Neocortex

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Neocortex
Gray754.png
A representative column of neocortex. Cell body layers are labeled on the left, and fiber layers are labeled on the right.
Identifiers
MeSH D019579
NeuroNames 757
NeuroLex ID birnlex_2547
TA98 A14.1.09.304
A14.1.09.307
TA2 5532
FMA 62429
Anatomical terms of neuroanatomy

The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, [1] spatial reasoning and language. [2] The neocortex is further subdivided into the true isocortex and the proisocortex. [3]

Contents

In the human brain, the cerebral cortex consists of the larger neocortex and the smaller allocortex, respectively taking up 90% and 10%. [4] The neocortex is made up of six layers, labelled from the outermost inwards, I to VI.

Etymology

The term is from cortex, Latin, "bark" or "rind", combined with neo-, Greek, "new". Neopallium is a similar hybrid, from Latin pallium, "cloak". Isocortex and allocortex are hybrids with Greek isos, "same", and allos, "other".

Anatomy

The neocortex is the most developed in its organisation and number of layers, of the cerebral tissues. [5] The neocortex consists of the grey matter, or neuronal cell bodies and unmyelinated fibers, surrounding the deeper white matter (myelinated axons) in the cerebrum. This is a very thin layer though, about 2–4 mm thick. [6] There are two types of cortex in the neocortex, the proisocortex and the true isocortex. The pro-isocortex is a transitional area between the true isocortex and the periallocortex (part of the allocortex). It is found in the cingulate cortex (part of the limbic system), in Brodmann's areas 24, 25, 30 and 32, the insula and the parahippocampal gyrus.

Of all the mammals studied to date (including humans), a species of oceanic dolphin known as the long-finned pilot whale has been found to have the most neocortical neurons. [7]

Geometry

The neocortex is smooth in rodents and other small mammals, whereas in elephants, dolphins and primates and other larger mammals it has deep grooves (sulci) and ridges (gyri). These folds allow the surface area of the neocortex to be greatly increased. All human brains have the same overall pattern of main gyri and sulci, although they differ in detail from one person to another. [8] The mechanism by which the gyri form during embryogenesis is not entirely clear, and there are several competing hypotheses that explain gyrification, such as axonal tension, [9] cortical buckling [10] or differences in cellular proliferation rates in different areas of the cortex. [11]

Layers

The neocortex contains both excitatory (~80%) and inhibitory (~20%) neurons, named for their effect on other neurons. [12] The human neocortex consists of hundreds of different types of cells. [13] The structure of the neocortex is relatively uniform (hence the alternative names "iso-" and "homotypic" cortex), consisting of six horizontal layers segregated principally by cell type and neuronal connections. [14] However, there are many exceptions to this uniformity; for example, layer IV is small or missing in the primary motor cortex. There is some canonical circuitry within the cortex; for example, pyramidal neurons in the upper layers II and III project their axons to other areas of neocortex, while those in the deeper layers V and VI often project out of the cortex, e.g. to the thalamus, brainstem, and spinal cord. Neurons in layer IV receive the majority of the synaptic connections from outside the cortex (mostly from thalamus), and themselves make short-range, local connections to other cortical layers. [12] Thus, layer IV is the main recipient of incoming sensory information and distributes it to the other layers for further processing.

Cortical columns

The neocortex is often described as being arranged in vertical structures called cortical columns, patches of neocortex with a diameter of roughly 0.5 mm (and a depth of 2 mm, i.e., spanning all six layers). These columns are often thought of as the basic repeating functional units of the neocortex, but their many definitions, in terms of anatomy, size, or function, are generally not consistent with each other, leading to a lack of consensus regarding their structure or function or even whether it makes sense to try to understand the neocortex in terms of columns. [15]

Function

The neocortex is derived embryonically from the dorsal telencephalon, which is the rostral part of the forebrain. The neocortex is divided, into regions demarcated by the cranial sutures in the skull above, into frontal, parietal, occipital, and temporal lobes, which perform different functions. For example, the occipital lobe contains the primary visual cortex, and the temporal lobe contains the primary auditory cortex. Further subdivisions or areas of neocortex are responsible for more specific cognitive processes. In humans, the frontal lobe contains areas devoted to abilities that are enhanced in or unique to our species, such as complex language processing localized to the ventrolateral prefrontal cortex (Broca's area). [12] In humans and other primates, social and emotional processing is localized to the orbitofrontal cortex.

