A large part of our life remains a mystery. We spend roughly a third of our life with our eyes closed, resting, regenerating, and dreaming. Sleep is universal and common to humans and all animals, so one would imagine it to be one of the best-researched subjects in history. This is not the case – on the contrary, the neuroscience of sleep is a young discipline that confronts us with a number of difficult problems yet to be solved. Yuval Nir, researcher at Tel Aviv University’s Sackler School of Medicine, and his international collaborators are working hard to explain the role of sleep in cognition and how sleep keeps us disconnected from the world around us. Using a range of tools such as optogenetics, fMRI and recordings of brain activity from neurosurgical patients, the Nir Lab stimulates and measures electrical activity in sleeping brains in order to find the connections between activity patterns and differing states of consciousness. In a series of pioneering studies, Yuval and international colleagues recorded signals from individual brain cells during sleep, sleep deprivation, and during REM-sleep dreaming. Their findings demonstrated local waves of sleep that also invade the activity of the waking brain around lapses of attention. During REM sleep, brain activity showed links between sleepers’ eye movements and the switching of mental images – providing new insights about dreaming. At Falling Walls, Yuval reports on the exciting progress made in the neuroscience of sleep, progress that can help in revealing psychiatric and neurological health disorders and ultimately lift the veil on one of the most fascinating mysteries in the life sciences.