Further consideration of the learning impairment after aceperone in the marmoset: Effects of the drug on shape and colour discrimination and on an alternation task

Abstract

Ten marmosets ( Callithrix jacchus) learned to discriminate between pairs of small grey objects differing only in shape or small plain plaques differing only in colour, in a Wisconsin General Test Apparatus. Each day, each animal was presented with three consecutive visual discrimination problems in the order shape-colour-shape or colour-shape-colour. After aceperone, an α-noradrenergic antagonist, animals were impaired at learning the first but not the subsequent tasks of each trio. These results suggest that the previously observed impairment [10] on the first of a pair of object discrimination tasks after aceperone is a consequence of disruption of a mechanism common to both shape and colour discrimination learning. The fact that there is no impairment on task 2 in a dimension differing from task 1 suggests that the deficit is not one of attending to, or switching attention to, the appropriate visual dimension. Three further marmosets were trained to perform an alternation task and tested under aceperone. No impairment in performance was seen, suggesting that a variety of cognitive skills other than stimulus-reward association were intact. We conclude that the impairment following aceperone is a dysfunction of processes involved in association formation, but that it is one which is manifest only when the animal is faced with a type of task which has not recently been performed and that it can be overcome with persistence even when the animal encounters novel stimuli.