From will to action: sequential cerebellar contributions to voluntary movement.

The cerebellum is known to be involved in numerous motor related functions, but recent observations suggest that it also performs fundamental operations on nonmotor functions such as perception and cognition. Assuming that the cerebellum has to be consulted in a limited window of time, cerebellar activation should occur in a time-dependent manner in respect to the corresponding telencephalic areas. This hypothesis was tested by combining a simple motor task with the demand of a self-paced delay using event-related functional magnetic resonance imaging. Evaluation with a time-shifted canonical hemodynamic response function revealed spatially and temporally separated cerebral and cerebellar activation accompanying the entire process--from conscious planning to final motor output--within a time frame of 6 s. The cerebral activations spread from the anterior cingulate cortex through the supplementary motor and premotor area to the primary motor and sensory cortices. This cascade was temporally in parallel with cerebellar activations propagating from the neo- to the spinocerebellum. An early lateral cerebellar recruitment 3 s prior movement onset confirms its involvement in cognitive processing. A later medial activation occurring close to movement onset most probably reflects spinocerebellar kinesthetic feedback. Between these two points a striking lateromedial succession was found, which is in line with the hypothesis of the existence of multiple internal models residing in the cerebellum, each communicating with its own corresponding telencephalic region.