A sophisticated and magical structure hidden in your body

Produced by: Science Popularization China

Produced by: Zhou Yingying (Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences)

Producer: Computer Network Information Center, Chinese Academy of Sciences

We are often asked, “What is going on in your mind?”

If human organs could talk, then upon hearing this question, the heart would probably say, "What? I don't even have the ability to think!"

The brain may feel even more aggrieved: "Why ask your heart what it is thinking? It's obviously me! I'm the one who has been 'thinking' all the time!"

Image source: veer gallery

The brain actually carries the thought of "thinking".

Because of "thinking", the brain, an organ that accounts for only 2% of human body weight, consumes 20% of the body's oxygen consumption and 17% of the body's ATP (energy), so it is known as the "CPU" of the human body.

It has the most complex neural network structure and is also the "existence" with the strongest computing power known in the world.

On March 15, 2016, the famous Go player Lee Sedol played against Google AlphaGo. Although he eventually lost to AlphaGo with a score of 1:4, the game required the computing power of 1,202 CPUs, 176 GPUs and more than 100 scientists, while Lee Sedol only needed his brain and a cup of coffee.

You must be curious about how the brain achieves high-speed computing and information transmission?

What's so magical about it?

In this intertwined network, nerve cells tell endless "secrets" (Image source: veer Gallery)

What does a brain “map” look like?

Our brain is made up of 14 billion neurons, which are like a surging ocean, working for us 24 hours a day. Different brain regions are highly ordered, each with its own functions, finely regulating our bodies.

In the structure of the human brain, the cerebral cortex is the highest center of the entire central nervous system, and the high degree of evolution of the cerebral cortex is also a sign of mammalian evolution.

The main structure and function of the cerebral cortex (Image source: Wikipedia-Cerebral cortex, adapted by the author)

When we talk about the brain, we usually refer to the cerebral cortex and some important structures under the cortex, such as the cingulate gyrus, basal ganglia, limbic system, ventral tegmental area, etc.

As shown in the figure, in addition to the cerebrum, the human brain also includes structures such as the corpus callosum, diencephalon, pons, cerebellum, and spinal cord, which together constitute our central nervous system.

The main structures and functions of the human brain (Image source: Principles of Neurobiology, adapted by the author)

Do you remember the "gun-swallowing suicide" scene that is often played in TV dramas? In fact, the gun in the throat is facing the medulla oblongata of the brain stem, and the medulla oblongata is an important brain area that controls our breathing, heartbeat and digestion. Once the medulla oblongata is damaged, the person will immediately lose his life.

Therefore, when encountering danger, we must protect the back of our head!

In an accident, if the spinal cord is damaged, the pathway between the brain and the body is broken. At this time, the brain can neither receive sensory information from the body nor send movement commands to the body, which will lead to hemiplegia. Therefore, at the scene of a car accident or an accidental fall, do not turn the injured person over at will to avoid aggravating the spinal cord injury and causing irreversible consequences.

How does the smart brain transmit signals to command the body?

Neurons are the most basic unit of brain activity, accounting for about 1/10 of nerve cells. Neurons can transmit external sensory signals and issue motor commands, just like a general commander.

In addition to neurons, the brain also has glial cells, which support neurons and other tissues surrounding them. Glial cells account for 9/10 of nerve cells and are like guards, fulfilling the responsibility of keeping the brain moving in an orderly and efficient manner.

Glial cells protect, nourish and support neurons (Image source: www.visiblebody.com)

Secondly, the unique shape and structure of neurons help the nervous system to transmit signals quickly. Neurons have many dendrites, which are like "antennas". After receiving a signal, they cause the neuron to become excited and transmit the signal to the next neuron through the axon.

The basic structure of a neuron (Image source: www.visiblebody.com)

If the signal is a movement signal, when the signal is transmitted to the motor cortex of the brain, the motor neurons will issue movement commands, which will be transmitted to the brainstem after being regulated by the cortical-subcortical motor circuit and reach various parts of the body, precisely controlling each of our actions.

