Dorsolateral prefrontal cortex: comparative cytoarchitectonic analysis in the human and the macaque brain and corticocortical connection patterns

The cytoarchitecture of the human and the macaque monkey dorsolateral prefr ontal cortex has been examined in a strictly comparative manner in order to resolve major discrepancies between the available segmentations of this co rtical region in the human and the monkey brain. In addition, the connectio ns of the dorsolateral prefrontal cortical areas were re-examined in the mo nkey. The present analysis showed that only a restricted portion of what ha d previously been labelled as area 46 in the monkey has the same characteri stics as area 46 of the human brain; the remaining part of this monkey regi on has the characteristics of a portion of the middle frontal gyrus in the human brain that had previously been included as part of area 9. We have la belled this cortical area as 9/46 in both species. These two areas (i.e. 46 and 9/46), which constitute the lower half of the mid-dorsolateral frontal cortex, have a well-developed granular layer IV, and can easily be disting uished from area 9, on the upper part of the mid-dorsolateral region, which does not have a well-developed granular layer IV. Area 9 has the same basi c pattern of connections as areas 46 and 9/46, but, unlike the latter areas , it does not receive input from the lateral parietal cortex. Caudal to are a 9, on the dorsomedial portion of the frontal cortex, there is a distinct strip of cortex (area 8B) which, unlike area 9, receives significant input from the prestriate cortex and the medial parietal cortex. The present resu lts provide a basis for a closer integration of findings from functional ne uroimaging studies in human subjects with experimental work in the monkey.