Modulation of pain by affective touch: effects of childhood trauma, depression, chronic pain, and spinal segment.

Chronic pain is highly prevalent, and non-pharmacological tools are a crucial part of a multimodal approach to reducing burden of pain. Among these touch-based interventions such as massage have long been popular, yet their underlying pain-relieving mechanisms are poorly understood. Touch-based therapies often involve gentle stroking associated with the C-tactile afferent pathway and deep pressure. Although chronic pain patients often find touch less pleasant than individuals without pain, the effects of chronic pain on touch-pain modulation have not been directly studied. In the current study we systematically investigated two affective forms of touch - gentle brushing and deep pressure (compression) - on heat pain perception, testing their effects both within-segment and between-segment to explore their neural mechanism. We compared touch-pain modulation effects in pain-free controls and patients with fibromyalgia (FM), a condition characterized by sensory hypersensitivity and affective alterations, hypothesizing that touch-pain modulation would be reduced in FM. We further examined the role of trauma and depression, which are highly prevalent in FM. Significant touch-pain modulation occurred only for between-segment brushing. No significant differences in touch-pain modulation were observed between FM patients and controls. Notably, trauma history and depression emerged as the strongest predictors of touch-pain modulation. These findings suggest that touch-pain modulation involves supraspinal mechanisms that are preserved in FM and are strongly shaped by trauma history and psychological factors. Our results provide novel insight into biopsychosocial determinants of touch-related pain relief and its relevance to FM. KEY POINTS: Touch-based interventions such as massage are common non-pharmacological approaches for chronic pain, but their mechanisms are poorly understood. Chronic pain patients often exhibit reduced touch pleasantness and endogenous pain modulation, but effects of chronic pain on touch-pain modulation have not been directly studied. We tested the effects of gentle brushing and deep pressure (compression) on heat pain perception, testing both within-segment (same dermatome) and between-segment (between dermatome) conditions in no-pain controls and patients with fibromyalgia (FM). Brushing significantly reduced heat pain in the between-segment condition and did not differ by pain status; trauma history and depression emerged as the strongest predictors of touch-pain modulation. These findings suggest that touch-pain modulation involves supraspinal mechanisms that are preserved in FM and strongly shaped by trauma history and psychological factors.