How cognitive functions work

Even our ability to recognize an object by touch depends on the brain.

Table of Contents

Cognitive functions help us talk, plan, and get to know the world around us. Neurologist Anna Moroz tells about how they work and what hinders them. She is one of the co-authors of the book “Medicine for the Smart. Modern Aspects of Evidence-Based Medicine for Thinking Patients ”, which was co-written by 18 doctors.

With permission from Bombora, Lifehacker publishes an excerpt from the section on the brain.

I get the impression that many people consider cognitive function and memory to be almost synonymous. This is understandable, because memory interruptions are very noticeable. Without memories, a person loses himself, ceases to exist as a person. And even the slightest forgetfulness of words or dates can be very alarming, it is too noticeable in everyday life.

In fact, there are a lot of cognitive functions, and they are not limited only to memory. Cognitive functions of the brain are a collection of certain skills that provide a person’s awareness. This is the ability of a person to receive and analyze information, store it in memory, recognize an object encountered earlier, draw conclusions, think in concepts, find similarities and differences, speak and accurately articulate their ideas, make informed decisions, concentrate attention, find solutions to problems, make purposeful actions.

These complex functions are performed mainly by the mysterious tertiary cortex. It integrates a lot of data from numerous areas of the primary and secondary cortex and only then produces something that so strongly distinguishes most people from other animals – a conscious action.


Probably, speech has been studied better than other cortical functions of the brain. The appearance of such a unique opportunity for a person – to communicate with each other, and even not with simple sounds and gestures, but with complex sentences, shows how developed our brain is from an evolutionary point of view. We cannot even imagine how complex and intricate the organization of the speech centers in the brain is. We cannot imagine what our life would turn into without the ability to communicate.

There are several speech centers in the human brain, and they are located in almost all people in the left hemisphere.

Speech is not only the ability to pronounce a conceived word, it is a lot of other skills. Reading, writing, talking to oneself, understanding the speech heard, a sense of grammar and semantics are all part of the complex structure of speech. With the perverted work of at least one of these subunits, the entire harmonious system of the speech function of the brain breaks down, and the person turns out to be unable to communicate with the world.

If we accept the fact that speech is not only scratching with the tongue, but also much more, it becomes obvious that many cortical centers participate in its organization. This is the visual cortex – without it, you would not be able to read; and the auditory cortex – after all, listening is important in a conversation ; motor cortex – to send impulses to the muscles of the vocal cords and tongue, which generate sounds, or to the muscles of the arm, which write or type text in the messenger; it is also memory – after all, it is important not only to hear, but also to remember the meaning of the word and to imagine what it is about.

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The Broca Center, named after the scientist who discovered it, is in the left frontal lobe. Broca’s center is responsible for speech production, that is, precisely for pronunciation.

The story of the opening of the Broca Center is very well known. The respected surgeon and anatomist Paul Brock in the second half of the 19th century was invited to assess the condition of a patient who had been under the close attention of doctors for a long time. The man suddenly stopped talking. He understood what he was being told, he could answer with the help of gestures, but he could not utter a single word except the syllable “tan”, which was escaping from him every time he tried to say something.

A few weeks after the examination, the patient died, and Brock, like a true doctor, immediately opened his skull and removed his brain! It turned out that there was a real hole in the left frontal lobe. Probably, at one time the man had a stroke, which so unsuccessfully captured this strategically important area of ​​the brain. At that moment, the patient lost his speech, and over time, a cyst formed at the site of the stroke, which Brock saw at the autopsy.

He was able to confirm his hypothesis by observing a few years later an elderly man who lost his speech after a fall and a bruise of the head. Brock was able to get to his brain and again discovered changes in that very left frontal lobe.

Of course, in the modern world, no one opens the cranium of people in order to confirm one or another hypothesis about the localization of functions in the brain. Now in the arsenal of scientists there are a lot of methods that allow them to study the work of the brain during their lifetime and without causing serious harm to the patient’s health. When it comes to activating the brain in response to a stimulus, then, of course, this is a method of fMRI – functional magnetic resonance imaging of the brain.

