Causal Dynamics of Scalp Electroencephalography Oscillation During the Rubber Hand Illusion
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Rubber hand illusion (RHI) is an important phenomenon for the investigation of body ownership and self/other distinction. The illusion is promoted by the spatial and temporal contingencies of visual inputs near a fake hand and physical touches to the real hand. The neural basis of this phenomenon is not fully understood. We hypothesized that the RHI is associated with a fronto-parietal circuit, and the goal of this study was to determine the dynamics of neural oscillation associated with this phenomenon. We measured electroencephalography while delivering spatially congruent/incongruent visuo-tactile stimulations to fake and real hands. We applied time–frequency analyses and calculated renormalized partial directed coherence (rPDC) to examine cortical dynamics during the bodily illusion. When visuo-tactile stimulation was spatially congruent, and the fake and real hands were aligned, we observed a reduced causal relationship from the medial frontal to the parietal regions with respect to baseline, around 200 ms post-stimulus. This change in rPDC was negatively correlated with a subjective report of the RHI intensity. Moreover, we observed a link between the proprioceptive drift and an increased causal relationship from the parietal cortex to the right somatosensory cortex during a relatively late period (550–750 ms post-stimulus). These findings suggest a two-stage process in which (1) reduced influence from the medial frontal regions over the parietal areas unlocks the mechanisms that preserve body integrity, allowing RHI to emerge; and (2) information processed at the parietal cortex is back-projected to the somatosensory cortex contralateral to the real hand, inducing proprioceptive drift.
KeywordsRubber hand illusion Electroencephalography Causal relationship Body ownership
This study was supported by the program of Research Fellowships for Young Scientists Grant numbers 26780418 and 16H05958 (Japan Society for the Promotion of Science [JSPS], Japan) and by the Institutional Program for Young Researcher Overseas Visits (The University of Tokyo). In addition, the Center of Innovation Program from the Japan Science and Technology Agency (JST) partially supported this research. Finally, we are grateful to the two anonymous reviewers whose detailed and stimulating suggestions greatly improved the previous version of this article.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
Ethical Approval for Research Involving Humans
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee (approval 2014-028) and with the 1964 Helsinki declaration and its later amendments.
Informed consent was obtained from all individual participants included in the study.
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