The vestibulo-masseteric reflex and the acoustic-masseteric reflex: a reliability and responsiveness study in healthy subjects

The vestibulo-masseteric reflex (VMR or p11 wave), the acoustic-masseteric reflex (AMR or p1/n21 wave) and the mixed
vestibulo-cochlear p11/n21 potential are responses of masseter muscles to sound that can be employed to evaluate brainstem
function. This study was aimed at establishing the test–retest reliability and responsiveness of these reflex parameters
according to the type of electrode configuration. Twenty-two healthy volunteers (M:F = 11:11; mean age 25.3 ± 5.2 years)
participated in two testing sessions separated by one week. Zygomatic and mandibular montages were compared following
unilateral and bilateral stimulations. For reliability purposes, intraclass correlation coefficient (ICC), coefficient of variation
of the method error (CVME) and standard error of measurement (SEM) were calculated. The minimal detectable difference
(MDD) was also determined as a measure of responsiveness. Both VMR (p11 wave) and AMR could be consistently
evoked from test to retest, although the frequency rate was significantly higher (all p values ≤ 0.009) with zygomatic (VMR:
97.7–100%; AMR: 86.9–97.6%) than mandibular montage (VMR: 84.7–89.8%; AMR: 65.0–67.8%), with no significant
differences between unilateral and bilateral stimulations. Good-to-excellent reliability and responsiveness (high ICC, low
CVME,
SEM and MDD scores) were detected for corrected amplitudes and peak latencies for all reflex responses, whereas
raw amplitudes were associated to poor reliability. The reliability of the zygomatic montage proved superior to the mandibular
montage for all reflex responses. Given their high test–retest consistency and capability to study different features
of the reflex arch, both peak latencies and corrected amplitudes should be reported and considered in the interpretation of
reflex testing results.