Archicortex
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The archicortex, or archipallium, is the 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 cerebrum. Amphibians develop an archipallium and paleopallium.
In humans, the archicortex makes up the three cortical layers of the hippocampus.<ref name="Purves1">Template:Cite book</ref> It has fewer cortical layers 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">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Because the number of cortical layers that make up a type of cortical tissue seems to be directly proportionalTemplate:Clarify 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.<ref name="Purves 2011">Template:Cite book</ref>
LocationEdit
The archicortex is most prevalent in the olfactory cortex and the hippocampus,<ref>Template:Cite journal</ref> which are responsible for processing smells and forming memories, respectively.<ref name="Haberly 1990">Template:Cite book</ref> Because olfaction is considered to be the phylogenetically oldest sensory modality,<ref>Template:Cite journal</ref> and the limbic system, of which the hippocampus is a part, is one of the oldest systems in the brain,<ref name=":0">Template:Cite journal</ref> it is likely that the archicortex was one of the first types of tissue to develop in primitive nervous systems.<ref name=":0" />
Archicortical precursor cells are also present in the dentate gyrus of the developing mammalian embryo.<ref>Template:Cite journal</ref>
StructureEdit
The archicortex is largely made up of memorizing cells with two types of afferent synapses: excitatory and unmodifiable inhibitory synapses.<ref name=":1">Template:Cite journal</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" />
MemoryEdit
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 alsoEdit
ReferencesEdit
Template:Cortex types Template:Hippocampal formation Template:Commissural fibers Template:Authority control