Vestibulo-spinal and vestibulo-ocular reflexes are modulated when standing with increased postural threat.

Vestibulo-spinal and vestibulo-ocular reflexes are modulated when standing with increased postural threat.

J Neurophysiol. 2015 Dec 2;:jn.00626.2015

Authors: Naranjo EN, Cleworth TW, Allum JH, Inglis JT, Lea J, Westerberg BD, Carpenter MG

Abstract
OBJECTIVE: to investigate how vestibulo-spinal reflexes (VSR) and vestibulo-ocular reflexes (VOR) measured through vestibular evoked myogenic potentials (VEMP) and video head impulse test (vHIT) outcomes, respectively, are modulated when standing under conditions of increased postural threat.
METHODS: 25 healthy young adults stood quietly at low (0.8m from the ground) and high (3.2m) 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; 500Hz; 4 ms) delivered via headphones. A sub-set of subjects (n=19) also received horizontal and vertical head thrusts (approx. 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.
RESULTS: 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 (Rho=0.44 to 0.59, p<0.05). VEMP amplitude for the IO also positively correlated with fear (Rho = 0.43, p = 0.03).
CONCLUSION: 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 nuclei complex through excitatory inputs from neural centers involved in processing fear, anxiety, arousal and vigilance.

PMID: 26631147 [PubMed - as supplied by publisher]

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