The moving platform after-effect reveals dissociation between what we know and how we walk

Gait adaptation is crucial for coping with varying terrain and biological needs. It is also important that any acquired adaptation is expressed only in the appropriate context. Here we review a recent series of experiments which demonstrate inappropriate expression of gait adaptation. We showed that a brief period of walking onto a platform previously experienced as moving results in a large forward sway despite full awareness of the changing context. The adaptation mechanisms involved in this paradigm are extremely fast, just 1-2 discrete exposures to the moving platform results in a motor after-effect. This after-effect still occurs even if subjects deliberately attempt to suppress it. However it disappears when the location or method of gait is altered, indicating that after-effect expression is context dependent. Conversely, making gait self-initiated increased sway during the after-effect. This after-effect demonstrates a profound dissociation between knowledge and action. The absence of generalisation suggests a simple form of motor learning. However, persistent expression of gait after-effects may be dependent on an intact cerebral cortex. The fact that the after-effect is greater during self-initiated gait, and is context dependent, would be consistent with the involvement of supraspinal areas.