Assessmentofmedialolivocochlearsystemfunctioninpre-term andfull-termnewbornsusingarapidtestoftransientotoacoustic emissions T. MORLET,  A. HAMBURGER, y J. KUINT, z D. ARI-EVEN ROTH, y M. GARTNER,§ C. MUCHNIK, y L. COLLET§ & M. HILDESHEIMER y  Kresge Hearing Research Laboratory of the South, New Orleans, LA, USA, ySpeech and Hearing Center, zNeonatal Department, The Chaim Sheba Medical Center, Tel Hoshomer, Sackler School of Medicine, Tel Aviv University, Israel, and §UMR 5020 Neurosciences et Systemes Sensoriels, Lyon, France Accepted for publication 13 June 2003 MORLET T., HAMBURGER A ., KUINT J ., ARI-EVEN ROTH D ., GARTNER M ., MUCHNIK C ., COLLET L ., HILDESHEIMER M . (2004) Clin. Otolaryngol. 29, 183±190 Assessment of medial olivocochlear system function in pre-term and full-term newborns using a rapid test of transient otoacoustic emissions This study was conducted to investigate maturation of the medial olivocochlear efferent system (MOCS) in pre- and full-term neonates using Quickscreen (Otodynamics Ltd) and to con®rm previous ®ndings on transient otoacoustic emission (TEOAE) suppression in neonates. MOCS maturation was investigated in 46 neonates born at the Chaim Sheba Medical Center, Tel Hashomer, Israel, using Quickscreen. All neonates were normal with no family history of general or auditory disease and no risk factors for hearing impairment. MOCS function appears gradually in human pre-term neonates and is considered to reach maturity shortly after term birth. The clinical value of MOCS testing in speci®c populations of newborns at risk for hearing and/or brainstem function can be legitimately raised as activation of the MOCS clearly alters cochlear output. The present results can be interpreted to support the testing of infants at risk of developing abnormal MOCS function using a commercially available rapid TEOAE measurement system. Keywords MOCS TEOAEs newborn maturation outerhaircells The function of the medial olivocochlear efferent system (MOCS), which synapses on the cochlear outer hair cells (OHCs), appears gradually in human pre-term neonates and is thought to reach maturity in the ®rst weeks following term birth. 1±6 The MOCS is one of the two efferent systems ending in the cochlea, allowing higher structures of the brainstem to in¯uence the coding of sounds. The MOCS is composed of large myelinated neurones originating from the medial nuclei of the superior olivary complex. These neurones project mainly contralaterally to innervate OHCs. The MOCS is the target of efferent projections from the central nervous system, with most of the efferents coming from the primary auditory cortex via the medial geniculate nucleus, the inferior colliculus and the medial superior olivary complex. 7,8 MOCS activity can be tested in humans using an acoustic stimulus coupled with the recording of one of the different types of otoacoustic emissions (OAEs; i.e. transient OAEs (TEOAEs), spontaneous OAEs or distortion product OAEs (DPOAEs)), which are byproducts of cochlear active mechan- isms. 9±11 Activation of the MOCS with an ipsilateral, con- tralateral or binaural stimulation leads to a decrease in OAE level. The ®ndings of control studies indicate that the MOCS effect on TEOAEs is not likely to be the sign of middle ear muscle re¯ex activation 11 or acoustic cross-talk 9 and probably re¯ects MOCS function alone. In pre-term neonates, the amount of suppression of TEOAEs was found to be signi®- cantly and positively correlated with increasing conceptional age. 2 Additionally, development of MOCS function appeared to follow an asymmetrical pattern supposedly in relation to the well-known right ear advantage. 2,12 TEOAEs are commonly recorded using one of the ILO systems manufactured by Otodynamics Ltd, which provides a post-stimulus time Clin. Otolaryngol. 2004, 29, 183±190 # 2004 Blackwell Publishing Ltd 183 Correspondence: Thierry Morlet, PhD, Kresge Hearing Research Laboratory of the South, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA (e-mail: tmorle@lsuhsc.edu).