Amputees usually perceive vivid awareness of their lost body parts after the amputation (phantom limbs). Phantom limb pain (PLP) is intense pain that is felt in the phantom limb. The mechanism of PLP is still unclear, but the major hypothesis is that it is derived from dysfunction of the brain. There are a few neurorehabilitation techniques using a mirror or virtual reality (VR) that present the visual image of a phantom limb to the patients, and this produce the movement perception of their phantom limb. Here, we developed a multimodal (visual, auditory, and tactile) VR system to obtain the perception of voluntary phantom limb movements. We applied this system to five PLP patients for three tactile feedback conditions as a pilot study. In conclusion, four of the five patients reported pain amelioration, up to 86% decrease in the tactile feedback condition. In addition, our results demonstrated that the best suited condition of feedback-sense modalities depends on the patient. These results suggest that this system can be applied to a rehabilitation platform to offer flexible neurorehabilitation regimens for each patient.

BackgroundPrevious studies have tried to relieve deafferentation pain (DP) by using virtual reality rehabilitation systems. However, the effectiveness of multimodal sensory feedback was not validated. The objective of this study is to relieve DP by neurorehabilitation using a virtual reality system with multimodal sensory feedback and to validate the efficacy of tactile feedback on immediate pain reduction.MethodsWe have developed a virtual reality rehabilitation system with multimodal sensory feedback and applied it to seven patients with DP caused by brachial plexus avulsion or arm amputation. The patients executed a reaching task using the virtual phantom limb manipulated by their real intact limb. The reaching task was conducted under two conditions: one with tactile feedback on the intact hand and one without. The pain intensity was evaluated through a questionnaire.ResultsWe found that the task with the tactile feedback reduced DP more (41.8 ± 19.8 %) than the task without the tactile feedback (28.2 ± 29.5 %), which was supported by a Wilcoxon signed-rank test result (p < 0.05).ConclusionsOverall, our findings indicate that the tactile feedback improves the immediate pain intensity through rehabilitation using our virtual reality system.Electronic supplementary materialThe online version of this article (doi:10.1186/s12984-016-0161-6) contains supplementary material, which is available to authorized users.

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