THE DEVELOPMENTAL EMERGENCE OF THE REPRESENTATION OF AUDITORY AZIMUTHIN 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 describe d in the external nucleus of the inferior colliculus (ICX) of the guin ea-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 azim uth along the rostro-caudal axis of the ICX. The following paper consi ders the emergence of that map and the role of developmental experienc e in its elaboration. Multi-unit responses to free-field broad-band au ditory stimuli were recorded in the ICX. At threshold stimulation inte nsities, multi-unit receptive fields (MURFs) obtained from younger ani mals showed the same discrete spatial tuning as found in MURFs from an imals older than 35 DAB (days after birth). However, a normal adult to pographic representation was not present until animals were at least 3 0-32 DAB. Visual deprivation, by dark-rearing from birth until mapping (at 35-43 DAB), had no obvious detrimental effects on auditory recept ive field size or topographic order in the ICX. Auditory deprivation w as achieved by rearing animals in an environment of continuous omnidir ectional noise from birth until mapping (47-53 DAB). Following auditor y deprivation, receptive fields remained relatively discrete, but no c orrelation between rostro-caudal position of the recording site and th e angle of the best response was observed. Thus, the representation of auditory azimuth in the ICX appears to be unperturbed by developmenta l visual deprivation but is susceptible to developmental auditory depr ivation.