Neural correlates of sound localisation: across-frequency integration and adaptation

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Sound localization is an important ability of animals and man. How exactly sounds are localized and how this information is represented in the brain has been controversially discussed in the last decade. This proposal will concentrate on the neural representation of one sound-localization parameter, the interaural time difference in the brain of an auditory specialist, the barn owl. The goal of this proposal is to investigate the relation between adaptation and frequency integration in the inferior colliculus of the barn owls inferior colliculus. Three work packages are proposed, and a stimulus paradigm consisting of a first or reference stimulus and a second or test stimulus is employed. This paradigm mimics the behavioral situation in barn-owl hunting. An adaptation occurring during an ongoing stimulus will be called spike-frequency adaptation in the following. By contrast, if a first stimulus is followed by a second stimulus, the influence of the first on the second stimulus will be called response adaptation. The first work package is designed to yield basic data on spike-frequency adaptation and response adaptation. In work package 2 double recordings will be used to study simultaneously the responses at 2 locations in the external nucleus of the inferior colliculus, one corresponding to the location of the reference stimulus and the other corresponding to the location of the test stimulus. Work package 3 combines investigations of across-frequency integration with the study of adaptation and tries to unravel whether and how these two phenomena are related. The applicant expects important new findings about neural mechanisms underlying both across-frequency integration and adaptation and their relation and new insights in how the nervous system handles adaptation occurring in behaviorally relevant situations.