title: Frequency-specific modulation of vestibular-evoked sway responses in humans.
abstract: Galvanic vestibular stimulation (GVS) results in characteristic muscle and whole-body responses in humans maintaining standing balance. However, the relationship between these two vestibular-evoked responses remains elusive. This study seeks to determine whether mechanical filtering from conversion of lower-limb muscle activity to body sway, during standing balance, can be used to attenuate sway while maintaining biphasic lower-limb muscle responses using frequency-limited stochastic vestibular stimulation (SVS). We hypothesized that SVS deprived of frequencies <2 Hz would evoke biphasic muscle responses with minimal whole-body sway due to mechanical filtering of the higher-frequency muscle responses. Subjects were exposed to five stimulus bandwidths: two meant to induce sway responses (0-1 and 0-2 Hz) and three to dissociate vestibular-evoked muscle responses from whole-body sway (0-25, 1-25, and 2-25 Hz). Two main results emerged: 1) SVS-related sway was attenuated when frequencies <2 Hz were excluded, whereas multiphasic muscle and force responses were retained; and 2) the gain of the estimated transfer functions exhibited successive low-pass filtering of vestibular stimuli during conversion to muscle activity, anteroposterior (AP) moment, and sway. This successive low-pass filtering limited the transfer of signal power to frequencies <20 Hz in muscle activity, <5 Hz in AP moment, and <2 Hz in AP trunk sway. Consequently, the present results show that SVS delivered at frequencies >2 Hz to standing humans do not cause a destabilizing whole-body sway response but are associated with the typical biphasic lower-limb muscle responses.
authors.affiliation: School of Human Kinetics, University of British Columbia, Vancouver, BC, Canada V6T 1Z1.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Dakin
authors.forename: Billy L
authors.initials: BL
authors.lastname: Luu
authors.forename: Kees
authors.initials: K
authors.lastname: van den Doel
authors.forename: John Timothy
authors.initials: JT
authors.lastname: Inglis
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Blouin
mesh_terms: D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods; D004856:Postural Balance / Q000502:physiology*; D014722:Vestibule, Labyrinth / Q000502:physiology*; D055815:Young Adult