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Purpose of review: Akinesia, rigidity and low-frequency rest tremor are the three cardinal motor signs of Parkinson's disease and some Parkinson's disease animal models. However, cumulative evidence supports the view that akinesia/rigidity vs. tremor reflect different pathophysiological phenomena in the basal ganglia. Here, we review the recent physiological literature correlating abnormal neural activity in the basal ganglia with Parkinson's disease clinical symptoms.

Recent findings: The subthalamic nucleus of Parkinson's disease patients is characterized by oscillatory activity in the beta-frequency (~15 Hz) range. However, Parkinson's disease tremor is not strictly correlated with the abnormal synchronous oscillations of the basal ganglia. On the other hand, akinesia and rigidity are better correlated with the basal ganglia beta oscillations.

Summary: The abnormal basal ganglia output leads to akinesia and rigidity. Parkinson's disease tremor most likely evolves as a downstream compensatory mechanism.

(C) 2009 Lippincott Williams & Wilkins, Inc.