Rapid goal-directed arm movements attenuate vestibular control of standing balance

Vestibular feedback is used to help us maintain upright standing posture. However, recent research has demonstrated that the human motor system decreases its use of vestibular information for balance control around the onset of voluntary lower-limb movement, measured as reduced coherence between the delivered electrical vestibular stimulation (EVS) signals and recorded ground reaction forces (GRFs). The objective of this study was to examine if EVS-GRF coherence is reduced before and during the initiation of voluntary upper-limb movements. Fifteen (10 female) participants performed reaching tasks with their right arm while grasping a KINARM manipulandum and standing on a force plate to measure GRFs. While reaching to target sequences of different lengths, participants received stochastic EVS (0-25Hz, ±4mA peak-to-peak amplitude, 1mA root mean square). Coherence was then calculated between the delivered EVS signals and mediolateral GRF (i.e., the direction of EVS-induced vestibular error) for the period 1000ms before to 2000ms after movement onset. Confidence intervals calculated from the coherence 1000-600ms before movement onset were used to determine if coherence significantly decreased during the analyzed timeframe. For every target, all participants experienced a significant reduction of EVS-GRF coherence before upper limb movement onset. These results demonstrate attenuation of the contribution of vestibular feedback to balance control around the onset of a rapid, voluntary, and goal-directed upper-limb movement, similar to movement of the lower limbs.