FUNCTIONAL ORGANIZATION OF THE INFERIOR COLLICULUS

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The proposed studies will evaluate the neural encoding and representation of binaural and spatial information within the "60 kHz" isofrequency lamina of the mustache bat's inferior colliculus (IC). In recent studies we have found that the central nucleus of the bat's IC has 3 functional divisions distingusished on both physiological and architectural criteria. The largest is the dorsoposterior division (DPD) in which all neurons have virtually the same best frequency. The DPD is a greatly enlarged, but fundamentally standard mammalian isofrequency contour, or lamina. Since the mammalian IC is constructed from serially stacked laminae, the DPD is a basic unit of neuronal architecture present in highly magnified form. I intend to exploit this adaptation in order to evaluate: 1) How binaural information is encoded by DPD neurons. Particular attention will be given to determining whether neurons can encode interaural phase or time disparities. 2) How neurons having common binaural properties are organized within the DPD. 3) What influence the pinnae have upon the directional features of 60 kHz sounds reaching the cochlea. 4) How neural processes interact with pinna effects to shape the spatial selectivity of DPD neurons. 5) What correlations exist between DPD neurons having common binaural characteristics and the specificity of projection systems originating from lower auditory centers in the brainstem.