Increased gain of vestibulospinal potentials evoked in neck and leg muscles when standing under height-induced postural threat

Abstract

ObjectiveTo measure changes in amplitudes of vestibular evoked myogenic potentials (VEMPs) elicited from neck, upper and lower limb muscles during a quiet standing task with increased postural threat achieved by manipulating surface height. Methods: Twenty eight subjects were tested while standing on a platform raised to 0.8m and 3.2m from the ground. Surface electromyography was recorded from the ipsilateral sternocleidomastoid (SCM), biceps brachii (BB), flexor carpi radialis (FCR), soleus (SOL) and medial gastrocnemius (MG) muscles. Stimulation was with air-conducted short tone bursts (4ms). After controlling for background muscle activity, VEMP amplitudes were compared between heights and correlated with changes in state anxiety, fear and arousal. Results: VEMP amplitude significantly increased in SCM (9%) and SOL (12.7%) with increased surface height (p<0.05). These modest increases in SCM VEMP amplitude were significantly correlated with anxiety (Rho=0.57, p=0.004) and confidence (Rho=−0.38, p=0.047) and those for SOL were significantly correlated with anxiety (Rho=0.33, p=0.049) and fear (Rho=0.36, p=0.037). Conclusion: Postural threat significantly increased vestibulospinal reflex (VSR) gains. Results demonstrate that VEMPs can be used to test different VSR pathways simultaneously during stance. Since fear and anxiety are prevalent with vestibular disorders, they should be considered as potential contributing factors for clinical vestibular outcome measures.