Rapid adaptation to coriolis force perturbations of voluntary body sway

Abstract

Studying adaptation to Coriolis perturbations of armmovements has advanced our understanding of motor control andlearning. We have now applied this paradigm to two-dimensionalpostural sway. We measured how subjects (n=8) standing at thecenter of a fully enclosed rotating room who made voluntary anteriorposteriorswaying movements adapted to the Coriolis perturbationsgenerated by their sway. Subjects underwent four voluntary swaytrials prerotation, 20 per-rotation at 10 rpm counterclockwise, and 10postrotation. Each trial lasted 20 s, and subjects were permittednormal vision. Their voluntary sway during rotation generated Coriolisforces that initially induced rightward deviations of their forwardsway paths and leftward deviations of their backward sway. Sagittalplane sway was gradually restored over per-rotation trials, and amirror image aftereffect occurred in postrotation trials. Dual forceplate data analysis showed that subjects learned to counter the Coriolisaccelerations during rotation by executing a bimodal torque patternthat was asymmetric across legs and contingent on forward vs.backward movement. The experience-dependent acquisition andwashout of this compensation indicate that an internal, feedforwardmodel underlies the leg-asymmetric bimodal torque compensation,contingent on forward vs. backward movement. The learned torqueasymmetry we observed for forward vs. backward sway is not consistentwith parallel two-leg models of postural control.