Editing Hippocampus (section)

==Anatomy==
{{See also |Hippocampus anatomy}}
[[File:Sobo 1909 639.png|thumb|right|220px| Cross-section of [[cerebral hemisphere]] showing structure and location of hippocampus]]
[[File:Brainmaps-macaque-hippocampus.jpg|thumb|220px| [[Coronal plane|Coronal]] section of the brain of a [[macaque]] monkey, showing hippocampus (circled)]]
The hippocampus is a five centimeter long ridge of [[Gray matter|gray matter tissue]] within the [[parahippocampal gyrus]] that can only be seen when the gyrus is opened up.<ref name="Fogwe2023">{{cite journal |last1=Fogwe |first1=Leslie A. |last2=Reddy |first2=Vamsi |last3=Mesfin |first3=Fassil B. |title=Neuroanatomy, Hippocampus |url=https://www.ncbi.nlm.nih.gov/books/NBK482171/#:~:text=The%20hippocampus%20has%20three%20distinct,and%20entorhinal%20and%20other%20cortices. |website=StatPearls |publisher=StatPearls Publishing |date=2025|pmid=29489273 }}</ref><ref name="Purves">{{cite book|title=Neuroscience|date=2011|publisher=Sinauer|isbn=978-0-87893-695-3 |edition=5th|location=Sunderland, MA|pages=730–735| vauthors = Purves D }}</ref> The hippocampus is an inward fold of three-layered  [[archicortex]] (one of three regions of the [[allocortex]]) into the [[Temporal lobe#Medial temporal lobe|medial temporal lobe]] of the brain, where it elevates into the floor of each [[lateral ventricle]] [[Lateral ventricle#Inferior horn of lateral ventricle|inferior horn]].<ref name="Morris and Amaral2024">{{cite book |last1=Morris |first1=Richard |last2=Amaral |first2=David |title=The Hippocampus Book |date=2024 |pages= 49–50|publisher=Oxford University Press, Incorporated |location=Oxford |isbn=9780190065324 |edition=2nd}}</ref><ref name="Creutzfeldt">{{cite journal |last1=Creutzfeldt |first1=O.D. |title=The allocortex and limbic system |journal=Cortex Cerebri: Performance, Structural and Functional Organisation of the Cortex |date=27 April 1995 |pages=486–540 |doi=10.1093/acprof:oso/9780198523246.003.0009|isbn=978-0-19-852324-6 }}</ref><ref name="Anderson"/><ref>{{cite journal | vauthors = Bachevalier J | title = Nonhuman primate models of hippocampal development and dysfunction | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 116 | issue = 52 | pages = 26210–26216 | date = December 2019 | pmid = 31871159 | pmc = 6936345 | doi = 10.1073/pnas.1902278116 | doi-access = free | bibcode = 2019PNAS..11626210B }}</ref> The hippocampus stretches along its anterior-posterior axis, from the [[amygdala]] to the [[Corpus callosum#Splenium|splenium of the corpus callosum]], with the head, body, and tail regions as subdivisions of this axis.<ref name="Sun">{{cite journal |vauthors=Sun F, Shuai Y, Wang J, Yan J, Lin B, Li X, Zhao Z |title=Hippocampal gray matter volume alterations in patients with first-episode and recurrent major depressive disorder and their associations with gene profiles |journal=BMC Psychiatry |volume=25 |issue=1 |pages=134 |date=February 2025 |pmid=39955494 |doi=10.1186/s12888-025-06562-4 |doi-access=free |pmc=11829352 |url=}}</ref><ref name="Fogwe2023"/> The [[dentate gyrus]], CA subfields, [[Fimbria (neuroanatomy)|fimbria]], and [[subiculum]] are divisions across the short axis, the proximal-distal axis.<ref name="Sun"/>

