DISCHARGE CORRELATES OF HIPPOCAMPAL COMPLEX SPIKE NEURONS IN BEHAVINGRATS PASSIVELY DISPLACED ON A MOBILE ROBOT

This study investigated location-, movement-, and directional-selectiv ity of action potential discharges of hippocampal neurons in awake rat s subjected to passive displacements in order to estimate vestibular c ontributions to this activity. Water-deprived rats were habituated to being restrained in a sling mounted on a moving robot. The extracellul ar activity of single complex-spike cells in area CA1 of the hippocamp us was recorded with glass micropipettes in the rats during passive tr anslations, rotations, and immobility. The robot made a standardized s eries of trajectories starting from each of four corners of a square e nclosure surrounded by black curtains. A drop of water was delivered t o the rat each time the robot arrived at one designated corner of the arena. The activities of 29 neurons were investigated in 45 recording sessions (16 of which were in total darkness) in four rats. Hippocampa l neurons recorded in 31 sessions (9 sessions in the dark) had signifi cant location-selective increases or decreases in firing rate as the r at was passively displaced or immobile within the experimental arena. In 20 sessions (6 in the dark) direction-selective discharges were fou nd when the rat was in the corners. In six sessions, cells discharged selectively during movement initiation or termination. These data sugg est that information essential for path integration is present in the hippocampus and that inertial cues could play a vital role in hippocam pal spatial functions. These results resemble those of O'Mara et al. ( [1994] J Neurosci 14:6511) using the same protocol in macaques, sugges ting similarities in hippocampal processing and function. (C) 1998 Wil ey-Liss, Inc.