Title 1 Anesthetic state modulates excitability but not spectral tuning or

25 26 The majority of sensory physiology experiments have used anesthesia to facilitate the 27 recording of neural activity. Current techniques allow researchers to study sensory 28 function in the context of varying behavioral states. To reconcile results across multiple 29 behavioral and anesthetic states, it is important to consider how and to what extent 30 anesthesia plays a role in shaping neural response properties. The role of anesthesia 31 has been the subject of much debate, but the extent to which sensory coding properties 32 are altered by anesthesia has yet to be fully defined. Here we ask how urethane, an 33 anesthetic commonly used for avian and mammalian sensory physiology, affects the 34 coding of complex communication vocalizations (songs) and simple artificial stimuli in 35 the songbird auditory midbrain. We measured spontaneous and song-driven spike 36 rates, spectrotemporal receptive fields, and neural discriminability from responses to 37 songs in single auditory midbrain neurons. In the same neurons, we recorded 38 responses to pure tone stimuli ranging in frequency and intensity. Finally, we assessed 39 the effect of urethane on population-level representations of birdsong. Results showed 40 that intrinsic neural excitability is significantly depressed by urethane, but spectral 41 tuning, single neuron discriminability and population representations of song do not 42 differ significantly between unanesthetized and anesthetized animals. 43 44