Postural adjustments preceding rapid arm movements in parkinsonian subjects.

The electromyographic (EMG) responses in postural (thigh and trunk) and agonist (shoulder) muscles were examined in standing parkinsonian subjects and healthy controls prior to visual reaction time and self-paced rapid arm flexion movements. Recruitment of postural muscles typically preceded arm displacement in normals, but was less frequent, of shorter duration, and characterized by multiple EMG bursts which extended to the agonist in parkinsonians. Moreover, parallel delays in EMG recruitment times relative to the visual signal for both postural and agonist muscles were observed in akinetic patients. These abnormalities suggest that the basal ganglia may serve a preparatory motor function, by linking synergistic muscles through a common selection process.