Do you ever think about what happens in your head after you've nodded off? Researchers are only just beginning to figure that out, but what they do know is that the sleeping brain is one busy noggin.
One key role of sleep is to allow your brain to consolidate memories. That's when your thoughts about brand new knowledge and experiences crystalize into long-term memories.
Of course, you learn new things while you're awake, but it's when you're deep in dreamland that new information becomes integrated with the memories stored in your brain. That's according to a study from Gareth Gaskell, Ph.D., a professor of psychology at the University of York in England. He and his colleagues found that not only do you learn new information better if you sleep on it, but shut-eye also helps your brain organize this new material.
“It seems to be putting this new knowledge in just the right place so you can make best use of it after sleep,” explains Dr. Gaskell.
In the study, Gaskell and his colleagues had people learn new made-up words like "cathedruke." They judged how well people integrated a new word with the rest of their vocabulary by seeing whether learning it slows them down when identifying similar words, like "cathedral," now that they’re reconciling both words at once. The researchers found that this new knowledge integration correlated with sleep spindle activity—quick bursts of brain activity that happen as you transition into deeper sleep, when your hippocampus (memory storage deep in the brain) interacts with your neocortex (an area responsible for higher functions including conscious thought and language).
Sleep Helps Store Emotional Memories
As it turns out, your brain is particularly partial to storing emotional memories while you’re sleeping. When you're awake, your memories and related emotions can dwindle with time. But research shows that feelings surrounding unpleasant memories seem to remain just as sharp after hitting the sack.
Rebecca Spencer, Ph.D., a psychology professor at University of Massachusetts Amherst, was curious about how sleep helps preserve your memory of and feelings about positive and negative events.
Here’s what she found: “Sleep makes something that seemed negative seem just as negative,” Dr. Spencer says. “But sleep doesn’t do that for positive memories. So if you just got married, you say, 'Should I get a good night of sleep on my marriage night because I want to protect that happy feeling I had around my wedding day?' Sleep might help you better store all those images from the day, but it's not going to do anything preferential for that happy feeling you have for it.”
Spencer suggests that there's a greater evolutionary advantage to remembering the emotional tone related to bad events: to make sure they don't happen again. Imagine a child who has put her hand near a hot stove, only to have her mom panic. "The child needs to not only remember this negative event," Spencer explains, “but they also need to remember their own emotional reaction, because if they don't remember those things then they won't respond appropriately in the future.”
In the case of a horrific memory of a scenario you're unlikely to encounter again, your body has a sleep-related strategy as well. "With severe trauma," she says, “the body's biological response is to go through a period of insomnia." Such lengthened wakefulness can help take away the sharpness of your recalled feelings.