Evaluation of the frequency selectivity of contralateral acoustic stimulation on the active mechanisms of the organ of corti by analyzing the changes in the amplitude of transitory evoked otoacoustic emissions and distortion products.

INTRODUCTION

The central nervous system can regulate the input of acoustic information to the cochlea by means of the olivocochlear efferent system's action on the organ of Corti. The aim of this study was to determine whether the suppressor effect of contralateral acoustic stimulation shows frequency selectivity in active cochlear mechanisms by recording transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs).

MATERIAL AND METHOD: We conducted a prospective study of 56 subjects with normal-hearing ears aged 20 to 22 years (mean 5 20.9 years); 50% were male and 50% were female. We studied the amplitude of each TEOAE and DPOAE frequency band before and after contralateral acoustic stimulation with broadband white noise, 0 to 20,000 Hz frequency range, and pure tones of 700, 1000, 1500, 2000, 3000, 4000, 5000, and 6000 Hz, at an intensity of 60 dB HL.

RESULTS

TEOAE recording amplitudes decreased 84% after contralateral acoustic stimulation. White noise and pure tones of 1000, 1500, and 2000 Hz had the greatest suppressor effects on the TEOAEs. The suppressor effect was higher in 1000 to 4000 Hz frequency bands, with a statistically significant decrease in amplitudes of 0.5 to 2.5 dB. Distortion product amplitude decreased 75%. Stimulation with white noise and pure-tone contralateral stimulation at 1000 and 1500 Hz showed the highest decrease in DPOAE amplitude. Suppression was concentrated in DPOAEs obtained with F2 of 1500 and 2000 Hz.

CONCLUSION

Contralateral acoustic stimulation causes selective frequency modulation of the cochlear micromechanisms, which can be assessed by recording TEOAEs and DPOAEs.