Effects of scopolamine on learning and memory in monkeys

The effects of scopolamine were evaluated in monkeys responding under operant procedures designed to evaluate drug effects on learning and memory. In one procedure, responding was maintained by food presentation under a multiple schedule. One component of the multiple schedule was a repeated-acquisition task in which the discriminative stimuli for left- and right-key responses changed each session (learning). In the other component, the discriminative stimuli for responses were the same each session (performance). In both components of the multiple schedule, scopolamine produced dose-related decreases in responding; there was little evidence of differential rate-decreasing effects between components. Percent errors in learning were increased in a dose-related manner, whereas percent errors in performance were generally unaffected except at high doses, which also produced substantial decreases in response rate. These results suggest that acquisition is more sensitive to the disruptive effects of scopolamine than is performance. The second procedure utilized repeated acquisition and delayed performance as a technique to study the effects of scopolamine on memory. In this procedure, each session was divided into three phases: acquisition, delay and performance. After a 24-h delay, scopolamine had little or no effect on retention, accuracy or rate of responding. In contrast, after a 60-min delay, scopolamine decreased retention in a dose-related manner. These data suggest that scopolamine produces a greater disruptive effect on short (60-min) versus long (24-h) delays.