A reduced responsiveness to external stimuli is the main characteristic of sleep. In this study we show that the LC, a small nucleus in the brainstem and the main source of noradrenaline, plays a central role in our ability to disconnect from the environment during sleep. We recorded rats cerebral cortical activity (Electroencephalogram; EEG) in order to identify epochs of sleep while playing sounds indifferent intensities. We showed that the activity of the LC just before the sound was played was correlated to the probability to wake up. Next, increase of LC activity by optogenetics cause rats awakenings more frequently in a response to a sound compared to the exact same sound, when the LC is not activated. Also, an activity decrease of the LC, makes it harder to wake up the rats, meaning that they are more disconnected from the environment.