SIMPLE AND CONFIGURAL ASSOCIATION LEARNING IN RATS WITH BILATERAL QUISQUALIC ACID LESIONS OF THE NUCLEUS BASALIS MAGNOCELLULARIS

We hypothesized that bilateral quisqualic acid lesions of the nucleus basalis magnocellularis (NBM) in rats would impair configural but not simple association learning. In experiment 1, rats were tested in a ne gative patterning operant discrimination where they were food-reinforc ed for responding to a light or a tone (L+, T+) but not for responding to the configural stimulus consisting of the light and tone presented simultaneously (LT-). Consistent with our hypothesis, NBM-lesioned ra ts showed a transient but significant impairment, responding normally to L+ and T+ but responding more often to LT-, in addition to respondi ng more often during the inter-trial interval (ITI) than controls. In experiment 2, rats were tested in a simple operant discrimination wher e rats were food-reinforced for responding to a light (L+) but not for responding to a tone (T-). Although NBM-lesioned rats again responded normally to L+ as predicted, NBM-lesioned rats were transiently impai red, making more T- responses and more ITI responses than controls. To gether, these results suggest that the NBM is involved in both configu ral and simple association learning but that this involvement is limit ed to learning to withhold responding to non-reinforced contextual or discrete stimuli. Finally, rats from experiment 2 underwent extinction trials, where results showed no difference between NBM-lesioned and c ontrol groups, suggesting that the NBM is not involved in the extincti on of conditioned responding to previously reinforced stimuli. (C) 199 7 Elsevier Science B.V.