Effects of superior olivary complex lesions on binaural responses in rat inferior colliculus

Unilateral or bilateral lesions of the superior olivary complex (SOC) were made by local injection of kainic acid through a micropipette lowered stereotaxically into the rat's auditory brainstem. The lesions had the effect of destroying cell bodies in the superior olive without disrupting fibers of passage. After a recovery period of approximately one month, physiological recordings were made with tungsten micro-electrodes from the central nucleus of the inferior colliculus of animals with SOC lesions. For animals with unilateral lesions recordings were made either ipsilateral or contralateral to the site of damage. Results were compared with data from normal control cases. Monaural and binaural tone bursts were presented through a sealed sound delivery system and binaural interaction patterns were determined. Both binaural summation and suppression responses were still present following unilateral SOC lesions. Interaural intensity difference thresholds were within the normal range and no differences were found between animals with lesions placed ipsilateral or contralateral to the recording site. Binaural summation and suppression responses were also present following bilateral lesions. Bilateral lesions had the effect of shifting the average interaural intensity difference thresholds in favor of the contralateral ear. But, in general, binaural interactions were remarkably little affected by bilateral destruction of the SOC.