Why Do We Need to Sleep?

Sleep-inducing substances may come from the process of making new connections between neurons. Chiara Cirelli and Giulio Tononi, sleep researchers at the University of Wisconsin, suggest that since making these connections, or synapses, is what our brains do when we are awake, maybe what they do during sleep is scale back the unimportant ones, removing the memories or images that don’t fit with the others, or don’t need to be used to make sense of the world.