Abstract
During the rubber hand illusion (RHI), subjects experience an artificial hand as part of their own body, while the real hand is subject to a sort of 'disembodiment'. Can this altered belief about the body also affect physiological mechanisms involved in body-ownership, such as motor control? Here we ask whether the excitability of the motor pathways to the real (disembodied) hand are affected by the illusion. Our results show that the amplitude of the motor-evoked potentials recorded from the real hand is significantly reduced, with respect to baseline, when subjects in the synchronous (but not in the asynchronous) condition experience the fake hand as their own. This finding contributes to the theoretical understanding of the relationship between body-ownership and motor system, and provides the first physiological evidence that a significant drop in motor excitability in M1 hand circuits accompanies the disembodiment of the real hand during the RHI experience.
Highlights
The sense of body ownership (Gallagher, 2000) is a fundamental aspect of self-consciousness
The main behavioral results showed that both proprioceptive drift towards the rubber hand (RH) and embodiment questionnaire rating were significantly higher in the synchronous than in the asynchronous condition (drift=mean ± sd: 4.51 ± 4.2 cm vs. 2.08 ± 2.75 cm; t(23)=2.783, p=0.0105, dz=0.58; emb-q-rating=mean ± sd: 2.4 ± 0.64 vs. À2 ± 0.9, Z=4.2857, p=0.000018, dz=3.88; Figure 2A1 and A2; see Figure 2—source data 1)
In order to investigate the link between body-ownership and motor system, we took advantage of the well-established rubber hand illusion (RHI) paradigm (Botvinick and Cohen, 1998; Ehrsson et al, 2004; Tsakiris et al, 2010; Longo et al, 2008; Moseley et al, 2008; Kammers et al, 2011; Rohde et al, 2013; Folegatti et al, 2009; Lewis and Lloyd, 2010; Valenzuela Moguillansky et al, 2013; Tsakiris and Haggard, 2005), a useful tool to manipulate the sense of body ownership in normal subjects
Summary
The sense of body ownership (i.e. the belief that a specific body part belongs to one’s own body) (Gallagher, 2000) is a fundamental aspect of self-consciousness. It has been suggested that the feeling that our body belongs to us presumably depends on multisensory integration processes arising within a fronto-parietal network, where sensory inputs coming from different modalities are realigned in a unique reference frame (Blanke et al, 2015). Within this network, the ventral premotor cortex seems to play a crucial role, establishing, both in monkeys (Graziano, 1999) and in humans (Makin et al, 2008; Ehrsson et al, 2004), an anatomical link between the sense of body ownership and the motor system.
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