The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain In Psychology, memory is an organism's ability to store retain and subsequently retrieve information Attention is the Cognitive process of selectively concentrating on one aspect of the environment while ignoring other things In Biological psychology, awareness comprises a human's or an animal's perception and Cognitive reaction to a condition or event Thought and thinking are mental forms and Processes respectively ("thought" is both A language is a dynamic set of visual auditory or tactile Symbols of Communication and the elements used to manipulate them Consciousness has been defined loosely as a constellation of attributes of Mind such as Subjectivity, Self-awareness, Sentience, and the In non-living, preserved brains, the outermost layer of the cerebrum has a grey color, hence the name grey matter. The telencephalon (tɛlɛnˈsɛfəlɒn cerebrum, or forebrain is the most Anterior or especially in humans most Dorsal region of the Grey matter is formed by neurons and their unmyelinated fibers, whereas the white matter below the grey matter of the cortex is formed predominantly by myelinated axons interconnecting different regions of the central nervous system. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. The human cerebral cortex is 2-4 mm (0. 08-0. 16 inches) thick.

The surface of the cerebral cortex is folded in large mammals, wherein more than two-thirds of the cortical surface is buried in the grooves, called "sulci. In Neuroanatomy, a sulcus ( Latin: "furrow" pl sulci) is a depression or fissure in the surface of the brain " The phylogenetically most recent part of the cerebral cortex, the neocortex, is differentiated into six horizontal layers; the more ancient part of the cerebral cortex, the hippocampus (also called archicortex), has at most three cellular layers, and is divided into subfields. The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of The hippocampus is a part of the Forebrain, located in the medial Temporal lobe. The Hippocampus is a neural structure in the medial Temporal lobe. Relative variations in thickness or cell type (among other parameters) allow us to distinguish between different neocortical architectonic fields. The geometry of these fields seems to be related to the anatomy of the cortical folds, and, for example, layers in the upper part of the cortical grooves (called gyri) are more clearly differentiated than in its deeper parts (called sulci). A gyrus (pl gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci.

Contents 1 Development 2 Laminar pattern 3 Connections of the cerebral cortex 3.1 Sensory areas 3.2 Association areas 3.3 Motor areas 4 Classification 5 Cortical thickness 6 See also 7 Further reading 8 References 9 External links

Development

The cerebral cortex develops from the most anterior part of the neural plate, a specialized part of the embryonic ectoderm. In human Embryology, formation of neural plate is the first step of Neurulation. A germ layer is a collection of cells formed during animal Embryogenesis. The neural plate folds and closes to form the neural tube. In the developing vertebrate the neural tube is the Embryo 's precursor to the Central nervous system, which comprises the Brain and Spinal cord 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 ventricular system is a set of structures in the Brain continuous with the Central canal of the Spinal cord. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Glial cells, commonly called neuroglia or simply glia (Greek for "glue" are non- Neuronal cells that provide support and nutrition The most anterior (frontal) part of the neural tube, the telencephalon, gives rise to the cerebral hemispheres and cortex. The telencephalon (tɛlɛnˈsɛfəlɒn cerebrum, or forebrain is the most Anterior or especially in humans most Dorsal region of the

Cortical neurons are generated within the ventricular zone, next to the ventricles. At first, this zone contains "progenitor" cells, which divide to produce glial and neuronal cells ^[1]. 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 pia mater (Latin "tender mother" itself a translation from Arabic) is the delicate innermost layer of the Meninges - the membranes surrounding the The first divisions of the progenitor cells are symmetric, which duplicates the total number of progenitor cells at each mitotic cycle. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei 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. Astrocytes (also known collectively as astroglia) are characteristic star-shaped glial cells in the Brain and Spinal cord. Ependyma is the thin epithelial membrane lining the Ventricular system of the Brain and the Spinal cord. The migrating daughter cells become the pyramidal neurons of the cerebral cortex. A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral ^[2]

The layered structure of the mature cerebral cortex is formed during development. The first pyramidal neurons generated migrate out of the ventricular zone and form the preplate. A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral 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. The marginal zone is the region at the interface between the non-lymphoid Red pulp and the Lymphoid White-pulp of the Spleen. Subplate neurons are among the first generated Neurons in the Mammalian Cerebral cortex. 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.

