title: Vestibulo-spinal and vestibulo-ocular reflexes are modulated when standing with increased postural threat.
abstract: We investigated how vestibulo-spinal reflexes (VSRs) and vestibulo-ocular reflexes (VORs) measured through vestibular evoked myogenic potentials (VEMPs) and video head impulse test (vHIT) outcomes, respectively, are modulated during standing under conditions of increased postural threat. Twenty-five healthy young adults stood quietly at low (0.8 m from the ground) and high (3.2 m) surface height conditions in two experiments. For the first experiment (n = 25) VEMPs were recorded with surface EMG from inferior oblique (IO), sternocleidomastoid (SCM), trapezius (TRP), and soleus (SOL) muscles in response to 256 air-conducted short tone bursts (125 dB SPL, 500 Hz, 4 ms) delivered via headphones. A subset of subjects (n = 19) also received horizontal and vertical head thrusts (∼150°/s) at each height in a separate session, comparing eye and head velocities by using a vHIT system for calculating the functional VOR gains. VEMP amplitudes (IO, TRP, SOL) and horizontal and vertical vHIT gains all increased with high surface height conditions (P < 0.05). Changes in IO and SCM VEMP amplitudes as well as horizontal vHIT gains were correlated with changes in electrodermal activity (ρ = 0.44-0.59, P < 0.05). VEMP amplitude for the IO also positively correlated with fear (ρ = 0.43, P = 0.03). Threat-induced anxiety, fear, and arousal have significant effects on VSR and VOR gains that can be observed in both physiological and functional outcome measures. These findings provide support for a potential central modulation of the vestibular nucleus complex through excitatory inputs from neural centers involved in processing fear, anxiety, arousal, and vigilance.
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada;
authors.forename: E N
authors.initials: EN
authors.lastname: Naranjo
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada;
authors.forename: T W
authors.initials: TW
authors.lastname: Cleworth
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; Department of Otolaryngology, University Hospital, Basel, Switzerland;
authors.forename: J H J
authors.initials: JH
authors.lastname: Allum
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada; Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada; and.
authors.forename: J T
authors.initials: JT
authors.lastname: Inglis
authors.affiliation: BC Rotary Hearing and Balance Centre at St. Paul's Hospital, Vancouver, British Columbia, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Lea
authors.affiliation: BC Rotary Hearing and Balance Centre at St. Paul's Hospital, Vancouver, British Columbia, Canada.
authors.forename: B D
authors.initials: BD
authors.lastname: Westerberg
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada; International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada; Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada; and mark.carpenter@ubc.ca.
authors.forename: M G
authors.initials: MG
authors.lastname: Carpenter
mesh_terms: D000328:Adult; D001143:Arousal; D019054:Evoked Potentials, Motor; D005133:Eye Movements; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D004856:Postural Balance; D011187:Posture; D012027:Reflex, Vestibulo-Ocular; D013116:Spinal Cord / Q000502:physiology*; D014726:Vestibular Nuclei / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000294:innervation / Q000502:physiology*
keywords: anxiety; arousal; fear; head impulse test; standing; vestibular evoked myogenic potential; vestibulo-ocular reflex; vestibulo-spinal reflex