Editing Place cell (section)

===Sensory input===
Place cells were initially believed to fire in direct relation to simple sensory inputs, but studies have suggested that this may not be the case.<ref name="Jeffery 2003 201–218"/> Place fields are usually unaffected by large sensory changes, like removing a landmark from an environment, but respond to subtle changes, like a change in color or shape of an object.<ref name="Moser-2008" /> This suggests that place cells respond to complex stimuli rather than simple individual sensory cues. According to the functional differentation model, sensory information is processed in various cortical structures upstream of the hippocampus before actually reaching the structure, so that the information received by place cells is a compilation, a functional derivative, of different stimuli.<ref name="Jeffery 2003 201–218"/>
[[File:CajalHippocampus (modified).png|thumb|Anatomy of the [[hippocampal formation]], including the [[entorhinal cortex]] (EC), the [[dentate gyrus]] (DG) and the different hippocampal subfields (CA1 and CA3). Inset shows the wiring between these different areas.]]
Sensory information received by place cells can be categorized as either metric or contextual information, where metric information corresponds to where place cells should fire and contextual input corresponds to whether or not a place field should fire in a certain environment.<ref name="Jeffery 2007 775–785">{{cite journal|last=Jeffery|first=Kathryn|title=Integration of the Sensory Inputs to Place Cells: What, Where, Why, and How?|journal=Hippocampus|date=5 July 2007|volume=17|issue=9|pages=775–785|doi=10.1002/hipo.20322|pmid=17615579|s2cid=3141473}}</ref> Metric sensory information is any kind of spatial input that might indicate a distance between two points. For example, the edges of an environment might signal the size of the overall place field or the distance between two points within a place field. Metric signals can be either linear or directional. Directional inputs provide information about the orientation of a place field, whereas linear inputs essentially form a representational grid. Contextual cues allow established place fields to adapt to minor changes in the environment, such as a change in object color or shape. Metric and contextual inputs are processed together in the [[entorhinal cortex]] before reaching the hippocampal place cells. Visuospatial and [[Olfactory system|olfactory]] inputs are examples of sensory inputs that are utilized by place cells. These types of sensory cues can include both metric and contextual information.<ref name="Jeffery 775–785" />

====Visuospatial inputs====
Spatial cues such as geometric boundaries or orienting landmarks are important examples of ''metric'' input. An example is the walls of an environment, which provides information about relative distance and location.<ref name="okeefe1999" /> Place cells generally rely on set distal cues rather than cues in the immediate proximal environment,<ref name="Jeffery 775–785" /> though local cues can have a profound impact on local place fields.<ref name="Moser-2008" /><ref>{{Cite journal|last1=Bourboulou|first1=Romain|last2=Marti|first2=Geoffrey|last3=Michon|first3=François-Xavier|last4=El Feghaly|first4=Elissa|last5=Nouguier|first5=Morgane|last6=Robbe|first6=David|last7=Koenig|first7=Julie|last8=Epsztein|first8=Jerome|date=2019-03-01|editor-last=Burgess|editor-first=Neil|editor2-last=Behrens|editor2-first=Timothy E|editor3-last=Burke|editor3-first=Sara N|title=Dynamic control of hippocampal spatial coding resolution by local visual cues|journal=eLife|volume=8|pages=e44487|doi=10.7554/eLife.44487|pmid=30822270|pmc=6397000|issn=2050-084X |doi-access=free }}</ref> Visual sensory inputs can also supply important ''contextual'' information. A change in color of a specific object or the walls of the environment can affect whether or not a place cell fires in a particular field.<ref name="Jeffery 775–785" /><ref name="Anderson-2003" /> Thus, visuospatial sensory information is critical to the formation and recollection of place field.