Any increase in the activity of one or another part of the brain leads to an increase in blood flow in it. By placing a person in a tomograph, you can register these changes in blood flow as you perform simple mental tasks: speech, counting, singing, thinking about food, memories of your beloved daughter who is waiting at home, fantasies about a bike ride along the coast. It is surprising that each of these actions activates strictly its own, rather compact area of ​​the brain, but it activates strongly, which can be registered with the help of a magnetic tomograph and software.

Paul Broca’s hypothesis was later repeatedly proven using modern techniques, and now there is no doubt that the center of speech production is located precisely in the left frontal lobe. At one time, when the hypothesis of a clear division of functions in the hemispheres into creative and analytical was in vogue, it was believed that Broca’s center was on the left in right-handers, and in left-handers on the right. However, this assumption was not confirmed. The use of fMRI has shown that in about 4–5% of left-handers, Broca’s center may indeed be located in the right frontal lobe, but in the overwhelming majority of people it is on the left, regardless of other features.

Damage to Broca’s area, whether it be a stroke or trauma, always leads to the same symptoms – impaired spontaneous speech, Broca’s aphasia, or motor aphasia. Patients with motor aphasia have difficulty finding words and cannot articulate what they think. With partially preserved speech, it nevertheless becomes poor, the logic of the construction of sentences is violated. With coarser forms, a complete absence of speech is possible and the formation of so-called verbal emboli – sounds or syllables that the patient pronounces with or without reason.

This is surprising, because the articulation apparatus, vocal cords, oropharyngeal muscles, lips – everything is normal, it works, but the sounds do not add up to words.

Such patients understand the addressed speech very well. They easily communicate with gestures, sometimes they can draw something, indicate something. Nevertheless, writing also most often suffers, because written speech is, in fact, the same spontaneous speech activity, only expressed on paper, and not spoken out loud. Such is an extremely unpleasant state, thoughts are locked up and do not have the ability to break out.

I will never forget my very first patient. I just graduated from the university and entered the residency. A man was admitted to the hospital, close to 60, with a stroke. Strong, vigorous enough, with a thick mustache and a wide smile, he could not utter a word. The only thing he could do was “so-so-so”, uttered in response to any of my questions and accompanied by a smile, at the same time friendly and sad from the fact that I do not understand him.

The first day he was with his wife, who somehow understood his gestures better and faster than me, but then she left, and we were left alone with his aphasia. Every day I regularly measured the patient’s blood pressure and pulse, prescribed medications, tested him on a bunch of scales, sometimes just ran in to ask how he was doing. Each time he tried to ask me for something, but I did not understand him at all. He tried to write on paper, draw, type SMS, but nothing came of it, and I did not understand him. Each of my visits ended the same way, he gave up, waved his hand at me and, distressed, turned away to the corner. There were still two weeks of misunderstanding ahead.

On the fifth day, I broke into his room, opening the door and almost knocking down a neighbor with it, with the words “I will not leave here until I understand what you need.” After some time and a lot of pictures revised on the phone (so that he could poke at the desired image and convey his thoughts to me), I understood! Permission to walk! It was a real victory for me, I was able to really help my first patient. And for him it was the light at the end of the tunnel, he realized that communication is possible.

After a year of regular classes with a speech therapist, the extraordinary care of a loving wife, a joint study of letters with her granddaughter (she was just about four, he and the child re-learned sounds, letters and syllables), he began to speak. Isn’t that a miracle? The neurons that surrounded the stroke zone grew new processes, formed new synapses, took over the functions of dead comrades and learned to generate speech again!

Speech perception works completely differently. The Wernicke center, the second strategically important speech center, located in the temporal region, also on the left, is responsible for the analysis of speech information heard by the ears and read by the eyes. The history of the opening of this speech center is quite classic.

Karl Wernicke, a German neuropathologist, observed a man who had a stroke. The man showed extremely interesting symptoms, which were later described as Wernicke’s aphasia, or sensory aphasia. The patient’s hearing was completely preserved, as well as speech – he easily pronounced a lot of sounds, words, phrases. However, he did not understand the speech at all, could not fulfill requests, did not follow instructions. And his own spontaneous speech was a collection of words that were completely unrelated to each other. As usual, after the death of the patient, the brain was removed and thoroughly studied. Then it became clear that the centers of speech perception and its reproduction are different, and they are located quite far from each other.

