Organisation of binaural interactions in the primary and dorsocaudal fields of the guinea pig auditory cortex

This study investigated the nature and topography of binaural interactions in the primary auditory field (AI) and dorsocaudal field (DC) of the uretha ne anaesthetised guinea pig auditory cortex. Single and multi-units were cl assified by their responses to monaural and binaural stimulation. In both A I and DC, units displayed binaural facilitation, binaural inhibition, or a level dependent mixture of facilitation and inhibition. There was a signifi cant difference in the distribution of binaural response types between the two fields. Facilitated units predominated in DC (facilitated: 58%; inhibit ed: 24%; mixed: 6%; non-interacting: 12%), while inhibited units were the m ost common class in AI (facilitated: 15%; inhibited: 44%; mixed: 18%; non-i nteracting: 22%). It has previously been suggested that inhibited and facil itated units are concerned with processing different areas of space suggest ing a possible separation of function between the two core fields. Topograp hically, the binaural response properties in AI and DC varied along isofreq uency bands, with neurones displaying similar interactions aggregating in c lusters. These clusters were similar in size for the two fields and often o verlapped neighbouring isofrequency bands. However, their shape and positio n varied between different animals. This clustered organisation of binaural interactions is similar to that reported in recent studies of AI in other mammals. (C) 2000 Elsevier Science B.V. All rights reserved.