Role of brain-stem auditory structures in sound localization. II. Inferior colliculus and its brachium.

Abstract

In cats with intact auditory systems each of the discriminations is learned quickly and training on one lateralization discrimination (L vs. R) transfers to the 2nd (LR vs. RL). Bilateral ablation of the inferior colliculus, which is deep enough to divorce the forebrain from auditory structures in the hindbrain, renders a cat incapable of using either time or intensity cues for sound lateralization. Bilateral ablation of the apical region of the inferior colliculus, which spares a large portion of the underlying lemniscal pathways, does not impair discrimination of lateralized sounds. Lesions which sever the rostral projections of the tectum but spare the inferior colliculus itself abolish lateralization based on binaural time difference (LR vs. RL). In these cases the impairment of lateralization based on intensity differences (L vs. R) may be related to the depth to which the lesion invades the lateral teg-mentum.