Sleep is a universal behavior. One functional hypothesis proposes that during sleep perceptual or procedural activity experienced during the prior day is recapitulated, with some memories consolidated and others erased. This hypothesis is supported by observations of individual neurons in the zebra finch forebrain nucleus RA that exhibit neuronal replay, similar patterns of bursting activity during singing and later during undisturbed sleep and in response to song playback. Directly testing the hypothesis, however, is hampered by the lack of procedures to analyze temporal patterns of neuronal activity, especially during sleep in the absence of a time-reference. The proposed research will develop essential statistical modeling and neurophysiological experiments to directly examine functional models of sleep. In the first experiment, the hypothesis of sleep replay in RA will be rigorously statistically tested. Patten filtering methods will be developed to assess matching not only for individual bursts but also for trains of bursts. The statistical significance of replay patterns will be described and a more complete description of the replay phenomenon at the single cell level will be derived. In the second experiment, the hypothesis that sleep replay occurs in nuclei afferent to RA will be tested. The activities of different projection classes of neurons in the afferent nucleus HVc will be recorded. Information-based and metric-based alignment techniques for temporal alignment will be developed to accommodate the lower temporal resolution of these neurons, as compared to RA neurons. The internal noise, and context-dependent temporal precision will be considered to maximize spike alignment. In the third experiment, the specific hypothesis that afferent input from IMAN modifies RA activity on a nocturnal cycle will be tested. A new statistical model, adaptive pattern filtering, will be developed to assess when during sleep are burst patterns first recognized that are destined to be expressed in singing behavior the following day. The memory consolidation hypothesis will be tested by assessing the prediction that after IMAN lesions there should be fewer or no changes in RA burst patterns following periods of sleep. The fourth experiment will record directly from RA in juvenile birds learning to sing. In this case, behavior (singing) and neurophysiological activity during the day as well as during sleep is likely to exhibit high variability which will require statistical modeling. Changes in behavior will be assessed with entropy and other statistical measures. The hypothesis that RA burst patterns change during sleep in a direction that predicts singing behavior the following day will be directly tested.