Sleep is a physiological state often associated with a cutoff from the external world, and especially loss of conscious perception of sensory stimuli. Even though brain signatures of sleep have been studied for years, the mechanisms that prevent sensory information from reaching consciousness remain to be elucidated. Recently published findings suggest that the loss of perception experienced in anesthesia may be due to neurons population activity coding of stimuli in the cortex collapsing into the spontaneous activity subspace, therefore reflecting internally generated dynamics rather than evoked sensory responses. In our study, we examined whether this property is also at play during sleep. We used two-photon calcium imaging to record the responses to sounds of hundreds of neurons simultaneously in the primary auditory cortex of awake and naturally asleep mice. The analysis of the population activity revealed that, contrary to anesthesia, sounds were encoded with highly similar population activity patterns between the awake and NREM sleep states. This conservation of sounds representations between wakefulness and sleep suggests that sensory processing is impacted by qualitatively different mechanisms in anesthesia and in sleep. Moreover, while under anesthesia sounds representations in the cortex are highly deteriorated, our result indicates that high-level cortical representation of sounds is intact during NREM sleep, a property that is at odd with the classical view that the thalamus gates sensory information to the cortex during sleep, but which may however be critical for survival.