Cortex: The Brain’s Outer Layer
The cortex is the outermost layer of the brain that covers the cerebrum, the largest part of the brain. The cortex is responsible for many complex functions, such as thinking, learning, memory, language, emotion and consciousness. The cortex is also known as the gray matter because it lacks the fatty covering called myelin that gives the white matter its color.
The cortex has a wrinkled appearance due to its many folds and grooves. These folds increase the surface area of the cortex, allowing more nerve cells to fit in a smaller space. The cortex is divided into four lobes: frontal, parietal, temporal and occipital. Each lobe processes different types of information from the senses and controls different aspects of behavior.
The frontal lobe is located at the front of the brain and is involved in planning, decision-making, problem-solving, personality and voluntary movement. The parietal lobe is located at the top of the brain and is involved in spatial awareness, touch, pain and body sensations. The temporal lobe is located at the sides of the brain and is involved in hearing, language, memory and emotion. The occipital lobe is located at the back of the brain and is involved in vision.
The cortex is composed of six layers of nerve cells that communicate with each other and with other parts of the brain. The cortex also contains specialized regions that perform specific functions, such as the motor cortex that controls movement, the sensory cortex that receives sensory input and the association cortex that integrates information from different sources.
The cortex is considered to be the most evolved part of the brain and is unique to mammals. Most of the cortex is called the neocortex, which means new cortex, because it developed relatively recently in vertebrate evolution. The neocortex accounts for 90% of the human cortex and is responsible for higher cognitive abilities.
The cortex is essential for human intelligence, creativity and personality. It allows us to perceive the world, communicate with others, learn from experience and express ourselves. The cortex also enables us to be aware of ourselves and our surroundings.
Cortex Development: How the Brain’s Outer Layer is Formed
The development of the cortex, also known as corticogenesis, is a complex and dynamic process that occurs during embryonic and fetal stages of mammalian development. The cortex is formed by the migration and differentiation of neural progenitors that originate from the ventricular zone, a layer of cells lining the fluid-filled cavities of the brain. The cortex consists of up to six layers of neurons that have different functions and connections. The cortex is also regionally organized into specialized areas that are responsible for different aspects of cognition, perception and behavior.
The development of the cortex involves several steps and mechanisms that are regulated by both intrinsic and extrinsic factors. The intrinsic factors include the genetic and epigenetic programs that determine the identity and fate of neural progenitors and their progeny. The extrinsic factors include the environmental cues that influence the proliferation, migration, differentiation and survival of neural cells. These cues can come from various sources, such as neighboring cells, growth factors, neurotransmitters, hormones and pathogens.
The first step in corticogenesis is the formation of the preplate, a thin layer of cells that covers the surface of the brain. The preplate contains pioneer neurons that guide the migration of later-born neurons. The preplate also splits into two layers: the marginal zone, which will become layer I of the cortex, and the subplate, which will serve as a temporary scaffold for thalamic inputs and cortical outputs.
The second step in corticogenesis is the formation of the cortical plate, which will become layers II to VI of the cortex. The cortical plate is formed by successive waves of neurons that migrate from the ventricular zone to their final positions in an inside-out manner. This means that the earliest-born neurons occupy the deepest layer (layer VI), while the latest-born neurons occupy the most superficial layer (layer II). The migration of neurons is mediated by various modes and molecules, such as radial glia, intermediate progenitors, multipolar cells and Reelin.
The third step in corticogenesis is the maturation and integration of cortical neurons. This involves the establishment of synaptic connections between cortical neurons and between cortical and subcortical regions. The synaptic connections are refined by activity-dependent processes, such as synaptic pruning and plasticity. The maturation and integration of cortical neurons also depend on the expression of specific genes and proteins that regulate neuronal morphology, function and survival.
The development of the cortex is a remarkable example of how genetic and environmental factors interact to shape the structure and function of the brain. The cortex is also highly vulnerable to various insults and disorders that can affect its normal development and lead to neurological and psychiatric conditions. Understanding how the cortex develops can provide insights into how the brain works and how it can be repaired.