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 live on this planet, the animal kingdom, to which we belong, is one of the most visible, interesting and debatable in the collective imagination.
In most of this realm it is possible to find one of the organs that makes our survival and the control of our organism and behavior possible: the brain. In this organ evolution has produced the appearance and development of diverse structures, many of them presenting a similar evolution in the majority of the animals that have been harnessed.
However, in some species a structure of great relevance has been developed to explain the capacity to organize, reflect or have self-awareness, being this structure especially developed in the higher primates and in us, the human beings. This structure is the neocortex .
What is neocortex?
The neocortex, neocortex or isocortex is the structure that in humans forms most of the cerebral cortex, specifically 90% of it . It is the most recent phylogenetic part of the brain. It is mainly made up of grey matter, i.e. somas (the “bodies” of the neurons, where the cell nucleus is located) and dendrites of the neurons that form part of the brain.
Depending on the area, this structure is between two and four millimetres thick. In spite of its little thickness, it is a structure of great extension that due to its situation inside the skull has to be condensed and folded, reason why the human brain has circumvolutions 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 a unique case in the animal kingdom in terms of its ability to distribute many neural somas in relatively little space.
Thus, the neocortex makes it possible for there to be a multitude of neurons distributed along several layers of the brain folded back on themselves, and this, in turn, has great advantages for our mental performance.
On the other hand, e he neocortex is not a uniform structure, but is divided into the two cerebral hemispheres . In addition, the neocortex forms most of the different brain lobes, affecting the integration and consolidation of practically all the information that arrives through the senses.
Its functions, therefore, are many and varied, as we will see below.
Bearing in mind that it makes up 90% of the cerebral cortex, it is logical to think that this part of the brain has great importance in the normal functioning of the human being. But what functions does this area have that make it so important to us?
The neocortex or neocortex is considered the brain area responsible for our reasoning capacity , allowing logical thinking and consciousness. It is the area of the brain that allows all the higher mental functions and executive functions (especially located in the frontal lobe). The ego and self-awareness are considered to be due to the functioning of this structure.
It is a set of neurons and glial cells whose function is not to give a stereotypical and predictable response to certain stimuli, but work on contents already processed by other nerve cells 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 the awareness of these, contributing to form a more precise mental image of reality. It allows for the in-depth analysis of information, reflection and decision-making capacity.
This 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.
Skills 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. Similarly, long-term memory also depends to a great extent on the neocortex, being the zone where new information is “recorded” and from which it is taken to the working memory in order 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 a social level, the neocortex also plays a fundamental role, since it makes it possible to control and manage impulses, emotions and behaviour. This implies that it allows the existence of consideration towards others, the negotiation of goals and, in general, the coexistence with other members of our same species.
In addition to its functional division into different brain lobes and two hemispheres, it is necessary to take into account that the neocortex does not have a homogeneous composition throughout its length.
In fact, this part of the brain is divided into six distinct layers mainly because of the type and organization of the nerve cells found in them.
Layer I: External Plexiform Layer
Also called 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 in charge of 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 Cajal cells, 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 association layer at an intracortical level, that is, it integrates different types of information creating larger and more significant units
Layer II: Small pyramidal or external granular cell layer
This layer of the neocortex is mainly composed of pyramidal and star-shaped cells , whose dendrites are located in the external plexiform layer and the axons in lower layers. Like the previous one, it serves as an association mechanism between the different parts of the crust, although on another level.
Layer III: Outer pyramidal layer
Composed mainly of pyramidal cells of variable size , although generally superior to that of the external granular layer. The axons of these cells form fibers of projection and association. It serves as an area of intracortical association. Likewise, some of its neurons project contralaterally (to the other brain hemisphere), so that a bridge is established between these two halves of the upper central nervous system.
Layer IV: Granular inner layer
This layer is mainly composed of star-shaped cells. This layer does not exist in some areas, such as in the motor cortex. It receives information from the thalamus, which is distributed by this layer in what are known as thalamocortical striae. Its fibers project to the basal ganglia, spinal cord, and brain stem.
Layer V: Internal pyramidal or ganglionic layer
The fifth layer of the neocortex is made up of large pyramidal cells , along with other star cells, which send information to other areas of the brain. Within this layer we can observe the Baillarger band, a grouping of nerve fibers located horizontally and which can be distinguished from the adjacent areas that make up the neocortex.
Layer VI: Polyformal layer
Formed by irregularly shaped, polymorphous cells, this layer of the neocortex performs efferent functions, sending connections to the white substance and traveling many of its neurons through the corpus callosum. In other words, it sends information to relatively distant areas, more than it receives directly from them.
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