IS IT time to dream up a fresh theory of sleep? We are all familiar with the concept a power nap, but it could be the very process of falling asleep that鈥檚 beneficial to the brain. Perhaps sleep itself is a mere side effect.
鈥淎 nap of just 10 minutes can reduce drowsiness, even though most models of sleep suggest you need more time to see an effect,鈥� says Derk-Jan Dijk at the University of Surrey, UK. 鈥淚t鈥檚 an anomaly 鈥� there is a discrepancy between how much sleep we think we need and the data.鈥�
Now, Olaf Lahl at the University of D眉sseldorf, Germany, has shown that simply falling asleep does more than refresh the brain 鈥� it can improve recall. Lahl鈥檚 team asked students to memorise a list of words and tested their ability to recall the list after an hour of playing solitaire. Some of them were allowed a 5-minute catnap at the start. The catnapping students recalled significantly more words than the students who were constantly awake (Journal of Sleep Research, ).
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鈥淚t seems that much more is happening during the initialisation of sleep than we once thought,鈥� says Lahl. 鈥淢aybe much of sleep鈥檚 functional aspects are accomplished at its very beginning.鈥�
Robert Stickgold of Harvard University agrees that sleep researchers have underestimated the importance of napping. Just before sleep, the brain replays recent events. Dreamlike sensations and 鈥渃razy鈥� thoughts are common, he says, and could help explain the benefit of the power nap. 鈥淚t鈥檚 as if the brain is sifting through new material to figure out what to work on.鈥�
Studies like Lahl鈥檚 suggest that it is this short period of 鈥渢hought marshalling鈥�, rather than a period of prolonged sleep, that is crucial for good recall. 鈥淵ou might not even need sleep after that hypnagogic period,鈥� says Stickgold. But Jerry Siegel of the University of California in Los Angeles remains unconvinced. 鈥淚t鈥檚 hard to imagine any aspect of sleep onset that would initiate a consolidation process that was not then sleep-dependent,鈥� he says. Lahl agrees that long periods of sleep may carry different benefits to a catnap. 鈥淧erhaps sleep onset triggers memory processing; subsequent slow wave sleep is important for 鈥榗ore functions鈥� like neuronal repair,鈥� he says.
The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
