Title: Adaptation of goal-directed whole-body postural movement to a repeated electrical vestibular perturbation.
Supervisors: Dr. Mark G. Carpenter, Dr. J. Timothy Inglis
Committee member: Dr. Romeo Chua
Abstract:
The vestibular system plays a crucial role in the neural control of posture and balance. Vestibular loss patients and astronauts returning to Earth initially exhibit postural deficits but can eventually adapt to their new vestibular environment, highlighting the importance of understanding the processes underlying vestibular adaptation. In a lab setting, balance perturbation can be evoked in healthy adults by applying an electrical current through electrodes placed on the skin behind the ears, a technique called electrical vestibular stimulation (EVS). When repeatedly exposed to EVS over multiple weeks or in a single session, participants show adaptation in standing balance (Dilda, 2014; Héroux, 2015), however it is unclear how they would adapt their dynamic balance. The purpose of this thesis is to use a sensorimotor adaptation paradigm to investigate the adaptation of goal-directed whole-body forward lean to a target when repeatedly exposed to a vestibular perturbation induced by EVS.
Participants will be standing in front of a screen displaying online visual feedback of their trunk position and will be asked to lean forward to bring their trunk cursor straight through a target. Trials will be performed without vision (occlusion goggles), but participants will receive visual terminal feedback of their performance at the end of some trials. Leaning movements will be perturbed by delivering a bell-shaped EVS stimulus (2 mA, 1.3 sec) triggered 0.5 sec prior to the start of the trial. Kinematics of the head, trunk and pelvis will be recorded with motion capture markers. Force plate data will be used to calculate the center of pressure. Trunk path (i.e. peak lateral deviation) and end-point accuracy (i.e. distance between the target and the cursor) will be used to assess task performance. In the pre-test, we expect participants to accurately lean through the target with a straight path. When introducing the EVS in the exposure block, we expect participants to deviate towards the anode (i.e. positive electrode) and miss the target but to gradually improve their performance after receiving terminal feedback of their error over multiple trials. To assess the aftereffects of the perturbation, the EVS will be removed during the post-test block (expected) and in a couple of catch trials throughout the exposure block (unexpected). In the post-test, aftereffects characterized by errors in the opposite direction as the perturbation would indicate an implicit adaptation to the altered vestibular input. Results from this thesis will thus provide insights into the mechanisms underlying the short-term adaptation of voluntary postural movement to external vestibular perturbations.