Unilateral striatal lesions impair response execution on a lateralised choice reaction time task

Abstract

A novel lateralised reaction time task is described and used to evaluate the effects of d-amphetamine injections and unilateral dorso-striatal lesions in rats. The task involves a two-lever Skinner box adaptation of the nine-hole box visual choice reaction time task first developed by Carli et al. d-Amphetamine had a dose dependent effect on nearly all aspects of task performance. Low and the intermediate doses of d-amphetamine speeded reaction time and movement time, and abolished the delay-dependent pattern of responding in the task. The highest dose of amphetamine disrupted the animals' ability to perform reliably, the task contingencies. Unilateral lesions in the dorsal neostriatum resulted in an increase of error trials, produced a bias to respond towards the ipsilateral side, and decreased the accuracy of responding to contralateral stimuli. The overall mean reaction time to contralateral stimuli was not influenced by the lesions, but the movement time was increased selectively when responding to contralateral stimuli. The data suggest that striatal activation by amphetamine increases motor readiness, which can enhance reaction time performance at the cost of increased errors due to anticipation of cue presentation, in particular at long holding delays. Conversely, striatal lesions induce lateralised defects in executive, rather than sensory, processes, and impair the animals' ability to execute movement towards the contralateral side.