Cortico-cortical connections of two electrophysiologically identified arm representations in the mesial agranular frontal cortex.

Neuronal tracers (diamidino yellow or wheat germ agglutinin conjugated with horseradish peroxidase) were injected in the arm representations of area 6a alpha (mesial surface, area F3), in the arm representation of area 6a beta (mesial surface) as well as in the eye field of area 6a beta (dorso-medial surface). The results showed that the arm representation of area F3 receives topographically organized afferents from motor and premotor areas (areas F1, F2, F4 and F5). A further connection was found with that part of cingulate cortex that sends projections to the spinal cord. In contrast, the arm representation of area 6a beta receives afferents chiefly from area F5, the prefrontal cortex and that part of cingulate sulcus which has few, if any, connections with the spinal cord. No connections were found with the precentral motor cortex (area F1). The area 6a beta eye field receives afferents mostly from the frontal eye field. Further connections are with the prefrontal cortex and cingulate gyrus. It is suggested that the so called "low level" motor functions of supplementary motor area are due to the activity of area F3, whereas the so called "high level" motor functions depend upon an independent area located in area 6a beta.