Organization of the zebra finch song control system: I. Representation of syringeal muscles in the hypoglossal nucleus

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Abstract
Understanding the representation of learned skills in the brain requires that one know the neural substrate for those skills. The avian song control system uses auditory information to establish and modify motor programs, which provide patterns for the excitation of individual muscles. In the present study, a combination of neurophysiological and anatomical techniques was used to map the representation of syringeal muscles in the tracheosyringeal part of the hypoglossal nucleus of adult male zebra finches. Microstimulation revealed that control zones for individual muscles are arranged along the rostrocaudal axis of the nucleus. The ventralis and dorsalis muscles have the largest domains, located at the rostral and caudal ends of the nucleus, respectively. The retrograde tracer fluorogold was applied to the muscles and confirmed this pattern. The muscle map obtained will provide a useful tool for further study of the convergence of muscle representation and sound representation in the more central portions of the song control pathway. This knowledge is essential for understanding how learned sounds are perceived and produced.