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The neocortex is the most recent part of the mammalian brain to evolve. It is located in the outer cerebral hemisphere and is comprised of six separate layers which enable specific skills. The six-layered neocortex is a unique feature in mammals since it is found in all mammalian brains but not other animal brains.
There is neocortical involvement in specific skills such as sensory perception, spatial reasoning, motor commands, conscious language, and thought processes. The frontal, occipital, temporal and parietal lobes which exist within the neocortical area enable this. For instance, emotional and social skill processing occurs in the orbitofrontal cortex, which is in the frontal lobe. Visual functioning in the primary visual cortex is within the occipital lobe. Auditory functioning in the primary auditory cortex is located within the temporal lobe while the frontal lobe contains areas relevant to language processing.
Inside the neocortex, there are two main types of neurons. There is the excitatory pyramidal neuron and the inhibitory interneuron. Pyramidal neurons, distinguished by their triangular-shaped cell body and the presence of single axons, are part of a process which results in motor functioning, cognitive processing, and visual processing ability. The inhibitory interneurons in the brain regulate myriad functions within the neocortical area, such as perception.
Neurons within the neocortex are arranged vertically within neocortical columns. In the human brain, the neocortex has 500,000 of these particular columns and each column is in turn comprised of 60,000 neurons. The neocortical columns have a diameter of approximately one-half millimeter and a depth of approximately 2 millimeters. In functioning, each of the columns usually responds to sensory stimulus which represents some specific part of the body or which represents vision or sound in some way.
Also within the neocortex, there is unmyelinated fiber and gray matter which surrounds the deeper myelinated axons located inside the cerebrum. In addition, the neocortical area in the brain has an appearance which differs depending on the type of mammal. For instance, in rodents, the neocortex appears to be smooth, but in larger mammals such as primates, it is comprised of deep grooves and has a wrinkled appearance. The deep grooves increase the surface area available within the neocortex, and this accounts for 76 percent of brain volume in humans. This has enabled primates such as humans to have very highly developed speech, memory, and language skills.