The avian song control system provides a model for many aspects of neural integration and plasticity. Songbirds learn their songs by imitating external models. The major brain nuclei involved in vocal behavior have been identified. These nuclei are sexually dimorphic and develop under hormonal influence. Lesion studies have shown that the motor pathway for song includes the telencephalic nuclei hyperstriatum ventralis, pars caudale (HVc) and robustus archistriatalis (RA). HVc projects to RA and RA projects to the caudal portion of the hypoglossal nucleus (nXIIts), which in turn controls the muscles of the syrinx, the bird's vocal organ. Recent work has shown that nXIIts and RA contain subregions involved in the control of individual syringeal muscles. In addition, a specialized subregions of RA projects to the dorsomedial nucleus (DM) of the intercollicular area. How is learned song represented in these brain structures? The present work uses physiological, anatomical, and behavioral methods to study the organization and operational principles of this system. Properties of both motor and sensory pathways involved in song learning and production will be studied, discussing on the function of input and output pathways to RA. The detailed organization of inputs from HVc will be studied as will the sources and nature of auditory input. The role of the projection to the midbrain nucleus DM in respiratory-vocal coordination will be examined. This organization will initially be examined in adult male birds and then in developing birds receiving controlled hormonal manipulations and auditory exposure. In addition, the central control of this behavior, including possible lateralization phenomena, will be studied using recordings from HVc, RA and syringeal muscles in awake, singing birds. The results of this investigation will help to elucidate the way in which perceptual and motor components of a learned skill are represented in the brain, including their coexistence or segregation into separate hemispheres. A better understanding of the principles involved in this form of memory may in turn reveal conditions that encourage or limit learning.
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