[Human supplementary motor area: a role in voluntary movements and its clinical significance].

There were two hypotheses of functions of supplementary motor area (SMA): supplementary vs. supramotor, in 1980s. Clinically, SMA can develop a very intractable seizure focus characterized by unique ictal motor symptoms, and its dysfunction is also strongly related to the cardinal clinical features in patients with Parkinson's disease and dystonia. In patients with intractable partial seizures arising from the mesial frontal area who needed clinically chronic implantation of the subdural electrode grids for 1-2 weeks prior to the focus resection, we recorded movement-related cortical potentials or Bereitschaftspotentials (BPs) prior to the voluntary movements. As the results, 1) SMA proper, a caudal part of SMA showed a somatotopy of BP generators in accordance with each part of the voluntary movements in the body, 2) bilateral SMAs were involved in each side of the body movements equally, and the amplitude did not differ from one in the contralateral primary motor area (MI), and thus it proved that SMA proper played as a significant role in preparation for voluntary movements as MI. Furthermore, we clarified the functional significance of pre-SMA with regard to sensorimotor integration, decision making, repetitive rate of voluntary movements, voluntary motor inhibition and negative motor response. Clinically we also clarified the pathophysiology of SMA seizures, and impairment of SMA function in Parkinson's disease and dystonia. We look forward to clinical application of brain potentials from SMA in the field of brain-computer interface such as assessment and restorative approach in patients with spinal cord injury, paraplegia or motor neuron disease.