Nucleus basalis lesions impair memory in rats trained on nonspatial and spatial discrimination tasks

Ibotenic acid-induced lesions of the nucleus basalis of Meynert (nbM) in rats produced severe memory impairments when subjects were required to acquire a brightness discrimination and learn its reversal (Experiment 1). Lesion-induced impairments were also observed when a complex (30-choice) spatial discrimination task served as the assessment instrument (Experiment 2). The memory deficits observed in Experiment 2 were evident despite an approximate 4-month postoperative recovery period and prior brightness discrimination training. Identical nbM lesions failed to produce memory decrements when rats were trained and tested 24 hr later on a simple (2-choice) right vs. left spatial discrimination task. It is concluded that nbM lesions impair memory for both nonspatial and spatial tasks and that, at least with tests of spatial memory, task difficulty may be an important determinant of this impairment.