Tested 14 rhesus monkeys with lesions limited to the superior and/or inferior banks of the middle 3rd of sulcus principalis on retention of 5-sec spatial delayed alternation and place reversal. Ablations of the superior or inferior banks had no consistent behavioral effects, while lesions which involved both banks, either in the depths or superficial regions of the sulcus, resulted in deficits on both spatial tasks. Ss that failed to relearn delayed alternation also evidenced deficits on place reversal. Findings suggest that both tasks involved a common factor mediated by cortex within the middle 3rd of the sulcus. (PsycINFO Database Record (c) 2006 APA, all rights reserved)