What are the folds of the brain for?

When we talk about the brain, one of the most typical comparisons made is that it resembles the shape of a walnut, since it has a wrinkled shape.

These characteristic wrinkles of the organ are due to the fact that its surface is folded on itself, allowing it to fit better. However, other than for this, What are the folds of the brain for? Do they have something to do with intelligence? Let's see it next.

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What are the folds of the cerebral cortex used for?

The main reason why the human brain is wrinkled is because folding in on itself allows it to gain some space. The cerebral folds are what are more appropriately called gyri, while the grooves or fissures are the depressions between these wrinkles.. The human brain is so wrinkled that if we could spread it out on a table, we would have about 2,500 square centimeters, the size of a small tablecloth.

According to Lisa Ronan, a researcher at the University of Cambridge, the cortex of the human brain, the outermost surface of the brain, expands during fetal development. Contrary to what many believe, the brain has a consistency similar to that of jelly.

Being such a soft organ, this makes it a tremendously vulnerable part of the body when pressure is exerted on it. For prevent, during the growth of the brain during pregnancy, the cerebral cortex from colliding with the walls of the skull, it folds in on itself, gaining a little space.

This space-gaining strategy is not exclusive to the human species. It can also be seen in other mammalian species, such as dolphins, elephants, and whales. It is for this reason that scientists have defined the concept of gyrification, which makes refers to how folded in on itself is the cerebral cortex in a given species.

Traditionally, gyrification has been viewed as the result of a high degree of neurogenesis and dendrite growth. In our species, as can be deduced by looking at a photograph of the brain, we present a fairly high rate of gyrification and, For this reason, having more folds has been associated with having higher cognitive abilities, as occurs in the humans.

However, and after analyzing other mammalian brains, something truly paradoxical has been seen. Despite the fact that human beings are the animal species with the highest intelligence, There are other animals that have brains with a greater number of turns. The most notable cases are the brain of elephants, whales and dolphins.

Other functions of the gyri and sulci

As we have already seen, these folds, called cerebral gyri and sulci, have as their main function the allow more space and prevent the cerebral cortex from being pressed against the walls cranial. This causes more neurons to accumulate in the cortex and, for this reason, it has been believed that a greater number of folds was synonymous with a greater capacity to process information.

In turn, these folds are used by neuroanatomists as criteria for dividing the brain into regions, functioning as borders on a cartographic map. In this way, and thanks to these wrinkles, the human cortex is divided into two hemispheres that, In turn, they are divided into four lobes: frontal lobe, temporal lobe, parietal lobe, and temporal lobe. occipital.

Although the idea of ​​the brain wrinkling up more to allow more neurons to be packed makes sense and is physically possible, which would, in turn, make sense of the theory that the more wrinkles, the more cognitive capacity; an attempt has also been made to give another explanation for this. It has been seen that the larger the animal, the more likely it is to have a brain with many folds. The larger the brain is during gestation, the more it needs to wrinkle in on itself.

This would explain why there are very small animals, such as rats and mice, which have a smooth cerebral cortex. D.uring fetal development, your brain does not grow large enough to need to fold in on itself to save space. On the other hand, this would also solve the question of why elephants and whales have more wrinkled brains than ours. Being bigger, their brains need to wrinkle more while they are forming in the womb.

However, and despite the fact that this explanation is quite convincing, there are cases of animals that have smoother brains than they should be considering their size, as is the case with manatees. It is for this reason that another explanation was proposed, halfway between the traditional one that more roughness is equivalent to greater cognitive ability and the theory of the relationship with the size of the brain. The key would be in the physical properties of certain parts of the crust.

There are brain regions that are thinner than others, which would make them tend to bend more easily. Depending on how they folded according to which areas, not only could their physical properties be elucidated, but it could also be related to the specific function they can perform.

It has also been suggested that, depending on the type of behavior that the animal species presents, its brain will present a greater or lesser amount of wrinkles. It has been seen that some mammals with brains few wrinkles tend to form and live in small social groups, while animals with more folds would have more extensive social networks, something that humans, whales and dolphins share.

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The case of the brain without folds

Some time ago, an image of a brain, supposedly human, without wrinkles appeared on the Internet. This brain was far removed from the traditional comparison of it being a walnut. More than a nut, this particular brain was reminiscent of a fish, a dropfish specifically.

This brain was found by photographer Adam Voorhes, who was doing a photo shoot in the brain sample racks at the University of Texas. What is known about this group of brains, in which the smooth brain is found, is that they belonged to patients at the Mental Hospital in the city of Austin, in the state of Texas. These brains had been left in the dark of oblivion for 20 years, in a cabinet in the university's animal laboratory.

An attempt has been made to find out who was the person who housed such a curious and, at the same time, chilling brain in his skull. How did he behave? Was he able to speak? Did he have a properly human conscience? The only thing that can be known based on his brain is that the subject suffered from a serious case of lissencephaly, that is, a brain with fewer convolutions than it should, although in his case the lack of wrinkles was total.

Normally, cases of lissencephaly are due to errors in neuronal migration during fetal development.. It is believed that it could be caused by the action of certain pathogens, especially viruses, which would occur during the first trimester of pregnancy. It has also been theorized that it could be caused by a lack of blood supply while the fetus is forming, although the idea that it is a rare genetic disorder has some strength.

Among the symptoms suffered by people with this strange disease are having a facial appearance unusual, swallowing problems, severe psychomotor retardation, abnormalities in the hands and feet, spasms and seizures. The treatment is symptomatic, only being able to improve, within what is humanly possible, the well-being of the affected person, although their life expectancy is not more than two years.

Bibliographic references:

• Mathias, S. R et al (2020). Minimal Relationship between Local Gyrification and General Cognitive Ability in Humans. Cerebral Cortex, 0(0), 1-12. https://doi.org/10.1093/cercor/bhz319
• Ronan L, Voets N, Rua C, Alexander-Bloch A, Hough M, Mackay C, Crow TJ, James A, Giedd JN, Fletcher PC (2013), Differential Tangential Expansion as a Mechanism for Cortical Gyrification. Brain Cortex.