Virtual pleasant touch and pain modulation in patients with Fibromyalgia

Fibromyalgia (FM) is a syndrome characterized by widespread musculoskeletal pain. To investigate affective touch and pain perception in FM we implemented two experiments using Virtual Reality and physiological recordings. In the first, participants (FM, healthy controls) observed 12 pleasant(caress), 12 neutral(ball), and 12 painful(syringe) stimuli administered on a virtual hand presented in first-person perspective. Perceived pleasantness and intensity were collected (0-100 Visual Analogue Scales, VAS) after each stimulus, and a brief embodiment questionnaire was presented at the end of the paradigm. The second experiment consisted in two blocks showing a series of 12 repeated pleasant(caress) and neutral(ball) virtual stimuli. Perceived pleasantness, intensity, and ownership over the virtual hand were collected after each stimulus (VAS). Pain intensity ratings were collected before and after each block. Skin Conductance Response and Heart Rate were recorded during each trial in both experiments. In line with previous literature, painful stimuli were judged more unpleasant as compared to the other stimuli, while pleasant stimuli were rated as more intense. Pleasantness, intensity, and embodiment ratings did not differ between the two groups showing that FM are not hypersensitive to virtual stimulations. An interesting trend towards pain reduction emerged in FM after the pleasant, repeated virtual stimulation.