Playing sounds while you slumber might help to strengthen some memories while weakening others, research suggests, with experts noting the approach might one day help people living with traumatic recollections.
Previous work has shown that when a sound is played as a person learns an association between two words, the memory of that word association is boosted if the same sound is played while the individual sleeps.
Now researchers have found fresh evidence the approach could also be used to weaken such memories.
“We can an actually induce forgetting of specific material whilst people are asleep,” said Dr Aidan Horner, co-author of the study 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 place word, such as office, or a person, such as David Beckham.
The process was repeated for 60 different object words, and in the course of the process both possible pairings were shown, resulting in 120 associations. As the pairs flashed up, participants heard the object word being spoken out loud.
The team tested the participants on a subset of the associations, presenting them with one of the words and asking them to select a paired word from a list of six options.
Participants then spent a night in the team’s sleep laboratory. Once they had entered a particular sleep state – as judged by electrodes placed on their heads – they were played audio of 30 of the object words.
The team tested participants on the word associations the next day. The results reveal participants’ ability to recall the first word they had learned to pair with an object word was boosted if audio of the latter was played as they slept, compared with if it was not played. However, their ability to recall the second word they learned to associate with the same object decreased relative to the audio-free scenario.
“Just looking at the actual raw scores, the performance goes down from about 50% to just over 40%,” said Horner. However, the team found the effects were only present when the pairings had not been tested pre-sleep – suggesting other instances of recall are also important.
Horner said the findings backed up previous studies that found repeatedly triggering participants’ memories of one word pairing while awake led them to forget the second association with the same word.
“What we’re doing here is essentially setting up a situation where there are two competing memories, and that interference is leading to forgetting one of those memories,” he said.
While the mechanism at play remains unclear, Horner said it might eventually be possible to harness the approach to tackle painful recollections of traumatic events.
But, he added: “There’s a lot of steps that we need to take to see whether we can actually induce this forgetting for real world memories.”