Cortical-subcortical motor circuit, Cortex cortex; Basal ganglia: basal ganglia; Brain stem/Spinal cord; Cerebellum; Thalamus (Image source: Movement Disorders. 2019 Aug;34(8):1130-1143)

The manipulated brain

In science fiction movies, we often see people with super powers controlling other people's brains. But in real life, can the brain really be controlled?

In 2017, Professor Ivan E de Araujo of Yale University used optogenetics (activating neurons through light) to control the process of mice preying on crickets. Among them, the central amygdala CeA and the corresponding target periaqueductal gray PAG play an important role in the predatory behavior of mice.

As shown in the video, when the blue laser is off, the mouse will react with "curiosity" and "fear" when seeing the cricket, and then slowly move away from it. Once the blue laser is turned on and the CeA →PAG neural circuit is activated through optogenetics, the mouse will immediately run over to prey on the cricket. This shows that in the experiment, the mouse's brain is controlled by light signals.

Video: Mice are stimulated by blue light to prey on crickets (Video source: Cell. 2017 Jan 12;168(1-2):311-324.e18)

Human brain - the most powerful brain on earth!

What is the difference between the brains of humans and animals? Why did humans, rather than other animals, create social civilization?

The brains of different mammals vary greatly in structure and proportion, and the special characteristics of the human brain have laid the physiological foundation for the creation of human civilization. In comparison, the brains of humans, gorillas and dolphins have many folds, while the cerebral cortex of rats and rabbits is relatively smooth.

Comparison of brains of different mammals (Image source: Neuroscience: Exploring the Brain (2007)-Chapter 7)

The formation of wrinkles depends on two parameters: the growth rate and thickness of the cerebral cortex. During the development of the cerebral cortex, changes in the number, size, shape and position of nerve cells lead to the expansion of the cortex on the surface of the brain, while the white matter below the cortex does not change much, which makes the cerebral cortex mechanically unstable under physical pressure, eventually forming a wrinkled structure.

Although both orangutans and dolphins have more "grooved" cerebral cortexes, the chimpanzee's cortex area is only 600 square centimeters, while the human's cerebral cortex area is about 2,400 square centimeters. The area and structure of the human cerebral cortex are very different from those of orangutans, especially the proportion of the frontal lobe of the human cerebral cortex is much larger than that of orangutans, which also leads to higher intelligence in humans.

Dolphins are animals with relatively high intelligence. Their cerebral cortex area reaches 2,600 square centimeters and they have more neurons than humans. However, the functions of dolphin brains are far from comparable to those of humans. Why is that?

This is because the ancestors of humans and dolphins chose different evolutionary paths: dolphins chose to evolve in the ocean, and their limbs evolved into fins.

In order to adapt to the complex and vast ocean environment, although the cerebral cortex of dolphins is well developed, most of it is used to manage and control their sonic positioning system. What's more interesting is that in order to maintain the ability to move, communicate and hunt 24 hours a day, the left and right brains of dolphins can even take turns sleeping.

Dolphin echolocation system (Image source: https://dolphinquest.com/)

Humans chose land and evolved flexible fingers. The evolution of hands created complex tools, and the learning and making of complex tools further developed the brain and hands. This cycle gradually led to our ancestors evolving from primitive humans to Homo sapiens, and the rapid increase in brain capacity allowed Homo sapiens to distinguish and produce more phonemes, and eventually developed a language and writing unique to humans, thus creating social civilization.

The structure of the brain continues to evolve towards complexity, adapting to the ever-changing and complex environment. At the same time, changes in the environment have prompted the "upgrade" of the brain structure. In this way, we have embarked on a long evolutionary journey in constant change.

References:

1. Han, W., et al., Integrated Control of Predatory Hunting by the Central Nucleus of the Amygdala. Cell, 2017. 168(1-2): p. 311-324 e18.

2. Parker, JG, et al., Diametric neural ensemble dynamics in parkinsonian and dyskinetic states. Nature, 2018. 557(7704): p. 177-182.

3. Wichmann, T., Changing views of the pathophysiology of Parkinsonism. Mov Disord, 2019. 34(8): p. 1130-1143.

4. Why are there so many wrinkles on the surface of the brain?

5. If dolphins persist on land, perhaps dolphin civilization will replace our human civilization Personal Library