Editing Hippocampus (section)

===Subfields===
[[File:Hippocampus coronal section176157.fig.004.jpg|thumb|260px| Hippocampal subregions, and [[Hippocampal subfields|subfields]]]]
[[File:Golgi Hippocampus.jpg|thumb|260px| Drawing by Italian pathologist [[Camillo Golgi]] of a hippocampus [[Staining|stained]] using [[silver nitrate]]]]
[[Hippocampal subfields]], and subregions, head, body, and tail, are functionally and anatomically differentiated, and connect differently to other brain regions.<ref name="Xiao2023">{{cite journal |vauthors=Xiao Y, Hu Y, Huang K |title=Atrophy of hippocampal subfields relates to memory decline during the pathological progression of Alzheimer's disease |journal=Front Aging Neurosci |volume=15 |issue= |pages=1287122 |date=2023 |pmid=38149170 |pmc=10749921 |doi=10.3389/fnagi.2023.1287122 |doi-access=free |url=}}</ref><ref name="Canada2020">{{cite journal |vauthors=Canada KL, Botdorf M, Riggins T |title=Longitudinal development of hippocampal subregions from early- to mid-childhood |journal=Hippocampus |volume=30 |issue=10 |pages=1098–1111 |date=October 2020 |pmid=32497411 |pmc=8500647 |doi=10.1002/hipo.23218 |url=}}</ref> Their cells are morphologically different.<ref name="Ezama">{{cite journal |vauthors=Ezama L, Hernández-Cabrera JA, Seoane S, Pereda E, Janssen N |title=Functional connectivity of the hippocampus and its subfields in resting-state networks |journal=Eur J Neurosci |volume=53 |issue=10 |pages=3378–3393 |date=May 2021 |pmid=33786931 |pmc=8252772 |doi=10.1111/ejn.15213 |url=}}</ref> They also have different levels of vulnerability to disease.<ref name="Xiao2023"/>

In humans the head of the hippocampus is termed the anterior hippocampus, the body is the intermediate hippocampus, and the tail the posterior hippocampus. The subregions all serve different functions, project with different [[neural pathway]]s, and have varying numbers of [[place cell]]s.<ref name=Fanselow2010>{{cite journal | vauthors = Fanselow MS, Dong HW | title = Are the dorsal and ventral hippocampus functionally distinct structures? | journal = Neuron | volume = 65 | issue = 1 | pages = 7–19 | date = January 2010 | pmid = 20152109 | pmc = 2822727 | doi = 10.1016/j.neuron.2009.11.031 | ref = refFanselow2010 }}</ref> (In other primates the terms used are rostral and caudal, and in rodents they are termed ventral and dorsal).<ref name="Dalton">{{cite journal |vauthors=Dalton MA, D'Souza A, Lv J, Calamante F |title=New insights into anatomical connectivity along the anterior-posterior axis of the human hippocampus using in vivo quantitative fibre tracking |journal=eLife |volume=11 |issue= |pages= |date=November 2022 |pmid=36345716 |pmc=9643002 |doi=10.7554/eLife.76143 |doi-access=free |url=}}</ref> The posterior hippocampus serves for spatial memory, verbal memory, and learning of conceptual information. Using the [[radial arm maze]] in rats, lesions in the dorsal hippocampus were shown to cause spatial memory impairment. Its projecting pathways include the [[medial septal nucleus]], and [[supramammillary nucleus]].<ref>{{cite journal | vauthors = Pothuizen HH, Zhang WN, Jongen-Rêlo AL, Feldon J, Yee BK | title = Dissociation of function between the dorsal and the ventral hippocampus in spatial learning abilities of the rat: a within-subject, within-task comparison of reference and working spatial memory | journal = The European Journal of Neuroscience | volume = 19 | issue = 3 | pages = 705–712 | date = February 2004 | pmid = 14984421 | doi = 10.1111/j.0953-816X.2004.03170.x | ref = refPothuizen2004 | s2cid = 33385275 }}</ref> In the rat the dorsal hippocampus also has more place cells than both the ventral and intermediate hippocampal regions.<ref>{{cite journal | vauthors = Jung MW, Wiener SI, McNaughton BL | title = Comparison of spatial firing characteristics of units in dorsal and ventral hippocampus of the rat | journal = The Journal of Neuroscience | volume = 14 | issue = 12 | pages = 7347–7356 | date = December 1994 | pmid = 7996180 | pmc = 6576902 | doi = 10.1523/JNEUROSCI.14-12-07347.1994 | ref = refJung1994 }}</ref>

