THE DEVELOPMENTAL EMERGENCE OF THE REPRESENTATION OF AUDITORY AZIMUTH IN THE EXTERNAL NUCLEUS OF THE INFERIOR COLLICULUS OF THE GUINEA-PIG - THE EFFECTS OF VISUAL AND AUDITORY DEPRIVATION

A topographic representation of the auditory azimuth has been described in the external nucleus of the inferior colliculus (ICX) of the guinea-pig [3]. This representation is characterized by directional multi-unit responses, at threshold stimulation intensities, with directional preferences organized in such a way as to represent the auditory azimuth along the rostro-caudal axis of the ICX. The following paper considers the emergence of that map and the role of developmental experience in its elaboration. Multi-unit responses to free-field broad-band auditory stimuli were recorded in the ICX. At threshold stimulation intensities, multi-unit receptive fields (MURFs) obtained from younger animals showed the same discrete spatial tuning as found in MURFs from animals older than 35 DAB (days after birth). However, a normal adult topographic representation was not present until animals were at least 30-32 DAB. Visual deprivation, by dark-rearing from birth until mapping (at 35-43 DAB), had no obvious detrimental effects on auditory receptive field size or topographic order in the ICX. Auditory deprivation was achieved by rearing animals in an environment of continuous omnidirectional noise from birth until mapping (47-53 DAB). Following auditory deprivation, receptive fields remained relatively discrete, but no correlation between rostro-caudal position of the recording site and the angle of the best response was observed. Thus, the representation of auditory azimuth in the ICX appears to be unperturbed by developmental visual deprivation but is susceptible to developmental auditory deprivation.