Feeling numb: temperature, but not thermal pain, modulates feeling of body ownership.

There is an important link between pain, regulation of body temperature, and body ownership. For example, an altered feeling of body ownership - due to either chronic pain or "rubber-hand illusions" (RHI) - is associated with reduced temperature of the affected limb. However, the causal relationships within this triad are not well understood. We therefore investigated whether external manipulation of body temperature can influence body ownership. We used a thermode to make the right hand of healthy participants either painfully cold, cool, neutral, warm or painfully hot. Next, we induced the RHI and investigated its effects on the perceived position of the hand, on the subjective feeling of body ownership, and on physical changes in hand temperature. We replicate previous reports that inducing the RHI produces a decrease in limb temperature. Importantly, we demonstrate for the first time a causal effect in the opposite direction. Cooling down the participant's hand increased the strength of the RHI, while warming the hand externally decreased the strength of the RHI. Finally, we show that the painful extremes of these temperatures do not modulate the RHI. Hence, while thermosensation is an important driver of body ownership, pain seems to bypass the multisensory mechanisms of embodiment.