The neocortex (also: neopallium or isocortex) is the largest part of the brain related to the higher cognitive processes such as language, speech, consciousness, thought, spatial reasoning, motor commands, as well as perception. This part of the brain is where attention and episodic memory are also processed.
In addition to the aforementioned, the neocortex contains all the major processing centers in the brain. It plays a big role in the regulation of vision, balance, touch, hearing, and movement.
Anatomy, Structure, and Function of the Neocortex
The neocortex is the outermost, cortical part of the human brain. It’s a highly organized structure responsible for processing, regulation, and control of cognitive and sensory information, as well as consciousness, emotions, and stimulations (arousal).
This brain structure is the largest part of the cerebral cortex. In essence, it’s a large sheet of gray matter folded in gyri (bumps) and sulci (furrows). The gyri and sulci create anatomical borders among the insula and the 4 brain lobes: the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. Each of the lobes is a center responsible for the processing of specific stimuli.
Based on the functionality of the different areas in the neocortex, we can make the following distinction:
- Primary areas of the neocortex – Parts of the neocortex responsible for the basic motor and sensory functions. They are the first to receive the sensory stimuli information, gained from the sensory organs of sight, hearing, and touch.
We distinguish the primary visual area (V1), primary somatosensory area (S1), primary auditory area (A1), primary body area, and primary inner ear/cochlea area.
- Secondary areas of the neocortex – Areas that integrate and process the signals from the sensory stimuli, received from the primary areas of the cerebral cortex. Conveniently enough, they are positioned around the primary sensory areas.
- Associative areas of the neocortex – These are the centers of the brain where different information gained from various types of stimuli are associated and integrated with the previously stored data, processed, and translated into emotions, actions, or reactions.
The structures that comprise the neocortex are organized both vertically and horizontally.
Horizontal Organization of the Neocortex’s Structures
The neurons of the neocortex are aligned with the brain’s surface, creating 6 cortical layers or laminas:
- Molecular (plexiform) layer (lamina molecularis) – (I) – It contains only a few horizontal Cajal-Retzius cells. These nerve cells support the development of the cerebral cortex.
- External granular layer (lamina granularis externa) – (II) – A layer that consists of stellate cells and small pyramidal cells. It’s a thin layer densely knitted with these two types of neuron cells.
Their dendrites are able to form association fibers that protrude the white matter in order to transmit the chemical or electrical signal to the dedicated centers of the central nervous system.
- External pyramidal layer (lamina pyramidalis externa) – (III) – This layer of the neocortex consists of medium-sized pyramidal cells. After the dendrites reach the molecular layer, the processes occurring at the cell base transfer via axons to the white matter and the cortex.
- Internal granular layer (lamina granularis interna) – (IV) – A layer that contains both stellate and pyramidal cells. This layer serves as the primary area where the peripheral stimuli are received.
While the axons of the stellate cells form synapses with the adjacent neuronal cells, the axons of the pyramidal cells spread either deeper in the cortex, or they pass through the cortex to link with the fibers of the white matter of the brain.
- Internal pyramidal layer – (lamina pyramidalis interna) – (V) – This layer consists of both medium-sized and large pyramidal cells. These cells send their dendrites from the motor cortex to the other neuronal cells in order to create synapses with different brain centers in the subcortical region.
- Multiform (fusiform) layer (lamina multiformis) – (VI) – Consisting of small fusiform nerve cells, as well as pyramidal cells and interneurons, this layer of the neocortex is the deepest one of all. It spreads directly over the white matter of the brain.
Evidently, these 6 layers of the neocortex are developed differently in different parts of the cerebral cortex. While the granular layers are more developed in the sensory areas, the pyramidal layers of the neocortex are more developed in the motor centers of the cerebral cortex.
Vertical Organization of the Structures of the Neocortex
The cortical layers can also be analyzed vertically, in structures labeled as columns of the neocortex. These functional units of the cerebral cortex are perpendicularly positioned to its surface and contain all 6 of the aforementioned layers.
