Whether anesthesia impacts brain sensory processing is a highly debated and important issue. There is a general agreement that anesthesia tends to diminish neuronal activity, but its potential impact on neuronal " tuning " is still an open question. Here we show, based on electrophysiological recordings in the primary auditory area of a female songbird, that anesthesia induces neuronal responses towards biologically irrelevant sounds and prevents the seasonal neuronal tuning towards functionally relevant species-specific song elements. These results demonstrate a clear impact of anesthesia on sensory and cognitive processes. They demonstrate the need to better understand the actions of these drugs. They also open new lines of thought on the differentiation between sensory basic processing and the brain processing of behaviorally relevant items that require high vigilance.