Children with comorbid attention‐deficit‐hyperactivity disorder and tic disorder: Evidence for additive inhibitory deficits within the motor system

Abstract

For children with attention-deficit-hyperactivity disorder (ADHD) or tic disorder (TD), we recently reported deficient inhibitory mechanisms within the motor system by using transcranial magnetic stimulation. These deficits--stated as reduced intracortical inhibition in ADHD and shortened cortical silent period in TD--could be seen as neurophysiological correlates of motor hyperactivity and tics, respectively. To investigate neurophysiological aspects of comorbidity, we measured motor system excitability for the first time also in children with combined ADHD and TD. The findings of a reduced intracortical inhibition as well as a shortened cortical silent period in these comorbid children provide evidence for additive effects at the level of motor system excitability.

Atomoxetine treatment of ADHD in Tourette Syndrome: Reduction in motor cortex inhibition correlates with clinical improvement

“…SICI is significantly diminished (larger ratios) in children with ADHD (Moll et al, 2001). We have previously found consistent correlations between reductions in SICI and ADHD symptom severity in TS (Gilbert et al, 2004a.…”

“…The reduction in pTMS-evoked SICI in ADHD, consistently identified in several independent neurophysiological laboratories, has been presumed to represent a cortical deficiency (Moll et al, 2001). The finding that a single, low dose of a psychostimulant partially normalized SICI in children with ADHD (Moll et al, 2000) supported this interpretation.…”

“…Prior studies employing pTMS have in motor cortex have shown that SICI is decreased in ADHD (Gilbert et al, 2004a,Moll et al, 2001, that SICI correlates consistently over one month with ADHD symptom severity in TS (Gilbert et al, 2004a), and that SICI changes in response to single doses of both stimulants and norepinephrine reuptake inhibitors (Gilbert et al, 2006b,Moll et al, 2000. No prior studies have used pTMS to assess longer-term ATX-induced SICI changes and their relationship to clinical benefit.…”

Comparison of the Inhibitory and Excitatory Effects of ADHD Medications Methylphenidate and Atomoxetine on Motor Cortex

“…TMS has been used to study cortical changes in ADHD (Buchmann et al, 2003;Gilbert et al, 2004a;Moll et al, 2001;Ucles et al, 1996) and is sensitive to the effects of many drugs (Daskalakis et al, 2002;Ziemann 2004), including those affecting monoaminergic systems. TMS is a noninvasive, welltolerated (Garvey et al, 2001), safe (Gilbert et al, 2004b), and easily replicated (Gilbert et al, 2005) procedure for studying the physiological state of neural circuits in the human motor cortex.…”

“…Paired pulse TMS studies have consistently demonstrated abnormally reduced SICI in ADHD (Gilbert et al, 2004a(Gilbert et al, , 2005Moll et al, 2001). However, it remains unclear whether reduced SICI in ADHD represents a lesion, as previously suggested (Moll et al, 2000), or a process compensating for a defect elsewhere.…”