Somatosensory coding of visual self-identity

How does the brain process our bodily identity? This question has long fascinated scientists because of its potential implications for the study of self-awareness. Here, to test the idea that the somatosensory system is directly involved in coding bodily self-identity even when conveyed through vision, we probed the somatosensory system with tactile stimuli while participants observed hand images, either belonging to them (self-hand) or to another person (other-hand). In three psychophysical experiments (discovery, replicating and control samples), we found faster reaction times to tactile stimuli when paired with the self- than the other-hand image. To explore the neural basis of this effect, we conducted two electrophysiological experiments (discovery and replicating samples), and we observed that visual activity did not vary as a function of bodily identity, whereas the activity of the primary (at around 40 ms) and secondary (from 100 ms) somatosensory cortices did vary, as revealed by significantly higher somatosensory responses to tactile probes when presenting the self- than the other-hand image. We propose that this somatosensory coding of visual self-identity may be the result of associative learning mechanisms, through which individuals learn that the association between visual and somatosensory input only pertains to the own body, thus representing a possible prerequisite for establishing self-awareness

Like the back of my hand: Visual ERPs reveal a specific change detection mechanism for the bodily self

The ability to identify our own body is considered a pivotal marker of self-awareness. Previous research demonstrated that subjects are more efficient in the recognition of images representing self rather than others' body effectors (self-advantage). Here, we verified whether, at an electrophysiological level, bodily-self recognition modulates change detection responses. In a first EEG experiment (discovery sample), event-related potentials (ERPs) were elicited by a pair of sequentially presented visual stimuli (vS1; vS2), representing either the self-hand or other people's hands. In a second EEG experiment (replicating sample), together with the previously described visual stimuli, also a familiar hand was presented. Participants were asked to decide whether vS2 was identical or different from vS1. Accuracy and response times were collected. In both experiments, results confirmed the presence of the self-advantage: participants responded faster and more accurately when the self-hand was presented. ERP results paralleled behavioral findings. Anytime the self-hand was presented, we observed significant change detection responses, with a larger N270 component for vS2 different rather than identical to vS1. Conversely, when the self-hand was not included, and even in response to the familiar hand in Experiment 2, we did not find any significant modulation of the change detection responses. Overall our findings, showing behavioral self-advantage and the selective modulation of N270 for the self-hand, support the existence of a specific mechanism devoted to bodily-self recognition, likely relying on the multimodal (visual and sensorimotor) dimension of the bodily-self representation. We propose that such a multimodal self-representation may activate the salience network, boosting change detection effects specifically for the self-hand

Different tool training induces specific effects on body metric representation

Morphology and functional aspects of the tool have been proposed to be critical factors modulating tool use-induced plasticity. However, how these aspects contribute to changing body representation has been underinvestigated. In the arm bisection task, participants have to estimate the length of their own arm by indicating its midpoint, a paradigm used to investigate the representation of the metric properties of the body. We employed this paradigm to investigate the impact of different actions onto tool embodiment. Our findings suggest that a training requiring actions mostly with proximal (shoulder) or distal (wrist) parts induces a different shift in the perceived arm midpoint. This effect is independent of, but enhanced by, the use of the tool during the training and in part influenced by specific demands of the task. These results suggest that specific motor patterns required by the training can induce different changes of body representation, calling for rethinking the concept of tool embodiment, which would be characterized not simply by the morphology of the tools, but also by the actions required for their specific use