Non‐invasive brain stimulation of motor cortex induces embodiment when integrated with virtual reality feedback

Abstract

Previous evidence highlighted the multisensory‐motor origin of embodiment – that is, the experience of having a body and of being in control of it – and the possibility of experimentally manipulating it. For instance, an illusory feeling of embodiment towards a fake hand can be triggered by providing synchronous visuo‐tactile stimulation to the hand of participants and to a fake hand or by asking participants to move their hand and observe a fake hand moving accordingly (rubber hand illusion). Here, we tested whether it is possible to manipulate embodiment not through stimulation of the participant's hand, but by directly tapping into the brain's hand representation via non‐invasive brain stimulation. To this aim, we combined transcranial magnetic stimulation (TMS), to activate the hand corticospinal representation, with virtual reality (VR), to provide matching (as contrasted to non‐matching) visual feedback, mimicking involuntary hand movements evoked by TMS. We show that the illusory embodiment occurred when TMS pulses were temporally matched with VR feedback, but not when TMS was administered outside primary motor cortex, (over the vertex) or when stimulating motor cortex at a lower intensity (that did not activate peripheral muscles). Behavioural (questionnaires) and neurophysiological (motor‐evoked‐potentials, TMS‐evoked‐movements) measures further indicated that embodiment was not explained by stimulation per se, but depended on the temporal coherence between TMS‐induced activation of hand corticospinal representation and the virtual bodily feedback. This reveals that non‐invasive brain stimulation may replace the application of external tactile hand cues and motor components related to volition, planning and anticipation.

Losing my hand. Body ownership attenuation after virtual lesion of the primary motor cortex

“…However, important methodological details can account for this difference. Indeed, the present study was devised to record MEPs at the end of the experimental procedure as a physiological measure of the M1 excitability, as well as a recent study showing that M1 stimulation induces embodiment when integrated with virtual reality feedbacks and obtaining similar negative data on the MEPs amplitude (Bassolino et al., ). On the contrary, the previous study of della Gatta et al.…”

Virtual reality and non-invasive brain stimulation for rehabilitation applications: a systematic review

“…Recently, evidence has emerged showing promising therapeutic applications for the combined use of VR and tES (more specifically tDCS) [ 23 – 26 ], as well as VR and TMS [ 27 – 29 ], with outcomes not achievable by using either technique individually. Despite the reported promising results, the literature still lacks a systematic review covering the reported methods, outcomes, and potential therapeutic applications in neurological rehabilitation, on the combination of VR and NIBS techniques.…”

Transcranial Magnetic Stimulation Meets Virtual Reality: The Potential of Integrating Brain Stimulation With a Simulative Technology for Food Addiction

“…Nevertheless, the generalizability of the findings is limited by the number and the heterogeneity of the studies included. Bassolino et al (2018) induced embodiment for an artificial hand in a virtual environment through TMS over corticospinal tract, without tactile cues on the hand's skin, typically used to ease rubber hand illusion. Authors argued that this illusory embodiment was determined by neuro-visual integration between TMS over primary motor cortex (and connections with sensory cortex) and hand twitches with visual VR feedback (Bassolino et al, 2018).…”

“…Bassolino et al (2018) induced embodiment for an artificial hand in a virtual environment through TMS over corticospinal tract, without tactile cues on the hand's skin, typically used to ease rubber hand illusion. Authors argued that this illusory embodiment was determined by neuro-visual integration between TMS over primary motor cortex (and connections with sensory cortex) and hand twitches with visual VR feedback (Bassolino et al, 2018). This effect did not occur when sham TMS was delivered, suggesting that the temporal synchrony between active TMS and VR feedback determined the illusory embodiment.…”