The inferior colliculus (IC) is a nexus in the auditory system since it processes and integrates almost all ascending acoustic information from lower centers and thereby determines what form of information is conveyed to higher regions in the forebrain. Consistent with the large convergence of projections, the response properties of IC neurons are highly diverse. The diversity is due to the particular complement of inputs that innervate each neuron and to their intrinsic ion channels. Inhibition is particularly important, because inhibition sculpts a wide range of emergent response properties from the backdrop of more expansive and less specific excitatory innervation. Because inhibition cannot be directly seen with extracellular recordings, I will use in vivo whole cell recordings from IC neurons to obtain a more direct and detailed view of sound evoked inhibition, and generate a unique and more comprehensive picture of the response properties of IC neurons, the mechanisms with which they process acoustic information and their morphologic features. The response features include their intrinsic properties, revealed by responses to injected current steps, the tuning of their tone evoked synaptic responses and discharges with particular attention directed at sound evoked inhibition, their responses to natural communication calls, and their directional preferences for upward or downward FM sweeps. What makes these experiments unique is that this constellation of response features has never been recorded in individual IC cells, and they will be used to evaluate how intrinsic channels interact with ligand-gated events to shape the response properties in IC cells. The proposed studies focus on the roles of inhibition, and inhibition in the IC is important for a number of pathological conditions and hearing impairments. The roles of inhibition may be especially relevant for the decline of speech perception in the elderly, which is correlated with age related loss of GABAergic neurons in the auditory system. Since the proposed studies will evaluate the role of inhibition in the processing of communication calls, they may provide insights into the processing of speech, and hence into why the elderly often experience a decline in speech perception.
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