Cerebral fissures: what are they, characteristics and types?

A summary of the main brain fissures and their characteristics.

Throughout evolution, the brain has become more complex by optimizing the way it organizes its structure, using such a valuable resource as the cystic folds or fissures, small indentations and grooves with which it extends its surface by folding inward.

This mechanism has allowed our species to improve certain higher cognitive functions.

In this article we explain what are the cerebral fissures and what are their main functions and characteristics. We will also describe the most relevant cysplasias, including the convolutions and sulci, of our brain.

What are the cysplasias of the brain?

The human brain is an extremely complex organ formed by millions of nerve cells, as well as glial cells and Blood vessels. It is a fundamental part of the central nervous system, responsible for centralizing and processing information from our organism and the environment to generate the best possible responses, depending on the demands of each situation.

The brain can be divided into hemispheres: the right hemisphere and the left hemisphere; and in turn, into lobes: the frontal lobe, which is responsible for language and executive functions; the temporal lobe, responsible for hearing or speech; the parietal lobe, responsible for sensory-perceptual functions; the occipital lobe, whose main function is visual processing; and the insula or insular cortex, which separates the temporal and inferior parietal lobes and plays a key role in emotional processing and subjective experience.

In neuroanatomy, when describing the various brain structures, account is taken of the fissures, which cover the surface of the brain's cortex and give it that peculiar rough characteristic.. These "wrinkles" are essential for this organ to function properly; their absence can lead to serious disorders, such as lissencephaly (or "smooth brain"), which can cause motor problems, seizures and other disorders.

The fissures of the brain can be divided into convolutions and sulci that are found over the entire surface of the cortex.The brain's complexity has increased over the years, with the consequent increase and improvement of certain cognitive functions in the human species, such as language or intelligence, as the brain has retracted inward, so that, evolutionarily speaking, the more the brain has retracted inward, the more complexity it has gained over the years.

Characteristics and functions.

The cystic folds of the brain, whether they are convolutions or grooves of greater or lesser depth, fulfill important functions; on the one hand, as we commented in the introduction, these folds increase the surface area of the cerebral cortex and the neuronal density (without having to increase the size (without having to increase the size of the head), with the consequent improvement of higher cognitive functions in the medium and long term.

At an evolutionary level, this is a great qualitative leap, since otherwise, increasing the size of the head and skull would only have been a problem for the birth of females.

According to most scientific studies, this folding most often occurs in species with larger brains, such as ours, although there seem to be exceptions (as in the case of manatees, with fewer folds than expected for a brain of their size).

However, the formation of the fissures depends on other factors beyond the growth and expansion of the surface area of the brain cortex, such as the physical properties of some parts of the cerebral cortex; for example, thinner regions of the brain tend to fold more easily and the brain folds in specific and consistent patterns..

On the other hand, although the brain is an interconnected organ, the different fissures are used to separate and delimit areas and structures with different functions, acting as boundaries that help in the division of tasks.

The main sulci of the brain

There are a multitude of sulci or clefts in the brain. Below, we will discuss the most well-known and relevant ones.

1. The interhemispheric sulcus

The interhemispheric sulcus or fissure, also known as the longitudinal fissure, is a fissure located in the cortex that divides the brain into two hemispheres, joined together by a set of nerve fibers called the corpus callosum. This fissure contains a fold of the dura mater (the outer meninx that protects the central nervous system) and the anterior cerebral artery..

2. The lateral sulcus

The lateral sulcus or Sylvian fissure is one of the most visible in the brain, since it runs transversely across practically the entire surface of its cortex. It is located in the lower part of the hemispheres of the brain, delimiting the boundary between the lobe and the lobe of the brain.It is located in the inferior part of the hemispheres of the brain, delimiting the border between the temporal lobe and the parietal lobe. It is also one of the deepest clefts, and below it lies another important structure of the brain: the insula.

3. The central sulcus

The central sulcus or Rolando's fissure is a fissure located in the upper part of the brain and separates the frontal lobe from the temporal lobe, bordering on one side with the motor cortex and on the other side with the primary somatosensory cortex. This fissure would act as a bridge between motor and sensory information, integrating both.

4. The parieto-occipital sulcus

The parieto-occipital sulcus or external perpendicular fissure is a fissure that originates in the interhemispheric fissure.The parietal lobe is present on the inner aspect of each cerebral hemisphere. As its name indicates, it separates the parietal lobe from the occipital lobe.

The lateral part of the sulcus is located in front of the occipital pole of the brain and the medial part runs downward and forward. It joins the calcarine fissure below and behind the posterior end of the corpus callosum.

5. The calcarine sulcus

The calcarine sulcus or calcarine fissure is a cleft located in the occipital area of the inner or medial aspect of the cerebral hemispheres, separating the visual cortex into two parts. It follows a horizontal trajectory until it joins the parietooccipital sulcus..

6. The callosal sulcus

The sulcus callosum is located on the medial brain surface and separates the corpus callosum from the cingulum, which has important functions within the limbic system. Although the cingulum is usually delimited as a separate structure, it is part of the frontal and parietal lobes.

The main convolutions of the brain

As with the sulci we have seen above, there are also a multitude of cysplasias in the brain in the form of convolutions or gyri, characterized by being folds with less depth than the sulci, and located inside the and located inside the different cerebral lobes. The following are some of the most important ones.

1. Circumvolution or fusiform gyrus

The fusiform gyrus is located on the basal surface of the cerebral hemisphere, specifically in the temporal lobe, between the inferior temporal gyrus (outside) and the hippocampal gyrus (inside).

This fissure is part of the limbic system, responsible for affective processing.It is responsible for affective processing and plays an important role in facial recognition; damage to this area of the brain can cause prosopagnosia, also called face blindness.

2. Circumduction or cingulate gyrus

The cingulate gyrus is an arc-shaped fissure or fold in the brain, located above the corpus callosum. Its main function is to act as a link or bridge between the limbic system and the higher cognitive functions located in the neocortex.It therefore plays a fundamental role in connecting volitional, motor, mnestic, cognitive and affective aspects.

3. Circumvolution or angular gyrus

The gyrus is a fissure located in the parietal lobe, more specifically between the intraparietal sulcus and the horizontal branch of the Sylvian fissure.

The functions of the angular gyrus include the processing and interpretation of language, visual and auditory information.. It has connections with Wernicke's area, responsible for the auditory decoding of linguistic information.

4. Hippocampal gyrus or hippocampal gyrus

This gyrus is located in the inner part of the temporal lobe, surrounding the hippocampus, a fundamental structure in the formation of new memories and spatial localization.

Bibliographical references:

• Allen, J. S., Bruss, J., & Damasio, H. (2005). Structure of the human brain. Research and Science, 340, 68-75.
• Clark, D.L.; Boutros, N.N.; & Mendez, M.F.. (2012). The brain and behavior: neuroanatomy for psychologists. 2nd ed. El Manual Moderno. Mexico
• Snell, R.S. (1999). Neuroanatomía Clínica. Buenos Aires: Editorial Médica Panamericana, S.A:267