Modifiable Arousal in ADHD and its Etiological Association with Fluctuating Reaction Times

Background: Cognitive theories of attention-deficit/hyperactivity disorder (ADHD) propose that high within-subject fluctuations of cognitive performance in ADHD, particularly reaction time (RT) variability (RTV), may reflect arousal dysregulation. Yet, direct evidence of arousal dysregulation and how it may account for fluctuating reaction times in ADHD is limited. We used skin conductance (SC) as a measure of peripheral arousal and aimed to investigate its phenotypic and familial association with RTV in a large sample of ADHD and control sibling pairs. Methods: 292 adolescents and young adults, consisting of 73 participants with ADHD and their 75 siblings, as well as 72 controls and their 72 siblings, completed the baseline (slow, unrewarded) and fast-incentive conditions of a RT task, whilst SC was simultaneously recorded. Results: A significant group by condition interaction emerged for SC level (SCL). Participants with ADHD had decreased SCL, compared to controls, in the baseline but not fast-incentive condition. Baseline SCL was negatively associated with RTV and multivariate model fitting demonstrated that the covariance of SCL with RTV, and of SCL with ADHD, was mostly explained by shared familial effects. Conclusions: ADHD is associated with decreased, but modifiable, tonic peripheral arousal. A shared familial etiology underlies the relationship between arousal and RTV, and between arousal and ADHD. Given the malleability of SCL, if our findings are replicated, it warrants further exploration as a potential treatment target for ADHD.