Exploratory findings with virtual reality for phantom limb pain; from stump motion to agency and analgesia

Purpose. Phantom limb pain is chronic and intractable. Recently, virtual reality (VR) and motion capture technology has replicated the mirror box device of Ramachandran (Ramachandran et al. Nature 1995, 377, 489-490; Ramachandran and Rogers-Ramachandran Proc R Soc Biol Sci 1996, 263, 377-386) and led to reductions in this pain. We present results from a novel variation on this method which captures motion data directly from a patient's stump (rather than using the opposite remaining limb) and then transforms it into goal directed, virtual action enacted by an avatar in a VR environment. Method. A sample of subjects with 'arm' (n = 7) and 'leg' (n = 7) amputations underwent trials of a virtual reality (VR) system, controlled by motion captured from their stump which was translated into movements of a virtual limb within the VR environment. Measures of pain in the phantom limb were elicited from patients before and during this exercise as they attempted to gain agency for the movement they saw, and feel embodied within the limb. After this each subject was interviewed about their experiences. Results. Five subjects in each group felt the virtual limb to be moved by them and felt sensations of movement within it. With this they also reported reductions in their phantom limb pain greater than expected from distraction alone. No carry over effect was seen. Conclusions. This technique, which has shown similar success rates to trials of a virtual mirror box, is relatively cheap and portable, and will allow further trials in a home environment.