The relationship between sleep loss and chronic pain has been chronicled by scientists and researchers for many years. Around 60 percent of patients suffering chronic pain also report consistent sleep disruptions. This connection is perhaps unsurprising, after all, if you are in pain it is undoubtedly difficult to sleep. But what if sleep loss was actively increasing a person's sensitivity to pain?
A team of American researchers homed in on that very question with a new study using functional Magnetic Resonance Imaging (fMRI) to identify the differences in brain activity while processing pain, between sleep deprived subjects and well rested subjects.
The study first examined the pain thresholds of 25 healthy, well-rested adult participants. While examining brain activity in a fMRI scanner, a pad pressed against the subject's leg gradually increased in heat until it was reported to reach an unbearable temperature. On average, the peak temperature threshold for well-rested subjects was around 111 degrees Fahrenheit (44 degrees Celsius) but repeating the test after a sleep-deprived night dropped the average peak threshold to about 107 degrees Fahrenheit.
These results were not especially unexpected, with a solid volume of prior research affirming that sleep disruption can increase a person's pain sensitivity. However, the fMRI data revealed some unexpected results. When subjected to pain, a sleep-deprived subject displayed heightened activity in the somatosensory cortex. This was expected, as it is the brain region known for sensing pain signals across the body. The surprising discovery was that a decrease in activity was identified in the nucleus accumbens and insular cortex. These regions of the brain are known to regulate the body's dopamine levels in response to pain.
"Sleep loss not only amplifies the pain-sensing regions in the brain, but blocks the natural analgesia centers, too," explains Matthew Walker, senior author on the new study.
The study also examined the relationship between subtle changes in sleep on a person's pain sensitivity. Using a self-reported survey of over 230 adults the researchers discovered that very small shifts in a person's sleep/wake pattern seemed to clearly correlate with pain sensitivity changes. This suggests that the link between sleep and pain is bi-directional, and subject to modest day-to-day changes.
"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," explains Adam Krause, lead author on the study.
The interesting implication from this study is that a greater focus should be made on optimizing sleep as a way of managing and reducing pain. If a good night's sleep effectively increases the brain's analgesic response to pain, then environments such as hospitals, notorious for being noisy and disruptive to sleep, need to find better ways to offer patients more uninterrupted stretches of sleep.
"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," says Walker.
The new study was published in the journal JNeurosci.
Source: UC Berkeley