FEEDFORWARD POSTURAL ADJUSTMENTS IN A SIMPLE 2-JOINT SYNERGY IN PATIENTS WITH PARKINSONS-DISEASE

Patients with Parkinson's disease, age-matched controls and young cont rol subjects performed discrete elbow or wrist movements in a sagittal plane under the instruction to move one of the joints ''as fast as po ssible.'' Relative stability of the other, postural joint was comparab le in all 3 groups, while movement time was the highest in the patient s and the lowest in young controls. Typically, EMG patterns in both mu scle pairs acting at the joints demonstrated a commonly observed ''tri -phasic'' pattern. A cross-correlation analysis of the EMGs confirmed virtually simultaneous bursts in the wrist and elbow flexors and in th e wrist and elbow extensors. In all 3 groups, there were no signs of a nticipatory activation of postural muscles in about 90% of movements. We consider postural anticipation not a separate process, but a separa te peripheral pattern of a single control process that may involve a n umber of joints and muscles. We conclude that the postural deficits in Parkinson's disease are not related to a basic deficit in the ability to generate feedforward postural adjustments but to other factors tha t may include the specificity of maintaining the vertical posture in t he field of gravity.