ORIGIN OF THALAMOCORTICAL PROJECTIONS TO THE PRESUPPLEMENTARY MOTOR AREA (PRE-SMA) IN THE MACAQUE MONKEY

The presupplementary motor area (pre-SMA) is a recently defined cortic al motor area that is located immediately rostral to the supplementary motor area (SMA) and is considered to play more complex roles in moto r control than the SMA. In the present study, we examined the distribu tion of cells of origin of thalamocortical projections to the pre-SMA in the macaque monkey. Under the guidance of intracortical microstimul ation mapping, the retrograde tracer biotinylated dextran amine was in jected into the pre-SMA. Retrogradely labeled neurons were distributed primarily in the parvicellular division of the ventroanterior nucleus (VApc), oral division of the ventrolateral nucleus (VLo), area X, and mediodorsal nucleus (MD). Some labeled neurons were also observed in the medial and caudal divisions of the ventrolateral nucleus. The resu lts indicate that the pre-SMA may receive not only basal ganglia input s via the VApc, VLo, and MD, but also a cerebellar input via the X.