The Protomap is a primordial molecular map of the functional areas of the mammalian
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 ...
during early
embryonic development
In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...
, at a stage when
neural stem cells are still the dominant cell type.
The protomap is a feature of the
ventricular zone, which contains the principal cortical progenitor cells, known as
radial glial cells. Through a process called '
cortical patterning', the protomap is patterned by a system of signaling centers in the embryo, which provide positional information and cell fate instructions.
These early genetic instructions set in motion a development and maturation process that gives rise to the mature functional areas of the cortex, for example the visual, somatosensory, and motor areas.
The term protomap was coined by
Pasko Rakic.
The ''protomap hypothesis'' was opposed by the ''protocortex hypothesis'', which proposes that cortical proto-areas initially have the same potential, and that regionalization in large part is controlled by external influences, such as axonal inputs from the
thalamus
The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...
to the cortex. However, a series of papers in the year 2000 and in 2001 provided strong evidence against the protocortex hypothesis, and the protomap hypothesis has been well accepted since then.
The protomap hypothesis, together with the related
radial unit hypothesis, forms our core understanding of the embryonic development of the cerebral cortex. Once the basic structure is present and cortical neurons have migrated to their final destinations, many other processes contribute to the maturation of functional cortical circuits.
See also
*
Radial unit hypothesis
*
Neural stem cell
*
Stem cell
*
Neurogenesis
*
Cellular differentiation
*
Cortical patterning
*
Gyrification
Gyrification is the process of forming the characteristic folds of the cerebral cortex. The peak of such a fold is called a ''gyrus'' (pl. ''gyri''), and its trough is called a ''Sulcus (neuroanatomy), sulcus'' (pl. ''sulci''). The neurons of the ...
References
Neuroanatomy
Neuroscience
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