Discriminating among complex signals: the roles of inhibition for creating response selectivities

The review deals largely with studies from my laboratory that were prompted by conversations I had with Gerhard Neuweiler more than 15 years ago. The studies were conducted on bats and dealt with mechanisms that enable the population of neurons in the inferior colliculus (IC) to respond selectively to the variety of signals bats emit for both communication and echolocation. The first section is concerned with how neurons in the dorsal nucleus of the lateral lemniscus (DNLL), the nucleus ventral to the IC, respond to species-specific signals and how they compare to responses of IC neurons evoked by the same signals. Those studies showed that DNLL neurons have no sideband inhibition and their responses are determined by excitation. In contrast, inhibition dominates in the IC where it carves out highly selective discharge properties. Those studies, in turn, raised questions about the quantitative features of inhibition that could only be answered with more sophisticated techniques. In the second section, results from analyses with spectrotemporal receptive fields (STRFs) are presented, and in the final section I show data derived from in vivo whole cell recordings that illustrate how features of inhibition interact with excitation to generate directionality selective responses in the IC.