Isabelle Arnulf is a neurologist and the director of a unit on sleep pathologies at La Pitié-Salpêtrière Hospital, in Paris. She studies nocturnal behaviour disorders by observing dream exteriorisation during paradoxical sleep.

For a long time, the world of dreams was the monopoly of those who believed dreams had a hidden meaning. However, a lesser-known, scientific approach has existed for the past fifty years. We can now access giant banks with the dreams of ordinary people of all ages who have allowed researchers to find answers to such questions as: Do men and women dream differently? Does everyone dream of flying? Are sexual dreams all that common? Recent studies of the dreams of the blind, of paraplegics and of amputees have demonstrated our cerebral machinery’s marvellous capacity for compensation. The neurology and medicine of sleep have revealed a number of dream disorders where patients are simultaneously asleep and awake: hallucinations, sleepwalking, night-time fears, narcolepsy and behaviour disorders during paradoxical sleep.
Watching a sleeping person fighting off lions while lying in bed, or discovering that a semi-invalid has ‘returned’ to health in his sleep, is to witness the strange process by which, every night, we become the playthings of our brains. Thanks to the patients who were filmed nightly for the purposes of this study — and who became as fascinated as the researchers with the results — we have been able to learn a bit more about how dreams function.

• Isabelle Arnulf opens a window to the fascinating world of current dream research and describes some amazing cases gleaned from her meetings with contemplative monks who dream of the devil, her encounters with patients who are capable of bolting down tobacco sandwiches in their sleep, from her own laboratory experiments and her efforts to replay Inception.
• This form of ‘night-time ethology’ is an exceptional tool that has enabled scientists to test several hypotheses concerning mind-body interactions during sleep and to detect specific mechanisms that can help identify those patients who are at risk of developing Parkinson’s disease or dementia.