A fundamental issue in cognitive neuroscience concerns the extent to which the brain continues to respond to external stimuli during sleep. Falling asleep leads to a loss of sensory awareness and the inability to interact with the environment. Yet, while this was traditionally thought as a consequence of the brain shutting down to external inputs, it is now acknowledged that environmental stimuli continue to be processed, at least to some extent, during sleep. For instance, auditory stimuli with a relevant meaning (e.g. own names, own baby's cry, fire alarm) are more likely to lead to awakening. More compelling are recent studies from our lab showing that the sleeping brain, despites the absence of consciousness and overt behavioural response, continues to analyses and even prepare for acting on relevant stimuli. These studies rely on high-density electroencephalography (EEG), with signatures of semantic processing and motor preparation (N400, Lateralized readiness potentials on premotor cortex) to probe neural responses during sleep. In this new project, we will test whether the sleeping brain, despite any overt behavioural responses, can ‘focus attention’ towards the most relevant/meaningful auditory stream in a noisy multi-stream environment.