Monaural and Binaural Contributions to an Auditory Space Map in the Guinea-Pig Superior Colliculus

Abstract

The superior colliculus (SC) is not part of the classical auditory pathway but nevertheless receives direct projections from several auditory nuclei including the superior olive and the inferior colliculus (Edwards et al. 1979). We have recently demonstrated that cells in the deep layers of the guinea-pig SC respond more strongly or more reliably when sounds originate from a limited horizontal angle (Palmer and King 1982, King and Palmer, 1983). This ‘spatial tuning’ was obvious in some cells only for near threshold stimuli whilst in others it was maintained even when stimuli up to 35 dB above threshold were employed. Within this nucleus the cells are organized so that those responding best to sounds behind the animal are located at the caudal extreme and those responding to sounds in front are located rostrally with intermediate sound locations represented at appropriate positions in between. Thus, in the SC there is a topographical representation of at least the horizontal plane of auditory space similar to that previously demonstrated directly in the midbrain auditory nucleus and optic tectum of the barn owl (Knudsen and Konishi 1978, Knudsen 1982) and indirectly in the superior colliculus of other mammals (e. g. Gordon 1973, Chalupa and Rhoades 1977, Dräger and Hubel 1975)..