Inhibitory Circuits and Their Role in the Analysis of Complex Sounds

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9421180 Hall JC Complex biological sounds are particularly important in communication for many animals, as well as speech for humans. Such sounds contain information in both spectral (sound wavelength, or pitch) and temporal (patterning) domains. These properties are encoded in responses of neurons in the auditory nerve carrying signals from the ear to the brain. The coded signals are further transformed in two important relay centers in the brainstem and in the midbrain, as excitatory and inhibitory processes converge in particular ways on particular neurons. Some of the neurons in these centers are highly selective in their responses to particular spectral and temporal features of vocalizations by animals of the same species. Selectivity is created by combinations of excitation and inhibition from neuronal inputs to these cells. This project uses frogs, with their highly specialized calls, as a model system for exploring the mechanisms of stimulus selectivity in auditory networks. A combination of electrophysiology and pharmacology is used in a novel approach to clarify how not just one, but two different inhibitory compounds, called GABA and glycine, shape these responses and sharpen the stimulus selectivity of the system in the different stages. Results will add to our knowledge of how time and frequency filters are constructed and interact in the auditory system, and enhance our general understanding of the biological and computational mechanisms that underlie complex sound recognition. The impact will extend beyond sensory neurobiology to studies of communication behavior, to engineering of artificial speech, and to recognition systems for communications.