Subvert your cognition! Is it true that a vegetative person can tickle himself?

Recently, a saying has been circulating on a certain social platform: a vegetative person can tickle himself... Many people find it incredible when they see it. Is this true?

Image source: Screenshot of a platform

Let me first give you the answer: a vegetative person cannot be tickled. Professionals said that in this case, the vegetative person's twitching was probably mistaken for tickling.

So, will a vegetative person sleep for many years and suddenly wake up like in TV dramas? Before answering this question, let's first understand what a vegetative person is.

What is a vegetative state?

The term used to describe a "vegetative state" is a persistent vegetative state (PVS). In layman's terms, the so-called vegetative state refers to a state of awakening lacking conscious content that occurs after severe brain damage due to various reasons . The patient's language, thinking and other high-level brain functions are all lost. The patient may open his eyes spontaneously or reflexively, or may cry and laugh spontaneously and meaninglessly, and have an avoidance reaction to painful stimuli.

The cerebrum is responsible for the advanced functions of the brain, such as the language and thinking mentioned above, which are all completed by the cerebrum, and the cerebellum is mainly responsible for balance. The brainstem is quite special. From the perspective of shape and position, it is just the connecting part between the brain and the spinal cord, but in fact it has an extremely important function, which is to maintain the most basic activities of our lives. For example, breathing and heartbeat, which are the most important things for us, are all controlled by the brainstem.

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To summarize briefly, the brain can be seen as three parts. The cerebellum is responsible for balance, which has little to do with what we are discussing at the moment; the cerebrum is responsible for advanced functions, and it can be said that it is its powerful functions that make us stand out from other creatures; and the most basic life centers are concentrated in the brain stem. Once it has problems, our lives will be endangered at any time.

Knowing the basic structure and function of the brain, we can do a simple subtraction problem. When the brain function is "subtracted", the advanced neural functions that make us "human" will disappear. If our brain function is only the brain stem, our body will only have the most basic life-sustaining functions such as breathing and heartbeat. When a person is in this state and cannot recover, it is a persistent vegetative state, which is what we commonly call a vegetative state.

What conditions can cause a person to become a vegetative state?

This question is not difficult to answer. Regardless of the cause, as long as the brain function is lost but the brain stem function is still intact, it is possible to become a vegetative state. Therefore, this question can be asked in another way: Under what circumstances will brain damage occur?

There are several ways to classify brain injury. We will adopt a more understandable one and divide it into primary brain injury and secondary brain injury.

The so-called primary brain injury is the damage that occurs almost immediately when the brain tissue is subjected to external force. Generally speaking, when the external force is large enough that even the solid skull cannot protect the brain tissue, primary trauma will bring quite serious consequences, and even form the persistent vegetative state mentioned above.

Secondary brain injury occurs some time after the injury. In this case, the skull, which is supposed to protect the brain tissue, becomes an accomplice in causing brain damage. Because the brain tissue is extremely important, during the long process of evolution, the brain tissue has obtained the strongest protection of the whole body, that is, a complete bony structure, forming an extremely strong armor, which is the cranial cavity composed of several bones.

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But on the other hand, the space in this suit of armor is very limited. If more things are put in it, it will squeeze the brain tissue, leading to serious consequences. For example, when a person is injured, cerebral blood vessels rupture and cause intracranial hemorrhage. The formation of intracranial hematoma stimulates various inflammatory factors and causes edema of the surrounding brain tissue. The edema will reach a peak within 3 to 5 days. This symptom is just like our daily sprain, except that the edema of the ankle soft tissue is not restricted by the bone structure and can expand outward without causing damage to blood vessels and nerves.

Therefore, due to the fixed capacity of the cranial cavity, once the area of ​​cerebral edema expands, normal brain tissue will be squeezed and stretched, and it will inevitably be damaged. In severe cases, brain herniation will occur. The so-called "herniation" can be generally understood as human tissue moving from where it should be to where it should not be. Brain herniation means that the brain tissue is forced to leave the cavity it originally occupied. In addition, the brain tissue is very soft, so the severity of brain herniation can be imagined.

Above, we understand the serious brain damage caused by trauma. In fact, there are many other reasons that can cause similar damage. For example, in neuropathology, the vegetative state is mainly caused by damage to the cortex or white matter and thalamus, rather than brainstem damage. Traumatic injuries have been found to be associated with diffuse damage to the subcortical white matter (or diffuse axonal injury). On the other hand, cases of non-traumatic injuries have been found to have extensive necrosis in the cerebral cortex, which is almost always related to thalamic damage, such as hemorrhage, poisoning, hypoxia, infection, etc. When these injuries are severe enough, they will form a "vegetative" state in which brain function is lost but the brainstem can still work normally.

Can a vegetative state be restored?

Back to the question we started with, in movies and TV shows, people who have been sleeping for years in a vegetative state often suddenly regain consciousness, and can even return to the same state as before. However, in reality, this is a very rare phenomenon, and the reason for this is easy to explain, that is, the differentiation of cell function.

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In the process of nurturing life, the formation of the fertilized egg is the beginning of everything. The fertilized egg undoubtedly has unlimited potential, because this tiny cell can divide and develop into countless cells with different forms and functions, and finally form a complete human body. From this perspective, the fertilized egg is an omnipotent cell because it has unlimited possibilities.

However, during the reproduction process, cells gradually differentiate, and different cells have different characteristics. A very important point is that the regeneration ability of different cells is also very different. For example, the cells in our oral mucosa have a very strong regeneration ability, so the damage to the oral mucosa recovers very quickly. On the contrary, nerve cells have a regeneration ability close to zero, so functional damage to the nervous system is very difficult to recover, which also adds a bit of sadness to the "persistence" in "persistent vegetative state".

Planning and production

Author: Sun Yifei, Director of the Medical Education History Research Office, Hebei Medical University

Reviewer: Tang Qin, Director and Researcher of the Science Popularization Department of the Chinese Medical Association

Planning丨Xu Lai

Editor: Yinuo

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