Sensory aphasia, unlike motor aphasia described earlier, does not affect spontaneous speech. The problem is that a person does not understand speech by ear, and therefore cannot control his own either. In such patients, long phrases, sentences are born, intonation and rhythm are preserved, only there is no sense in what has been said. When you listen to such patients, you get the impression that they speak a foreign language: it seems that there is a structure, and the verbal flow is divided into sentences, but, alas, it is extremely difficult to understand them.

Presumably, the patients themselves also seem to be on a journey to an exotic country: they can see and hear, but nothing is clear.

Needless to say, the only thing that helps to restore speech is only constant persistent speech therapy classes aimed at training the surviving neurons and stimulating the branching of their processes.

Very interesting features of the speech system were revealed using fMRI. For example, when reading individual letters that are not folded into words and do not carry a semantic load, only the visual cortex is activated, and when reading words and sentences, the excitation from the visual cortex passes to Wernicke’s zone. It is the same with hearing: the perception of simple sounds activates only the auditory cortex, while spoken words excite the auditory cortex, followed by Wernicke’s center. The brain is able not only to perceive information, but also to understand whether it is worth disturbing the superior cortex and sending it a signal or not.


Another brain skill that is highly developed in the human is praxis. Praxis means the ability to perform complex, purposeful movements according to a premeditated plan. This is not about pulling the hand away from a hot frying pan or, say, breathing movements – these actions are carried out reflexively, we do not think about them. After all, even if you try to purposefully hold your breath and limit the access of oxygen to the body, you should lose consciousness, and the brain will immediately send a signal to the respiratory muscles to start exhaling carbon dioxide and inhaling oxygen as soon as possible (do not repeat at home).

We are talking about complex actions that consist of many simple ones. For example, take a toothbrush, paste, unscrew the cap, squeeze a little paste onto the brush, twist the cap, get into your mouth with the brush, thoroughly brush your teeth, not forgetting about the wisdom teeth. Or, for example, the ability to repeat actions after someone, as in dance lessons, looking both at the teacher and at your crooked stand, reflected in the mirror.

Such complex motor acts are formed with the participation of a colossal number of systems, and not just motor systems, as one might assume.

Firstly, this is information coming to the sensitive cortex from proprioceptors. These are special receptors of muscles and joints that tell the brain how the body is located in space: at what angle the arm is bent at the elbow joint, which leg the owner is leaning on, the priest sits on a chair, or just leans slightly against the wall.

Secondly, these are the eyes and the visual cortex, because movement, especially multicomponent, is always carried out under the control of vision.

Thirdly, these are the ears and the auditory cortex. Imagine yourself learning a new skill. Agree if clear instructions are given and a sequence of actions is voiced, it is much easier to learn.

Finally, there is the motor system with the motor cortex. If the limbs are involved in the movement, this is one part of it, if the speech and the articulatory apparatus, then another, in strict accordance with the map of the body, the homunculus. It is here that the idea of ​​movement is born and a signal is sent to a pile of muscles, which must contract in a strictly defined sequence and produce a movement that is beautiful, accurate and coordinated.

If you suspect a violation of praxis, the neurologist at the reception may ask the patient to repeat the simple movements of the fingers after him. The doctor shows a fig, a victoria or a horned goat, a patient with motor apraxia sees, understands what they want from him, but can’t get his fingers crossed.

Dysfunction of praxis is called apraxia. Apraxia, like speech impairment – aphasia, is a composite concept that includes various symptoms and syndromes: it all depends on which link in the chain of praxis is broken. In practice, apraxia looks very strange. People with a violation of this function cannot perform this or that action, the muscles literally do not obey. It is curious that the strength of the muscles themselves is completely preserved, the same parts of the body take part in simpler motor acts without any problems, fully performing their functions.

Unlike speech, the brain does not have a specific area of ​​the cortex responsible for praxis. Praxis is encoded in connections between areas of sensory, motor, visual, auditory, and other cortical centers. As a rule, the development of apraxia is caused by those diseases that affect the white matter and fibers connecting the distant parts of the cerebral cortex or parts of the tertiary cortex. It can be a stroke, a
multiple sclerosis plaque , neurodegeneration, or an infection of the brain tissue. The result is the same – a violation of the motor act.

