Archicortex

In anatomy of animals, the archicortex, or archipallium, is the phylogenetically oldest region of the brain's pallium or 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, whereas reptiles develop an archipallium, paleopallium and a primitive neopallium. In humans, the archipallium makes up the hippocampus.

Archicortex
The archicortex in humans is a synonym of the hippocampal formation. The hippocampal formation is shown here, as drawn by Santiago Ramon y Cajal: DG: dentate gyrus. Sub: subiculum. EC: entorhinal cortex. CA1-CA3: hippocampus proper
Details
Part of	cerebral cortex or pallium
System	Olfactory system
Identifiers
Latin	Archicortex
NeuroNames	170
NeuroLex ID	birnlex_715
TA	A14.1.09.302
TE	E5.14.3.4.3.1.32, E5.14.3.4.3.1.31
FMA	62424
Anatomical terms of neuroanatomy

The archicortex is also defined as a type of cortical tissue that consists of three cortical laminae (layers of neuronal cell bodies).[1] It has fewer laminae than both the neocortex, which has six, and the paleocortex, which has either four or five. The archicortex, along with the paleocortex and periallocortex, is a type of allocortex.[2] 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, the archicortex is thought to be the oldest and most basic type of cortical tissue.[1]

Location

The archicortex is most prevalent in the olfactory cortex and the hippocampus,[3] which are responsible for processing smells and forming memories, respectively.[4] Because olfaction is considered to be the phylogenetically oldest sensory modality,[5] and the limbic system, of which the hippocampus is a part, is one of the oldest systems in the brain,[6] it is likely that the archicortex was one of the first types of tissue to develop in primitive nervous systems.[6]

Archicortical precursor cells are also present in the dentate gyrus of the developing mammalian embryo.[7]

Structure

The archicortex is largely made up of memorizing cells with two types of afferent synapses: excitatory and unmodifiable inhibitory synapses.[8] Memorizing cell inhibition serves two functions; one is controlling synaptic modification conditions in the memorizing cell dendrites during learning and the other is controlling cell thresholds during recall.[8] The archicortex may also contain codon cells.[8] Unlike the neocortex, the archicortex lacks climbing fibers (fibers involved in the clustering part of neocortical classification).[8] Consequently, the archicortex is not adapted for this type of classification.[8]

Memory

Unlike the neocortex, current theories of the archicortex argue that it performs simple memorization without changing the input's format in any complex manner.[8] The archicortex is unable to classify inputs. It has two main uses: free simple memory and directed simple memory.[8]

See also

• Paralimbic cortex
• Regions in the human brain

References

1. Purves, Dale; Augustine, George J; Fitzpatrick, David; Hall, William C; LaMantia, Anthony-Samuel; White, Leonard E (2011). Neuroscience (5th ed.). Sinauer Associates Inc. ISBN 9780878936465.
2. "Paleocortex". BrainInfo. University of Washington. Retrieved 5 May 2013.
3. Wills, Tom J.; Cacucci, Francesca; Burgess, Neil; O'Keefe, John (18 June 2010). "Development of the Hippocampal Cognitive Map in Preweanling Rats". Science. 328 (5985): 1573–1576. Bibcode:2010Sci...328.1573W. doi:10.1126/science.1188224. PMC 3543985. PMID 20558720.
4. Haberly, Lewis B (1990). "Comparative Aspects of Olfactory Cortex". Cerebral Cortex (8B ed.). pp. 137–166. ISBN 978-1-4615-3824-0.
5. Albrecht, J.; Wiesmann, M. (August 2006). "Das olfaktorische System des Menschen". Der Nervenarzt. 77 (8): 931–939. doi:10.1007/s00115-006-2121-z. PMID 16871378.
6. Rajmohan, V.; Mohandas, E. (April–June 2007). "The limbic system". Indian Journal of Psychiatry. 49 (2): 132–139. doi:10.4103/0019-5545.33264. PMC 2917081. PMID 20711399.
7. Pellegrini, M.; Mansouri, A.; Simeone, A.; Boncinelli, E.; Gruss, P. (December 1996). "Dentate gyrus formation requires Emx2". Development. 122 (12): 3893–3898. PMID 9012509.
8. Marr, D.; Brindley, Giles Skey (1971-07-01). "Simple memory: a theory for archicortex". Philosophical Transactions of the Royal Society B: Biological Sciences. 262 (841): 23–81. Bibcode:1971RSPTB.262...23M. doi:10.1098/rstb.1971.0078. PMID 4399412.