Because the real brain is ugly and not cute at all. Humans are disgusting.

But in the past month, I have been looking at sticky and bloodshot brain pictures in Google Pictures, which is simply hell. Now you are going through the same experience, so please be prepared.

Now let's start from the outermost layer. I think one of the advantages of biology is that it is sometimes quite organized, and there are some organized places in the brain. First, the human head structure is like a Russian doll.

The outermost layer of your head is hair, and the scalp is below, and then you think it will reach the skull next-but in fact, there are about 19 layers in the middle to reach the skull.

Between your skull and your brain [1], there is another pile of these things:

Under the skull, the brain is wrapped in three layers of film.

The outermost layer is the dura mater, which is a firm and uneven waterproof membrane. The dura mater will cling to the skull. I heard that there is no pain perception area in the brain, but there is one on the dura mater-it is as sensitive as facial skin-and the pressure or impact on the dura mater often causes severe headaches.

The lower layer is called arachnoid membrane, and you can see that the space under this membrane is covered with some elastic fibers. I always thought my brain was just immersed in some kind of liquid, and then it floated inside the skull. But in fact, the only gap between the outside of the brain and the inside of the skull is this arachnoid membrane. These fibrous substances can fix the position of the brain and prevent it from moving around. They can also act as a buffer when the head is hit. This area is filled with spinal fluid with a density close to that of water, which can keep the buoyancy of the brain.

The last layer is the pia mater, which is closely connected with the outer layer of the brain. Do you know why every time I see a picture of the brain, there are always sticky blood vessels covering it? These blood vessels are not actually on the surface of the brain, but embedded in the pia mater. If you are not afraid of nausea, this video can see a professor peeling the pia mater from the human brain. )

Here is the whole picture of the brain, and this should be the pig brain:

From left to right, you will see the skin (pink layer), then two layers of scalp, then the skull, dura mater and arachnoid membrane, and at the far right is the brain wrapped under the pia mater.

If we peel off everything in the outer layer, we will see this pink thing:

This funny-looking thing is the most complex object known in the universe-although it weighs only three pounds, neuroscientist Tim Hansen calls it "the thing with the highest information density, the highest structure and the most complete self-organization known at present". With such a powerful brain, its running power is only 20 watts (an equally powerful computer will need 24 million watts to start).

Polina Anikeeva, a professor at MIT, described the brain as "a soft pudding that can be scooped out with a spoon". The description given by brain surgeon Ben rapoport feels more scientific: "The shape between pudding and jelly". He said that if you put a brain on a table, it will flatten under the action of gravity, a bit like a jellyfish. We usually don't expect the brain to be so soft, because it is usually suspended in liquid.

But this is who we are. You see your body and face in the mirror, and you think it's you-but it's just a piece of skin. What you really look like is a grotesque jelly ball. I hope you don't mind saying so.

Strange as it sounds, you can't blame Aristotle or the ancient Egyptians, although they once concluded that the brain is just a meaningless "skull filler" (Aristotle thinks the heart is the source of intelligence). [2]

Later, humans gradually learned more about the truth about the brain, but only partially.

For example, Professor Krishna Shenoy said that our understanding of the brain is like1the understanding of the whole world map at the beginning of the 6th century.

Another professor, Jeff Lichtman, was even harsher. In the first class of his course, he always asks the students a question: "If the knowledge contained in the brain is one mile, how far have we come in this journey?" He said that the students answered a third, half and a quarter-but the professor gave the answer "about 3 inches".

The third professor is the neuroscientist Moran CERF. He shared with me an old saying in neuroscience, which pointed out why trying to fully understand the brain is an unattainable paradox: "If the human brain is so easy to understand, then we can't understand the brain with such a simple brain. 」

With the help of the huge knowledge base that mankind is building, we may be able to do this one day in the future. Now, let's take a look at the current human understanding of the brain-from a macro perspective.

Let's first look at the main structure of the brain through the following cross-sectional view of the hemisphere:

Now let's take out the brain and remove the left hemisphere so that we can see the structure clearly.

