Neurocognitive heterogeneity is increasingly recognized as a valid phenomenon in ADHD, with most estimates suggesting that executive dysfunction is present in only about 33%-50% of these children. However, recent critiques question the veracity of these estimates because our understanding of executive functioning in ADHD is based, in large part, on data from single tasks developed to detect gross neurological impairment rather than the specific executive processes hypothesized to underlie the ADHD phenotype. The current study is the first to comprehensively assess heterogeneity in all three primary executive functions in ADHD using a criterion battery that includes multiple tests per construct (working memory, inhibitory control, set shifting). Children ages 8-13 (M = 10.37, SD = 1.39) with and without ADHD (N = 136; 64 girls; 62% Caucasian/Non-Hispanic) completed a counterbalanced series of executive function tests. Accounting for task unreliability, results indicated significantly improved sensitivity and specificity relative to prior estimates, with 89% of children with ADHD demonstrating objectively-defined impairment on at least one executive function (62% impaired working memory, 27% impaired inhibitory control, 38% impaired set shifting; 54% impaired on one executive function, 35% impaired on two or all three executive functions). Children with working memory deficits showed higher parent- and teacher-reported ADHD inattentive and hyperactive/impulsive symptoms (BF = 5.23 × 10), and were slightly younger (BF = 11.35) than children without working memory deficits. Children with vs. without set shifting or inhibitory control deficits did not differ on ADHD symptoms, age, gender, IQ, SES, or medication status. Taken together, these findings confirm that ADHD is characterized by neurocognitive heterogeneity, while suggesting that contemporary, cognitively-informed criteria may provide improved precision for identifying a smaller number of neuropsychologically-impaired subtypes than previously described.

Hyperactivity, or excess gross motor activity, is considered a core and ubiquitous characteristic of ADHD. Alternate models question this premise, and propose that hyperactive behavior reflects, to a large extent, purposeful behavior to cope with environmental demands that interact with underlying neurobiological vulnerabilities. The present review critically evaluates the ubiquity and environmental modifiability of hyperactivity in ADHD through meta-analysis of 63 studies of mechanically measured activity level in children, adolescents, and adults with ADHD relative to typically developing (TD) groups. Random effects models corrected for publication bias confirmed elevated gross motor activity in ADHD (d = 0.86); surprisingly, neither participant age (child vs. adult) nor the proportion of each ADHD sample diagnosed with the Inattentive subtype/presentation moderated this effect. In contrast, activity level assessed during high cognitive load conditions in general (d = 1.14) and high executive functioning demands in particular (d = 1.39) revealed significantly higher effect sizes than activity level during low cognitive load (d = 0.36) and in-class schoolwork (d = 0.50) settings. Low stimulation environments, more rigorous diagnostic practices, actigraph measurement of movement frequency and intensity, and ADHD samples that included fewer females were also associated with larger effects. Overall, the results are inconsistent with DSM-5 and ADHD models that a) describe hyperactivity as ubiquitous behavior, b) predict a developmental decline in hyperactivity, or c) differentiate subtypes/presentations according to perceived differences in hyperactive behavior. Instead, results suggest that the presence and magnitude of hyperactive behavior in ADHD may be influenced to a considerable extent by environmental factors in general, and cognitive/executive functioning demands in particular.

