When I roll out of bed in the morning and stagger to the bathroom, normally stationary walls leap out at me, and an errant slipper becomes a deadly obstacle. Rather than having just awakened from a good night’s sleep, I look like I just came in from a good all-night party.
There’s a word—two, actually—for that morning muzziness: “sleep inertia.” And a new study by researchers at the University of Colorado at Boulder has getting a good night’s sleep does nothing to alleviate it: n fact, when people wake up after eight hours of sound sleep their thinking and memory skills are actually more impaired than those of people who haven’t slept for more than 24 hours—and previous studies have shown that people deprived of sleep for more than 24 hours are as impaired as if they were drunk.
The lead author of the study, which appeared in the January 11 issue of the Journal of the American Medical Association, was Assistant Professor Kenneth Wright of the university’s integrative physiology department. His co-authors were Adam Wertz of the same department and Joseph Ronda and Charles Czeisler of Brigham and Women’s Hospital in Boston (affiliated with Harvard Medical School), where Wright was previously a neuroscientiest.
Nine paid volunteers each slept eight hours a night during the month leading up to the study (and just where does one sign up for such a study?). They had no medical, psychiatric or sleep disorders and took no alcohol, caffeine, nicotine, recreational or medical drugs.
They then spent six days in the hospital’s sleep lab. During their waking hours, they practiced a math test (involving adding randomly generated two-digit numbers). The results were then compared to their results when given the same kind of test immediately upon awakening.
Sleep inertia most impaired the subjects during the first three minutes after awakening. The most severe effects generally dissipated within 10 minutes, but some effects could linger for up to two hours.
Previous research seems to indicate that parts of the brain, in particular the prefrontal cortex, responsible for problem solving, emotion and complex thought, take longer to come on-line (to put it in computer terms) than other areas.
Sleep inertia can be hazardous if you have to take quick action upon awakening. For most of us, the only time that might arise is in the event of a fire alarm. For medical residents, though, who work long hours and get by with catnaps, it’s a constant problem, since they may be called upon to make life-or-death decisions moments after they wake up. Emergency workers sometimes have to go straight from sleep to driving a fire truck or ambulance. And truck drivers who wake from naps in their sleeping cabs and immediately begin driving again could also be putting themselves and others at risk.
That’s not to say that naps (scientifically defined as any sleep that is less than half as long as an individual’s average nocturnal sleep period) aren’t worthwhile. Studies have shown that “prophylactic” naps, taken before a prolonged period of sleep loss, can improve performance for hours afterward.
Naps taken after a period of sleep loss are called “replacement” naps, while those taken in the middle of a period of sleep loss are called “maintenance” naps. I’ve always hated these kinds of naps because I always feel worse after waking up than I did before I lay down–sleep inertia, again.
Sleep inertia after napping seems to correlate with the time of day the nap is taken and the length of time since the last major sleep period. It also seems to be related to the stage of sleep the napper reaches before being awakened—the more deeply asleep you are when you wake up, the more sleep inertia you suffer. And that post-nap grogginess can affect performance for up to half an hour, according to some studies, which sounds about right from my experience.
There’s still much more to be learned about sleep inertia, and sleeping in general—amazing, really, considering we all sleep every day (and, in fact, must sleep to survive—sleep deprivation can kill you faster than food deprivation).
Every report I’ve ever read about a sleep study, including this most recent one, includes a paragraph that begins something like, “Further studies are needed…”
I wholeheartedly agree. In fact, I believe I’ll study the subject of sleep further tonight…and tomorrow night…and the night after that…
