Studies of the cerebellar contribution to multijoint coordination focussed on planar 2-joint arm movements. Mathematical modeling preliminarily suggests that the cerebellum controls force transitions by linearly processing velocity feedback signals from both joints. A second issue is the role of the cerebellum in kinesthesia, the sense of movement. Results show a deficit in appreciation of velocity and duration in patients with cerebellar deficits. Other studies have focused on the control of balance and gait. Patients with cerebellar disorders and progressive supranuclear palsy are being studied. Using O-15 labelled water as a marker for cerebral blood flow in positron emission tomography (PET) studies, we have been working on methods for improved anatomic correlation of regions of metabolic change by superimposing the PET image onto an MRI image. In studies of PET and functional MRI we have shown plasticity of the motor cortex with transient limb deafferentation produced by ischemic block and internodal plasticity in the early blind. We have also shown frequency-dependent, differential activation of sensorimotor cortical areas using repetitive movements and repetitive peripheral nerve stimulation. We have also demonstrated activation of cortical regions including primary motor cortex with imagination of movement. Studies of somatosensory evoked potentials, movement related cortical potentials (MRCP), event related desynchronization, EEG coherence have been integrated with results from PET and functional MRI scanning. These techniques now provide complementary topographic and timing details of pre- and intramovement brain activity. A model of MRCP sources has been validated though comparison with areas of PET activation and subdural electrode potentials. Studies of changes in scalp potentials and cortical oscillations with voluntary muscle relaxation are ongoing. Studies are ongoing to record muscle spindle and cutaneous mechanoreceptor activity during voluntary movements and passive stretch. Results suggest that both are adequate in providing signals to the nervous system related to movement velocity.
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