Objective: Executive function deficits are well-established in ADHD. Unfortunately, replicated evidence indicates that executive function training for ADHD has been largely unsuccessful. We hypothesized that this may reflect insufficient targeting, such that extant protocols do not sufficiently and specifically target the neurocognitive systems associated with phenotypic ADHD behaviors/impairments. Method: Children with ADHD ages 8–12 (M = 10.41, SD = 1.46; 12 girls; 74% Caucasian/Non-Hispanic) were randomized with allocation concealment to either central executive training (CET; n = 25) or newly developed inhibitory control training (ICT; n = 29). Detailed data analytic plans were preregistered. Results: Both treatments were feasible/acceptable based on training duration, child-reported ease of use, and parent-reported high satisfaction. CET was superior to ICT for improving its primary intervention targets: phonological and visuospatial working memory (d = 0.70–0.84). CET was also superior to ICT for improving go/no-go (d = 0.84) but not stop-signal inhibition. Mechanisms of change analyses indicated that CET-related working memory improvements produced significant reductions in the primary clinical endpoints (objectively assessed hyperactivity) during working memory and inhibition testing (indirect effects: β ≥ −.11; 95% CIs exclude 0.0). CET was also superior to ICT on 3 of 4 secondary clinical endpoints (blinded teacher-rated ADHD symptoms; d = 0.46–0.70 vs. 0.16–0.42) and 2 of 4 feasibility/acceptability clinical endpoints (parent-reported ADHD symptoms; d = 0.96–1.42 vs. 0.45–0.65). CET-related gains were maintained at 2–4 month follow-up; ICT-related gains were maintained for attention problems but not hyperactivity/impulsivity per parent report. Conclusions: Results support the use of CET for treating executive function deficits and targeting ADHD behavioral symptoms in children with ADHD. Findings for ICT were mixed at best and indicate the need for continued development/study.

Background: This study tested model-driven predictions regarding working memory's role in the organizational problems associated with ADHD. Method: Children aged 8-13 (M = 10.33, SD = 1.42) with and without ADHD (N = 103; 39 girls; 73% Caucasian/Non-Hispanic) were assessed on multiple, counterbalanced working memory tasks. Parents and teachers completed norm-referenced measures of organizational problems (Children's Organizational Skills Scale; COSS). Results: Results confirmed large magnitude working memory deficits (d = 1.24) and organizational problems in ADHD (d = 0.85). Bias-corrected, bootstrapped conditional effects models linked impaired working memory with greater parent-and teacher-reported inattention, hyperactivity/impulsivity, and organizational problems. Working memory predicted organization problems across all parent and teacher COSS subscales (R 2 = .19-.23). Approximately 38%-57% of working memory's effect on organization problems was conveyed by working memory's association with inattentive behavior. Unique effects of working memory remained significant for both parent-and teacher-reported task planning, as well as for teacher-reported memory/materials management and overall organization problems. Attention problems uniquely predicted worse organizational skills. Hyperactivity was unrelated to parent-reported organizational skills, but predicted better teacher-reported task planning. Conclusions: Children with ADHD exhibit multisetting, broad-based organizational impairment. These impaired organizational skills are attributable in part to performance deficits secondary to working memory dysfunction, both directly and indirectly via working memory's role in regulating attention. Impaired working memory in ADHD renders it extraordinarily difficult for these children to consistently anticipate, plan, enact, and maintain goal-directed actions.

Objective Working memory deficits have been linked experimentally and developmentally with ADHD-related symptoms/impairments. Unfortunately, substantial evidence indicates that extant working memory training programs fail to improve these symptoms/impairments. We hypothesized that this discrepancy may reflect insufficient targeting, such that extant protocols do not adequately engage the specific working memory components linked with the disorder’s behavioral/functional impairments. Method The current study describes the development, empirical basis, and initial testing of central executive training (CET) relative to gold-standard behavioral parent training (BPT). Children with ADHD ages 8–13 (M=10.43, SD=1.59; 21 girls; 76% Caucasian/Non-Hispanic) were treated using BPT (n=27) or CET (n=27). Detailed data analytic plans for the pre/post design were preregistered. Primary outcomes included phonological and visuospatial working memory, and secondary outcomes included actigraphy during working memory testing and two distal far-transfer tasks. Multiple feasibility/acceptability measures were included. Results The BPT and CET samples did not differ on any pre-treatment characteristics. CET was rated as highly acceptable by children, and was equivalent to BPT in terms of feasibility/acceptability as evidenced by parent-reported high satisfaction, low barriers to participation, and large ADHD symptom reductions. CET was superior to BPT for improving working memory (group x time d=1.06) as hypothesized. CET was also superior to BPT for reducing actigraph-measured hyperactivity during visuospatial working memory testing and both distal far-transfer tasks (group x time d=0.74). Conclusions Results provide strong support for continued testing of CET and, if replicated, would support recent hypotheses that next-generation ADHD cognitive training protocols may overcome current limitations via improved targeting.