Our brains sort words as we sleep

Vigilance in slumber may explain how meaningful sounds wake a person

woman sleeping

ALWAYS LISTENING  Even while sound asleep, people’s brains could still distinguish animal words from object words, a new study finds.


A soundly sleeping brain still monitors and responds to its surroundings, researchers report September 11 in Current Biology. The results, in which a person’s snoozing brain correctly sorts words into categories, represent the latest feat the brain achieves while sleeping (SN: 12/29/12).

Researchers led by Sid Kouider of CNRS, France’s National Center for Scientific Research in Paris, recorded brain signals from awake people as they classified spoken words as either animals or objects. Participants pushed a button with their right hand when they heard an animal name, for instance, and a button with their left hand for objects.

After nodding off, the participants heard a different set of words, and their brains continued sorting the words into their proper categories, EEG recordings revealed. When participants heard “horse,” their brain activity looked as if they were preparing the right hand, not the left, to hit a button.

By describing one way in which the brain stays vigilant during sleep, the results may help explain how meaningful sounds, such as a baby crying or a spoken name, creep unconsciously into the slumbering mind and wake a person more readily than other sounds. 

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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