A cortical column is the functional unit of the cerebral cortex composed of a vertical constellation of cortical neurons diffused in 6 different layers.
The cortical columns are cell-patterns in the brain that support complex processes, such as myelin distribution, connectivity, and the magnitude of gene expression.
Each of the cortical columns consists of two parts:
- Supragranular part – This part interacts with the other columns by both projecting and receiving cell fibers from their neurons. It is made from the most superficial layers of the neocortex, labeled from I to III.
- Infragranular part – This part receives signals from the supragranular parts of the cortical columns. It’s made of the layers labeled as V and VI.
(Apart from being a sort of anatomical border, layer IV has no particular function in relation to these two parts of the cortical columns.)
Activation of the Cortical Columns
The cortical columns can be activated in two ways, according to the level of activity – they can be partially activated or fully activated.
When a column is partially activated, it means that the neurons are in a state of anticipation, i.e. they are waiting or searching for information.
A plastic illustration for this activation would be the moment when we try to spot a particular object among many others. During the time we search for the object by looking around, our hands are still. But, the moment we spot the object, our hands receive an order to reach for it.
When a column is fully activated, the infragranular part of the cortical column sends information to the motor neurons which triggers their contraction. This further leads to action and motion.
What Happens If the Neocortex Becomes Damaged or Dysfunctional?
A head injury or a specific neurological disease can lead to severe damage to the neocortex and disturbance of the functions related to its centers that regulate specific processes.
Due to damage to any of the lobes, the affected individual may lose cognitive abilities such as speech, eyesight, and motor control.
Furthermore, semantic memory can also be affected. In the most severe case, a complete loss of memory can occur.
Some neurodegenerative diseases can interrupt the functioning of the neocortex. These include the following:
- Alzheimer’s disease
- Semantic amnesia
- Dementia
- Anterograde amnesia
- Broca’s and Wernicke’s aphasia
- Amnesia
To Sum Up
The neocortex is the largest part of the cerebral cortex of the brain which regulates and controls the higher cognitive processes and functions. It takes control of our cognitive activities, among which we could mention writing, speaking, and the ability to create and maintain social connections and interactions.
The neocortex functions as a bridge to the other parts of our brain by building junctions among the neural cells from different areas of the cerebral cortex.
A person could lose the ability to speak and to orient themselves in space, due to a head injury or damage to the neocortex, and can suffer the loss of motor control and memory.
Some of the neurological conditions and diseases can lead to paralysis, blindness, lack of motivation and attention, and forgetfulness, as well as render the affected individual unable to control their feelings.
Fun Facts
Did you know?
- The neocortex takes up to 76% of the capacity of the human brain.
- The neocortex is home to the largest number of brain cells.
- If you enjoy contemplating the meaning of life and other philosophical themes, then you’re actively getting help from the neocortex.
- From an evolutionary point of view, the suffix ‘neo’ in the neocortex (meaning: new) suggests that the neocortex is the most recently discovered and analyzed part of the human brain.
- The derogatory term ‘bird brain’ which implies that a person is stupid, turns out to be quite inaccurate. Namely, this term has been coined after the fact that birds lack a neocortex. However, some of them have proven to be incredibly intelligent, which makes the designated meaning of the phrase false.
- An adult neocortex supports the process of neurogenesis, i.e. even in adulthood, when the cognitive processes of the brain are supposed to show signs of fatigue, this part of the brain keeps regrowing new neurons.
- A cortical column comprises of about 100 cortical neurons.
- The ability of the cortical columns to choose a corresponding action upon the state they’re in and the nature of the signal they receive is called automatization. It’s a problem-solving process that occurs within the columns.
The columns set the goal, define the probable actions and the goals that need to be accomplished while striving for the primary goal, and finally reach the goal by accomplishing the previously stated elements of the functional pattern.
- All of the knowledge we accumulate during our life creates wrinkles in our neocortex. Thus, the more wrinkled our brain is, the smarter we are!
- The sense of smell is the only one of the group of 5 major senses whose information is not processed by the neocortex.