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Origin of sound-evoked EMG responses in human masseter muscles

Deriu, Franca and Ortu, Enzo and Capobianco, Francesco Saverio and Giaconi, Elena and Melis, Francesco and Aiello, Elena and Rothwell, John C. and Tolu, Eusebio (2007) Origin of sound-evoked EMG responses in human masseter muscles. The Journal of Physiology, Vol. 580 (1), p. 195-209. eISSN 1469-7793. Article.

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DOI: 10.1113/jphysiol.2006.123240


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.

Item Type:Article
ID Code:626
Uncontrolled Keywords:Masseter muscles, EMG responses
Subjects:Area 06 - Scienze mediche > MED/32 Audiologia
Area 06 - Scienze mediche > MED/34 Medicina fisica e riabilitativa
Area 05 - Scienze biologiche > BIO/09 Fisiologia
Divisions:001 Università di Sassari > 01 Dipartimenti > Scienze biomediche
001 Università di Sassari > 03 Istituti > Oftalmologia, Otorinolaringoiatria e Urologia
001 Università di Sassari > 03 Istituti > Clinica neurologica
Publisher:The Physiological Society, Blackwell Publishing
Deposited On:18 Aug 2009 10:02

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