Direct skin-to-skin versus indirect touch modulates neural responses to stroking versus tapping

It remains unclear whether direct interpersonal contact is processed differently from similar soft touch applied through inanimate objects. We performed a functional MRI experiment in healthy volunteers, whereby activity during gentle stroking or tapping was compared between stimuli delivered using the experimenter's hand or a velvet stick. Stroking with a hand elicited larger responses than the other three conditions in the contralateral primary and secondary somatosensory areas and in the posterior insula. The observed effects likely originate from a combination of perceptual differences and cognitive and emotional correlates of contact with another person. This empirical observation indicates that, to ensure ecological validity, studies of affective touch processing should be performed with stimuli delivered with direct interpersonal contact rather than inanimate objects.