This article reminded me why I love working with a brain that looks cute and clean, like this one:
Because the real brain is very unpleasant and sad to look at. People are rude.
But I've spent the last month at the bottom of Google's gleaming, bloodshed section of images, and now you'll have to check it out, too. So relax.
Now let's go in from afar. There is such a moment in biology - it sometimes makes you think, and the brain also sometimes makes you don't want to. The first is the situation with the matryoshka in your head.
Under your hair is skin, and under it - you thought a skull? - no, there are 19 points, and then only the skull. Then comes the skull and a whole bunch of things that await on the way to the brain.
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There are three membranes under the skull and above the brain.
Outside, the dura mater (Latin), a durable, rough, waterproof layer. It is flush with the skull. I've heard that the brain does not have a pain-sensitive area, but the dura has one - about as sensitive as the skin on your face. And the pressure on the dura mater during a concussion is often the cause of severe headaches.
Below is the arachnoid mater, arachnoid, or arachnoid meninges, which is a layer of skin and then an open space with elastic fibers. I always thought my brain was just floating aimlessly in my head in some kind of fluid, but in fact the only real gap between the brain and the inner wall of the skull is the arachnoid meninges. These fibers stabilize the brain in position so that it does not move too much, and act as a shock absorber when your head hits something. This area is filled with cerebrospinal fluid, which keeps the brain as if floating, because its density is similar to that of water.
Finally, there is the pia mater, the pia mater, a thin, delicate layer of skin that merges with the outside of the brain. Remember, when you look at the brain, it is always covered with blood vessels? So they are not on the surface of the brain, they are, as it were, enclosed in the pia mater.
Here's a complete overview using what appears to be a pig's head.
On the left you see the skin (pink), then two layers of the scalp, then the skull, then the dura mater, the arachnoid, and on the right, the brain, covered only by the pia mater.
As soon as we remove all unnecessary, we are left face-to-face with this stupid boy.
This strange-looking thing is one of the most complex known objects in the Universe - a kilogram, as neuroengineer Tim Hanson says, "one of the most information dense, structural and self-organized substances among all known." All this works with only 20 watts of energy (a computer of equivalent power eats 24,000,000 watts).
Polina Anikeeva, a professor at the Massachusetts Institute of Technology, calls it "a soft pudding that you can scrape off with a spoon." Brain surgeon Ben Rapoport described it more scientifically: a cross between pudding and jelly. He says that if you put your brain on a table, gravity will cause it to blur like a jellyfish. It’s hard to imagine the brain so messy, because it usually floats in water.
But this is what we are all about. You look in the mirror, you see your body and your face, and you think it’s you, but in reality it’s just a car that you drive. In fact, you are a strange-looking jelly-like ball. How do you like this analogy?
Given the strangeness of all this, one should not blame Aristotle or the ancient Egyptians, or many others, for considering the brain to be a meaningless cranial filling. Aristotle believed that the heart was the center of the mind.
In the end, people figured out what's what. But not in full.
Professor Krishna Shenoy compares our understanding of the brain to how humanity imagined a map of the world in the early 1500s.
Another professor, Jeff Lichtman, is even tougher. He begins his class with a question addressed to students: "If all you need to know about the brain is a mile, how far have we come this mile?" He says that students usually answer "three quarters," "half a mile," "a quarter mile," and so on. But the real answer, in his opinion, is "about three inches."
A third professor, neuroscientist Moran Cerf, shared with me an old adage from neuroscientists that trying to understand the brain is a gimmick-22: “If the human brain were so simple that we could understand it, we would be so simple. that they could not [understand him]."
Perhaps, with the help of the large tower of knowledge that our species builds, we will come to this at some point. For now, let's look at what we know about the jellyfish in our heads, starting with the big picture.
Brain from afar
Let's look at large sections of the brain using a hemispherical cross section. This is what the brain looks like in your head:
Now let's take the brain out of the head and remove the left hemisphere, which will give us the best view inside.
Neurologist Paul McLean made a simple diagram that illustrates the basic idea we discussed earlier, touching on the reptilian brain in the process of revolution, the subsequent superstructure of the mammalian brain, and finally our own third brain.
In the form of such a map, this is superimposed on our real brain:
Let's take a look at each section:
Brain stem (and cerebellum)
This is the most ancient part of our brain.
