ASA 127th Meeting M.I.T. 1994 June 6-10

1pPP5. Effects of bilateral olivocochlear lesions on pure tone intensity discrimination in cats.

Bradford J. May

Shelly J. McQuone

Dept. of Otolaryngol.---HNS, The Johns Hopkins Univ. School of Med., 720 Rutland Ave., Baltimore, MD 21205

The effects of olivocochlear efferent lesions on intensity discrimination were examined in five cats. Cats were trained with food reinforcement to signal the detection of a change in the intensity of a pure tone by releasing a response lever. Intensity cues were conveyed by 1- and 8-kHz tone bursts in quiet and in the presence of continuous broadband noise. After the collection of baseline behavioral data, the olivocochlear bundle (OCB) was sectioned with bilateral knife cuts on the floor of the IVth ventricle. The completeness of OCB lesions was evaluated with cochlear acetylcholinesterase staining procedures. Although intensity discrimination was not negatively affected by OCB lesions when tests were conducted in quiet, performance deficits were noted when intensity discrimination was measured in the presence of noise. These data suggest that olivocochlear feedback may play an important role in the auditory processing of acoustic signals in noise backgrounds. Behavioral results will be discussed in terms of electrophysiological measures of intensity encoding. [Work supported by NIDCD Grant No. DC00979 and the W. M. Keck Foundation.] <@q pa>