World Library  
Flag as Inappropriate
Email this Article

Cerebral cortex

Article Id: WHEBN0000058686
Reproduction Date:

Title: Cerebral cortex  
Author: World Heritage Encyclopedia
Language: English
Subject: Human brain, Neurotransmitter, Expressive aphasia, Flexible brain-computer interface, Neurocomputational speech processing
Publisher: World Heritage Encyclopedia

Cerebral cortex

Cerebral cortex
The cerebral cortex is the outer layer
depicted in dark violet.
Golgi-stained neurons in the cortex.
Latin Cortex cerebri
Part of Telencephalon
NeuroLex ID Cerebral cortex
Anatomical terms of neuroanatomy

The cerebral cortex is the cerebrum's (brain) outer layer of neural tissue in humans and other mammals. It is divided into two cortices, along the sagittal plane: the left and right cerebral hemispheres divided by the medial longitudinal fissure. The cerebral cortex plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. The human cerebral cortex is 2 to 4 millimetres (0.079 to 0.157 in) thick.[1]

In large mammals the cerebral cortex is folded, giving a much greater surface area in the confined volume of the skull. A fold or ridge in the cortex is termed a gyrus (plural gyri) and a groove or fissure is termed a sulcus (plural sulci). In the human brain more than two-thirds of the cerebral cortex is buried in the sulci.

The cerebral cortex is gray matter, consisting mainly of cell bodies and capillaries. It contrasts with the underlying white matter, consisting mainly of the white myelinated sheaths of neuronal axons. The phylogenetically most recent part of the cerebral cortex, the neocortex (also called isocortex), is differentiated into six horizontal layers; the more ancient part of the cerebral cortex, the hippocampus, has at most three cellular layers. Neurons in various layers connect vertically to form small microcircuits, called cortical columns. Different neocortical regions known as Brodmann areas are distinguished by variations in their cytoarchitectonics (histological structure).


Layered structure

Three drawings of cortical lamination by Santiago Ramon y Cajal, each showing a vertical cross-section, with the surface of the cortex at the top. Left: Nissl-stained visual cortex of a human adult. Middle: Nissl-stained motor cortex of a human adult. Right: Golgi-stained cortex of a 1½ month old infant. The Nissl stain shows the cell bodies of neurons; the Golgi stain shows the dendrites and axons of a random subset of neurons.
Micrograph showing the visual cortex (predominantly pink). Subcortical white matter (predominantly blue) is seen at the bottom of the image. HE-LFB stain.

The different cortical layers each contain a characteristic distribution of neuronal cell types and connections with other cortical and subcortical regions. There are direct connections between different cortical areas and indirect connections via the thalamus, for example. One of the clearest examples of cortical layering is the Stria of Gennari in the primary visual cortex. This is a band of whiter tissue that can be observed with the naked eye in the fundus of the calcarine sulcus of the occipital lobe. The Stria of Gennari is composed of axons bringing visual information from the thalamus into layer four of the visual cortex.

Staining cross-sections of the cortex to reveal the position of neuronal cell bodies and the intracortical axon tracts allowed neuroanatomists in the early 20th century to produce a detailed description of the laminar structure of the cortex in different species. After the work of Korbinian Brodmann (1909) the neurons of the cerebral cortex are grouped into six main layers, from outside (pial surface) to inside (white matter):

