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

Vestibular feedback is used to help us maintain an 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 whether EVS-GRF coherence is reduced before and during the initiation of voluntary upper limb movements. Fifteen (10 females) 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 one, two, or three targets, participants received stochastic EVS (0-25 Hz, ±4 mA peak-to-peak amplitude, 1 mA root mean square). Coherence was then calculated between the delivered EVS signals and mediolateral GRFs (i.e., the direction of EVS-induced vestibular error) for the period 1,000 ms before to 2,000 ms after movement onset. Confidence intervals calculated from the coherence 1,000-600 ms before movement onset were used to determine whether coherence significantly decreased during the analyzed timeframe. Regardless of the number of targets, all participants experienced a significant reduction of EVS-GRF coherence before upper limb movement onset. These results demonstrate the 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.<b>NEW & NOTEWORTHY</b> Upper limb reaching movements were found to cause a temporary reduction of coherence (i.e., reduced similarity) between vestibular feedback and postural responses before and during movement onset. Thus, the online contribution of vestibular feedback is limited during the performance of the initial portions of upper limb reaching movements. These results provide evidence for processes other than online vestibular feedback integration being used to maintain balance while initiating reaching movements.