Zahra M. Aghajan

Hippocampal Activity in Real and Virtual Environments

Wednesday 15th of April 2015 at 12:00pm
560 Evans

The hippocampus is linked to our ability to form episodic memories by pro- viding a spatial cognitive map together with the content of experiences. In rodents, the focus has largely been on the role of hippocampus in the representation of space but despite decades-long research, the underlying mechanisms remain unknown. It has been shown that multiple sensory and motor inputs reach the hippocampus and can modulate its activity. In real world (RW) environments however, the contributions of these inputs are con- founded. Thus, to dissociate these contributions and thereby elucidate the mechanisms of spatial selectivity, we used a virtual reality (VR) setup. We found comparable levels of hippocampal spatiotemporal selectivity on linear tracks in RW and VR. In contrast, during random foraging in two-dimensions, spatial selectivity was severely diminished in VR. Neverthe- less, most spikes occurred within 2-s-long hippocampal motifs|with similar structure to that in RW|within which hippocampal temporal code was in- tact, demonstrating a decoupling between the spatial and the temporal codes. Further, additional experiments and analysis revealed signicant directional selectivity in the hippocampus in RW and VR. Notably, contrary to the im- pairment of spatial selectivity in VR, the degree of directional selectivity was identical in both worlds and determined by the angular information con- tained in the visual cues. Taken together, these results suggest that while visual cues alone are insucient to generate a stable localized representation in the spatial domain, they are sucient to elicit|and play a causal role in|hippocampal directional selectivity.

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