The role of the mid-dorsolateral prefrontal cortex in working memory

Recent studies with nonhuman primates have shown that lesions of the mid-do rsolateral prefrontal cortex, which extends from the lip of the dorsal bank of the sulcus principalis to the midline (i.e., dorsal area 46 and 9/46 an d area 9), give rise to severe and long-lasting impairments on self-ordered and externally ordered tasks designed to tax executive processing within w orking memory, rather than short-term memory per se. Lesions limited to are a 9 give rise to a mild impairment on these tasks. Thus, the mid-dorsolater al prefrontal region has been shown to be critical for the monitoring of mu ltiple events in working memory. The mid-dorsolateral prefrontal region rec eives visuospatial input from the posterior dorsolateral region (areas 8 an d 6) and from the cortex within the middle part (sulcal area 46) and the ca udal part (area 8) of the sulcus principalis. Nonspatial visual input origi nates from the ventrolateral prefrontal cortex. Thus, lesions focused on th e middle to caudal part of the sulcus principalis would affect visuospatial input, but would not affect the flow of nonspatial visual object informati on that reaches the mid-dorsolateral prefrontal region from the ventrolater al prefrontal cortex. Lesions of the sulcus principalis produce a spatially selective impairment, whereas lesions of the mid-dorsolateral prefrontal r egion produce a more general impairment of the monitoring and manipulation of information in working memory. The results of recent functional neuroima ging studies with human subjects are consistent with the above findings fro m work with the monkey.