Toward a Unified Social Motor Cognition Theory of Understanding Mirror-Touch Synaesthesia

Mirror-touch synaesthesia (MTS) is a conscious tactile sensation in the observer when watching somebody else being touched. Two disparate theories have been suggested to explain MTS. The threshold theory links MIS to hyper-activity in the parietal-frontal mirror neuron system, while the self-other theory attributes MIS to impaired self-other representations in temporal parietal junction (TPJ) and medial prefrontal cortex (mPFC). Here, I propose that these two theories can be synthesized under a unified social motor cognition theory which states that action observation engages two complementary levels of cognitive processing: a lower-level, physical process regarding basic sensory-motor aspects of the action, which supports motor imitation and goal understanding, and an abstract mental level concerning attribution of mental states, which supports interring others' minds and self-other distinctions. While the physical process preferentially recruits the mirror neuron system, the mental process depends critically on the mentalizing network comprised of TPJ and mPFC. Importantly, despite of these anatomical and functional dissimilarities, the mirroring and mentalizing processes involve shared predictive coding, which is a general computational principle for a wide range of prominent concepts in motor cognition.