No pain relief with the rubber hand illusion

Abstract

The sense of body ownership can be easily disrupted during illusions and the most common illusion is the rubber hand illusion. An idea that is rapidly gaining popularity in clinical pain medicine is that body ownership illusions can be used to modify pathological pain sensations and induce analgesia. However, this idea has not been empirically evaluated. Two separate research laboratories undertook independent randomized repeated measures experiments, both designed to detect an effect of the rubber hand illusion on experimentally induced hand pain. In Experiment 1, 16 healthy volunteers rated the pain evoked by noxious heat stimuli (5 s duration; interstimulus interval 25 s) of set temperatures (47°, 48° and 49°C) during the rubber hand illusion or during a control condition. There was a main effect of stimulus temperature on pain ratings, but no main effect of condition (p = 0.32), nor a condition x temperature interaction (p = 0.31). In Experiment 2, 20 healthy volunteers underwent quantitative sensory testing to determine heat and cold pain thresholds during the rubber hand illusion or during a control condition. Secondary analyses involved heat and cold detection thresholds and paradoxical heat sensations. Again, there was no main effect of condition on heat pain threshold (p = 0.17), nor on cold pain threshold (p = 0.65), nor on any of the secondary measures (p<0.56 for all). We conclude that the rubber hand illusion does not induce analgesia.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Experimental 1 & 2– experimental set-up.

Figure 2. Experiment 1 results: Mean (columns) and standard error (error bars) for ratings to the illusion questions (Q1–Q3) and control questions (Q4–Q6) for the illusion (dark gray) and the control (light gray) conditions.

The scale ranges from ‘+3′ (‘I agree strongly’) to ‘−3′ (‘I disagree strongly’) with ‘0′ denoting uncertainty.

Figure 3. Experiment 1 results: Mean (columns) and standard error (error bars) for pain ratings after exposure to synchronous versus asynchronous visuo-tactile stimulation with the rubber hand for high (painful) and low (non-painful) temperature stimulation.

Figure 4. Experiment 2 results: Mean (rectangle) and standard deviation (error bars) heat pain threshold (HPT), cold pain thresholds (CPT) and thermal sensory lymen (TSL) in °C for the rubber hand illusion (rubber hand illusion; open shapes) control conditions.

Right panels show pain ratings on a 0–10 scale for the pain experienced for the threshold stimuli for heat pain threshold and cold pain threshold condition. The circled 32° reflects the baseline from which a ramping stimulus was used to determine both heat PT and cold PT.