The effect of methylphenidate on three forms of response inhibition in boys with AD/HD

The current study was aimed at (a) investigating the effect of three doses methylphenidate (MPH) and placebo on inhibition of a prepotent response, inhibition of an ongoing response, and interference control in Attention Deficit/Hyperactivity Disorder (AD/HD), and (b) studying dose-response relations for the three forms of response inhibition. To meet these aims, the following tasks were selected: two versions of the Stop Paradigm for inhibition of a prepotent response, a Circle Tracing Task and a recently developed Follow Task for inhibition of an ongoing response, and the Stroop Color-Word Test and an Eriksen Flanker Task for interference control. These tasks were administered to 23 boys with AD/HD during four treatment conditions: 5 mg MPH, 10 mg MPH, 20 mg MPH, and placebo. A pseudorandomized, multiple-blind, placebo-controlled, within-subject design was used. As hypothesized, inhibitory control in children with AD/HD improved under MPH compared to placebo. However, this effect was only significant for inhibition of a prepotent response and inhibition of an ongoing response (as measured by the Follow Task), but not for interference control. The relation between treatment condition and response was linear. However, this linear relation was due to improved inhibitory control under MPH compared to placebo, because no effects of MPH dose were observed for any of the response inhibition measures.     

Effects of Reward and Response Cost on Response Inhibition in AD/HD, Disruptive, Anxious, and Normal Children

In previous research, children with attention deficit/hyperactivity disorder (AD/HD) have demonstrated impaired response inhibition on the stop paradigm. In this study we examined whether this impairment in fact reflects a motivational deficit. Four groups of children (age range 7–13 years) participated in the study: 14 AD/HD children, 21 normal controls, 14 disruptive children, and 14 anxious children. The psychopathological groups were recruited from special educational services and mental health outpatient clinics. Parent, teacher, and child questionnaires were used to select children with pervasive disorders. Normal controls attended regular classes and scored low on all questionnaires. Children were tested once with reward contingencies and once with response cost contingencies in a randomized cross-over design. We hypothesized that if a motivational deficit underlies poor response inhibition in AD/HD children, this deficit will be remedied by response contingencies. Despite the presence of response contingencies, AD/HD children showed poor response inhibition compared with normal controls. Findings argue against a motivational explanation for the response inhibition deficit in AD/HD children     

Neurocognitive Functioning in AD/HD,Predominantly Inattentive and Combined Subtypes

The Predominantly Inattentive (PI) and Combined (CB) subtypes of AD/HD differ in cognitive tempo, age of onset, gender ratio, and comorbidity, yet a differentiating endophenotype has not been identified. The aim of this study was to test rigorously diagnosed PI, CB, and typical children on measures selected for their potential to reveal hypothesized differences between the subtypes in specific neurocognitive systems (anterior vs. posterior attentional systems) and processes (arousal vs. activation). Thirty-four CB and 26 PI children meeting full DSM-IV criteria for subtype both in school and at home, without confounding reading disability or emotional disorder, were enrolled along with 20 typically developing children. Neurocognitive functions measured included attention, inhibitory control, working memory, learning, and executive functions. Tasks included the Stroop, Wisconsin Card Sorting Test, Continuous Performance Test (CPT). Buschke Selective Reminding Test, ad the Tower of London (TOL), as well as instruments developed by Posner and Sternberg, and tasks assessing the impact on reaction time of [corrected] varying preparatory intervals and stimulus/response complexity. After co-varying for IQ, subtypes differed primarily on measures of impulsivity during tests of vigilance (CPT) and executive function (TOL), with the CB group showing greater impulsivity than both other groups. In addition, the PI group showed worse performance than CB and control groups on the WISC-III Processing Speed Index. Whether analyzed with or without an IQ co-variate, there was no support in the data for hypothesized differences between subtypes in functioning of the anterior vs. posterior attentional systems, nor in involvement of arousal vs. activation processes. The results indicate that the PI and CB subtypes are best differentiated by ratings, observations and tests of cognitive tempo and behavioral impulsivity. Neuropsychological methods have yet to identify critical neuropsychological [corrected] substrates of these differences.     

ADHD的抑制缺陷和厌恶延迟—来自双通道理论的解释

行为抑制理论认为抑制功能的落后是ADHD的核心缺损所在,Sonuga-Barke的厌恶延迟理论认为ADHD起因是厌恶延迟而非抑制缺损,但该理论并不能解释ADHD的全部症状,Sonuga-Barke将厌恶延迟理论作了修正,提出了双通道模型。该模型认为ADHD的抑制缺陷和厌恶延迟同时存在,相互独立,模型的认知发展通道关注抑制控制缺陷对ADHD的影响,而动机发展通道则认为ADHD儿童是因奖励回路紊乱而引起异常的厌恶延迟的动机风格。本文介绍了双通道理论及相关的研究及其应用于ADHD诊断和干预的价值和局限性。