Influence of visual cues on gait in Parkinson's disease: contribution to attention or sensory dependence?

Sensory cueing is used for a long time to improve gait in patients with Parkinson's disease. This has been established for visual cues such as stripes on floor and for rhythmic auditory cues. Concerning visual cueing two main mechanisms of action have been suggested and may be suitable depending on the instruction given to the patients. Stripes placed on the walking surface may draw attention to the stepping process if patients are talked to put their feet on the stripes. In another paradigm, the stripes on floor are just used to enhance the optical flow and the motion of the stripes is essential to improve gait. These findings are not found in normal controls suggesting that patients with Parkinson's disease are more dependent on dynamic visual cues for gait control than controls. Several common characteristics exist between attention and sensory contribution in gait control. First, their potential beneficial effect may be contre-balanced by a negative influence: visual information may be helpful for gait in patients or may disrupt locomotion and induce freezing (for example passing a door). Attention focused on gait allows a partial correction of the troubles by intentional modulation of the stride length but a dual task flowing attention away produces deterioration. Another point is that both strategies are probably used by the central nervous system to compensate deficits: visual dependence to compensate an impaired kinesthetic feed-back and attentional processing to alleviate automaticity in locomotion and so, to by-pass the deficit of internal cueing.