Quantifying excessive mirror overflow in children with attention-deficit/hyperactivity disorder

Abstract

Objectives: Qualitative observations have revealed that children with attention-deficit/hyperactivity disorder (ADHD) show increased overflow movements, a motor sign thought to reflect impaired inhibitory control. The goal of this study was to develop and implement methods for quantifying excessive mirror overflow movements in children with ADHD.

Methods: Fifty right-handed children aged 8.2-13.3 years, 25 with ADHD (12 girls) and 25 typically developing (TD) control children (10 girls), performed a sequential finger-tapping task, completing both left-handed (LHFS) and right-handed finger sequencing (RHFS). Phasic overflow of the index and ring fingers was assessed in 34 children with video recording, and total overflow in 48 children was measured by calculating the total angular displacement of the index and ring fingers with electrogoniometer recordings.

Results: Phasic overflow and total overflow across both hands were greater in children with ADHD than in TD children, particularly during LHFS. Separate gender analyses revealed that boys, but not girls, with ADHD showed significantly more total phasic overflow and total overflow than did their gender-matched control children.

Conclusions: The quantitative overflow measures used in this study support past qualitative findings that motor overflow persists to a greater degree in children with ADHD than in age-matched TD peers. The quantitative findings further suggest that persistence of mirror overflow is more prominent during task execution of the nondominant hand and reveal gender-based differences in developmental neural systems critical to motor control. These quantitative measures will assist future physiologic investigation of the brain basis of motor control in ADHD.

Figure 1. Goniometers

(A) Goniometers attached with tape and Velcro to index and ring fingers. (B) Goniometer angle measurement of the metacarpophalangeal (MCP) joint. (C) Goniometer data recorded in AcqKnowledge Software during right-handed finger sequencing.

Figure 2. Laterality of overflow measures

Means and SE for phasic overflow (typically developing [TD] group, n = 17; attention-deficit/hyperactivity disorder [ADHD] group, n = 17) during left-handed finger sequencing (LHFS) (A) and right-handed finger sequencing (RHFS) (B) and total overflow (TD, n = 24; ADHD, n = 24) during LHFS (C) and RHFS (D). Children with ADHD exhibited more phasic (A, **p = 0.006) and total (C, *p = 0.01) overflow than TD children during LHFS, but not during RHFS (B, D).

Figure 3. Overflow measures by diagnosis within gender groups

Means and SE for phasic overflow (typically developing [TD] group, n = 17, 7 girls; attention-deficit/hyperactivity disorder [ADHD] group, n = 17, 7 girls) across both hands and total overflow (TD group, n = 24, 9 girls; ADHD group, n = 24, 11 girls) across both hands. Boys with ADHD exhibited more phasic (*p = 0.01) and total (*p = 0.02) overflow than TD boys, but there were no differences between girls with ADHD and TD girls.