to subtract artifacts from eye movements and facial muscles. As a result, there is a real opportunity to learn how to control your muscles and eyes, and not your brain (and the subconscious works in such a way that the more you try not to do this, the worse it will turn out). In addition, the signal-to-noise ratio in the rhythms itself is quite low, and the interface works slowly and inaccurately (if you can correctly guess the state with an accuracy of more than 70%, this is already an achievement). And the scientific basis for states other than relaxation and concentration is, to put it mildly, shaky. However, if implemented correctly, the method can have its uses.

An important subtype of interfaces on rhythms is the representation of movements. Here the person is asked not to imagine something abstractly relaxing, but to imagine the movement of, say, his right hand. If you do this correctly (and learning the correct representation is difficult), you can detect a decrease in the mu rhythm in the left hemisphere. The accuracy of such interfaces also revolves around 70%, but they are used in simulators for recovery from strokes and injuries , including with the help of various exoskeletons, so they are still needed.

Another class of EEG neurointerfaces is based on the use of evoked activity of all sorts. These interfaces are characterized by very high reliability, with a successful combination of circumstances approaching 100%.

The most popular type of neural interfaces includes the P300 potential. It occurs when a person tries to identify one stimulus he needs among many unnecessary ones.

For example, if we try to count how many times the letter “A” will light up, and at the same time ignore all the others, then in response to this stimulus, when averaging, we will see a red line, and when averaging all the others, we will see a blue line. The difference between them is noticeable to the naked eye, and training a classifier that will distinguish between them is not difficult.

Such interfaces are usually not very beautiful, and not very fast (typing one letter will take about 10 seconds), but they can be useful for completely paralyzed patients.

In addition, the BCI-P300 has a cognitive component - it is not enough to just look at a letter, you must actively pay attention to it. This allows, under certain conditions, to make quite interesting games using this technology (but this is a topic for another article).

Due to the fact that P300 is a cognitive potential, it is not very important for it what is actually shown to a person, the main thing is that he can react to it. As a result, the interface will work even if the letters change each other at the same point - this is useful for patients who cannot move their eyes.

There are other interesting evoked potentials, in particular SSVEP (Stable State Potentials). If we look for analogies in the field of communications, then the P300 works like a walkie-talkie - signals from different stimuli are separated by time, and SSVEP is classic FDMA - separation by carrier frequency, as in GSM communications.

be careful, epileptic lights

You need to show a person several stimuli that flash at different frequencies. When choosing a stimulus, just look at it carefully, and after a few seconds its frequency will magically appear in the visual cortex, from where it can be pulled out by correlation or spectral methods. This is faster and easier than counting letters for the P300, but it’s hard to look at such blinking for a long time.

Where there is FDMA, there is a place for CDMA:

be careful, even more epileptic flashing lights

Gray is a binary sequence, color is the activity caused by it in all channels, the map is the distribution of potential intensity in the EEG. It can be seen that the maximum is at the back of the head - in the visual areas

It is possible to modulate the blinking of stimuli not by frequencies and phases, but by orthogonal binary sequences, which will also end up in the visual cortex and classified using correlation analysis. This can help to slightly optimize the classifier training and speed up the interface - one letter can take less than 2 seconds. By choosing the right colors, you can make the interface a little less eye-popping, although you won’t be able to get rid of blinking completely. Unfortunately, the cognitive component here is not so pronounced - tracking eye movements gives comparable results, but is technically simpler, cheaper and more convenient.

When I talk about how well certain types of interfaces can work, I have to constantly deal with the signal-to-noise ratio. Indeed, evoked potentials have a low amplitude - about 5 microvolts, despite the fact that the background alpha rhythm can easily have an amplitude of 20. Such a weak signal seems quite difficult to classify, but in fact it is all quite simple if the experiment is carried out correctly and It's good to record the EEG. Currently, most academic research is focused on the development of new classifiers, including the use of neural networks, but a fairly good level can be achieved with the simplest linear classifiers from scikit-learn. For example, a good dataset with P300 and code is here.

Brain computer interfaces are an emerging technology that look like magic, especially to an untrained person. However, in reality this is a method with many unobvious difficulties. The secret here, as with any technology, is to take into account all the limitations and find applications where these limitations do not interfere with the work.