title: Sharing social touch in the primary somatosensory cortex.
abstract: Touch has an emotional and communicative meaning, and it plays a crucial role in social perception and empathy. The intuitive link between others' somatosensations and our sense of touch becomes ostensible in mirror-touch synesthesia, a condition in which the view of a touch on another person's body elicits conscious tactile sensations on the observer's own body [1]. This peculiar phenomenon may implicate normal social mirror mechanisms [2]. Here, we show that mirror-touch interference effects, synesthesia-like sensations, and even phantom touches can be induced in nonsynesthetes by priming the primary somatosensory cortex (SI) directly or indirectly via the posterior parietal cortex. These results were obtained by means of facilitatory paired-pulse transcranial magnetic stimulation (ppTMS) contingent upon the observation of touch. For these vicarious effects, the SI is engaged at 150 ms from the onset of the visual touch. Intriguingly, individual differences in empathic abilities, assessed with the Interpersonal Reactivity Index [3], drive the activity of the SI when nonsynesthetes witness others' tactile sensations. This evidence implies that, under normal conditions, touch observation activates the SI below the threshold for perceptual awareness [4]; through the visual-dependent tuning of SI activity by ppTMS, what is seen becomes felt, namely, mirror-touch synesthesia. On a broader perspective, the visual responsivity of the SI may allow an automatic and unconscious transference of the sensation that another person is experiencing onto oneself, and, in turn, the empathic sharing of somatosensations [2].
authors: Department of Psychology, University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy; Laboratory of Neuropsychology, IRCCS Istituto Auxologico Italiano, Via Mercalli 32, 20122 Milano, Italy. Electronic address: nadia.bolognini@unimib.it.
authors: Nadia
authors: N
authors: Bolognini
authors: Department of Psychology, University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy; Laboratory of Neuropsychology, IRCCS Istituto Auxologico Italiano, Via Mercalli 32, 20122 Milano, Italy.
authors: Angela
authors: A
authors: Rossetti
authors: Department of Psychology, University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy.
authors: Martina
authors: M
authors: Fusaro
authors: Department of Psychology, University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy; Laboratory of Neuropsychology, IRCCS Istituto Auxologico Italiano, Via Mercalli 32, 20122 Milano, Italy.
authors: Giuseppe
authors: G
authors: Vallar
authors: Department of Clinical and Experimental Sciences, University of Brescia, Viale Europa 11, 25123 Brescia, Italy; Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Via Pilastroni 4, 25125 Brescia, Italy.
authors: Carlo
authors: C
authors: Miniussi
mesh_terms: D006801:Humans; D059167:Mirror Neurons / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology; D010468:Perceptual Disorders / Q000503:physiopathology*; D010775:Photic Stimulation; D013003:Somatosensory Cortex / Q000502:physiology*; D000080311:Synesthesia; D014110:Touch / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation