Allocortex

Last updated
Allocortex
Identifiers
NeuroNames 1598
NeuroLex ID nlx_143557
TA98 A14.1.09.305
TA2 5529
FMA 83687
Anatomical terms of neuroanatomy

The allocortex (from Latin allo-, meaning other, and cortex, meaning bark or crust), 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%. [1] It is characterized by having just three cortical layers (one main neural layer), in contrast with the six cortical layers of the neocortex. [2] There are three subtypes of allocortex: the paleocortex, the archicortex, and the periallocortex—a transitional zone between the neocortex and the allocortex. [3]

Contents

The specific regions of the brain usually described as belonging to the allocortex are the olfactory system and the hippocampus.

Allocortex is termed heterogenetic cortex, because during development it never has the six-layered architecture of homogenetic neocortex. It differs from heterotypic cortex, a type of cerebral cortex, which during prenatal development, passes through a six-layered stage to have fewer layers, such as the agranular cortex such as Brodmann area 4 that lacks granule cells. [4]

Structure

The allocortex has three layers (one main neuronal layer) in contrast to the six layers of the neocortex. [2] There are three subtypes of allocortex: the paleocortex, archicortex and periallocortex. [5]

Paleocortex is a type of thin, primitive cortical tissue that consists of three cortical laminae (layers of neuronal cell bodies). [6] [7] The two granular layers II and IV of neocortex are absent in paleocortex. The main areas of paleocortex are the olfactory bulb, olfactory tubercle and piriform cortex.

Archicortex is a type of cortical tissue that consists of four laminae (layers of neuronal cell bodies). [8] The main areas of archicortex are the hippocampus and dentate gyrus.

Periallocortex is a transitional form between neocortex and either paleo- or archicortex. It thus can be either peripaleocortex (anterior insular cortex) or periarchicortex (entorhinal cortex, presubicular cortex, retrosplenial, supracallosal, and subgenual areas).

Because the number of laminae that compose a type of cortical tissue seems to be directly proportional [ citation needed ] to both the information-processing capabilities of that tissue and its phylogenetic age, and also because olfaction is a major sensory modality in phylogenetically early animals, paleocortex is thought to be the most primitive form of cortex. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Central nervous system</span> Brain and spinal cord

The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts. It is a structure composed of nervous tissue positioned along the rostral to caudal axis of the body and may have an enlarged section at the rostral end which is a brain. Only arthropods, cephalopods and vertebrates have a true brain, though precursor structures exist in onychophorans, gastropods and lancelets.

<span class="mw-page-title-main">Entorhinal cortex</span> Area of the temporal lobe of the brain

The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning; the association of impulses from the eye and the ear occurs in the entorhinal cortex.

<span class="mw-page-title-main">Hippocampus</span> Vertebrate brain region involved in memory consolidation

The hippocampus is a major component of the brain of humans and other vertebrates. The hippocampus is part of the limbic system, and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. In humans, and other primates the hippocampus is located in the archicortex, one of the three regions of allocortex, with neural projections to the neocortex. The hippocampus, as the medial pallium, is a structure found in all vertebrates. In the human brain, it contains two main interlocking parts: the hippocampus proper, and the dentate gyrus.

<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 the part of the brain responsible for cognition.

Proisocortex or pro-isocortex is one of two subtypes of cortical areas in the areas belonging to the neocortex. The other subtype is termed the true isocortex. Proisocortical areas are transitional areas placed between areas of true isocortex and areas of periallocortex. The histological structure of proisocortex is also transitional between true isocortex and either peripaleocortex or periarchicortex, depending on with which subtype of periallocortex the given proisocortical area borders.

<span class="mw-page-title-main">Neocortex</span> Mammalian structure involved in higher-order brain functions

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, spatial reasoning and language. The neocortex is further subdivided into the true isocortex and the proisocortex.

In the anatomy of animals, paleoencephalon refers to most regions in the brain that are not part of the neocortex or neoencephalon.

<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. In older species, such as fish, the archipallium makes up most of the cerebrum. Amphibians develop an archipallium and paleopallium.

