Quantitative demonstration of comparable architectonic areas within the ventromedial and lateral orbital cortex in the human and the macaque monkey brains

The orbital and ventromedial frontal cortical regions of the human and the macaquebrains are composed of several spatially discrete areas which are defined histologicallyby their distinctive laminar architecture. While considerable information has beencollected on the function and anatomical connections of specific architectonic areaswithin the orbital and ventromedial frontal cortex of the macaque monkey, the exactlocation of comparable areas in the human brain remains controversial because, untilnow, interspecies comparisons have relied upon imprecise qualitative descriptions ofthe cortical architecture. We resolved this problem by quantifying the areal densities ofcortical layers IV and Va in a large sample of the orbital and ventromedial frontal cortexin both species. We present here the first quantitative demonstration ofarchitectonically comparable cortical areas in the human and the macaque brains.Further, we found that the quantified architectonic features arrange areas within theorbital and ventromedial frontal cortex along two dimensions: an anterior-to-posteriorand a medial-to-lateral dimension. On the basis of these findings, and in light of knownanatomical connections in the macaque, we suggest that this region of the humancortex contains at least two hierarchically structured networks of areas