Quantifying age-related changes in mirror overflow in children and adolescents with attention-deficit/hyperactivity...

Children with attention-deficit/hyperactivity disorder (ADHD) show excessive mirror overflow (particularly in the nondominant hand); however, patterns of age-related decrease of overflow remain unclear. This study aimed to quantify age-related changes in mirror overflow in youth with and without ADHD.

Average mirror overflow was examined during left-hand finger tapping (LHFT; nondominant finger tapping) and right-hand finger tapping (RHFT; dominant finger tapping) using electronic finger twitch transducers in a cross-sectional sample of youth with ADHD (n = 77) and typically developing (TD) youth (n = 75) ages 8-18 years. Effects of age and ADHD diagnosis on LHFT, RHFT, and a summed "total" overflow (TOF) across hands were examined across the sample age range and within childhood (8-12 years) and adolescence (13-18 years).

ADHD youth showed a decrease in overflow with age, including a large effect for TOF, with a very large age effect for LHFT but a more moderate age effect for RHFT. TD youth showed a moderate decrease in overflow with age for TOF, with a large decrease for LHFT but no significant decrease for RHFT. Additionally, we found that large effects of ADHD-related excessive overflow in childhood diminished in adolescence.

Findings suggest that mirror overflow in ADHD youth diminishes into adolescence but does not resolve completely, suggesting ADHD-associated increased mirror overflow may reflect both a developmentally resolving effect and a somewhat persistent atypicality. Future studies with larger and longitudinal samples would provide additional insight into mechanisms contributing to excessive mirror overflow and its relationship to both clinical and neurobiological aspects of ADHD-associated disinhibition.