Corticospinal projections from mesial frontal and cingulate areas in the monkey.

We injected neural tracers into the lateral funiculus of the spinal cord in order to relate the sites of origin of the spinal projections from the mesial cortical surface with the cytoarchitectonic organization of this region. We found a close correlation between the origin sites and density of corticospinal projections and the areal organization. The areas most densely labelled were F3 (SMA-proper) and area 24d, whereas F6 (pre-SMA) and area 24c showed a low density of labelling. The segmental topography of the corticospinal projections fitted well with the somatotopy of the mesial cortical areas. We conclude that in the agranular mesial cortex there are four independent motor representations: F3 and 24d where the whole body is represented, and F6 and 24c which are mostly related to arm movements.