Evidence for an amygdaloid projection to premotor cortex but not to motor cortex in the monkey.

Previous studies in the cat have demonstrated a direct projection from the amygdaloid complex to motor and premotor regions of the neocortex. In the present study both anterograde and retrograde tracer techniques have been used to determine whether a similar projection exists in the monkey brain. We have found that the dorsal, magnocellular division of the basal nucleus of the amygdaloid complex gives rise to a projection to the premotor cortex (Area 6), which terminates principally in layers I and II, and to a lesser extent in layer VI. No component of the amygdaloid complex has been found to project to the motor cortex (Area 4). The amygdaloid projection to Area 6 in the monkey appears to be substantially weaker than other rostrally directed projections from the basal amygdaloid nucleus to orbitofrontal and medial frontal areas, and also relatively weaker than the projection that has been described in the cat.