Relating lab to life: Decrements in attention over time predict math productivity among children with ADHD

Cognitive mechanisms of methylphenidate in ADHD: Do improvements in sustained attention mediate behavioral improvements in the natural environment?

The relation between sustained attention in the laboratory and behaviors exhibited in naturalistic settings among children with Attention Deficit/Hyperactivity Disorder (ADHD) remains unclear. Additionally, research on stimulant medication effects in these areas and their association with one another remains scarce. Twenty-one children with ADHD and 21 children without ADHD completed a novel continuous performance test (CPT) involving high cognitive demands (e.g., visual search). Participants with ADHD also attended a Summer Treatment Program and received three doses of stimulant medication (placebo, low, and high). Their behavior in classroom and peer settings was observed and recorded, and they completed the CPT in each medication condition. The CPT measures of bias and sensitivity were used in analyses. Results indicated that children with ADHD had impaired overall performance and worse bias during the second half of the task compared to controls. Methylphenidate improved both naturalistic behavior and overall CPT performance but did not specifically improve the sustained attention deficit. Despite improvements in overall CPT performance, medication-related improvement in CPT performance did not mediate medication-related improvement in observed behavior in classroom or recreational settings. As such, our findings suggest that although children with ADHD do demonstrate a sustained attention deficit, salutary psychostimulant effects on CPT performance are not indicative of, or causally linked to, psychostimulant effects on presenting problems in naturalistic settings.

Aspects of attention and inhibitory control are associated with on-task classroom behaviour and behavioural assessments, by both teachers and parents, in children with high and low symptoms of ADHD

There is often weak association between performance on cognitive tasks and the behavioural symptoms of ADHD. One possible reason is the use of rating scales rather than direct observations of behaviours. This exploratory study used well established measures of attention and response inhibition with both direct observation and behavioural rating scales to examine these associations. Twenty-two children (mean age 9.6 years) identified by their teachers as displaying high levels of ADHD symptoms, and 22 matched controls (mean age 9.8 years), completed the Fixed and Random Sustained Attention to Response Tasks (SART). Their on-task classroom behaviour was assessed using the ASEBA Direct Observation Form (DOF). ADHD symptoms were also assessed using the Conners 3 Short Form and the SWAN. Children with high symptoms of ADHD performed the SARTs with more errors of commission and were more variable with their responding, and spent less time on-task in the classroom than controls. Performance on the Fixed SART was not associated with on-task classroom behaviour; in contrast three Random SART measures, commission and omission errors, moment-to-moment variability, were negatively associated with on-task classroom behaviour. There were strong associations between the commission error counts on both SARTs and the Teacher SWAN scores, and one of the Parent SWAN scores. The Teacher SWAN scores were associated with on-task classroom behaviour; the Parent SWAN scores were not. These findings provide preliminary evidence of an association between cognitive measures of inhibitory control and some measures of inattention, and both observed behaviour and the ADHD behavioural symptoms.

How do stimulant treatments for ADHD work? Evidence for mediation by improved cognition

BACKGROUND

Stimulant medications such as methylphenidate (MPH) are the frontline treatment for Attention-Deficit/Hyperactivity Disorder (ADHD). Despite their well-documented efficacy, the mechanisms by which stimulants improve clinical outcomes are not clear. The current study evaluated whether MPH effects on classroom behavior were mediated by improved cognitive functioning.

METHODS

Children with ADHD (n = 82; 9-12 years old) participated in a week-long summer research camp, consisting of cognitive testing, classroom periods, and recreational activities. After a baseline day, participants completed a 3-day randomized, double-blind, placebo-controlled trial of MPH (at doses approximating 0.3 and 0.6 mg/kg of immediate-release MPH dosed TID). Cognitive domains included inhibitory control (Stop Signal Task and prepulse inhibition of startle), attention (Continuous Performance Task and reaction time variability), and working memory (forward and backward spatial span). Clinical outcomes included math seatwork productivity and teacher-rated classroom behavior. A within-subjects path-analytic approach was used to test mediation. MPH-placebo and dose-response contrasts were used to evaluate drug effects.

RESULTS

Methylphenidate improved seatwork productivity and teacher ratings (ds = 1.4 and 1.1) and all domains of cognition (ds = 0.3-1.1). Inhibitory control (Stop Signal Task, SST) and working memory backward uniquely mediated the effect of MPH (vs. placebo) on productivity. Only working memory backward mediated the impact of MPH on teacher-rated behavior. The dose-response (0.6 vs. 0.3 mg/kg) effects were more modest for clinical outcomes (ds = 0.4 and 0.2) and cognition (ds = 0-0.3); there was no evidence of cognitive mediation of the clinical dose-response effects.

CONCLUSIONS

These findings are novel in demonstrating that specific cognitive processes mediate clinical improvement with stimulant treatment for ADHD. They converge with work on ADHD theory, neurobiology, and treatment development in suggesting that inhibitory control and working memory may be mechanisms of stimulant treatment response in ADHD. More work is necessary to evaluate the degree to which these findings generalize to chronic treatment, a broader array of clinical outcomes, and nonstimulant treatments.