Neocortex (cerebrum): structure and functions.

The brain region responsible for reasoning and abstract thought.

Since life appeared on Earth, a great diversity of structures and beings have been appearing, evolving and dying. Among the different beings that have lived and still live on this planet, the animal kingdom, to which we belong, is one of those that has produced the greatest visibility, interest and debate in the collective imagination.

In most of this kingdom it is possible to find one of the organs that makes possible our survival and the control of our organism and behavior: the brain. In this organ, evolution has produced the appearance and development of several structures, many of them presenting a similar evolution in most chordate animals.

However, in some species a structure of great relevance to explain the capacity to organize, reflect or have self-awareness has developed to a great extent, being this structure especially developed in higher primates and in us, human beings. This structure is the neocortex or neocortex..

What is neocortex?

The neocortex, neocortex or isocortex is the structure that in humans makes up most of the cerebral cortex, specifically 90% of it.. It is the part of the brain with the most recent appearance at the phylogenetic level. It consists mainly of gray matter, i.e., somas (the "bodies" of neurons, where the cell nucleus is located) and dendrites of the neurons that are part of the encephalon.

Depending on the area, this structure is between two and four millimeters thick. Despite its small thickness, it is a very large structure that, due to its location within the skull, must be condensed and folded, which is why the human brain has convolutions and curvatures. In fact, although the neocortex occupies approximately the area of a pizza in its folded state, unfolded, it would occupy two square meters. The human brain is unique in the animal kingdom in its ability to distribute many neural somas in relatively little space.

Thus, the neocortex makes it possible to have a multitude of neurons distributed over several layers of the brain folded in on themselves, and this, in turn, has great advantages for our mental performance.

On the other hand, the neocortex is not a uniform structure, but is divided into the two cerebral hemispheres.. In addition, the neocortex shapes most of the different cerebral lobes, affecting the integration and consolidation of practically all the information that arrives through the senses.

Its functions, therefore, are multiple and varied, as we shall see below.

Main functions

Considering that it makes up 90% of the cerebral cortex, it is logical to think that this part of the brain is of great importance in the normal functioning of the human being. But what are the functions of this area that make it so important to us?

The neocortex or neocortex is considered to be the brain area responsible for our reasoning capacity, allowing logical thought and logical thinking.It is the area of the brain that enables logical thinking and consciousness. It is the area of the brain that enables all higher mental functions and executive functions (especially located in the frontal lobe). It is considered that the ego and self-consciousness are due to the functioning of this structure.

It is a set of neurons and glial cells whose function does not have to do with giving a stereotypical and predictable response to certain stimuli, but working on content already processed by other nerve cells to be able to "improvise" original responses in real time.

Reasoning, reflection, decision making?

Likewise, the neocortex serves as an area of association and integration of the different perceptions and their and awareness of these, helping to form a more accurate mental image of reality. It allows deep analysis of information, reflection and decision-making capacity.

It is the part of the brain that allows planning and anticipation of results, recreating possible scenarios and allowing on this basis the establishment of a strategy or behavior to follow.

Abilities such as calculation and language also depend on the neocortex, requiring the integration of different information and its transformation in different areas of this structure. and their transformation in different areas of this structure. Similarly, long-term memory also depends to a large extent on the neocortex, being the area where new information is "recorded" and from which it is taken to the working memory in order to be able to operate with it.

It also allows the development and optimization of the remaining parts of the brain, being able to control behavior, manage emotions and inhibit non-adaptive behavior patterns, as well as record and consolidate new ones.

At the social level, the neocortex also plays a fundamental role, since it makes possible the control and management of impulses, emotions and behaviors. This implies that it allows the existence of consideration for others, the negotiation of goals and, in general, the coexistence with other members of the same species.

Layered organization

In addition to its functional division into different cerebral lobes and two hemispheres, it is necessary to take into account that the neocortex does not have a homogeneous composition throughout its extension.

In fact, this part of the brain is divided this part of the brain is divided into six layers, which are differentiated mainly by the type and organization of the nerve cells found in them.

Layer I: Outer plexiform layer

Also called the molecular layer, this is the outermost and most superficial layer of the neocortex, being covered by the pia mater (one of the meninges). This first layer contains relatively few neurons. It is responsible for receiving fibers from various brain systems that send information of different types from various parts of the central nervous system.

Its composition is mainly based on horizontal cells of Cajal, dendrites of different types of neurons and interneurons and some axons of cells from other more internal layers and structures such as the thalamus. It is a layer that functions as an intracortical association layer, that is, it integrates different types of information creating larger and more significant units.

Layer II: Layer of small pyramidal cells or external granular cells.

This layer of the neocortex is mainly composed of pyramidal and stellate (star-shaped) cells whose (star-shaped) cells, whose dendrites are located in the outer plexiform layer and axons in lower layers. Like the previous one, it serves as a mechanism of association between the different parts of the cortex, although at another level.

Layer III: Outer pyramidal layer

Composed mainly of pyramidal cells of variable size, although generally larger than that of the external granular layer.The axons of these cells form fibers that are usually larger than those of the external granular layer. Their axons form projection and association fibers. It serves as an intracortical association area. Also, some of its neurons project contralaterally (to the other cerebral hemisphere), so that a bridge is established between these two halves of the upper part of the central nervous system.

Layer IV: Internal granular layer

This layer is mainly composed of star-shaped cells. This layer does not exist in some areas, such as the motor cortex. It receives information from the thalamus, which is distributed through this layer in what are known as thalamocortical striae. Its fibers project to the basal ganglia, spinal cord and brainstem.

Layer V: Inner pyramidal or ganglionic layer

The fifth layer of the neocortex is made up of large pyramidal cells, together with stellate cells.The fifth layer of the neocortex is made up of large pyramidal cells, together with other stellate cells, which send information to other areas of the brain. Within this layer can be observed Baillarger's band, a grouping of nerve fibers located horizontally and can be distinguished from the adjacent areas that make up the neocortex.

Layer VI: Polyform layer

Formed by cells of irregular and polymorphous shapes, this layer of the neocortex performs efferent functions, sending connections to the white matter and many of its neurons and many of its neurons travel through the corpus callosum. That is, it sends information to relatively distant areas, more than it receives directly from them.

Bibliographical references:

• Hall, J. (2011). Guyton and Hall textbook of medical physiology. Philadelphia: Saunders/Elsevier.
• Jerison, H.J. (1991). Fossil brains and the evolution of neocortex. In Finlay, B.L.; Innocenti, G. & Scheich, H. (eds.). The neocortex. Ontogeny and phylogeny. New York: Ed. Plenum Press; p. 5-19.
• Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principios de neurociencia. Madrid: McGraw Hill.
• Lewis, W.B. (1978). On the comparative structure of the cortex cerebri. Brain; 1: 79-86.
• Morgan, A.J. (2001). El cerebro en evolución. Editorial Ariel neurociencia.