Computer game is a winner for dyslexic children

A new study on the platypus suggests that REM (rapid eye movement) sleep, when we dream, first evolved to maintain basic brain machinery located in the brainstem rather than to service higher intellectual functions, as previously thought.

The platypus "changes our view of dreaming, indicating that this is something that has been grafted on to a more essential primitive function, analogous to the way talking has been grafted on to breathing", Prof Jerome Siegel of the UCLA School of Medicine said. He said his study, at the University of Queensland, Australia, marked the first recording of sleep in this primitive egg-laying mammal.

The meeting was told that the platypus has REM sleep, a type of sleep previously linked to higher intellectual functions, and in fact has more than six times the amount of human REM sleep.

"The present study shows that the platypus, the most primitive mammal and one previously thought to have no REM sleep, has more REM sleep than any other animal," Prof Siegel said. "If early mammals had such large amounts of REM sleep, then their progenitors probably had REM sleep.

"Prior to this study it had been thought that REM sleep evolved in mammals during the last 150 million years." This had suggested that this type of sleep evolved twice, in birds and mammals.

But the platypus study suggests that REM sleep evolved only once in the common ancestors of birds and mammals, reptiles that lived 250 million years ago. The study indicates that dinosaurs may have had REM sleep.

However, it is doubtful that the dinosaurs had dreams. The platypus study did not reveal the type of brain waves that accompany dreaming in humans. "Therefore REM sleep may have evolved long before dreaming evolved," Prof Siegel said. "Our finding supports the notion that REM sleep has its most important original role in maintaining brainstem systems and instinctively programmed behaviour."