Everyone knows someone who they say can “sleep through an earthquake”. Scientists are closer to understanding why some people can sleep through the night undisturbed while others wake with even the slightest noise. Researchers from Massachusetts General Hospital and Harvard Medical School in Boston have found specific brain structures that some have that help block out noise, producing a sounder sleep.
Sensory information, including sound, is passed through a structure in the brain called the thalamus before reaching the cortex where communication signals are processed. During the deeper stages of non-REM sleep, brain wave patterns slow down but are interspersed with brief, rapid pulses called spindles. Earlier research suggests that spindles help block sensory information from reaching the thalamus so that sleep is not interrupted.
Using electroencephalography (EEG), the researchers observed brain wave rhythms in 12 healthy individuals, ages 20-46, during the different stages of sleep over a three day period. Communication between the thalamus and cortex during sleep were captured by the EEG.
On the first night of the study, the laboratory was kept quiet. On the second and third nights, participants were exposed to 10-second sounds at 40 decibels while sleeping. Those who were able to consistently sleep peacefully through sounds such as a telephone ringing and traffic sounds had higher spindle rates on their EEG’s.
Dr. Jeffrey Ellenbogen, chief of the division of sleep medicine at Massachusetts General Hospital and lead researcher for the study said, "If a spindle occurs at the same time as a sound, then the sound is likely blocked from perception, keeping the person asleep. More spindles makes it more likely that noises will collide with this sleep-protecting rhythm.”
“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."
According to a 2009 survey by the US Centers for Disease Control and Prevention, about one in 10 Americans report difficulty sleeping. More than 50 million Americans have chronic sleep disorders, such as insomnia. Chronic sleep deficit causes detrimental health effects such as the inability to remain alert and attentive, depression and may contribute to obesity.