Post-auricular muscle reflex in the Middle Latency Evoked Auditory Response

Abstract

The Middle Latency Auditory Evoked Response may be influenced by the post-auricular muscle reflex which occurs at the same latency of this potential.

Aim: to evaluate the muscle reflex influence on the middle latency response, identifying the most appropriate place for response recording.

Materials and methods: Prospective study in which 40 normal hearing individuals, ranging in age from 18 to 40 years old, were assessed by Middle Latency Response with electrodes placed first on the mastoids, and then on the earlobes.

Results: significant statistical differences were seen between the values found with electrodes placed on the mastoids and on the earlobes concerning the Na-Pa amplitude in C3/A1, C3/A2 and C4/A2, concerning the Na wave latency in C3/A2 and C4/A2, and concerning the Pa wave latency in C3/A1 and C3/A2. We found a higher occurrence of the post-auricular reflex when the electrode was placed on the mastoids, in all studied modalities.

Conclusion: there was post-auricular muscle reflex interference upon the Middle Latency Response obtained when the electrodes were placed on the mastoid, and the most efficient electrode disposition in order to capture and to register more accurately this potential was on the earlobe.

Figure 1

Presence and absence of myogenic response in face of sound stimulus in different electrode positions - L = left C3 = Left side temporoparietal junction A1 = Left earlobe M1 = Left mastoid