A number of comorbidities, including depression and anxiety, are associated with chronic pain. This begs the question: are people with depression or anxiety disorders more likely to develop chronic pain after injury, or is it chronic pain itself that causes these modalities?
This is the question that Catherine Bushnell, PhD, scientific director in the division of intramural research, and senior investigator in the Pain and Integrative Neuroscience Branch at the National Center for Complementary and Integrative Health, addressed during her plenary lecture at the American Academy of Pain Management’s annual meeting, which took place last month in San Antonio, Texas.1
In a study that Dr Bushnell and colleagues published in Neuroscience Letters, rats subjected to nerve injury show anxiety-like behaviors.2 According to the authors, these results indicate that cognitive dysfunction observed in chronic pain patients arises-at least in part-from the chronic pain state.
The Role of Empathy
The feeling of empathy for a loved one who is experiencing pain activates limbic areas in the observer and enhances observer’s pain.3 These results, which were reported in Science, seem to indicate that “only the part of the pain network associated with its affective qualities, but not its sensory qualities, mediates empathy,” and not the entire “pain matrix,” according to researchers.
Similar results, obtained by Dr Bushnell’s group, show that study participants who display higher levels of empathy feel more pain than their less empathetic counterparts.4 The findings of another study performed by the same group show that the pain experience is affected by mood through the modulation of “pain unpleasantness.”5
This led the investigators to conclude that “this finding could potentially help health professionals to treat pain symptoms in patients with altered mood, suggesting methods of pain management aimed at easing the affective, along with the sensory, components of pain.”
Exercise to Relieve Pain?
It is generally thought that exercise helps alleviate chronic pain. However, evidence supporting this notion is scarce. A systematic review and meta-analysis investigating the benefits of walking in patients (from 26 studies, n=2384 participants) with chronic musculoskeletal pain, indicated small-to-moderate improvements in pain, as well as function, in the short- and medium-terms.6
In addition to this lack of evidence for the benefits of exercise for chronic pain, getting patients who are in pain to exercise can be challenging. Indeed, patients with chronic pain may reduce their activity, thus increasing their disability, producing a vicious circle, as disability may itself promote further pain.
Using an animal model of rheumatoid arthritis (RA), researchers found exercise to be beneficial to the health of rats.7 Voluntary exercise also produced analgesic effects, as indicated by an increase in weight-bearing capacity and latency in response to a heat stimulus in exercise vs sedentary animals.7
In addition, while injury was shown to increase the levels of stress, voluntary running brought those levels down to control levels in those animals.
Reducing the Impact of Chronic Pain on the Brain Through Positive Lifestyle
A number of studies have indicated a reduction in cortical thickness and reduced availability of µ-opioid receptors in the brain of chronic pain patients.9,10
Dr Bushnell suggests practicing yoga, as long-term yogis have higher pain tolerance and increased gray matter—including in pain-modulating brain areas—compared with that of non-practitioners.11
- Catherine Bushnell. Non-pharmacological modulation of chronic pain. Presented at: AAPM 2016. San Antonio, TX; September 21-25, 2016.
- Low LA, Millecamps M, Seminowicz DA, et al. Nerve injury causes long-term attentional deficits in rats. Neurosci Lett. 2012;529(2):103-107.
- Singer T, Seymour B, O’doherty J, Kaube H, Dolan RJ, Frith CD. Empathy for pain involves the affective but not sensory components of pain. Science. 2004;303(5661):1157-1162.
- Loggia ML, Mogil JS, Bushnell MC. Empathy hurts: compassion for another increases both sensory and affective components of pain perception. Pain. 2008;136(1-2):168-176.
- Loggia ML, Mogil JS, Bushnell MC. Experimentally induced mood changes preferentially affect pain unpleasantness. J Pain. 2008;9(9):784-791.
- O’connor SR, Tully MA, Ryan B, et al. Walking exercise for chronic musculoskeletal pain: systematic review and meta-analysis. Arch Phys Med Rehabil. 2015;96(4):724-734.e3.
- Pitcher MH, Rauf IZ, Bushnell MC. Voluntary exercise and weight control attenuate nociceptive hypersensitivity in a rat model of rheumatoid arthritis. Presented at: the Society for Neuroscience 2014. Washington, DC; November 15-19, 2014.
- Tarum F, Pitcher M, Imran R, Bushnell M. Amount of exercise is not related to exercise-induced analgesia in a rat model of persistent inflammatory pain. Presented at: the Society for Neuroscience 2015. Chicago, IL; October 17-21, 2015.
- Seminowicz DA, Laferriere AL, Millecamps M, Yu JS, Coderre TJ, Bushnell MC. MRI structural brain changes associated with sensory and emotional function in a rat model of long-term neuropathic pain. Neuroimage. 2009;47(3):1007-1014.
- Harris RE, Clauw DJ, Scott DJ, Mclean SA, Gracely RH, Zubieta JK. Decreased central mu-opioid receptor availability in fibromyalgia. J Neurosci. 2007;27(37):10000-10006.
- Villemure C, Ceko M, Cotton VA, Bushnell MC. Insular cortex mediates increased pain tolerance in yoga practitioners. Cereb Cortex. 2014;24(10):2732-2740.