One of the central goals of neuroscience research is to understand how the brain learns. One model system that has contributed to our understanding of learning is vocal learning in songbirds. Song learning and production in passerine birds is governed by the song system, a set of discrete brain nuclei. Because the song system is both experimentally accessible and dedicated to the production of a learned behavior, researchers have generated a great deal of information about how the avian brain learns and produces song. Both song learning and song maintenance require constant auditory feedback to the song system. In fact, there is a population of neurons in the song system which respond selectively to the bird?s own song. These song-selective auditory responses are modulated by the behavioral state of the animal. This observation, in combination with the extensive existing knowledge of the anatomy, development, and function of the song system, makes the avian song system a prime candidate for studying the modulation of complex sensory processing. Therefore, the proposal outlined below focuses on determining how thalamic input to the song system modulates auditory responses by song system neurons. An interdisciplinary approach will be used, including neuroanatomical techniques and intra and extracellular electrophysiology. The main hypothesis guiding this work is that modulation of activity in a thalamic song system nucleus mediates state-dependent regulation of auditory inputs to the main song system pathways.