Dynamics of sensorimotor reweighting: How light touch alters vestibular-evoked balance responses

Abstract Integrated multisensory feedback plays a crucial role in balance control. Minimal fingertip contact with a surface (light-touch), reduces center of pressure (CoP) by adding sensory information about postural orientation and balance state. Electrical vestibular stimulation (EVS) can increase sway by adding erroneous vestibular cues. This juxtaposition of conflicting sensory cues can be exploited to explore the dynamics of sensorimotor reweighting. We used continuous stochastic EVS (0-25Hz; ±4mA; 200-300s) to evoke balance responses in CoP (Exp-1, Exp-2) and segment accelerations (Exp-2). Systems analyses (coherence, gain) quantified coupling and size of balance responses to EVS. We had participants either touch (TOUCH; <2N) or not touch (NO-TOUCH) a load cell during EVS (Exp-1, Exp-2), or we intermittently removed the touch surface (Exp-2) to measure the effects of light touch on vestibular-evoked balance responses. We hypothesized that coherence and gain between EVS and CoP would decrease, consistent with the CNS down-weighting vestibular cues that conflict with light touch. Light touch reduced CoP displacement, but increased variation in the CoP signal explained by EVS input. Significant coherence between EVS and CoP was observed up to ∼30Hz in both conditions but was significantly greater in the TOUCH condition from 12-28.5-Hz. Conversely, EVS-CoP gain was 63% lower in TOUCH, compared to NO-TOUCH. Our findings show that light touch can re-weight vestibular-evoked responses by reducing their size but also increasing high frequency vestibular contributions for sway. This suggests that the CNS can use novel sensory inputs to alter balance behavior but cannot completely ignore a salient balance cue. New and Noteworthy This study reveals that minimal fingertip contact (light touch) during balance tasks not only diminishes the impact of electrical vestibular stimulation (EVS) on sway, but also enhances the central nervous systems ability to integrate high-frequency vestibular cues. Specifically, light touch decreases the magnitude of EVS-induced sway while increasing coherence with EVS at higher frequencies, illustrating the central nervous system’s capacity to adaptively reweight sensory inputs for improved balance control without fully disregarding dominant cues.