The evaluation and brain representation of pleasant touch in chronic and subacute back pain

Abstract

If touch is perceived as pleasant, it can counteract the experience of pain. However, its pain-inhibitory function might be disturbed in chronic pain and this could contribute to pain-related interference. We investigated the perception of pleasant touch and its brain correlates in chronic back pain patients (CBP) compared to subacute back pain patients (SABP) and healthy controls (HC) using soft brush strokes. CBP showed less positive evaluations of touch. We found the highest activation in somatosensory and insular cortices in CBP, ventral striatum (VS) in SABP, and the orbitofrontal cortex in HC. Brain responses were significantly positively correlated with pleasantness ratings in HC and SABP, but not CBP. Further, the insula responses in CBP were positively correlated with pain-related interference and the VS activation in SABP correlated negatively with affective distress. Brain and behavioral changes in the processing of touch and its pleasantness may be a marker of pain chronicity and raise questions about the therapeutic value of pleasant touch in pain prevention and treatment. Keywords: Pleasant touch, Brain, Chronic pain, Subacute pain, Chronicity