ORBITOFRONTAL EXECUTIVE FUNCTIONS AND ADHD SYMPTOM SEVERITY: MODERATING EFFECTS OF MORNING CORTISOL AND AGE

Executive functions (EFs) and hypothalamic-pituitary-adrenal axis activity alterations have each been implicated in the aetiology of Attention-Deficit/Hyperactivity Disorder (ADHD). This study examined whether morning cortisol levels and age moderate the relationship between orbitofrontal EFs and ADHD symptom severity. 124 children (aged 8-17 years) and 114 adults (aged 18-24 years) completed ADHD symptom questionnaires (Conners-4 or ASRS), underwent assessment using orbitofrontal tasks from the BANFE battery, and provided salivary cortisol samples: immediately upon waking and 30 minutes after. Moderation models were tested, examining age and cortisol (waking, 30 min after, and cortisol awakening response) as moderators of the relationship between EFs and ADHD symptom severity. The model using waking cortisol showed the best fit, explaining 7% of the variance in ADHD symptoms (R² = 0.07, F(5, 224) = 3.38, p = .0058). Orbitofrontal scores on their own were not associated with symptom severity, but their interaction with morning cortisol was (ΔR² = .029, F(1, 224) = 6.91, p = .009). Age did not act as a significant independent moderator; however, its inclusion improved model fit. Conditional effects revealed a negative association between orbitofrontal scores and ADHD symptom severity when morning cortisol was low in adults, whereas this relationship was positive for children and adolescents with high cortisol. This suggests that the relationship between orbitofrontal EFs and ADHD is moderated by morning cortisol levels and likely shifts with age. As the orbitofrontal cortex and related circuits mature, emerging executive capacities may act as compensatory mechanisms that mitigate symptom expression and morning hypoarousal.