A brain rhythm signifies an individual's vulnerability to disturbance by the outside world while asleep, a new study has found.
The team from the Massachusetts General Hospital (MGH) Division of Sleep Medicine used EEG to detect subtle fluctuations in the alpha rhythm during sleep.
They found that greater alpha intensity is associated with increased sleep fragility.
"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," says Scott McKinney.
Generated when the brain is relaxed but awake, the alpha rhythm fades as consciousness recedes and seems to disappear when sleep begins.
However, a mathematical technique called spectral analysis reveals that fluctuations in the alpha rhythm persist during sleep at levels that cannot be detected by visual inspection of an EEG.
Since alpha activity is associated with both wakefulness and receptiveness to sensory signals, the researchers hypothesized that it also could indicate a sleeper's sensitivity to environmental stimuli.
To test this theory, they monitored EEG rhythms in 13 healthy volunteers who spent three nights in the MGH Sleep Lab. At frequent intervals through each night the volunteers were exposed to 10 seconds of typical background noises like traffic or a ringing telephone, repeated at successively louder levels until the EEG reflected that sleep had been disturbed.
Results revealed that how easily volunteers could be disturbed at the moment the measurement was taken, with a more intense alpha signal associated with more delicate sleep.
"This technology may someday allow the development of adaptive sleep-inducing agents that can be guided by real-time feedback from neural activity - a great enhancement over conventional sleep drugs that act like sledgehammers, inducing a blanket sedation throughout the brain for an entire night," said McKinney.
The study appears in Plos One.