Pleasant touch moderates the subjective but not objective aspects of body perception

Abstract

Un-myelinated C tactile afferents (CT afferents) are a key finding in affective touch. These fibers, which activate in response to a caress-like touch to hairy skin (CT afferents are not found in palm skin), may have more in common with interoceptive systems encoding body ownership, than afferent systems processing other tactile stimuli. We tested whether subjective embodiment of a rubber hand (measured through questionnaire items) was increased when tactile stimulation was applied to the back of the hand at a rate optimal for CT afferents (3 cm/s) vs. stimulation of glabrous skin (on the palm of the hand) or at a non-optimal rate (30 cm/s), which should not activate these fibers. We also collected ratings of tactile pleasantness and a measure of perceived limb position, proprioceptive drift, which is mediated by different mechanisms of multisensory integration than those responsible for feelings of ownership. The results of a multiple regression analysis revealed that proprioceptive drift was a significant predictor of subjective strength of the illusion when tactile stimuli were applied to the back of the hand, regardless of stroking speed. This relationship was modified by pleasantness, with higher ratings when stimulation was applied to the back of the hand at the slower vs. faster stroking speed. Pleasantness was also a unique predictor of illusion strength when fast stroking was applied to the palm of the hand. However, there were no conditions under which pleasantness was a significant predictor of drift. Since the illusion was demonstrated at a non-optimal stroking speed an integrative role for CT afferents within the illusion cannot be fully supported. Pleasant touch, however, does moderate the subjective aspects of the rubber hand illusion, which under certain tactile conditions may interact with proprioceptive information about the body or have a unique influence on subjective body perception.

Interoceptive ingredients of body ownership: Affective touch and cardiac awareness in the rubber hand illusion

“…This findings are still controversial, and further investigations of this measure and the physiological condition of participant's own arm are needed. Taken together, these results confirmed previous findings on the facilitatory role of affective touch in subjective ownership (Crucianelli et al, 2013;Lloyd et al, 2013;but see van Stralen et al, 2014, for proprioceptive drift effects). However, as stated in the introduction (see also Lloyd et al, 2013), it remains to be specified whether these effects are caused by bottom-up signals relating to the CT-system or by top-down factors such as learned expectations of sensory pleasure relating to the seen slow touch.…”

“…In particular, slow, caress-like touch that activates CT afferents optimally can enhance the experience of owning a rubber hand more than fast, emotionally neutral touch that does not cause optimal CT activation (Crucianelli, Metcalf, Fotopoulou & Jenkinson, 2013;Lloyd, Gillis, Lewis, Farrell & Morrison, 2013;van Stralen, van Zandvoort, Hoppenbrouwers, Vissers, Kappelle et al, 2014). Additionally, Lloyd and colleagues (2013) showed that slow/CT-optimal touch enhanced the subjective embodiment of the rubber hand also in the condition when touch was applied to glabrous (non-hairy) skin, known to lack CT afferents (Vallbo, Olausson & Wessberg, 1999).…”

Salivary Oxytocin Concentration Associates with the Subjective Feeling of Body Ownership during the Rubber Hand Illusion

“…From these results, we speculate that there are different mechanisms for spatial updating and plastic changes in body ownership. In line with the speculation, proprioceptive drift arises even when participants do not feel ownership of the rubber hand (Holle et al, 2011; Rohde et al, 2011; Lloyd et al, 2013), although a subjective feeling of the illusion causes proprioceptive drift (Abdulkarim and Ehrsson, 2016). This suggests that oxytocin may modulate plastic changes in body ownership after visuotactile integration rather than during the visuotactile integration itself.…”

Sense of body ownership in patients affected by functional motor symptoms (conversion disorder)

“…For example, recent studies have found that affective touch can modulate the sense of body ownership during the RHI. Specifically, slow, caress-like touch that is thought to be mediated by a specialized, interoceptive system (Löken, Wessberg, Morrison, McGlone, & Olausson, 2009) can increase subjective and objective measures of body ownership during the illusion more than fast, emotionally neutral touch (Crucianelli et al, 2013;Lloyd, Gillis, Lewis, Farrell, & Morrison, 2013;Löken et al, 2009;Moseley et al, 2008;Suzuki et al, 2013). Testing such multi-directional interactions between interoception and body ownership can thus shed further light into the neuroaffective components of functional motor disorders and related pathologies.…”