High-frequency priming stimulation has been shown repeatedly to increase the ability of 1 Hz stimulation to produce long-term depression in hippocampal synapses. Since 1 Hz repetitive transcranial magnetic stimulation (TMS) produces robust depression of the excitability in the motor cortex, we have studied healthy individuals to look at the effect of 6 Hz priming stimulation on this effect. Preliminary data suggest that motor cortex depression from 1 Hz stimulation is longer-lasting when preceded 6 Hz priming. If borne out in more subjects, priming stimulation may make TMS treatments more effective in disorders such as epilepsy and chronic pain. While it is known that patients with Parkinson disease and other movement disorders have an altered response to paired TMS of the motor cortex, it is not known whether this measure correlates with disease severity or whether the pattern of findings is specific to the disorder. This uncertainty is due largely to the lack of large and well-controlled studies. In order to answer this question, we initiated two large studies, one in Parkinson disease and one in tic disorder with age-matched healthy controls. These conditions were chosen because they differ widely in their physiology and clinical phenotype. We took measures of clinical severety and administered multiple psychological and cognitive tests in order to look for individual characteristics, independent of disease, that might interact with the physiological dependent variables. In a preliminary analysis, the patterns of physiological response differ significantly among the disease and control groups. Low-intensity DC polarization of focal cortical areas is known to alter the function of neurons in animals and humans. We are investigating the properties of this kind of brain stimulation and testing its ability to alter cognitive function in healthy subjects. Preliminary data suggest effects on psychomotor and language tests that depend on the polarity of the current.
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