The nervous system responds to changes in external or internal conditions by altering the behavior of neurons through multiple forms of neural plasticity. A specific form of plasticity, "homeostatic plasticity", stabilizes neural activity by driving the excitability of neurons toward a "set-point" level of activity. Over the last six years, new data have come to light showing that the vestibular system also possess a robust capacity to modulate sensitivity to self-motion cues in response to prolonged periods of motion. Collectively, these studies have demonstrated a capacity to use motion perturbations (i.e., low, or high levels of vestibular stimulation) to dynamically adjust the sensitivity of the vestibular system on both the single neuron and behavioral levels. The ability to use subthreshold motion stimuli to drive plasticity in the vestibular system motivates this study. The investigators aim to determine the impact of subthreshold motion on (a) balance performance and (b) balance training in individuals with peripheral vestibular hypofunction.
Must be able to stand for 5 minutes unassisted
No leg or foot amputations
No lower limb braces
Not currently pregnant by self-report
Severe head trauma or traumatic brain injury
History of seizures
Alternative neurologic illness or condition known to impact vestibular or balance function (e.g., stroke, neurodegenerative disorders, demyelinating illness)
Major psychiatric (e.g., panic disorder, psychosis, etc.) disorder
Single group
Subthreshold Vestibular Conditioning
BehavioralSubthreshold vestibular conditioning will be performed while seated on a motion platform and blindfolded. The stimulus will consist of a pseudorandom sum-of-sinusoids roll tilt motion (\~0.08 to 1 Hz) delivered at a peak velocity equal to 57.4% of the measured baseline roll tilt perceptual threshold (e.g., 0.574°/s for a 1 °/s threshold). The participant will be informed that while the chair may vibrate or move slightly, the motion will not occur in any particular direction.
Balance Training
BehavioralBalance training will consist of progressive exposure to continuous one-dimensional roll 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. Roll tilt perturbations will be progressed by gradually increasing the displacement/velocity/acceleration of the platform motion.
Balance Training Plus Subthreshold Conditioning
Other interventionSubthreshold vestibular conditioning will be performed while seated on a motion platform and blindfolded prior to each bout of balance training. Subthreshold conditioning will consist of a pseudorandom sum-of-sinusoids roll tilt motion (\~0.08 to 1 Hz) delivered at a peak velocity equal to 57.4% of the measured baseline roll tilt perceptual threshold (e.g., 0.574°/s for a 1 °/s threshold). The participant will be informed that while the chair may vibrate or move slightly, the motion will not occur in any particular direction. Balance training will consist of progressive exposure to continuous two-dimensional (2D) pseudorandom platform perturbations delivered using a 6DoF motion platform. 2D perturbations (roll and pitch tilt) will be progressed by gradually increasing the displacement/velocity/acceleration of the motion stimulus.
Perturbed Stance Postural Control
The RMSD of mediolateral (ML) and anteroposterior (AP) postural sway will be measured in response to pseudorandom two-dimensional mediolateral and anteroposterior tilts of the support surface delivered using a 6DoF motion platform. Participants will stand with eyes closed and feet at a standardized distance on top of the motion platform. The platform will tilt simultaneously in both the roll and pitch planes, with each plane of tilt having independent frequency spectra (\~0.08 to 1 Hz). The perturbation test will last approximately 2 minutes.
Vestibular Perceptual Thresholds - 0.5Hz Roll Tilt
Vestibular perceptual thresholds will be measured using a forced-choice direction recognition task using methods that the investigators have used extensively. Subjects will be tilted in the coronal plane (i.e., roll tilt) in one of two directions (e.g., towards the left or right) in complete darkness while seated on a 6DoF platform. To mask potential auditory directionality cues, auditory "noise" - uncorrelated with motion (amplitude, direction, or type) - will be applied at approximately 60 dB SPL. Motion stimuli will consist of single cycles of sinusoidal acceleration. After each motion, the participant will be asked to judge the direction of the tilt stimulus, with the threshold being defined as the smallest velocity of tilt that can be accurately perceived.
Symptom Severity
Each participant will complete standardized questionnaires to assess symptom severity including: (a) dizziness (Dizziness Handicap Inventory), a measure of perceived handicap due to dizziness, with higher scores indicating more severe disability related handicap; (b) balance confidence (Activities Balance Confidence Scale), a measure of balance confidence, with higher scores indicating a higher degree of confidence in balance; and (c) impact of vestibular symptoms on daily life (Vestibular Activities of Daily Living Scale), a measure describing the impact of vestibular symptoms on activities of daily living, with higher scores indicating a greater impact of vestibular symptoms.
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Creighton University
Lead sponsor
National Institute on Deafness and Other Communication Disorders (NIDCD)
Collaborator
