PAIN-EX: Probing Alternative Interventions for Neutralizing pain EXperiences via Embodiment in Virtual Reality

Current Challenges in Pain Management

Pain constitutes a complex, multidimensional, and primarily subjective sensation of factual or potential tissue damage. While acute pain serves as a warning system that protects the body against serious injury or damage, the function of chronic pain is less clear. Criteria for chronic pain are met if the pain persists for more than 3 months, if it is accompanied by emotional distress and/or functional disabilities, and if symptoms cannot be better explained by another diagnosis. ¹ Treatment of chronic pain is a particularly difficult and complex venture. Considering that pharmacological therapy has side effects and is not sufficiently effective, nonpharmacological options are more pertinent. Among the most promising are fully immersive virtual reality (VR) technologies. ²

To date, VR has primarily been used as distraction technique in the context of acute ³ and chronic ⁴ pain treatment. By covering the entire field of view, and by allowing dynamic interactions with the virtual environment, VR technologies are thought to occupy attentional resources better and to block out external information more efficiently than classical distraction methods (i.e., playing a game on a 2D screen). Recent meta-analyses provide support for the effectiveness of VR-based distraction techniques in the context of acute ³ and chronic ¹ pain.

Yet, VR technologies offer the opportunity not only to interact dynamically with the environment but also to apply changes to the virtual body in ways that are not physically possible. ⁴ As we readily adopt any given virtual body and experience a sense of ownership over it (i.e., embodiment), any manipulations and changes made to the virtual body have direct effects on bodily experiences. This opens unique options for novel therapeutic avenues for pain management. ⁵ Particularly, the possibility of tailoring VR programs to the patients' individual pathology and personalizing specific interventions is thought to be a distinct advantage of VR over traditional therapeutic methods.

Interoceptive Modeling for Pain Management

One of the tailored approaches that is particularly promising for chronic pain treatment is the one described by Daniele Di Lernia and colleagues as “interoceptive modeling.” ⁶ It assumes the existence of residual interoceptive images (so-called ghosts) of pain. These mental representations of pain may be overwritten to induce permanent alterations to the cognitive and neurological system by a two-step process. First, the interoceptive representation of pain is visualized through external feeds in an internally coherent and multisensorily congruent mode to best fit the pain experienced by the patient (mimicking phase). Second, these internal representations are gradually manipulated to counteract the internal feed (modeling phase).

Here, virtual embodiment provides optimal grounds for mimicking and modeling interoceptive information. The embodied virtual body part may be visually customized to fit the person's interoceptive pain experience and subsequently counteracted to alter pain representations effectively. ⁶ Initial experimental studies underline the potential of visually altering the affected body part in VR. For instance, changing the color (i.e., blue) or material (i.e., stone) of a virtual arm significantly impacts the person's perception of this arm (i.e., to be colder or heavier). ⁴ Despite these positive results, the usefulness of virtual embodiment, and of interoceptive modeling in particular, for therapeutic pain management is unclear. To our knowledge, interoceptive modeling has only been theorized so far. ⁶ Empirical evidence is needed to test its suitability for pain treatment.

Objectives of the PAIN-EX Project

In view of this desideratum, the PAIN-EX project aims to test whether interoceptive modeling in a fully immersive VR is effective in decreasing pain intensity. For this purpose, the Pediatric Virtual Reality Laboratory at the Department of Pediatrics and Adolescent Medicine at the Medical University of Vienna and the Humane Technology Laboratory at the Department of Psychology of the Catholic University of Milan in collaboration with the Faculty of Computer Science at the University of Vienna will develop and test a novel VR-based application. A customized virtual version of participants' arms matching their actual size and skin tone, as well as visuomotor feedback, will be used to induce embodiment. ⁵ All participants will receive topical application of capsaicin cream to the inner side of the nondominant forearm to induce thermal pain experimentally.

Interoceptive modeling shall then be implemented by visually altering the virtual model of the affected arm in two steps: first by gradually changing the size, color saturation, and movement (frequency of flickering) of the painful area to fit the interoceptive pain information best (“mimicking phase”), and second by altering the visual makeover of the painful area to counteract the painful representation (“modeling phase”; starting from the previously selected settings, the visual representation will be changed automatically and gradually to counteract the pain). These specific visual changes were selected based on the set of visualizations pertaining particularly to thermal pain in the McGill Questionnaire. ⁷ Furthermore, only female participants will be included in the study to control for possible effects of sex on pain tolerance.

Capsaicin was chosen as an optimal pain stimulus for this study, as it may serve as a prediction model for chronic pain conditions, particularly neuropathic pain (NP). ⁸ There is evidence that the same type of fibers is affected in NP and heat pain. This is reinforced by the fact that NP is frequently compared to a burning sensation by affected patients. The results from this study are hence expected to be predictive of the potential effectiveness of interoceptive modeling for pain therapy.

Conclusions

In conclusion, this proof-of-concept study not only aims to test the concept of “interoceptive modeling” ⁶ but also to lay the ground for its clinical use. The tailored approach of interoceptive modeling combines a highly personalized visualization of individual pain experiences with the potent mechanism of embodiment. As such, it is expected to complement existing nonpharmacological therapeutic interventions with a compelling innovative mechanism. In addition to adult patients with chronic pain conditions, this approach may also be particularly useful for children and adolescents.

To date, most studies with pediatric patients have focused on examining 2D environments as a distraction tool. Research in children and adolescents that explores immersive VR and manipulates embodiment experiences is still pending. ²

According to Dr. Sandy Siegert, pediatric neurologist and researcher at the Department of Pediatrics and Adolescent Medicine at the Medical University of Vienna, “This is a significant drawback, given that especially young patients may benefit from VR technologies. Modern pediatric approaches aim to provide advanced methods to reduce pain in children. The impression of being fully immersed in the virtual environment is expected to distract children and adolescents, thus drawing attention away from the pain. Also, we believe that embodiment will work well in these patients, all the more, if it makes use of gamification elements. Integrating the process of interoceptive modeling into a narrative could be a viable approach. For instance, children may be instructed that they possess extraordinary powers and that after mimicking the pain, they may make it disappear from their affected limb by using their own magic spell. Thereby we assume that VR technologies can be powerful tools to strengthen or even regain self-confidence, especially in pediatric pain patients.” In this sense, the present project is expected to prepare the ground for further clinical testing in both adult and pediatric patients with chronic pain conditions.