ANTICIPATORY POSTURAL ADJUSTMENTS DURING SELF-INFLICTED AND PREDICTABLE PERTURBATIONS IN PARKINSONS-DISEASE

This study investigated the relation between impaired anticipatory pos tural adjustments and bradykinesia in Parkinson's disease. Patients wi th Parkinson's disease and age matched controls stood on a platform. I n one series of experiments, they performed fast, discrete shoulder fl exion or extension movements. In another series, they were required to press a trigger with the right thumb and thus to release a load that was suspended from a bar which they were holding in front of them in e xtended arms. One more series included catching a load on the same bar . Anticipatory changes in the activity of postural muscles before fast voluntary movements occurred in patients and controls although the pa tients showed higher variability of anticipatory patterns. During load dropping and catching, control subjects had reproducible, although sm aller, anticipatory changes in postural muscle activity. Such changes were absent in all but one patient. Two sources of these postural pert urbations were analysed. The anticipatory postural adjustments in diff erent muscle groups may counteract perturbations of different origin. The distal to proximal sequencing of joint involvement in postural rea ctions may be related to different reference points and working points associated with these tasks compared with reaching limb movements. Th e deficit in anticipatory postural adjustments in Parkinson's disease is likely to be unrelated to bradykinesia and is more likely to reflec t the deficits in the basic processes of preparation and initiation of a motor act.