TABLE 1.

Summary and characteristics of immersive VR studies using embodiment for pain relief.

Authors	Year	Sample	Intervention	Primary outcomes
Martini, M., Pérez Marcos, D., and Sanchez-Vives, M. V.	2013	30 healthy participants	The color of the embodied virtual arm was modified (blue, red, or green). Increasing ramps of heat stimulation applied on the participants’ arm were delivered concomitantly with the gradual intensification of different colors on the embodied avatar’s arm.	Reddened arm significantly decreased the pain threshold compared with normal and bluish skin.
Llobera, J., González-Franco, M., Perez-Marcos, D., Valls-Solé, J., Slater, M., and Sanchez-Vives, M. V.	2013	One patient with a fixed posture dystonia of the upper limb. 5 healthy controls.	The virtual hand would open either automatically or through a cognitive task assessed through a BCI that required to focus attention on the virtual hand.	The results reveal that body ownership induced changes on electromyography and BCI performance in the patient that were different from those in five healthy controls.
Martini, M., Perez-Marcos, D., and Sanchez-Vives, M. V.	2014	32 healthy participants	Passive movement of the index finger congruent with the movement of the virtual index finger was used in the “synchronous” condition to induce ownership of the virtual arm. The pain threshold was tested by thermal stimulation under four conditions: (1) synchronous movements of the real and virtual fingers, (2) asynchronous movements, (3) seeing a virtual object instead of an arm, and (4) not seeing any limb in real world.	The ownership of a virtual arm per se can significantly increase the thermal pain threshold.
Martini, M., Kilteni, K., Maselli, A., and Sanchez-Vives, M. V.	2015	24 healthy participants	Participants observed four different levels of transparency of the virtual arm (0, 25, 50, and 75%), while they were tested for pain threshold by increasing ramps of heat stimulation.	Body ownership illusion decreases when the body becomes more transparent. Further, providing invisibility of the body does not increase pain threshold.
Romano, D., Llobera, J., and Blanke, O.	2015	21 healthy participants	Participants observed a manipulated visual size (small, normal, big) of an embodied virtual body during painful stimulation.	The results suggest that pain processing is modulated during illusory states of body self-consciousness and that these changes are greater for larger virtual bodies.
Pozeg, P., Palluel, E., Ronchi, R., Solcà, M., Al-Khodairy, A. W., Jordan, X., et al.	2017	20 patients with SCI with paraplegia 20 healthy controls	Participants were submitted to a virtual leg illusion (VLI) and received asynchronous or synchronous visuotactile stimulation to the participant’s back (either immediately above the lesion level or at the shoulder) and to the virtual legs.	Patients with SCI were less sensitive to illusory leg ownership (as compared to HC) and that leg ownership decreased with time since SCI. VLI and full body illusion were both associated with mild analgesia that was only during the VLI specific for synchronous visuotactile stimulation.
Solcà, M., Ronchi, R., Bello-Ruiz, J., Schmidlin, T., Herbelin, B., Luthi, F., et al.	2018	24 patients with CRPS 24 age-and sex-matched healthy controls	Participants were immersed in a virtual environment and shown a virtual depiction of their affected limb that was flashing in synchrony (or in asynchrony in the control condition) with their own online detected heartbeat (heartbeat-enhanced virtual reality).	Heart-enhanced VR reduced pain ratings, improved motor limb function, and modulated a physiologic pain marker (HRV). These significant improvements were reliable and highly selective, absent in control HEVR conditions, not observed in healthy controls.
Matamala-Gomez, M., Gonzalez, A. M. D., Slater, M., and Sanchez-Vives, M. V.	2018	9 patients with CRPS type 1 10 patients with PNI	Participants were immersed in VR and the virtual arm was shown at four different transparency levels (0, 25, 50, 75%), and three sizes (small, normal, big).	All seven conditions globally decreased pain ratings to half. Increasing transparency decrease pain in CRPS but not in PNI. Increasing size increased pain ratings only in CRPS.