Parcellation of the lateral premotor cortex of the macaque monkey based onstaining with the neurofilament antibody SMI-32

In macaque monkey, frontal and parasagittal brain sections were stained wit h SMI-32, an antibody directed against a nonphosphorylated neurofilament pr otein that labels pyramidal cells. The goal of this investigation was to fi nd reliable criteria with which to draw the border between the motor (M1) a nd premotor (PM) cortex and delineate subdivisions within the lateral PM. T wo-dimensional reconstruction of the staining patterns was also performed b y flattening the series of frontal sections. The distribution of SMI-32 imm unoreactivity in layers III and V of the cortex revealed the existence of t hree subregions in the ventral rostral PM and a clear mediolateral boundary within the dorsal PM defined by clusters of SMI-32-positive pyramidal cell s in layer V, The border between M1 and PM was easily distinguished at the level of the dorsal PM by a strong loss of immunoreactive pyramidal cells i n layers III and V, At the level of the ventral PM there was no clear disru ption of layer V pattern, and the border was set using the pattern of layer III immunoreactivity.