Induction of mirror-touch synaesthesia by increasing somatosensory cortical excitability

Understanding others' tactile sensations is a fundamental component of social behaviour. This complex process is most likely supported by a 'mirror' network for touch, which allows for an automatic and unconscious simulation of others' somatic states [1]. In everyday life, we are typically unaware of this process, because the system is physiologically active below the threshold of perceptual awareness. In a minority of persons with synaesthesia, however, the sight of a touch on another person elicits conscious tactile experiences on their own bodies - mirror-touch synaesthesia [2]. This peculiar crossmodal experience has been attributed to an unusual activation of the mirror mechanisms for touch - a visual stimulus that elicits a tactile sensation [3] - but this hypothesis requires empirical support. Here, we report the existence of a causal brain-behaviour relationship between increased excitability of two key areas of the tactile mirror system and the emergence of synaesthesia-like effects in non-synaesthetes. Furthermore, we show that individual differences in empathic capacity may modulate the ability to resonate with others' somatic feelings.