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How your sleeping brain makes decisions without you

Ever get the feeling you can’t shut your mind off? That’s because you can’t. The brain is constantly working — and now scientists have begun to map the amazing things it can do even while the conscious mind has gone to sleep.

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By Valerie Franklin (The Cascade) – Email

Print Edition: September 24, 2014

It turns out the little voice in your mind doesn’t actually do most of the “thinking” work. (Illustration: Anthony Biondi)

Ever get the feeling you can’t shut your mind off? That’s because you can’t. The brain is constantly working — and now scientists have begun to map the amazing things it can do even while the conscious mind has gone to sleep.

According to previous studies, a portion of the brain continues to stay alert while the body sleeps, in case of danger. However, a recent study from France’s École Normale Supérieure de Paris took that idea further: What if our sleeping brains not only remain alert, but are capable of processing ideas and making decisions without the conscious mind’s awareness?

In the experiment, led by cognitive neuroscientist Sid Kouider and PhD student Thomas Andrillon and published online in Current Biology, researchers hooked 18 participants up to an electroencephalogram (EEG), then instructed them to categorize words by pressing a button as they were falling asleep.

The subjects listened to a list of words and pressed either a left or right button to sort them into categories: first selecting words for animals or objects from the list, and then sorting real words like “hammer” from pseudo-words like“fabu.”

Once the subjects fell asleep, researchers repeated the experiment with a new set of words — with fascinating results. Despite the subjects being completely asleep, the EEG showed that their brains were still able to understand and categorize the new words just as accurately as they had when they were awake.

It took two to three times longer for the subjects to process the information than it had when they were awake. However, even the electrical activity that would have caused their fingers to press the left or right button was still present — although because they were asleep, their hands remained physically motionless.

“[The study shows] that the sleeping brain can be far more ‘active’ in sleep than one would think,” Kouider said to BBC. “This explains some everyday life experiences such as our sensitivity to our name in our sleep, or to the specific sound of our alarm clock, compared to equally loud but less relevant sounds.”

Even more fascinating is that when they woke up, the subjects had no memory of the tests that had occurred while they were asleep. That means that not only did they process and sort the information while asleep, but their brains did it entirely automatically, without any guidance from their conscious minds.

What does this mean for the average sleeper? Nothing yet — but it could pave the way to a future where you can wake up smarter than you were when you went to bed. Kouider told the Christian Science Monitor that there’s a lot of interest in harnessing the unconscious brain’s power to learn while we sleep.

“I don’t think it’s science fiction,” he said. “I think that’s where we’re going.”

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