The effect of Parkinson's disease and levodopa on adaptation of anticipatory postural adjustments.

Postural support alters anticipatory postural adjustments (APAs). Efficient adaptation to changes in postural support in reactive and centrally initiated postural synergies is impaired in Parkinson's disease (PD). This study examined whether APAs are affected differently by familiar and novel supports in people with PD, ON and OFF levodopa. The effect of PD and levodopa on the ability to immediately adapt APAs to changes in support and refine with practice was also investigated. Fourteen people with PD and 14 healthy control participants performed 20 single rapid leg lift tasks in four support conditions: unsupported, bilateral handgrip (familiar), bite plate (novel) and a combined handgrip+bite plate condition. APAs, identified from force plate data, were characterized by an increase in the vertical ground reaction force under the lifted leg as a result of a shift of weight toward the stance limb. Results showed the ability to incorporate familiar and novel external supports into the postural strategy was preserved in PD. Controls and PD patients in the OFF state further refined the postural strategy with practice as evidenced by changes in amplitude of vertical ground reaction forces and forces applied to support apparatus within conditions between the initial and final trials. In the ON state, people with PD failed to refine the use of postural supports in any condition. The results suggest that immediate postural adaptation is intact in people with PD and unaffected by levodopa administration but the ability to refine postural adaptations with task experience is compromised by dopamine therapy.