Neuroscientist Paul MacLean made a simple schematic diagram, explaining a basic concept we discussed before: in the process of evolution, the reptile's brain first appeared, and then mammals developed a second brain structure on this basis, and finally the appearance of human beings perfected the third brain structure.

Here are the corresponding positions of these structures on the real brain:

Next, let's take a look at each part here:

This is the oldest part of our brain:

This is the part of the brain where the frog boss is above. In fact, the frog's whole brain is very similar in shape to this part of our brain:

After understanding the functions of these parts, you will understand why they are ancient-frogs and lizards can do what these parts can do. The following are the main parts (click animation to view HD version):

The medulla oblongata just wants you to live. It is responsible for controlling some involuntary activities, such as heartbeat, breathing and blood pressure. In addition, if it thinks you are poisoned, it will make you vomit and do all kinds of thankless work.

The work of pons is very fragmentary. It is responsible for swallowing, bladder control, facial expression, chewing, saliva secretion, tears secretion and posture maintenance-basically doing everything according to mood.

The work of midbrain is even more incomplete than pons. If something done by one part of the brain has been taken care of by other parts, it must feel bad. What we are talking about here is the midbrain, which is responsible for what other parts of the brain are doing, such as vision, hearing, movement control, alertness and body temperature control. Other parts of the brain don't seem to like the midbrain very much, because you can see how different the proportions of "forebrain, midbrain and hindbrain" are, so it seems that the midbrain is rejected by other parts.

However, pons and midbrain also have a valuable job. They are also responsible for controlling the voluntary movement of the eyes, which is a serious problem. So if you roll your eyes, it means that your pons and midbrain are doing one of their full-time jobs.

This seems a little strange. What looks like the scrotum of the brain is your cerebellum. The cerebellum is responsible for keeping your balance, coordinating your hands and feet and walking normally. This is a video of Professor Calm showing the anatomical structure of cerebellum.

Above the brain stem is the limbic system-the part of the brain that makes people so crazy.

The marginal system is a survival system. Generally speaking, when you are doing what your dog will do-eating, drinking, mating, fighting, avoiding or avoiding terrible things-this is the limbic system in string pulling. Whether you want to admit it or not, as long as you are doing any of the above things, you are in the survival mode of primitive people.

The limbic system also controls your emotions, and emotions are also the need of survival in the final analysis-a more advanced survival mechanism, which is essential for animals living in complex social structures.

In my previous article, I mentioned instant rewards for monkeys, social survival mammoths and other animals-they all refer to the limbic system. Whenever there is an internal struggle in your brain, the job of the limbic system may be to encourage you to do something you will regret later.

I firmly believe that learning to control the limbic system is a sign of human maturity and the core struggle of human beings. This is not to say that we will live better without the marginal system-the marginal system is half the reason why we become human beings, and most of the fun in our lives is related to the satisfaction of emotions or animal instinctive desires-but the marginal system doesn't know that you live in a civilized society, and if you let it go too far, it will soon ruin your life.

Ok, let's take a closer look. Edge system consists of many widgets, but we only introduce some of the most important ones:

The amygdala can be said to be the concentration of negative emotions in the brain. It is responsible for anxiety, sadness and our response to fear. There are two amygdalas in the brain. Strangely, the amygdala on the left is more optimistic. In addition to the usual negative emotions, sometimes there will be happy emotions, and the one on the right has been in a bad mood.

The hippocampus (as the name implies, because it looks like the hippocampus) is like a drawing board of memory. If you put a mouse into a maze, it will slowly remember the maze path, because the memory of the maze path will be encoded into the hippocampus of the mouse-indeed. When the mouse walks to different positions in the maze, different parts of its two hippocampus will be awakened, because each part of the maze corresponds to a certain part of the hippocampus. But if the mouse does other tasks after remembering a maze and is put back into the original maze one year later, it will be difficult for it to remember how to get to the maze. Because at this time, most of the contents on the sketch board of hippocampus have been cleared, making room for remembering new things.

