Hippocampectomized rats are impaired in homing by path integration

Theoretical, behavioral, and electrophysiologic evidence suggests that the hippocampal formation may play a role in path integration, a form of spatia l navigation in which an animal can return to a starting point by integrati ng self-movement cues generated on its outward journey. The present study e xamined whether the hippocampus (Ammon's horn and the dentate gyrus) is inv olved in this form of spatial behavior. Control rats and rats with selectiv e ibotenic acid lesions of the hippocampus were tested in a foraging task i n which they retrieved large food pellets from an open field, which when fo und, they carried to a refuge for consumption. The experiments measured the rats' homing accuracy, returning to the starting location, under condition s in which visual, surface, and self-movement cues; surface and self-moveme nt cues; or only self-movement cues were available. Although both control r ats and rats without a hippocampus could use visual and surface cues, only control rats appeared to be able to use self-movement cues. The finding tha t hippocampal rats are impaired under conditions requiring the use of self- movement cues suggests that the hippocampus plays an essential role in path integration. (C) 1999 Wiley-Liss, Inc.