This thesis investigates circuits within the brain and spinal cord that contribute to -10 Hz physiological tremor and slow finger movement discontinuities. Electrophysiological recordings were made from the motor areas of two macaque monkeys trained to perform index finger flexion movements whilst tracking a moving target. We recorded local field potentials and single units from the primary motor cortex (Ml), deep cerebellar nuclei (DCN), pontomedullary reticular formation (PMRF) and the intermediate zone of the spinal cord (SC). Activity for all areas was coherent with finger acceleration at -10 Hz.