EDITOR'S CHOICE IN MOLECULAR BIOLOGY
A. Kim et al., “Optogenetically induced sleep spindle rhythms alter sleep architectures in mice,” PNAS, 109:20673-78, 2012.
Sleep spindles are EEG-detected oscillations in brain activity, lasting from 0.5 to 3 seconds, that occur during non-REM sleep. Earlier work had proposed that neurons generating sleep-spindle patterns might help maintain sleep, as studies tied increased sleep-spindle frequency to hypersomnia, or extended periods of sleep. But these were only correlations. Now, Hee-Sup Shin of the University of Science and Technology in Daejeon, Korea, and colleagues have shown for the first time that sleep spindles in fact are responsible for maintaining longer periods of non-REM sleep.
Shin’s group used optogenetics—a technique that activates selected neurons via a genetically inserted light receptor called channelrhodopsin2—to induce sleep spindles in mice. The researchers inserted the light-sensitive receptor into neurons in the region of the brain that generates the spindles and shone timed light flashes to initiate the sleep spindle rhythms. “It’s a really good example of the use of this relatively new technique,” says Stuart Fogel, a postdoctoral researcher at the University of Montreal.
The induction of sleep spindles extended the length of time the mice spent in non-REM sleep, “at the expense of waking,” says Shin. “In other words, they sleep more than the control groups.” REM sleep was unaffected by the optogenetic intervention.
Shin’s team concludes that sleep spindles protect sleep from disruption, making spindles an appealing target for the development of therapeutics. But such work is a long way off, and the researchers are focusing instead on examining other potential benefits related to sleep-spindle patterns, such as the memory consolidation essential for long-term memory.