Investigation of the mechanism of contralateral suppression by otoacoustic emission on people with tinnitus

The association of contralateral suppression mediated via medial efferent system and its outer hair cell regulatory function and tinnitus have been scarcely studied in adults. Our study group consisted on 30 adults, aged between 25 to 55 years and diagnosed as having unilateral tinnitus with auditory thresholds better than 30 dB as well as normal tympanometric findings. Control group comprised of 30 normal hearing subjects with no tinnitus and in the similar age range and sex. Both groups underwent pure tone audiometric measurements at 250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz frequencies, high frequency audiometric hearing threshold, TEOAE amplitudes (signal to noise ratio) centered at 1000, 1414, 2000, 2828, 4000 Hz. Contralateral ear was masked using white noise only. The results of this study indicated that before and after suppression, TEOAE amplitudes were similar in the tinnitus and control groups (p>0.05). It can be said that people with tinnitus might have normal findings regarding suppression characteristics of outer hair cell function. The rate of people with suppression presence on at least three frequencies was 86.7 % (26/30) for the group of people with tinnitus and 96.7 % (29/30) for the control group and there was no significant difference between the groups. As if there was no significant difference at OAE levels between tinnitus and control groups after contralateral suppression, we concluded that suppression of the efferent system did not function pathologically. Regarding to the data of OAE levels after suppression, it is also shown that presence of tinnitus did not cause any difference on medial olivocochlear system.