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The project described here encompasses two major studies assessing the association between individual differences using self-report questionnaires and self-other distinction indexed by the Imitation-Inhibition Task. The goals, hypothesis, and analysis plan for each study will be separately described, although data collection procedures were shared by both studies. More information about this project can be found at https://osf.io/mu8vr/. Study 1. The role of interoception in self-other distinction: What can it teach us about empathy and alexithymia? Palmer & Tsakiris (2018) proposed an explanatory model addressing the complex interaction between interoceptive accuracy, self-other distinction, and social cognitive performance. These authors argued that in social tasks requiring high levels of self-other distinction, subjects with high levels of interoceptive accuracy should display better performance as they are able to keep a more stable representation of their own bodily self. Conversely, in tasks where less self-other distinction is required (e.g., emotional contagion), subjects with low interoceptive accuracy may display enhanced performance. This model provides a valuable framework to test the associations between self-other distinction and individual differences in interoception, empathy, and alexithymia, constructs that have been widely associated with each other within the field. First, within this model, it would be expected that self-other distinction would be enhanced in subjects with high interoceptive accuracy. Secondly, we argue that the cognitive empathy domain requires higher self-other distinction, as this empathy domain often requires that people effectively represent mental states of others that are incongruent with their own mental states. Consequently, cognitive empathy would be positively associated with interoceptive accuracy, as observed in a previous sample collected by our research group (Campos, Barbosa, et al., 2020). Conversely, affective empathy may imply lower levels of self-other distinction, as we are required to effectively share an isomorphic affective state which is being experienced by others. Thus, it will be expected that affective empathy is negatively associated with interoceptive accuracy or unrelated to it, as observed in our previous work (Campos, Barbosa, et al., 2020). Finally, this model could also provide a valuable framework to examine the association between self-other distinction and alexithymia. Alexithymia has been consistently negatively associated with interoceptive (Trevisan et al., 2019). Hence, it would be expected a similar negative association between self-other distinction and alexithymia. Regardless of these hypotheses, several other questions and inconsistencies in the field also remain to be answered. For instance, Palmer & Tsakiris (2018) described the association between interoceptive accuracy and self-other distinction, but the recent 2 x 2 factorial framework to categorize individual differences in interoception argues that this construct can be clearly divided into two unrelated domains: interoceptive attention, the degree to which interoceptive signals are the object of attention; and interoceptive accuracy, the ability to accurately perceive interoceptive signals (Campos, Barbosa, et al., 2020; Campos, Murphy, et al., 2020; Gabriele et al., 2020; J. Murphy et al., 2019, 2020). Thus, it would be valuable to examine whether interoceptive attention and accuracy are differentially associated with self-other distinction. Another important issue is that we will be operationalizing self-other distinction using the Inhibitory-Imitation Task (Hogeveen et al., 2015). In this task, subjects are required to inhibit the motor representation of the other person’s movements and to enhance their self-generated motor representation to perform the task successfully. Previous data examining the association of imitation-inhibition (indexing self-other distinction) with empathy, interoception, and alexithymia does not seem to adequately fit the model proposed by Palmer & Tsakiris (2018), although there are some limitations to existing evidence. For instance, there is meta-analytical evidence suggesting that self-other distinction (index by imitation-inhibition) is not associated with either cognitive or affective empathy (Cracco et al., 2018). However, almost all studies included in this review used the Interpersonal Reactivity Index to measure empathy, a measure that has faced some criticism due to its poor psychometric proprieties (Chrysikou & Thompson, 2016; B. A. Murphy et al., 2020; B. A. Murphy & Lilienfeld, 2019; Wang et al., 2020). Thus, there is a need to further test the association of the Inhibitory-Imitation Task with cognitive and affective empathy, using a questionnaire that more