Praxis has two main types of disturbance – a violation of the action itself, the sequence of movements, and vice versa, a violation of the idea of ​​movement, an incorrect message from the brain. For clarity, let’s look at some examples.

A person with motor apraxia is unable to perform a purposeful action. For example, it gets dark and the room gets dark. Based on the experience and memory, the brain realizes that it would be necessary to press the switch, and then the electricity will do its job. The neurons of the motor cortex send signals to the hand, tell it to pull away from the knee, straighten up, turn to the right and pull the cord of the floor lamp. Alas, this is not possible with motor apraxia. The hand does not listen to the head. She can move, move to the right or to the left, but it is impossible to collect these simple movements into a chain of sequential actions.

Ideatorial apraxia is due to the loss of an action plan. Patients with this type of apraxia can hardly perform any movement on demand, that is, the muscles listen to the brain and move, but an initially incorrect plan of action leads to a meaningless set of movements. If you ask a person with ideatorial apraxia to show how he would light a cigarette with matches and light it , he will most likely do the following: take a cigarette, strike a box at it, and then bring a match to his mouth.

To test this area of ​​activity at the reception, we ask patients to imitate some actions. For example, you might be asked to brush your teeth with an imaginary toothbrush, or to comb with an invisible comb and pull your hair into a ponytail. It turns out that such simple tasks can put a person with apraxia into a stupor: someone will raise their hand only to shoulder level, someone will bring the brush to their mouth, but they will forget to brush their teeth, or they will look at a nonexistent comb in their hand and think, how the same hairstyle is done.

A fairly common symptom that occurs in the elderly is gait apraxia. With normal leg strength, intact sensitivity, intact vestibular function, a person suddenly forgets how to walk. The gait in this condition resembles the gait of a baby who is just mastering the skills of walking. The stride is short and asymmetrical, the legs are wide apart, careful visual control and support on a cane or grandson are required.

It is interesting that patients themselves often cannot describe their condition, instability and change in step are subjectively perceived as dizziness, although the vestibular apparatus is working quite well. The unsteadiness without the feeling of a “helicopter”, nausea and vomiting, neurologists call “non-systemic vertigo.”

Unfortunately, quite often, even too often, complaints of “non-systemic dizziness” lead doctors to think about circulatory disorders in the cerebellum (there is a rational grain, because it is responsible for the coordination of movements). The result of a hasty decision is the appointment of an incorrect treatment, designed to cleanse, in the end, these dirty vessels that carry blood to the cerebellum.

The trouble is that gait apraxia develops when the frontal lobes of the brain are affected, not the cerebellum.

And it is treated (or at least kept at the existing level) by constant exercises, physical activity, learning to walk anew. Ourconnectome does not sleep, it only needs to be constantly fed with signals from our body.

According to the unscrupulous, gossip-seeking media, Daniel Radcliffe has mild apraxia in his legs. Judging by the fact that she is not progressing, and the actor is quite adapted, most likely this is a consequence of some kind of perinatal lesion. Nevertheless, according to the actor himself, it is much more difficult for him to act on stage than in front of the camera. On stage, you have to move a lot more, there is no way to shoot multiple takes or focus on the face. Difficulties arise for him precisely when running, dancing , jumping on various elements of the scenery, while ordinary walking is easy for him.

Agree, an extremely curious function of the brain. So necessary and at the same time so inconspicuous. Who would have thought how subtle and thoughtful the traffic regulation system is. We perform an incredible number of complex motor acts every day. Morning marafet, cooking and eating breakfast , walking with the dog and washing dirty paws, driving (especially with a manual gearbox!) Or maneuvering in the flow of people on the subway at rush hour, work, shopping in the supermarket, packing children in three layers of padding polyester and transportation to the right circle at the right time. But how radically life can change, if praxis is violated.


But that’s not all. The human brain is big, it can do amazing things. For example, another function is the ability to recognize. The ability of the brain to recognize objects seen, heard, smelled and felt is called gnosis. Obviously, various senses supply the brain with strictly specific information: visual, auditory, tactile, and so on.