This is the section of our brain section above where the frog boss lives. In fact, the entire frog brain is like this lower part of our brain:
When you understand the function of these parts, the fact that they are ancient makes sense - whatever these parts do, frogs and lizards can do. The largest sections are:
Medulla
The medulla oblongata takes care of your death. It performs the thankless tasks of managing involuntary processes such as heart rate, breathing, and blood pressure, and makes you vomit when it thinks you've been poisoned.
Pons
Varoliev Bridge does a bit of everything. He is responsible for swallowing, bladder control, facial expressions, chewing, saliva, tears and stool - in short, everything.
Midbrain
The midbrain has an even greater personality crisis than the pons. You understand that a part of the brain has problems when almost all of its functions are performed by another part of the brain. In the case of the midbrain, it is about vision, hearing, motor skills, alertness, temperature control, and a host of other things that other parts of the brain do. The rest of the brain also doesn't look much like a midbrain, given how ridiculously uneven the “forebrain, midbrain, hindbrain,” as if deliberately isolating the midbrain.
For which one should separately thank the pons and the midbrain, because they control voluntary eye movement. Therefore, if you move your eyes now, then processes are taking place in the bridge and the midbrain.
Cerebellum
This strange-looking thing, similar to the scrotum of your brain, is the cerebellum, or cerebellum, which is Latin for "small brain". He is responsible for balance, coordination and normal movement.
Limbic system
Above the brain stem is the limbic system - the part of the brain that makes people incredible.
The limbic system is a survival system. An important part of her job is that whenever you do what your dog can do - eat, drink, have sex, fight, hide or run away from something scary - the limbic system is at the wheel. Whether you like it or not, when you do any of the above, you are in a primitive survival mode.
Your emotions also live in the limbic system, and just in case, emotions are also responsible for survival - these are more advanced survival mechanisms needed by animals living in a complex social structure.
Whenever an internal struggle unfolds somewhere in your head, it's worth thanking your limbic system for doing something that you will later regret.
I'm pretty sure that controlling your limbic system is both a definition of maturity and a basic human struggle. It's not that we're better off without our limbic systems - they make us human, after all, and much of life's high is associated with emotions and meeting animal needs. It's just that your limbic system does not take into account that you live in a civilized society, and if you give it too much power to control your life, it will quickly destroy it.
Anyway, let's take a closer look at it. There are many small parts of the limbic system, but we will focus on the most famous ones.
Amygdala
The amygdala is a kind of emotional disorder of the brain structure. She is responsible for anxiety, sadness and a sense of fear. There are two tonsils, and strangely, the left is in a better mood - sometimes it produces a happy feeling in addition to an unpleasant one. The second is always in a bad mood.
Hippocampus
Your hippocampus (from the Greek for "seahorse" because it looks the same) is a drawing board for memory. When rats begin to memorize directions in the maze, the memories are encoded in their hippocampus - literally. Different parts of the two rat hippocampus will be activated in different parts of the maze, because each section of the maze is stored in its assigned part of the hippocampus. But if, after memorizing one maze, the rat is given another task and returned to the original maze a year later, it will hardly remember it, because the drawing board of the hippocampus will be erased in order to make room for a new memory.
The story in the Memento movie is real - anterograde amnesia - and is caused by damage to the hippocampus. Alzheimer's also starts in the hippocampus before making its way through other parts of the brain, so due to the many devastating effects of the disease, memory problems appear first.
Thalamus
In its central position in the brain, the thalamus also serves as a sensory messenger that receives information from your senses and sends it to the cerebral cortex for processing. When you sleep, the thalamus is sleeping with you, which means the sensory mediator is not working. Therefore, in deep sleep, sound, light, or touch may not wake you up. If you want to push someone who is deeply asleep, you have to try to reach out to the thalamus.
The exception is your sense of smell, which is the only sensation that bypasses the thalamus. Therefore, odorous salts are used to awaken a burnt person. And since we're here, here's a cool fact: the sense of smell is a function of the olfactory bulb and is the oldest sense. Unlike other senses, the sense of smell is deeply rooted in the limbic system, where it works in close contact with the amygdala and hippocampus, which is why smell is so closely associated with memory and emotion.
Bark
Finally, we arrived at the cortex, the cortex. Cortex. Neocortex. Cerebrum. Pallium.
The most important part of the whole brain cannot decide on a name. And that's why:
The Cortex is responsible for just about everything - it processes what you see, hear and feel, along with language, movement, thinking, planning, and personality.