The [[hippocampal formation]] refers to the hippocampus, and its related adjoining parts to include the dentate gyrus, the subiculum, the [[presubiculum]], [[parasubiculum]], and the [[entorhinal cortex]].<ref name="Morris and Amaral2024"/> Sometimes the subiculum, presubiculum, and parasubiculum are grouped together as the ''subicular complex'', but the regions are neuroanatomically distinct. Some sources may only include the hippocampus, dentate gyrus, and subiculum, being regions of the hippocampal three-layered archicortex.<ref name="Morris and Amaral2024"/> But the six regions are linked together serially by almost unidirectional neural pathways.<ref name="Morris and Amaral2024"/> Other sources include the [[indusium griseum]], [[gyrus fasciolaris]], the [[medial longitudinal stria|medial]] and [[longitudinal striae]], and [[uncus]], and exclude subicular regions.<ref name="Singh">{{cite book |last1=Singh |first1=Vishram |title=Textbook. of Anatomy Vol III |date=2017 |publisher=Elsevier |isbn=9788131237274 |page=402}}</ref><ref name="Chauhan">{{cite journal |last1=Chauhan |first1=Pradip |last2=Jethwa |first2=Kinjal |last3=Rathawa |first3=Ashish |last4=Chauhan |first4=Girish |last5=Mehra |first5=Simmi |title=The Anatomy of the Hippocampus |url=https://www.ncbi.nlm.nih.gov/books/NBK575732/ |website=Cerebral Ischemia |publisher=Exon Publications |access-date=19 March 2025 |date=2021|pmid=34905307 }}</ref> The neural layout and pathways within the hippocampal formation are very similar in all mammals.<ref name="Anderson">{{cite book|vauthors= Anderson P, Morris R, Amaral, Bliss T, O'Keefe J|veditors= Anderson P, Morris R, Amaral, Bliss T, O'Keefe J|title= The hippocampus book|edition= first|year= 2007|publisher= Oxford University Press|location= New York|isbn= 978-0195100273|pages=3–77 |chapter = The hippocampal formation|chapter-url= https://books.google.com/books?id=zg6oyF1DziQC&pg=PA3|access-date= 2016-12-15|archive-date= 2020-03-15|archive-url= https://web.archive.org/web/20200315125212/https://books.google.com/books?id=zg6oyF1DziQC&pg=PA3|url-status= live}}</ref>

The hippocampus has a generally similar appearance across the range of mammals, from [[Monotreme|egg-laying mammals]] such as the [[echidna]], to humans and other [[primate]]s.<ref>{{cite book | ref=refWest1990 | vauthors = West MJ | title = Stereological studies of the hippocampus: a comparison of the hippocampal subdivisions of diverse species including hedgehogs, laboratory rodents, wild mice and men | volume = 83 | pages = 13–36 | year = 1990 | pmid = 2203095 | doi = 10.1016/S0079-6123(08)61238-8 | isbn = 978-0-444-81149-3 | series = Progress in Brain Research | chapter = Chapter 2 Stereological studies of the hippocampus: A comparison of the hippocampal subdivisions of diverse species including hedgehogs, laboratory rodents, wild mice and men }}</ref> The hippocampal-size-to-body-size ratio broadly increases, being about twice as large for primates as for the echidna. It does not, however, increase at anywhere close to the rate of the [[neocortex]]-to-body-size ratio. Therefore, the hippocampus takes up a much larger fraction of the cortical mantle in rodents than in primates. In adult humans the volume of the hippocampus on each side of the brain is about 3.0 to 3.5&nbsp;cm<sup>3</sup> as compared to 320 to 420&nbsp;cm<sup>3</sup> for the volume of the neocortex.<ref>* {{cite journal | vauthors = Suzuki M, Hagino H, Nohara S, Zhou SY, Kawasaki Y, Takahashi T, Matsui M, Seto H, Ono T, Kurachi M | title = Male-specific volume expansion of the human hippocampus during adolescence | journal = Cerebral Cortex | volume = 15 | issue = 2 | pages = 187–193 | date = February 2005 | pmid = 15238436 | doi = 10.1093/cercor/bhh121 | ref = refSuzuki2005 | doi-access = free }}</ref> There is also a general relationship between the size of the hippocampus and spatial memory. When comparisons are made between similar species, those that have a greater capacity for spatial memory tend to have larger hippocampal volumes.<ref name="Jacobs2003">{{cite journal | vauthors = Jacobs LF | title = The evolution of the cognitive map | journal = Brain, Behavior and Evolution | volume = 62 | issue = 2 | pages = 128–139 | year = 2003 | pmid = 12937351 | doi = 10.1159/000072443 | ref = refJacobs2003 | s2cid = 16102408 }}</ref>