The long-term objectives of this research program are to understand how temporal patterns in communication sounds are represented and processed in the central auditory system. Much of the information in communication signals, including human language, resides in their temporal structure. An understanding of how the temporal structure of sounds is represented and processed in the nervous system, therefore, is vital to understanding the neural bases of communication and communicative disorders. The research will be conducted on the auditory system of anurans because the temporal structure of their vocalizations has been shown to be important in their reproductive biology and behavioral studies can be conducted to delineate their temporal processing abilities. Presently, little is known concernng the neural mechanisms of temporal processing in the auditory system. At a basic level, the temporal structure of sound consists of how its amplitude and frequency changes, i.e., is modulated, over time. The specific goals of this research are to gain insight into how amplitude modulations are represeted in the brain and the transformations in these representations. In a number of vertebrate species, including mammals, there is a transformation from a periodicity coding of the rate of amplitude modulation to an AM filter representation; most neurons in the midbrain respond best over a particular range of AM rate, i.e., are band-pass. The mechanisms underlying this transformation are poorly understood. The specific experiments outlined in this research proposal are designed to test hypotheses concerning the generation of band-pass AM selectivity. The roles of recovery processes and temporal integration will be investigated. Other experiments should reveal whether an 'AM map' exists in the midbrain.