This research examined whether rats can use idiothetic cues to form spatial memories in the radial-arm maze (RM) and whether the hippocampus is involved in such ability. A possible contribution of the vestibular system to RM performance was also investigated. Rats with excitotoxic hippocampal lesions and sham-operated controls were trained on two versions of the RM task. In the Light condition, a unique visual insert was apposed on each arm floor and rats could choose which arm to enter next by relying on visual and/or idiothetic stimuli. In the Dark condition, the task was administered in darkness and success required processing of idiothetic cues to remember visited locations on the maze. In experiment 1, the performance of lesioned rats was impaired in the Light condition, but both control and lesioned rats learned to avoid already visited arms. In the Dark condition, the performance of controls improved over time whereas a severe deficit was observed in rats with hippocampal lesions. Thus, control rats, but not hippocampal lesioned rats, can form spatial memories by processing idiothetic inputs. Experiment 2 showed that vestibular lesions disrupt performance in both the Light and the Dark conditions and confirmed that rats use idiothetic information, especially vestibular cues, while navigating in the RM. Therefore, cues generated during locomotion play an important role in hippocampal-dependent spatial memory.
(c) 2007 Wiley-Liss, Inc.