THE EFFECTS OF CROSSED OLIVOCOCHLEAR BUNDLE SECTION ON TRANSIENT EVOKED OTOACOUSTIC EMISSIONS

The purpose of this study was to investigate the effect of sectioning the crossed olivocochlear bundle (COCB) on transient evoked otoacousti c emissions (TEOAEs) in anesthetized adult chinchillas. Of particular interest is the role of cochlear efferents to the outer haircells (OHC s) and how they control mechanisms responsible for otoacoustic emissio ns. Specifically the experiment addressed whether a tonic level of inh ibitory control is reduced by COCB section. The nonlinear component of TEOAEs was measured before and after COCB section. Analysis was made of the 1, 2, 3, 4, and 5 kHz frequency components and of the total emi ssion, as quantified by fast Fourier transform (FFT) of the raw (time domain) response. After COCB section, the amplitude of the total respo nse and of the 2, 3, 3, and 5 kHz components increased whereas the amp litude of the 1 kHz component decreased. The results indicate that COC B section reduces inhibitory control of the OHC mechanisms responsible for nonlinear TEOAE generation. It is not clear whether the nerve sec tion eliminates a spontaneous level of activity in COCB efferents, or whether it results in the interruption of a stimulus-evoked feedback l oop.