Hippocampal formation

During the nineteenth and early twentieth centuries, based largely on the observation that, between species, the size of the olfactory bulb varies with the size of the parahippocampal gyrus, the hippocampal formation was thought to be part of the olfactory system.{{cite book |last1= Finger|first1= S|title= Origins of neuroscience: a history of explorations into brain function|year= 2001|publisher= Oxford University Press|location= Oxford/New York|isbn= 0-19-506503-4|page= 286|chapter= Defining and controlling the circuits of emotion}}

In 1937, Papez theorized that a circuit (the Papez circuit) including the hippocampal formation constitutes the neural substrate of emotional behavior,{{cite journal |last1= Papez|first1= JW|title= A proposed mechanism of emotion|journal= Archives of Neurology and Psychiatry|year= 1937|volume= 38|issue= 4|pages= 725–43|doi=10.1001/archneurpsyc.1937.02260220069003}} and Klüver and Bucy reported that, in monkeys, surgical removal of the hippocampal formation and the amygdaloid complex has a profound effect on emotional responses.{{cite journal |last1= Klüver|first1= H|last2= Bucy|first2= PC|title= "Psychic blindness" and other symptoms following bilateral temporal lobectomy in Rhesus monkeys|journal= American Journal of Physiology|year= 1937|volume= 119|pages= 352–53}}{{cite journal |last1= Klüver |first1= H|last2= Bucy|first2= PC|title= Preliminary analysis of functions of the temporal lobes in monkeys|journal= Archives of Neurology and Psychiatry|year= 1939|volume= 42|issue= 6|pages= 979–1000|doi=10.1001/archneurpsyc.1939.02270240017001}} As a consequence of these publications, the idea that the hippocampal formation is entirely dedicated to olfaction began to recede.{{cite book |last1= Nieuwenhuys|first1= R|last2= Voogd|first2= J|last3= van Huijzen|first3= C|title= The human central nervous system|edition= fourth|year= 2008|publisher= Springer-Verlag|location= Berlin/Heidelberg/New York|isbn= 978-3-540-13441-1|page= 917|chapter= The greater limbic system|chapter-url= https://books.google.com/books?id=vAiFe7gZLhoC&pg=PT916}}

File:Medial surface of cerebral cortex - entorhinal cortex.png

In an influential 1947 review, Alf Brodal pointed out that mammal species thought to have no sense of smell nevertheless have fully intact hippocampal formations, that removal of the hippocampal formation did not affect the ability of dogs to perform tasks dependent on olfaction, and that no fibers were actually known that carry information directly from the olfactory bulb to any part of the hippocampal formation.{{cite journal |doi= 10.1093/brain/70.2.179 |last1= Brodal|first1= A|title= Hippocampus and the sense of smell|journal= Brain|year= 1947|volume= 70 |issue= Pt 2|pages= 179–222|pmid= 20261820}} Though massive direct input from the olfactory bulb to the entorhinal cortex has subsequently been found,{{cite journal |doi= 10.1016/0361-9230(84)90148-5 |last1= Shipley|first1= MT|last2= Adamek|first2= GD|title= The connections of the mouse olfactory bulb: a study using orthograde and retrograde transport of wheatgerm agglutinin conjugated to horsradish peroxidase|journal= Brain Research Bulletin|year= 1984|volume= 12 |issue= 6|pages= 669–688|pmid= 6206930|s2cid= 4706475}} the current view is that the hippocampal formation is not an integral part of the olfactory system.

