Virtual reality: physiological and behavioral mechanisms to increase individual pain tolerance limits

Abstract

Immersive virtual reality (VR) consists of immersion in artificial environments through the use of real-time render technologies and the latest generation devices. The users feel just as immersed as they would feel in an everyday life situation, and this sense of presence seems to have therapeutic potentials. However, the VR mechanisms remain only partially known. This study is novel in that, for the first time in VR research, appropriate controls for VR contexts, immersive characteristics (ie, control VR), and multifaceted objective and subjective outcomes were included in a within-subject study design conducted on healthy participants. Participants received heat thermal stimulations to determine how VR can increase individual heat-pain tolerance limits (primary outcome) measured in degrees Celsius and seconds while recording concurrent autonomic responses. We also assessed changes in pain unpleasantness, mood, situational anxiety, and level of enjoyment (secondary outcomes). The VR induced a net gain in heat-pain tolerance limits that was paralleled by an increase of the parasympathetic responses. VR improved mood, situational anxiety, and pain unpleasantness when participants perceived the context as enjoyable, but these changes did not influence the increases in pain tolerance limits. Distraction increased pain tolerance limits but did not induce such mood and physiological changes. Immersive VR has been anecdotally applied to improve acute symptoms in contexts such as battlefield, emergency, and operating rooms. This study provides a mechanistic framework for VR as a low-risk, nonpharmacological intervention, which regulates autonomic, affective (mood and situational anxiety), and evaluative (subjective pain and enjoyment ratings) responses associated with acute pain.

Conflict of interest statement

Competing interests.

LC reports grants from NIDCR and NCCIH, grants from PCORI, grants from MPowering the State, grants from UM Grants, personal fees from Elsevier during the conduct of the study. NR, YW, TA, BBC, GCC, CK, AV, SM have no competing interests to declare.

Copyright © 2020 International Association for the Study of Pain.

Figures

Figure 1.. Experimental paradigm and conditions

(a). Participants went through five conditions including VR Ocean, VR Opera, Control VR Ocean, Control VR Opera, and 2-Back Working Memory Task. First, participants underwent the pain sensitivity assessment followed by a Baseline familiarization phase before starting the VR/control interventions. The 6-min immersive VR and the control conditions were therefore delivered to assess changes in heat warmth, pain threshold and heat-pain tolerance limits. The condition to which the participants were first exposed was counterbalanced, and the order of conditions following was randomized after generating five sequences to control for time effects. Participants were able to stop the heat stimulation using a controller. Participants stopped the self-delivered heat stimulations and levels of degrees Celsius intensities and duration of the stimulations were recorded. At the end of the VR and control interventions, participants rated the overall perceived pain intensity, unpleasantness, mood, situational anxiety and level of enjoyment. Autonomic measurements were collected continuously. (b) Representative screen shot of VR Ocean condition (left) and screen shot of VR Opera condition (right). (c) We first assessed pain sensitivity. Afterwards a baseline familiarization phase was conducted followed by the assessment of warm detection, heat-pain threshold and heat-pain tolerance limit, respectively. Three series of stimuli were delivered for each modality under each VR and control conditions.

Figure 2.. Heat-pain tolerance limit changes and heart rate variability SDNN among the five conditions.

(a) The VR Ocean condition yielded higher limits for pain tolerance compared to VR Opera and control VR conditions, but it did not show significant differences from the 2-Back Working Memory Task condition. Heat-pain tolerance limit increases are expressed in degrees Celsius and as median ± quartile (b) The SDNN during VR Ocean condition was significantly higher than the other four conditions suggesting a greater level of parasympathetic system action. (c) Positive correlation between SDNN and temperature changes during VR Ocean condition. (d) GSR changes in the five experimental conditions. The area under curve (AUC) was calculated to represent the level of GSR response. The AUC for the VR Ocean condition was significantly larger than the AUC in Control Ocean condition (p=0.014).

Figure 3.. The differences in pain unpleasantness, mood, level of enjoyment, and situational anxiety among the five conditions.

(a) Pain unpleasantness ratings for VR Ocean were significantly lower than in the other four conditions. (b) Mood ratings for VR Ocean was significantly higher than the remaining four conditions. (c) Situational anxiety level for the VR Ocean condition was significantly lower than VR Opera, Control Ocean and 2-Back Working Memory Task conditions. (d) Level of enjoyment for the VR Ocean condition was significantly higher than the other four conditions. Participants rated each outcome at the end of the experimental session. Data are expressed as median ± quartiles.

Figure 4.. Median splitting of study participants into opera likers and dislikers.

(a) Distribution of likers (in red) and dislikers (in yellow) based in the median of the enjoyment ratings (Fig. 4a). (b) Those who liked opera did have a negative correlation between VAS pain unpleasantness and VAS enjoyment ratings (Pearson correlation r=−0.43, p=0.034, Fig. 4b) and VAS pain unpleasantness and VAS situational anxiety ratings (Pearson correlation r=−0.52, p=0.009, Fig. 4c). There was a significant positive correlation between VAS mood and VAS enjoyment ratings (Pearson correlation r=0.898, p