Insight into dopamine-dependent planning deficits in Parkinson's disease: A sharing of cognitive and sensory resources


Attention and sensorimotor processes are needed for successful planning of footsteps during complex gait situations, but their response to dopaminergic treatment is poorly understood. In the current study, we evaluated walking and gaze behaviours while planning an approach toward an obstacle to be stepped over. The obstacle clearance task was completed both ON and OFF dopaminergic medication by individuals with Parkinson's disease (n=20) and compared to healthy age-matched control participants (n=19), as well as with and without an auditory digit monitoring dual task. Gait and gaze data were synchronized. Each trial was split into an early and late phase prior to the obstacle, providing a unique opportunity to examine dopamine-dependent planning deficits in Parkinson's disease. Interestingly, only patients in the OFF medication state showed greater deceleration in the late phase (i.e. just before the obstacle), as well as an increase in step time variability (also in this late phase) with the additional demands of a dual task. Although there were differences in gait between groups, gaze behaviors were the same for all participants irrespective to phase and dual-task condition. Surprisingly, the gaze behavior of the PD OFF group showed no interactions with phase or condition suggesting that the deceleration and increased variability when approaching an obstacle is the result of a greater demand for online sensory feedback that cannot be compensated for with visual strategies. We conclude that dopamine influences planning by limiting sensorimotor processing capacity, especially in the presence of increased cognitive demand in Parkinson's disease.

Acknowledgments: CFI; CNPq