Adaptive plasticity in the control of locomotor trajectory.

Eight human subjects were exposed to 2 h of walking on the perimeter of a horizontally rotating disc with the body remaining still in space. After adaptation to this experience subjects were blindfolded and asked to walk straight ahead on firm ground. When doing so all subjects generated curved walking trajectories of radii ranging from 65 to 200 inches and angular velocities from 7 to 20 deg/s. Subsequent trials over the next half hour revealed retained, but decreasing, trajectory curvature. Angular velocities associated with these trajectories were well above vestibular sensory threshold, yet all subjects consistently perceived themselves as walking straight ahead. The blindfolded subjects were also asked to propel themselves in a straight line in a wheel chair. Post-adaptation wheel chair trajectories showed no change from those before adaptation. Hence we infer that it was the relation between somatosensory/motor elements of gait and the perception of trunk rotation that had been remodelled during walking on the turning disc. This novel form of adaptive plasticity presumably serves to maintain optimal values of central neural parameters that control the trajectory of locomotion. The findings may have significant implications for the diagnosis and rehabilitation of locomotor and vestibular disorders.