Tuesday, October 27, 2015

The Black-White Sleep Gap

In 2005, re­search­ers at the Uni­versity of Cali­for­nia, San Diego, began an ex­per­i­ment that would last five years. One by one, they brought 164 study par­ti­cipants to a sleep lab at the U.C. San Diego Med­ic­al Cen­ter, a room with a sweep­ing view of the city and the sur­round­ing val­ley. There, par­ti­cipants un­der­went poly­so­m­no­graphy, the most com­pre­hens­ive sleep test known to sci­ence. A poly­so­m­no­graphy ma­chine is an oc­topus of a med­ic­al device: It has scalp sensors to re­cord brain-wave pat­terns; eye track­ers to as­sess rap­id eye move­ments; breath­ing sensors that are placed on the nose, mouth, and around the chest; a blood-oxy­gen sensor for the fin­gers; and sensors on the legs to track move­ment. The ma­chine pro­duces a chart—re­sem­bling a cross between a mu­sic­al com­pos­i­tion and a seis­mo­gram—that traces the brain and body minute by minute through the night.

"I think it's quite beau­ti­ful per­son­ally," says Li­anne Tom­fohr, who was the lead au­thor on the study and is now a psy­cho­logy pro­fess­or at the Uni­versity of Cal­gary. "We can put [sensors] on their head and, through the elec­tri­city in their brains, see how deeply they are sleep­ing. It's a little bit mys­tic­al to me that it is even pos­sible."

The San Diego re­search­ers planned to use the poly­so­m­no­graphy ma­chine to doc­u­ment slow-wave sleep—the phase of sleep "when it's really hard to wake you up," as Tom­fohr de­scribes it. Slow-wave sleep is thought to be the most res­tor­at­ive peri­od of sleep, and it's im­port­ant to good health: Ex­per­i­ments where people are denied slow-wave sleep on pur­pose have shown that bod­ies quickly change for the worse. (One pa­per, pub­lished in the Pro­ceed­ings of the Na­tion­al Academy of Sci­ences in 2007, found that study par­ti­cipants who were denied slow-wave sleep for three nights—re­search­ers would sound an alarm in their ears when they entered this sleep phase—be­came less sens­it­ive to in­sulin, a pre­curs­or to dia­betes.)

But it wasn't just slow-wave sleep in gen­er­al that in­ter­ested the re­search­ers; they spe­cific­ally hoped to com­pare how blacks and whites ex­per­i­enced slow-wave sleep. And what they found was dis­turb­ing. Gen­er­ally, people are thought to spend 20 per­cent of their night in slow-wave sleep, and the study's white par­ti­cipants hit this mark. Black par­ti­cipants, however, spent only about 15 per­cent of the night in slow-wave sleep.

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