Rose-scented sleep improves memory
Bursts of scent during the night can help solidify learning.
It's often said that optimistic people look at the world through rose-tinted spectacles. Now it seems that rose-tinted smells can have benefits too.
Taking a whiff of rose scent while learning a task and then being exposed to the same smell during sleep helps memories to set, researchers have found. The discovery could see students frantically spraying themselves with perfume before exams — although the effect is tricky to replicate at home.
Jan Born of the University of Lübeck and his colleagues exposed people to the smell of roses one evening while they learned the locations of various picture cards laid in a square. Half of them were then given the same odour to smell as they slept, while the other half had an odour-free night. When they were tested the next day, those who'd had a rosy sleep remembered 97% of the locations — without the roses this figure was 86%.
The team's findings, published in Science1, supports theories about how memories are solidified in the brain during sleep.
Researchers think that a part of the brain called the hippocampus is like the scratch-pad of memory, where we put new things that have been experienced or learned until they can be filed for long-term storage. During sleep, these memories are 'reactivated' and transferred to the cortex.
Odours are known to have a potent effect on the hippocampus. Born and his team speculated that an odour could thus help to trigger the 'reactivation' process during sleep, making permanent memory storage more efficient. Their tests support this theory. "By experimentally inducing it, we can show that reactivation enhances memory," says Born.
On again, off again
Volunteers in the study had to be exposed during so-called slow-wave sleep, when the hippocampus is triggered into replaying memories. Passing roses under the nose during lighter, REM (rapid eye movement) sleep, when most dreams occur, had no effect on memory.
But because people get used to odours very quickly, the odour had to be turned on and off at the right times to get the memory effect.
You might think that a whiff of roses the following day, while being tested, would help the volunteers remember the card locations. But the researchers found that this didn't improve the volunteers' scores — though Born doesn't rule it out. The same mechanisms are involved in securing memory during sleep and when awake, he says — the difference is that the hippocampus is more sensitive when its owner is sleeping.
Don't do this at home
It's hard to tell the difference between slow-wave and other types of sleep without being hooked up to a brain scanner, making it a difficult technique to perfect at home. "It's difficult to imagine that we can create a machine that can improve memory during sleep," says Philippe Peigneux, a sleep researcher at the Brussels Free University in Belgium. For students, simply revising what you have to learn and then getting a good night's shut-eye might prove infinitely more practical.
The smell trick is useful only for certain types of learning. It won't be useful for remembering the skills needed for playing the piano or riding a bike, for example, because these activity-related memories don't rely on the hippocampus.
But the finding might provide a friendlier way to improve memory than other suggested techniques, says Born.
Born's group published a study in Nature last year that showed an increase in memory when people's brains were stimulated with a mild electric current2. "Everyone's afraid of shocking the brain," he says. "Odour presentation is a much 'softer' method."
- Rasch B., et al. Science, 315 . 1426 - 1429 (2007).
- Marshall L., et al. Nature, 444 . 610 - 613 (2007).