If you’re a college student thinking of cramming for finals, you might want to adopt a more restful strategy.
Scientists have shown that sleep plays a crucial role in memory. As the brain goes down for the night – or even for a nap – what’s been experienced during the day is carefully sorted through and then filed away in permanent storage for easy access later.
Building on that discovery, German researchers have shown in an intriguing experiment that the improvements in memory that we get during our slumbers be boosted even further if we’re exposed to a very specific kind of sound when we’re in deep sleep.
The researchers suspected that little clicking sounds played in synchrony with our brain’s natural oscillations during deep sleep might pump up the oscillations, thereby improving sleep – and also memory.
“Imagine the sleeping brain as a swing which oscillates slowly back and forth,” says study co-author Jan Born, a professor of neuroscience at the University of Tubingen. “The auditory stimulation acts as a gentle nudge of the swing at its highest point [to enhance] the down swinging direction.”
For the new study, Born and his colleagues asked 11 volunteers to memorize 120 word pairs. The words in each pair were related to one another to make them easier to remember, so, for example, “brain” might be paired with “consciousness” and “problem” with “solution.”
In the evening, the volunteers were tested. A researcher would say one of the words from the pair and the volunteer was to try to remember the other.
Then the volunteers were sent off to the sleep lab where their brain activity was monitored throughout the night.
In the first part of the experiment, clicking noises were played through headphones when volunteers reached deep – or slow wave – sleep. In the morning, they were again tested on how well they remembered the word pairs.
A week later the volunteers were again brought into the lab and the experiment was run exactly as it had been the first time, except that there were no clicking sounds during the night.
To see whether the sounds had improved memory, the researchers subtracted the scores from the evening tests (taken before sleep) from the scores from the morning tests.
In both parts of the experiment, morning scores were improved over evening ones. When there was no clicking during the night, people, on average, remembered 13 more word pairs in the morning than in the evening. But the biggest difference was when people were exposed to clicking during the night. They remembered 22 more word pairs in the morning than they had in tests the evening before. That’s almost double the improvements brought on by sleep alone.
So, will college students be rushing out to buy new-fangled headphones that click in the middle of the night?
Not just yet, Born says.
“The creation of head phones that automatically apply auditory stimuli following the stimulation protocol presented in our publication is possible, [but] not so easy,” he explains. “There is ongoing work on these applied frontiers and therefore the development of such devices in the long-term is not so far-fetched.”
One big hurdle to developing a memory enhancing device is that the clicking sound must be in rhythm with the brain’s oscillations. And that, currently, requires the sleeper to be hooked up to an EEG in a sleep lab so brain waves can be monitored.
In the meantime, specialists may want to use the new method to improve sleep quality in people who are restless during the night, Born says.
“The most obvious application for our finding is in clinical settings, in order to enhance the slow oscillation sleep rhythm and thus improve slow wave sleep in certain forms of insomnia,” he explains.