The disease described in the movie Memento is real-anterograde amnesia is caused by the damage of hippocampus. The onset of Alzheimer's disease begins in the hippocampus and then slowly spreads to other parts of the brain, which is why patients with Alzheimer's disease first become forgetful and then have a series of other serious symptoms.

The thalamus is located in the center of the brain. It's like a middleman in the sensory system. It is responsible for receiving information from the sensory organs and then transmitting it to the cerebral cortex for processing. When you are sleeping, the thalamus sleeps with you, which means that the intermediary responsible for transmitting the senses is off duty. So during deep sleep, you usually don't wake up because of slight sound, light or touch. If you want to wake a person who is in a deep sleep, you must be loud enough to wake up the thalamus.

The only exception is the sense of smell, which is the only feeling that can bypass the thalamus. That's why smelling salts can be used to wake the unconscious. Now that I'm here, I'd like to add a cold knowledge: the sense of smell is the function of the olfactory bulb and the oldest sense. Different from other senses, the sense of smell is located in the depths of the limbic system, and it is closely related to both the amygdala and the hippocampus-that is why the sense of smell can evoke specific memories and emotions.

Finally, we talked about cortex, which is also called cortex, neocortex, brain and cerebral cortex.

As the most important part of the whole brain, it can't even figure out its own name. What's going on here?

The cortex is almost omnipotent-it is responsible for processing auditory, visual and sensory information, as well as language, action, thinking, planning, personality and many other aspects.

The cortex can be divided into four leaves:

The responsibilities of these parts are really not coherent, because each part has done a lot of things and there are many overlapping functions between them, but we can briefly summarize them:

The frontal lobe is responsible for your personality and a series of things that we think are related to "thinking", including functions such as reasoning, planning and execution. Among them, most of your thinking and behavior takes place in the front part of the frontal lobe called the prefrontal cortex-the wise man in your brain. In the aforementioned internal brain struggle, the prefrontal cortex is the opposite of the limbic system. It is the rational decision-maker who urges you to finish the work; Tell you not to worry about the internal voice of other people's opinions; I hope you don't haggle over every ounce.

If you think these tasks are not troublesome enough, the frontal lobe is also responsible for the movement of your body. The anterior gyrus at the top of the frontal lobe is your "primary motor cortex".

One of the functions of the parietal lobe is tactile control, and the most important one is the "primary somatosensory cortex", which is just behind the main motor cortex.

The main motor cortex and the main somatosensory cortex next to each other are particularly interesting because neuroscientists have found that each of their positions corresponds to a certain part of the body. This leads to the most frightening picture in the text-"Homuculus".

Dwarf figure was put forward by Wilder Penfield, a pioneer of neurosurgery, which vividly shows the corresponding body parts of the main motor cortex and the main somatosensory cortex. The greater the proportion of body parts in the picture, the greater the area in the corresponding cortex. Here are some interesting findings:

First of all, the brain is more responsible for facial and hand movements and sense of touch than all other body parts combined. Although it sounds incredible, it is actually understandable, because we need to make very subtle facial expressions, and our hands need to be extremely dexterous, but other parts of the body, such as shoulders, knees and back, do not need such meticulous movements and feelings. This is why humans can play the piano with their fingers, but not with their toes.

Secondly, the proportion of body parts corresponding to these two cortex is also highly similar. I can understand this, but I never thought that the part of the body that needs motion control most is also the most sensitive part.

Finally, I happened to see the following picture, which has been lingering in my mind ever since, so now I will let you experience this feeling-a 3D version of a dwarf.

Let's move on—

The temporal lobe stores most of your memories. In addition, because it is next to your ear, it is also the location of the auditory cortex.

Finally, in the back of your head is the occipital lobe, which is almost entirely used to process visual information.

For a long time, I thought these brain lobes were the parts that make up the brain-just like the partitions we see in the 3D model. But in fact, the cortex only occupies the outermost layer of the brain by 2 mm-equivalent to the thickness of a coin-and the space below the surface layer is basically a complex connection of various nerve tissues.

