Megan E. Narad

Evidence for Higher Reaction Time Variability for Children With ADHD on a Range of Cognitive Tasks Including Reward and Event Rate Manipulations

OBJECTIVE The purpose of the research study was to examine the manifestation of variability in reaction times (RT) in children with attention deficit hyperactivity disorder (ADHD) and to examine whether RT variability presented differently across a variety of neuropsychological tasks, was present across the two most common ADHD subtypes, and whether it was affected by reward and event rate (ER) manipulations. METHOD Children with ADHD-combined type (n = 51), ADHD-predominantly inattentive type (n = 53), and 47 controls completed five neuropsychological tasks (Choice Discrimination Task, Child Attentional Network Task, Go/No-Go task, Stop Signal Task, and N-back task), each allowing trial-by-trial assessment of RTs. Multiple indicators of RT variability including RT standard deviation, coefficient of variation and ex-Gaussian tau were used. RESULTS Children with ADHD demonstrated greater RT variability than controls across all five tasks as measured by the ex-Gaussian indicator tau. There were minimal differences in RT variability across the ADHD subtypes. Children with ADHD also had poorer task accuracy than controls across all tasks except the Choice Discrimination task. Although ER and reward manipulations did affect childrens RT variability and task accuracy, these manipulations largely did not differentially affect children with ADHD compared to controls. RT variability and task accuracy were highly correlated across tasks. Removing variance attributable to RT variability from task accuracy did not appreciably affect between-groups differences in task accuracy. CONCLUSIONS High RT variability is a ubiquitous and robust phenomenon in children with ADHD.

Reaction Time Variability in ADHD: A Review

For the past decade, intra-individual variability in reaction times on computerized tasks has become a central focus of cognitive research on Attention-Deficit/Hyperactivity Disorder (ADHD). Numerous studies document increased reaction time variability among children and adults with ADHD, relative to typically developing controls. However, direct comparisons with other disorders with heightened reaction time variability are virtually nonexistent, despite their potential to inform our understanding of the phenomenon. A growing literature examines the sensitivity of reaction time variability to theoretically and clinically relevant manipulations. There is strong evidence that stimulus treatment reduces reaction time variability during a range of cognitive tasks, but the literature is mixed regarding the impact of motivational incentives and variation in stimulus event rate. Most studies of reaction time variability implicitly assume that heightened reaction time variability reflects occasional lapses in attention, and the dominant neurophysiological interpretation suggests this variability is linked to intrusions of task-negative brain network activity during task performance. Work examining the behavioral and neurophysiological correlates of reaction time variability provides some support for these hypotheses, but considerably more work is needed in this area. Finally, because conclusions from each of domains reviewed are limited by the wide range of measures used to measure reaction time variability, this review highlights the need for increased attention to the cognitive and motivational context in which variability is assessed and recommends that future work always supplement macro-level variability indices with metrics that isolate particular components of reaction time variability.

Effects of Stimulant Medication, Incentives, and Event Rate on Reaction Time Variability in Children With ADHD

This study examined the effects of methylphenidate (MPH) on reaction time (RT) variability in children with attention deficit hyperactivity disorder (ADHD). Using a broad battery of computerized tasks, and both conventional and ex-Gaussian indicators of RT variability, in addition to within-task manipulations of incentive and event rate (ER), this study comprehensively examined the breadth, specificity, and possible moderators of effects of MPH on RT variability. A total of 93 children with ADHD completed a 4-week within-subject, randomized, double-blind, placebo-controlled crossover trial of MPH to identify an optimal dosage. Children were then randomly assigned to receive either their optimal MPH dose or placebo after which they completed five neuropsychological tasks, each allowing trial-by-trial assessment of RTs. Stimulant effects on RT variability were observed on both measures of the total RT distribution (ie, coefficient of variation) as well as on an ex-Gaussian measure examining the exponential portion of the RT distribution (ie, τ). There was minimal, if any, effect of MPH on performance accuracy or RT speed. Within-task incentive and ER manipulations did not appreciably affect stimulant effects across the tasks. The pattern of significant and pervasive effects of MPH on RT variability, and few effects of MPH on accuracy and RT speed suggest that MPH primarily affects RT variability. Given the magnitude and breadth of effects of MPH on RT variability as well as the apparent specificity of these effects of MPH on RT variability indicators, future research should focus on neurophysiological correlates of effects of MPH on RT variability in an effort to better define MPH pharmacodynamics.

