Why the less you sleep, the more it hurts

Single Night Of Sleep Deprivation Reduces A Person’s Pain Threshold By Over 15%: Study

 Public Roads AdministratVeteran insomniacs know in their bones what science has to say about sleep deprivation and pain: that the two travel together, one fuelling the other.

For instance, people who develop chronic pain often lose the ability to sleep well, and quickly point to a bad back, sciatica or arthritis as the reason. The loss of sleep, in turn, can make a bad back feel worse, and the next night’s slumber even more difficult.

Why sleep deprivation amplifies pain is not fully worked out, but it has to do with how the body responds to an injury. First, it hurts, as nerves send a blast up the spinal cord and into the brain. There, a network of neural regions flares in reaction to the injury and works to manage, or blunt, the sensation.

In a sleep-lab experiment, the researchers found that a single night of sleep deprivation reduced a person’s pain threshold by over 15% and left aclear signature in the brain’s pain-management centers.

In a separate experiment, the team determined that small deviations in the average amount of sleep from one day to another predicted the level of overall pain felt the next day.

“What’s exciting about these findings is that they will stimulate, and justify, doing more research to figure this system out,” said Michael J Twery, director of the sleep disorders branch of the National Heart, Lung and Blood Institute, who was not involved in the new study. “Once we understand how sleep deprivation changes how these pathways function, we should be able to manage pain more effectively.”

The study team, led by Adam J Krause and Matthew P Walker of the University of California, Berkeley, had 25 adults come into the lab on two occasions to measure their pain threshold for heat. Two measurements were taken from each subject, one in the morning after a full night’s sleep, and one in the morning after staying up all night. The two visits occurred at least a week apart, and included measurements in a brain-imaging machine.

The subjects judged the pain sensation of having a small, heated pad pressed against their skin, near the ankle. By gradually adjusting the temperature up and down, the researchers identified the level of pain that each person graded as 10, or “unbearable,” on a scale of 1 to 10.

Pulling an all-nighter increased everyone’s sensitivity to heat the next morning, by 15 to 30% on the pain scale. But the brain imaging added a new dimension: For each participant, activity spiked in pain perception regions, and plunged in regions thought to help manage or reduce pain. The biggest peaks were in the somatosensory cortex, a strip of neural tissue that runs across the top of the brain like a headphone band.

In a separate trial, the research team recruited 60 adults online who reported having daily pain. For each individual, poor sleep quality predicted higher ratings on the daily pain scale. The duration of sleep was not the critical factor, the study found; what mattered were alterations to deep sleep, the mostly dreamless period of rich slumber.