Implicit adaptation to galvanic vestibular perturbations during goal-directed postural movements

The vestibular system plays a crucial role in our dynamic control of posture and spatial orientation. While long-term adaptation to novel vestibular inputs occurs naturally in vestibular loss patients and astronauts, less is known about short-term adaptation of voluntary postural movements to vestibular perturbations. Using a sensorimotor adaptation paradigm, this thesis investigated implicit adaptation of whole-body goal-directed movement to a vestibular perturbation induced by galvanic vestibular stimulation (GVS). Twenty-six healthy young adults performed voluntary forward leans without vision toward a known target. Movements were perturbed with an L+ or R+ bell-shaped GVS stimulus (2mA, 1.3s). Trunk position was tracked with a VR tracker and terminal visual feedback was provided after each trial. Performance was quantified by lateral displacement and trajectory heading angles of the trunk at mid-trajectory and endpoint. Center of pressure and head, trunk and pelvis kinematics were also recorded. Our results showed that, during baseline, participants accurately leaned to the target with straight trajectories. When initially exposed to GVS, participants deviated towards the anode and missed the target, but after 100 trials, they successfully leaned to the target despite showing persistent trajectory deviations. Notably, unlike typical adaptation studies, we did not observe an exponential improvement in performance, nevertheless catch trials revealed progressively increasing errors in the direction opposite to the initial perturbation, indicating a progression in learning. Upon GVS removal, participants exhibited strong aftereffects, deviating and missing the target in the same direction as the catch trials. After 30 trials, endpoint accuracy gradually returned to baseline while trajectory curvature persisted. The observed aftereffects provided strong evidence for implicit sensorimotor adaptation, suggesting that participants recalibrated their cerebellar internal model of postural control by updating their expectations of vestibular consequences during self-generated movements. Moreover, the lack of exponential adaptation to the perturbation during the exposure may highlight the unique characteristics of vestibular adaptation compared to other sensory modalities. To our knowledge, these findings represent the first report of short-term aftereffects to GVS in voluntary dynamic standing postural control. These findings further our understanding of vestibular central processing during whole-body movement and may inform rehabilitation strategies for populations with balance deficits.