Dissociable roles of mid-dorsolateral prefrontal and anterior inferotemporal cortex in visual working memory

Functional neuroimaging in human subjects and studies of monkeys with lesio ns limited to the mid-dorsolateral (MDL) prefrontal cortex have shown that this specific region of the prefrontal cortex is involved in visual working memory, although its precise role remains a matter of debate. The present study compared the effect on visual working memory of lesions restricted to the mid-dorsolateral prefrontal cortex of the monkey with that of lesions to the anterior inferotemporal cortex, a region of the temporal cortex spec ialized for visual memory. Increasing the delay during which information ha d to be maintained in visual working memory impaired performance after lesi ons of the anterior inferotemporal cortex, but not after mid-dorsolateral p refrontal lesions. By contrast, increasing the number of stimuli that had t o be monitored impaired the performance of animals with mid-dorsolateral pr efrontal lesions, but not that of animals with anterior inferotemporal lesi ons. This demonstration of a double dissociation between the effects of the se two lesions provides strong evidence that the role of the mid-dorsolater al prefrontal cortex in visual working memory does not lie in the maintenan ce of information per se, but rather in the executive process of monitoring this information. In addition, the present study demonstrated that lesions limited to area 9, which constitutes the superior part of the mid-dorsolat eral prefrontal region, give rise to a mild impairment in the monitoring of information, whereas lesions of the complete mid-dorsolateral prefrontal r egion yield a very severe impairment.