Neurogenesis persists into adulthood in many vertebrates including humans. An understanding of the factors that control neuron addition and survival may ultimately lead to insights on the functions of adult neurogenesis and suggest mechanisms for brain repair. In adult warm-blooded vertebrates, the most widespread production of neurons occurs in the avian telencephalon. In songbirds, many new neurons are inserted into the High Vocal Center (HVC), a region necessary for the perception and production of learned vocalizations. New HVC neurons replace older neurons that have died. Recent work shows that auditory input is necessary for normal rates of neuronal replacement. Available data suggest that deafening decreases the numbers of HVC neurons incorporated and prolongs their subsequent survival. Proposed work will directly test whether the life span of neurons that have been successfully incorporated into HVC prior to deafening is augmented. Additional studies will determine whether deafening influences the production or early survival of adult-formed neurons. A lesion study will test whether the lateral magnocellular nucleus of the anterior neostriatum (lMAN), an area necessary for song learning, participates in the auditory control of HVC neuron turnover. Playbacks of conspecific song produce increased rates of HVC neuron activity and maximal rates are obtained with playbacks of the bird's own song. Thus, the effects of deafening on HVC neuronal turnover may be due to depriving birds of song-related auditory stimulation. Proposed experiments will systematically deprive hearing-intact birds of access to self-generated auditory feedback and/or conspecific song to test this hypothesis. We will contrast these effects with those following manipulations that alter, without completely blocking, self-generated auditory feedback from singing. Collectively, these studies will explore the sensory requirements for the control of adult neuron addition and loss within a discrete, well-characterized neural system controlling a learned vocal behavior.
