New findings about brain rhythms could lead to the development of improved sleep treatments, a new study suggests.
A team at Massachusetts General Hospital found that a brain rhythm regarded as the emblem of wakefulness persists in a hidden form during sleep, where it becomes more intense at certain times - something that appears to affect people's vulnerability to being awakened by noise or other disturbances.
To test their theory, the researchers used computerised electroencephalography (EEG) rhythms in 13 volunteers who slept - or at least tried to - three nights in the MGH Sleep Lab. At many intervals throughout each night, the volunteers were exposed to 10 seconds of typical background noises, such as traffic or a ringing telephone. The sounds were repeated at increasingly louder levels until the EEG showed that sleep had been disrupted.
An analysis of the EEG measurements showed that the intensity of the alpha signal predicted how easily volunteers could be disturbed at the moment the measurement was taken, with a stronger alpha signal linked to more fragile sleep.
Sleep study reveals sleep states
"We found that the alpha rhythm is not just a marker of the transition between sleep and wakefulness but carries rich information about sleep stability," said study author Scott McKinney, informatics manager at the MGH Sleep LAB.
"This suggests that sleep - rather than proceeding in discrete stages - actually moves along a continuum of depth. It also opens the door to real-time tracking of sleep states and creates the potential for sleep-induction systems that interface directly with the brain," he added.
Although the alpha rhythm was discovered nearly 100 years ago, researchers once thought it disappeared when sleep began because they no longer saw it on an EEG. However, a technique called spectral analysis can pick up subtle fluctuations in the alpha rhythm during sleep levels that are not apparent when visually inspecting an EEG.
The study appears in the journal PLoS One.
"This finding paves the way toward futuristic sleep treatments in which medication or other therapies are delivered moment-to-moment, only when needed, to protect sleep when the brain is most vulnerable but otherwise let natural brain rhythms run their course," study senior author Dr Jeffrey Ellenbogen, chief of the MGH Division of Sleep Medicine, said.
"Learning more about the mechanism behind this association between the alpha rhythm and sleep fragility should lead to an even greater understanding of the factors that maintain sleep's integrity in the face of noise and other nuisances," he added.
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