The magnitude of somatosensory evoked potentials (SEPs) elicited by simultaneous electrical stimulation of adjacent digits is generally less than the sum of potentials evoked by stimulation of each digit individually. This under-additivity suggests suppression between representations of adjacent skin regions and may reflect a process of lateral inhibition by interneurons in somatosensory cortex. Given that simply viewing the body enhances tactile acuity and that tactile acuity depends on cortical lateral inhibition, we investigated how viewing the body modulates suppressive interactions between simultaneous afferent volleys from adjacent fingers. We recorded SEPs evoked by electrical stimulation of the right index and middle fingers, either individually or simultaneously, while participants viewed either their own hand or an object. In between trains of electrical stimuli, participants discriminated the orientation of tactile gratings applied to either finger. Consistent with previous findings, viewing the hand enhanced tactile acuity. Furthermore, viewing the hand increased the suppression of the P50 potential due to simultaneous electrical stimulation of both fingers. Moreover, the visual enhancement of tactile performance correlated across participants with the visual modulation of suppression. These results demonstrate that vision enhances somatosensation by modulating activity of inhibitory interneuronal circuits in the somatosensory cortex.

The perception of tactile stimuli on the face is modulated if subjects concurrently observe a face being touched; this effect, termed visual remapping of touch (VRT), is maximum for observing one's own face. In the present fMRI study, we investigated the neural basis of the VRT effect. Participants in the scanner received tactile stimuli, near the perceptual threshold, on their right, left, or both cheeks. Concurrently, they watched movies depicting their own face, another person's face, or a ball that could be touched or only approached by human fingers. Participants were requested to distinguish between unilateral and bilateral tactile stimulation. Behaviorally, perception of tactile stimuli was modulated by viewing a tactile stimulation, with a stronger effect when viewing one's own face being touched. In terms of brain activity, viewing touch was related with an enhanced activity in the ventral intraparietal area. The specific effect of viewing touch on oneself was instead related with a reduced activity in both the ventral premotor cortex and the somatosensory cortex. The present findings suggest that VRT is supported by a network of fronto-parietal areas. The ventral intraparietal area might remap visual information about touch onto tactile processing. Ventral premotor cortex might specifically modulate multisensory interaction when sensory information is related to one's own body. Then this activity might back project to the somatosensory cortices, thus affecting tactile perception.

Our perceptual systems integrate multisensory information about objects that are close to our bodies, which allow us to respond quickly and appropriately to potential threats, as well as act upon and manipulate useful tools. Intriguingly, the representation of this area close to our body, known as the multisensory 'peripersonal space' (PPS), can expand or contract during social interactions. However, it is not yet known how different social interactions can alter the representation of PPS. In particular, shared sensory experiences, such as those elicited by bodily illusions such as the enfacement illusion, can induce feelings of ownership over the other's body which has also been shown to increase the remapping of the other's sensory experiences onto our own bodies. The current study investigated whether such shared sensory experiences between two people induced by the enfacement illusion could alter the way PPS was represented, and whether this alteration could be best described as an expansion of one's own PPS towards the other or a remapping of the other's PPS onto one's own. An audio-tactile integration task allowed us to measure the extent of the PPS before and after a shared sensory experience with a confederate. Our results showed a clear increase in audio-tactile integration in the space close to the confederate's body after the shared experience. Importantly, this increase did not extend across the space between participant and confederate, as would be expected if the participant's PPS had expanded. Thus, the pattern of results is more consistent with a partial remapping of the confederate's PPS onto the participant's own PPS. These results have important consequences for our understanding of interpersonal space during different kinds of social interactions.

Localizing touch in space is essential for goal-directed action. Because body posture changes, the brain must transform tactile coordinates from an initial skin-based representation to external space by integrating information about current posture. This process, referred to as tactile remapping, generally results in accurate localization, but accuracy drops when skin-based and external spatial representations of touch are conflicting, e.g., after crossing the limbs. Importantly, frequent experience of such postures can improve localization. This suggests that remapping may not only integrate current sensory input but also prior experience. Here, we demonstrate that this can result in rapid changes in localization performance over the course of few trials. We obtained an implicit measure of tactile localization by studying the perceived temporal order of two touches, one on each hand. Crucially, we varied the number of consecutive trials during which participants held their arms crossed or uncrossed. As expected, accuracy dropped immediately after the arms had been crossed. Importantly, this was followed by a progressive recovery if posture was maintained, despite the absence of performance feedback. Strikingly, a significant improvement was already evident in the localization of the second pair of touches. This rapid improvement required preceding touch in the same posture and did not occur merely as a function of time. Moreover, even touches that were not task relevant led to improved localization of subsequent touch. Our findings show that touches are mapped from skin to external space as a function of recent tactile experience.