adequately operationalizes these empathy domains. There is also evidence suggesting that self-other distinction (indexed by imitation-inhibition) is negatively associated with interoceptive accuracy (Ainley et al., 2014) and positively associated with alexithymia (Sowden et al., 2016), which would not be consistent with the premises proposed by Palmer & Tsakiris (2018). However, both these studies operationalized interoceptive accuracy using performance-based cardiac tasks which only provide information about one interoceptive modality. Thus, using a self-report interoceptive accuracy scale that assesses several interoceptive signals may provide valuable insights into the association between self-other distinction and interoception. In sum, Study 1 has the following main goals: - Examine the associations between self-other distinction (indexed by imitation-inhibition) and individual differences in interoceptive attention and accuracy, cognitive and affective empathy, and alexithymia. - Investigate whether the associations between self-other distinction and individual differences in interoception, empathy, and alexithymia are independent of broader inhibitory control abilities (indexed by non-imitative inhibitory control. - Explore the complex interplay between interoception, empathy, and alexithymia. Study 2. Self-other distinction across psychopathy dimensions: evidence from the Imitation-Inhibition Task Psychopathy is a multidimensional personality construct encompassing affective (e.g., callousness, lack of empathy) and interpersonal traits (e.g., deceitfulness, social dominance), as well as maladaptive manifestations closely related to antisocial behavior (e.g., disinhibition, impulsivity; (Hare & Neumann, 2008; Patrick et al., 2009). Currently, there are two major frameworks to measure psychopathy traits: (1) the classical 2-factors model, encompassing interpersonal-affective (Factor 1) and impulsive-antisocial features (Factor 2; Hare et al., 1990; Hare & Neumann, 2008). These broader factors can be further decomposed into four more specific facets (facet 1: interpersonal traits, facet 2: affective traits, facet 3: impulsive lifestyle, facet 4: antisocial behavior) without losing model fit (Hare & Neumann, 2008); (2) the more contemporary 3-dimensional models that cover both adaptive and maladaptive expressions of psychopath (Patrick et al., 2009). This model includes boldness-fearlessness traits, a dimension which maps positive adjustment indicators (e.g., low reactivity to stress, resilience, persuasion), meanness/cold-heartedness traits, encompassing attributes related to cruelty, insensitivity, deficient empathy, and contempt for close attachments with others, and disinhibition, referring to behavioral deficits in impulse control. Empathy is a fundamental process underpinning human interactions and is widely regarded as a hallmark of psychopathy. A recent meta-analysis by our research team found differential associations between empathy domains (cognitive and affective empathy) and the psychopathy dimensions preconized by the main theoretical models of psychopathy (Campos et al., 2021). However, there is still a need to understand which mechanisms may underlie the different empathic profiles observed across psychopathy dimensions. Recent social cognition models have highlighted the important role of self-other distinction in social behavior (Bird & Viding, 2014; Happé et al., 2017; Lamm et al., 2016; Palmer & Tsakiris, 2018), which can be an interesting candidate to explain the complex interaction between empathy and psychopathy dimensions. Individuals with high psychopathy traits display abnormal brain activation when instructed to take the “other perspective” on empathy for pain tasks (Decety et al., 2013). Conversely, these individuals display typical empathy-related brain activations when they are explicitly asked to empathize with others (Meffert et al., 2013), suggesting that psychopathy may be associated with a top-down self-other distinction mechanism that compensates for the absence of automatic emotional responses (Lamm et al., 2016) . However, there is still a need to refine the association between self-other distinction and psychopathy by contemplating the multidimensional nature of this personality construct. We argue that using the self-other distinction framework proposed by Palmer & Tsakiris (2018) it is feasible to hypothesize and test how psychopathy dimensions are related to self-other distinction, especially when considering their previously observed empathic profiles (Campos, Barbosa, et al., 2020; Campos et al., 2021). To accomplish this, we will operationalize self-other distinction using the Imitation-Inhibition task (Hogeveen et al., 2015). To our knowledge, there is only one study assessing the association between psychopathy traits and self-other distinction assessed