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Brain Waves Show Why Some Sleep Through Noise

Research May Lead to New Approaches in Treating Sleep Disorders

By Katrina Woznicki
WebMD Health News

Reviewed By Laura J. Martin, MD

Aug. 9, 2010 -- The brains of people who can sleep through the night undisturbed may be better wired to block out noise, according to a small study.

Understanding who has an easier time sleeping than others may help researchers develop more targeted approaches to treating sleep disorders. Environmental noises can affect sleep quality, which can ultimately impact overall health. According to a 2009 survey by the CDC, about one in 10 Americans report difficulty sleeping. Only 30% say they get enough sleep; more than 50 million Americans have chronic sleep disorders, such as insomnia.

Researchers from Massachusetts General Hospital and Harvard Medical School in Boston tracked brain waves among 12 healthy individuals using electroencephalography (EEG) imaging to quantify sleep quality. The team wanted to observe the differences in brain wave rhythms, which were captured by EEG and changed as people moved through different stages of sleep.

Sensory information, including sound, passes through a structure in the brain called the thalamus before reaching the cortex where communication signals are processed. Communication between the thalamus and cortex continue during sleep and are represented by the brain waves captured by EEG.

During the deeper second and third stages of non-REM sleep, brain wave patterns slow down but are interspersed with brief, rapid pulses called spindles, which only appear during sleep. Earlier research has suggested spindles help block sensory information from reaching the thalamus, so Jeffery Ellenbogen, MD, chief of Massachusetts General Hospital's Division of Sleep Medicine, and colleagues tested this theory by having participants spend three nights at a sleep laboratory.

Measuring Brain Activity

The researchers altered the sensory information over the three-day period; the first night was quiet and the second and third nights were noisy.They measured brain wave activity every night to compare differences.

Participants were exposed to 10-second sounds at 40 decibels while sleeping in the sleep laboratory.Those who were able to consistently peacefully sleep through the telephone ringing and traffic sounds had a higher spindle rates on their EEGs.Their findings are reported in Current Biology.

"We were surprised by the magnitude of the effect," Ellenbogen says in a news release. "We designed the study to follow participants for three nights to capture a lot of data, but the effect was so pronounced that we could see it after a single 'noisy' night. Now we want to study behavioral techniques, drugs or devices that may enhance sleep spindles and see if they can help people stay asleep when confronted with noise and maintain otherwise healthy, natural sleep. Understanding the tools and techniques the brain naturally uses could help us harness and expand those responses to help stay asleep in noisy environments."

SOURCES: Vu, D. Current Biology, August 2010.

News release, Massachusetts General Hospital.

News release, Harvard Medical School.

Morbidity and Mortality Weekly Report; Oct. 30, 2009; vol 58: pp 1175-1179.

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