MOST OF OUR DAILY activities are effortless, but they require an interplay of sensory inputs and cognitive strategies. Getting out of bed, finding your glasses, putting them on, charting and finding a path between the obstacles on the ground left there accidentally, and going to the bathroom need more than good movements, particularly at night, when the visual input is impoverished. When you ask patients with Parkinson disease (PD) to close their eyes and continue with the previously executed rhythmic movement, such as moving their finger to and fro between your 2 outstretched arms, they will stop after the first few movements, as if frozen. Normally, healthy people can continue to walk for seconds even with closed eyes along a path they have taken. Apparently, in healthy people a visual map persists for several seconds and helps to guide locomotion. Parkinsonian patients may freeze in their walk even with open eyes. Some can break the frozen episode by looking at visual markers, such as stripes painted on the ground. The common consideration for freezing is that it relates to loss of will, decreased motor activity, and general poverty of behavior. These symptoms are usually explained by motor impairment owing to striatonigral dopaminergic deficiency. However, the PD-specific importance of visual reinforcement on locomotion does not simply fit into this model.
Bodis-Wollner I. Visualizing the Next Steps in Parkinson Disease. Arch Neurol. 2002;59(8):1233-1234. doi:10.1001/archneur.59.8.1233