A COMPARISON OF THE EFFECTS OF FRONTAL CORTICAL AND THALAMIC LESIONS ON MEASURES OF SPATIAL-LEARNING AND MEMORY IN THE RAT

Two experiments were conducted to compare the effects of radiofrequenc y lesions of thalamus and frontal cortex on three measures of spatial learning and memory: delayed non-matching to sample (DNMTS), radial ar m maze with imposed delays, and serial reversal learning. Thalamic les ions were aimed at the lateral internal medullary lamina (L-IML) and c ortical lesions at the projection areas of the mediodorsal nucleus alo ng the medial wall (MW) and dorsal to the rhinal sulcus (RS) in fronta l cortex. In Experiment 1 rats were trained on DNMTS prior to surgery. After recovery, rats with MW lesions showed persistent deficits on DN MTS that were significantly greater than for RS lesions. The deficits observed in MW lesioned animals were comparable to the effects of L-IM L lesions on this task that have been described in previous studies. I n Experiment 2 animals were trained to perform the radial arm maze tas k prior to treatment. After recovery, animals with L-IML lesions were impaired on the radial arm maze and on subsequent acquisition of the s erial reversal task. Rats with RS and MW lesions showed transient impa irments on the radial arm maze task, but otherwise performed as well a s controls on both these tasks.