  1. Layer I, the molecular layer, contains few scattered neurons and consists mainly of extensions of apical dendritic tufts of pyramidal neurons and horizontally oriented axons, as well as glial cells.[2] Some Cajal-Retzius and spiny stellate cells can be found here. Inputs to the apical tufts are thought to be crucial for the ‘‘feedback’’ interactions in the cerebral cortex involved in associative learning and attention.[3] While it was once thought that the input to layer I came from the cortex itself,[4] it is now realized that layer I across the cerebral cortex mantle receives substantial input from ‘‘matrix’’ or M-type thalamus cells[5] (in contrast to ‘‘core’’ or C-type that go to layer IV).[6]
  2. Layer II, the external granular layer, contains small pyramidal neurons and numerous stellate neurons.
  3. Layer III, the external pyramidal layer, contains predominantly small and medium-size pyramidal neurons, as well as non-pyramidal neurons with vertically oriented intracortical axons; layers I through III are the main target of interhemispheric corticocortical afferents, and layer III is the principal source of corticocortical efferents.
  4. Layer IV, the internal granular layer, contains different types of stellate and pyramidal neurons, and is the main target of thalamocortical afferents from thalamus type C neurons[6] as well as intra-hemispheric corticocortical afferents.
  5. Layer V, the internal pyramidal layer, contains large pyramidal neurons which give rise to axons leaving the cortex and running down to subcortical structures (such as the basal ganglia). In the primary motor cortex of the frontal lobe, layer V contains Betz cells, whose axons travel through the internal capsule, the brain stem and the spinal cord forming the corticospinal tract, which is the main pathway for voluntary motor control.
  6. Layer VI, the polymorphic or multiform layer, contains few large pyramidal neurons and many small spindle-like pyramidal and multiform neurons; layer VI sends efferent fibers to the thalamus, establishing a very precise reciprocal interconnection between the cortex and the thalamus.[7] This is, layer VI neurons from one cortical column connect with thalamus neurons that provide input to the same cortical column. These connections are both excitatory and inhibitory. Neurons send excitatory fibers to neurons in the thalamus and also send collaterals to the thalamic reticular nucleus that inhibit these same thalamus neurons or ones adjacent to them.[8] One theory is that because the inhibitory output is reduced by cholinergic input to the cerebral cortex, this provides the brainstem with adjustable "gain control for the relay of lemniscal inputs".[8]

The cortical layers are not simply stacked one over the other; there exists characteristic connections between different layers and neuronal types, which span all the thickness of the cortex. These cortical microcircuits are grouped into cortical columns and minicolumns. It has been proposed that the minicolumns are the basic functional units of the cortex.[9] In 1957, Vernon Mountcastle showed that the functional properties of the cortex change abruptly between laterally adjacent points; however, they are continuous in the direction perpendicular to the surface. Later works have provided evidence of the presence of functionally distinct cortical columns in the visual cortex (Hubel and Wiesel, 1959),[10] auditory cortex, and associative cortex.

Cortical areas that lack a layer IV are called agranular. Cortical areas that have only a rudimentary layer IV are called dysgranular.[11] Information processing within each layer is determined by different temporal dynamics with that in the layers II/III having a slow 2 Hz oscillation while that in layer V having a fast 10–15 Hz one.[12]


Based on the differences in lamination the cerebral cortex can be classified into two parts, the large area of neocortex and the much smaller area of allocortex:

  • The neocortex (also known as the isocortex or neopallium), is the part of the mature cerebral cortex with six distinct layers. Examples of the neocortex are the granular primary motor cortex, also known as Brodmann area 4 and striate Brodmann area 17. The neocortex has two types of cortex, the true isocortex and the proisocortex. The proisocortex contains Brodmann areas 24, 25, and 32
  • The allocortex, is the part of the cerebral cortex with less than six layers and has three regions, the archicortex with three cortical laminae and the paleocortex which has four or five, and a transitional area adjacent to the allocortex, the periallocortex. Examples of allocortex are the olfactory cortex and the hippocampus.

There is a transitional area between the neocortex and the allocortex called the paralimbic cortex, where layers 2, 3 and 4 are merged. This area incorporates the proisocortex of the neocortex and the periallocortex of the allocortex.

In addition, the cerebral cortex may be classified on the basis of gross topographical conventions into four lobes: the temporal lobe, occipital lobe, parietal lobe and frontal lobe:


Human cortical development between 26 and 39 week gestational age

The cerebral cortex develops from the most anterior part of the neural plate, a specialized part of the embryonic ectoderm.[13] The neural plate folds and closes to form the neural tube. From the cavity inside the neural tube develops the ventricular system, and, from the epithelial cells of its walls, the neurons and glia of the nervous system. The most anterior (front, or cranial) part of the neural plate, the prosencephalon, which is evident before neurulation begins, gives rise to the cerebral hemispheres and its later cortex.[14] The development of the neocortex arises in an inside-out manner as mitotically dividing progenitor cells migrate outward along radial glia. The first neurons to differentiate migrate to what will become Layer VI. As the G1 phase of mitosis is elongated, in what is seen as selective cell-cycle lengthening, the newly-born neurons migrate to more superficial layers of the cortex.[15]

