Modulating pain with augmented reality

Background/aims Being able to modulate pain through visual input raises the possibility that visually distorting body size also will reduce pain. The aim of the present study was to investigate whether experimental cold/heat pain could be modulated through a visual illusion of an increased/decreased hand size and whether pain perception correlated with the perceived sense of control of movement. Methods 20 healthy right-handed volunteers were recruited. Hand sizes were modulated through an AR setting designed to act as a mirror. Four conditions were included: (1) No AR setting; (2) left/right hands were the same size; (3) left hand enlarged; (4) left hand decreased. Pain thresholds (PT) for both hands were alternately assessed using two thermodes, placed on each palmar side of the hands. After each condition subjects rated the following statement: "I could control the movements of my left/right hand". Results Heat pain: no main effect for conditions or hands (left/right). Cold pain: Significant main effects for conditions, but not for hands - condition (2) is significantly more painful than all conditions. Control of movements when the left hand is stimulated: the more control subjects have of right hand in condition (4), the higher the cold PT for the left hand in conditions (1) and (2). Control of movements when the right hand is stimulated: the more control subjects have of the right hand in condition (4), the higher the heat PT in the right hand for condition (2). Conclusions Visual illusions can modulate pain, however the modulating factors do not only depend on the size of the limbs that are been viewed but also on how much control subjects feel they have of the movements in their hands-specifically the relationship to the right hand condition (4) seems to have an analgesic effect for cold pain and heat pain.