Evidence for limb-independent control of locomotor trajectory.

After stepping in place on a rotating treadmill, individuals exhibit involuntary turning in the direction opposite treadmill rotation when stepping in place on a stationary surface without vision. This response is called podokinetic after-rotation (PKAR). It remains unclear where the control center for PKAR is located and whether separate, independent podokinetic control centers exist for each lower limb. To better understand neural mechanisms underlying locomotor trajectory adaptation, this study asked whether PKAR transfers between lower limbs. Thirteen healthy adults underwent separate 15-min sessions where one (trained) leg or both legs stepped on the rotating surface. Afterward, all subjects exhibited PKAR during one-legged hopping on a stationary surface, whether hopping on the trained or untrained limb. There were no significant differences in mean turning velocity across conditions. Our results support the absence of independent podokinetic control centers for lower limbs, indicating that a single center may control locomotor trajectory.