THE EFFECTS OF LESIONS TO THE MAMMILLARY REGION AND THE HIPPOCAMPUS ON CONDITIONAL ASSOCIATIVE LEARNING BY RATS

Rats with extensive lesions to the mammillary body region, the hippoca mpus, or rats which had received a control operation were trained post operatively on two visuo-spatial conditional associative learning task s in which they had to learn to associate spatial cues with particular visual/auditory stimuli, The animals were subsequently trained on a s patial working memory task, the eight-arm radial maze, Rats with lesio ns to the mammillary body region were able to acquire the conditional associative learning tasks at a rate comparable to that of operated co ntrol animals, whereas those with hippocampal lesions were not. By con trast, rats with a lesion of the mammillary body region or the hippoca mpus were significantly impaired in comparison with the operated contr ol animals in the radial maze. The findings suggest that lesions to th e mammillary body region impair spatial working memory without affecti ng the capacity to associate particular exteroceptive cues with spatia l locations.