The temporoparietal junction (TPJ) is a key node within the "social brain". Several studies suggest that the TPJ controls representations of the self or another individual across a variety of low-level (agency discrimination, visual perspective taking, control of imitation) and high-level (mentalizing, empathy) sociocognitive processes. We explored whether sociocognitive abilities relying on on-line control of self and other representations could be modulated with transcranial direct current stimulation (tDCS) of TPJ. Participants received excitatory (anodal), inhibitory (cathodal), or sham stimulation before completing three sociocognitive tasks. Anodal stimulation improved the on-line control of self-other representations elicited by the imitation and perspective-taking tasks while not affecting attribution of mental states during a self-referential task devoid of such a requirement. Our findings demonstrate the efficacy of tDCS to improve social cognition and highlight the potential for tDCS to be used as a tool to aid self-other processing in clinical populations.

Previous studies using the dot perspective task have shown that adults are slower to verify the number of dots they can see in a picture when a human figure in the picture, an avatar, can see a different number of dots. This "self-consistency effect," which occurs even when the avatar's perspective is formally task-irrelevant, has been interpreted as evidence of implicit mentalizing; that humans can think about the mental states of others via dedicated, automatic processes. We tested this interpretation by giving participants 2 versions of the dot perspective task. In some trials, the avatar was presented as in previous experiments, and in other trials the avatar was replaced by an arrow with similar low-level features. We found self-consistency effects of comparable size in the avatar and arrow conditions, suggesting that self-consistency effects in the dot perspective task are due to domain-general processes such as those that mediate automatic attentional orienting.

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Although neuroimaging studies have consistently identified the temporoparietal junction (TPJ) as a key brain region involved in social cognition, the literature is far from consistent with respect to lateralization of function. For example, during theory‐of‐mind tasks bilateral TPJ activation is found in some studies but only right hemisphere activation in others. Visual perspective‐taking and imitation inhibition, which have been argued to recruit the same socio‐cognitive processes as theory of mind, are associated with unilateral activation of either left TPJ (perspective taking) or right TPJ (imitation inhibition). The present study investigated the functional lateralization of TPJ involvement in the above three socio‐cognitive abilities using transcranial direct current stimulation. Three groups of healthy adults received anodal stimulation over right TPJ, left TPJ or the occipital cortex prior to performing three tasks (imitation inhibition, visual perspective‐taking and theory of mind). In contrast to the extant neuroimaging literature, our results suggest bilateral TPJ involvement in imitation inhibition and visual perspective‐taking, while no effect of anodal stimulation was observed on theory of mind. The discrepancy between these findings and those obtained using neuroimaging highlight the efficacy of neurostimulation as a complementary methodological tool in cognitive neuroscience.

The control of neurological networks supporting social cognition is crucially important for social interaction. In particular, the control of imitation is directly linked to interaction quality, with impairments associated with disorders characterized by social difficulties. Previous work suggests inferior frontal cortex (IFC) and the temporoparietal junction (TPJ) are involved in controlling imitation, but the functional roles of these areas remain unclear. Here, transcranial direct current stimulation (tDCS) was used to enhance cortical excitability at IFC and the TPJ prior to the completion of three tasks: (i) a naturalistic social interaction during which increased imitation is known to improve rapport, (ii) a choice reaction time task in which imitation needs to be inhibited for successful performance and (iii) a non-imitative control task. Relative to sham stimulation, stimulating IFC improved the context-dependent control of imitation—participants imitated more during the social interaction and less during the imitation inhibition task. In contrast, stimulating the TPJ reduced imitation in the inhibition task without affecting imitation during social interaction. Neither stimulation site affected the non-imitative control task. These data support a model in which IFC modulates imitation directly according to task demands, whereas TPJ controls task-appropriate shifts in attention toward representation of the self or the other, indirectly impacting upon imitation.

In the director task (DT), participants are instructed to move objects within a grid of shelves while ignoring those objects that cannot be seen by a human figure, the "director," located beyond the shelves. It is widely assumed that, since they are explicitly instructed to do, participants use mentalizing in this communicative task; they represent what the director can see, and therefore the DT provides important information about how and when mentalizing is used in adult life. We tested this view against a "submentalizing" hypothesis suggesting that DT performance depends on object-centered spatial coding, without mentalizing. As predicted by the submentalizing account, we found that DT performance was unchanged when the director was replaced by an inanimate object, a camera, and that participants with autism spectrum disorders were unimpaired, relative to matched control participants, in both the director and camera conditions. In combination with recent critical analyses of "implicit mentalizing," these findings support the view that adults use mentalizing sparingly in psychological experiments and in everyday life.

Mentalizing is a fundamental process underpinning human social interaction. Claims of the existence of 'implicit mentalizing' represent a fundamental shift in our understanding of this important skill, suggesting that preverbal infants and even animals may be capable of mentalizing. One of the most influential tasks supporting such claims in adults is the dot perspective-taking task, but demonstrations of similar performance on this task for mentalistic and non-mentalistic stimuli have led to the suggestion that this task in fact measures domain-general processes, rather than implicit mentalizing. A mentalizing explanation was supported by fMRI data claiming to show greater activation of brain areas involved in mentalizing, including right temporoparietal junction (rTPJ), when participants made self-perspective judgements in a mentalistic, but not in a non-mentalistic condition, an interpretation subsequently challenged. Here we provide the first causal test of the mentalizing claim using disruptive transcranial magnetic stimulation of rTPJ during self-perspective judgements. We found no evidence for a distinction between mentalistic and non-mentalistic stimuli: stimulation of rTPJ impaired performance on all self-perspective trials, regardless of the mentalistic/non-mentalistic nature of the stimulus. Our data support a domain-general attentional interpretation of performance on the dot perspective-taking task, a role which is subserved by the rTPJ.

Individuals with mirror touch synaesthesia (MTS) experience touch on their own body when observing others being touched. A recent account proposes that such rare experiences could be linked to impairment in self-other representations.Here we tested participants with MTS on a battery of social cognition tests and found that compared to non-synaesthete controls, the MTS group showed impairment in imitation-inhibition but not in visual perspective taking or theory of mind. Although all of these socio-cognitive abilities rely on the control of selfother representations, they differ as to whether the self, or the other, should be preferentially represented. For imitation-inhibition, representations of the other should be inhibited and self-representations should be enhanced, whereas the opposite is true for visual perspective taking and theory of mind. These findings suggest that MTS is associated with a specific deficit in inhibiting representation of other individuals and shed light on the fractionability of processes underlying typical social cognition.