Effects of electrical stimulation and electrocoagulation in cortex and thalamus on delayed response in monkeys.

Eighteen brain points in prefrontal and thalamic areas of each of three adult male macaques were tested for the effects of electrical stimulation and coagulation during the delayed response test. During the delay period, stimulation of prefrontal areas and dorsomedial thalamus caused severe impairment in two subjects. Stimu!ation caused less impairment during the baiting period than during the delay period; continuous stimulation throughout the test caused less impairment than intermittent stimulation ; intermittent stimulation throughout the test was the most effective mode of stimulation. Distraction tests produced the same standard of performance achieved during control tests; peripheral shocks produced a slightly impaired performance. Even aversive peripheral stimuli did not produce as many errors as did central stimuli which produced no behavioral effects. Prefrontal lesions had more disruptive and longer-lasting effects than did thalamic lesions, but the order in which the lesions were made had no effect on performance. The results substantiate previous conclusions that electrical stimulation of points along the banks of the principal sulcus can impair the delayed response performance of overtrained subjects, but, on the other hand, stimulation of dorsomedial nucleus of thalamus has the same effect.