It's not completely clear if sleep spindles are directly interfering with sound transmission to the brain, although that's the current hypothesis, Ellenbogen 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," he said. Alternatively, it's possible that the spindle is simply a sign of an as-yet-unknown brain process that controls noise sensitivity.
Each person's spindle rate was similar across all three nights, suggesting that it's a stable trait for an individual across time, although "little is known about what makes one person produce more spindles than another," Ellenbogen said.
Understanding sleep spindle production may someday help researchers devise behavioral or pharmaceutical methods of increasing resilience to noise during sleep, although such applications remain far off, he noted.
"Certain drugs make sleep spindles more prominent, particularly those that are considered sleep drugs," Ellenbogen said. "It is not known, however, whether these synthetically made spindles behave similarly to those naturally occurring. We are currently investigating that important question."
Studies of sleep spindles may also have implications for other aspects of sleep besides noise sensitivity, Akerstedt said. "Spindles may be a good new physiological indicator of sleep quality," he said. "This may be important, since we lack consensus on what constitutes physiologically good sleep."
There's more on the study of sleep at the National Sleep Foundation.
SOURCES: Jeffrey M. Ellenbogen, M.D., chief, division of sleep medicine,
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