SPATIAL AND BEHAVIORAL-CORRELATES OF STRIATAL NEURONS IN RATS PERFORMING A SELF-INITIATED NAVIGATION TASK

To investigate the spatial and behavioral correlates of striatal neuro ns during displacement movements, the rostromedial dorsal striata (AP 1.0-2.2, ML 1.5-2.0) of five rats were surgically implanted with advan ceable bundles of fine wire electrodes. After recovery, the rats were deprived of water and trained in a square-walled open field in a dark room. The behavioral task required alternating visits to water reservo irs in the center and in the four corners. A certain corner contained the first reward for each trial; after this reward, a cue card appeare d in this corner for the rest of the trial. The firing rates of striat al units were compared as the rat moved between the center and the fou r corners of the arena. Analyses were made of 30 units. Eight of these had firing rates that significantly increased or decreased by 62-480% while the rat was in one or more quadrants of the arena. Six of these manifested such firing rate changes only as the rat performed certain behavioral sequences in the quadrant. Three other units fired as the rat's head was in a certain orientation relative to the arena walls, i n all parts of the arena. To determine the principal controlling cues and hence the frame of reference of spatial selectivity of these units , the arena, while the rat was still inside, was rotated in total dark ness. The first water reward was then presented at the same position r elative to the outside room as before the rotation. The cue card was t hen illuminated in this corner as a visual cue for the extra-arena ref erence frame. All 11 neurons demonstrated spatial selectivity that rot ated with the arena; thus, this activity was in the frame of reference of the arena and was not controlled by the visual cue. Six other unit s fired at rates up to six times their resting discharge or stopped fi ring completely in synchrony with initiation or execution of displacem ent movements, and two of these were also location selective. Four oth er units were silent as the rat performed the task, but fired tonicall y following arena rotations or other interruptions of the session, ind ependent of the rat's location or movements. Nine analyzed units had v ery low firing rates (< 1 impulse/sec) and showed no discernible chang es in activity as the rat performed the task. These patterns of unit a ctivity indicate that fundamental informational components required fo r navigation are coded in the striatum. These include the rat's locati on, heading direction, and the timing of the initiation and execution of displacement movements.