Turn-signal utilization by rats with either unilateral or bilateral posterior parietal cortex injuries

Abstract

Rats with sham, unilateral, or bilateral aspiration lesions of the posterior parietal cortex (PPC) were trained in a water T-maze to use flashing lights located along the starting alley (two each) and inner walls of the goal alleys (two each) to find a hidden escape platform. Thereafter, the performance of the spatial response was tested under several conditions. Rats with bilateral PPC lesions were significantly inferior to unilateral- and sham-injured rats in learning the “turn-signal” cued spatial task. Also, left-PPC-injured rats committed significantly more errors than did the control animals. After mastering the task, cue saliency was reduced and the amount of spatial discontiguity between the stimuli and escape site was increased in two stages. That is, the flashing light closest to the escape platform was turned off for one testing session. On the following day, animals were required to rely on information located within the starting alley to make the correct spatial response at the choice point. Animals with bilateral or left PPC lesions were significantly impaired on the task with cues located only in the starting alley. The animals were then tested with competing constant illumination of the lights on the side of the apparatus opposite the flashing-light cues. The performance of all animals dropped to chance and failed to improve with training. Finally, three of the sham-operated controls were retrained to criterion on the original discrimination and prepared with bilateral PPC injuries. Substantial savings was observed. The results reveal a greater role of the left PPC than the right in the use of local sensory cues for spatial navigation, and they show that the PPC is not the repository of the “engram” for this learned visuospatial behavior.