An apical dendrite is a dendrite that emerges from the apex of a pyramidal cell. Apical dendrites are one of two primary categories of dendrites, and they distinguish the pyramidal cells from spiny stellate cells in the cortices. Pyramidal cells are found in the prefrontal cortex, the hippocampus, the entorhinal cortex, the olfactory cortex, and other areas. Dendrite arbors formed by apical dendrites are the means by which synaptic inputs into a cell are integrated. The apical dendrites in these regions contribute significantly to memory, learning, and sensory associations by modulating the excitatory and inhibitory signals received by the pyramidal cells.

In the rodent, the parasubiculum is a retrohippocampal isocortical structure, and a major component of the subicular complex. It receives numerous subcortical and cortical inputs, and sends major projections to the superficial layers of the entorhinal cortex.

<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.

In the rodent, the parasubiculum is a retrohippocampal isocortical structure, and a major component of the subicular complex. It receives numerous subcortical and cortical inputs, and sends major projections to the superficial layers of the entorhinal cortex.

<span class="mw-page-title-main">Ganglionic eminence</span>

The ganglionic eminence (GE) is a transitory structure in the development of the nervous system that guides cell and axon migration. It is present in the embryonic and fetal stages of neural development found between the thalamus and caudate nucleus.

<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.

Mesocortex is the transitional areas of the cerebral cortex, formed at borders between true isocortex and true allocortex. Parts of mesocortex that lie closer to the true isocortex and have more resemblance to the isocortex in their cytoarchitectonics and histology, are called proisocortex. Parts of mesocortex that lie closer to the true allocortex and have more resemblance to the allocortex in their cytoarchitectonics and histology, are called periallocortex.

Sharp waves and ripples (SWRs) are oscillatory patterns produced by extremely synchronised activity of neurons in the mammalian hippocampus and neighbouring regions which occur spontaneously in idle waking states or during NREM sleep. They can be observed with a variety of imaging methods, such as EEG. They are composed of large amplitude sharp waves in local field potential and produced by tens of thousands of neurons firing together within 30–100 ms window. They are some of the most synchronous oscillations patterns in the brain, making them susceptible to pathological patterns such as epilepsy.They have been extensively characterised and described by György Buzsáki and have been shown to be involved in memory consolidation in NREM sleep and the replay of memories acquired during wakefulness.

Cajal–Retzius cells are a heterogeneous population of morphologically and molecularly distinct reelin-producing cells. They are found in the marginal zone/layer I of the developing cerebral cortex and in the immature hippocampus of different species and at different times during embryogenesis and postnatal life.

Periallocortex is one of three subtypes of allocortex, the other two subtypes being paleocortex and archicortex. The periallocortex is formed at transition areas where any of the other two subtypes of allocortex borders with the neocortex.

Peripaleocortex is one of two subtypes of periallocortex, the other being periarchicortex. Peripaleocortex is formed at borders between isocortex (neocortex) and paleocortex. It shows slow histological transition from the three-layered structure characteristic of paleocortex to the typical six-layered structure characteristic of isocortex. The main peripaleocortex area is anterior insular cortex.

References

  1. Saladin, K (2012). Anatomy & physiology : the unity of form and function (6th ed.). New York, NY: McGraw-Hill. p. 417. ISBN   9780073378251.
  2. 1 2 Insausti, R; Muñoz-López, M; Insausti, AM; Artacho-Pérula, E (2017). "The Human Periallocortex: Layer Pattern in Presubiculum, Parasubiculum and Entorhinal Cortex. A Review". Frontiers in Neuroanatomy. 11: 84. doi: 10.3389/fnana.2017.00084 . PMC   5632821 . PMID   29046628.
  3. "periallocortex". University of Washington. Archived from the original on 2024-09-01. Retrieved 2024-12-14.
  4. Crosby EC; Humphrey T; Lauer EW (1962)Correlative Anatomy of the Nervous System. New York: MacMillan
  5. Filimonoff, IN (1947). "A rational subdivision of the cerebral cortex". Arch Neurol Psychiatry. 58 (3): 296–311. doi:10.1001/archneurpsyc.1947.02300320047002. PMID   20265596.
  6. "Paleocortex". BrainInfo. University of Washington. Retrieved 5 May 2013.
  7. 1 2 Purves, Dale; Augustine, George J; Fitzpatrick, David; Hall, William C; LaMantia, Anthony-Samuel; White, Leonard E (2011). Neuroscience (5th ed.). Sinauer Associates Inc. p. 666. ISBN   9780878936465.
  8. "Archicortex". BrainInfo. University of Washington. Retrieved 17 March 2017.