Absence of reliable physiological signature of illusory body ownership revealed by f ine-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 infleuntial model, selfhood relates to internal agency and higher-order interoceptive representation, inferred from the predicted impact of efferent autonomic nerves 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 electrodermal activity, electrocardiography, and non-invasive measurement of multiunit skin sympathetic nerve activity (SKNA) from the chest. We compared measures 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. Subjective reports and observed proprioceptive drift confirmed the efficacy of synchronous vs asynchronous condition in inducing illusory hand ownership. Stringent discriminant analysis classified 24 /37 individuals as experiencing the rubber hand illusion. Electrodermal activity, heart rate, heart rate variability, 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 confirmed there was substantial evidence for no physiological differences. In contrast to earlier reports, our cardiac and electrodermal autonomic data, including fine grained SKNA measurement, provide substantial evidence for the absence of a reliable change in physiological state during induction or experience of the rubber hand illusion. If illusory body ownership is 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 illusion.