Brain imaging studies have shown the existence of a mirror network for touch, which allows for an automatic and unconscious simulation of others’ somatic states (Keysers et al., 2010). In everyday life, we are typically unaware of this process likely because the system is physiologically active below the threshold of perceptual awareness. However, in persons with mirror-touch synaesthesia, the sight of a touch on another person elicits conscious tactile experiences on their own bodies (Blakemore et al., 2005). In a sham-controlled study (healthy participants, N=32), by combining anodal transcranial direct current stimulation (tDCS, 1.5 mA, 16 min) with a vision-touch interference task developed for studying mirror-touch synaesthesia (Banissy & Ward 2007), we show that the enhancement of cortical excitability in the primary somatosensory cortex promotes the emergence of synaesthesia-like effects even in non-synaesthetes. Interestingly, these effects are linked with inter-individual differences in cognitive aspects of empathy. Conversely, increasing excitability in the premotor cortex facilitates the integration of spatially congruent viewed and felt touches, without inducing synaesthesia-like effects; the crossmodal facilitation by premotor tDCS is not associated with empathy, thereby confirming the functional dissociation between somatosensory and premotor areas within the tactile mirror system. This evidence indicates that mirror-touch synaesthesia reflects general crossmodal mechanisms associated with emphatic abilities: by increasing the excitability of the tactile mirror system, synaesthesia-like responses may be revealed in non-synaesthetic individuals.

mirror-touch synaesthesia, tDCS