FRONTAL LESIONS AND BEHAVIORAL DEFICITS IN MONKEY

Abstract

In order to determine the effects of frontal ablation in the squirrel monkey (Saimiri sciureus), 6 subjects were tested on pre- and post-operative test programs. Surgery consisted of removal of frontal granular cortex on lateral surfaces of both hemispheres. Postoperative testing revealed a marked deficit in performance on delayed-response problems[long dash]problems which require the subject to remember for a few seconds under which one of two identical blocks a reward has been placed. There was no evidence of postoperative hyperactivity. A preoperatively learned discrimination between unlike objects showed no impairment following surgery. When required to learn many (1000) independent discrimination problems, each with a different pair of unlike objects, frontal subjects revealed a learning-to-learn function[long dash]i.e., gradual improvement in rate of learning[long dash]showing efficiency equaling that of unoperated control subjects. Response latencies following a "punished"[long dash]i.e., slapped[long dash]reaching response were very prolonged prior to surgery but diminished considerably following frontal ablation. The delayed-response results were interpreted as indicating that frontal ablation in the squirrel monkey interferes primarily with ability to "store" information without the cues provided by differential stimulus objects. Other results demonstrate nonequipotentiality of associative cortex and definite frontal area involvement with emotional behavior.