The notion of secondary motor areas, including the supplementary motor
area (SMA 1 ), arose from electrical-stimulation studies of the cerebral
cortex (Penfield and Welch 1951; Woolsey et al. 1952). It is only in recent
years that the SMA has emerged as a hierarchically more prominent cortical
field than it had previously been thought to be. This change in view
has been brought about by investigations of changes in regional cerebral
blood flow (rCBF; Lassen and Ingvar 1972) and of 'readiness potentials',
which occur up to l s before actual movement onset in man (Kornhuber
and Deecke 1965). It was soon recognized that also areas outside the
precentral motor cortex were activated when subjects were asked to perform
repetitive movements. Roland et al. (1980a) and Orgogozo and
Larsen (1979) attributed particular importance to the SMA, which, like
the motor cortex, displayed an increased rCBF when patients performed a
manual task.