Scientists have found that inadequate sleep ramps up activity in pain-sensing regions of the brain. At the same time, brain areas responsible for how we perceive painful stimuli decreased in activity.
The fact that sleep and pain have an intertwined relationship, feeding off of one another, is well established. Previously, a study published in the journal PAIN performed a pain sensitivity test by having participants submerge their hands in cold water. The findings showed that 42% of participants with insomnia were more likely to take their hands out early compared to only 31% of the insomnia-free participants, and that the pain sensitivity increased with the frequency and severity of insomnia. Another study published in 2006 found that just one night of poor sleep was enough to increase a person's sensitivity to pain.
Sleep deprivation may make a person more sensitive to pain because it enhances the production of pro-inflammatory proteins called cytokines. These are the molecules that stimulate the movement of inflammatory cells such that, in the event of a foreign invader, the body may respond by calling white blood cells to the site of infection. Usually, inflammation is helpful because it leads to healing. However, when the inflammatory reaction is constantly stimulated, the white blood cells can end up affecting healthy organs, tissues, and cells. If a person is already suffering from arthritis or fibromyalgia, sleep deprivation can aggravate their symptoms and may even disrupt how that person responds to medication.
In two new studies led by Matthew Walker, a Professor of Neuroscience and Psychology at the University of California, Berkeley, and founder of the Center for Human Sleep Science, researchers investigated how the brain processes pain after sleep deprivation. In the first part of the study, participants were recruited from Amazon's Mechanical Turk and had to report how their pain sensitivity fluctuated after sleeping poorly the night before. In the second part, participants had their brain activity scanned while they were kept awake through the night in the lab.
The results suggest that sleep-deprived individuals who performed a pain sensitivity task showed increased activity in the primary somatosensory cortex (which is responsible for detecting pain) and reduced activity in regions of the striatum and insular cortex (which have many cognitive roles, among them perception).
About 50 to 70 million Americans suffer from some degree of sleep deprivation, from insomnia to obstructive sleep apnea, to chronic sleep deprivation. The results are important in this context -- perhaps better sleep could be an effective way to manage pain, especially in a hospital setting.
The findings appeared in the Journal of Neuroscience.