Parent- Teacher Agreement on ADHD Symptoms Across Development

Parent-teacher agreement on attention-deficit/hyperactivity disorder (ADHD) symptom ratings ranges from low to moderate. Most studies evaluating parent-teacher agreement have not assessed measurement invariance across raters. Hence, it is unclear whether discordance across raters is due to differing ADHD constructs across raters or other factors (e.g., subjective differences across raters). Additionally, the effect of development on parent-teacher agreement is relatively unknown. To address these limitations, the present study used parent and teacher ADHD ratings from a large (N = 6,659) developmentally diverse (ages 4-17) sample. Using exploratory structural equation modeling on half the sample, and then confirmatory factor analysis (CFA) on the other half of the sample, confirmed a 2-factor structure with significant cross-loadings for the 18 ADHD symptoms. CFA invariance analyses demonstrated that the 2-factor symptom structure was similar across raters and age groups. After confirming measurement invariance, the correlation between latent factors within and across raters was examined for each age group as well as across age groups. Parents reported greater severity of ADHD symptoms than did teachers, and both parents and teachers reported higher levels of hyperactivity/impulsivity in younger children than in older children and consistent levels of inattention across development. Finally, correlations between parent-teacher ratings of like factors were weak for inattention and moderate-strong for hyperactivity/impulsivity, and the magnitude of parent-teacher agreement did not vary across development. In conclusion, while parent and teacher ratings of ADHD behaviors are only weakly to moderately correlated, each reporter provides unique and valid clinical information as it relates to ADHD symptom presentation.

Impact of Distraction on the Driving Performance of Adolescents With and Without Attention-Deficit/Hyperactivity Disorder

IMPORTANCE This study extends the literature regarding attention-deficit/hyperactivity disorder (ADHD)-related driving impairments to a newly licensed, adolescent population. OBJECTIVE To investigate the combined risks of adolescence, ADHD, and distracted driving (cell phone conversation and text messaging) on driving performance. DESIGN, SETTING, AND PARTICIPANTS Adolescents aged 16 to 17 years with (n = 28) and without (n = 33) ADHD engaged in a simulated drive under 3 conditions (no distraction, cell phone conversation, and texting). During each condition, one unexpected event (eg, another car suddenly merging into drivers lane) was introduced. INTERVENTIONS Cell phone conversation, texting, and no distraction while driving. MAIN OUTCOMES AND MEASURES Self-report of driving history, average speed, standard deviation of speed, standard deviation of lateral position, and braking reaction time during driving simulation. RESULTS Adolescents with ADHD reported fewer months of driving experience and a higher proportion of driving violations than control subjects. After controlling for months of driving history, adolescents with ADHD demonstrated more variability in speed and lane position than control subjects. There were no group differences for braking reaction time. Furthermore, texting negatively impacted the driving performance of all participants as evidenced by increased variability in speed and lane position. CONCLUSIONS To our knowledge, this study is one of the first to investigate distracted driving in adolescents with ADHD and adds to a growing body of literature documenting that individuals with ADHD are at increased risk for negative driving outcomes. Furthermore, texting significantly impairs the driving performance of all adolescents and increases existing driving-related impairment in adolescents with ADHD, highlighting the need for education and enforcement of regulations against texting for this age group.

Behavioral Correlates of Reaction Time Variability in Children With and Without ADHD

OBJECTIVE Reaction time (RT) variability is often purported to indicate behavioral attention. This study seeks to examine whether RT variability in children with Attention Deficit Hyperactivity Disorder (ADHD) is associated with observed behavioral indicators of attention. METHOD One-hundred 47 participants with and without ADHD completed five computerized neuropsychological tasks and an analog math task. Linear mixed models were utilized to examine the relationship between observations of behavioral inattention during the analog task and measures of RT variability from the neuropsychological tasks. RESULTS Significant associations were observed between RT variability and mean duration of on-task behavior on the analog math task. Secondary analyses indicated that on-task behavior during the math task was also related to accuracy on the neuropsychological tasks. CONCLUSIONS RT variability, especially the portion of RT variability characterized by long RTs, appears to measure a cognitive phenomenon that relates to successful on-task academic behavior across children with and without ADHD. The relationship between RT variability and on-task behavior is present across multiple neuropsychological tasks and does not appear to be moderated by age, sex, or the presence of anxiety or depression.

The relationship between ADHD symptom dimensions, clinical correlates, and functional impairments.

