Early and late activity in somatosensory cortex reflects changes in bodily self-consciousness: An evoked potential study

Abstract

Abstract-How can we investigate the brain mechanisms underlying self-consciousness? Recent behavioural studies on multisensory bodily perception have shown that multisensory conflicts can alter bodily self-consciousness such as in the ''full body illusion'' (FBI) in which changes in self-identification with a virtual body and tactile perception are induced. Here we investigated whether experimental changes in self-identification during the FBI are accompanied by activity changes in somatosensory cortex by recording somatosensory-evoked potentials (SEPs). To modulate self-identification, participants were filmed by a video camera from behind while their backs were stroked, either synchronously (illusion condition) or asynchronously (control condition) with respect to the stroking seen on their virtual body. Tibial nerve SEPs were recorded during the FBI and analysed using evoked potential (EP) mapping. Tactile mislocalisation was measured using the crossmodal congruency task. SEP mapping revealed five sequential periods of brain activation during the FBI, of which two differed between the illusion condition and the control condition. Activation at 30-50 ms (corresponding to the P40 component) in primary somatosensory cortex was stronger in the illusion condition. A later activation at $110-200 ms, likely originating in higher-tier somatosensory regions in parietal cortex, was stronger and lasted longer in the control condition. These data show that changes in bodily self-consciousness modulate activity in primary and higher-tier somatosensory cortex at two distinct processing steps. We argue that early modulations of primary somatosensory cortex may be a consequence of (1) multisensory integration of synchronous vs. asynchronous visuo-tactile stimuli and/or (2) differences in spatial attention (to near or far space) between the conditions. The later activation in higher-tier parietal cortex (and potentially other regions in temporo-parietal and frontal cortex) likely reflects the detection of visuo-tactile conflicts in the asynchronous condition.

The development of bodily self‐consciousness: changing responses to the Full Body Illusion in childhood

“…The current study accords well with the findings of adult studies using the same FBI paradigm (e.g., Aspell et al., ; Aspell et al., ; Lenggenhager et al., ; Lenggenhager et al., ). In our set‐up, participants viewed the body from a third‐person perspective – that is, as if seen by someone else, and not from a first‐person perspective, in the visual reference frame of one's own body.…”

“…The phenomenon of mislocalizing (or mis‐referring) touch to a virtual body is present in adults (e.g., Lenggenhager et al., ; Lenggenhager et al., ; Pomés & Slater, ). It can be measured through questionnaires, and is further evident in implicit measures, that is, changes in cross‐modal congruency effects (Aspell et al., ) and somatosensory evoked potentials (Aspell et al., ) during the illusion. The present study assessed the development of touch referral, and we found that the magnitude of difference between baseline‐corrected questionnaire responses in the synchronous condition and the asynchronous condition increased strikingly with age.…”

“…It also induces a stronger feeling of ownership of (self‐identification with) the virtual body, and illusory percepts of touch on the virtual body. Recent studies have shown that the FBI affects additional aspects of bodily processing, inducing, for example, changes in tactile processing (Aspell, Lenggenhager, & Blanke, ; Aspell, Palluel, & Blanke, ), pain perception (Hänsell, Lenggenhager, Känell, Curatolol, & Blanke, ; Pamment & Aspell, ) and body temperature (Salomon, Lim, Pfeiffer, Gassert, & Blanke, ). Neuroimaging studies of full body illusions have demonstrated associated changes in a network of brain areas.…”

Altered bodily self-consciousness and peripersonal space in autism

“…The FBI data show that agreement with illusion statements was signfiicantly higher in synchronous than asynchronous body conditions in the non-ASD group -as found previously (Aspell et al, 2012;Cowie, McKenna, Bremner, & Aspell, 2017;Ionta et al, 2011;Lenggenhager et al, 2007) -but did not differ in the ASD group. Moreover, neurotypical participants showed significantly greater self-identification with the virtual body in the synchronous condition and a greater self-location drift towards the virtual body during the synchronous condition, but this was not found for ASD participants.…”

Bodily self‐relatedness in vicarious touch is reflected at early cortical processing stages

“…This is in line with earlier findings showing that prerequisite embodiment and the observation of highly self-related stimuli (touch on own face; Adler et al, 2016; anatomically matched touch on hands in first-person perspective; Rigato et al, 2019) are associated with vicarious touch effects over P45 specifically. P45 originates in S1 (Allison et al, 1989(Allison et al, , 1992Schubert et al, 2008), which is itself critically involved in vicarious touch for hands in first-person versus third-person perspectives (Schaefer et al, 2012) and in the sense of body ownership (Aspell, Palluel, & Blanke, 2012;Otsuru et al, 2014).…”