Introduction
There is evidence that viewing touch or pain can modulate the experience of tactile stimulation. The aim of this study was to investigate whether the observation of needle pricks to another person’s hand facilitates the detection of tactile stimuli applied to the hand. We hypothesized this would be different for a group of chronic pain patients compared to controls.

Method
Participants with fibromyalgia (n=39) and controls (n=38) were presented a series of videos showing hands being pricked (e.g. by needles) or control videos (e.g. a sponge being pricked), whilst receiving subtle tactile stimuli themselves in the same spatial location (congruent trials) or on the opposite hand (incongruent trials) as the visual stimuli. Participants were asked to detect the presence and location of the tactile stimulus. Signal detection theory was used to compare whether sensitivity was different for congruent and incongruent trials, and between the groups of participants.

Results
Perceptual sensitivity (d’) was significantly higher when videos contained a painful situation, compared to the control videos, and was higher when the videos were presented on the same side of the body as the tactile stimulus (congruency effect). The congruency effect was larger when a painful situation was shown compared to control videos. No difference in sensitivity was found between fibromyalgia patients and controls.

Discussion
This study suggests that the detection of somatic sensations can be facilitated by observing painful visual stimuli. The visual-somatosensory modulation was independent upon the presence of chronic pain.

vicarious sensations; somatosensory modulation; observation of pain