Laminar pattern

The different cortical layers each contain a characteristic distribution of neuronal cell types and connections with other cortical and subcortical regions. One of the most clear examples of cortical layering is the Stria of Gennari in the primary visual cortex. In the Human Brain, the stria of Gennari (also called the "band" or "line" of Gennari is a band of myelinated axons projecting into layer 4C of 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 visual cortex. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell The thalamus (from Greek θάλαμος = room chamber, IPA= /ˈθæləməs/ is a pair and symmetric part of the brain

Staining cross-sections of the cortex to reveal the position of the neuronal cell bodies and the intracortical axon tracts allowed neuroanatomists in the early 20th century to produced 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. The molecular layer I, which contains few scattered neurons and consists mainly of extensions of apical dendrites and horizontally-oriented axons; some Cajal-Retzius and spiny stellate neurons can be found
2. The external granular layer II, which contains small pyramidal neurons and numerous stellate neurons
3. The external pyramidal layer III, which 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. The internal granular layer IV, which contains different types of stellate and pyramidal neurons, and is the main target of thalamocortical afferents as well as intra-hemispheric corticocortical afferents
5. The internal pyramidal layer V, which contains large pyramidal neurons (such as the Betz cells in the primary motor cortex); it is the principal source of subcortical efferents
6. The multiform layer VI, which 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 (Creutzfeldt, 1995). Korbinian Brodmann ( November 17, 1868 - August 22, 1918) was a German Neurologist who became famous for his definition The term Cajal–Retzius cell is applied to Reelin -producing neurons of the human embryonic marginal zone which display as a salient feature radial ascending A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral Afferent is an Anatomical term with the following meanings Conveying towards a center for example the Afferent arterioles conveying blood In Neuroscience, stellate cells are neurons with several dendrites radiating from the cell body giving them a star shaped appearance A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral A pyramidal cell (or pyramidal neuron, or projection neuron) is a multipolar Neuron located in the Hippocampus and Cerebral A pyramid is a Building where the upper surfaces are triangular and converge on one point

It is important to note that the cortical layers are not simply stacked one over the other; there exist 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, the latter of which have been proposed to be the basic functional units of cortex (Mountcastle, 1997). A cortical column, also called hypercolumn or sometimes cortical module, is a group of neurons in the Brain cortex which can be successively 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), auditory cortex and associative cortex (Tanaka, 2003). Torsten Nils Wiesel (b June 3, 1924) was a Swedish co-recipient with David H

Cortical areas that lack a layer IV are called agranular. Cortical areas that have only a rudimentary layer IV are called dysgranular^[3].

Connections of the cerebral cortex

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. The thalamus (from Greek θάλαμος = room chamber, IPA= /ˈθæləməs/ is a pair and symmetric part of the brain The basal ganglia (or basal nuclei) are a group of nuclei in the Brain interconnected with the Cerebral cortex, Thalamus and 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 olfactory bulb is a structure of the Vertebrate Forebrain involved in Olfaction, the perception of Odors. In Anatomy of Animals the piriform cortex, or pyriform cortex is a region in the Brain. 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%.

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

Sensory areas

The sensory areas are the areas that receive and process information from the senses. A cortical area is a part of the Cerebral cortex. Functionally Defined Often a cortical area is functionally defined i Senses are the physiological methods of Perception. The senses and their operation classification and theory are overlapping topics studied by a variety of fields Parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas. The thalamus (from Greek θάλαμος = room chamber, IPA= /ˈθæləməs/ is a pair and symmetric part of the brain The senses of vision, audition, and touch are served by the primary visual cortex, primary auditory cortex and primary somatosensory cortex. The term visual cortex refers to the primary visual cortex (also known as striate cortex or The primary auditory cortex is the region of the Brain that is responsible for processing of auditory ( Sound) information The lateral postcentral gyrus is a prominent structure in the Parietal lobe of the human Brain and an important landmark In general, the two hemispheres receive information from the opposite (contralateral) side of the body. With regard to living things, a body is the integral physical material of an individual For example the right primary somatosensory cortex receives information from the left limbs, and the right visual cortex receives information from the left visual field. The organization of sensory maps in the cortex reflects that of the corresponding sensing organ, in what is known as a topographic map. A topographic map is the ordered projection of a sensory surface like the retina or the skin or an effector system like the musculature to one or more structures of the Central Neighboring points in the primary visual cortex, for example, correspond to neighboring points in the retina. The term visual cortex refers to the primary visual cortex (also known as striate cortex or The vertebrate retina is a light sensitive part inside the inner layer of the Eye. This topographic map is called a retinotopic map. A topographic map is the ordered projection of a sensory surface like the retina or the skin or an effector system like the musculature to one or more structures of the Central Retinotopy describes the spatial organization of the neuronal responses to visual stimuli In the same way, there exists a tonotopic map in the primary auditory cortex and a somatotopic map in the primary sensory cortex. Tonotopy (from Greek tono- and topos = place the place of tones is the spatial arrangement of where sound is perceived transmitted or received Somatotopic arrangement is the maintenance of spatial organisation within the Central nervous system. 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. The lateral postcentral gyrus is a prominent structure in the Parietal lobe of the human Brain and an important landmark The concept of a homunculus ( Latin for "little man" plural "homunculi" the diminutive of homo, "man" is often used to illustrate Areas with lots of sensory innervation, such as the fingertips and the lips, require more cortical area to process finer sensation.

