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The effects of auditory efferent activity on peripheral physiology may be examined by presenting broadband noise (BBN) to the contralateral ear during otoacoustic emission (OAE) recordings. The presentation of BBN typically produces a reduction of OAE amplitudes in comparison to a condition without BBN. This is termed contralateral suppression. Limited information exists regarding the effects of contralateral BBN on responses observed at higher levels in the auditory system. The present study employed this paradigm to investigate interactions of attention and laterality on the transient evoked otoacoustic emission (TEOAE), auditory brainstem response (ABR) and cortical auditory evoked potentials (CAEP) P1-N1-P2. TEOAEs were evoked by 60 dB SPL clicks; ABRs and CAEPs were evoked by 60 dB SPL 2.0 kHz tone pips in 15 normally hearing adults. Four conditions were employed for each ear: 1) quiet (no noise); 2) 60 dB SPL contralateral BBN; 3) words (at -3 dB SNR) embedded in 60 dB SPL contralateral BBN while subjects classified words as animal versus food items; 4) words from condition #3 played backwards and embedded in 60 dB SPL contralateral BBN. For TEOAEs: 1) more suppression was evident in the active attention condition than the passive listening conditions and 2) right ear OAE amplitudes for the 8-18 ms time period exhibited more suppression in the presence of BBN for all noise conditions, although this did not meet statistical significance. For the ABR experiment, amplitudes in the noise conditions decreased in all epochs for the right ear, but not for the left. For the CAEP experiment, asymmetries were evident in temporal regions and an effect of contralateral noise was evident. The outcome of this investigation suggests that efferent activation by noise and active attention has diverse modulatory effects on electroacoustic and electrophysiologic responses along the auditory pathway.

Although the suppressive effect of the medial olivocochlear system (MOCS) on peripheral auditory active mechanisms is well documented in humans, the effect of efferent inhibition over prolonged periods of acoustic stimulation is less well documented, especially as observed in suppression of transient evoked otoacoustic emissions (TEOAE’s). The present study therefore evaluated the relationship between the duration of contralateral acoustic stimulation and the suppression of TEOAE’s in ten adults with normal hearing. TEOAE recordings with linear clicks (60 dB sound pressure level) were measured at four intervals during 15 minutes of continuous contralateral white noise (45 dB sound pressure level), followed by two post-noise recordings. An identical within-subject control condition was recorded without contralateral noise. Experimental and control measurements were repeated three times, on separate days. Results revealed significant and sustained TEOAE amplitude reduction for the entire duration of contralateral stimulation. Suppression increased across the duration of contralateral noise, but not sufficiently to be statistically significant. After noise termination, TEOAE amplitudes increased to values significantly above control recordings. The sustained suppression of TEOAE’s indicates continuous efferent inhibition over time in normal adults, with a significant increase in TEOAE amplitude after noise cessation possibly indicating increased outer hair cell responsiveness after prolonged contralateral noise. / Dissertation (MCommunication Pathology)--University of Pretoria, 2009. / Speech-Language Pathology and Audiology / Unrestricted

