Abstract
SummaryThe Middle Latency Auditory Evoked Response may be influenced by the post-auricular muscle reflex which occurs at the same latency of this potential.Aimto evaluate the muscle reflex influence on the middle latency response, identifying the most appropriate place for response recording.Materials and MethodsProspective 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.Resultssignificant 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.Conclusionthere 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.
Highlights
The Middle Latency Evoked Auditory Potentials (MLEAP) were initially described in 19581 as early responses with an initial latency of approximately 20 milliseconds
One example of electrode placement which allows for a good response recording and, a good diagnosis is associated to placing the electrodes in the C4 and C3 positions, Cz and on the right and left side mastoids (M2 and M1) or right and left earlobes (A2 and A1) (10 - 20 International Electrode System) - C4 and C3 are considered active electrodes and M2, M1, A2 and A1 are considered reference electrodes
We found some papers discussing the possibility of changing the latency and amplitude values of MLEAP waves considering different electrode positions, using the presence of post-auricular reflex (PAR) with electrodes placed on the mastoid[9,19]
Summary
The Middle Latency Evoked Auditory Potentials (MLEAP) were initially described in 19581 as early responses with an initial latency of approximately 20 milliseconds (ms). One example of electrode placement which allows for a good response recording and, a good diagnosis is associated to placing the electrodes in the C4 and C3 positions (right and left side temporoparietal junctions), Cz (vertex) and on the right and left side mastoids (M2 and M1) or right and left earlobes (A2 and A1) (10 - 20 International Electrode System) - C4 and C3 are considered active electrodes and M2, M1, A2 and A1 are considered reference electrodes This electrode placement allows MLEAP to be registered ipsi and contralaterally to the stimulated ear (in many derivations), allowing for the comparison of wave latency and amplitudes between each hemisphere and the middle line
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