• E N Naranjo, T W Cleworth, Allum J H J JHJ School of Kinesiology, University of British Columbia, Vancouver, BC, Canada; Department of ORL, University of Basel Hospital, Basel, Switzerland., J T Inglis, J Lea, B D Westerberg, and M G Carpenter.
• School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
• Neuroscience. 2017 Sep 17; 359: 289-298.

AbstractNeuro-anatomical evidence supports the potential for threat-related factors, such as fear, anxiety and vigilance, to influence brainstem motor nuclei controlling eye movements, as well as the vestibular nuclei. However, little is known about how threat influences human ocular responses, such as eye saccades (ES), smooth pursuit eye tracking (SP), and optokinetic nystagmus (OKN), and whether these responses can be facilitated above normal baseline levels with a natural source of threat. This study was designed to examine the effects of height-induced postural threat on the gain of ES, SP and OKN responses in humans. Twenty participants stood at two different surface heights while performing ES (ranging from 8° to 45° from center), SP (15, 20, 30°/s) and OKN (15, 30, 60°/s) responses in the horizontal plane. Height did not significantly increase the slope of the relationship between ES peak velocity and initial amplitude, or the gain of ES amplitude. In contrast height significantly increased SP and OKN gain. Significant correlations were found between changes in physiological arousal and OKN gain. Observations of changes with height in OKN and SP support neuro-anatomical evidence of threat-related mechanisms influencing both oculo-motor nuclei and vestibular reflex pathways. Although further study is warranted, the findings suggest that potential influences of fear, anxiety and arousal/alertness should be accounted for, or controlled, during clinical vestibular and oculo-motor testing.Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

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