Multiple divisions of macaque precentral motor cortex identified with neurofilament antibody SMI-32

In brain sections stained with monoclonal antibody SMI-32, which recognizes non-phosphorylated neurofilament protein, we distinguished separate caudal, intermediate, and rostral subdivisions of gigantocellular precentral cortex (areas 4c, 4i, and 4r) in macaque monkeys. The divisions form bands extending mediolaterally across the major body-region representations of the primary motor cortex (M1). These observations provide additional evidence that primary motor cortex is not a single, structurally homogeneous cortical area.