'Sleeping on it' is a real thing - we make decisions in our sleep

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New research into the brain's activity during sleep has found that our minds are more active than we might think when unconscious.

The fallacy that our brains in some way "switch off" when we go to sleep is still widely believed, but new research shows that it can still process complex external stimuli while we're asleep and even make decisions.

A team of scientists from École normale supérieure in Paris conducted an experiment in which participants were asked to categorise spoken words (e.g "cat" and "hat" as an animal and object) by pressing buttons. They then repeated it after participants had drifted off.

"Of course, when asleep, participants stopped pressing buttons," Thomas Andrillon and Sid Kouider explain in a write-up of the Current Biology research for The Washington Post.

"So in order to check whether their brains were still responding to the words, we looked at the activity in the motor areas of the brain.

"Planning to press a button on your left involves your right hemisphere and vice-versa. By looking at the lateralization of brain activity in motor areas, it is possible to see whether someone is preparing a response and toward which side.

"Applying this method to our sleepers allowed us to show that even during sleep, their brains continued to routinely prepare for right and left responses according to the meaning of the words they were hearing."

Not only did the brain appear to be making decisions during sleep, but participants could later only recall words that were put to them while awake, meaning that the choices made during sleep were done unconsciously.

The scientists behind the study are now keen to find out if sentences or series of sentences can be processed, and while "sleeping on" complex problems like whether or not to take a job might be beyond the brain's ability, some form of learning can take place.

- Independent