CORTICAL REPRESENTATION OF AUDITORY SPACE

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DESCRIPTION (provided by applicant): Localization is a fundamental task of hearing. In higher mammals, normal function of the auditory cortex is essential for normal sound localization. Despite active research, basic principles of spatial representation in the cortex remain unknown. Proposed experiments will extend observations from the PI's laboratory that indicate that the temporal firing patterns of single cortical neurons can signal the locations of sounds panoramically, implying that the location of any sound source is represented by widely distributed neural populations. Specific Aim 1 will evaluate specialization for spatial coding among auditory cortical fields. Previous studies in cats, focusing on areas Al, A2, and AES, have not discovered any qualitative specialization. Other as yet unexplored areas show binaural and frequency specificity that seem particularly conducive to spatial selectivity, and our preliminary results show enhanced spatial selectivity in area PAF. We will test the hypothesis that cortical areas PAF and the dorsal part of area Al are specialized for spatial representation. Specific Aim 2 will contrast auditory spatial selectivity in cat cortical neurons during anesthetized, idle, visual-detection, and auditory-discrimination conditions. We will test the hypothesis that location specificity of neural spike patterns is enhanced in awake animals, particularly when the animal is engaged in an auditory task. Specific Aim 3 will explore the rules by which human listeners extract location cues from sound spectra. We will employ a new procedure that characterizes the proximal stimulus spectra that result in particular elevation judgments. We will discriminate between hypothetical broadband and single-feature mechanisms and will determine the level of frequency resolution by which spectral localization cues are recognized. Specific Aim 4 will relate elevation sensitivity of cortical neurons to characteristics of their frequency response areas. We will test the hypothesis that specific configurations of excitatory and inhibition domains underlie detection of spectral localization cues. This research will provide basic understanding of auditory cortical mechanisms that is needed for evaluation of temporal lobe pathology and for the design of therapeutic responses to injury and disease.