When we talk about the brain, one of the most typical comparisons is one reminiscent of the shape of a walnut, because it has a wrinkled shape.
These wrinkles so characteristic of the organ are due to the fact that the surface of the latter is folded back on itself, which allows it to adapt better. But otherwise, What are the folds of the brain used for? Do they have something to do with intelligence? Let’s see below.
What are the folds of the cerebral cortex used for?
The main reason the human brain is crumpled is because bending over itself saves space. The cerebral folds are what are more aptly called convolutions, while the furrows or fissures are the depressions between these wrinkles.. The human brain is so crumpled that if we could lay it out on a table, we would have about 2,500 square inches, 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 popular belief, the brain is similar in consistency to gelatin.
Being such a soft organ, it makes it an extremely vulnerable part of the body when pressure is put on it. by to avoid, during brain growth during pregnancy, the shock of the cerebral cortex against the walls of the skull, This one folds in on itself, gaining space.
This space saving strategy is not something unique to the human species. It can also be seen in other species of mammals, such as dolphins, elephants, and whales. It is for this reason that scientists have defined the concept of gyrification, which refers to how the cerebral cortex is folded in on itself in a given species.
Traditionally, gyrification has been viewed as the result of a high degree of neurogenesis and dendritic growth. In our species, as can be deduced by looking at a photograph of the brain, we exhibited a fairly high index of gyration and, for this reason, it was associated with having more folds with higher cognitive abilities, as is the case produced in humans.
However, and after analyzing other mammalian brains, something certainly paradoxical was observed. Although humans are the most intelligent animal species, there are other animals that have brains with more turns. The most notable cases are the brains of elephants, the brains of whales and the brains of dolphins.
Other functions of convolutions and grooves
As we have seen, these folds, called convolutions and cerebral furrows, have the main function of leaving more space and preventing the cerebral cortex from pressing towards the cranial walls. this it causes the accumulation of more neurons in the cortex and, for this reason, it was believed that more folding was synonymous with greater ability to process information.
In turn, these folds are used by neuroanatomists as a criterion for dividing the brain into regions, functioning as boundaries 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: the frontal lobe, the temporal lobe, the parietal lobe and the occipital lobe.
Although the idea of the brain wrinkling more to allow more neurons to be packed makes sense and is physically possible, which, in turn, would make sense of the theory that the more wrinkles there are. , the more cognitive skills she was also tried to give. another explanation for this. We saw that when the animal is larger it is more likely to have a brain with many folds. The bigger the brain is during pregnancy, the more it needs to wrinkle.
This would explain why there are very small animals, such as rats and mice, that have a smooth cerebral cortex. reDuring the development of your fetus, your brain is not developing enough to need to bend over and save space. On the other hand, it would also solve the question of why elephants and whales have more wrinkled brains than ours. As they get older, their brains need to wrinkle more as they form in the mother’s womb.
However, and while this explanation is quite convincing, there are cases of animals whose brains are smoother than they would have been given their size, such as manatees. It is for this reason that another explanation has been proposed, halfway between the traditional that more roughness equals greater cognitive ability and the theory of the relationship with brain size. The key would be in the physical properties of certain parts of the crust.
Some areas of the brain are thinner than others, which would make them bend more easily. Depending on how they bent depending on the areas, not only could their physical properties be elucidated, but they could also be related to the specific function they could perform.
It has also been suggested that, depending on the type of behavior of the animal species, its brain will exhibit a greater or lesser amount of wrinkles. We saw that some mammals with few wrinkled brains tend to form and live in small social groups, While animals with more folds would have more extensive social media behaviors, which humans, whales and dolphins share.
The case of the foldless brain
Some time ago the image of a so-called human brain without wrinkles appeared on the Internet. This brain was far removed from the traditional comparison that it was a new brain. More than a nut, this particular brain was reminiscent of a fish, a drop fish in particular.
This brain was discovered by photographer Adam Voorhes, Who was doing a photoshoot on the brain sample shelves 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 Austin City Psychiatric Hospital in Texas. These brains had been left in the dark of oblivion for 20 years, in the closet of a university animal laboratory.
Attempts were made to find out who was the person who housed such a curious and at the same time frightening brain in his skull. How did he behave? Could he speak? Did he have a properly human conscience? The only thing that we can know from his brain is that the subject was suffering from a severe case of lysencephaly, that is to say from a brain with fewer convolutions than he does. should, even if the absence of wrinkles was complete.
Typically, cases of lysencephaly are due to errors in neuronal migration during fetal development.. It is thought that it could be caused by the action of certain pathogens, especially viruses, which are thought to occur during the first trimester of pregnancy. It has also been speculated that it could be caused by a lack of blood supply during fetal formation, although the idea that it is a rare genetic condition has some force.
Symptoms of people with this strange disease include an unusual facial appearance, swallowing problems, severe psychomotor retardation, abnormalities of the hands and feet, spasms and seizures. The treatment is symptomatic, it can only improve, as far as humanly possible, the well-being of the affected person, even if their life expectancy does not exceed two years.
- 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 cortical gyration mechanism. Cerebral cortex.