AUDITORY TECTO-THALAMIC PATHWAYS--INFORMATION PROCESSING

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Acoustic behavior relies on information conveyed by multiple pathways projecting from the inferior colliculus to the medial geniculate body, and then to the auditory cortex. The long term goal of this research is to evaluate information processing within these auditory pathways. The proposed research will specifically examine the organization of projections from the inferior colliculus to the medial geniculate body, and the physiological properties of neurons in the medial geniculate. Special attention will be placed on connections and mechanisms involved in sound localization and in the integration of acoustic information from different frequency bands. Binaural responses and sound localization cues are organized within isofrequency representations of the mustached bat's inferior colliculus. The ascending projections of the inferior colliculus will be studied by placing deposits of anterograde tracer in regions defined physiologically by their responses to binaural input and sound frequency. Two anterograde tracers, placed in dfferent binaural subdivisions, will be used to evaluate the degree of convergent input from binaural subdivisions in the inferior colliculus. Then, physiological studies of single and multi-unit responses in the medial geniculate will evaluate the physiology and functional organization of binaural responses. These studies will establish what information regarding binaural cues is conveyed from the inferior colliculus to the medial geniculate body, and how this information is processed by neurons within the medial geniculate. It will furthermore provide the basis for a deeper understanding of how the auditory cortex processes and represents binaural cues related to sound localization, and thus underlies this important acoustic behavior. Neuml mechanisms analyzing sound location and other acoustic features may depend upon the integration of information across different isofrequency representations. The convergence of frequency-specific input from the inferior colliculus onto subdivisions of the medial geniculate will be studied by placing deposits of two anterograde tracers in different frequency represenations of the inferior colliculus. Physiological studies of single units in the medial geniculate will then confirm the organization of convergent input, and identify the physiological responses of such neurons. These studies will provide information regarding integrative mechanisms by which sound location and other acoustic features are analyzed within the auditory system.