Cortical neurons are generated within the ventricular zone, next to the ventricles. At first, this zone contains progenitor cells, which divide to produce glial cells and neurons.[16] The glial fibers produced in the first divisions of the progenitor cells are radially oriented, spanning the thickness of the cortex from the ventricular zone to the outer, pial surface, and provide scaffolding for the migration of neurons outwards from the ventricular zone. The first divisions of the progenitor cells are symmetric, which duplicates the total number of progenitor cells at each mitotic cycle. Then, some progenitor cells begin to divide asymmetrically, producing one postmitotic cell that migrates along the radial glial fibers, leaving the ventricular zone, and one progenitor cell, which continues to divide until the end of development, when it differentiates into a glial cell or an ependymal cell. The migrating daughter cells become the pyramidal cells of the cerebral cortex.[17] The development process is time ordered and regulated by hundreds of genes and epigenetic regulatory mechanisms.[18]

The layered structure of the mature cerebral cortex is formed during development. The first pyramidal neurons generated migrate out of the ventricular zone and subventricular zone, together with reelin producing Cajal–Retzius neurons, from the preplate. Next, a cohort of neurons migrating into the middle of the preplate divides this transient layer into the superficial marginal zone, which will become layer one of the mature neocortex, and the subplate, forming a middle layer called the cortical plate. These cells will form the deep layers of the mature cortex, layers five and six. Later born neurons migrate radially into the cortical plate past the deep layer neurons, and become the upper layers (two to four). Thus, the layers of the cortex are created in an inside-out order. The only exception to this inside-out sequence of neurogenesis occurs in the layer I of primates, in which, in contrast to rodents, neurogenesis continues throughout the entire period of corticogenesis.[19]


For mammals, species with larger brains (in absolute terms, not just in relation to body size) tend to have thicker cortices.[20] The range, however, is not very great — only a factor of 7 between the thickest and thinnest cortices. The smallest mammals, such as shrews, have a neocortical thickness of about 0.5 mm; the ones with the largest brains, such as humans and fin whales, have thicknesses of 2.3—2.8 mm. There is an approximately logarithmic relationship between brain weight and cortical thickness.[20]

Magnetic resonance imaging (MRI) of the brain makes it possible to get a measure for the thickness of the human cerebral cortex and relate it to other measures. The thickness of different cortical areas varies but in general, sensory cortex is thinner than motor cortex.[21] One study has found some positive association between the cortical thickness and intelligence.[22] Another study has found that the somatosensory cortex is thicker in migraine sufferers, though it is not known if this is the result of migraine attacks or the cause of them.[23] A later study using a larger patient population reports no change in the cortical thickness in migraine sufferers.[24] A genetic disorder of the cerebral cortex, whereby increased folding in certain areas results in a microgyrus, where there are four layers instead of six, is in some instances seen to be related to dyslexia.[25]



The cerebral cortex is connected to various subcortical structures such as the thalamus and the basal ganglia, sending information to them along efferent connections and receiving information from them via afferent connections. Most sensory information is routed to the cerebral cortex via the thalamus. Olfactory information, however, passes through the olfactory bulb to the olfactory cortex (piriform cortex). The vast majority of connections are from one area of the cortex to another, rather than to subcortical areas; Braitenberg and Schüz (1991) put the figure as high as 99%.[26]

Cortical areas

The cortex is commonly described as comprising three parts: sensory, motor, and association areas.

Sensory areas

The sensory areas are the topographic map. Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina. This topographic map is called a retinotopic map. In the same way, there exists a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex. This last topographic map of the body onto the posterior central gyrus has been illustrated as a deformed human representation, the somatosensory homunculus, where the size of different body parts reflects the relative density of their innervation. Areas with lots of sensory innervation, such as the fingertips and the lips, require more cortical area to process finer sensation.

Motor areas

The motor areas are located in both hemispheres of the cortex. They are shaped like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa.

