Sleep to Remember

Your brain, says neuroscientist Ken Paller, is not like a laptop, shutting down when you close the lid. Instead, when you close your lids at night, your brain remains hard at work, consolidating information you’ve learned that day — and the days before.

Paller, a professor of psychology and director of Northwestern’s Cognitive Neuroscience Program, studies memory and other aspects of human cognition. In recent years his lab group has explored the connection between memory and sleep. Their goal is to understand fundamental mechanisms whereby memories are stored in the brain — and to reveal how the ability to remember gets a boost while you sleep.

Paller’s lab is exploring various types of memory that can be reinforced during sleep, and how memories are reactivated so that they can be consolidated. 

He says that to memorize new information — perhaps the name of someone you just met — you can rehearse that information, which is effective whether you do so intentionally or unintentionally. “This rehearsal is part of the consolidation process,” he says, “and perhaps that’s what the brain is doing during sleep when it’s bringing up recent memories, even though we don’t know it’s happening.”

Paller and his students showed that sounds strategically presented during sleep could improve retention of recently learned information. “Sensory input can change how memories are stored,” he says. “When the sounds specifically connect to recent learning, they can change brain networks — and because of these changes the ability to remember the next day is improved.”

Paller, who runs a sleep lab on the Evanston campus, is working with Marc Slutzky, an associate professor of neurology, who helps people regain fine motor control after a stroke by teaching them how to control individual muscles. “That rehab therapy could take advantage of what’s happening during sleep,” Paller says. “We use basically the same therapy except with special sounds linked to the particular movements people are learning to make. When those sounds are played during certain stages of sleep, learning might be reinforced so that the therapy works better.” Paller hopes that by exercising the brain networks during sleep, participants can speed up recovery time.

Paller is also working with Phyllis Zee, professor of neurology and director of the Feinberg School of Medicine’s Center for Circadian and Sleep Medicine, to improve slow-wave sleep, which is an important time for memory processing. The researchers play sound stimulation — such as the rush of a waterfall — synchronized to the rhythm of brain waves at particular intervals that mimic the slow-wave intervals, enhancing these slow waves. Studies using this method have shown improvements for the young and old and for people in the early stages of Alzheimer’s disease. “We found that one consequence of improving sleep is improved memory,” Paller says.

In a separate study, Paller and his team are also looking at ways to help people control their dreams. When you have the realization in the middle of a dream that you’re dreaming, “that’s termed a lucid dream,” he says. “And that’s a rare thing, but when people have that realization, they can master the ability to stay asleep and continue to explore the dream and then, in fact, control it.”

Paller and his team are exploring the ability to make study participants aware that they’re experiencing a dream and then help them change the content of the dream. “The dream is the original virtual reality,” Paller says. “When we inhabit a dream, we’re in a hallucinatory world, even though it can feel every bit as real as any waking experience.”

Although the value of dreaming remains somewhat mysterious, Paller also noted that research has been steadily making progress in revealing the many benefits of sleep. With mounting evidence of the importance of sleep for memory and health, it’s essential to prioritize your sleep.

“There are various pressures that can make us devalue sleep. We may try to get more done by getting less sleep,” he says. “But to really optimize, it’s critical to understand the various ways that sleep is helpful for us.”