It is divided into four parts:
It is not very pleasant to describe what each of them does, because each of them does a lot. But to simplify:
The frontal lobe governs your personality, along with what we consider "thinking" - consideration, planning, commitment. In particular, the kettle cooks most in the front of the frontal lobe, in the prefrontal cortex. The prefrontal cortex is another character in the inner battles of your life. The rationalist within you makes you work. An inner voice tries to convince you to stop worrying about what others think of you and just be yourself. A higher power that wants you to stop sweating.
In this case, the frontal lobe is responsible for the movement of your body. The upper lane of the frontal lobe is your primary motor cortex.
Among other functions, the parietal lobe controls your sense of touch, especially in the primary somatosensory cortex, a strip next to the primary motor cortex.
The motor and somatosensory cortex are located next to each other and are well studied. Neuroscientists know exactly which part of each band connects to each part of your body. Which brings us to the creepiest diagram in this article: the homunculus.
The homunculus, created by neurosurgeon Wilder Penfield, visually displays a map of the motor and somatosensory cortex. The larger a body part is depicted on a diagram, the more the cortex is devoted to its movement or touch. Some interesting facts on this topic:
First, it's amazing that more brain is devoted to the movement and sensations of your face and hands than the rest of your body, instead of being taken. It makes sense, though: you need to have an incredibly detailed facial expression, and your hands need to be very nimble, while the rest of the parts - shoulders, knees, back - can be much rougher. It's not for nothing that people play the piano with their fingers, not their feet.
Secondly, it is remarkable how similar these two crusts are to what they are associated with.
Finally, I came across this crap and now I live with it - so you too. 3D homunculus man.
Let's go further.
The temporal lobe (temporal) is where your memory lives, and because it is next to your ears, the auditory cortex also nests in it.
Finally, at the back of your head, there is the occipital lobe, which is almost entirely devoted to vision.
For a long time I thought that these large lobes were whole chunks of the brain - for example, segments of a general three-dimensional structure. But in reality, the cortex is just the outer two millimeters of the brain, and the meat underneath is just wiring.
If you remove the cortex from the brain, you can spread a 2 mm square sheet of the brain with an area of 48 x 48 centimeters. Dinner napkin.
This napkin is where most of the action takes place in your brain - which is why you can think, move, feel, see, hear, remember, speak and understand language. An elegant napkin, whatever one may say.
And remember that you are a jelly ball? When you try to become aware of yourself, it all happens in the cortex. That is, you are not a jelly ball, you are a napkin.
The magic of the folds in increasing the size of the napkin is evident when we place the rest of the brain on top of our peeled cortex.
So, while not perfect, modern science has acquired some understanding of the big picture when it comes to the brain. In principle, we understand the smaller picture quite well. Let's check?
Brain close
So, while we figured out a long time ago that the brain became the repository of our intelligence, it’s only recently that science has figured out what the brain is actually made of. Scientists knew his body was made of cells, but in the late 19th century, Italian physicist Camillo Golgi figured out how to apply staining to see what brain cells actually look like. The result was surprising:
It didn't look like cells. Golgi opened a neuron.
Scientists quickly realized that the neuron is the basic unit of the vast communication network that makes up the brain and nervous system of virtually all animals.
But it wasn't until the 1950s that scientists figured out how neurons communicate with each other.
The axon, the long process of a neuron that carries information, has a microscopic diameter - too small to study. But in the 1930s, the English zoologist J. Z. Jung figured out that squid could turn the way we think about the brain, because squid have incredibly large axons in their bodies and can be experimented with. Decades later, using a large squid axon, scientists Alan Hodgkin and Andrew Huxley definitely figured out how neurons convey information: action potential. This is how it works.
First of all, there are many different types of neurons:
For simplicity's sake, we'll discuss a simple, common neuron - a pyramidal cell, similar to the one found in the motor cortex. To make a diagram of a neuron, let's start with a guy:
And if we give him a few extra legs, a bit of hair, we take his hands off and stretch him out - that's the neuron.
Let's add more neurons.
Rather than go into a full, detailed explanation of how action potentials work - and draw on a lot of unnecessary and uninteresting technical information that you already came across in biology classes in grade 9 - let's jump straight to the main ideas that will help us.
The trunk of our guy's body - the axon of the neuron - has a negative "resting potential", that is, when he is at rest, his electrical charge is slightly negative. Several people are constantly kicking our guy's hair, the dendrites of the neuron, whether he likes it or not. Their legs dump chemicals onto his hair - neurotransmitters - that travel through his head (cell body, or soma) and, depending on the chemical, increase or decrease the charge in his body. This is not very pleasant for our neuron, but it is tolerable - and nothing else happens.
