Evidence for dissociation of impairment on auditory discrimination and delayed response following lateral frontal lesions in monkeys.

Impairments on both delayed-response and auditory-discrimination tasks have been reported to follow lateral frontal cortical lesions in monkeys. The present study is primarily concerned with the relationship of these two deficits. Three monkeys received ablations of sulcus principalis; three received ablations of lateral frontal cortex excluding sulcus principalis. Acquisition and retention of auditory-discrimination, delayed-response, and visual-discrimination tasks by the two groups were compared. Sulcus principalis lesions produced greater impairment on the delayed-response tasks. The lesions sparing sulcus principalis produced greater impairment on the auditory-discrimination tasks. The performance of the groups did not differ on the visual-discrimination tasks. These results suggest that the delayed-response deficit and the deficit in auditory discrimination that follow large frontal lesions may be dissociated by smaller frontal lesions. The results confirm that the focus for impairment on tests of the delayed-response type is in the region of sulcus principalis. The experimental data do not indicate the focus (if any) for the auditory-discrimination deficit, nor do they permit the definition of the nature of this deficit including its modality specificity.