April 13, 2013
Rehearsing Memories During Sleep Helps You Remember More
April Flowers for redOrbit.com — Your Universe Online
A group of researchers at Northwestern University wondered, “why do some memories last a lifetime while others disappear quickly?”
When a memory has a high value -- for example, associated with making more money -- the memory is more likely to be rehearsed and consolidated during sleep. This insures that it will be remembered later. The researchers, through the use of a direct manipulation of sleep, revealed a way to encourage reactivation of low-value memories.
Participants were asked to remember the location of objects on a computer screen during the experiment designed by Delphine Oudiette, a postdoctoral fellow in the department of psychology at Northwestern. Each object had a different value assigned, informing the participants how much money they could make if they remembered it later on the test.
"The pay-off was much higher for some of the objects than for others," explained Ken Paller, professor of psychology at Northwestern. "In other words, we manipulated the value of the memories -- some were valuable memories and others not so much, just as the things we experience each day vary in the extent to which we'd like to be able to remember them later."
Each object was accompanied by a characteristic sound as it was shown on the screen — for example, a whistling sound would accompany a tea kettle. Some of the sounds were played alone, softly, during both states of wakefulness and sleeping to remind participants of low-value items. The research team found the participants remembered low-value associations better when the sounds were presented during sleep.
"We think that what's happening during sleep is basically the reactivation of that information," Oudiette said. "We can provoke the reactivation by presenting those sounds, therefore energizing the low-value memories so they get stored better."
"The research poses provocative implications about the role memory reactivation during sleep could play in improving memory storage," said Paller, director of the Cognitive Neuroscience Program at Northwestern. "Whatever makes you rehearse during sleep is going to determine what you remember later, and conversely, what you're going to forget."
A large number of memories that are stored during the day are not remembered.
"We think one of the reasons for that is that we have to rehearse memories in order to keep them. When you practice and rehearse, you increase the likelihood of later remembering," Oudiette said. "And a lot of our rehearsal happens when we don't even realize it -- while we're asleep."
The selectivity of memory consolidation is not well understood, according to Paller. The majority of prior research into memory has focused on what happens when you first form a memory and when you retrieve a memory.
"The in-between time is what we want to learn more about, because a fascinating aspect of memory storage is that it is not static," Paller said. "Memories in our brain are changing all of the time. Sometimes you improve memory storage by rehearsing all the details, so maybe later you remember better -- or maybe worse if you've embellished too much.
"The fact that this critical memory reactivation transpires during sleep has mostly been hidden from us, from humanity, because we don't realize so much of what's happening while we're asleep," he said.