Organization of working memory processes in monkeys: the effects of a dopamine receptor agonist

Abstract

The effects of the dopamine receptor agonist agroclavin on cognitive processes associated with mechanisms of visual recognition and long-term and working (short-term) memory were studied in delayed visual differentiation and delayed spatial selection tasks in monkeys (rhesus macaques). Measurements made before and after p.o. pharmacological treatment with this agent were used to identify the p.o. dose (5 mg/kg) inducing a significant effect. The psychotropic effect of agroclavin, which induced cognitive dysfunction, was present in all the monkeys studied to one extent or another. Behavioral criteria were: the probability of correct solutions of the visual differentiation task, the probability of refusals to resolve the task, and the time taken for correct motor responses. Despite individual differences in these behavioral characteristics in monkeys, significant changes due to agroclavin were consistently evident in all animals. There was a reduction in the probability of correct solutions, due to worsening of the characteristics of short-term memory; most monkeys showed increases in the numbers of refusals to solve tasks and increases in the time for correct motor responses during these solutions. In fact, all monkeys showed no increases in the number of erroneous solutions in visual differeniation and spatial selection tasks without delays, though in most cases there were increases in the time taken for correct motor reactions and the number of refusals to solve tasks. Data were obtained indicating that the effect of agroclavin was not uniform with respect to different types of visual information. The possible structural-functional organization of processes underlying working memory is discussed on the basis of the conclusion that the behavioral characteristics studied here reflect different components of cognitive processes realized by structures with different functional properties and different locations.