Made available in DSpace on 2016-04-27T18:12:19Z (GMT). No. of bitstreams: 1 Aline Mizozoe de Amorim.pdf: 732085 bytes, checksum: f7174c593105dc9cfa002fc341359bb0 (MD5) Previous issue date: 2007-02-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Objective: The objective of this research was to study the occurrence and magnitude of the transient otoacoustic emissions suppression in pre-term infants of high risk for hearing loss. Methods: The was carried out in 15 preterm infants. The equipment used was the ILO USB II V6 Clinical OAE Software from Ododynamics. The stimulation used was linear click presented at the intensity of 60 dB pe SPL (± 5). The contralateral noise (white noise) was at 60 dB SPL (± 5). Results: The results showed that there was significant statistical difference between the sides of the ears, with bigger magnitude of the suppression on the right ear and sex, with bigger magnitude of suppression on the masculine sex. Conclusions: The white noise presented contralaterally reduced the response level of the transient otoacoustic emissions, demonstrating the participation of efferent system for de effect was 93,3% on the studied population, being 66.6% for both ears and 33.4% for only of the ears. The average magnitude of the suppression was 2,1 dB SPL for the right ear and 1,3 dB SPL for the left ear. It did not have difference in the magnitude of suppression between the groups, according to gestacional age (p=0,8411). For group 1 and group 2 according to chronological age, had significant statistical difference (p= 0,457) being the magnitude of bigger suppression in group 2 / Objetivo: A presente pesquisa teve como objetivo, verificar a ocorrência e magnitude do efeito de supressão das emissões otoacústicas evocadas por estímulo transiente em lactentes nascidos pré-termo, com indicadores de risco para perda auditiva. Métodos: A supressão das emissões otoacústicas evocadas por estímulo transiente, foi realizada em 15 lactentes nascidos pré-termo. O equipamento utilizado foi o ILO USB II V6 Clinical OAE Software da Ododynamics,. O estímulo clique linear foi apresentado á uma intensidade de 60 dB pe NPS (± 5) e o ruído contralateral (ruído branco) á uma intensidade de 60 dB NPS (± 5). Resultados: Os resultados encontrados demonstraram que há diferença estatisticamente significante entre os lados da orelha, sendo a magnitude de supressão maior do lado direito, e para o sexo, sendo a magnitude de supressão maior no sexo masculino. Conclusões: O ruído branco apresentado contralateralmente reduziu o nível de resposta das EOAT, demonstrando a participação do sistema eferente medial no efeito de supressão das EOAT. A ocorrência do efeito de supressão foi de 93,3% na população estudada, sendo 66,6 % o efeito bilateral e 33,4% efeito unilateral. A magnitude de supressão média foi de 2,1 dB NPS para a orelha direita e 1,3dB NPS para a orelha esquerda. Não houve diferença na magnitude de supressão entre os grupos, segundo a idade gestacional (p=0,8411). Para o Grupo 1 e o Grupo 2 segundo a idade cronológica, houve diferença estatisticamente significante (p= 0,457) sendo a magnitude de supressão maior no Grupo 2

Le système auditif possède deux particularités. En périphérie, les mécanismes cochléaires actifs (MCA), sous-tendus par la motilité des cellules ciliées externes (CCE), interviennent dans la sensibilité auditive et la sélectivité fréquentielle. Sur le versant central, le système efférent olivocochléaire médian (SEOCM), qui se projette sur les CCE et module les MCA, améliore la perception auditive en milieu bruité. Sur le plan exploratoire, ces deux processus peuvent être évalués grâce aux otoémissions acoustiques provoquées (OEAP) et leur suppression controlatérale. Par ailleurs, des résultats expérimentaux chez l’animal ont montré l’existence d’un rétrocontrôle exercé par le système auditif corticofuge descendant (SACD) sur la cochlée, via le SEOCM.Le présent travail comporte trois études réalisées chez l’humain, visant à explorer les interactions entre SACD, SEOCM et MCA. Les études 1 et 2, utilisant une méthodologie innovante chez des patients épileptiques réalisant une stéréo-électroencéphalographie, ont révélé un effet atténuateur différentiel de la stimulation électrique intracérébrale sur l’amplitude des OEAP, en fonction des modalités de stimulation, ainsi qu’une variabilité de cet effet selon les caractéristiques de l’épilepsie. L’étude 3 a montré un renforcement bilatéral de l’activité du SEOCM chez des musiciens professionnels.Pris dans leur ensemble, ces résultats fournissent d’une part, des arguments directs et indirects en faveur de l’existence d’un SACD fonctionnel chez l’humain. D’autre part, des phénomènes de plasticité à long terme, pathologique ou supranormale, seraient susceptibles de modifier l’activité de cette voie cortico-olivocochléaire. / The auditory system has two special features. At peripheral level, active cochlear micromechanisms (ACM), underlain by motility of outer hair cells (OHC), are involved in auditory sensitivity and frequency selectivity. At central level, the medial olivocochlear efferent system (MOCES), which directly projects onto OHC to modulate ACM, improves auditory perception in noise. From an exploratory point of view, both processes can be assessed through transient evoked otoacoustic emissions (TEOAE) and the procedure of contralateral suppression. In addition, experimental data in animals have disclosed a top-down control exerted by corticofugal descending auditory system (CDAS) on cochlea, via MOCES.The present work comprises three studies carried out in human, aiming to investigate interactions between CDAS, MOCES and ACM. The first and second studies, based on an innovative experimental procedure in epileptic patients undergoing presurgical stereoelectroencephalography, have revealed a differential attenuation effect of intracerebral electrical stimulation on TEOAE amplitude depending on stimulation modalities, as well as a variability of this effect depending on the clinical history of epilepsy. The third study has shown a bilateral enhancement of MOCES activity in professional musicians.Taking together, these results provide direct and indirect evidence for the existence of a functional CDAS in humans. Moreover, possible long-term plasticity phenomenon, either pathological –as in epileptic patients– or supernormal –as in professional musicians– may change cortico-olivocochlear activity.