The neocortex has also been shown to play an influential role in sleep, memory and learning processes. Semantic memories appear to be stored in the neocortex, specifically the anterolateral temporal lobe of the neocortex. [16] It is also involved in instrumental conditioning; responsible for transmitting sensory information and information about plans for movement to the basal ganglia. [16] The firing rate of neurons in the neocortex also has an effect on slow-wave sleep. When the neurons are at rest and are hyperpolarizing, a period of inhibition occurs during a slow oscillation, called the down state. When the neurons of the neocortex are in the excitatory depolarizing phase and are firing briefly at a high rate, a period of excitation occurs during a slow oscillation, called the up state. [16]

Clinical significance

Lesions that develop in neurodegenerative disorders, such as Alzheimer's disease, interrupt the transfer of information from the sensory neocortex to the prefrontal neocortex. This disruption of sensory information contributes to the progressive symptoms seen in neurodegenerative disorders such as changes in personality, decline in cognitive abilities, and dementia. [17] Damage to the neocortex of the anterolateral temporal lobe results in semantic dementia, which is the loss of memory of factual information (semantic memories). These symptoms can also be replicated by transcranial magnetic stimulation of this area. If damage is sustained to this area, patients do not develop anterograde amnesia and are able to recall episodic information. [18]

Evolution

The neocortex is the newest part of the cerebral cortex to evolve (hence the prefix neo meaning new); the other part of the cerebral cortex is the allocortex. The cellular organization of the allocortex is different from the six-layered neocortex. In humans, 90% of the cerebral cortex and 76% of the entire brain is neocortex. [12]

For a species to develop a larger neocortex, the brain must evolve in size so that it is large enough to support the region. Body size, basal metabolic rate and life history are factors affecting brain evolution and the coevolution of neocortex size and group size. [19] The neocortex increased in size in response to pressures for greater cooperation and competition in early ancestors. With the size increase, there was greater voluntary inhibitory control of social behaviors resulting in increased social harmony. [20]

The six-layer cortex appears to be a distinguishing feature of mammals; it has been found in the brains of all mammals, but not in any other animals. [2] There is some debate, [21] [22] however, as to the cross-species nomenclature for neocortex. In avians, for instance, there are clear examples of cognitive processes that are thought to be neocortical in nature, despite the lack of the distinctive six-layer neocortical structure. [23] Evidence suggest the avian pallium to be broadly equivalent to the mammalian neocortex. [24] [25] In a similar manner, reptiles, such as turtles, have primary sensory cortices. A consistent, alternative name has yet to be agreed upon.

Neocortex ratio

The neocortex ratio of a species is the ratio of the size of the neocortex to the rest of the brain. A high neocortex ratio is thought to correlate with a number of social variables such as group size and the complexity of social mating behaviors. [26] Humans have a large neocortex as a percentage of total brain matter when compared with other mammals. For example, there is only a 30:1 ratio of neocortical gray matter to the size of the medulla oblongata in the brainstem of chimpanzees, while the ratio is 60:1 in humans. [27]

See also

Related Research Articles

<span class="mw-page-title-main">Brain</span> Organ that controls the nervous system in vertebrates and most invertebrates

The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. In vertebrates, a small part of the brain called the hypothalamus is the neural control center for all endocrine systems. The brain is the largest cluster of neurons in the body and is typically located in the head, usually near organs for special senses such as vision, hearing and olfaction. It is the most energy-consuming organ of the body, and the most specialized, responsible for endocrine regulation, sensory perception, motor control, and the development of intelligence.

<span class="mw-page-title-main">Cerebellum</span> Structure at the rear of the vertebrate brain, beneath the cerebrum

The cerebellum is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or even larger. In humans, the cerebellum plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language as well as emotional control such as regulating fear and pleasure responses, but its movement-related functions are the most solidly established. The human cerebellum does not initiate movement, but contributes to coordination, precision, and accurate timing: it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity. Cerebellar damage produces disorders in fine movement, equilibrium, posture, and motor learning in humans.

<span class="mw-page-title-main">Cerebral cortex</span> Outer layer of the cerebrum of the mammalian brain

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 role in attention, perception, awareness, thought, memory, language, and consciousness. The cerebral cortex is part of the brain responsible for cognition.

<span class="mw-page-title-main">Brodmann area</span> Region of the brain

A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. The concept was first introduced by the German anatomist Korbinian Brodmann in the early 20th century. Brodmann mapped the human brain based on the varied cellular structure across the cortex and identified 52 distinct regions, which he numbered 1 to 52. These regions, or Brodmann areas, correspond with diverse functions including sensation, motor control, and cognition.

