[Changes in human spontaneous otoacoustic emissions with contralateral acoustic stimulation]

According to current cochlear concepts, spontaneous otoacoustic emissions (SOAEs) are thought to be the product of outer hair cell (OHCs) movement. Furthermore, efferent neurofibers from the olivocochlear bundle primarily innervate OHCs. Thus, we designed this investigation to determine changes in SOAE under conditions of contralateral acoustic stimulation. Fouty-two normal ears of 34 subjects with uni- or bilateral SOAEs were examined. The sound pressure level (SPL) of SOAE was measured 3 times in each subject and was initially averaged. The white noises of 30 or 40dBSPL, believed not to affect the other side, were then loaded contralaterally and the SPL of SOAEs were measured and compared with the non-loaded data. The SPL of single SOAEs were actually suppressed with 40dBSPL stimulation while the SPL of multiple SOAEs showed typical changes. Interestingly, no significant suppression of SOAEs was noticed under conditions of contralateral acoustic stimulation of the impaired ear. These data suggest that contralateral acoustic stimulation could affect OHC function via the olivocochlear bundle.