Association areas

Association areas function to produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language. In Psychology and the Cognitive sciences perception is the process of attaining awareness or understanding of sensory Information. The parietal, temporal, and occipital lobes - all located in the posterior part of the cortex - organize sensory information into a coherent perceptual model of our environment centered on our body image. The parietal lobe is a lobe in the Brain. It is positioned above (superior to the Occipital lobe and behind (posterior to the Frontal lobe. The temporal lobes are parts of the cerebrum that are involved in speech, Memory, and Hearing. The occipital lobe is the visual processing center of the Mammalian Brain containing most of the anatomical region of the Visual cortex. Body image is a term which may refer to the Perceptions of a human's own Physical appearance, or the internal sense of having a body which is interpreted by the brain The frontal lobe or prefrontal association complex is involved in planning actions and movement, as well as abstract thought. The frontal lobe is an area in the Brain of Mammals It is located at the front of each Cerebral hemisphere and positioned anterior to (in front of the Our language abilities are localized to the association areas of the parietal-temporal-occipital complex, typically in the left hemisphere. Wernicke's area relates to understanding language while Broca's area relates to its use. Wernicke's area is a part of the Human cerebrum that forms part of the cortex, on the posterior section of the Superior temporal gyrus, encircling the Broca's area is a section of the human brain that is involved in Language processing, speech or sign production and comprehension

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:

• Primary motor cortex, which executes voluntary movements
• Supplementary motor areas and premotor cortex, which select voluntary movements. The primary motor cortex (or M1) works in association with pre-motor areas to plan and execute movements The supplementary motor area (SMA is a part of the sensorimotor Cerebral cortex (perirolandic i The premotor cortex is an area of Motor cortex in the Frontal lobe of the Brain.

In addition, motor functions have been described for:

• Posterior parietal cortex, which guides voluntary movements in space
• Dorsolateral prefrontal cortex, which decides which voluntary movements to make according to higher-order instructions, rules, and self-generated thoughts. The posterior parietal cortex is a portion of the Parietal lobe which manipulates mental images and integrates sensory and motor portions of the brain The dorsolateral prefrontal cortex (DL-PFC or DLPFC is the last area (45th to develop ( myelinate) in the human cerebrum

Classification

Based on the differences in lamination the cerebral cortex can be classified into two major groups:

• Isocortex (homotypical cortex), the part of the cortex with six layers
• Allocortex (heterotypical cortex) with variable number of layers, e. The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of The allocortex is a part of the Cerebral cortex characterized by fewer cell layers than the Isocortex, or Neocortex (i g. , olfactory cortex and hippocampus. The Olfactory helps and relates sense of smell. The olfactory system is the Sensory system used for Olfaction. The hippocampus is a part of the Forebrain, located in the medial Temporal lobe.

Auxiliary classes are:

• Mesocortex, classification between isocortex and allocortex where layers 2, 3, and 4 are merged
• Proisocortex, Brodmann areas 24, 25, 32
• Periallocortex, comprising cortical areas adjacent to allocortex. Proisocortex is an area in the Cerebral cortex. It is a transitional area between the (true Isocortex and Periallocortex. A Brodmann area is a region of the cortex defined based on its Cytoarchitecture, or organization of cells Brodmann area 24 is part of the Anterior cingulate in the Human brain. Brodmann area 25 (BA25 is an area in the Cerebral cortex of the Brain and delineated based on its cytoarchitectonic characteristics The Brodmann area 32, also known in the Human Brain as the dorsal anterior cingulate area 32, refers to a subdivision of the cytoarchitecturally The allocortex is a part of the Cerebral cortex characterized by fewer cell layers than the Isocortex, or Neocortex (i

Based on supposed developmental differences the following classification also appears:

• Archicortex, which phylogenetically is the oldest cortex
• Paleocortex
• Neocortex or Neopallium, which corresponds to the isocortex. Archicortex is basically categorized under Allocortex. It is any cortex with fewer than six areas specifically three layered hippocampal cortexes The paleocortex is a layer of the Cerebral cortex intermediate phylogenetically between the Neocortex and Archicortex. The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of

