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 urethane anaesthetised guinea pig auditory cortex. Single and multi-units were classified by their responses to monaural and binaural stimulation. In both AI and DC, units displayed binaural facilitation, binaural inhibition, or a level dependent mixture of facilitation and inhibition. There was a significant difference in the distribution of binaural response types between the two fields. Facilitated units predominated in DC (facilitated: 58%; inhibited: 24%; mixed: 6%; non-interacting: 12%), while inhibited units were the most common class in AI (facilitated: 15%; inhibited: 44%; mixed: 18%; non-interacting: 22%). It has previously been suggested that inhibited and facilitated units are concerned with processing different areas of space suggesting a possible separation of function between the two core fields. Topographically, the binaural response properties in AI and DC varied along isofrequency bands, with neurones displaying similar interactions aggregating in clusters. These clusters were similar in size for the two fields and often overlapped neighbouring isofrequency bands. However, their shape and position varied between different animals. This clustered organisation of binaural interactions is similar to that reported in recent studies of AI in other mammals.