The following is Part 1 of a three-part series of selected talks from the 34th Annual Scientific Meeting of the American Pain Society (APS) held May 13-16, 2015, in Palm Springs, California, US. Also see Part 2 and Part 3.
Sleep and pain are intimately related: an estimated 70-88 percent of people with pain conditions experience sleep disturbances, and about half of people with insomnia have chronic pain (Smith and Haythornthwaite, 2004). Researchers are investigating the factors that underlie these associations and how targeted treatments might improve sleep and ease pain (see PRF related news).
Pain and sleep disturbance were thought to influence one another reciprocally—each leading to the other—but a recent review of studies from the past decade by Patrick Finan, Johns Hopkins University, Baltimore, US, found that sleep disturbance predicts pain better than the other way around (Finan et al., 2013).
Positive emotions seem to confer resilience against chronic pain. “Among patients with chronic pain, those who are able to generate positive emotions tend to adapt better to their pain conditions and have better outcomes, such as lower pain levels, better physical function, and more prosocial behavior,” Finan said. Meanwhile, several studies have shown that sleep loss leads to impaired positive affect, without appreciably changing negative affect, indicating that sleep loss might sap patients of good feelings and render people more vulnerable to pain.
Positive emotions are not simply the opposite of negative emotions, Finan said. “Positive emotions are complex,” he stressed. Finan mentioned three beloved fictional characters from television and movies to illustrate positive emotions: Homer Simpson with his donut feels content, appreciative, and relaxed; Anchorman’s Ron Burgundy embodies a self-assured, confident, fearless man; and Derek Zoolander’s “Blue Steel” look signals he is alert, attentive, and determined.
Finan presented new data from his lab supporting the notion that positive affect provides a link between pain and sleep, and that the association is rooted in the brain’s reward system. Healthy subjects spent a night in a sleep lab with either unrestricted sleep or a forced-awakening (FA) condition in which subjects were awakened every hour throughout the night and then allowed to go back to sleep. As part of the study, Finan first showed that continual sleep disruption—as people with chronic pain might experience—compromised subjects’ self-reported emotional state on a questionnaire. “Positive affect was significantly attenuated following forced awakening,” Finan reported, whereas negative affect did not change significantly.
The researchers also measured subjects’ threshold for pressure pain. Subjects allowed to sleep saw little change in pain sensitivity compared to their responses the day before their night in the lab. But following FA, pain thresholds shifted in subjects to varying degrees, depending on subjects’ ability to hold on to positive emotions. “When they were subjected to an acute stressful situation, those who could maintain positive affect were able to withstand more pain,” Finan said.
Positive emotions are governed by the brain’s dopaminergic reward system, which Finan hypothesizes is the key link between sleep and pain (Finan and Smith, 2013). In ongoing research, Finan is working to determine how sleep disruption changes other behaviors associated with activation of the reward system, such as motivation, reward responsiveness, and impulsivity. For example, Finan’s preliminary data suggest that FA lowers people’s motivation to obtain a reward.
The practical upshot of Finan’s findings is that improved positive affect can protect against pain. To enhance current treatments for pain, Finan concluded, “researchers and clinicians should consider either developing new therapies or augmenting existing therapies such as cognitive behavioral therapy (CBT), acceptance and commitment therapy (ACT), and mindfulness-based stress reduction (MBSR) with a focus on helping people generate and maintain positive emotions.”
Mandeep Chahal, a research assistant working in Sean Mackey’s group at Stanford University, Palo Alto, US, examined relationships between sleep and the negative pattern of emotional and cognitive reactions to real or anticipated pain called catastrophizing, which is thought to worsen chronic pain prognoses (Wertli et al., 2014). Chahal found that pain catastrophizing (PC) was highly correlated with sleep disturbances in people with chronic pain, but that relationship depended on anxiety.
Chahal analyzed data from 637 chronic pain patients at the Stanford Pain Management Center who are part of the Collaborative Health Outcomes Information Registry (CHOIR), a patient health outcomes platform and learning health system (see CHOIR website). Chahal analyzed subjects’ self-reported measures of PC, anxiety, sleep disturbance, and pain intensity over the prior seven days. She used computer-based adaptive questionnaires that are part of the Patient Reported Outcomes Measurement Information System (PROMIS) also developed at Stanford and the NIH (see PRF related news). The higher subjects scored on the catastrophizing scale, the more likely they were to report sleep disturbances. Anxiety and sleep disturbance were also highly correlated with one another, and with further analysis, Chahal found that anxiety levels were the basis of the sleep-catastrophizing association. “Once we accounted for anxiety, the relationship between sleep disturbance and catastrophizing completely fell apart,” Chahal told PRF. That suggests that therapies targeting anxiety might improve sleep—and, in turn, pain.
Image credit: American Pain Society
Stephani Sutherland, PhD, is a neuroscientist, yogi, and freelance writer in Southern California.