The development of neural replacement therapies for brain repair after trauma, stroke, and neurodegenerative disease is focused along two main fronts: transplanting neural precursors derived from exogenous stem cells into damaged brain regions, and harnessing endogenous neuron production to direct migrating cells to target areas. The goal of both programs is to introduce healthy neural tissue to regions which do not normally undergo adult neurogenesis. Toward this aim, understanding the natural regulation of adult neuronal turnover will establish the basis for therapeutic advancement. In addition, it is critical that we also understand the behavior of newly generated neurons in systems outside of the hippocampus and olfactory bulb if we are to target new neuron incorporation into diverse brain regions. The avian song system provides a powerful model for studying adult neuron replacement across brain regions. In this system, new neurons are incorporated into a sensorimotor nucleus essential for song production, providing a highly tractable brain-behavior model in which to study adult neurogenesis in association with a rich array of singing related behaviors. The long term objective of the proposed research is to understand the relationship between behavior of the organism, or neural experience, and the regulation of neuronal lifespan in brain regions that undergo neuronal turnover. The ultimate goal of gaining this understanding is its application in designating conditions which encourage and maintain healthy neuronal replacement in the human brain as well as in developing treatments for individuals with increased neuron cell death due to illness or injury. The specific aim of this project is to identify behavioral factors that impact neuron cell death. Neuronal experience is known to influence neuron lifespan. However, to date, neuronal experience has been synonymous with neural demand, or the amount of use or activity in a particular brain region, and variations in the quality of the experience has not yet been identified as a determinant of neuronal lifespan. For instance, the amount of song produced is correlated with the number of new neurons in the song motor pathway (Li et al., 2000). In contrast, we have recently discovered that aberrant song production results in a dramatic decrease in the number of new neuron in this pathway. This suggests that not only a quantitative measure of motor output, but also the quality of behavioral feedback, may influence neuronal turnover. In the proposed work, we will determine whether aberrant song production and feedback triggers neuron cell death in the song motor pathway. Song production is distorted by partially paralyzing the vocal muscles using botox. In this way, sensory feedback that is received during singing is mismatched to the expected sensory feedback. We will then assess cell death in cohorts of neurons of different ages using immunocytochemistry to label dying cells, neuron-specific markers, and markers of cell birthdate. Different responses among neurons of different age groups will provide the basis for subsequent investigation of the mechanisms by which feedback-induced neuron death may occur.