Influence of the Click Evoked Myogenic Potentials (CMEP)

Pralong, E.1, Bisdorff, A.3, Campanella, S.1,2, Villemure, J. G1, Maeder-Ingvar, M.1, Despland, P. A.2, Tetreault, M. H.1, and Debatisse, D.1,3
1UNN Neurosurgery, CNP and Neurology, CHUV, Lausanne, Switzerland; 2Catholic University of Louvain-la-Neuve, Belgium; 3Department of Neurology, HVEA, Luxemburg

In response to auditory stimulation, a vestibular evoked potential defined as a short latency electromyogram and called “click evoked myogenic potential” (CEMP), can be recorded from surface electrodes over the tonically contracted sternocleidomastoid muscles. Now, it is well established that, in normal subjects, the earliest response, p13-n23, is dependent upon vestibular activation, specifically saccular afferents. During EEG and CEPs recordings, subjects are generally tested in sitting position. In this study, we investigated whether a CEMP can be recorded in classical brainstem and middle latency auditory evoked potentials (BAEP, MAEP) by using A1-Cz, A2-Cz and sterncleidomastoid derivations (40 subjects). We studied the effect of the CEMP in multichannel cognitive evoked potentials (32 channels during auditory oddball tasks). The important points are: (1) CEMP potential should not be confused with a neural response; (2) this would allow us to simultaneously get information –during a classical BAEP recording- on the brainstem auditory pathway and on reflexes mediated through the vestibular nerve and the saccula; (3) the use of extraencephalic references (A1-A2) is able to contaminate the neurophysiological acquisitions of CEPs, such as the P50 or even the latter components, induced by auditory stimulations (i.e. during auditory oddball paradigm). It is therefore possible that due to the filters used for this type of CEPs analysis and because of the seated position commonly chosen for this testing, the CEMP could be a part of the observed early and middle latency CEPs components.