Effects of Frontal Cortex Lesions on Learning Set

Abstract

REPORTS have conflicted about the effect of frontal cortex ablations on the development of vikudi discrimination learning set^1–3. Brush et al.¹, using eleven trials/problem, found that such ablations caused an impairment. This was particularly marked on those problems where the monkey's response on the first trial was not rewarded, and they concluded^1,4 that the impairment was due to the frontal monkeys' difficulty in reversing their initial stimulus preferences rather than to a generalized learning deficit. In contrast, Oscar and Wilson², using a similar testing regime, and Oxbury and Weiskrantz³, using three trials/problem, failed to find a frontal deficit. Mishkin⁴ has suggested that the cortical focus for the deficit may be the inferior frontal convexity—that is, cortex ventrolateral to sulcus principalis and the adjoining cortex on the lateral portion of the orbital surface of the frontal lobe. It is possible that the failures to find a deficit have been due to relative sparing of this area. The experiment reported here has tested this possibility.