The medial and lateral entorhinal cortex of the rat represent item and context with overlap in a context cued object discrimination paradigm
Bladon, John H.
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The entorhinal cortex is the main input to the hippocampus and is crucial for episodic memory. The medial entorhinal cortex (MEC) is distinct from the lateral entorhinal cortex (LEC) in that the former processes spatial information, whereas the lateral is implicated in processing objects. However, there is significant overlap in function between the two areas. The spatial representation in the MEC is modulated by behavioral contingencies. Similarly, the LEC shows spatial modulation in the presence of objects. It is clear that the MEC and LEC share some but not all mnemonic and navigational functions. To better understand the mnemonic functions of the entorhinal cortex, this study monitored single unit activity with both the MEC and LEC of the rat during a context cued object discrimination task. In short, the rat was rewarded by choosing object X over object Y in context A and object Y over object X in context B regardless of position within each context. It was hypothesized that cells in the MEC would be more context or location modulated whereas cells within the LEC would be object, or object-in-context modulated. To further characterize the spatial selectivity of cells, units were also recorded while rats foraged in an open field. Cells were found within the LEC that responded selectively to context entry. Some cells in the LEC showed object preference, but the pattern was unstable across 90 trials. These results are anomalous, as other studies found cells with the LEC that selected objects in comparable object discrimination tasks. We found cells within the MEC that selected right vs. left context entry, that showed spatial selectivity, and that showed object selectivity. These results indicate that both the MEC and LEC show task-relevant firing, but that the MEC may have a larger role in object-context associations.
Thesis (M.A.)--Boston University