Absence of reliable physiological signature of illusory body ownership revealed by fine-grained autonomic measurement during the rubber hand illusion

Abstract

The neural representation of a ‘biological self’ is linked theoretically to the control of bodily physiology. In an influential model, selfhood relates to internal agency and higher-order interoceptive representation, inferred from the predicted impact of efferent autonomic nervous activity on afferent viscerosensory feedback. Here we tested if an altered representation of physical self (illusory embodiment of an artificial hand) is accompanied by sustained shifts in autonomic activity. Participants (N = 37) underwent procedures for induction of the rubber hand illusion (synchronous stroking of own unseen hand and observed stroking of artificial hand) and a control condition (asychronous stroking). We recorded electrocardiography, electrodermal activity, and a non-invasive measure of multiunit skin sympathetic nerve activity (SKNA) from the chest. We compared these autonomic indices between task conditions, and between individuals who did and did not experience the illusion. Bayes factors quantified the strength of evidence for and against null hypotheses. Observed proprioceptive drift and subjective reports confirmed the efficacy of the synchronous (vs asynchronous) condition in inducing illusory hand ownership. Stringent discriminant analysis classified 24/37 individuals as experiencing the rubber hand illusion. Surprisingly, heart rate, heart rate variability, electrodermal activity, and SKNA measures revealed no autonomic differences between synchronous vs asynchronous conditions, nor between individuals who did or did not experience the rubber hand illusion. Bayes factors indicated substantial evidence for no physiological differences. In contrast to earlier reports, our autonomic data show the absence of a reliable change in physiological state during the rubber hand illusion. More encompassing perturbations of self-experience, for example in full body illusions, may nevertheless be coupled to, or facilitated by, changes in efferent autonomic activity and afferent viscerosensory feedback. Our findings suggest that such changes in bodily physiology are not sustained as an obligatory component of the rubber hand illusion.

Do interoception and attending to the upper limbs affect body ownership and body representation in the grasp illusion?

“…Importantly, the strength of the grasp illusion was not related to a person’s level of interoceptive accuracy, which is in line with some [ 27 – 29 ], but not all previous studies [ 21 , 22 ]. Moreover, it was not related to scores from the Noticing subscale the MAIA-2 scale, which capture the Awareness of Bodily Sensations dimension of interoceptive sensibility.…”

“…This aspect of interoception relates to a person’s ability to detect and track internal bodily signals [ 23 ] and is typically assessed with a heartbeat counting task [ 24 – 26 ]. However, more recent studies have failed to replicate this finding [ 27 – 29 ].…”

Embodying an artificial hand increases blood flow to the investigated limb

“…Furthermore, increased fluctuations in the skin conductance correlate with the onset and the strength of the illusion during the RHI 37 . On the other hand, the relationship between RHI-generated ownership and these interoceptive measures was not always reported 38 while other interoceptive indexes were not found to be correlated with illusion strength: e.g. the scores in heartbeat counting tasks 39 , 40 .…”

A temporal parcellation of the sensory-evoked responses during the rubber hand illusion reveals manipulation- and illusion-specific correlates

“…We complemented the EEG recordings with measurements of skin conductance and questionnaires. Skin conductance has been shown to index autonomous responses that are sensitive to the embodiment of the rubber hand (Armel and Ramachandran, 2003;Critchley et al, 2021;D'Alonzo et al, 2020;Ehrsson et al, 2007). This also allowed us to ask whether the neurophysiological (EEG) correlates of the illusory state are related to those physiological correlates obtained from the skin conductance.…”