How can some sleepers doze through anything from the rattle of a jackhammer to the blast of a jet engine? According to a new study, an extra helping of brain activity in the thalamus--a region tied to the senses--may give some people a better chance at blocking sleep-disturbing sounds.
"I hear complaints a lot as a sleep doctor that noises are interrupting people’s sleep all the time,’’ said Dr. Jeffrey M. Ellenbogen, chief of the division of sleep medicine at Harvard Medical School [and co-author of the study]. “What is it in the brain that makes it have less response to noise at night, and how can we enhance that natural occurring brain-based process to help people sleep?” he said. [The New York Times]
Researchers at the Harvard Medical School asked twelve healthy volunteers to spend three nights in a sleep lab. The first night the researchers let them sleep soundly, but monitored their brain activity. The following two nights, they used four speakers aimed at the sleepers' heads to play sounds of air and car traffic, ringing telephones, and "hospital-based mechanical sounds," among other things. They found that those people whose thalami produced more high-frequency signals called "sleep spindles" lasted the longest when barraged with noises: the more sleep spindles, apparently, the better the sleep. The study appears today in Current Biology. The correlation between sleep spindles--so called because the brain wave pattern looks like spindles of thread--and deeper sleep doesn't necessarily mean causation, but the team suggests that the mechanism that produces the spindles in the thalamus could be "colliding" with the incoming sounds. This would prevent the sensory information from being passed on to the rest of the cortex, and could allow sleepers to get their shut-eye despite a noisy background. The New York Times reports that older people produce fewer sleep spindles, and notes that people often become lighter sleepers as they age. The researchers wonder if the number of spindles may serve as a good prediction for deep sleep capabilities:
In the meantime, testing a person's spindle activity may help predict an individual's tolerance to noise, Ellenbogen added. This could help with life decisions, he said, such as: "Should I take the job that puts me in the city, where I'm [in] urban chaos?" [National Geographic]
The researchers also question if this line of research will change how leading sleep medications are manufactured, since sedating the brain (as many current sleep aids do) means sedating the thalamus, the sleep spindle-maker.
“Although our computer vernacular uses 'sleep' to refer to a process of temporary shut-down, that’s not the way our brain works,” Ellenbogen wrote in an email to Wired.com. “During sleep, our neurons are busy doing very complicated processing, including, this study shows, generating sleep spindles to protect us from being awoken from noises in the environment.” [Wired]
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