This information enters the primary cortex of the corresponding modality. Further, it is transmitted to the secondary and tertiary regions of the cortex, where recognition takes place, also in strict accordance with the type of information received.

From this we can conclude that gnosis can also be visual, sensitive, auditory, and so on.

Have you ever thought that you can very easily identify an object by touch without even looking at it? Here my very short-sighted comrades in misfortune should understand me. You wake up in the morning, it’s still dark outside, and let’s poke around with our hands on the bedside table in search of glasses. And after all, it is great to guess what the hand grabbed: glasses, a phone, a pen or a glass of water.

Or, for example, the phone rings, it is somewhere at the bottom of the bag, mixed with cosmetics and lunch, and you are in a cramped bus, and it is an unacceptable luxury to start gutting the contents of the bag? Indeed, the brain perfectly understands what lies in the palm of your hand. Understands due to various receptors and the ability to compare many facts: hard or soft, cold or warm, prickly or fluffy.

An object touching the skin affects many receptors: heat, pain, and pressure receptors. And also those cunning receptors of muscles and joints scream about how wide the palm has opened and the fingers extended to grab the mysterious object. Adding all the data, multiplying by memories and solving this complex equation, the brain guesses: “Yeah, it’s a cucumber, again the hostess is on a diet , but it is clearly not him who calls, we are looking further.”

Violation of gnosis in neurology and psychology is called agnosia. One of the types of agnosia is associated precisely with a violation of the recognition of objects by touch, it is called astereognosis. In this state, people are unable to understand what they are holding in their hand if there is no way to see the object.

Interestingly, the sensitivity on the hands is completely preserved. A person feels the temperature, structure and size of an object, but cannot recognize and, therefore, name it. As soon as you open your eyes and see what is in your hand, everything falls into place at once. The condition is extremely uncomfortable for existence, however, visual control quickly helps to adapt, and often people stop noticing their defect, deftly adapting to life in new conditions.

The situation is much more unpleasant when visual gnosis is disturbed. With preserved vision and normal eye function, a person suddenly ceases to recognize the things around him. This condition is very frightening and decently reduces the quality of life. Usually people with visual agnosia see an object, can even describe it, understand that it is, say, glass, transparent, hollow inside, but they are not able to combine all these parameters and recreate the image of a glass in their head.

One of the interesting forms of agnosia is not recognizing faces, or prosopagnosia. This condition develops when a small area of ​​the occipital cortex is affected. With prosopagnosia, vision is preserved, recognition of any other objects is preserved, but faces do not give in. Typically, patients with prosopagnosia gradually adapt and learn to recognize relatives and friends by other distinctive features: by voice, for example, or gait.

Sometimes tattoos or piercings , an unusual birthmark on the face, or a beard help . True, with the current fashion for brutality and a beard, I would not have pinned great hopes on this attribute (I found out that men who deliberately adhere to a rough style of clothing and increased hairiness on their heads and faces are called lumbersexuals, or lumberjacks, as the domestic Wikipedia calls them ). The most unpleasant thing is that people with face agnosia sometimes do not even recognize their own face in the mirror. An extremely unpleasant thing.

In 2011, the movie Faces in the Crowd was filmed with Milla Jovovich in the title role. As a result of the attack, the heroine of the film receives a head injury, after which she develops prosopagnosia. I will not spoil, those who are interested can watch the film. Of course, this is not Fellini , but the state of the heroine, the way she learns to live with her new flaw, what she feels, conveyed, in my opinion, is quite worthy from a neurological point of view.

Prosopagnosia is congenital – about 2% of the world’s population has impaired perception of persons of varying severity since childhood. Nobody knows the exact reasons for the development of congenital prosopagnosia. It is known that the incidence of this condition is slightly higher in people with Asperger’s syndrome . Some associate it with head injuries in early childhood. I have my own version of this, but there is very little data available in the literature to confirm or refute it.

The brain of a human cub is extremely immature at the time of birth, and the fibers are covered with a protective sheath, myelin, only as the little man grows up. There are conditions (especially in children who have undergone difficult childbirth, or in children in whom myelin, due to a genetic predisposition, is formed somewhat slower than others), in which areas of incomplete myelination remain in the brain after maturation.