<span class="mw-page-title-main">Cerebrum</span> Large part of the brain containing the cerebral cortex

The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex, as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In the human brain, the cerebrum is the uppermost region of the central nervous system. The cerebrum develops prenatally from the forebrain (prosencephalon). In mammals, the dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into approximately symmetric left and right cerebral hemispheres.

<span class="mw-page-title-main">Cortical minicolumn</span>

A cortical minicolumn (also called cortical microcolumn) is a vertical column through the cortical layers of the brain. Neurons within the microcolumn "receive common inputs, have common outputs, are interconnected, and may well constitute a fundamental computational unit of the cerebral cortex". Minicolumns comprise perhaps 80–120 neurons, except in the primate primary visual cortex (V1), where there are typically more than twice the number. There are about 2×108 minicolumns in humans. From calculations, the diameter of a minicolumn is about 28–40 μm. Minicolumns grow from progenitor cells within the embryo and contain neurons within multiple layers (2–6) of the cortex.

<span class="mw-page-title-main">Cortical column</span> Group of neurons in the cortex of the brain

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 Mountcastle in 1957. He later identified minicolumns as the basic units of the neocortex which were arranged into columns. Each contains the same types of neurons, connectivity, and firing properties. Columns are also called hypercolumn, macrocolumn, functional column or sometimes cortical module. Neurons within a minicolumn (microcolumn) encode similar features, whereas a hypercolumn "denotes a unit containing a full set of values for any given set of receptive field parameters". A cortical module is defined as either synonymous with a hypercolumn (Mountcastle) or as a tissue block of multiple overlapping hypercolumns.

<span class="mw-page-title-main">Archicortex</span> Phylogenetically oldest part of the cerebral cortex or pallium

The archicortex, or archipallium, is the phylogenetically second oldest region of the brain's cerebral cortex. It is often considered contiguous with the olfactory cortex, but its extent varies among species. In older species, such as fish, the archipallium makes up most of the cerebrum. Amphibians develop an archipallium and paleopallium.

<span class="mw-page-title-main">Gyrus</span> Ridge on the cerebral cortex of the brain

In neuroanatomy, a gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci. Gyri and sulci create the folded appearance of the brain in humans and other mammals.

The allocortex, or heterogenetic cortex, and neocortex are the two types of cerebral cortex in the brain. In the human brain, the allocortex is the much smaller area of cortex taking up just 10%; the neocortex takes up the remaining 90%. It is characterized by having just three or four cortical layers, in contrast with the six layers of the neocortex. There are three subtypes of allocortex: the paleocortex, the archicortex, and the periallocortex—a transitional zone between the neocortex and the allocortex.

<span class="mw-page-title-main">Sulcus (neuroanatomy)</span> Fold in the surface of the brain

In neuroanatomy, a sulcus is a depression or groove in the cerebral cortex. It surrounds a gyrus, creating the characteristic folded appearance of the brain in humans and other mammals. The larger sulci are usually called fissures.

The projection fibers consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the spinal cord. In human neuroanatomy, bundles of axons called tracts, within the brain, can be categorized by their function into association fibers, projection fibers, and commissural fibers.

<span class="mw-page-title-main">Radial glial cell</span> Bipolar-shaped progenitor cells of all neurons in the cerebral cortex and some glia

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 oligodendrocytes. Their cell bodies (somata) reside in the embryonic ventricular zone, which lies next to the developing ventricular system.

<span class="mw-page-title-main">Paleocortex</span> Region within the telencephalon in the vertebrate brain

In anatomy of animals, the paleocortex, or paleopallium, is a region within the telencephalon in the vertebrate brain. This type of cortical tissue consists of three cortical laminae. In comparison, the neocortex has six layers and the archicortex has three or four layers. Because the number of laminae that compose a type of cortical tissue seems to be directly proportional to both the information-processing capabilities of that tissue and its phylogenetic age, paleocortex is thought to be an intermediate between the archicortex and the neocortex in both aspects.

<span class="mw-page-title-main">Paralimbic cortex</span> Area of three-layered cortex

The paralimbic cortex is an area of three-layered cortex that includes the following regions: the piriform cortex, entorhinal cortex, the parahippocampal cortex on the medial surface of the temporal lobe, and the cingulate cortex just above the corpus callosum.

