Vestibular-Evoked Balance Responses in the Upper Limb During Arm-Supported Balance

Michael Kennefick1, Sophia Furlan1, Paul van Donkelaar1, Brian H. Dalton1

1School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada

The vestibular system encodes head movement in space, which provides essential information for estimation of self-motion, gaze stabilization and balance control. Recently, vestibular-driven signals were shown to be relevant for sensorimotor processing during the preparation phase of arm movements. However, previous evidence is based on unilateral, arm-supported reaching tasks. Thus, the purpose of this study was to probe vestibular-evoked responses of the arm during unilateral and bilateral arm-supported and unsupported balance. This was accomplished via stochastic binaural, bipolar electrical vestibular stimulation (EVS; 0-25 Hz, RMS = 0.9 mA) deliveredfor 120 sover the mastoid processes in 5 experimental conditions with vision occluded. Participants performed either unsupported or arm-supported unimanual and bilateral whole-body balancing tasks. During the unsupported task, participants rested both arms by their sides or grasped a dumbbell at 90° elbow flexion. In contrast, the arm-supported task required participants tograsp an earth-fixed stationary handle either unilaterally or bilaterally. Vestibular-evoked responses were quantified in the time domain with a cross-correlation analysis (i.e., cumulant density function) between the EVS input and the motor output (i.e., elbow flexor and extensor surface electromyography). Cumulant density estimates surpassed 95% confidence intervals in the elbow flexors and extensors only when the muscles were involved in arm-supported balance, but not when holding the dumbbell. These findings indicate vestibular driven signals produce myogenic responses in muscles that are engaged actively in the whole-body balance task and not during irrelevant muscle activity (i.e., holding a dumbbell).