View source for Archicortex

{{short description|Phylogenetically oldest part of the cerebral cortex or pallium}}
{{Infobox Brain
| Name            = Archicortex
| Latin           = archicortex
| Image           = CajalHippocampus (modified).png
| Caption         = 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
| Image2          =
| Caption2        =
| IsPartOf        = [[cerebral cortex]] or [[Pallium (neuroanatomy)|pallium]]
| System          = [[Olfactory system]]
}}

The '''archicortex''', or '''archipallium''', is the [[Phylogenetics|phylogenetically]] second oldest region of the [[brain]]'s [[cerebral cortex]] (the oldest is the [[paleocortex]]). In older species, such as fish, the archipallium makes up most of the [[telencephalon|cerebrum]]. [[Amphibian]]s develop an archipallium and [[paleopallium]]. 

In humans, the archicortex makes up the three [[cortical layer]]s of the [[hippocampus]].<ref name="Purves1">{{cite book |last1=Purves |first1=Dale |title=Neuroscience |date=2012 |location=Sunderland, Mass. |isbn=9780878936953 |page=731 |edition=5th}}</ref> It has fewer [[cortical layer]]s 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 subtype of [[allocortex]].<ref name="BrainInfo Paleocortex">{{cite web|title=Paleocortex|url=http://braininfo.rprc.washington.edu/centraldirectory.aspx?type=a&ID=2336|work=BrainInfo|publisher=University of Washington|access-date=5 May 2013}}</ref> Because the number of cortical layers that make up a type of cortical tissue seems to be directly proportional{{clarify|date=February 2024}} to both the information-processing capabilities of that tissue and its [[phylogenetics|phylogenetic age]], the archicortex is thought to be the oldest and most basic type of cortical tissue.<ref name="Purves 2011">{{cite book|author=Purves, Dale|author2=Augustine, George J|author3=Fitzpatrick, David|author4=Hall, William C|author5=LaMantia, Anthony-Samuel|author6=White, Leonard E|title=Neuroscience|year=2011|publisher=Sinauer Associates Inc.|isbn=9780878936465|edition=5th}}</ref>

==Location==
The archicortex is most prevalent in the [[primary olfactory cortex|olfactory cortex]] and the [[hippocampus]],<ref>{{cite journal|last1=Wills|first1=Tom J.|last2=Cacucci|first2=Francesca |last3=Burgess|first3=Neil|last4=O'Keefe|first4=John|title=Development of the Hippocampal Cognitive Map in Preweanling Rats|journal=Science|date=18 June 2010|volume=328|issue=5985 |pages=1573–1576|doi=10.1126/science.1188224|pmid=20558720|pmc=3543985|bibcode=2010Sci...328.1573W}}</ref> which are responsible for processing smells and forming memories, respectively.<ref name="Haberly 1990">{{cite book|last=Haberly|first=Lewis B|title=Cerebral Cortex|year=1990|isbn=978-1-4615-3824-0 |pages=137–166|edition=8B|chapter=Comparative Aspects of Olfactory Cortex|publisher=Springer }}</ref> Because olfaction is considered to be the phylogenetically oldest sensory modality,<ref>{{cite journal|last1=Albrecht|first1=J.|last2=Wiesmann|first2=M.|title=Das olfaktorische System des Menschen|journal=Der Nervenarzt|date=August 2006|volume=77|issue=8 |pages=931–939|doi=10.1007/s00115-006-2121-z|pmid=16871378}}</ref> and the [[limbic system]], of which the hippocampus is a part, is one of the oldest systems in the brain,<ref name=":0">{{cite journal |last1=Rajmohan|first1=V.|last2=Mohandas|first2=E.|title=The limbic system|journal=Indian Journal of Psychiatry|date=April–June 2007|volume=49|issue=2|pages=132–139 |doi=10.4103/0019-5545.33264|pmid=20711399|pmc=2917081 |doi-access=free }}</ref> it is likely that the archicortex was one of the first types of tissue to develop in primitive [[nervous system]]s.<ref name=":0" />

Archicortical precursor cells are also present in the [[dentate gyrus]] of the developing [[mammal]]ian [[embryo]].<ref>{{cite journal|last1=Pellegrini|first1=M.|last2=Mansouri |first2=A.|last3=Simeone|first3=A.|last4=Boncinelli|first4=E.|last5=Gruss|first5=P.|title=Dentate gyrus formation requires Emx2|journal=Development|date=December 1996|volume=122|issue=12 |pages=3893–3898|doi=10.1242/dev.122.12.3893|pmid=9012509|hdl=11858/00-001M-0000-0013-00C2-8|hdl-access=free}}</ref>

== Structure ==
The archicortex is largely made up of memorizing cells with two types of afferent synapses: excitatory and unmodifiable inhibitory synapses.<ref name=":1">{{Cite journal|last1=Marr|first1=D.|last2=Brindley|first2=Giles Skey|date=1971-07-01|title=Simple memory: a theory for archicortex|journal= Philosophical Transactions of the Royal Society B: Biological Sciences|volume=262|issue=841|pages=23–81|doi=10.1098/rstb.1971.0078|pmid=4399412|bibcode=1971RSPTB.262...23M|doi-access=}}</ref> 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.<ref name=":1" />  Unlike the [[neocortex]], the archicortex lacks climbing fibers (fibers involved in the clustering part of neocortical classification).<ref name=":1" /> Consequently, the archicortex is not adapted for this type of classification.<ref name=":1" />

== 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.<ref name=":1" /> The archicortex is unable to classify inputs. It has two main uses: free simple memory and directed simple memory.<ref name=":1" />

==See also==
* [[Paralimbic cortex]]
* [[List of regions in the human brain|Regions in the human brain]]

==References==
{{Reflist}}

{{Cortex types}}
{{Hippocampal formation}}
{{Commissural fibers}}
{{Authority control}}

[[Category:Cerebrum]]
[[Category:Cerebral cortex]]
[[Category:Neuroanatomy]]
[[Category:Hippocampus (brain)]]


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