Nov. 19, 2009 -- Researchers are learning more and more about how our senses aid memory and learning while we sleep.
Now a new study suggests sound can do the same thing.
Study participants were better able to recall a newly learned memory when they were exposed to sound cues for the memory while they napped, even though they did not remember hearing the sounds upon awaking.
“We have known that the memory system is quite active during sleep and that the memory can be strengthened at this time,” researcher John D. Rudoy, of Northwestern University, tells WebMD.
In the new study, which appears in the Nov. 20 issue of Science, Rudoy and colleagues examined whether sound cues associated with newly learned information help the brain retain the new memories.
The study included 12 young adults who were asked to learn a new task and then take a nap.
During the learning phase of the experiment, the participants were shown 50 images, which appeared one at a time at different locations on a computer screen.
Each image had a corresponding sound cue, such as the sound of shattering glass with the image of a wine glass, a meow with a picture of a cat, and so on.
The memory task involved placing the images in their original location when they were shown a short time later with the sound cue. This phase of the study ended when the participants did this twice with all of the images.
Within an hour of completing the learning phase, the participants were asked to take a nap in a quiet, dark room after electrodes were placed on their scalps to monitor brain activity.
After verifying that participants were in a deep sleep, the researchers played 25 of the 50 sound cues heard during the learning phase of the experiment and 25 new sound cues.
Upon awaking, the participants were given the memory test again. Their post-nap scores were worse than their pre-nap scores, showing some loss of memory with time.
But they had far better recall of the correct location of specific images when exposed to the sound cues for those images while they slept, even though they did not remember having heard the sounds.
“Our study showed that our brain works on memories while we sleep, and that this can contribute to our ability to have lasting memories,” Northwestern professor of psychology Ken Paller, PhD, tells WebMD. “We also found that sounds presented softly during sleep can influence this phenomenon by functioning as reminders.”
Sleep Boosts Memory, Not New Learning
So could sound exposures during sleep help students cram for tests or help actors learn their lines?
The Northwestern researchers say it is too soon to say if the findings have practical implications for learning and memory.
And although existing memories can be strengthened during sleep, studies indicate that new learning does not take place.
Howard Eichenbaum, PhD, who directs the Center for Memory and Brain at Boston University, says the brain replays memories during sleep, and sounds may trigger specific memories.
He tells WebMD more research is needed to understand the practical implications, if any, of the link.
He adds that it would be useful to compare the magnitude of memory retention associated with sleep sounds to that seen with more traditional learning methods, like studying.
“That is, which is more effective -- listening during sleep or just studying a bit more when awake?” he asks.