Zahra M. Aghajan
Hippocampal Activity in Real and Virtual Environments
Wednesday 15th of April 2015 at 12:00pm
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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