Sex Effects on Mirror Overflow during Finger Tapping in Children with ADHD

Abstract

Objectives: The presence of excessive mirror overflow in children with Attention Deficit/Hyperactivity Disorder (ADHD) is discussed in numerous published reports. These reports, however, include a limited age range in their samples. The objective of this study is to examine the effects of diagnosis and sex on mirror overflow and standard deviation (SD) of tap time in children with and without ADHD across a larger age range (5-12 years) of children.

Methods: One-hundred and forty-eight children with ADHD and 112 age- and sex-matched typically developing (TD) children completed a finger sequencing task. Mirror overflow, SD of tap time, and mean tap time were measured using finger twitch transducers.

Results: Results reveal a significant diagnostic effect on mirror overflow such that boys and girls with ADHD demonstrate increased overflow compared to same-sex TD children. Boys with ADHD demonstrated more variable tap times compared to TD boys; no diagnostic effect was observed in the girls.

Conclusions: Boys with ADHD exhibit anomalous motor variability; girls with ADHD show similar levels of variability as TD girls. Boys and girls with ADHD exhibit similar levels of excessive mirror overflow. This lack of sex differences on mirror overflow is distinct from reports finding sex effects on overflow and could result from an examination of a broader age range than is included in prior reports. Adolescent data would provide a greater understanding of the trajectory of anomalous mirror overflow across development. Examination of functional and structural connectivity would expand the current understanding of the neurobiological foundation of motor overflow.

Keywords: Child developmental disorder; Developmental disabilities; Motor skills; Preschool children; Psychomotor performance; School-age population.

Figures

Figure 1:

(A) Finger twitch transducers affixed over the metacarpopholangeal joint of the index and ring fingers with tape and Velcro straps. (B) Finger twitch transducer data collected in AcqKnowledge software during left hand finger sequencing. The left finger channels show sequential tapping movements; the right finger channels show mirror overflow movements.

Figure 2:

Both children with ADHD and TD control children show significant correlations between age and total overflow (ADHD: r = −.375, p < .0001; TD: r = −.610, p < .0001), mean tap time (ADHD: r = −.453, p < .0001; TD: r = −.537, p < .0001), and standard deviation of tap time (ADHD: r = −.453, p < .0001; TD: r = −.430, p < .0001). These associations suggest that as children age between 5–12 years old tap speed, tap variability, and mirror overflow decrease.

Figure 3:

Boys with ADHD show more total overflow than their TD peers, F(1, 172)=9.2, p=.003, np2 =.035. Girls with ADHD show a trend for more total overflow than their TD peers, F(1, 84)=3.8, p=.052, np2 =.015. Boys with ADHD exhibit longer mean tap times than their TD peers, F(1, 172)=4.9, p=.028, np2 =.019. Girls with ADHD do not exhibit longer mean tap times than their TD peers, F(1, 84)=0.4, p=.538, np2 =.002. Boys with ADHD demonstrate more variable tap times compared to TD boys, F(1, 172)=17.1, p<.001, np2 =.063, whereas girls with ADHD do not, F(1, 84)<0.01, p=.942, np2 <.001.

Figure 4.

Standard deviation of tap times at the mean age and one standard deviation above and below the mean age within sex and diagnosis. This Diagnosis*Sex interaction does not moderate the relationship between age and standard deviation of tap time (p=.150).