If you peel off the cerebral cortex, you can get a 2 mm thick area of 2,000 to 2,400 square centimeters, [4] which is equivalent to a square napkin of 48cm×48cm( 19 x 19 inches).

This napkin is where most of your brain behavior takes place-it is the reason why you can think, move, feel, see, listen, remember, speak and understand language. This is simply the best napkin ever.

Remember when I said, "You're just a jelly ball"? In fact, what you think of yourself is mainly your cerebral cortex. In other words, you are actually a napkin.

When the whole brain is put together with the peeled cortex, we can clearly see that these folds increase the napkin area:

Although it is not perfect, modern science has basically mastered the whole picture of the brain. In addition, we also know something about the details of the brain. Next is an introduction to the details of the brain:

Although we have long understood that the brain is the source of human intelligence, the scientific community did not understand the structure of the brain until recently. Scientists have known that the human body is composed of cells, but it was not until the end of 19 that Italian surgeon camillo golgi discovered a staining method to reveal the true face of brain cells. What he finally found was surprising:

This doesn't look like what cells should look like. Gorky didn't realize that what he discovered was actually a "neuron".

Scientists later realized that for almost all animals, neurons are the core units of the brain and nervous system, and they are also huge communication networks within them.

But it was not until A.D. 1950 that scientists further discovered the way of communication between neurons.

Axons, the slender protrusions on neurons that carry information, are usually very small in diameter-too small for scientists to use them for experiments until recently. In the1930s, J·Z· Young, a British zoologist, made an unexpected discovery that subverted traditional cognition-squid has an unusually large axon, which can be used for experiments. Decades later, scientists Allen Hodgkin and Andrew Huxley finally found a way for neurons to transmit information-action potential by using giant axons of squid. Its principle is this:

First of all, there are many types of neurons:

For simplicity, we only discuss a simple and common neuron-vertebral cells, which you can find in the motor cortex. If we want to draw a neuron icon, we can draw a villain first:

Then add some legs and hair to him, take off his arm, and finally lengthen him-so we draw a neuron.

Then we add some neurons.

I don't intend to explain the detailed principle of action potential here, because it will involve many unnecessary and boring professional contents, which you should have learned in junior high school biology class. If you want to fully understand the relevant information, I suggest you take a look at this high-quality popular science article of Khan Academy. Next, we only know some basic concepts related to the theme of this article.

Now, our neuronal villain's tail-axon-has a negative "resting potential", which means that it will be slightly negatively charged at rest. Our neuron villain's hair (dendrites) will always be touched by other villain's feet [5], although he may be reluctant. Other people's feet will drop a chemical called neurotransmitter on his hair, which will pass through his head (cell body, or "somatic cell"), and depending on the nature of the chemical, he will slightly change the charge carried by his body. Although this will make our little neuron people a little uncomfortable, it's not a big problem-nothing else will happen.

But if enough chemicals touch his hair to make his charge rise to a certain value, that is, the "threshold potential" of neurons, then the little man will be in action potential, that is, he will be shocked.

This is an either-or state: our villain is either completely unchanged or completely shocked. He won't be partially or excessively shocked-either not at all or to the same extent every time.

When this happens, an electric current will flow from his body (axon) to his foot (axon tip), which will touch the hair of other villains (this contact point is called synapse). In this process, the charge of the villain's body will temporarily change from negative to positive, and then quickly return to his normal negative potential state. When this action potential reaches the foot of the villain, the axon tip will release chemicals to the hair it touches, which may cause the touched villain to get an electric shock, just like before.

This is the way information is transmitted in the nervous system-chemical information is transmitted through tiny gaps between neurons, and current information is triggered by neurons-but when the body needs to transmit a signal quickly, neurons can also transmit information through current.

