Abstract
Hippocampal neurons encode a cognitive map of space. These maps are thought to be updated during learning and in response to changes in the environment through activity-dependent synaptic plasticity. Here we examine how changes in activity influence spatial coding in rats using halorhodopsin-mediated, spatially selective optogenetic silencing. Halorhoposin stimulation leads to light-induced suppression in many place cells and interneurons; some place cells increase their firing through disinhibition, whereas some show no effect. We find that place fields of the unaffected subpopulation remain stable. On the other hand, place fields of suppressed place cells were unstable, showing remapping across sessions before and after optogenetic inhibition. Disinhibited place cells had stable maps but sustained an elevated firing rate. These findings suggest that place representation in the hippocampus is constantly governed by activity-dependent processes, and that disinhibition may provide a mechanism for rate remapping.
Highlights
Hippocampal neurons encode a cognitive map of space
When grid cell activity is disrupted by the inactivation of the medial septum, the spatial selectivity of place cells remains, suggesting that the inputs from border cells and other spatially tuned medial entorhinal cortex (MEC) cells are sufficient for place-related firing in the hippocampus[21]
By contrast, increasing the firing rate of place cells through disinhibition did not lead to place field remapping; cells fired more intensely inside their place fields after the light application than before, albeit at a lower rate than during the disinhibition
Summary
Hippocampal neurons encode a cognitive map of space. These maps are thought to be updated during learning and in response to changes in the environment through activity-dependent synaptic plasticity. Changing features of the recording enclosure can lead to rate remapping in which the in-field firing rates of cells change without affecting the location of their place fields[5] Both rate and field remapping may occur as a result of changes in afferent inputs, as might be expected by the rapid emergence of spatially selective firing on exposure to a new environment[6]. Both selecting the region of space in which a cell fires and the intensity of firing within its place field may be, in part, governed by activity-dependent processes and by experience[7,8]. These results demonstrate that activity-dependent mechanisms can trigger lasting changes in the spatial firing of place cells
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