Body ownership in complementary painful and pleasure conditions: an electrophysiological study

Objective In the Rubber Hand Illusion paradigm (RHI), if an artificial hand and the subject’s (hidden) hand are stroked repeatedly and synchronously, the subject feels the artificial hand as part of her/his own body. A distributed temporal-parietal and medial-prefrontal network seems to play a crucial role in defining the ownership illusion but less in known about the potential modulation role of threatening and pleasing stimulation of the fake hand on its incorporation. The present study then aimed at exploring subjective and electrophysiological correlates of the RHI experience and of its potential perturbation through the presentation of threatening vs. innocuous stimulations. Participants and methods 20 healthy subjects took part in the experiment. Experimental design included three counterbalanced stimulation blocks composed by three times-blocks, where participants underwent a baseline recording, the administration of the RHI-inducing procedure, and experiences the threatening (knife) or pleasant (cotton swab) stimulation of the rubber hand or the stimulus missing (blank). After every block participants were presented with a questionnaire on their experience (Rubber Hand Embodiment Scale, RHES). Cortical activity was recorded by electroencephalography. Results During baseline recording, when influenced by knife presentation, data showed an increasing of Delta band. The pleasant stimulus brought an increasing of Alpha band lateralized in occipital area and seemed to be linked to stimuli pleasantness or threatening. Data derived from RHES questionnaire showed more elevated scores in the first experimental condition, in which subjects received the knife before the cotton swab, for items referred to the possibility to feel pain and to the incorporation vividness. Conclusion The knife seemed to influence not only the rubber hand incorporation, but also the following pleasant stimulus, perceived as less comfortable compared to the second condition. Finally, threatening condition specifically seemed to exert greater effect in modulating reported ownership perception.