Sectioning the efferent bundle decreases cochlear frequency selectivity.

Cochlear frequency selectivity was tested in rats and cats before and after sectioning the vestibular nerve which carries the efferent bundle to the cochlea. Compound action potential tuning curve were obtained by a simultaneous masking procedure. Transection of the efferent bundle resulted, in all group of animals, in an enlargement of the tip segment of the tuning curve. The Q10 dB value decreased by about 30% without any significant threshold change. These results taken together with previous developmental findings, suggest that efferents to outer hair cells could play a role in sharpening the frequency selectivity of the cochlea.