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The secret structure of the brain: Do you know what the six layers of the cerebral cortex are?
The cerebral cortex is the core of mammalian cognitive functions, and the most complex structure is the neocortex, which is the six-layered cortex. The term comes from the Latin "cortex", which means "bark" or "outer bark", and "neo" which is the Greek word for "new". The neocortex occupies about 90% of the brain, and its functions cover perception, cognition, motor command generation, and even higher-level brain functions such as language and spatial reasoning.
The neocortex is the most recently evolved part of the brain. It has a six-layer structure, showing complex neural connections and diverse neuron types.
The structure of these six layers varies significantly between species. In rodents, the neocortex is usually smooth, whereas in elephants, dolphins, and other large mammals it displays deeply concave grooves (crypts) and ridges (gyri), folds that make its surface area substantial increase. The first to sixth layers of the human brain each perform different functions and work together through the connections of neurons.
Structure of the neocortex
The neocortex contains stimulatory and inhibitory neurons, with a ratio of approximately 80% and 20%. Each layer has its own specific combination of cells and neural connections. Although their structure is relatively stable, there is variability in function. For example, in the primary motor cortex, layer IV is smaller or even missing.
Layer IV is the primary recipient of most incoming sensory information and distributes this information to other layers for further processing.
It is worth mentioning that the neurons between these six layers are arranged into a vertical structure called "cortical columns". These columnar structures are considered to be the basic functional units of the neocortex, although the definition of cortical columns and There is no unified consensus on functionality.
Function and regional division of cerebral cortex
As the neocortex evolved, it was divided into different regions, which were divided by the boundaries between cranial sutures and brain bones, including the frontal, parietal, occipital, and temporal lobes, each with different functions. For example, the occipital lobe contains the primary visual cortex, while the temporal lobe contains the primary auditory cortex.
At a higher level, the areas within the frontal lobe are also responsible for humans' unique advanced language processing and other abilities.
In addition, the neocortex also plays an important role in the memory and learning process. The storage of semantic memory is mainly concentrated in the anterolateral temporal lobe. During sleep, the activity frequency of neocortical neurons will also affect the quality of slow-wave sleep, causing neurons to be inhibited or excited in specific states, causing specific brain wave fluctuations.
Clinical significance
In neurodegenerative diseases such as Alzheimer's disease, damage to the neocortex can disrupt the transmission of sensory information, causing cognitive decline and personality changes, further leading to the development of dementia. If the anterolateral temporal lobe of the neocortex is damaged, people may experience semantic amnesia, a loss of memory manifested by forgetting factual information.
Damage to neurons affects the conversion of perception and memory, making people unable to effectively process information from the environment.
In this context, researchers' exploration of the neocortex not only focuses on understanding its structure and function, but also involves its changes in various pathological conditions, hoping to find potential treatments.
The evolution of neocortex and differences between species
As the brain evolved, the expansion of the neocortex was closely related to the development of the social structure of the species. According to theory, the population size of a species is directly proportional to the neocortex ratio, which explains why humans have a larger neocortex ratio. The evolution of the neocortex not only facilitates the autonomous inhibition of social behavior but also enhances the peace and harmony of group cooperation.
The definition of the neocortex is controversial among different species, but regardless, it is a structure unique to mammals.
Although some structures with cognitive processing capabilities have also been found in other species such as birds, the lack of six-layer structures still requires further discussion on cross-species naming and classification.
As we study the neocortex more and more deeply, there are still many unsolved mysteries waiting for scientists to explore. This also reminds us how far we still have to go to understand this instrument of conscience. Want to leave?
