VESTIBULAR EVOKED MYOGENIC POTENTIALS IN ALTERED GRAVITY

Recently, new clinical testing of saccular and utricular function have been developed and validated, the so-called vestibular-evoked myogenic potentials - VEMP (Brantberg et al. 2009, Cornell et al. 2009, Curthoys 2010, Manzari et al. 2012). Among them, the cervical VEMP (cVEMP) are short-latency electromyographic (EMG) modulations of the contracted sternocleidomastoid muscles in responses to vibration applied on the forehead. The clinical literature suggests that cVEMP are almost entirely saccular in origin (Halmagyi et al 1995).

The aim of our research is to evaluate changes in the otolith function in microgravity and hypergravity using this clinical test. Cervical vestibular-evoked myogenic potentials (cVEMP) will be recorded by surface EMG electrodes in response to bone conducted vibration to specifically assess saccular function (Halmagyi et al 1995). The primary measures will include muscle activity response amplitudes and the stimulus intensity threshold at which the cVEMP is detected.

Given that there is an off-loading of the saccules in microgravity and an increased loading in hypergravity, we hypothesize that there will be a reduction in cVEMP amplitude in microgravity and an increase in cVEMP amplitude in hypregravity compared to normal gravity. These changes in amplitude will be accompanied by changes in the threshold of the stimulus level required to elicit a cVEMP.