Brain Spindles Protect the Brain from Disturbances During Sleep
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.”