Motor cortex inhibition

Abstract

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...

Motor overflow in children with attention-deficit/hyperactivity disorder is associated with decreased extent of neural activation in the motor cortex

“…Supportive evidence for this framework also comes from recent transcranial magnetic stimulation (TMS) studies revealing reduced M1 cortical inhibition in children with ADHD (Gilbert et al, 2011; Wu et al, 2012). Our finding that increased motor overflow is associated with decreased extent of neural activation in M1 contralateral to the voluntary movement likely reflects dendritic activity, as increased overflow movements would be expected to be associated with increased firing of pyramidal cells in M1.…”

Physical Exercise Alleviates ADHD Symptoms: Regional Deficits and Development Trajectory

“…Applying a rate of spontaneous eye blinks, the acoustic startle eye blink response (ASER), and motor lack of persistence, Tantillo et al (2002) observed an interaction between sex and exercise intensity, with induced improvements that were not explained by physical fitness, activity history, or selected personality attributes after following maximal/submaximal exercise in 8-12-year-old ADHD boys and girls. In the case of cognitive domains, there are consistent deficits in behavioral inhibition (Casey et al 1997;Gilbert et al 2011), attention regulation (Arnsten and Pliszka 2011), working memory (Beck et al 2010;Martinussen et al 2005), planning (Chamberlain et al 2011Scheres et al 2010), and motor coordination (Chan et al 2010;Ghanizadeh, 2010). Physical exercise appears to improve performance in both cognitive and motor domains of disorder, whether in patients or healthy controls: In order to test the hypothesis that physical activity may be particularly beneficial for ADHD children, Gapin et al (2011) have reviewed the evidence supporting that hypothesis and have provided preliminary results from 16 ADHD volunteers who performed the neuropsychological tasks prior to and following a treatment period.…”

Online Transcranial Magnetic Stimulation Protocol for Measuring Cortical Physiology Associated with Response Inhibition

“…However, our laboratory historically used 60%*RMT as the conditioning pulse intensity to detect SICI differences in pediatric case-control TMS studies. 19,20 Since this conditioning pulse intensity also elicits significant M1 SICI 29 , we used 60%*RMT for conditioning pulse in this fTMS/S-H task.…”

“…11,12,13,14 This functional TMS (fTMS) approach requires online TMS measurements while participants are performing behavioral tasks, thus allowing one to probe cortical changes that are state-dependent with high temporal resolution. Providing real-time information on neurophysiologic changes in such a manner broadens the physiologic investigation of motor control 15,16 and neuropsychiatric conditions 17,18,19,20 .…”