Pathophysiology of Involuntary Movements and Volitional Disorders

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The pathophysiology of psychogenic movement disorders (PMD) is very poorly understood. These disorders are common in the population, diagnosis is difficult and treatment typically ineffective. We are studying the mechanisms underlying these disorders using cognitive tasks, neurophysiological testing, psychiatric measures, and functional imaging. One functional imaging study is an fMRI comparison of patients with tremor, and preliminary results show abnormal activation in dorsolateral prefrontal cortex. We also want to look for abnormal activations related to tasks that probe functions such as emotional expression and movement inhibition. We will also investigate these patients for their sense of agency during fMRI studies, similar to the way we have studied normal subjects. Another major problem is the differentiation of conversion from malingering. There are no clinical methods available for this important distinction. We will be attempting to do this with fMRI. Using the Libet clock method of timing of subjective experience, it is possible to determine the time of the sense of willing a movement. It is possible that patients with distorted sense of volition will have abnormal timing of the sense of willing with respect to the timing of the movement itself. Initial studies in this regard are being undertaken in schizophrenia and for the tics in Tourette Syndrome. The origin of tics is generally unknown, and we have been approaching physiology in several ways. Tourette syndrome patients report "premonitory urge" and other sensory abnormalities associated with the presence of tics. We have been studying tic genesis with functional neuroimaging and EEG, and intend a series of studies looking at the physiology of the sensory urge. For many years, we have been collecting families with essential tremor looking for possible genetic abnormalities, and in several families found an area suggestive of genetic linkage on chromosome 6 and 11. This work is being done in conjunction with Dr. Lev Goldfarb.