ACQUISITION, RETENTION, AND EXTINCTION OF OPERANT DISCRIMINATIONS IN RATS WITH NUCLEUS BASALIS MAGNOCELLULARIS LESIONS

Effects of bilateral ibotenic acid lesions of nucleus basalis magnocel lularis (NBM)and scopolamine treatment on different aspects of learnin g and memory in an operant discrimination task were assessed. In Exper iment 1, NBM lesions impaired acquisition performance. In Experiment 2 , scopolamine lowered response rates but did not affect discrimination accuracy in lesioned or control rats. In Experiment 3, although pretr ained rats showed transient increases in commission errors, percentage correct responding remained above chance levels after lesion. During extinction in Experiment 4, operant responding diminished more quickly in pretrained NBM-lesioned rats than in controls, but subsequent reac quisition performance was equivalent in both groups. Results suggest t he NBM is importantly involved in discrimination learning, but choline rgic activity may be less critical for memory retention than for acqui sition.