Bimanual coordination deficits with Parkinson's disease: the influence of movement speed and external cueing

Continuous coordinated movement of the upper limbs performed at different movement frequencies, and with different external timing conditions, was examined in individuals with Parkinson's disease (PD) and healthy, age- and gender-matched controls. Participants performed symmetric in-phase movements toward and away from the midline of the body, and isodirectional anti-phase movements at one of three metronome speeds (0.75, 1.25, and 1.75 Hz), and in two different auditory cueing conditions (cue present, cue absent). Measures of relative phase accuracy (absolute mean error) and stability (standard deviation) revealed that individuals with PD performed in-phase movements as well as the controls, while anti-phase movements were performed with greater mean error and variability. The adverse effects of PD on the anti-phase task were also reflected by freezing (8.1% of anti-phase trials) and hypometric deficits (5.1% of anti-phase trials) during movement. None of these PD-related impairments occurred during in-phase trials. The overall accuracy or stability of movement coordination was not improved with the presence of external pacing cues, suggesting that although execution impairments of individuals with PD may be dramatically influenced by attention, external cueing does not necessarily improve movement performance.