Increased bradykinesia in Parkinson's disease with increased movement complexity: elbow flexion-extension movements.

The present research investigates factors contributing to bradykinesia in the control of simple and complex voluntary limb movement in Parkinson's disease (PD) patients. The functional scheme of the basal ganglia (BG)-thalamocortical circuit was described by a mathematical model based on the mean firing rates of BG nuclei. PD was simulated as a reduction in dopamine levels, and a loss of functional segregation between two competing motor modules.