It is commonly accepted that sleep can be an important tool when it comes to enhancing memory and learning skills. Now, a new study sheds light on the role that dreams play in this important process.
Led by scientists at Beth Israel Deaconess Medical Center (BIDMC), Boston, the new findings suggest that dreams may be the sleeping brain’s way of telling us that it is hard at work on the process of memory consolidation, integrating our recent experiences to help us with performance-related tasks in the short run and, in the long run, translating this material into information that will have widespread application to our lives. The study is reported in the April 22 online issue of Current Biology.
"What’s got us really excited is that after nearly 100 years of debate about the function of dreams, this study tells us that dreams are the brain’s way of processing, integrating and really understanding new information," explains senior author Robert Stickgold, PhD, director of the Center for Sleep and Cognition at BIDMC and associate professor of psychiatry at Harvard Medical School. "Dreams are a clear indication that the sleeping brain is working on memories at multiple levels, including ways that will directly improve performance."
At the outset, the authors hypothesized that dreaming about a learning experience during non-rapid eye movement (NREM) sleep would lead to improved performance on a hippocampus-dependent spatial memory task. (The hippocampus is a region of the brain responsible for storing spatial memory.)
To test this hypothesis, the investigators had 99 subjects spend an hour training on a "virtual maze task," a computer exercise in which they were asked to navigate through and learn the layout of a complex 3D maze with the goal of reaching an endpoint as quickly as possible. Following this initial training, participants were assigned to either take a 90-minute nap or engage in quiet activities but remain awake. At various times, subjects were also asked to describe what was going through their minds, or, in the case of the nappers, what they had been dreaming about. Five hours after the initial exercise, the subjects were retested on the maze task.
The results were striking. The non-nappers showed no signs of improvement on the second test—even if they had reported thinking about the maze during their rest period. Similarly, the subjects who napped, but who did not report experiencing any maze-related dreams or thoughts during their sleep period, showed little, if any, improvement. But the nappers who described dreaming about the task showed dramatic improvement, 10 times more than that shown by those nappers who reported having no maze-related dreams.
"These dreamers described various scenarios—seeing people at checkpoints in a maze, being lost in a bat cave, or even just hearing the background music from the computer game," explains first author Erin Wamsley, PhD, a postdoctoral fellow at BIDMC and Harvard Medical School. These interpretations suggest that not only was sleep necessary to "consolidate" the information, but that the dreams were an outward reflection that the brain had been busy at work on this very task.
Of particular note, say the authors, the subjects who performed better were not more interested or motivated than the other subjects. But, they say, there was one distinct difference that was noted.
"The subjects who dreamed about the maze had done relatively poorly during training," explains Wamsley. "Our findings suggest that if something is difficult for you, it’s more meaningful to you and the sleeping brain therefore focuses on that subject—it ‘knows’ you need to work on it to get better, and this seems to be where dreaming can be of most benefit."