Holmes NP, Christensen LOD, Miall RC (2002) Reaching to a target is disrupted by repetitive transcranial magnetic stimulation (rTMS) over the cerebellum: Empirical support for state-estimation by feed-forward internal models. MSc Thesis, Wolfson College, University of Oxford, 31pp.
The role of the cerebellum in the control of movement remains to be explicitly defined. Recent theoretical approaches assume the existence of internal models in the cerebellum, which perform both forward and inverse computations in predicting the sensory and motor consequences of movement commands. We hypothesised that repetitive transcranial magnetic stimulation (rTMS) over the right lateral cerebellum would disrupt the end-points of fast reaching movements to a remembered visual target. The task incorporated a steady lateral movement to create start-point uncertainty and irregularity between trials, and a final fast-reaction reaching movement. Application of rTMS immediately before the reaching movement significantly perturbed the distribution of end-points for stimulated versus unstimulated trials. Stimulation over the motor cortex had a smaller effect on movement accuracy, and in the opposite direction to the cerebellar perturbation. These results provide support for the existence of forward models in the cerebellum computing state-estimations of the motor system in the feed-forward control of fast reaching movements