Activity in ventrolateral and mid-dorsolateral prefrontal cortex during nonspatial visual working memory processing: Evidence from functional magnetic resonance imaging

Whole-brain functional magnetic resonance imaging was used to study five he althy human subjects while they performed two nonspatial visual working mem ory tasks and one control task. In the first memory task, the subjects were required to view a sequence of three pattern stimuli, randomly selected fr om a familiar set of four stimuli, and then identify which one of three sim ultaneously presented stimuli was the one that had not been presented in th e previous array. In the other task, the subjects were required to observe an identical sequence of three randomly selected pattern stimuli and then t o respond by Selecting those same stimuli in the order presented. In compar ison to a baseline control task, increases in signal intensity were observe d, bilaterally, in the mid-dorsolateral frontal cortex and in the right ven trolateral frontal cortex in both memory tasks. When the two tasks were com pared directly, however, the first memory task, which had the higher monito ring requirement, yielded significantly greater signal intensity changes in area 9/46 of the right mid-dorsolateral frontal cortex. These results prov ide further evidence for the precise functional contribution made by the mi d-dorsolateral frontal cortex in visual working memory tasks and concur clo sely with findings in nonhuman primates. (C) 2000 Academic Press.