| Summary: | Understanding the roles played by spatially firing cells, notably hippocampal place cells and entorhinal grid cells, in encoding, storing and retrieving spatial memories is a key question in neuroscience. Of particular interest is the interaction between these two distinct cell types. Using chronic electrophysiology in freely moving rats, CA1 place cells and medial entorhinal grid cells were recorded simultaneously. The changes in spatial firing of these cells were investigated in two separate paradigms each forming an experimental chapter of the thesis. The first experimental chapter investigates the effects of non-geometric, “contextual” (colour and odour) changes in an otherwise stable environment on the firing of grid cells and place cells. It was found that grid cells, in addition to place cells, can be modulated by and remap to such contextual changes. Grid cells responded predominantly to odour changes, as well as to combinations of colour and odour and seemed to keep a fixed orientation. Consistent with previous reports, simultaneously recorded place cells responded in a heterogeneous manner to changes in context. However, simultaneously recorded grids cells displayed a more homogenous response. The second experimental chapter investigates how both cell types generate a spatial representation for a novel environment. Spatial firing was monitored simultaneously in both cell populations as animals first experienced a familiar environment and then a geometrically identical novel environment differing in its colour, texture and location. Consistent with previous reports, grids realigned while place cell firing was completely reorganized. Moreover, in the novel environment grids also displayed an increase in scale and a reduction in hexagonal regularity. Concurrently, place cells displayed, on average, larger field sizes. With repeated exposure to the novel environment these effects became less pronounced. These findings provide insight into how the entorhinal cortex and hippocampus may collaborate in the generation of neural spatial representations.
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