EVALUATION OF THE COCHLEAR AND EFFERENT FUNCTION IN NORMAL HEARING TINNITUS SUBJECTS: ANALYSIS OF MULTIPARAMETRIC GLOBAL FEATURES AND TIME-FREQUENCY FINE STRUCTURE OF OTOACOUSTIC EMISSIONS

Paglialonga P (1), Tognola G (1), Parazzini M (1), del Bo L (2), Ravazzani P (1).

(1) CNR Institute of Biomedical Engineering, Milan, Italy; (2) Fondazione Ascolta e Vivi, Milan, Italy.

Background: A number of questions still remain unanswered as to the origin of subjective tinnitus, especially when tinnitus develops in the absence of hearing loss. Recently, it was postulated that when tinnitus develops in normal-hearing subjects, a minor cochlear damage (mainly of OHCs), not necessarily implying decreased hearing thresholds, may act as a trigger of tinnitus. The question whether the phenomena triggering tinnitus occur in the peripheral hearing system still remains unanswered.

Aims: This study was aimed to assess if minor OHC dysfunction and/or defective cochlear efferent system functionality in subjects with normal hearing might be considered a necessary condition for the generation of tinnitus.

Methods: Differently from previous studies, simultaneous evaluation of both multiparametric global features and Wavelet-derived time-frequency (TF) fine structure of TEOAEs and DPOAEs in normal-hearing tinnitus subjects (N=28) and control subjects was carried out. The TF approach here applied is a powerful tool to improve OAE sensitivity in detecting possible slight differences in cochlear and/or efferent function between tinnitus and non tinnitus ears that might be too subtle to be detected just by comparing OAE global features. The inhibitory function of the medial olivo-cochlear efferent system was assessed by measuring OAEs in the presence of contralateral acoustic stimulation (CAS).

Results: No statistically significant differences between tinnitus patients and controls could be detected both in DPOAEs and TEOAEs and in CAS. Also, analysis of TF fine structure of TEOAEs revealed no statistically differences both in the latency of TEOAE frequency components and in the slope of the latency vs. frequency curve in tinnitus and control subjects. Overall, results seem to reveal that minor OHC dysfunction and/or defective cochlear efferent system functionality in subjects with normal hearing might not be considered a necessary condition for the generation of tinnitus.

Email: gabriella.tognola@polimi.it