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UBC Theses and Dissertations

Modulation of vestibular-evoked reflexes and oculomotor function when standing under height-induced states of fear, anxiety and arousal Naranjo Naranjo, Eduardo

Abstract

As an important source of information for postural control, the Vestibular System may contribute to anxiety-related effects on balance control during stance and gait, particularly through increases in the vestibulospinal reflex (VSR) gain. While vestibulo-ocular reflex (VOR) gain has been associated with chronic anxiety, it is unclear if VOR and VSR gains are also sensitive to acute threat-related changes in fear, anxiety and arousal. Vestibular Evoked Myogenic Potentials (VEMPs) and Head Impulse Tests (HIT) can be used to test the gain of VSR and VOR pathways. Having subjects stand at the edge of an elevated platform can be used to threaten standing balance and induce arousal, anxiety and fear related to falling; known as a height-induced postural threat. The first aim of this thesis was to investigate how postural threat-related changes in arousal, anxiety and fear influence VEMP and HIT outcomes. Since the VOR depends also on visual pathways receiving signals relating to visual field motion and eye movements, a second study was designed to examine the independent effect of postural threat on oculomotor function using eye saccades, smooth pursuit and optokinetic nystagmus. For the first time, VEMPs were simultaneously recorded while standing from different muscles representing the three distinct vestibular reflexes. Likewise, this thesis is the first to investigate functional VOR and oculomotor outcomes with changes in state anxiety. The results from both studies provide robust evidence for increased VSR and VOR gain with acute negative emotional states. Furthermore, the observed increased gain of oculomotor function suggests that part of the VOR modulation occurs in neural centres not related to the vestibular system. These observations not only shed a light on how the VOR and gaze control are affected by state anxiety, fear and arousal, confirming previous reports on the VSR, but have also shown how emotions could alter the outcomes of clinical tests commonly used for assessing the vestibular and oculomotor function.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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