In 1900, the Russian neurologist Vladimir Bekhterev described two patients with a significant memory deficit who, on autopsy, were found to have softening of hippocampal and adjacent cortical tissue;{{cite journal |last1= Bekhterev|first1= V|title= Demonstration eines gehirns mit zerstörung der vorderen und inneren theile der hirnrinde beider schläfenlappen |journal= Neurologische Zeitenblatte|year= 1900|volume= 19|pages= 990–991}} and, in 1957, William Beecher Scoville and Brenda Milner reported memory loss in a series of patients subsequent to their removal of the patients' medial temporal lobes.{{cite journal | last =Scoville | first =WB |author2=Milner B | title = Loss of Recent Memory After Bilateral Hippocampal Lesions | journal =Journal of Neurology, Neurosurgery, and Psychiatry| volume = 20| pages =11–21 | year =1957 | doi = 10.1136/jnnp.20.1.11 | pmid =13406589 | issue =1 | pmc =497229 }} Thanks to these observations and a great deal of subsequent research, it is now broadly accepted that the hippocampal formation plays a role in some aspects of memory.{{cite book |last1= Anderson|first1= P|last2= Morris|first2= R|last3= Amaral|first3= D|last4= Bliss|first4=T|last5=O'Keefe|first5=J|editor1-first= P|editor1-last= Anderson|editor2-first= R|editor2-last= Morris|editor3-first= D|editor3-last= Amaral|editor4-first= T|editor4-last= Bliss|editor5-last= I'Keefe|title= The hippocampus book|edition= first|year= 2007|publisher= Oxford University Press|location= New York|isbn=9780195100273|pages= 9–36|chapter= Historical perspective: Proposed functions, biological characteristics, and neurobiological models of the hippocampus|chapter-url= https://books.google.com/books?id=zg6oyF1DziQC&pg=PA9}}

EEG evidence from 1938 to the present, stimulation evidence from the 1950s, and modern imaging techniques together suggest a role for some part of the hippocampal formation (in concert with the anterior cingulate cortex) in the control of attention.

In 1971, John O'Keefe and his student Jonathan Dostrovsky discovered place cells: neurons in the rat hippocampus whose activity relates to the animal's location within its environment.{{cite journal|author= O'Keefe J, Dostrovsky J |title= The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat |journal= Brain Res|volume= 34|pages= 171–75|year= 1971|pmid= 5124915|doi= 10.1016/0006-8993(71)90358-1|issue= 1}} Despite skepticism from other investigators, O'Keefe and his co-workers, including Lynn Nadel, continued to investigate this question, in a line of work that eventually led to their very influential 1978 book The Hippocampus as a Cognitive Map.{{cite book | last =O'Keefe | first =J | author2 =Nadel L | title =The Hippocampus as a Cognitive Map | year =1978 | publisher =Oxford University Press | url =http://www.cognitivemap.net/HCMpdf/HCMChapters.html | isbn =0-19-857206-9 | access-date =2010-01-23 | archive-date =2011-03-24 | archive-url =https://web.archive.org/web/20110324042731/http://www.cognitivemap.net/HCMpdf/HCMChapters.html | url-status =dead }} The discovery of place cells, together with the discovery of grid cells by May-Britt Moser and Edvard Moser, and the mapping of the function of the hippocampal formation in spatial awareness, led to the joint award of the Nobel Prize in Physiology or Medicine in 2014. In addition to place cells and grid cells, two further classes of spatial cell have since been identified in the hippocampal formation: head direction cells and boundary cells. As with the memory theory, there is now almost universal agreement that the hippocampal formation plays an important role in spatial coding, but the details are widely debated.{{cite journal | last =Moser | first =EI |author2=Moser M-B

| title =Functional differentiation in the hippocampus| journal =Hippocampus| volume = 8| year =1998| pmid =9882018

| doi =10.1002/(SICI)1098-1063(1998)8:6<608::AID-HIPO3>3.0.CO;2-7| pages =608–19 | issue =6| s2cid =32384692 }}

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{{Commons category|Hippocampal formation}}

• [http://brainatlases.ucdavis.edu/index.php?y2=hippocampal%20formation&y=HF&species=mus%20musculus Image] University of California Davis Brain Atlas

{{Cerebral cortex}}

{{Rostral basal ganglia and associated structures}}

{{Olfactory system}}

Category:Hippocampus (brain)