What are the folds of the brain used for?

Why do we have folds in the cerebral cortex? Let's see what is known about this phenomenon.

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

These characteristic wrinkles of the organ are due to the fact that the surface of the organ is folded on itself, allowing it to fit better. However, apart from this, what are the folds of the brain used for? Do they have anything to do with intelligence? Let's see below.

What are the folds of the cerebral cortex for?

The main reason why the human brain is wrinkled is because folding in on itself allows it to gain some space. The brain folds are what are more appropriately called convolutions, while the sulci 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. To to prevent the cerebral cortex from colliding with the walls of the skull during the growth of the brain during gestation, the cerebral cortex folds in on itself.The cerebral cortex folds in on itself, gaining a little space.

This space-gaining strategy is not unique 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 refers to how folded back on itself the cerebral cortex is in a given species.

Traditionally, gyrification has been seen 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 have a fairly high rate of gyrification and, for this reason, having more folds has been associated with having higher cognitive capacities, as is the case in humans.

However, and after analyzing other mammalian brains, something certainly paradoxical has been found. Although humans are the animal species with the highest intelligence, there are other animals that have brains with a greater number of twists and turns.. The most notable cases are the brains of elephants, whales and dolphins.

Other functions of the gyri and sulci

As we have already seen, the main function of these folds, called gyri and sulci, is to provide more space and prevent the cerebral cortex from being pressed against the cranial walls. This This allows more neurons to accumulate in the cortex and, for this reason, it has been 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 a criterion for dividing the brain into regions, functioning like the borders on a cartographic map. In this way, and thanks to these wrinkles, the human cortex is divided into two hemispheres which, in turn, are divided into four lobes: frontal lobe, temporal lobe, parietal lobe and occipital lobe.

Although the idea that the brain wrinkles more to allow packing more neurons makes sense and is physically possible, which would, in turn, give sense to the theory that the more wrinkles the more cognitive capacity, another explanation for this has also been tried. It has been seen that the larger the animal, the more likely it is to have a brain with many wrinkles.. The larger the brain is during gestation, the more it needs to wrinkle in on itself.

This would explain why there are animals of very small size, such as rats and mice, which have a smooth cerebral cortex. During fetal development, the 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 larger, their brains need to wrinkle more while they are forming in the mother's womb.

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

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

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

The case of the brain without folds

Some time ago an image appeared on the Internet of a brain, supposedly human, that lacked wrinkles. This brain was a far cry from the traditional comparison of it being a nut. Rather than a nut, this particular brain was reminiscent of a fish, a drop fish specifically.

This brain was found by photographer Adam Voorheswho was conducting 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 of the Mental Hospital of the city of Austin, in the Texan state. These brains had been left in the darkness of oblivion for 20 years, in a closet of the animal laboratory of the university.

Attempts have been made to find out who was the person who housed in his skull such a curious and, at the same time, creepy brain. How did he behave? Was he able to speak? Did he have a properly human consciousness? 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 have, 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 rare disease are unusual facial appearance, swallowing problems, severe psychomotor retardation, hand and foot abnormalities, spasms and seizures. Treatment is symptomatic, only being able to improve, as far as humanly possible, the well-being of the affected person, although their life expectancy does not exceed 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. Cerebral Cortex.