Corticogenesis is the process during which the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

of the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

is formed as part of the

development of the nervous system The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The fiel ...

of mammals including its development in humans. The cortex is the outer layer of the brain and is composed of up to six layers.

Neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

s formed in the

ventricular zone In vertebrates, the ventricular zone (VZ) is a transient embryonic layer of tissue containing neural stem cells, principally radial glial cells, of the central nervous system (CNS). The VZ is so named because it lines the ventricular system, whi ...

migrate to their final locations in one of the six layers of the cortex. The process occurs from embryonic day 10 to 17 in mice and between gestational weeks seven to 18 in humans. The cortex is the outermost layer of the brain and consists primarily of

gray matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distingui ...

, or neuronal cell bodies. Interior areas of the brain consist of

myelinated Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

axons An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

and appear as

white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributi ...

Cortical plates

Preplate

The preplate is the first stage in corticogenesis prior to the development of the cortical plate. The preplate is located between the

pia mater Pia mater ( or ),Entry "pia mater"
in
pioneer neuron A pioneer neuron is a cell that is a derivative of the preplate in the early stages of corticogenesis of the brain. Pioneer neurons settle in the marginal zone of the cortex and project to sub-cortical levels. In the rat, pioneer neurons are onl ...

s. These neurons are mainly thought to be Cajal-Retzius cells, a transient cell type that signals for

cell migration Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in particular dire ...

and organization.

Subplate

Corticogenesis_in_a_wild-type_mouse_with_captions_in_english_copy

The preplate also contains the predecessor to the subplate, which is sometimes referred to as a layer. As the cortical plate appears, the preplate separates into two components. The Cajal-Retzius cells go into the marginal zone, above the cortical plate, while the subplate moves inferior to the 6 cortical layers. Appropriate functioning and development of the subplate is highly dependent upon organization and connectivity. Disruptions during the transition from preplate to cortical plate can lead to significant malformation and disruption in function of the thalamus, inhibitory neuron activity, and maturation of cortical response. Injuries during the second trimester of human development have been associated with disorders such as

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, spasticity, stiff muscles, Paresis, weak muscles, and tremors. There may be p ...

and

epilepsy Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...

. The cortical plate is the final plate formed in corticogenesis. It includes cortical layers two through six. The subplate is located beneath the cortical plate. It is named for both its location relative to the cortical plate and for the time frame in which it is created. While the cortical plate matures, the cells located in the subplate establish connections with neurons that have not yet moved to their destination layer within the cortical plate. Pioneer cells are also present in the subplate and work to create neuronal

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses fr ...

s within the plate. In early development, synaptic connections and circuits continue to proliferate at an exponential rate.

Cortical zones

In humans the intermediate zone is located between the ventricular zone and the cortical plate. The intermediate zone contains

bipolar cells A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell ...

and

multipolar cells A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron ce ...

. The multipolar cells have a special type of

migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum l ...

known as

multipolar migration The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The fiel ...

, they do not resemble the cells migrating by locomotion or somal translocation. Instead these multipolar cells express neuronal markers and extend multiple thin processes in various directions independently of the radial glial fibers. This zone is only present during corticogenesis and eventually transforms into adult white matter. The ventricular and subventricular zones exist inferior to the intermediate zone and communicate with other zones through cell signalling. These zones additionally create neurons destined to migrate to other areas in the cortex.Antypa, M., Faux, C., Eichele, G., Parnavelas, J. G., & Andrews, W. D. (2011). Differential gene expression in migratory streams of cortical interneurons. European Journal of Neuroscience, 34(10), 1584-1594. doi: 10.1111/j.1460-9568.2011.07896.x The marginal zone, along with the cortical zone, make up the 6 layers that form the cortex. This zone is the predecessor for layer I of the cortex.

Astrocytes Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of endo ...

form an outer limiting membrane to interact with the pia. In humans it has been found that the cells here also form a subpial layer. Cajal-Retzius cells are also present in this zone and release

reelin Reelin, encoded by the ''RELN'' gene, is a large secreted extracellular matrix glycoprotein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this impor ...

along the radial axis, a key signaling molecule in neuronal migration during corticogenesis.Kwon, H. J., Ma, S., & Huang, Z. (2011). Radial

glia Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...

regulate Cajal-Retzius cell positioning in the early embryonic cerebral cortex. Developmental Biology, 351(1), 25-34. doi: 10.1016/j.ydbio.2010.12.026

Formation of layers

The cerebral cortex is divided into layers. Each layer is formed by

radial glial cell Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and ol ...

s located in the ventricular zone or subventricular zone, and then migrate to their final destination. Corteza cerebral

Layer I

Layer I, the molecular layer, is the first cortical layer produced during neurogenesis at mice at embryonal days 10.5 to 12.5 (E10.5 to E12.5). Of the six layers found within the neocortex, layer I is the most superficial and is composed of

Cajal–Retzius cell Cajal–Retzius cells (CR cells) (also known as Horizontal cells of Cajal) are a heterogeneous population of morphologically and molecularly distinct reelin-producing cell types in the marginal zone/layer I of the developmental cerebral cortex an ...

s and

pyramidal cell Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal co ...

s.Germain, N., Banda, E., & Grabel, L. (2010). Embryonic Stem Cell Neurogenesis and Neural Specification. Journal of Cellular Biochemistry, 111(3), 535-542. doi: 10.1002/jcb.22747 This layer is unique in the aspect that these cells migrate to the outer edge of the cortex opposed to the migration experienced by the other 5 layers. Layer I is also characterized by expression of

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...

T-box brain 1, and cortical migratory neuronal marker.Meyer, G. (2007). Genetic Control of Neuronal Migrations in Human Cortical Development(Advances in Anatomy, Embryology and Cell Biology). F. F. Beck, Melbourne, F. Clascá, Madrid, M. Frotscher, Freiburg, D. E. Haines, Jackson, H-W. Korf, Frankfurt, E.Marani, Enschede, R. Putz, München, Y. Sano, Kyoto, T. H. Schiebler, Würzburg & K. Zilles, Düsseldorf (Eds). New York, NY:Springer.

Layers II and III

The second and third layers, or the external granular layer and

external pyramidal layer The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting ...

respectively, are formed around mouse embryonal ages 13.5 to 16 days (E13.5 to E16). These layers are the last to form during corticogenesis and include

pyramidal neurons Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal co ...

, astrocytes, Stellates, and radial glial cells. In humans the pyramidal and stellate neurons express ''

SATB2 SATB is an initialism that describes the scoring of compositions for choirs, and also choirs (or consorts) of instruments. The initials are for the voice types: S for soprano, A for alto, T for tenor and B for