Considerable progress has been made in developing models of cerebellar function in sensorimotor control, as well as in identifying key problems that are the focus of current investigation. In this consensus paper, we discuss the literature on the role of the cerebellar circuitry in motor control, bringing together a range of different viewpoints. The following topics are covered: oculomotor control, classical conditioning (evidence in animals and in humans), cerebellar control of motor speech, control of grip forces, control of voluntary limb movements, timing, sensorimotor synchronization, control of corticomotor excitability, control of movement-related sensory data acquisition, cerebro-cerebellar interaction in visuokinesthetic perception of hand movement, functional neuroimaging studies, and magnetoencephalographic mapping of cortico-cerebellar dynamics. While the field has yet to reach a consensus on the precise role played by the cerebellum in movement control, the literature has witnessed the emergence of broad proposals that address cerebellar function at multiple levels of analysis. This paper highlights the diversity of current opinion, providing a framework for debate and discussion on the role of this quintessential vertebrate structure.

Objective: This study aimed at identifying the impact of subcortical stroke on the interaction of cortical motor areas within and across hemispheres during the generation of voluntary hand movements. Methods: Twelve subacute stroke patients with a subcortical ischemic lesion and 12 age-matched control subjects were scanned using 3-Tesla functional magnetic resonance imaging. Subjects performed visually paced hand movements with their left, right, or both hands. Changes of effective connectivity among a bilateral network of core motor regions comprising M1, lateral premotor cortex, and the supplementary motor area (SMA) were assessed using dynamic causal modeling. Results: The data showed significant disturbances in the effective connectivity of motor areas in the patients group: Independently from hand movements, the intrinsic neural coupling between ipsilesional SMA and M1, and the interhemispheric coupling of both SMAs was significantly reduced. Furthermore, movements of the stroke-affected hand showed additional inhibitory influences from contralesional to ipsilesional M1 that correlated with the degree of motor impairment. For bimanual movements, interhemispheric communication between ipsilesional SMA and contralesional M1 was significantly reduced, which also correlated with impaired bimanual performance. Interpretation: The motor deficit of patients with a single subcortical lesion is associated with pathological interhemispheric interactions among key motor areas. The data suggest that a dysfunction between ipsilesional and contralesional M1, and between ipsilesional SMA and contralesional M1 underlies hand motor disability after stroke. Assessing effective connectivity by means of functional magnetic resonance imaging and dynamic causal modeling might be used in the future for the evaluation of interventions promoting recovery of function.

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Brain stimulation is a safe and promising tool to induce plastic changes in the cortical sensorimotor network to improve motor behavior after stroke. However, several methodological issues remain to be answered to further improve the effectiveness of these new approaches.