While in graduate school at Harvard Dr. Sara Mednick, assistant professor of psychology at the University of California, Riverside, became fascinated with the work of Professor Robert Stickgold, whose research focused on how sleep improved cognition.
Stickgold studied nighttime sleep, but Mednick was more interested in the science behind daytime napping because of her personal experience.
“My father was a great napper, and none of the research could explain why someone could take an hour long nap and feel great,” Mednick told the Observer.
She set up a bed and a portable EEG machine in her office, and over the course of her career, she has found that even short naps can have cognitive benefits, lecturing and writing books on the phenomenon.
Mednick’s most recent research in this area was the focus of a study published in the Proceedings of the National Academy of Sciences. She and her team focused on the autonomic nervous system (ANS) which is responsible for bodily functions that are not controlled consciously, such as heartbeat, breathing and digestion. There is already evidence that memory improves when the ANS is active during waking hours, and Mednick, the study’s senior author, wanted to find out if ANS activity during sleep led to memory improvement as well.
“We know sleep is important for memory, but we didn’t have a great sense of what exactly about sleep helped the most,” she said.
To find out the team recruited 81 participants (including 20 controls) and had them take two versions of the Remote Associates Test (RAT), which evaluates creativity. The patients were shown three words and asked to provide a fourth term that linked them together—for example, given the words “cottage,” “Swiss” and “cake” the correct answer is “cheese.”
There was a twist, however—after the first test, doctors also gave the patients a series of analogies which, unbeknownst to them, offered clues for the second memory test they would take later in the day.
“They would need to use the primed word for a different purpose,” Mednick explained.
“What goes on below the neck plays a big role in memory consolidation. A lot of heart rate variation is healthy for the brain in waking and sleeping.” – Dr. Sara Mednick
The experimental group took a nap before the second test, while the control group watched a video. After regrouping, scientists found that during the second test, those who napped performed better on both the questions they had been clued in on and the RAT in general.
“They had no idea that they’d even seen the primes before,” Mednick said.
Rapid eye movement (REM) sleep on its own accounted for 40 percent of test score improvement—Mednick said that was because this deep sleep leads to “fanciful dreams and associative processing,” even when napping.
Autonomic activities also played a sizable role in the improved scores, however. The team found that heart rate variability in REM sleep, a function of the ANS, contributed to a 33 percent increase in test performance—total improvement when REM and ANS activities were combined was close to 73 percent.
“What goes on below the neck plays a big role in memory consolidation,” Mednick said. “A lot of heart rate variation is healthy for the brain in waking and sleeping.”
High profile sleep advocates hope studies like Mednick’s help the general public understand sleep’s many benefits.
“We really are living in a golden age of sleep science,” Arianna Huffington, editor in chief of The Huffington Post and author of The Sleep Revolution, told the Observer in an email. “Every week, new research reveals how vital sleep is to our health, happiness, job performance and relationships. The science is fueling a broad cultural shift.”