Cerebellar and Cerebellar Thalamic Contributions to Motor Adaptation

Motor control theories have proposed that the brain controls movements through internal models which perform two reciprocal computations: given the motor action, predict sensory consequences (forward model) and given the desired sensory states, generate the appropriate motor action (inverse model). To produce accurate movements, the brain must continually calibrate or adapt these models. In this thesis, I explore the critical role played by the cerebellum in the formation and adaptation of these internal movement models, in both the reaching motor system and the saccadic system. For reaching movements it has been hypothesized that the cerebellum influences planned motor output through the cerebello-thalamo-cortical (CTC) pathway. We tested this hypothesis by studying patients with deep brain stimulation (DBS) electrodes placed in the cerebellar thalamus for the treatment of tremor. If the cerebellar thalamus relays both the normal signals related to motor adaptation as well as the abnormal oscillatory activity related to tremor, then stimulating the nucleus would produce both the desired tremor relief and the unintended disruption of motor adaptation. Indeed, we found that patients’ ability to adapt their reaching movements to novel force fields was impaired by DBS in a voltage dependent fashion: the larger the stimulation voltage, the bigger the impairment. We next investigated how the CTC pathway encodes motor adaptation by recording thalamic neural activities while patients made reaching movements during the microelectrode mapping phase of the DBS neurosurgery. We found preliminary evidence that thalamic activity is modulated by adaptation. To further understand the mechanism of adaptation, we turned to the sac-