The transmission speed of action potential is between 1 and 100 meters per second. Part of the reason for such a wide range of changes is that another cell in the nervous system-Schwann cell-is like an old lady who always thinks that her grandson has not enough clothes and has been covering her axon with a thick blanket-myelin sheath. The whole process is like this:

Besides protection and insulation, myelin sheath is the main reason that affects the information transmission speed of neurons-when the axon is wrapped by myelin sheath, the transmission speed of action potential will be much faster. [7]

Let's take an example to illustrate the influence of myelin sheath on the speed of information transmission: for example, when your toe kicks something, you will immediately realize what you have just done, but it may take a second or two before you begin to feel the dull pain in your toe. You can immediately feel something kick, a sharp pain, because the pain information is transmitted to the brain through axons wrapped in myelin sheath, and later you begin to feel dull pain because this pain is transmitted through "class C nerve fibers" without myelin sheath protection, and its transmission speed is about 1 m per second.

In a sense, neurons are much like transistors in computers-they all transmit information in the binary language of "1" (action potential activation) and "0" (non-action potential activation). But unlike computer transistors, neurons in the brain are always changing.

You must have had such an experience. You learned a new skill and mastered it well, but the next day you found that you couldn't. The reason why you can learn this skill on the first day is that the number or concentration of chemicals that transmit signals between neurons has changed. Repetitive behavior will lead to changes in these chemicals and make you make progress, but the next day, the chemicals that have been adjusted before will return to the normal level, and your previous progress will disappear.

But if you keep practicing, you will eventually master this skill for a long time. In this process, you are actually telling the brain that "this will not happen overnight", and then the neural network of the brain will make structural adjustments, which can last for a long time. Neurons will change their shape and position, strengthen or weaken different connections, and establish fixed paths according to the skills they need to learn.

Neurons can change themselves chemically, structurally and even functionally, and constantly optimize the neural network of the brain according to the outside world. This phenomenon is called neuroplasticity. The baby's brain has the highest neuroplasticity. After the baby is born, his brain has no idea what kind of life he will live in the future: a first-class medieval warrior with fencing? A17th century musician who is good at playing harpsichord? Or a modern scholar who not only wants to remember and sort out massive information, but also wants to manage complex interpersonal relationships? In any case, the baby's brain is ready to constantly adjust itself and can cope with any form of life in the future.

Although babies have the strongest neural plasticity, this ability will accompany us all our lives, so human beings can grow, change and learn new knowledge, which is also the reason why we can form new habits and change old ones-habits are actually a reflection of the existing neural structure of the brain. If you want to change your habits, you need to exert great willpower to overthrow the neural path established by your brain before, but if you can persist long enough, your brain will eventually be instructed to change the previous path, and new behavior habits no longer need the support of willpower. The brain has made corresponding physiological changes to new habits.

This unimaginable huge neural network consists of about 654.38+000 billion neurons in the brain-this number is similar to the number of stars in the Milky Way, and it is more than ten times the global population. Among them, 150 to 20 billion neurons are located in the cortex, and the rest are located in the lower part of the brain (surprisingly, the number of neurons in the cerebellum is more than three times that of the cortex).

Now let's take a closer look at another cross-sectional view of the brain-but this time, instead of dividing the brain into two hemispheres, we cut it from the middle:

The substances in the brain can be divided into gray matter and white matter. Gray matter looks darker and consists of cell bodies, dendrites and axons of brain neurons. The main component of white matter is the axon responsible for transmitting information between nerve cell bodies or other parts of the body. White matter is white because these axons are usually wrapped by myelin sheath, which is some white adipose tissue.

Gray matter mainly exists in two areas of the brain-the limbic system and the brain stem as mentioned above, and the coin-thick cerebral cortex. The white matter between them is mainly composed of axons of cortical neurons. The cortex is like the command center of the brain, which transmits instructions through a large number of axons existing in the underlying white matter.

The following is the most beautiful concept map of gray matter and white matter I have ever seen, which was made by Dr. Greg. Dunn and Dr. Brian Edwards. You can clearly see the structural differences between the outer gray matter and the lower white matter (click the picture to view the HD version):

These cortical axons may transmit information to other parts of the cortex, to the subcortical brain, or to other parts of the body through the spinal cord (the informing function of the nervous system). [8]

Let's take a look at what a complete nervous system looks like: