INFLUENCES OF VESTIBULAR AND VISUAL-MOTION INFORMATION ON THE SPATIALFIRING PATTERNS OF HIPPOCAMPAL PLACE CELLS

Hippocampal place cells show location-specific firing as animals locom ote in an environment. A possible explanation for these place fields i s that each cell is simply driven by environmental sensory inputs avai lable in its field. This cannot provide the full explanation, however, since cells can maintain stable place fields even in the absence of r eliable environmental orienting cues. This suggests the cells are also influenced by movement-related information, since this is the only av ailable, ongoing indicator of current location when external orienting cues are not present. Two candidates for the movement-related informa tion are vestibular activation, and visual motion. To test for these i nfluences, place cells were recorded as animals locomoted in a cylindr ical apparatus that was made so that its wall (painted with vertical b lack and white stripes) and floor could be independently rotated, to p rovide visual motion and vestibular inputs, respectively. The results showed that both these inputs could influence place fields. Sometimes they caused a predictable locational shift, so that the field rotated its location on the apparatus floor in a way that was compatible with the movement indicated by the vestibular and/or visual motion input. T his updating was most reliably obtained when the two inputs were prese nted in combination. In other cases, the apparatus rotations caused un predictable changes in firing characteristics, so that cells either st opped firing, or developed place fields that were altered in overall s ize, shape, and eccentricity. Interestingly, the probability of these changes increased with experience with the rotational manipulations, s uggesting a learned component.