The new Northwestern University study shows that when the information that makes up a memory has a high value (associated with, for example, making more money), the memory is more likely to be rehearsed and consolidated during sleep and, thus, be remembered later.
Also, through the use of a direct manipulation of sleep, the research demonstrated a way to encourage the reactivation of low-value memories so they too were remembered later.
Delphine Oudiette, a postdoctoral fellow in the department of psychology at Northwestern and lead author of the study, designed the experiment to study how participants remembered locations of objects on a computer screen.
A value assigned to each object informed 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," Ken Paller, professor of psychology at Northwestern and co-author of the study, said.
"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," he said.
When each object was shown, it was accompanied by a characteristic sound. For example, a tea kettle would appear with a whistling sound.
During both states of wakefulness and sleep, some of the sounds were played alone, quite softly, essentially reminding participants of the low-value items.
Participants remembered the low-value associations better when the sound presentations occurred 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," Paller, director of the Cognitive Neuroscience Program at Northwestern, said.
"Whatever makes you rehearse during sleep is going to determine what you remember later, and conversely, what you're going to forget," he said.