Background: The Social Motivation Theory proposes that social reward processing differences underlie autism. However, low social motivation has also been linked to higher anxiety. Given the co-occurrence between autism and anxiety, it is possible that anxiety drives the association between social motivation and autistic characteristics. This study tests the mechanisms underlying the association between social motivation and autistic traits.

Methods: Participants were 165 adolescents (71 male), aged 10-16 years, from the Mapping profiles of cognition, motivation and attention in childhood (C-MAPS) study, enriched for autistic traits (70 participants with an autism diagnosis, 37 male). Participants completed a battery of online experimental tasks, including a Choose-a-Movie social motivation task and social cognition measures (theory of mind; emotion recognition), alongside parent-reported child anxiety and autistic traits.

Results: Higher social motivation was significantly associated with lower autistic traits (β = -.26, p < .001). Controlling for social cognition did not change the association between social motivation and autistic traits. Controlling for anxiety did significantly reduce the strength of the association (unstandardized coefficient change: p = .003), although social motivation remained associated with autistic traits (β = -.16, p = .004). Post hoc analyses demonstrated differential sex-effects: The association between social motivation and autistic traits was significant only in the females (β = -.38, p < .001), as was the attenuation by anxiety (unstandardized coefficient change: p < .001).

Conclusions: The association between social motivation and autistic traits could be partially attributed to co-occurring anxiety. Sex-specific effects found in females may be due to environmental factors such as increased social demands in adolescent female relationships. Results are consistent with self-report by autistic individuals who do not identify as having reduced social motivation.