Subthreshold Vestibular Stimulation as a Strategy for Rehabilitation

The subthreshold vestibular conditioning protocols will be performed while seated on a motion platform in a dark room. A 0.5Hz whole-body tilt conditioning stimulus will be delivered. The stimulus will consist of whole-body sinusoidal motions (similar to those used when measuring tilt perceptual thresholds) delivered at 57.4% of the measured baseline threshold (e.g., 0.574°/s for a 1 °/s threshold); the frequency (0.5Hz) was chosen to match the baseline threshold tasks. The participants and experimenter will be blinded to the nature of the condition and will be informed that while the chair may vibrate or move slightly, the motion will not occur in any particular direction. Music, audiobooks, or podcasts of the subject's choosing will be played to further discourage attention to the conditioning stimulus.

Balance training will consist of progressive exposure to continuous pseudorandom platform perturbations delivered using a 6DoF motion platform. Participants will stand on a MOOG hexapod motion platform and will be secured using a safety harness tethered to the ceiling and a full enclosure of safety rails. Balance training will be progressed by (a) gradually increasing the number of degrees of freedom (e.g., 1DOF to 6DOF) in the perturbation, (b) removing visual cues, (c) narrowing the base of support, and (d) increasing the amplitude, velocity, and/or acceleration of the platform motion. In the event that subject experiences a loss of balance, the level of difficulty will be modified accordingly. Each balance training block will include 5 minutes of perturbations followed by 3 minutes of rest, repeated 5 times for a total of 40 minutes of training.