As a rule, they are located around the posterior parts of the ventricles of the brain, just in the occipital lobes, but after all, the area of ​​the brain responsible for recognizing faces is located right here, side by side. In the overwhelming majority, such areas of insufficient myelination do not manifest themselves in any way, the brain works completely fully.

The adaptive abilities of the brain are immense, the brain can adapt and master absolutely any function.

Neurons build complex connections bypassing the “defective area” and easily form a complete connection. Probably, sometimes, nevertheless, incomplete myelination partially captures the fibers that rush to the cortex that recognizes faces, then a collapse occurs: a person cannot recognize a face.

Most often, of course, congenital prosopagnosia is milder than that acquired as a result of a stroke or trauma in adulthood. As a rule, it is manifested by difficulties in remembering and further recognizing unfamiliar people, while such people are able to identify relatives and their own reflection in the mirror or their photos. As Brad Pitt admitted to Esquire a few years ago , he has congenital prosopagnosia. The actor laments that he is considered an arrogant, arrogant ass, because he sometimes does not recognize the people with whom he worked and ignores them. Although, maybe this is a well-thought-out PR move.

You can endlessly talk about the violation of praxis and gnosis, even if you write whole volumes. I’ll tell you about the last, extremely curious type of agnosia – ignorance, or ignorance. If the parietal lobe of the right hemisphere is affected (usually a stroke or tumor), the patient ceases to notice the left half of his body. When checking the sensitivity (when a malicious neurologist mercilessly pokes the patient with a needle or a toothpick), it turns out that the entire left half of the body is deaf to the injections: the patient simply does not feel anything, does not even notice how he is being pricked.

When looking at objects on the left, the patient does not see them, although the eyes and visual cortex are in order. He may not even react in any way to the doctor if he stands on the left and says something quietly into his left ear. When washing, shaving, combing, people with hemineglect will take care of only half of the face. If you ask such a person to draw a picture, he will depict on paper exactly what he sees and feels: half a house, half a still life, half a self-portrait. And the most curious thing is that patients often do not realize their defect, this condition is called anosognosia – not recognizing their disease.

German artist Lovis Corinth suffered a stroke in 1911, after which his work changed in a strange way. It is assumed that he developed the same hemineglect syndrome. Observing the works of the late period of his work, one can see the chronology of the development of events and the gradual restoration of Kornit as a patient.

In the paintings painted immediately after the stroke, part of the plot is missing, which should be located on the left. However, the brain gradually recovered, and the artist began to draw on the left half of the canvas, at first poorly and inaccurately, forgetting to add color and draw details, but gradually more and more fully.

Yes, yes, these are all neural connections. Neurons branch and form contacts constantly, both in a child and in a post-stroke old man.

In the arsenal of neurologists and psychologists, there are many interesting tests for detecting cognitive impairment, including praxis and gnosis. One of the most convenient and quick, which allows at the reception to roughly determine whether there is a deviation in the patient’s cognitive sphere, is the clock drawing test. The patient is given a sheet of paper, preferably without a ruler, and a pen.

The task is extremely simple: you need to draw a dial, place numbers on it and display with arrows the time “ten minutes past eleven” (and the wording should be exactly that, since the differently named “eleven hours ten minutes” is perceived easier by ear and can serve hint). In a healthy person with preserved cognitive functions, the task will not cause any difficulties, rather it will provoke a nervous laugh and resentment against the doctor: “For whom are you holding me?” A person with various disorders of praxis, gnosis and memory will get an extremely strange clock, which will easily give odds to the Dali clock.

A person with motor apraxia will not be able to start drawing and will have difficulty drawing the dial itself. Problems with the presentation of arrows and the indication of the given time will indicate a violation of praxis and spatial perception. Patients with neglect are more likely to place all 12 digits in one half of the dial,
leaving the other blank (or even not closing the clock circuit). Using the test, you can assess the dynamics of the patient’s condition, how he is recovering from a stroke or, conversely, worsens as Alzheimer’s disease or vascular dementia progresses.

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