A multitude of functional imaging studies revealed a mass activation effect at the
level of the sensorimotor cortex during repetitive finger-tapping or finger-to-thumb
opposition tasks in terms of either a stepwise or a monotonic relationship between
movement rate and hemodynamic response. With respect to subcortical structures of
the centralmotor system, there is, by contrast, some preliminary evidence for nonlinear
rate/response functions within basal ganglia and cerebellum. To further specify these
hemodynamic mechanisms, functional magnetic resonance imaging (fMRI) was performed
during a finger-tapping task in response to acoustic stimuli (six different frequencies:
2.0, 2.5, 3.0, 4.0, 5.0 and 6.0 Hz; applied via headphones). Passive listening to
the same auditory stimuli served as a control condition. Statistical evaluation of
the obtained data considered two approaches: categorical and parametric analysis.
As expected, the magnitude of the elicited hemodynamic response within left sensorimotor
cortex (plateau phase at frequencies above 4 Hz) and mesiofrontal cortex paralleled
movement rate. The observed bipartite mesial response pattern, most presumably, reflects
functional compartmentalization of supplementary motor area (SMA) in a rostral component
(pre-SMA) and in a caudal (SMA proper) component. At the level of the cerebellum,
two significant hemodynamic responses within the hemisphere ipsilateral to the hand
engaged into finger tapping (anterior/posterior quadrangular lobule and posterior
quadrangular lobule) could be observed. Both activation foci exhibited a stepwise
rate/response function. In accordance with clinical data, these data indicate different
cerebellar contributions to motor control at frequencies below or above about 3 Hz,
respectively. Caudate nucleus, putamen, and external pallidum of the left hemisphere
displayed, by contrast, a negative linear rate/response relationship. The physiological
significance of these latter findings remains to be clarified.