If you’re struggling to get enough quality sleep each night, you may find yourself more sensitive to pain during the day. That finding has often surfaced in sleep research over the years, but, as with most associations of its type, the “why and how” have been hard to identify. A new study that combined a lab experiment with brain imaging may have nudged the answers a little closer to clarity.
Many of us can attest to the sleep-pain connection from our day-to-day experience. Not uncommonly, a short night’s sleep accompanies a headache, or perhaps painful muscle tension in the neck and shoulders. We all have our versions of the connection in real time, and pain in turn makes sleeping more difficult. The cycle is real.
This study took its lead from that point with a lab experiment that required a couple dozen brave volunteers, all of whom were free from known sleep or pain disorders.
The researchers first took a baseline of the volunteers’ pain thresholds after a full night’s sleep by applying increasingly uncomfortable levels of heat to their legs while examining their brain activity with an fMRI machine. They then repeated the process after depriving the volunteers of sleep, assessing their reactions along the way by having them rate levels of pain on a scale of one to 10.
Across the group, the pain ratings increased with less heat when the volunteers were sleep deprived.
“They were feeling discomfort at lower temperatures, which shows that their own sensitivity to pain had increased after inadequate sleep,” said lead study author Adam Krause, a PhD student at UC Berkley. “The injury is the same, but the difference is how the brain assesses the pain without sufficient sleep.”
The brain imaging phase of the study provides part of the “why”, by showing a significant increase in activity in the somatosensory cortex, a brain area central to the pain response. At the same time the imaging showed deactivation in brain areas thought to be responsible for managing pain, the nucleus accumbens and insular cortex. This combination suggests a “neural malfunction” in how the brain deals with pain.
“The optimistic takeaway here is that sleep is a natural analgesic that can help manage and lower pain,” said senior study author Matthew Walker, a UC Berkeley professor of neuroscience and psychology and author of the book, Why We Sleep.
The researchers conducted another part of the study online using Amazon’s Mechanical Turk site. About 230 participants recorded their nightly hours of sleep and pain levels the following day over the course of a few days. The results suggested that even small changes in sleep accompany noticeable increases in pain.
“The results clearly show that even very subtle changes in nightly sleep—reductions that many of us think little of in terms of consequences—have a clear impact on your next-day pain burden,” Krause added.
The lab part of this study was relatively small and the levels of sleep deprivation were on the extreme side (more than what most of us experience day to day), and the online part was a survey that relied on self-reporting, so we can’t say the results from either part are conclusive. What we can say, however, is that the results line up well with what more and more research suggests: lack of sleep is linked to an intensification of certain experiences in the brain, most notably pain (as found in this case) and anxiety.
The findings also add to our ever-growing list of reasons to improve both the quantity and quality of our sleep – one of the most significant health challenges of our frenetic and distraction-driven times.
The study was published in The Journal of Neuroscience.