We used to think of sleep as a state of suspended activity and unconsciousness. Nowadays, we regard sleep as an inconvenience at best, a weakness at worst. Sleep has considerable benefits. It makes us feel better and helps our brains find solutions to everyday problems. ‘Sleep through the ages’ describes sleep patterns of the past, when we slept for longer periods of time than we do now. Sleep has been studied for at least 2,500 years starting with the Greek philosophers and physicians. The idea that the brain is central to sleep came in the 19th century.