<span class="mw-page-title-main">Evolution of the brain</span> Overview of the evolution of the brain

There is much to be discovered about the evolution of the brain and the principles that govern it. While much has been discovered, not everything currently known is well understood. The evolution of the brain has appeared to exhibit diverging adaptations within taxonomic classes such as Mammalia and more vastly diverse adaptations across other taxonomic classes. Brain to body size scales allometrically. This means as body size changes, so do other physiological, anatomical, and biochemical constructs connecting the brain to the body. Small bodied mammals have relatively large brains compared to their bodies whereas large mammals have a smaller brain to body ratios. If brain weight is plotted against body weight for primates, the regression line of the sample points can indicate the brain power of a primate species. Lemurs for example fall below this line which means that for a primate of equivalent size, we would expect a larger brain size. Humans lie well above the line indicating that humans are more encephalized than lemurs. In fact, humans are more encephalized compared to all other primates. This means that human brains have exhibited a larger evolutionary increase in its complexity relative to its size. Some of these evolutionary changes have been found to be linked to multiple genetic factors, such as proteins and other organelles.

<span class="mw-page-title-main">Pallium (neuroanatomy)</span> Layers of grey and white matter that cover the upper surface of the cerebrum in vertebrates

In neuroanatomy, pallium refers to the layers of grey and white matter that cover the upper surface of the cerebrum in vertebrates. The non-pallial part of the telencephalon builds the subpallium. In basal vertebrates, the pallium is a relatively simple three-layered structure, encompassing 3–4 histogenetically distinct domains, plus the olfactory bulb.

Gyrification is the process of forming the characteristic folds of the cerebral cortex.

Agranular insula is a portion of the cerebral cortex defined on the basis of internal structure in the human, the macaque, the rat, and the mouse. Classified as allocortex (periallocortex), it is in primates distinguished from adjacent neocortex (proisocortex) by absence of the external granular layer (II) and of the internal granular layer (IV). It occupies the anterior part of the insula, the posterior portion of the orbital gyri and the medial part of the temporal pole. In rodents it is located on the ventrolateral surface of the cortex rostrally, between the piriform area ventrally and the gustatory area or the visceral area dorsally.

<span class="mw-page-title-main">Radial unit hypothesis</span> Conceptual theory of cerebral cortex development

The Radial Unit Hypothesis (RUH) is a conceptual theory of cerebral cortex development, first described by Pasko Rakic. The RUH states that the cerebral cortex develops during embryogenesis as an array of interacting cortical columns, 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 cells.

