Top-down effect of body representation on pain perception

Abstract

Many studies on body representation intend to change the perceived size, material, and structure of the body. However, whether the perception of a stimulus can be modified by manipulating body representation remains largely unexplored. Thus, the current study investigated the relationship between transparency of body representation and pain perception. Using augmented reality technology, we made the participants’ limbs transparent and analyzed changes in body representation. Using a questionnaire, we confirmed that the participants perceived their limb as transparent. Simultaneously, their sense of ownership of the limb decreased, because they felt that it no longer belonged to their body. The participants were given an electrical stimulus to assess their subjective perception of pain intensity. An increase in limb opacity decreased the perception of pain, which, in turn, increased the feeling of transparency. These results suggested that the feeling of transparency in their limb favored the decrease in perceived pain. This effect was modified by body ownership, where high levels reinforced the analgesic effect. However, body ownership displayed a positive relationship with perceived pain. The study suggests that body transparency may constitute a strategy for decreasing refractory pain given that body ownership is retained at a high level.

Abrupt visibility modifications affect specific subjective (not objective) aspects of body ownership

“…In the present study, while the objective measures of the RHI (proprioceptive drift) were modulated by the type of visuo-tactile Stimulation and Visibility, separately, there was no interaction between these two factors. Therefore, while our data confirm previously reported increases in illusory ownership associated with augmented visibility (Martini et al, 2015;Matsumuro et al, 2022) and visuo-tactile synchrony (Botvinick & Cohen, 1998;Tsakiris & Haggard, 2005), this finding was unspecific. The dissociation between visibility/stimulation-affected subjective (questionnaire) and visibility/stimulation-unaffected objective aspects of the RHI (proprioceptive drift) found in the present study is in line with previous evidence that questionnaires and proprioceptive do not necessarily correlate (Gallagher et al, 2021;Holle et al, 2011;Rohde et al, 2011).…”

“…Previous studies reported that illusory body ownership can decrease with the visibility (transparency) of the rubber hand (Martini et al, 2015;Matsumuro et al, 2019), and that illusory ownership can occur even if the rubber hand/body-part is not visible (D'Angelo et al, 2017;D'Angelo et al, 2020;Guterstam et al, 2013;Guterstam et al, 2015). However, in Martini et al (2015) the evaluation of the RHI was limited to only one Embodiment statement, corresponding to S2 of the present study.…”

“…However, in Martini et al (2015) the evaluation of the RHI was limited to only one Embodiment statement, corresponding to S2 of the present study. Conversely, Matsumuro et al (2022) seemed to implement more ownership statements (Matsumuro et al, 2022), but irrespective to the factor Loadings described in Longo et al (2008). In addition, none of these previous studies comprised both the manipulation of visibility and the visual absence of the rubber hand.…”

“…This interpretation that motor and perceptual embodiment separately, but not in conjunction, are sensitive to the visual presence of the rubber hand, corroborates previous suggestions that the RHI likely "displaces" the proprioceptive input related to the real hand (de Vignemont, 2011;Longo et al, 2008) and that and this shift can be detected also through visual misrepresentations. Importantly, while visibility changes correspond to the modulation of a bottom-up element (perception of light), RHI-induced illusory changes are a top-down phenomenon (Longo et al, 2008;Matsumuro et al, 2019). Therefore, the embodiment experience related to the RHI would emerge from an interplay between immediate bottom-up bodily sensations and top-down updating and comparison with stored body representations (Lewis & Lloyd, 2010;Longo et al, 2008).…”

An illusion of disownership over one’s own limb is associated with pain perception

“…Martini and colleagues showed that the subjective ratings of owning a transparent virtual arm are negatively correlated with heat pain threshold, suggesting a high sensitivity to painful stimuli when seeing the virtual body that visually fades away 51 (for the opposite see Ref. 52 ). Authors speculate that the general reduction of pain threshold could function as an alert system since the blurred boundary of one’s own body decreases the predictability of potential damage.…”