Neurobiologist and lecturer of Physiology at the University of Cambridge Colin Blakemore explores the human need for sleep in his second Reith lecture from his series entitled 'Mechanics of the Mind'.

In this lecture entitled 'Chang Tzu and the Butterfly', Professor Colin Blakemore examines the human need for sleep. The study of human sleep remains the most direct experimental approach to the question of consciousness. Our nightly appointment with death is the most profound loss of awareness that most of us are likely to experience throughout our lives. We shall spend more than 20 years of our lifetime asleep-unconscious, almost oblivious to the demands, the joys and the dangers of the world around us.

The problem of human consciousness has stirred up fierce debate between the reductionists and holists and Professor Blakemore asks the question, why do we sleep?