External emotional stimulation interferes with the conditioned pain mechanism : A quasi-randomized controlled trial

Sammanfattning

Objectives: Pain processing is affected by cognitive-emotional factors and sensitivity to nociceptive stimuli is altered by the conditioned pain modulation (CPM) mechanism. The aim of the study was to examine how external boring or humorous stimulation with simultaneous pain could affect Pressure Pain Thresholds (PPTs), pain tolerance, pain intensity and pain related negative affect. Participants: Inclusion criteria were pain-free individuals above 18 years with Swedish comprehension. Study Method: This quasi-randomized experimental study included 160 participants in two different emotional conditions (boring; humorous) and control with simultaneous pain induction. PPTs were measured using a manual Somedic algometer, and pain was induced with a cold pressor apparatus (1°C). Pain intensity and pain-related negative affect were rated using the Numerical Rating Scale (NRS). Short videos (150 sec) induced emotional states. PPTs were measured bilaterally in m.trapezius and m.tibialis anterior before and after inductions. Pain tolerance, pain intensity and pain-related negative affect were compared between conditions. Findings: Significantly elevated PPTs were found in the right m.trapezius after external boring stimulation (p<.006), in the left m.tibialis anterior after external humorous stimulation (p<.013), and bilaterally in m.trapezius in the control condition (left p<.003; right p<.001). No significant differences were found in secondary outcomes. Conclusions: The CPM mechanism was stronger without external stimulation, reported by elevated PPTs in two out of four body locations in the control condition compared to only one out of four body locations in the conditions with external emotional stimulation. The results contribute to an increased understanding of pain processing mechanisms.