mVEMP: The New Kid on the Block

In the late 1970s, there were no practical clinical textbooks that covered sensory evoked potentials. Without them, we learned about evoked potentials the “old fashioned way” and that was by reading an article (i.e., usually published in the journal Electroencephalography and Clinical Neurophysiology) and then attempting to replicate the author's findings.

A failure in an attempt to replicate the author's findings by multiple investigators cast a pall over an original report. In those times, and currently, it was, and is, essential for authors to publish numeric data, as well as representative and replicated evoked potential tracing so that a reader could determine how similar the product of their efforts was to the published evoked responses.

One of the evoked responses we attempted to record was a sonomotor reflex that authors Meire-Ewert and colleagues referred to as the “Acoustic Jaw Reflex.”[1] At that time, Craig Newman and I were working at the Veterans Administration Medical Center in Cleveland and Craig Newman was a VA trainee. We had just obtained one of the first Nicolet CA-1000 clinical evoked potential machines.

I remember that Craig was the subject (after all, he was the trainee). We carefully placed our non-inverting and inverting electrodes at the prescribed locations (non-inverting electrode over the ipsilateral masseter muscle) and as described by Meire-Ewert et al. At that time, we used an unfiltered and high intensity click stimulus (e.g., ∼85–90 dB nHL). Much like the cervical vestibular evoked myogenic potential (VEMP), the acoustic jaw reflex was thought to represent a stimulus-synchronized attenuation of an electrically activated muscle. The pathway underlying that response was believed to be cochlea to cochlear nuclei to the brainstem nucleus of the trigeminal nerve to the trigeminal nerve and from there to the masseter muscle.

To activate the muscle, Craig bit on a gauze-wrapped tongue depressor. We presented the clicks at a rate of 1–2 Hz and signal-averaged over a 100 millisecond epoch. After 100 samples had been acquired, it was clear that we had recorded the acoustic jaw reflex.

Now, in 2021, there has been a rebirth of interest in this reflex, in much the same way that interest in the middle latency auditory evoked potentials disappeared in the middle 1960s until the mid-1990s. This response appears to have vestibular sensory origins. The available evidence suggests that the afferent limb of this reflex is the saccule and inferior vestibular nerve.

In their report titled, “Tone Burst Masseter Vestibular Evoked Myogenic Potentials: Normative Values and Test-Retest Reliability,” Vignesh et al[2] present a thorough assessment of the normal characteristics of the masseter VEMP (i.e., mVEMP) in a sample of 44 subjects who were between 18 and 50 years of age. A subsample of 10 subjects underwent repeat testing, so that the normal variability of the response could be estimated. Since this is a bilateral reflex (i.e., as is the R2 response of the blink reflex), the investigators were interested in the amplitude and latency of both the ipsilaterally and contralaterally recorded mVEMP. Lastly, the investigators were interested in the sex and gender differences in the response parameters.

The editors recommend this article, which introduces our readership to a relatively new evoked response. Enjoy!

Publication History

Article published online:
10 August 2021

• References

• 1 Meier-Ewert K, Gleitsmann K, Reiter F. Acoustic jaw reflex in man: its relationship to other brain-stem and microreflexes. Electroencephalogr Clin Neurophysiol 1974; 36 (06) 629-637
• 2 Vignesh SS, Singh NK, Rajalakshmi K. Tone burst masseter vestibular evoked myogenic potentials: normative values and test-retest reliability. J Am Acad Audiol 2021; 32: 308-314