Functional magnetic resonance imaging (fMRI) studies have demonstrated changes in the processing of both social and non-social reward stimuli in autism spectrum disorder (ASD). A new study, supported in part by an Explorer Award to SFARI Investigator Vanessa Troiani, demonstrates that analysis of pupil diameter can serve as a simpler measure of both reward sensitivity and ASD diagnostic status.

Changes in reward processing in ASD are thought to play a part in both the social features and the restricted and repetitive behaviors seen in ASD. Yet the rigors of an fMRI study have made it difficult to assess individuals with more severe forms of ASD, limiting our understanding of the specific ways in which alterations in reward processing may underlie core ASD features. In contrast, analyses of baseline pupil diameter and changes in pupil constriction are simple to perform and represent accepted biomarkers of arousal and motivation, reflecting locus coeruleus-norepinephrine effects on the autonomic nervous system. Pupil size is influenced by arousal state, attention and cognitive effort, including reward-based cognitive tasks.

Differences in pupil size have also been linked to clinical features of ASD. Troiani’s laboratory previously demonstrated that individual differences in pupil dilation patterns, in response to a simple alternating light-dark stimulus, are quantitatively associated with ASD traits (DiCriscio & Troiani, Sci. Rep., 2017). In addition, group-level differences in baseline pupil diameter, that appear to correlate with levels of norepinephrine, are predictive of ASD status (Anderson & Colombo, Dev. Psychobiol.,2009; Anderson et al., Dev. Psychobiol., 2013).

In the current study, Troiani and colleagues examined whether pupil size and pupil changes are associated with sensitivity to reward and punishment, and whether this also relates to individual differences in ASD clinical features. Using two questionnaire-based parental reports of reward/punishment sensitivity, the group assessed the relationship between reward/punishment behaviors and ASD diagnosis. The group also assessed resting pupil diameter and functional pupil responses in a passive eye-tracking task. The study was performed in children ranging in age from 5–14, both with a clinical ASD diagnosis and without.

Troiani’s group found a significant and linear relationship between reward/punishment sensitivity, individual differences in ASD diagnosis, and both resting and functional pupil responses. In particular, measures of pupil dilation during dark adaptation could be quantitatively substituted for parental reports of reward/punishment sensitivity in a regression model, supporting a linear relationship between pupil dilation, reward/punishment sensitivity and individual ASD diagnostic status.

These findings provide further evidence that changes in reward processing are linked to ASD behavioral presentations. Future studies, using even larger numbers of individuals and more refined clinical diagnoses, will help to further clarify the relationship between reward processing, pupil measures and clinical presentation across neurodevelopmental disorders. This work, along with prior individual-differences analyses from the Troiani laboratory (DiCriscio & Troiani, Sci. Rep., 2017), also suggests that variability in pupil responses could serve as an accessible, and clinically useful, measure of ASD traits.