The ability to learn during the hours of sleep might seem like only a dream to college students, but a new study suggests that learning during sleep is actually possible.
The study, published in Nature Neuroscience, shows that the human mind can make learning associations even while it is asleep. The researchers used a simple form of classical conditioning to test their hypothesis.
While 55 healthy participants slept in a laboratory wearing masks, they were exposed to pleasant or unpleasant odors such as perfumes, shampoo, rotting fish and carrion. Different tunes accompanied the smells.
During an ideal night, subjects were exposed to a three-second presentation 40 times — 20 times to the pleasant and 20 times to the unpleasant odor, said Anat Arzi, a graduate student of the Weizmann Institute of Science in Rehovot, Israel, in an email interview.
Subjects inhaled deeply when they were exposed to a pleasant smell. Their breathing shortened when unpleasant odors accompanied the music.
The study suggested that even when they were awake, the subjects changed their sniffs in accordance with the attractiveness of the odor.
Boston sleep researchers said the results of the study make sense.
“There has been a lot of research on sleep and memory and learning,” said Dr. Sanford Auerbach, director of the Sleep Disorders Center at Boston Medical Center. “Sleep is a good utility in optimizing learning so that while we sleep, our bodies develop biochemical changes. If you don’t sleep, you can’t have good memory function, which is associated with increased levels of sleep.”
Arzi’s paper studied the “sniff response” of the subjects. Pleasant odors drove stronger sniffs and unpleasant odors drove weaker sniffs. Humans’ sniff response remained the same, even during sleep, the researchers found.
“This means that the sleeping brain can perceive the presence of the odor, process its valance and generate an adequate behavioral response,” Arzi said.
This research showed that participants were unaware of the sound-smell relation. Researchers saw the effect regardless of the phase of sleep, but the sniffing responses were more visible in participants during the rapid eye movement stage. The REM sleep cycle takes place typically during the second half of sleep.
While research similar to Arzi’s has been conducted in the past, this study is the first to explore sleep’s interaction with learning.
“Our study is the first to show that hippocampal-dependent learning is possible during natural adult human sleep,” Arzi said. “This still does not imply that you can place your homework under the pillow and know it in the morning.”
The Weizmann researchers are still running clinical trials to explore the future of the study, and they are currently trying to implement a helpful behavioral modification through sleep-learning, Arzi said.
“There will be clear limits on what we can learn in sleep, but I speculate that they will be beyond what we have demonstrated,” Arzi said.
When Tiaundra Smith, a junior in the College of Arts and Sciences majoring in neuroscience, heard that learning and knowledge could be consolidated during sleep, she tried to dream about it as she slept.
“I think it’s pretty cool,” Smith said. “Everything makes sense — when you’re sleeping, you’re forming new neuro-pathways.”
But she said that while the study may have more implications for the future, it should not preclude good sleeping and eating habits.
“Sometimes it worked, but the brain consolidates information while you sleep,” Smith said. “When you’re studying for a test, make sure you get enough sleep so you can remember the information you learned during the test.”
Natalie Banacos, a CAS senior and an executive board member of the Boston University Mind and Brain Society, said she found the sleep study fascinating.
“Evidence that we can learn to make associations that alter our behavior while sleeping sounds like a good argument for sleep studying,” Banacos said. “The retention of the information learned might even be longer than demonstrated by their experiment, because in real life, this extinction process may not happen, and the learned association might actually last longer.”
Banacos said she is particularly interested in learning about how the brain processes smells and that the study was unique in focusing on olfactory information or information that is associated to smells in the brain.
“Not all information makes its way through the brain in the same way that scents do — smell is a pretty unique sensory process,” Banacos said. “As the authors mention, using smells was an especially effective way to observe learning during sleep, but the results might not directly translate to better ways to study.”
Allison Macika, a junior in CAS, said she was familiar with existing sleep theories that suggest that when humans sleep, their brains consolidate information they have learned during the day into long-term memory.
“The idea that our brains could not only consolidate information while we sleep, but may also learn new associations, is really interesting to think about,” Macika said. “Like the article said, obviously people shouldn’t take this to mean that you can learn how to solve equations while you snooze, but I’m curious to see what practical applications researchers can pull out of this.”
Lucy Huang, a graduate student in the School of Education, said she was skeptical when she heard about the study.
“I sometimes dream in rhyming patterns or poems but I don’t think you can learn things,” Huang said. “I think if you read something before going to sleep, you might memorize it better.”