The Radial Unit Hypothesis (RUH) is a conceptual theory of

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. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

development, first described by

Pasko Rakic Pasko Rakic (; ; born May 15, 1933) is a Yugoslav-born American neuroscientist, who currently works in the Yale School of Medicine Department of Neuroscience in New Haven, Connecticut. His main research interest is in the development and evolut ...

. It states that the

develops during

embryogenesis An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male ...

as an array of interacting

cortical column A cortical column is a group of neurons forming a cylindrical structure through the cerebral cortex of the brain perpendicular to the cortical surface. The structure was first identified by Vernon Benjamin Mountcastle in 1957. He later identified c ...

s, or 'radial units', each of which originates from a transient stem cell layer called the ventricular zone, which contains neural stem cells known as

radial glial cell Radial glial cells, or radial glial progenitor cells (RGPs), are Bipolar neuron, 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 as ...

Cortical evolution

The reiterative nature of the cerebral cortex, in the sense that it is a vast array of repeating functional circuits, led to the idea that cortical evolution is governed by mechanisms regulating the addition of cortical columns, enabling additional functional areas to become specialized and incorporated into the brain. The addition of new radial units is thought to depend on control of the cell cycle (proliferation) of cortical stem cells lining the

ventricular system In neuroanatomy, the ventricular system is a set of four interconnected cavities known as cerebral ventricles in the brain. Within each ventricle is a region of choroid plexus which produces the circulating cerebrospinal fluid (CSF). The ventric ...

in the ventricular zone and

subventricular zone The subventricular zone (SVZ) is a region situated on the outside wall of each lateral ventricle of the vertebrate brain. It is present in both the embryonic and adult brain. In embryonic life, the SVZ refers to a secondary proliferative zon ...

Protomap

Intimately related to the RUH is the ' protomap' hypothesis, which states that the primordial identity of each functional area of the cerebral cortex is encoded within the cortical stem cells prior to the formation of the cortical layers. Within each developing radial unit, the process of

neurogenesis Neurogenesis is the process by which nervous system cells, the neurons, are produced by neural stem cells (NSCs). This occurs in all species of animals except the porifera (sponges) and placozoans. Types of NSCs include neuroepithelial cells ( ...

gives rise to post-mitotic (non-dividing) cortical

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s, which begin the process of radial neuronal migration from the ventricular zone and adjacent

to form the

cortical plate 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. It is the largest site of neural integration in the central nervous system, and plays a key ...

in the classic 'inside-out' manner beginning with the deep cortical layers. Once their final destination is achieved, cortical neurons begin to form circuits with other cortical and subcortical neurons, often taking on a columnar shape following the radial migration route. Some localized lateral dispersion takes place during cortical column development in the mouse, but the degree of dispersion is molecularly regulated and indeed could vary across species.

Principles of development

Together, the RUH and protomap hypothesis represent two core principles of early cerebral cortex development. After neurons arrive in the cortical plate, other processes—especially activity-dependent processes—govern the maturation of cortical circuitry.

References

{{Reflist Developmental neuroscience Cerebral cortex

Cortical evolution

Protomap

Principles of development

See also

References