====Olfactory inputs====
Although place cells primarily rely on visuospatial input, some studies suggest that olfactory input may also affect the formation and stability of place fields.<ref name=Save2000>{{cite journal|last=Save|first=Etienne|author2=Ludek Nerad |author3=Bruno Poucet |title=Contribution of multiple sensory information to place field stability in hippocampal place cells|journal=Hippocampus|date=23 February 2000|volume=10|issue=1|pages=64–76|doi=10.1002/(SICI)1098-1063(2000)10:1<64::AID-HIPO7>3.0.CO;2-Y|pmid=10706218|s2cid=34908637 }}</ref><ref>{{Cite journal|last1=Poucet|first1=Bruno|last2=Save|first2=Etienne|last3=Lenck-Santini|first3=Pierre-Pascal|date=2011|title=Sensory and Memory Properties of Hippocampal Place Cells|journal=Reviews in the Neurosciences|volume=11|issue=2–3|pages=95–112|doi=10.1515/REVNEURO.2000.11.2-3.95|pmid=10718148|s2cid=1952601|issn=2191-0200}}</ref><ref name="Jeffery-2003">{{Cite book|url=https://books.google.com/books?id=ZMLADwAAQBAJ&q=olfaction+%22place+cells%22&pg=PA48|title=The Neurobiology of Spatial Behaviour|last=Jeffery|first=Kathryn J.|date=2003|publisher=Oxford University Press|isbn=978-0-19-851524-1|language=en}}</ref> Olfaction may compensate for a loss of visual information,<ref name="Save2000" /><ref name="Jeffery-2003" /> or even be responsible for the formation of stable place fields in the same way visuospatial cues are.<ref name="Zhang 2013">{{cite journal|last=Zhang|first=Sijie|author2=Denise Manahan-Vaughn|date=5 September 2013|title=Spatial Olfactory Learning Contributes to Place Field Formation in the Hippocampus|journal=Cerebral Cortex|volume=25|issue=2|pages=423–432|doi=10.1093/cercor/bht239|pmc=4380081|pmid=24008582}}</ref> This has been confirmed by a study in a virtual environment that was composed of odor gradients.<ref name="Radvansky 2018">{{cite journal|last=Radvansky|first=Brad|author2=Daniel Dombeck|date=26 February 2018|title=An olfactory virtual reality system for mice|journal=Nature Communications|volume=9|issue=1|page=839|doi=10.1038/s41467-018-03262-4|pmc=5827522|pmid=29483530|bibcode=2018NatCo...9..839R}}</ref> Change in the olfactory stimulus in an environment may also cause the remapping of place cells.<ref name="Anderson-2003" /><ref name="Jeffery 775–785" />

==== Vestibular inputs ====
Stimuli from the [[vestibular system]], such as rotations, can cause changes in place cells firing.<ref name="Smith-Darlington2009">{{cite journal|last=Smith|first=Paul F.|author2=Darlington, Cynthia L.|author3=Zheng, Yiwen|date=29 April 2009|title=Move it or lose it—Is stimulation of the vestibular system necessary for normal spatial memory?|journal=Hippocampus|volume=20|issue=1|pages=36–43|doi=10.1002/hipo.20588|pmid=19405142|s2cid=10344864}}</ref><ref name="Jacob-2014">{{Cite journal|last1=Jacob|first1=Pierre-Yves|last2=Poucet|first2=Bruno|last3=Liberge|first3=Martine|last4=Save|first4=Etienne|last5=Sargolini|first5=Francesca|date=2014|title=Vestibular control of entorhinal cortex activity in spatial navigation|journal=Frontiers in Integrative Neuroscience|language=en|volume=8|pages=38|doi=10.3389/fnint.2014.00038|pmid=24926239|pmc=4046575|issn=1662-5145|doi-access=free}}</ref> After receiving vestibular input some place cells may remap to align with this input, though not all cells will remap and are more reliant on visual cues.<ref name="Jacob-2014" /><ref>{{Cite journal|last1=Wiener|first1=S. I.|last2=Korshunov|first2=V. A.|last3=Garcia|first3=R.|last4=Berthoz|first4=A.|date=1995-11-01|title=Inertial, substratal and landmark cue control of hippocampal CA1 place cell activity|journal=The European Journal of Neuroscience|volume=7|issue=11|pages=2206–2219|doi=10.1111/j.1460-9568.1995.tb00642.x|issn=0953-816X|pmid=8563970|s2cid=10675209}}</ref> [[Bilateral symmetry|Bilateral]] lesions of the vestibular system in patients may cause abnormal firing of hippocampal place cells as evidenced, in part, by difficulties with spatial tasks such as the [[radial arm maze]] and the [[Morris water navigation task]].<ref name="Smith-Darlington2009" />

==== Movement inputs ====
[[File:Path integration diagram.svg|thumb|upright=1.25|Grid and place cells contribute to [[path integration]], a process which sums the [[Euclidean vector|vector]]s of distance and direction travelled from a start point to estimate current position.]]

Movement can also be an important spatial cue. Mice use their self-motion information to determine how far and in which direction they have travelled, a process called [[path integration]].<ref name="Moser-2008" /> This is especially the case in the absence of continuous sensory inputs. For example, in an environment with a lack of visuospatial inputs, an animal might search for the environment edge using touch, and discern location based on the distance of its movement from that edge.<ref name="okeefe1999" /> Path integration is largely aided by [[grid cell]]s, which are a type of neuron in the entorhinal cortex that relay information to place cells in the hippocampus. Grid cells establish a grid representation of a location, so that during movement place cells can fire according to their new location while orienting according to the reference grid of their external environment.<ref name="Jeffery 775–785" />