By Pat Anson, PNN Editor
It’s no secret that chronic pain makes sleeping difficult. And lack of sleep often makes pain worse. But how exactly does poor sleep cause more pain?
For the first time, scientists at the University of California, Berkeley, have identified neural glitches in the sleep-deprived brain that can intensify and prolong pain. Their findings, published in the Journal of Neuroscience, help explain the self-perpetuating cycles that contribute to pain and sleep loss.
“Anyone who has had persistent back pain knows that they don’t sleep well when they are in pain. They also know that when they don’t sleep well, it hurts more the next day,” said senior author Matthew Walker, PhD, a UC Berkeley professor of neuroscience and psychology.
"If poor sleep intensifies our sensitivity to pain, as this study demonstrates, then sleep must be placed much closer to the center of patient care, especially in hospital wards.”
In a small study involving 25 healthy young adults, Walker and his colleagues found that nerves that process pain signals and activate the body’s pain relief hormones are disrupted by insufficient sleep. Study participants were given MRI brain scans twice – once after a good night’s sleep and once after a night of no sleep – and then subjected to a thermal pain test in the laboratory
“We found some surprising changes. The sleep-deprived brain seems to let more pain in,” Walker said.
Brain imaging showed increased activity in the brain's somatosensory cortex, but there was less activity in the nucleus accumbens, a region of the brain's reward circuitry that increases dopamine levels. Dopamine is a neurotransmitter that’s been called the “feel-good hormone” because it is associated with feelings of euphoria and happiness.
Another key brain region found to slow down in the sleep-deprived brain was the insula, which evaluates pain signals and prepares the body to respond.
"This is a critical neural system that assesses and categorizes the pain signals and allows the body's own natural painkillers to come to the rescue," said Adam Krause, lead author of the study and a doctoral student in Walker's Center for Human Sleep Science lab at UC Berkeley.
To further test the sleep-pain connection, researchers surveyed more than 230 adults of all ages nationwide. Respondents were asked to report their nightly hours of sleep, as well as their day-to-day pain levels. The results showed that even minor shifts in sleep patterns were correlated with changes in pain sensitivity.
"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 said.
"The optimistic takeaway here is that sleep is a natural analgesic that can help manage and lower pain," said Walker. "Yet ironically, one environment where people are in the most pain is the worst place for sleep -- the noisy hospital ward."
Walker's goal is to work with hospitals to create more sleep-friendly patient facilities.
"Our findings suggest that patient care would be markedly improved, and hospital beds cleared sooner, if uninterrupted sleep were embraced as an integral component of healthcare management," he said.
Several previous studies have found that getting a good night’s sleep helps reduce sensitivity to pain. Researchers in Norway measured pain sensitivity in more than 10,000 adults and found a strong link between pain and insomnia.
Another study in Norway found that women who have trouble sleeping are at greater risk of developing fibromyalgia – although it’s not clear if there’s a cause and effect relationship between the two symptoms.