The Role of Personality in Shaping Neural Processes Associated with Theory of Mind

Personality accounts for a significant amount of individual differences in people’s academic and life outcomes. In my dissertation, I focused on agreeableness, a personality trait from the Five Factor Model describing individual differences in altruism, empathy, and Theory of Mind (ToM) (Allen et al., 2017). Thus, my primary aim was to investigate whether and how agreeableness might modulate social and emotional processes associated with ToM in the general population and in young adults with Autism Spectrum Disorder (ASD) without language and intellectual impairments. All these aspects are introduced in Chapter 1 of my thesis, while the original experimental studies are described in the following Chapters (2-5). In Chapter 2, I report an fMRI study (Study 1) exploring whether neural variations during social content encoding are related to differences in agreeableness by assessing the degree of similarity between patterns of activation for social and non-social content across individuals. Results suggested that more agreeable individuals encode social and non-social information more distinctively compared with less agreeable individuals, whose encoding of the two contents is more similar in the dorso-medial prefrontal cortex (dmPFC), a brain region typically linked with ToM abilities (Saxe and Baron-Cohen, 2006). This result suggests that individual differences in agreeableness are associated with differences in processing social information. Based on this finding, I developed three studies that aimed at characterizing the neural correlates of agreeableness and different aspects of ToM by means of electroencephalography (EEG). This approach allowed me to identify at which stage of the neural processing agreeableness kicks in, in order to distinguish the impact on early, perceptual processes from slower, inferential processing. Since ToM involves distinct processes, I first set out to investigate the social (Study 2) and emotional dimensions (Study 3) separately; then I examined the same processes within a group of individuals within the autism spectrum (Study 4). Thus Chapter 3 contains Study 2 in which I assessed the impact of agreeableness on social interaction perception. Results revealed agreeableness allows a deeper processing of social stimuli compared to non-social ones, mainly in fronto-parietal areas. This relatively early effect in the whole sample and in females was more massive and extensive in males and translated into behavior as a tendency towards a better ability to discriminate social interactions. Chapter 4 contains Study 3 in which I investigated the modulation of agreeableness on the decoding of emotional cues by means of two tasks with different degrees of complexity spanning from the perception of basic emotional actions to the recognition of complex mental states. Results showed that agreeableness affects brain’s activity only during mental state decoding in male participants, mainly involving the ventro-mPFC, while in females this modulation seems to be negligible. Study 4, in Chapter 5, investigates the personality of young adults with ASD without language and intellectual impairment, and whether agreeableness might differentially modulate the same neural processes investigated in the previous two EEG studies in this population. This investigation underscored that while young adults with this diagnosis may exhibit lower scores in all the five traits, they do not uniformly fall into the extreme ends of all personality dimensions. Results further highlighted the role of agreeableness in shaping socio-emotional processing, particularly in the context of ToM tasks. Notably, ASD individuals showcased a capacity for compensatory mechanisms, achieving behavioral performance akin to less agreeable healthy controls despite differences in neural responses. Overall, the findings of my thesis advance our understanding of the neural determinants of agreeableness and its significance in the social domain. This has potential implications for clinical interventions by tailoring treatments to individual variations, thus enhancing effective therapeutic strategies. In the final Chapter 6, I contextualize these findings within the existing literature and I discuss their implications.