Same Potential, Different Muscle: Masseter Acoustic/Vestibular Evoked Myogenic Potentials Can Also Be Recorded From Temporalis Muscle.

Purpose: The masseter acoustic/vestibular evoked myogenic potential (mVEMP) is a recently developed electrophysiological tool used to assess otolithic function. The mVEMP assesses brainstem integrity and is sensitive in detecting brainstem lesions. The masseter muscles are supplied by the mandibular branch of the fifth cranial nerve and help stabilize the jaw in response to high-intensity sound. The temporalis and masseter muscles function together to stabilize the mandible. Both muscles are supplied by the trigeminal nerve. Hence, the study hypothesized that mVEMP could also be recorded from the temporalis muscle.

Method: Twenty healthy adults (13 males and seven females; age range: 18-28 years) were recruited for the study. mVEMPs were recorded using a 500-Hz tone burst with 125 dB peSPL for all individuals. Vestibular evoked myogenic potentials (VEMPs) were then recorded in the temporalis muscle of the same individuals. VEMPs from the masseter and temporalis muscles were recorded ipsilaterally, contralaterally, and bilaterally, respectively. A within-subject design was adopted, and purposive sampling was used to assign the subjects.

Results: Both VEMPs from the masseter and temporalis muscles elicited a 100% response rate. A paired t test revealed no significant difference (p > .05) in the p11 and n21 latencies for unilateral and bilateral stimulation between masseter and temporalis VEMPs. In addition, a paired t test revealed a significant difference (p < .05) in the p11-n21 rectified amplitude between the masseter and temporalis VEMPs. The rectified amplitude for the temporalis muscle was reduced than masseter muscle.

Conclusions: The study found that VEMPs recorded from the temporalis muscle are similar to mVEMPs. This preliminary finding supports that the temporalis serves as an alternate muscle to record mVEMP.