by the Imitation-Inhibition task, that only presented results regarding the classical 2-factor structure (Genschow, Bardi, et al., 2019). Also, the Imitation-Inhibition task version that we will be using includes a non-imitative inhibitory control manipulation. There have been several studies assessing the association between inhibitory control and psychopathy traits, although findings are somewhat inconsistent for some psychopathy dimensions (Derefinko, 2015; Feilhauer et al., 2012; Pasion et al., 2018; Weidacker et al., 2017; Williams, 2020). However, examining the association of psychopathy with both imitation-inhibition (indexing self-other distinction) and non-imitative inhibitory control conditions will allow us to understand whether each psychopathy dimension is specifically associated with impaired or enhanced self-other distinction, or if these postulated deficits are likely related to general inhibitory control abilities. Thus, Study 2 has the following goals: - Examine the associations between self-other distinction (indexed by imitation-inhibition) and psychopathy traits operationalized using different conceptual frameworks (triarchic model, classical 2-factor models, 4 facets model). - Investigate whether the associations between self-other distinction and psychopathy are independent or not from broader inhibitory control abilities (indexed by non-imitative inhibitory control). - Explore the complex interplay between psychopathy, empathy, interoception, and alexithymia.

Lesions to brain regions such as the temporoparietal junction (TPJ) and inferior frontal cortex (IFC) are thought to cause autism-spectrum disorder (ASD). Previous studies indicated that transcranial direct current stimulation (tDCS) of the right TPJ improves social cognitive functions such as imitation-inhibition and perspective-taking. Although previous work shows that tDCS of the right IFC improves imitation-inhibition, its effects on perspective-taking have yet to be determined. In addition, the role of the TPJ and IFC in determining the Autism-Spectrum Quotient (AQ), which is a measure of autism spectrum traits, is still unclear. Thus, the current study performed tDCS on the right TPJ and the right IFC of healthy adults, and examined its effects on imitation-inhibition, perspective-taking, and AQ scores. Based on previous studies, we hypothesized that anodal tDCS of the right IFC and right TPJ would improve imitation-inhibition, perspective-taking, and the AQ score. Anodal tDCS of the right TPJ or IFC significantly decreased the interference effect in an imitation-inhibition task and the cost of perspective-taking in a perspective-taking task, in comparison to the sham stimulation control. These findings indicated that both the TPJ and the IFC play a role in imitation-inhibition and perspective-taking, i.e. control of self and other representations. However, anodal stimulation of the right TPJ and the right IFC did not alter participants’ AQ. This finding conflicts with results from previous brain imaging studies, which could be attributed to methodological differences such as variation in sex, age, and ASD. Therefore, further research is necessary to determine the relationship between the TPJ and IFC, and the AQ.

Alexithymia is a subclinical condition traditionally characterized by difficulties identifying and describing one's own emotions. Recent formulations of alexithymia, however, suggest that the condition may result from a generalized impairment in the perception of all bodily signals ("interoception"). Interoceptive accuracy has been associated with a variety of deficits in social cognition, but recently with an improved ability to inhibit the automatic tendency to imitate the actions of others. The current study tested the consequences for social cognition of the hypothesized association between alexithymia and impaired interoception by examining the relationship between alexithymia and the ability to inhibit imitation. If alexithymia is best characterized as a general interoceptive impairment, then one would predict that alexithymia would have the same relationship with the ability to control imitation as does interoceptive accuracy. Forty-three healthy adults completed measures of alexithymia, imitation-inhibition, and as a control, inhibition of nonimitative spatial compatibility. Results revealed the predicted relationship, such that increasing alexithymia was associated with an improved ability to inhibit imitation, and that this relationship was specific to imitation-inhibition. These results support the characterization of alexithymia as a general interoceptive impairment and shed light on the social ability of alexithymic individuals-with implications for the multitude of psychiatric, neurological, and neurodevelopmental disorders associated with high rates of alexithymia. (PsycINFO Database Record