Scopolamine effects on Hamilton search task performance in monkeys

Abstract

The Hamilton search task, a test of spatial memory, was given to adult monkeys after administration of scopolamine. Three monkeys had been exposed to lead during development and two were controls. The task consisted of opening eight boxes, one per trial, for food reinforcement, with a 20 second delay between trials. The monkey had to remember which boxes it had already opened and avoid them to obtain the remaining reinforcements. Percents correct response, openings-to-repeat, trials per session, repetitive index and response latency were measured. There were no significant lead-related effects. Significant scopolamine-induced deficits were detected with four of the measures. The low doses of scopolamine (1–3 μg/kg) did not affect response accuracy, but 15 and 30 μg/kg caused impairments. Only 30 μg/kg substantially increased latency. This is like other memory tests in monkeys and rats in that it is sensitive to anticholinergic challenge. Cognitive performance deficits were detected at a dose ( 15 μg/kg) which did not cause increased response latency. The Hamilton search task is a flexible and sensitive memory task for monkeys, analogous to the radial arm maze in the rat.