If you have ever wondered how some people can sleep through anything while others wake at the slightest disturbance, then a group of US scientists may have the answer: they found that sound sleep has a distinct brain pattern.
To learn how Dr Jeffrey Ellenbogen, Chief of the Division of Sleep Medicine at Harvard Medical School, and colleagues made their discovery you can read their paper published online on 10 August in the journal Current Biology.
Quality sleep is important for our health and wellbeing, wrote Ellenbogen and colleagues in their background information, yet fractured sleep is now common in our society, and part of the reason is “insults from a variety of noises”.
They decided to investigate the mechanisms that might play a role in determining why some people can sleep soundly through any disturbance while others experience very fragile sleep.
For the study, Ellenbogen and colleagues observed electroencephalograph or EEG brain patterns of 12 volunteers as they slept in a lab at Boston’s Massachusetts General Hospital for three nights.
On the first night, the researchers exposed the volunteers to little noise, it was quiet.
However, on the second and third nights, the researchers exposed them to a variety of disturbing noises: a phone ringing, people talking, mechanical sounds from the hospital, aircraft sounds, and so on.
Ellenbogen, who is also Assistant Professor in Neurology at Harvard Medical School, told the press that they learned a lot from these observations:
“The more sleep spindles your brain produces, the more likely you’ll stay asleep, even when confronted with noise,” said Ellenbogen.
Sleep spindles are brief brief bursts of faster-frequency 11-15 Hz waves that intersperse the slow and organized rhythms that prevail during sleep. They originate in the thalamus, a part of the brain that initially processes all our sensory information apart from smell.
Ellenbogen said the thalamus is probably stopping sensory information from getting to the parts of the brain that perceive and react to sound: like setting up a roadblock that stops the signal traffic from reaching these other parts of the brain.
He said their study showed that “the sleep spindle is a marker of this blockade. More spindles means more stable sleep, even when confronted with noise”.
“We found that individuals who generated more sleep spindles during a quiet night of sleep went on to exhibit higher tolerance for noise during a subsequent, noisy night of sleep,” he and his colleagues wrote in their paper.
They also showed they were able to predict an individual’s ability to stay sound asleep through the noises from the spindles that appeared on their EEG chart.
However, what really surprised them was the size of the effect.
Ellenbogen said “the effect of sleep spindles was so pronounced that we could see it even after just a single night”.
He and his colleagues concluded that:
“This result shows that the sleeping brain’s spontaneous activity heralds individual resilience to disruptive stimuli.”
They hope this finding “sets the stage” for further studies that try to increase spindle production as a way to help people get a better night’s sleep when confronted with noise.
They suggested various ways this might be done, for example through behavioral techniques, drugs or devices, although exactly how is not yet clear.
Ellenbogen said that getting a good night’s sleep today is becoming increasing complex and problematic “with all the beeps and boops of our 24/7 modern, crowded lives”, and methods that help people improve their quality of sleep are likely to be very popular.
A particular challenge exists in hospitals where many of the sounds just can’t be suppressed or silenced such as alarms from heart monitors.
“Our goal is to find brain-based solutions that integrate a sleeping person into their modern environment, such that sleep is maintained even in the face of noises,” explained Ellenbogen, and this study “gets us one important step closer to realizing that goal”.
He sees a future where we will have several ways of helping us get a good night’s sleep, and only wake up when we want to, all based on sound sleep science and technology.
“In the meantime,” he said, “it still doesn’t hurt to put up a sign that says ‘Shhh!'”
Ellenborg also suggests if you are one of those people who has to have the radio or TV on to fall asleep, use a timer to switch it off automatically later, because the noises they emit affect the quality of your sleep, even if you don’t realize it.
“Spontaneous brain rhythms predict sleep stability in the face of noise.”
Thien Thanh Dang-Vu, Scott M. McKinney, Orfeu M. Buxton, Jo M. Solet, Jeffrey M. Ellenbogen.
DOI:10.1016/j.cub.2010.06.032
Additional source: Cell Press.
Written by: Catharine Paddock, PhD