A new way to cram for exams? Sounds played during deep stages of sleep may help us remember.
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SYDNEY: Listening to specific sounds during sleep may help you strengthen memories of information learned while awake, a study published in the U.S. journal Science has found.
The findings suggest that our mind continues to receive and interpret external signals outside of the rapid eye movement (REM) stage of sleep - when dreaming occurs - and during deeper stages of sleep, generally associated with low levels of brain activity.
If this is the case, individuals wanting to consolidate certain memories over others, such as students cramming for an exam or learning a foreign language, could find a whole new avenue open up to them.
Sleep processing
"This study tells us something about how memories are processed during sleep," said the study's lead author, John Rudoy, a neuroscientist at Northwestern University, in Chicago, USA.
"From previous scientific literature it seemed that memories could be strengthened by a period of sleep," he said. "This shows that the strengthening process is specific - certain memories can be strengthened in favour of others - and that it can be influenced by external stimuli."
For the study, 12 participants were shown 50 images of objects, such as a cat or a kettle, with corresponding sounds, such as a meow and a whistle. Each image had a unique location on a computer screen, which participants memorised before being taken into a dark room to nap.
Sound cues
Half of the sound cues were then played to the participants once they had reached the 'deep sleep' stage of their nap, as determined by electroencephalographic (EEG) recordings.
When tested post-nap, it was found that participants were able to place the sound-cued objects more accurately than those not played during their nap. However, in the control experiment, in which participants were played the additional sounds without any sleep, there was no marked improvement.
"This study is interesting because it relates back to the sorts of things people have thought about in the past, like helping kids by playing them their timetables at night," said John Rostas, neuroscientist from the University of Newcastle, in New South Wales, Australia. "It puts some scientific objectivity and solidarity behind something that has long been speculated about without much evidence."
While Rostas sees a high likelihood that similar techniques could be used for practical purposes in the future, he thinks it might be a long way off yet.
"There is still the problem that the stimulus has to be selective," he said. "Say you're trying to teach a child mathematics, or something equally complex, what aspect of the stimulus would you be playing while they sleep? This study is an example of proof of concept. In theory it could be possible, but the question is how to apply it in practice."
"We are working with some other scientists to look into further aspects of this phenomenon, but it's very early in the process," added Rudoy, who pointed out that there are still a number of unanswered questions, such as how long the increased memory capacity would last, and whether the same results could also come from spoken words, rather than simple non-linguistic sounds.
"The answers to these questions could help us understand just how the technique could be applied practically," he said.
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