In addition, cortex may be classified on the basis of gross topographical conventions into four lobes:

• Occipital Cortex
• Temporal Cortex
• Parietal Cortex
• Frontal Cortex

Cortical thickness

With magnetic resonance brain scanners, it is possible to get a measure for the thickness of the human cerebral cortex and relate it to other measures. The history of Neuroimaging, began in the early 1900s with a technique called Pneumoencephalography. One study has found some positive association between the cortical thickness and intelligence. Intelligence (also called intellect) is an Umbrella term used to describe a property of the Mind that encompasses many related abilities such as the capacities ^[4] Another study has found that the somatosensory cortex is thicker in migraine sufferers. Migraine is a neurological Syndrome characterized by altered bodily experiences painful headaches and nausea ^[5]

See also

• Cortical column
• Frontal lobe
• Limbic system
• List of regions in the human brain
• Microgyrus
• Occipital lobe
• Parietal lobe
• Temporal lobe
• Cerebral hemisphere
• Neocortex
• Subplate
• Brain-computer interface

Further reading

• Kandel, E. A cortical column, also called hypercolumn or sometimes cortical module, is a group of neurons in the Brain cortex which can be successively The frontal lobe is an area in the Brain of Mammals It is located at the front of each Cerebral hemisphere and positioned anterior to (in front of the The limbic system, or Paleomammalian brain is a term for a set of brain structures including the Hippocampus and Amygdala and anterior thalamic nuclei and a limbic Anatomical regions of the brain are listed vertically following hierarchies that are standard in Neuroanatomy. A microgyrus is an area of the Cerebral cortex that includes only four Cortical layers instead of six The occipital lobe is the visual processing center of the Mammalian Brain containing most of the anatomical region of the Visual cortex. The parietal lobe is a lobe in the Brain. It is positioned above (superior to the Occipital lobe and behind (posterior to the Frontal lobe. The temporal lobes are parts of the cerebrum that are involved in speech, Memory, and Hearing. A cerebral hemisphere ( hemispherium cerebrale) is defined as one of the two regions of the Brain that are delineated by the body's median plane. The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of Subplate neurons are among the first generated Neurons in the Mammalian Cerebral cortex. A brain-computer interface (BCI sometimes called a direct neural interface or a brain-machine interface, is a direct communication pathway between a human or animal R. , Schwartz, J. H. , and Jessell, T. M. Principles of Neural Science (Fourth Edition). 2000. New York, McGraw Hill. ISBN 0-8385-7701-6.
• Zigmond, M. J. , Bloom, F. E. , Landis, S. C. , Roberts, J. L, and Squire, L. R. Fundamental Neuroscience. 1999. San Diego, Academic Press. ISBN 0-12-780870-1.

References

• Angevine, J. and Sidman, R. 1961. Autoradiographic study of cell migration during histogenesis of cerebral cortex in the mouse. Nature, 192:766-768
• Creutzfeldt, O. 1995. Cortex Cerebri. Springer-Verlag.
• Marin-Padilla, M. 2001. Evolución de la estructura de la neocorteza del mamífero: Nueva teoría citoarquitectónica. Rev. Neurol, 33(9):843-853
• Mountcastle, V. 1997. The columnar organization of the neocortex. Brain, 120:701-722
• Noctor SC, Flint AC, Weissman TA, Dammerman RS, Kriegstein AR. (2001) Neurons derived from radial glial cells establish radial units in neocortex. "Nature" 409(6821):714-720. PMID 11217860
• Ogawa, M. et al. 1995. The reeler gene-associated antigen on Cajal-Retzius neurons is a crucial molecule for laminar organization of cortical neurones. Neuron, 14:899-912
• Rakic, P. 1988. Specification of cerebral cortical areas. Science, 241:170-176
• Friauf, J. 1991. Changing patterns of synaptic input to subplate and cortical plate during development of visual cortex.
• Braitenberg, V and Schüz, A 1991. "Anatomy of the Cortex: Statistics and Geometry" NY: Springer-Verlag

External links

• NeuroNames hier-20
• BrainMaps at UCDavis cerebral cortex

• Webvision - The primary visual cortex Comprehensive article about the structure and function of the primary visual cortex. NeuroNames is a system of nomenclature for the human and/or macaque Brain. BrainMaps is an NIH -funded interactive zoomable high-resolution digital brain atlas and virtual microscope that is based on more than 20 million megapixels (50 terabytes
• 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.

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