Increasing evidence indicates that anesthetics strongly affect sensory representations and network dynamics in the thalamo-cortical circuits. By contrast, processing in the early sensory systems is thought to be mostly preserved under anesthesia, based on stimulus tuning properties like those observed in wakefulness. However, in the absence of recordings tracking the activity of the same neurons across states, there is no evidence that anesthesia preserves peripheral one-to-one sensory representations. Here, tracking for the first time the same cochlear nucleus neurons across wakefulness and isoflurane anesthesia, we show that the amplitude, sign, and tuning width of single neuron responses to sounds are massively affected by anesthesia in the first relay of the auditory system. Moreover, using dimensionality reduction and classification techniques, we show that sound representations during wake and under anesthesia lie in different neural sub-spaces. Concurrently, representation of sounds in anesthesia cannot be decoded based on classifier trained on awake sound representations. Together, these results demonstrate a much larger effect of anesthesia than previously thought on peripheral auditory processing and indicate that anesthesia will strongly perturb the normal integration of sound information in downstream targets of the cochlear nucleus. This supports the use of awake animals to study the evolution of sound representations in any area of the sensory system. Interestingly, when performed separately on awake or anesthesia data, single cell tuning measures and population decoding showed similar tuning width properties and information levels. Hence, this explains why theses massive changes stay unnoticed when recording separately in the two states.