But if enough chemicals touch his hair to raise his charge, the "threshold potential" of the neuron, then this will trigger an action potential and our dude will be shocked.
This is a dual situation - either nothing happens to our guy, or he is completely electrocuted. It cannot be a little energized or too energized - either it is under it or not, and always to a certain extent.
When this happens, a pulse of electricity (in the form of a brief reversal of the normal charge of his body from negative to positive, and then quickly returning to normal negative) passes through his body (axon) into his legs - the terminals of the neuron axon - which themselves touch the hair of other people (points of contact are called synapses). When the action potential reaches his legs, he causes them to release chemicals into the hair of the people they touch, which either does or does not cause these people to be electrocuted, like himself.
This is how information normally travels through the nervous system - chemical information sent in the tiny gap between neurons triggers the transmission of electrical information through the neuron - but sometimes, when the body needs to move a signal faster, the neuron-neuronal connections can be electrical on their own.
Action potentials move from 1 to 100 meters per second. Part of the reason for this wide spread is that another type of nervous system cell - the Schwann cell - acts as a nurturing grandmother and constantly wraps certain types of axons in layers of fatty blankets called myelin sheaths. More or less like this:
Apart from protection and isolation, the myelin sheath is a major factor in the rate of communication - action potentials move much faster through axons when covered with myelin sheaths.
One good example of the difference in speed created by myelin: do you know what it feels like when you bump your finger, your body gives you one second to think about what you just did and how you feel now before the pain hits? You simultaneously feel the impact of the little finger on something hard and the sharp part of the pain, because the sharp information about the pain is sent to the brain through myelinated axons. It takes a second or two for the dull pain to appear, because it is sent through the unmyelinated "C-fibers" - at a speed of a meter per second.
Neural networks
Neurons are somewhat similar to computer transistors - they also transmit information in the binary language of zeros and ones (0s and 1s), without triggering and with triggering an action potential. But, unlike computer transistors, the brain's neurons are constantly changing.
Remember when you’re learning something new and you’re good at it, and the next day you try again, but no shit? The fact is that yesterday the concentration of chemicals in the signals between neurons helped you in learning. The repetition caused the chemicals to change, you got better, but the next day the chemicals returned to normal, so the improvements were canceled.
But if you keep practicing, you will eventually be good at something, and that will be for a long time. You kind of tell the brain “I need it more than once,” and the brain's neural networks respond by making structural changes accordingly. Neurons change shape and location and strengthen or weaken various connections in such a way as to create a network of pathways to skill, to the ability to do something.
The ability of neurons to change themselves chemically, structurally, and even functionally allows your brain's neural network to optimize itself for the outside world - a phenomenon called brain plasticity. The baby's brain is the most flexible. When a child is born, his brain has no idea what life to prepare for: for the life of a medieval warrior who will have to master swordsmanship, a 17th century musician who will have to develop an accurate muscle memory for playing the harpsichord, or a modern intellectual who will have to keep and work with a colossal amount of information. But the baby's brain is ready to change itself for any life that awaits him.
Babies are stars of neuroplasticity, but neuroplasticity persists throughout our lives, so people can grow, change and learn new things. And that's why we can form new habits and break old ones - your habits mirror existing patterns in your brain. If you want to change your habits, you have to exercise a lot of willpower to rewrite the neural pathways of the brain, but if you try, the brain will finally understand and change all these paths, after which the new behavior will no longer require willpower. Your brain will physically turn the change into a new habit.
In total, there are about 100 billion neurons in the brain, making up this incredibly vast network - like the number of stars in the Milky Way. About 15-20 billion of these neurons are found in the cortex, the rest in other parts of your brain. Surprisingly, even the cerebellum has three times as many neurons as the cortex.
Let's zoom out and look at another cross section of the brain. This time we will cut not along, but across.
The brain matter can be divided into so-called gray matter and white matter. Gray matter actually looks darker and consists of the cell bodies (soms) of brain neurons and their embryos, dendrites and axons - along with other material. White matter is composed primarily of electrically conductive axons that carry information from the soma to other somas or to a destination in the body. The white matter is white because these axons are usually wrapped in the myelin sheath, which is a white fatty tissue.
There are two main areas of gray matter in the brain: the inner cluster of the limbic system and parts of the brain stem that we talked about above, and a thick layer of cortex covered with a 2mm layer of cortex on the outside. The large chunk of white matter in between is composed primarily of the axons of cortical neurons. The cortex is a large command center, and many of its orders emanate from the mass of axons in its composition.
