Neocortex

The human brain is a complex structure. It contains a huge number of neurons and each of the neurons has 10,000 connections (synapses) with other neurons. The vast number of neurons and neuronal connections could store every experience in life including those all five senses.

The majority of the cells in the brain are found in the cerebellum and neocortex. Cerebellum makes use of a lot of cells for coordinated movement while the neocortex uses cells for high precision in planning complex behavior and sensory discrimination.

The neocortex is a part of the cerebral cortex and a cortical part of the limbic system. It consists of grey matter that surrounds the deeper white matter of the cerebrum. Neocortex accounts for about 76% of the total brain volume.

The neocortex is a Latin for “new rind” or “new bark.”The neocortex is a complex structure – dozens of cells, intricate connectivity patterns, and multiple layers.

The neocortex is the hallmark of mammalian brains and the most divergent part of mammalian species. It is called neo because it is the cerebral cortex’s newest part. If the neocortex is hurt, the cognitive ability of the person will be greatly affected. The neocortex has different subunits and each performs a distinct function. The substructure of the neocortex is called area and each area has a designated function.

Although the brain has different vital parts, the neocortex is said to be the most massive part. The cerebellum can be packed with many neurons but when it comes to the overall mass, the neocortex is the heaviest.

Neocortex controls a person’s language and consciousness. The size of the neocortex in human is larger than other animals, which makes the human capable of unique mental abilities. (1)

What are the Functions of Neocortex?

  • Sensory perception
  • Spatial reasoning
  • Conscious thought
  • Generating motor commands.
  • Neuronal computations of attention
  • Episodic memory.
  • Complex language processing
  • Social and emotional processing
  • Sleep, memory, and learning processes
  • Semantic memories
  • Instrumental conditioning
  • Transmit sensory information (2)

The functions of neocortex primarily depend on its structure. Neocortical organizations are derived from four major principles. They are the following:

  • The cortex is vertically arranged into six layers and each layer receives and sends connections to different brain sites.
  • The cortex has horizontal organizations into columns and exhibits the same physiological properties.
  • The majority of the cortical areas have one of more topographic maps.
  • Cortical areas are functionally separated and the cells in every area perform a specific function. (2)

The Anatomical Structure of the Neocortex

The neocortex has unmyelinated fibers and a grey matter called neuronal cell bodies surrounding the deeper white matter (myelinated axons) in the cerebrum. The cortex has two types: proisocortex and true isocortex. The former is the transitional part between the periallocortex and true isocortex and located in the cingulate cortex – one of the vital parts of the limbic system.

Rodents and small mammals have a smooth neocortex. Large mammals and primates have deep grooves enabling the surface area to increase significantly.

The neocortex is equipped with excitatory and inhibitory neurons and is uniform in structure. It has six horizontal layers separated by cell type and neuronal connections. Although they are uniform, there are a few exceptions. The fourth layer is a bit small and does not have a primary motor cortex.

The pyramidal neurons in layers II and III protect their axons to some parts of the neocortex. On the other hand, the pyramidal neurons of layers V and VI have most of the synaptic connections form the cortex’s outer part. (3)

Neocortex and Cortical columns

The neocortex is arranged in cortical columns (vertical structures). The patches of neocortex have a diameter of around 0.5 mm. the cortical columns are neocortex’s functional units. The neocortex is derived from the dorsal telencephalon in the rostral area of the forebrain.

It is subdivided into regions and demarcated by cranial sutures above the skull. Each cranial suture (frontal, parietal, occipital, and temporal) has a corresponding function.

Quick facts about the neocortex

  • Neocortex takes up most of the space in the brain. It accounts for 76% of the gray matter in the brain.
  • Birds and reptiles don’t have a neocortex.
  • The neocortex can be the seat of consciousness. It controls language and consciousness. The neocortex is also involved in higher functions like motor commands, sensory perception, conscious thought, and spatial reasoning.
  • It builds connections between the different parts of the brain.
  • An injury to the neocortex may lead to problems with communication. Various instances could lead to injury to the neocortex such as head trauma, accident, or surgery. Depending on the severity of the injury, the person could lose the ability to recognize space, speech, motor control, eyesight, and the ability to recognize social cues.
  • The neocortex is the newest addition to the brain and the crowning achievement of the beginning and biological substrate of the person’s mental prowess.
  • The neocortex is only found in mammals and is somewhat related to the forebrain structures of other vertebrate classes.
  • Neocortex evolved as part of the adaptations related to temperature homeostasis.
  • Neocortex stores information about the structure of the environment, which makes mammal capable of finding food and other resources needed to survive. (4)

Neocortex and memory

As a person grows older, new skills and being acquired. The neocortex will have semantic memories – things that people often forget with age. Semantic memories are the main functions of the temporal lobe of the brain.

Neocortex plays a major role in operant conditioning as it has the brain’s primary visual and auditory cortex. The visual and auditory cortex are the reasons why you immediately feel hungry every time you smell a freshly-baked bread.

Neocortex remains active even in the slow-wave sleep period. If you are going to take an exam the next morning, it is a must to attain the period of slow-wave sleep. Why? Because it is critical in memory consolidation or referred to as “sleep-dependent memory processing.” While you are asleep, the neurons move between rest and depolarizing phase (upstate). You get a good night’s sleep because of the functions of the neocortex.

About 80% of the neurons in neocortex are excitatory and 20% are inhibitory. The neocortex has a vital role in the person’s semantic memory. A semantic memory acts like a database wherein neurons move information from the different layers of the neocortex. It also plays an essential role in episodic memory – recalling important events in your life as well as spatial recognition, and auditory information, to name a few.

Various studies were made to establish the effect of the neocortex in memory retention. The latest one showed that the temporal lobe serves as a convergence zone where memories can develop. The temporal lobe is the region of the brain that is vulnerable to conditions like Alzheimer’s disease, semantic dementia, and other types of memory loss. Any problems in the neurons of the brain including the neocortex may make you susceptible to schizophrenia and other types of neuropsychiatric disorders. (5)

References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2913577/
  2. https://www.jneurosci.org/content/37/45/10877
  3. https://dev.biologists.org/content/141/1/11
  4. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0058596
  5. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0012853