Playing sounds while you sleep can help strengthen some memories while weakening others, research suggests, with experts noting that the approach could one day help people living with traumatic memories.
Previous work has shown that when a sound is played while a person learns an association between two words, the memory of that word association is enhanced if the same sound is played while the individual is asleep.
Now researchers have found fresh evidence that the approach can also be used to weaken such memories.
“We can actually induce forgetting of certain material while people sleep,” said study co-author Dr Aidan Horner from the University of York.
Writing in the journal Learning & Memory, Horner and colleagues report how 29 participants were shown pairs of words on a computer screen, one of which was an object word, such as bicycle, while the other was either a word for a place, such as an office, or a person, such as David Beckham.
The process was repeated for 60 different object words, and both possible pairs were shown during the process, resulting in 120 associations. As the pairs flashed, participants heard the object word spoken aloud.
The team tested participants on a subset of associations by presenting them with one of the words and asking them to choose a paired word from a list of six options.
Participants then spent a night in the team’s sleep lab. After they entered a certain sleep state – according to electrodes placed on their heads – they were played the sound of 30 of the subject’s words.
The team tested the participants on the word associations the next day. The results revealed that participants’ ability to recall the first word they learned to pair with an object word increased if the sound of the object word was played while they slept, compared to if it was not. However, their ability to recall the second word they had learned to associate with the same object decreased compared to the no-sound scenario.
“Just looking at the actual raw results, the performance drops from about 50% to just over 40%,” Horner said. However, the team found that the effects were only present when the pairs were not tested before falling asleep—suggesting that other instances of recall are also important.
Horner said the findings support previous studies that found that repeatedly triggering participants’ memories of one word pairing while awake caused them to forget the second association with the same word.
“What we’re doing here is essentially creating a situation where there are two competing memories, and this interference causes one of those memories to be forgotten,” he said.
While the mechanism at work remains unclear, Horner said it may eventually be possible to use the approach to deal with painful memories of traumatic events.
But he added: “There are many steps we need to take to see if we can actually induce this forgetting of real-world memories.”
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