Social distress and pain modulation: findings from healthy ans chronic pain patients

Pain is a complex experience that integrates sensory, emotional and cognitive dimensions. Understanding how these different dimensions integrate this experience and how each of these dimensions can modulate pain is thus a challenging task. Growing body of evidence showed in the last decades that the central nervous system can increase and decrease the noxious information via the descending pain modulatory system, a conjunction of pro-nociceptive and anti-nociceptive projections tracks that modulate pain. Deficiencies in this system have been proposed has a key element of some chronic pain conditions, mostly in those particularly known to involve central sensitization mechanisms, as Fibromyalgia syndrome. Among several emotional dimensions that can modulate pain, it has been proposed that social distress threatens well being in a similar mode as pain does, and may share neurocognitive resources and mechanisms with physical pain. In this view it would be expected that social distress would significantly modulate pain experience, but this prediction has not been well established in healthy subjects. Furthermore, this was not, to the best of our knowledge, tested in chronic pain, which is a huge public health problem that, according to the International Association for the Study of Pain, is believed to affect more than 20% of the population worldwide. Based on these theoretical grounds, two studies were developed with the aim of investigating how social distress manipulations modulate pain experience in healthy and chronic pain patients. In the first study, we aimed to understand the relationship between social distress and pain intensity and unpleasantness in healthy individuals. Sixty participants were enrolled to one condition of a well validated paradigm that induce social distress, the Cyberball game. Electrical stimulation protocol was induced before and after playing the game. It was found that participants that had a lower electrical unpleasantness threshold were also more distressed by the Cyberball game (p=0.012) and that the manipulation itself affected pain intensity ratings (p=0.001). The relationship between social distress and physical pain was not related to attachment styles or neuroticism. Overall, this study. provided evidence that sensitivity to social distress is related to sensitivity to physical pain and that social distress modulates pain in healthy individuals. In the second study, 90 participants were recruited to a study aimed to further investigate how social distress could modulate the pain experience in response to experimental pain models in healthy and two chronic pain conditions: Fibromyalgia, a condition that although recently recognized to have peripheral abnormalities is classically related to central sensitization mechanisms, and Rheumatoid Arthritis, a condition with a well described peripheral inflammation mechanism but less information regarding central sensitization mechanisms. Each participant played the Inclusion and Exclusion condition of Cyberball while pain was induced before and during each condition. In line with the first study, healthy controls (pain=-13.71±}45.28; unplesentness,=- 20.78±}28.7) and rheumatoid arthritis patients (pain=-7.50}34.54; unplesentness=- 5.60±}38.04) demonstrated a reduction in pain intensity ratings in response to the electrical induced pain in the Inclusion condition, suggesting the recruitment of the antinociceptive projections of the descending pain modulatory system, while in fibromyalgia patients, pain (7.50±}26.04, p=0.019) and unplesentness (2.86±}31.98, p=0.021) were significantly increased during the same condition. This suggests an impairment of the descending pain modulatory system in fibromyalgia. These results are discussed in line with evidence of impaired anti-nociceptive projections and changes related to chronic pain that have been found to occur in brain areas as insula, anterior cingulate and midbrain projections, fundamental areas for social connection. Further studies are needed to collect additional information on the nature of the descending pain modulatory system deficits in fibromyalgia. We hope that the increased knowledge regarding the relationships between social events and pain modulation will provide relevant insights for new social and emotional therapeutic approaches in chronic pain conditions, and ultimately contribute to reducing suffering.