Clue to getting a good night's sleep discovered
US researchers are a step closer to discovering why some people can sleep peacefully despite the noise of modern life.
A process in the brain plays a key role in blocking out sound during sleep, they say, and it appears to be more effective in certain individuals.
It may be possible to boost this effect using therapy, drugs or electronic devices, says a Harvard team.
The research is published in the journal Current Biology.
US researchers studied 12 healthy volunteers at a sleep clinic over the course of three nights.
The first night was quiet but during the second and third nights, volunteers were confronted with the sounds of telephones ringing, road and air traffic noises and the beep of hospital equipment.
They were monitored each night using an electroencephalograph (EEG), which records the electrical activity of the brain.
The team, led by Dr Jeffrey Ellenbogen of Harvard Medical School, Boston, detected patterns known as sleep spindles which are thought to block out the effects of sound and other sensory information passing through the brain.
Individuals with the highest rates of spindles on the quiet night were less likely to be woken by noises on the second and third nights, and some were not even aware their sleep had been disrupted, he said.
"In recent years, it has been discovered that the sleep spindle is generated by the thalamus," Dr Ellenbogen explained. "And since the thalamus is the gateway of sensory information to the brain, it has been hypothesised that spindles are markers of the blockade of noises during sleep.
"Our study demonstrates this finding in humans, and takes it one step further: one can use the sleep spindle as a biomarker for predicting whether a person will have difficulty in noisy environments or not in the future."
The researchers hope to eventually use this finding to enhance the natural brain rhythm that protects sleep.
"We have a lot of work to do before using this in people, mostly because we want to be absolutely clear that this is safe and effective," said Dr Ellenbogen. "But whether it's next year or next decade, this research will lay the groundwork for brain-based solutions to noisy environments."
Commenting on the study, Dr Chris Idzikowski, Director of the Edinburgh Sleep Centre in Scotland, said sleep spindles have always been regarded as the hallmark of sleep but their function has been unclear.
"This is an interesting paper which modestly links sleep spindles with blocking the effects of acoustic stimuli," he said.
Professor Jim Horne of the Sleep Research Centre at Loughborough University added: "Sleep spindles certainly help to block outside noise. There are other interpretations for this study, though, as those people with fewer spindles may simply be 'lighter sleepers' and more likely to wake up with the noise - hence less sleep and fewer spindles."