PHYSIOLOGICAL ANALYSIS OF VOLUNTARY MOVEMENT

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The goal of this project is to learn more about the control of movement in normal humans and in patients with voluntary movement disorders such as Parkinsons disease, cerebellar ataxia, hemiplegia from stroke and dystonia. One major scientific target of the Branch is to understand and possibly influence cortical reorganization in patients with congenital or acquired lesions of the central nervous system. A multi- modality approach (neuroimaging with PET and functional MRI, EEG, and transcranial magnetic stimulation) is being used to determine patterns of long-term reorganization of functional brain topography in individual stroke patients. Analysis of data from patients with subcortical lesions indicated that the reoganization of the cortical activity and excitability patterns depends on the site of the lesion within the internal capsule. Spectral power and coherence analyses of EEG are being employed to see how the brain communicates during different tasks. We have looked at EEG-EMG coherence to explore the motor cortex control of muscle. The cortico-muscular coherence in the higher frequencies (14-50 Hz) is mediated by the fast corticospinal tract and that coherence in the lower frequencies (3-13 Hz) is probably generated by a subcortical rhythm generator. The peak coherence value was not significantly affected by the produced force. However, a cortical-muscular coherence within the gamma band appeared as the strength of contraction increased up to 60% or more. This gamma band coherence at the higher force level most likely reflects the cortical control of the firing-rate modulation of the motor units and explains the generation of the muscle Piper rhythm, the 40 Hz grouping of muscle action potentials during maximal contraction. EEG coherence between the sensorimotor cortices on the two sides of the brain is similar for unimanual and bimanual tasks, but increases transiently when a new bimanual task is learned. In a study of bimanual coordination using fMRI, we found that areas which showed significantly more activation with antiparallel than parallel movement were the right SMA, the caudal cingulate motor area bilaterally and the right lateral premotor cortex. We have also studied different aspects of motor learning using PET and fMRI. Using PET, we confirmed prior EEG findings that the normal homuncular organization of the primary sensory cortex is degraded in patients with focal dystonia supporting the concept that sensory abnormalities play a pathogenetic role in dystonia. We have continued to treat patients with focal dystonias with botulinum toxin and demonstrate that patients with antibodies to type A can respond to type F. We studied a group of patients with Friedreichs ataxia using a new MRI sequence for iron and demonstrated an increased iron content in the dentate nucleus of the cerebellum consistent with the idea that iron is important in the pathophysiology. - Parkinson's disease, stroke, dystonia, EEG, positron emission tomography, functional MRI, ataxia, movement - Human Subjects