References

  1. ↑ Lodato S, Arlotta P (2015-11-13). "Generating neuronal diversity in the mammalian cerebral cortex". Annual Review of Cell and Developmental Biology. 31 (1): 699–720. doi:10.1146/annurev-cellbio-100814-125353. PMC   4778709 . PMID   26359774. The neocortex is the part of the brain responsible for execution of higher-order brain functions, including cognition, sensory perception, and sophisticated motor control.
  2. 1 2 Lui JH, Hansen DV, Kriegstein AR (July 2011). "Development and evolution of the human neocortex". Cell. 146 (1): 18–36. doi:10.1016/j.cell.2011.06.030. PMC   3610574 . PMID   21729779.
  3. ↑ "BrainInfo". braininfo.rprc.washington.edu.
  4. ↑ Saladin, K (2012). Anatomy & physiology : the unity of form and function (6th ed.). New York, NY: McGraw-Hill. p. 417. ISBN   9780073378251.
  5. ↑ Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier Saunders. 2012. p. 1238. ISBN   978-1-4160-6257-8.
  6. ↑ Kandel E (2006). Principles of neural science (5th ed.). Appleton and Lange: McGraw Hill. ISBN   978-0071390118.
  7. ↑ Mortensen HS, Pakkenberg B, Dam M, Dietz R, Sonne C, Mikkelsen B, Eriksen N (2014). "Quantitative relationships in delphinid neocortex". Frontiers in Neuroanatomy. 8: 132. doi: 10.3389/fnana.2014.00132 . PMC   4244864 . PMID   25505387.
  8. ↑ Moerel M, De Martino F, Formisano E (2006). "An anatomical and functional topography of human auditory cortical areas". Front. Neurosci. 8 (225): 225. doi: 10.3389/fnins.2014.00225 . PMC   4114190 . PMID   25120426. For example, in the human brain, the auditory cortex presents an expansion of cortical surface, with additional gyri and with a much larger inter-individual variability...
  9. ↑ Van Essen DC (January 1997). "A tension-based theory of morphogenesis and compact wiring in the central nervous system" (PDF). Nature. 385 (6614): 313–8. doi:10.1038/385313a0. PMID   9002514. S2CID   4355025.
  10. ↑ Richman DP, Stewart RM, Hutchinson JW, Caviness VS (July 1975). "Mechanical model of brain convolutional development". Science. 189 (4196): 18–21. doi:10.1126/science.1135626. PMID   1135626.
  11. ↑ Ronan L, Voets N, Rua C, Alexander-Bloch A, Hough M, Mackay C, Crow TJ, James A, Giedd JN, Fletcher PC (August 2014). "Differential tangential expansion as a mechanism for cortical gyrification". Cerebral Cortex. 24 (8): 2219–28. doi:10.1093/cercor/bht082. PMC   4089386 . PMID   23542881.
  12. 1 2 3 4 Noback CR, Strominger NL, Demarest RJ, Ruggiero DA (2005). The Human Nervous System: Structure and Function (Sixth ed.). Totowa, NJ: Humana Press. ISBN   1-59259-730-0.
  13. ↑ Berg, Jim; Sorensen, Staci A.; Ting, Jonathan T.; Miller, Jeremy A.; Chartrand, Thomas; Buchin, Anatoly; Bakken, Trygve E.; Budzillo, Agata; Dee, Nick; Ding, Song-Lin; Gouwens, Nathan W.; Hodge, Rebecca D.; Kalmbach, Brian; Lee, Changkyu; Lee, Brian R. (October 2021). "Human neocortical expansion involves glutamatergic neuron diversification". Nature. 598 (7879): 151–158. doi: 10.1038/s41586-021-03813-8 . ISSN   1476-4687. PMC   8494638 . PMID   34616067.
  14. ↑ Kurzweil R (2012). How to Create a Mind: The Secret of Human Thought Revealed. New York: Viking Penguin. p. 36. ISBN   978-0670025299.
  15. ↑ Horton JC, Adams DL (April 2005). "The cortical column: a structure without a function". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 360 (1456): 837–62. doi:10.1098/rstb.2005.1623. PMC   1569491 . PMID   15937015.
  16. 1 2 3 Carlson N (2013). Physiology of Psychology (Eleventh ed.). Pearson. ISBN   978-0-205-239481.
  17. ↑ Braak H, Del-Tredici K, Bohl J, Bratzke H, Braak E (2000). Annals of the New York academy of sciences, Vol. 911. New York, NY, US: New York Academy of Sciences. ISBN   1-57331-263-0.
  18. ↑ Carlson N (2013). Physiology of Behavior. Pearson. ISBN   978-0-205-23948-1.
  19. ↑ Dunbar RI, Shultz S (April 2007). "Understanding primate brain evolution". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 362 (1480): 649–58. doi:10.1098/rstb.2006.2001. PMC   2346523 . PMID   17301028.
  20. ↑ Bjorklund D, Kipp K (2002). Social cognition, inhibition, and theory of mind: The evolution of human intelligence. Mahwah, NJ: Lawrence Erlbaum Associate Publishers. ISBN   0-8058-3267-X.
  21. ↑ Jarvis ED, Güntürkün O, Bruce L, Csillag A, Karten H, Kuenzel W, et al. (February 2005). "Avian brains and a new understanding of vertebrate brain evolution". Nature Reviews. Neuroscience. 6 (2): 151–9. doi:10.1038/nrn1606. PMC   2507884 . PMID   15685220.
  22. ↑ Reiner A, Perkel DJ, Bruce LL, Butler AB, Csillag A, Kuenzel W, et al. (May 2004). "Revised nomenclature for avian telencephalon and some related brainstem nuclei". The Journal of Comparative Neurology. 473 (3): 377–414. doi:10.1002/cne.20118. PMC   2518311 . PMID   15116397.
  23. ↑ Prior H, Schwarz A, Güntürkün O (August 2008). De Waal F (ed.). "Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition". PLOS Biology. 6 (8): e202. doi: 10.1371/journal.pbio.0060202 . PMC   2517622 . PMID   18715117.
  24. ↑ Nieder, Andreas; Wagener, Lysann; Rinnert, Paul (September 25, 2020). "A neural correlate of sensory consciousness in a corvid bird". Science. 369 (6511): 1626–1629. doi:10.1126/science.abb1447. ISSN   0036-8075.
  25. ↑ Herculano-Houzel, Suzana (September 25, 2020). "Birds do have a brain cortex—and think". Science. 369 (6511): 1567–1568. doi:10.1126/science.abe0536. ISSN   0036-8075.
  26. ↑ Dunbar RI (1995). "Neocortex size and group size in primates: A test of the hypothesis". Journal of Human Evolution. 28 (3): 287–96. doi:10.1006/jhev.1995.1021.
  27. ↑ Semendeferi K, Lu A, Schenker N, Damasio H (March 2002). "Humans and great apes share a large frontal cortex". Nature Neuroscience. 5 (3): 272–6. doi:10.1038/nn814. PMID   11850633. S2CID   5921065.
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