Visual kinesthesia and locomotion in Parkinson's disease.

We investigated predominance of visual control in Parkinson's disease (PD) gait regulation and whether visual kinesthesia has systematic effects on gait parameters. Effects of artificial optic flow were studied on walking velocity (WV), stride length (SL), and stride frequency (SF) during treadmill walking in PD patients and young and elderly adults. The independent variable was relative optic flow (rOF), ranging from -1 times (forward flow, i.e., in walking direction) to 3 times WV (backward flow, natural direction). All walkers were influenced similarly by rOF, inducing systematic changes of WV. Backward flow caused a decrease and forward flow an increase of WV. Without effect of rOF, PD patients on average walked at 0.89 meters per second compared to 1.31 meters per second in the age-matched healthy group. The rOF-induced mean changes of WV in all PD patients amounted to 0.45 meters per second (50.4%), with 45.1% due to changes in SL and 5.3% to SF. In the age-matched, rOF-induced WV changes reached 0.18 meters per second (13.8%), with 10.8% due to SL and 3.2% to SF. Thus, compared to the results of the age-matched group, effects of rOF in PD patients were stronger, which increased WV to a normal level by normalization of SL. Contrary to the healthy subjects, no attenuation of optic flow effects over time was observed in the PD patients. Predominance of visual control in PD gait is suggested due to deficits in proprioception compensated by visual kinesthesia, causing exaggerated reaction to visual feedback. The results extend beyond earlier findings, generally stating improvement of PD gait by presence of visual feedback but show systematic effects on gait parameters due to reweighting of visual kinesthesia.