Scientists Unravel Secrets of Sound Sleep08/09/10
MONDAY, Aug. 9 (HealthDay News) -- Ever wonder how some people
can sleep through thunderstorms and traffic noise, while others
wake up at the slightest sound? Differences in people's brain
rhythms during sleep may hold the answer, scientists say.
While treatments based on the findings remain a long ways off,
"by knowing this information, we will better understand what can be
done to enhance natural sleep," said study senior author Dr.
Jeffrey Ellenbogen, chief of the division of sleep medicine at
Massachusetts General Hospital and assistant professor of neurology
at Harvard Medical School.
Reporting in the Aug. 10 issue of
Current Biology, Ellenbogen and his colleagues studied how sensitivity to noise during sleep is associated with a type of brain activity called sleep "spindles" -- bursts of fast brain rhythms that punctuate the otherwise slow-wave patterns characteristic of sleep.
These spindle rhythms are generated by a structure in the brain
called the thalamus, which is responsible for relaying sensory
information from the outside world to other parts of the brain.
It's thought that the thalamus might generate these sleep spindles
as a way to prevent sensory input (such as loud noise) from
reaching the sleeping brain.
To see if spindles might shield the brain from sound in the
environment, the researchers first measured spindle production in
the brains of 12 healthy adult volunteers during a quiet night of
sleep. On the next two nights, they evaluated the volunteers' sleep
behavior in the presence of noises like road and air traffic or a
The researchers found that people with higher rates of spindle
rhythms were consistently less likely to awake in response to these
"Spindles have previously been associated with suppression of incoming stimuli during sleep, so the results are logical," said one expert, Torbjorn Akerstedt, director of the Stress Research Institute at Stockholm University in Sweden.
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
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.
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