STEP INITIATION IN PARKINSONS-DISEASE - INFLUENCE OF LEVODOPA AND EXTERNAL SENSORY TRIGGERS

We studied anticipatory postural adjustments contributing to gait init iation deficits in patients with Parkinson's disease (PD) to determine if these deficits could be improved by administration of levodopa or by external stimuli. Ground reaction forces and body kinematics were r ecorded for self-generated and cutaneous cue-triggered step initiation in normal subjects and in PD subjects when OFF and when ON. The effec ts of assisting anticipatory postural sway with a surface translation coupled with a cutaneous cue were also examined. Decreased force produ ction, decreased velocity of movement, and slowed execution of the ant icipatory postural adjustments for self-generated step characterized s tep initiation in PD subjects when OFF. These impairments were signifi cantly less evident when the PD subjects were ON. Both PD and normal s ubjects increased force and velocity of movement when a cutaneous cue was used as a go signal. When subjects voluntarily initiated a step in response to the surface translation, both PD and normal subjects exec uted the anticipatory postural adjustments for step more rapidly, but the PD subjects, both ON and OFF, failed to increase force to execute push-off more rapidly. In conclusion, dopaminergic therapy and an exte rnal stimulus similarly improve the deficient force production for the anticipatory postural adjustments associated with step initiation in PD. The findings also suggest that force production during the postura l adjustment phase of self-generated, but not externally triggered, st ep initiation is influenced by dopaminergic pathways.