ROLES OF GABAERGIC INHIBITION FOR THE BINAURAL PROCESSING OF MULTIPLESOUND SOURCES IN THE INFERIOR COLLICULUS

This review explores the question of how spike trains that originate f rom lower auditory nuclei interact in the inferior colliculus to produ ce an output that synthesizes the information from all these sources. The focus is on the processing of interaural intensity disparities, th e cues animals use to localize high-frequency sounds, and the roles of the lateral superior olives and the dorsal nucleus of the lateral lem niscus (DNLL) in shaping the binaural properties of their targets in t he inferior colliculus. The main points advanced in this review are 1) that the DNLL shapes the binaural properties of many inferior collicu lar neurons, 2) that the inhibitory inputs to the DNLL allow it to act as a switch that can be turned on or off with appropriate acoustic st imulation, and 3) that when two or more stimuli are presented, each fr om a different region of space, the first stimulus can switch the DNLL to its off position. The consequence of the initial stimulus is that stimuli that follow shortly thereafter cannot activate the DNLL, and t hus the binaural properties of those collicular cells that receive inh ibition from the DNLL are changed. The implications of this switching action are that the location of the initial signal is coded appropriat ely, whereas the coding of the location of the signal or signals that follow the initial signal is smeared, and consequently, those followin g signals cannot be accurately localized. In short, it is proposed tha t the DNLL plays a pivotal role in the way the locations of multiple s ound sources are coded by the auditory system.