Distinct roles of the premotor and occipito-temporal cortices in the full-body illusion.

The sense of body ownership, a core aspect of self-recognition, has been studied using illusions such as the full-body illusion. Although the premotor cortex is considered central to body ownership in first-person full-body illusions, the occipitotemporal cortex-including the temporoparietal junction (TPJ) and the extrastriate body area (EBA)-also plays a critical role in third-person full-body illusions. However, their distinct contributions to the full-body illusion remain unclear, partly due to the challenges of applying neuroimaging in such experiments. This study employed functional near-infrared spectroscopy to investigate brain activity during a third-person full-body illusion in virtual reality. Eighteen healthy human adult males participated in the study. The experiment consisted of two sessions. In Session 1, participants observed an avatar's back receiving either synchronous or asynchronous visual-tactile stimulation. In Session 2, visual stimuli alone were presented to participants after they experienced the full-body illusion to induce visuotactile discrepancies. In the synchronous condition of Session 1, we found significant deactivation in the superior and middle temporal gyri (partially including the TPJ), followed by higher activity than in the asynchronous condition in the left middle occipital gyrus (likely EBA). The left premotor cortex also showed significant activation (uncorrected), although this did not survive multiple comparisons adjustment. In Session 2, the visuotactile discrepancy induced significant left premotor activation only in the synchronous condition (FDR-corrected). These findings suggest that the occipitotemporal cortex supports receptivity to third-person full-body illusions, whereas the premotor cortex contributes to maintaining illusory body ownership by reconciling multisensory conflicts.Significance Statement The relative importance of the premotor cortex versus the occipito-temporal cortex-including the temporo-parietal junction (TPJ) and the extrastriate body area (EBA)-in body ownership remains debated. To address this, we used functional near-infrared spectroscopy to measure brain activity during full-body illusion. Our findings revealed significant deactivation in the TPJ, followed by greater EBA activation in the illusion-induced condition than in the no-illusion condition, indicating the occipitotemporal cortex establishes receptivity to third-person full-body illusions. Furthermore, increased activity in the premotor cortex during sensory conflict may reflect its involvement in resolving multisensory conflicts and sustaining body ownership of the avatar. These results offer insights into the neural mechanisms underlying body ownership in the full-body illusion.