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This Article Full Text Full Text (PDF) All Versions of this Article: 580/1/195    most recent jphysiol.2006.123240v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Deriu, F. Articles by Tolu, E. Search for Related Content PubMed PubMed Citation Articles by Deriu, F. Articles by Tolu, E. Related Collections Neuroscience

¹ Department of Biomedical Sciences
² ENT Institute
³ Institute of Clinical Neurology, University of Sassari, Italy
⁴ Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK

Sound is a natural stimulus for both cochlear and saccular receptors. At high intensities it evokes in active masseter muscles of healthy subjects two overlapping reflexes: p11/n15 and p16/n21 waves, whose origin has not yet been demonstrated. Our purpose was to test which receptor in the inner ear is responsible for these reflexes. We compared masseter EMG responses induced in normal subjects (n = 9) by loud clicks (70–100 dB normal hearing level (NHL), 0.1 ms, 3 Hz) to those evoked in subjects with a selective lesion of the cochlea (n = 5), of the vestibule (n = 1) or with mixed cochlear-vestibular failure (n = 5). In controls, 100 dB clicks induced bilaterally, in the unrectified mean EMG (unrEMG), a clear p11 wave followed by a less clear n15 wave and a subsequent n21 wave. Lowering the intensity to 70 dB clicks abolished the p11/n15 wave, while a p16 wave appeared. Rectified mean EMG (rectEMG) showed, at all intensities, an inhibitory deflection corresponding to the p16/n21 wave in the unrEMG. Compared to controls, all deaf subjects had a normal p11 wave, together with more prominent n15 wave; however, the p16/n21 waves, and their corresponding inhibition in the rectEMG, were absent. The vestibular patient had bilaterally clear p11 waves only when 100 dB clicks were delivered bilaterally or to the unaffected ear. Stimulation of the affected ear induced only p16/n21 waves. Data from mixed patients were consistent with those of deaf and vestibular patients. We conclude that click-induced masseter p11/n15 waves are vestibular dependent, while p16/n21 waves depend on cochlear integrity.

(Received 20 October 2006; accepted after revision 11 January 2007; first published online 18 January 2007)
Corresponding author F. Deriu: Department of Biomedical Sciences, Section of Human Physiology and Bioengineering, Viale San Pietro 43/b, 07100 - Sassari, Italy. Email: deriuf{at}uniss.it