ADAPTIVE PLASTICITY IN THE CONTROL OF LOCOMOTOR TRAJECTORY

Eight human subjects were exposed to 2 h of walking on the perimeter o f a horizontally rotating disc with the body remaining still in space. After adaptation to this experience subjects were blindfolded and ask ed to walk straight ahead on firm ground. When doing so all subjects g enerated curved walking trajectories of radii ranging from 65 to 200 i nches and angular velocities from 7 to 20 deg/s. Subsequent trials ove r the next half hour revealed retained, but decreasing, trajectory cur vature. Angular velocities associated with these trajectories were wel l above vestibular sensory threshold, yet all subjects consistently pe rceived themselves as walking straight ahead. The blindfold subjects w ere also asked to propel themselves in a straight line in a wheel chai r. Post-adaptation wheel chair trajectories showed no change from thos e before adaptation. Hence we infer that it was the relation between s omatosensory/motor elements of gait and the perception of trunk rotati on that had been remodelled during walking on the turning disc. This n ovel form of adaptive plasticity presumably serves to maintain optimal values of central neural parameters that control the trajectory of lo comotion. The findings may have significant implications for the diagn osis and rehabilitation of locomotor and vestibular disorders.