PROBLEM: Out at the fringes of sleep research, small studies have shown that applying a "gentle electric current" can ease the brain into deep sleep, improving sleep quality and increasing overnight memory retention. But the potential therapy has yet to gain popular appeal, probably because the whole sticking electrodes to your head thing just screams "don't try this at home." (There are, of course, companies that are trying to sell you on trying it at home, but you'll need to find upwards of $600 and a doctor willing to write you a note.)
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METHODOLOGY: German researchers recruited 11 subjects to spend two nights in their sleep lab. During one night, as the participants approached deep sleep, the researchers played sounds ("pink noise") that were synchronized to their brain rhythms. As a control, no sounds were played the other night.
In addition, the participants were shown 120 pairs of words each night before going to bed. First thing in the morning, they were tested to see how many of the pairs they remembered.
RESULTS: While it didn't cause them to experience more deep sleep cycles, the pink noise appeared to prolong deep sleep and to increase the size of the subject's brain waves during that period, as evinced by their EEGs.
The slow brain waves that characterize deep sleep are implicated in information processing and memory formation, and sure enough, on the mornings after those brain waves appeared to have been enhanced, the participants remembered a higher number of word pairs (an average of 22, as opposed to 13).
IMPLICATIONS: Sound stimulation has been tried before, unsuccessfully. The key here, write the researchers, is that the frequency of the sounds was in sync with the subjects' brain waves. Were this technique to be further developed, it could potentially be used to improve sleep in general, and possibly even to enhance brain activity when we're awake. Although it's even less viable, for now, than electric brain stimulation, the latter has been proposed as a way of treating Alzheimer's, fighting depression, easing pain, and the ever-popular "boosting creativity."
"Auditory Closed-Loop Stimulation of the Sleep Slow Oscillation Enhances Memory" is published in Neuron.