In the early 20th century, the widely held view was that [[olfaction]] was a major hippocampal function.<ref name="Morris and Amaral2024a">{{cite book |last1=Morris |first1=Richard |last2=Amaral |first2=David |title=The Hippocampus Book |date=2024 |pages= 8–9|publisher=Oxford University Press, Incorporated |location=Oxford |isbn=9780190065324 |edition=2nd}}</ref> This view was argued against, pointing out that the hippocampus was present in some animals such as [[dolphin]]s and [[whale]]s, that did not have a sense of smell; and further that lesions in the temporal lobe in dogs had been shown to have no effect on their sense of smell.<ref name="Morris and Amaral2024a"/> These arguments were concluded in 1947 and held for a few more decades. In 1984, and 1987, studies in the rat showed that the entorhinal cortex receives substantial input from the olfactory bulb, with part of the EC being directly innervated by the [[lateral olfactory tract]].<ref name="Morris and Amaral2024a"/> Secondary inputs to the EC were also shown to include some from the periamygdaloid and piriform cortices, and CA1 in the ventral hippocampus was shown to sends axons to the main olfactory bulb.<ref name="Van Groen 1990">{{cite journal | vauthors = van Groen T, Wyss JM | title = Extrinsic projections from area CA1 of the rat hippocampus: olfactory, cortical, subcortical, and bilateral hippocampal formation projections | journal = The Journal of Comparative Neurology | volume = 302 | issue = 3 | pages = 515–528 | date = December 1990 | pmid = 1702115 | doi = 10.1002/cne.903020308 | s2cid = 7175722 }}</ref><ref name="Morris and Amaral2024a"/> It is evident that the hippocampus does have an involvement in memory for odors.<ref>{{cite book | vauthors = Eichenbaum H, Otto TA, Wible CG, Piper JM | veditors = Davis JL, Eichenbaum H | title=Olfaction | year=1991 | chapter=Ch 7. Building a model of the hippocampus in olfaction and memory | publisher=MIT Press | isbn=978-0-262-04124-9 |ref=refEichenbaum1991}}</ref><ref name="Eichenbaum">{{cite book |vauthors=Eichenbaum H, Cohen NJ| title = Memory, Amnesia, and the Hippocampal System | year =1993 | publisher =MIT Press | ref = refEichenbaum1993 }}</ref>

The intermediate hippocampus has overlapping characteristics with both the ventral and dorsal hippocampus.<ref name=Fanselow2010/> Studies in 2002, showed that alterations to the ventral hippocampus reduced the amount of information sent to the amygdala by the dorsal and ventral hippocampus, consequently altering fear conditioning in rats.<ref>{{cite journal | vauthors = Anagnostaras SG, Gale GD, Fanselow MS | title = The hippocampus and Pavlovian fear conditioning: reply to Bast et al | journal = Hippocampus | volume = 12 | issue = 4 | pages = 561–565 | year = 2002 | pmid = 12201641 | doi = 10.1002/hipo.10071 | url = http://homepage.mac.com/sanagnos/19bastreply2002.pdf | ref = refAnagnostaras2002 | url-status = dead | s2cid = 733197 | archive-url = https://web.archive.org/web/20050216104718/http://homepage.mac.com/sanagnos/19bastreply2002.pdf | archive-date = 2005-02-16 }}</ref> In 2007, studies using [[anterograde tracing]] methods, located the moderate projections to two primary olfactory cortical areas and prelimbic areas of the [[Prefrontal cortex#Interconnections|medial prefrontal cortex]]. This region has the smallest number of place cells. The ventral hippocampus functions in fear conditioning and affective processes.<ref>{{cite journal | vauthors = Cenquizca LA, Swanson LW | title = Spatial organization of direct hippocampal field CA1 axonal projections to the rest of the cerebral cortex | journal = Brain Research Reviews | volume = 56 | issue = 1 | pages = 1–26 | date = November 2007 | pmid = 17559940 | pmc = 2171036 | doi = 10.1016/j.brainresrev.2007.05.002 | ref = refCenquizca2007 }}</ref>