Editing Place cell (section)

==Episodic memory==
Place cells play an important role in [[episodic memory]]. One important aspect of episodic memory is the spatial context in which the event occurred.<ref name="Smith 2006 716–729">{{cite journal|last=Smith|first=David|author2=Sheri Mizumori |title=Hippocampal Place Cells, Context, and Episodic Memory|journal=Hippocampus|date=10 June 2006|volume=16|issue=9|pages=716–729|doi=10.1002/hipo.20208|pmid=16897724|citeseerx=10.1.1.141.1450|s2cid=720574}}</ref> Hippocampal place cells have stable firing patterns even when cues from a location are removed and specific place fields begin firing when exposed to signals or a subset of signals from a previous location.<ref name="Nakazawa-2004">{{cite journal|last=Nakazawa|first=Kazu|author2=Thomas McHugh |author3=Matthew Wilson |author4=Susumu Tonegawa |title=NMDA Receptors, Place Cells and Hippocampal Spatial Memory|journal=Nature Reviews Neuroscience|date=May 2004|volume=5|pages=368–369|doi=10.1038/nrn1385 |pmid=15100719 |issue=5|s2cid=7728258}}</ref> This suggests that place cells provide the spatial context for a memory by recalling the neural representation of the environment in which the memory occurred.<ref name="Smith 2006 716–729"/> By establishing spatial context, place cells play a role in completing memory patterns.<ref name="Nakazawa-2004" /><ref name="Rolls 2013 74">{{cite journal|last=Rolls|first=Edmund T.|year=2013|title=The mechanisms for pattern completion and pattern separation in the hippocampus|journal=Frontiers in Systems Neuroscience|volume=7|pages=74|doi=10.3389/fnsys.2013.00074|pmc=3812781|pmid=24198767|doi-access=free}}</ref> Furthermore, place cells are able to maintain a spatial representation of one location while recalling the neural map of a separate location, effectively differentiating between present experience and past memory.<ref name="Smith 2006 716–729"/> Place cells are therefore considered to demonstrate both pattern completion and pattern separation qualities.<ref name="Nakazawa-2004" /><ref name="Rolls 2013 74"/>

===Pattern completion===
Pattern completion is the ability to recall an entire memory from a partial or degraded sensory cue.<ref name="Rolls 2013 74"/> Place cells are able to maintain a stable firing field even after significant signals are removed from a location, suggesting that they can recall a pattern based on only part of the original input.<ref name="Moser-2008" /> Furthermore, the pattern completion exhibited by place cells is symmetric, because an entire memory can be retrieved from any part of it. For example, in an object-place association memory, spatial context can be used to recall an object and the object can be used to recall the spatial context.<ref name="Rolls 2013 74"/>

===Pattern separation===
{{See also|Dentate gyrus#Memory}}
Pattern separation is the ability to differentiate one memory from other stored memories.<ref name="Moser-2008" /> Pattern separation begins in the [[dentate gyrus]], a section of the hippocampus involved in memory formation and retrieval.<ref name="Leutgeb-2005">{{Cite journal|last1=Leutgeb|first1=Stefan|last2=Leutgeb|first2=Jill K|last3=Moser|first3=May-Britt|last4=Moser|first4=Edvard I|date=2005-12-01|title=Place cells, spatial maps and the population code for memory|journal=Current Opinion in Neurobiology|series=Motor systems / Neurobiology of behaviour|volume=15|issue=6|pages=738–746|doi=10.1016/j.conb.2005.10.002|pmid=16263261|s2cid=9770011|issn=0959-4388}}</ref> Granule cells in the dentate gyrus process sensory information using [[competitive learning]], and relay a preliminary representation to form place fields.<ref name="Leutgeb-2005" /> Place fields are extremely specific, as they are capable of remapping and adjusting firing rates in response to subtle sensory signal changes. This specificity is critical for pattern separation, as it distinguishes memories from one another.<ref name="Moser-2008" />

===Reactivation, replay, and preplay===
{{main|Hippocampal replay}}
Place cells often exhibit reactivation outside their place fields. This reactivation has a much faster time scale than the actual experience, and it occurs mostly in the same order in which it was originally experienced, or, more rarely, in reverse. Replay is believed to have a functional role in [[memory retrieval]] and [[memory consolidation]].<ref>{{Cite journal|last1=Ólafsdóttir|first1=H. Freyja|last2=Bush|first2=Daniel|last3=Barry|first3=Caswell|date=2018-01-08|title=The Role of Hippocampal Replay in Memory and Planning|url= |journal=Current Biology|language=en|volume=28|issue=1|pages=R37–R50|doi=10.1016/j.cub.2017.10.073|issn=0960-9822|pmid=29316421|pmc=5847173}}</ref> However, when replay is disturbed, it does not necessarily affect place coding, which means it is not essentially for consolidation in all circumstances.<ref>{{Cite journal|last1=Joo|first1=Hannah R.|last2=Frank|first2=Loren M.|date=2018|title=The hippocampal sharp wave–ripple in memory retrieval for immediate use and consolidation|journal=Nature Reviews Neuroscience|language=en|volume=19|issue=12|pages=744–757|doi=10.1038/s41583-018-0077-1|pmid=30356103|pmc=6794196|issn=1471-0048}}</ref> The same sequence of activity may occur before the actual experience. This phenomenon, termed preplay,<ref>{{Cite journal |last1=Dragoi |first1=George |last2=Tonegawa |first2=Susumu |date=January 2011 |title=Preplay of future place cell sequences by hippocampal cellular assemblies |journal=Nature |language=en |volume=469 |issue=7330 |pages=397–401 |doi=10.1038/nature09633 |issn=0028-0836 |pmc=3104398 |pmid=21179088|bibcode=2011Natur.469..397D }}</ref> may have a role in [[prediction]]<ref>{{Cite journal |last1=Liu |first1=Kefei |last2=Sibille |first2=Jeremie |last3=Dragoi |first3=George |date=September 2018 |title=Generative Predictive Codes by Multiplexed Hippocampal Neuronal Tuplets |journal=Neuron |language=en |volume=99 |issue=6 |pages=1329–1341.e6 |doi=10.1016/j.neuron.2018.07.047|pmid=30146305 |s2cid=52092903 |doi-access=free }}</ref> and [[learning]].<ref>{{Cite journal|last1=Buhry|first1=Laure|last2=Azizi|first2=Amir H.|last3=Cheng|first3=Sen|date=2011|title=Reactivation, Replay, and Preplay: How It Might All Fit Together|journal=Neural Plasticity|language=en|volume=2011|pages=203462|doi=10.1155/2011/203462|pmid=21918724|pmc=3171894|issn=2090-5904|doi-access=free}}</ref>