Two areas of the cortex are commonly referred to as motor:

In addition, motor functions have been described for:

Just underneath the cerebral cortex are interconnected subcortical masses of grey matter called basal ganglia (or nuclei). The basal ganglia receive input from the substantia nigra of the midbrain and motor areas of the cerebral cortex, and send signals back to both of these locations. They are involved in motor control. They are found lateral to the thalamus. The main components of the basal ganglia are the caudate nucleus, the putamen, the globus pallidus, the substantia nigra, the nucleus accumbens, and the subthalamic nucleus. The putamen and globus pallidus are also collectively known as the lentiform nucleus, because together they form a lens-shaped body. The putamen and caudate nucleus are also collectively called the corpus striatum after their striped appearance.[27][28]

Association areas

Association areas function to produce a meaningful Broca's area, for language expression and area 22, the Wernicke's area, for language reception. However, language is no longer limited to easily identifiable areas. More recent research suggests that the processes of language expression and reception occur in areas other than just those structures around the lateral sulcus, including the frontal lobe, basal ganglia, cerebellum, pons, and the caudate nucleus.[30]

Lateral surface of the human cerebral cortex
Medial surface of the human cerebral cortex

Clinical significance

Neurodegenerative diseases such as Alzheimer's disease and Lafora disease, show as a marker, an atrophy of the grey matter of the cerebral cortex.[31]

Other animals

The cerebral cortex is derived from the pallium, a layered structure found in the forebrain of all vertebrates. The basic form of the pallium is a cylindrical layer enclosing fluid-filled ventricles. Around the circumference of the cylinder are four zones, the dorsal pallium, medial pallium, ventral pallium, and lateral pallium, which are thought respectively to give rise to the neocortex, hippocampus, amygdala, and olfactory cortex.

Until recently no counterpart to the cerebral cortex had been recognized in invertebrates. However, a study published in the journal Cell in 2010, based on gene expression profiles, reported strong affinities between the cerebral cortex and the mushroom bodies of ragworms.[32] Mushroom bodies are structures in the brains of many types of worms and arthropods that are known to play important roles in learning and memory; the genetic evidence indicates a common evolutionary origin, and therefore indicates that the origins of the earliest precursors of the cerebral cortex date back to the early Precambrian era.

