Sensory reweighting dynamics following removal and addition of visual and proprioceptive cues

Removing or adding sensory cues from one sensory system during standing balance causes a change in the contribution of remaining sensory systems, a process referred to as sensory reweighting. While reweighting changes have been described in many studies under steady state conditions, less is known about the temporal dynamics of reweighting following sudden transitions to different sensory conditions. The current study changed sensory conditions by periodically adding or removing visual (lights On/Off) or proprioceptive cues (surface sway referencing On/Off) in 12 young, healthy subjects. Evidence for changes in sensory contributions to balance were obtained by measuring the time course of medial-lateral sway responses to a constant amplitude 0.56 Hz sinusoidal stimulus applied as support surface tilt (proprioceptive contribution), as visual scene tilt (visual contribution), or as binaural galvanic vestibular stimulation (vestibular contribution), and by analyzing the time course of sway variability. Sine responses and variability of body sway velocity showed significant changes following transitions and were highly correlated under steady state conditions. A dependence of steady state responses on upcoming transitions was observed suggesting that knowledge of impending changes can influence sensory weighting. Dynamic changes in sway in the period immediately following sensory transitions were very inhomogeneous across sway measures and in different experimental tests. In contrast to steady state results, sway response and variability measures were not correlated with one another in the dynamic transition period. Several factors influence sway responses following addition or removal of sensory cues, partly instigated by, but also obscuring the effects of reweighting dynamics.

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