Significant cognitive decline in Parkinson's disease exacerbates the reliance on visual feedback during upper limb reaches

While upper limb reaches are often made in a feed-forward manner, visual feedback during the movement can be used to guide reaching hand towards target. In Parkinson's disease (PD), there is evidence that utilisation of this increased. However, it unclear if due solely characteristic slowness movements PD providing more opportunity for incorporating modify reach trajectories, or whether cognitive decline impacting (feed-forward) planning ability. To investigate this, we compared reaction times and target groups patients with normal cognition (PD-NC), mild impairment (PD-MCI) dementia (PD-D), controls (CON-NC) (CON-MCI). Reaches were undertaken full (at ‘natural’ ‘fast-as-possible’ pace); reduced an illuminated target; without any remembered eyes closed. The PD-D group exhibited slower than all other across conditions, indicative less efficient planning. When closed, relative their natural pace feedback. Crucially, slowing was most pronounced group, PD-MCI PD-NC groups, suggesting substantial exacerbates dependence on reaches.