The coolest illustration of this concept is a collection of artistic representations by Dr. Greg Dunn and Brian Edwards. See the clear difference between the structure of the outer layer of the gray matter crust and the white matter below it.
These cortical axons can transmit information to another part of the cortex, to the lower part of the brain, or through the spinal cord - the nervous system's superhighway - and to the rest of the body.
Let's take a look at the entire nervous system.
The nervous system is divided into two parts: the central nervous system - your brain and spinal cord - and the peripheral nervous system - made up of neurons that radiate from the spinal cord to the rest of the body.
Most types of neurons are interneurons that communicate with other neurons. When you think, there are a bunch of interneurons in your head talking to each other. Interneurons are mainly found in the brain.
The other two types of neurons are sensory neurons and motor neurons - these travel down the spinal cord and make up the peripheral nervous system. These neurons can be one meter long. Here is a typical structure for each type:
Remember our two stripes?
These stripes are found where the peripheral nervous system is born. The axons of sensory neurons travel down from the somatosensory cortex, through the white matter of the brain, into the spinal cord (which is simply a massive bundle of axons). From the spinal cord, they go to all parts of your body. Every part of your skin is lined with nerves that originate in the somatosensory cortex. A nerve, by the way, is a series of bundles of axons tied together into a small cord. Here is a cross-section of the nerve:
The nerve is everything in the purple circle, and the four large circles inside are the bundles of axons.
If a fly lands on your hand, the following happens:
The fly touches your skin and stimulates a bundle of sensory nerves. The axon terminals in the nerves begin to work with potential, transmitting this signal to your brain to signal the fly. Signals go to the spinal cord and somas of the somatosensory cortex. The somatosensory cortex then signals the motor cortex to lazily move the shoulder to brush away the fly. Certain somas in the motor cortex, which are connected to the arm muscles, initiate potentials, sending signals back to the spinal cord and from there to the arm muscles. The axon terminals at the end of the neurons stimulate the muscles in the arm, which shake it to chase the fly away. The fly's nervous system goes through its cycle, and it flies away.
Then your amygdala looks around and realizes that an insect is sitting on you, tells the motor cortex to twitch with hostility, and if it is a spider instead of a fly, it also orders your vocal cords to involuntarily scream and destroy your reputation.
So we understand how the brain works? Why then, if the professor asked this question - how many miles have we traveled if this mile is all we need to know about the brain - the answer is three inches?
And the secret is this.
We know how a single computer sends e-mail and fully understand any concepts of the Internet, for example, how many people are there, which sites are the biggest, which trends are leading. But all this stuff at the center - the internal processes of the Internet - they are a little confusing.
Economists can tell you all about how the individual consumer operates, the basic concepts of macroeconomics, and the overarching forces at play - but they can never tell you exactly how the economy works to the nearest second, or what will happen to it in a month or a year.
The brain is somewhat similar. We have a small picture - we know everything about how neurons are activated. And we have a big picture - we know how many neurons are in the brain, what are the largest lobes and structures, how they control the body, and how much energy the system consumes. But somewhere in between - what every part of the brain does - we are completely lost.
We just don't understand.
What really shows us just how confused we are is how neuroscientists talk about the parts of the brain we understand best. Like the visual cortex. We understand the visual cortex well because it is easy to map.
Scientist Paul Merolla described it to me as follows:
So far good. But he continues:
And the motor cortex, another of the most well-studied areas of the brain, on closer inspection turns out to be even more complex than the visual cortex. Because, although we know which general areas of the motor cortex map correspond to certain areas of the body, individual neurons in these areas of the motor cortex are not topographically aligned, and the specifics of their joint work to create body movement are absolutely unclear.
The neuroplasticity that makes our brains so useful also makes them incredibly difficult to understand, because the way our brains work is based on how the brain shapes itself in response to specific environments and experiences. This is not a soulless piece of meat or something that you, I, Aunt Masha, Uncle Petit and Bill Gates will have the same at least in appearance - deep inside, the brain of each person is unique in the highest meaning of the word.
Part One: The Human Colossus
Part Two: The Brain
Part Three: Flying Over the Nest of Neurons
Part four: neurocomputer interfaces
Part Five: The Neuaralink Problem
Part Six: Age of Wizards 1
Part Six: Age of Wizards 2
Part Seven: The Great Fusion