Objective: To better understand how heterogeneity in attention-deficit hyperactivity disorder (ADHD) symptoms relates to heterogeneity in functional impairment domains in children with ADHD after accounting for demographic variables and comorbidities, in particular oppositionality and internalizing symptoms. Methods: Parents and teachers (n = 5663) rated child/adolescent impairments across impairment domains in the International Classification of Functioning, Disability and Health as well as symptoms of ADHD and comorbidities. Hierarchical regressions were conducted to assess the relationship between parent and teacher ratings of ADHD symptom domains and functional impairments after accounting for personal factors and comorbid disorders. Results: Symptoms of inattention were the strongest predictors of ratings of academic (math, writing, and so on) functioning, while hyperactivity/impulsivity symptoms were the strongest predictor of classroom disruption even after accounting for the presence of learning disorders and oppositional symptoms. Symptoms of ADHD accounted for minimal variance in interpersonal functioning or participation in organized activities after controlling oppositional symptoms. Conclusion: The ADHD symptom domains demonstrate domain-specific relations with various ADHD-related functional impairments. In addition, the results highlight the role of oppositionality in interpersonal relationship difficulties and participation in organized activities.

Neurocognitive and Behavioral Predictors of Math Performance in Children With and Without ADHD

Objective: This study examined neurocognitive and behavioral predictors of math performance in children with and without ADHD. Method: Neurocognitive and behavioral variables were examined as predictors of (a) standardized mathematics achievement scores, (b) productivity on an analog math task, and (c) accuracy on an analog math task. Results: Children with ADHD had lower achievement scores but did not significantly differ from controls on math productivity or accuracy. N-back accuracy and parent-rated attention predicted math achievement. N-back accuracy and observed attention predicted math productivity. Alerting scores on the attentional network task predicted math accuracy. Mediation analyses indicated that n-back accuracy significantly mediated the relationship between diagnostic group and math achievement. Conclusion: Neurocognition, rather than behavior, may account for the deficits in math achievement exhibited by many children with ADHD.

Mediators of methylphenidate effects on math performance in children with attention-deficit hyperactivity disorder.

Objective: Stimulant medications, such as methylphenidate (MPH), improve the academic performance of children with attention-deficit hyperactivity disorder (ADHD). However, the mechanism by which MPH exerts an effect on academic performance is unclear. We examined MPH effects on math performance and investigated possible mediation of MPH effects by changes in time on-task, inhibitory control, selective attention, and reaction time variability. Methods: Children with ADHD aged 7 to 11 years (N = 93) completed a timed math worksheet (with problems tailored to each individuals level of proficiency) and 2 neuropsychological tasks (Go/No-Go and Child Attention Network Test) at baseline, then participated in a 4-week, randomized, controlled, titration trial of MPH. Children were then randomly assigned to their optimal MPH dose or placebo for 1 week (administered double-blind) and repeated the math and neuropsychological tasks (posttest). Baseline and posttest videorecordings of children performing the math task were coded to assess time on-task. Results: Children taking MPH completed 23 more math problems at posttest compared to baseline, whereas the placebo group completed 24 fewer problems on posttest versus baseline, but the effects on math accuracy (percent correct) did not differ. Path analyses revealed that only change in time on-task was a significant mediator of MPHs improvements in math productivity. Conclusions: MPH-derived math productivity improvements may be explained in part by increased time spent on-task, rather than improvements in neurocognitive parameters, such as inhibitory control, selective attention, or reaction time variability.

Recovery trajectories of executive functioning after pediatric TBI: a latent class growth modeling analysis

Objective: To identify latent trajectories of executive functioning (EF) recovery overtime after childhood traumatic brain injury (TBI) and examine the predictive value of known risk factors within and across recovery trajectories using latent class growth modeling (LCGM). Method: A total of 206 children between the ages of 3 and 7 years with a moderate to severe TBI or orthopedic injury (OI) were included. LCGM was applied to identify longitudinal trajectories of postinjury EF as assessed by the Behavior Rating Inventory of Executive Functioning General Executive Composite (GEC). Separate models were estimated for the TBI and OI groups. Results: Two TBI trajectories—normal limits (70.8%) and clinically elevated (29.2%)—and 3 OI trajectories—normal limits (20.9%), subclinical (49.0%), and clinically elevated (30.17%)—were identified. Baseline GEC was the only predictor of class membership for all models. Both TBI trajectories demonstrated an increase in GEC over time, whereas only 1 of the 3 OI classes demonstrated this pattern. Family variables were associated with GEC across trajectories. Conclusion: The lack of association of injury characteristics with trajectory class membership highlights the heterogeneity in recovery after pediatric TBI. Associations of EF trajectories with family factors underscore the importance of involving the family in interventions for children with traumatic injuries.