Additional images

See also


  1. ^ Kandel, Eric R.; Schwartz, James H.; Jessell, Thomas M. (2000). Principles of Neural Science Fourth Edition. United State of America:  
  2. ^ Shipp, Stewart (2007-06-17). "Structure and function of the cerebral cortex". Current Biology 17 (12): R443–9.  
  3. ^ Gilbert CD, Sigman M (2007). "Brain states: top-down influences in sensory processing". Neuron 54 (5): 677–96.  
  4. ^ Cauller L (1995). "Layer I of primary sensory neocortex: where top-down converges upon bottom-up". Behav Brain Res 71 (1–2): 163–70.  
  5. ^ Rubio-Garrido P, Pérez-de-Manzo F, Porrero C, Galazo MJ, Clascá F (2009). "Thalamic input to distal apical dendrites in neocortical layer 1 is massive and highly convergent". Cereb Cortex 19 (10): 2380–95.  
  6. ^ a b Jones EG (1998). "Viewpoint: the core and matrix of thalamic organization". Neuroscience 85 (2): 331–45.  
  7. ^ Creutzfeldt, O. 1995. Cortex Cerebri. Springer-Verlag.
  8. ^ a b Lam YW, Sherman SM (2010). "Functional Organization of the Somatosensory Cortical Layer 6 Feedback to the Thalamus". Cereb Cortex 20 (1): 13–24.  
  9. ^ Mountcastle V (1997). "The columnar organization of the neocortex". Brain 120 (4): 701–722.  
  10. ^ HUBEL DH, WIESEL TN (October 1959). "Receptive fields of single neurones in the cat's striate cortex". J. Physiol. (Lond.) 148 (3): 574–91.  
  11. ^ S.M. Dombrowski , C.C. Hilgetag , and H. Barbas. Quantitative Architecture Distinguishes Prefrontal Cortical Systems in the Rhesus Monkey.Cereb. Cortex 11: 975-988. "...they either lack (agranular) or have only a rudimentary granular layer IV (dysgranular)."
  12. ^ Sun W, Dan Y (2009). "Layer-specific network oscillation and spatiotemporal receptive field in the visual cortex". Proc Natl Acad Sci U S A 106 (42): 17986–17991.  
  13. ^ Natasha Warren, Damira Caric1, Thomas Pratt, Julia A. Clausen, Pundit Asavaritikrai, John O. Mason, Robert E. Hill, David J. Price;  
  14. ^ Larsen, W J. Human Embryology 3rd edition 2001. pp 421-422 ISBN 0-443-06583-7
  15. ^ Calegari, F; Haubensack W; Haffner C; Huttner WB (2005). "Selective lengthening of the cell cycle in the neurogenic subpopulation of neural progenitor cells during mouse brain development.". J Neurosci. 25 (28): 6533–8.  
  16. ^ Stephen C. Noctor, Alexander C. Flint,  
  17. ^ P. Rakic (1988). "Specification of cerebral cortical areas".  
  18. ^ Hu, X.L.; Wang,Y. & Shen, Q. (2012). "Epigenetic control on cell fate choice in neural stem cells". Protein & Cell 3 (4): 278–290.  
  19. ^ Zecevic N, Rakic P (2001). "Development of layer I neurons in the primate cerebral cortex".  
  20. ^ a b Nieuwenhuys R, Donkelaar HJ, Nicholson C (1998). The central nervous system of vertebrates, Volume 1. Springer. pp. 2011–2012.  
  21. ^ Frithjof Kruggel, Martina K. Brückner, Thomas Arendt, Christopher J. Wiggins and D. Yves von Cramon (2003). "Analyzing the neocortical fine-structure". Medical Image Analysis 7 (3): 251–264.  
  22. ^ Katherine L. Narr, Roger P. Woods, Paul M. Thompson, Philip Szeszko, Delbert Robinson, Teodora Dimtcheva, Mala Gurbani, Arthur W. Toga and Robert M. Bilder (2007). "Relationships between IQ and Regional Cortical Grey Matter Thickness in Healthy Adults".  
  23. ^ Alexandre F.M. DaSilva, Cristina Granziera, Josh Snyder and Nouchine Hadjikhani (2007). "Thickening in the somatosensory cortex of patients with migraine".   News report:
  24. ^ Datte R, Detre JA et al. (Oct 2011). "Absence of changes in cortical thickness in patients with migraine". Cephalagia 31 (14): 1452–8.  
  25. ^ Habib M (2000). "The neurological basis of developmental dyslexia: an overview and working hypothesis". Brain 123 (12): 2373–99.  
  26. ^ Braitenberg, V and Schüz, A 1991. "Anatomy of the Cortex: Statistics and Geometry" NY: Springer-Verlag
  27. ^ Saladin, Kenneth. Anatomy and Physiology: The Unity of Form and Function, 5th Ed. New York: McGraw-Hill Companies Inc, 2010. Print.
  28. ^ Dorland’s Medical Dictionary for Health Consumers, 2008.
  29. ^ Yeo BT, Krienen FM, Sepulcre J, Sabuncu MR, Lashkari D, Hollinshead M, Roffman JL, Smoller JW, Zöllei L, Polimeni JR, Fischl B, Liu H, Buckner RL (2011). "The organization of the human cerebral cortex estimated by intrinsic functional connectivity". Journal of Neurophysiology 106 (3): 1125–1165.  
  30. ^ Cathy J. Price (2000). "The anatomy of language: contributions from functional neuroimaging". Journal of Anatomy 197 (3): 335–359.  
  31. ^ Ortolano S and Vieitez I et al. Loss of cortical neurons underlies the neuropathology of Lafora disease. Mol Brain 2014;7:7. PMCID:PMC3917365
  32. ^ Tomer, R; Denes, AS; Tessmar-Raible, K; Arendt, D (2010). "Profiling by image registration reveals common origin of annelid mushroom bodies and vertebrate pallium".  

External links

  • hier-20 at NeuroNames
  • Stained brain slice images which include the "cerebral cortex" at the BrainMaps project
  • Webvision - The primary visual cortex Comprehensive article about the structure and function of the primary visual cortex.
  • Webvision - Basic cell types Image of the basic cell types of the monkey cerebral cortex.
  • Development of the Cerebral Cortex Different topics on cortical development in the form of columns written by leading scientists.
  • Cerebral Cortex - Cell Centered Database
  • NIF Search - Cerebral Cortex via the Neuroscience Information Framework
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.