Getting a Handle on Why We Sleep

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Sleep. It’s something everyone likes to do and can’t seem to do without.

Yet many Americans do with a lot less than they’d like. Suffering from chronic insomnia, they know all too well the deadening fatigue that follows interrupted sleep. But while the mental misery of sleeplessness is well documented, some eye-opening new reports warn serious health woes may await those who don’t get enough shut-eye.

Sleep researchers at UCLA have found, for example, that losing even a single night’s sleep causes the body’s immune system to turn on healthy tissues. That may implicate sleep deficits in cardiovascular disease, some cancers, obesity, arthritis, diabetes and various autoimmune disorders.

Heavy snoring was found to be an independent risk factor for carotid atherosclerosis, raising the risk for stroke, according to research done at the University of Sydney in Australia, and a study by Dutch scientists showed that insomnia compromised cognitive processes related to verbal fluency, actually damping down the activity of the brain’s prefrontal cortex.

Researchers used to regard lost sleep as more of an inconvenience than a health risk, says Dr. Chiara Cirelli, a sleep researcher in the department of psychiatry at the University of Wisconsin, Madison. “Now we know that sleep restriction for even a week has very profound cognitive effects.”

It’s enough to keep one up at night. More than a third of adults report having had some insomnia symptoms within a given year, according to the American Insomnia Association, and 10 to 15 percent of adults suffer from chronic insomnia.

The good news is that nonpharmacological strategies can be effective in battling insomnia. These include cognitive-behavioral therapy, which cuts through the spiraling anxiety that perpetuates sleeplessness, and maintaining good bedtime routines.

Scientists still don’t know exactly why animals sleep, said Cirelli, whose recent study “Is Sleep Essential?” was published online by PLoS Biology. She and colleague Giulio Tononi considered the “null hypothesis” — that sleep is not essential. If that assumption, posed earlier this year by UCLA scientist Jerome Siegel, is correct, one would expect to find animals that don’t sleep and animals that don’t need recovery sleep when sleep-deprived. There also should be no serious consequences to going without sleep.

In “Do All Animals Sleep?” published in Trends in Neuroscience, Siegel cited some creatures that seem to do without sleep, including dolphins, which constantly surface to breathe. But dolphins exhibit “unihemispheric sleep,” in which one side of the brain remains active while the other rests.

“The existence of unihemispheric sleep is some of the best evidence that sleep is important,” Cirelli argued.

Cirelli and Tononi also discounted reports that some animals don’t seem to need recovery sleep, concluding, “Sleep is present and strictly regulated in all animal species that have been carefully studied so far.” Meanwhile, studies have shown that rats and flies die when deprived of sleep. Other creatures — including people — experience brief episodes of microsleep during waking hours as the brain tries to re-regulate itself.

Sleep-deprived people often don’t know just how badly they’re affected even though they are frequently drifting into microsleep, Cirelli said. “They get worse and worse, although subjectively they think they get better,” she said. “One second you are perfectly fine, and the next second you are bad. You keep oscillating up and down, up and down.”

But if sleep is indeed essential, what purpose does it serve? Cirelli and Tononi speculate that it has to do with how learning affects the brain’s synapses — the junctures where neurons meet and exchange neurotransmitters.

“The function of sleep is a very basic cellular function, which is to maintain synaptic homeostasis,” Cirelli said. As we go through our day, absorbing new information, the synapses become stronger, requiring ever-greater energy consumption. But during sleep, neurotransmitter levels drop as the neurons grow quiet and return to their original state.

Until recently, sleep research focused on behavior and the fluctuations of brain waves as measured by electroencephalograms (EEG). But now, thanks to functional magnetic resonance imaging (fMRI), scientists can get a real-time look at how the brain is affected by sleep deprivation.

In Amsterdam, Ellemarije Altena, a doctoral student at the Netherlands Institute for Neuroscience, recruited 21 older Dutch people suffering from chronic insomnia, matching them with 12 controls. The patients, who ranged from age 50 to age 75, had been suffering from insomnia for at least two and a half years.

According to a study titled “Prefrontal Hypoactivation and Recovery in Insomnia,” published recently in the journal Sleep, Altena and her collaborators had subjects perform verbal fluency tests while undergoing fMRI scans. And while the insomniacs did just as well on the tests (in which they might, for example, be asked to think of as many words as possible beginning with a certain letter), the scans showed they had less activity in the left medial prefrontal cortex and the left inferior frontal gyrus, two fluency-specific brain regions.

Altena said those regions are involved in verbal “inventiveness,” which often declines in patients with Parkinson’s or Alzheimer’s. The insomnia sufferers’ ability to handle the test may mean that the test wasn’t that difficult. Altena also speculates that there might be “some compensatory activation” of another part of the brain, although that might differ from one patient to another.

The study was significant because most previous research on sleep deprivation has occurred in laboratory conditions, Altena said. Thanks to fMRI and other new technology, “There’s now more focus on natural insomnia.”

The good news was that the deficits were at least partially reversible with sleep therapy. Patients, who kept a sleep diary, initially had their time in bed limited. As their sleep efficiency increased, they could stay in bed for longer periods. “The motivation for them to be treated for their insomnia was very, very high,” Altena explained.

Patients were provided with bright lights during the morning and evening to help reset their inner clock. They were also advised to take warm baths a couple of hours before retiring to dissipate heat and normalize their core temperature.

Sleep therapy improved the insomnia sufferers’ sleep efficiency by 14.5 percent. Moreover, their brain scans showed the affected prefrontal regions were partly restored. “It’s very important to investigate these tasks in other age groups and see if these results hold for the other age groups,” Altena said.

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