Scientists have discovered a possible mechanism for how deep-brain stimulation, a widely used treatment for movement disorders, exerts its therapeutic effects. Few medical treatments show results as rapid and dramatic as those seen with DBS, in which surgically implanted devices deliver electrical pulses to inner brain structures involved in movement. In most Parkinson's disease (PD) patients who receive the treatment, symptoms of slow movement, tremor, and rigidity sharply diminish soon after the stimulation device is activated, and quickly return if the device is turned off.