Objective: Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset behavioral diagnosis in which children often fail to meet age norms in development of motor control, particularly timed repetitive and sequential movements, motor overflow, and balance. The neural substrate of this motor delay may include mechanisms of synaptic inhibition in or adjacent to the motor cortex. The primary objective of this study was to determine whether transcranial magnetic stimulation (TMS)-evoked measures, particularly short interval cortical inhibition (SICI), in motor cortex correlate with the presence and severity of ADHD in childhood as well as with commonly observed delays in motor control. Methods:In this case-control study, behavioral ratings, motor skills, and motor cortex physiology were evaluated in 49 children with ADHD (mean age 10.6 years, 30 boys) and 49 typically developing children (mean age 10.5 years, 30 boys), all right-handed, aged 8-12 years. Motor skills were evaluated with the Physical and Neurological Examination for Subtle Signs (PANESS) and the Motor Assessment Battery for Children version 2. SICI and other physiologic measures were obtained using TMS in the left motor cortex. Results:In children with ADHD, mean SICI was reduced by 40% (p Ͻ 0.0001) and less SICI correlated with higher ADHD severity (r ϭ Ϫ0.52; p ϭ 0.002). Mean PANESS motor development scores were 59% worse in children with ADHD (p Ͻ 0.0001). Worse PANESS scores correlated modestly with less SICI (r ϭ Ϫ.30; p ϭ 0.01). Conclusion:Reduced TMS-evoked SICI correlates with ADHD diagnosis and symptom severity and also reflects motor skill development in children. Neurology ® 2011;76:615-621 GLOSSARY ADHD ϭ attention-deficit/hyperactivity disorder; ADHD-RS-IV ϭ ADHD Rating Scale IV; AMT ϭ active motor threshold; CPRS ϭ Conners' Parent Rating Scale-Revised; CSP ϭ cortical silent period; DSM-IV ϭ Diagnostic and Statistical Manual of Mental Disorders, 4th edition; GABA ϭ ␥-aminobutyric acid; ICF ϭ intracortical facilitation; MABC-2 ϭ Motor Assessment Battery in Children version 2; MEP ϭ motor evoked potential; PANESS ϭ Physical and Neurological Examination for Subtle Signs; RMT ϭ resting motor threshold; SICI ϭ short interval cortical inhibition; TD ϭ typically developing; TMS ϭ transcranial magnetic stimulation.Development of behavioral control and fine motor coordination are 2 fundamental maturational processes in childhood. Children with attention-deficit/hyperactivity disorder (ADHD) have ageinappropriate impulse control and fail to meet age norms on timed repetitive and sequential movements, develop accurate rhythm more slowly, and persist in immature patterns of motor overflow. 1 These developmental skills, rated using the Physical and Neurological Examination for Subtle Signs (PANESS), 2 consistently distinguish children with ADHD from typically developing (TD) children. 3 The neurobiologic underpinnings of these motor delays as well as of the cardinal ADHD behavioral symptoms are incompletely understood. A more quantita...

Slower and more variable reaction times to computerized tasks have been documented in children diagnosed with Attention Deficit Hyperactivity Disorder (ADHD). Recent research supports a role for attentional lapses in generating abnormally variable and slow responses. However, given the association between ADHD and impairments in motor control, we hypothesized that slower or more variable reaction times might also correlate with motor development. The aim of this case-control study was to explore the relationship between motor function, reaction speed and variability, and ADHD. After comprehensive educational and clinical assessments, motor skill development was evaluated in 35 children ages 9 to 14 (19 with ADHD) using the Physical and Neurological Examination for Subtle Signs (PANESS) test battery. Finger sequencing speed and variability were quantified with goniometers. Reaction times were measured with 20 trials each of computerized simple and choice (binary) tasks. Compared to healthy controls, children with ADHD had slower and more variable reaction times, and these findings correlated with impaired motor development (PANESS) and slow and variable finger sequencing (goniometers). Further studies of motor development in ADHD may identify factors influencing speed and variability of reaction times.