EEG-Indexed Conditional Salience Processing Mediates the Relationship between ASD Symptom Severity and Theory of Mind

Background: Theory of Mind (ToM) reasoning involves making attributions about others’ mental states and is critical for competent social functioning. Although impairments in ToM are a common feature of autism spectrum disorder (ASD; Baron-Cohen, 2001), individual differences in ToM ability exist across ASD (White et al., 2014), and do not consistently vary by ASD symptom severity. Such heterogeneity suggests upstream individual differences in the recruitment of neural mechanisms necessary for ToM reasoning. However, no research has examined whether individual differences in the association between ASD symptom severity and behavioral performance on ToM tasks are attributable to specific neurocognitive components. Two distinct event-related potentials (ERPs) have been elicited during ToM tasks in typically developing (TD) youth (Meinhardt, et al. 2011); the Late Positive Complex (LPC), associated with automatic processing of conditional salience, and the Late Slow Wave (LSW), related to making mental state attributions. It is essential to examine these neurocognitive components in conjunction with ASD symptom severity to understand whether they may account for variability in ToM deficits in youth with ASD.

Objectives: Investigate whether LPC and LSW are elicited in youth with and without ASD during a ToM task. Explore whether magnitude of the difference between ERPs elicited to correct vs. incorrect conditions is associated with ToM accuracy and ASD symptom severity.

Methods: Participants were 76 adolescents (47 ASD, 54 male) ages 11-17 (M_age=13.0, SD_age=1.8) with IQ ≥ 70. ASD symptom severity was measured using the ADOS-2 Calibrated Severity Score (CSS) in all participants. During EEG acquisition, participants viewed illustrated, narrated ToM vignettes and were asked to make mental state inferences about characters’ behavior (McKown et al., 2015). ERPs were time-locked to the presentation of correct and incorrect response options, measured at parietal electrode sites, and extracted as mean area amplitudes within post-stimulus time windows (LPC 300-600ms; LSW 600-1200ms). Residualized scores were calculated to index the difference between ERPs elicited to correct vs. incorrect conditions. Pearson correlations were used to assess the relationship between ERP residualized scores, ToM accuracy, and ADOS-2 CSS. Bootstrapped mediation analyses were performed to assess whether these components may explain the relationship between ToM accuracy and ADOS-2 CSS.

Results: LPC and LSW residualized scores correlated with ToM behavioral accuracy and ADOS-2 CSS (Table 1). Mediation analyses revealed LPC (but not LSW) partially mediates the relationship between ADOS CSS and ToM accuracy with a medium effect size (Figure 1).

Conclusions: Results show the LPC and LSW are elicited to a novel ToM EEG task in TD and ASD adolescents. ERPs were associated with ADOS-2 CSS and ToM in opposite directions. This suggests the ASD group may rely on compensatory neurocognitive mechanisms to engage in ToM, resulting in attenuated discrimination between ToM conditions. Furthermore, although ToM performance is related to ASD symptom severity, mediation analysis revealed that this relationship disappears when LPC magnitude is taken into account. Therefore, automatic processing of conditional salience during active ToM reasoning partially explains the relationship between ASD severity and individual differences in ToM ability in adolescents with and without ASD.