Mechanisms of disease: basic-research-driven investigations in humans--the case of hyperkinetic disorders

Recent studies have revealed that animal models of Huntington's disease and levodopa-induced dyskinesia show similar changes in corticostriatal transmission. In both conditions, corticostriatal long-term potentiation (LTP) is abnormally stable, causing persistent inhibition of the output nuclei of the basal ganglia, and involuntary movements. This finding has led to speculation that interventions that interfere with the maintenance of corticostriatal LTP might be useful as antidyskinetic treatments. One approach that is known to reduce cortical hyperexcitability in human disorders is the delivery of a long train of low-frequency ( approximately 1 Hz) stimulation using repetitive transcranial magnetic stimulation. This stimulation protocol is remarkably similar to that used in brain slices to reverse previously induced LTP, and consequently it has been used in patients with Huntington's disease or levodopa-induced dyskinesia to try to interfere with the abnormal corticostriatal plasticity postulated to underlie the motor disturbances in these conditions. Clear antidyskinetic effects of stimulation have been obtained in both disorders, without significant side effects. These findings could have implications for the treatment of hyperkinetic disorders in the clinic, and they illustrate how basic neuroscience can generate predictions to be tested in patients.