AGE-RELATED CHANGES IN MOTOR SUBTLE SIGNS AMONG GIRLS AND BOYS WITH ADHD

Abstract

Neuroanatomic structures involved in voluntary control of motor skills show substantial growth, elaboration, and myelination during early childhood.1 Developmental changes in motor control include improvements in speed as well as reduced frequency of “subtle signs,” such as overflow and dysrhythmia. Motor overflow refers to presence of involuntary movements that accompany the production of voluntary movements,2 and has been linked to impaired inhibitory control.3 Dysrhythmia involves improper timing or rhythm during controlled movements. While it is common to observe subtle signs in typically developing children younger than age 10,4 most basic motor skills are mastered by age 6 or 7,5 and persistence of subtle signs into late childhood and adolescence can indicate atypical neurologic development.6,7 The majority of studies examining atypical motor development in attention-deficit hyperactivity disorder (ADHD) have included predominantly male samples, with fewer studies exploring whether similar patterns emerge among girls with ADHD. Studies examining motor skills in typically developing children have shown sex-specific patterns, with girls maturing earlier than boys,8 a finding consistent with trajectories of brain development identified via neuroimaging.9 The purpose of this study was to examine differences in age-related changes in motor speed and subtle signs in boys and girls with and without ADHD. While typically developing children were hypothesized to show improvement with age in motor skills, children with ADHD were hypothesized to show fewer age-related improvements. Further, the inclusion of both boys and girls with ADHD in this study allows us to determine if sex-specific differences observed in brain development are also present within ADHD.