Inhibition, flexibility, working memory and planning in autism spectrum disorders with and without comorbid ADHD-symptoms

Background

Recent studies have not paid a great deal of attention to comorbid attention-deficit/hyperactivity disorder (ADHD) symptoms in autistic children even though it is well known that almost half of children with autism spectrum disorder (ASD) suffer from hyperactivity, inattention and impulsivity. The goal of this study was to evaluate and compare executive functioning (EF) profiles in children with ADHD and in children with ASD with and without comorbid ADHD.

Methods

Children aged 6 to 18 years old with ADHD (n = 20) or ASD (High-Functioning autism or Asperger syndrome) with (n = 20) and without (n = 20) comorbid ADHD and a typically developing group (n = 20) were compared on a battery of EF tasks comprising inhibition, flexibility, working memory and planning tasks. A MANOVA, effect sizes as well as correlations between ADHD-symptomatology and EF performance were calculated. Age- and IQ-corrected z scores were used.

Results

There was a significant effect for the factor group (F = 1.55; dF = 42; p = .02). Post-hoc analysis revealed significant differences between the ADHD and the TD group on the inhibition task for false alarms (p = .01) and between the ADHD group, the ASD+ group (p = .03), the ASD- group (p = .02) and the TD group (p = .01) for omissions. Effect sizes showed clear deficits of ADHD children in inhibition and working memory tasks. Participants with ASD were impaired in planning and flexibility abilities. The ASD+ group showed compared to the ASD- group more problems in inhibitory performance but not in the working memory task.

Conclusion

Our findings replicate previous results reporting impairment of ADHD children in inhibition and working memory tasks and of ASD children in planning and flexibility abilities. The ASD + group showed similarities to the ADHD group with regard to inhibitory but not to working memory deficits. Nevertheless the heterogeneity of these and previous results shows that EF assessment is not useful for differential diagnosis between ADHD and ASD. It might be useful for evaluating strengths and weaknesses in individual children.     

Attention-Deficit/Hyperactivity Disorder and Sluggish Cognitive Tempo Dimensions in Relation to Executive Functioning in Adolescents with ADHD

Previous research has failed to find a consistent relation between Sluggish Cognitive Tempo (SCT) and executive function (EF) in youth with Attention-Deficit/Hyperactivity Disorder (ADHD) when laboratory-based neuropsychological tasks of EF are used, whereas recent research with youth and adults suggests a significant relation between SCT and ratings of EF. The purpose of this study was to examine ADHD dimensions and SCT symptoms in relation to ratings of EF in adolescents with ADHD. Fifty-two adolescents (ages 12–16; 70 % male) participated in this study. Parents and teachers completed validated measures of SCT, ADHD symptoms, and EF in daily life. Adolescents’ intelligence and academic achievement were also assessed. ADHD and SCT symptoms were significantly correlated with ratings of EF. Regression analyses demonstrated that, as hypothesized, ADHD hyperactive-impulsive symptoms were strongly associated with behavioral regulation EF deficits, with ADHD inattentive and SCT symptoms unrelated to behavioral regulation EF when hyperactive-impulsivity symptoms were included in the model. The parent-reported SCT Slow scale measuring motivation, initiative, and apathy predicted both parent- and teacher-reported metacognitive EF deficits above and beyond youth characteristics and ADHD symptoms. In contrast, teacher-reported ADHD inattention was most clearly associated with teacher-reported metacognitive EF deficits. This study provides preliminary evidence for the importance of SCT symptoms in relation to metacognitive EF deficits among adolescents with ADHD and the need to further investigate the overlap and distinctiveness of SCT/ADHD. Further research is needed to replicate and extend these findings.     

Executive functions and adaptive functioning in young adult attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is associated with impairments in occupational, social, and educational functioning in adults. This study examined relations of adaptive impairment to ADHD symptom domains (inattentive-disorganized and hyperactive-impulsive) and to deficits in executive functioning (EF) in 195 well-characterized adults (105 ADHD, 90 non-ADHD, between ages 18 and 37). Participants completed a battery of EF measures as well as assessments of adaptive functioning. Confirmatory factor analyses were used to validate latent factors for adaptive functioning and EF. In a measurement model, weaker EF was associated with poorer adaptive functioning (r = -.30). When multi-informant composite variables for current inattentive-disorganized and hyperactive-impulsive ADHD symptoms were included in the structural model, EF no longer predicted adaptive functioning. While both symptom composites were similarly related to EF (inattentive-disorganized r = .36; hyperactive-impulsive r = .29), inattentive-disorganized symptoms accounted for more variance in adaptive functioning (67.2% vs. 3.6%). Furthermore, for retrospectively reported childhood symptoms of ADHD, only the inattentive-disorganized symptom domain was related to EF or adaptive impairment. These results suggest that, in adults with ADHD, inattentive-disorganized symptoms may be the primary contributor to key aspects of poorer adaptive function and may be the behavioral path through which EF deficits lead to adaptive impairment.     

Temperament,executive function,and attention-deficit/hyperactivity disorder (ADHD) in adolescents: The mediating role of effortful control

Introduction: Temperament dimensions may be related to executive functions (EF) and may be involved in the expression and maintenance of symptoms of attention-deficit/hyperactivity disorder (ADHD). The current study aimed to assess whether effortful control (EC) mediates the relationship between EF and inattentive symptoms, and whether surgency (S) and negative affectivity (NA) mediate the relationships between EF and hyperactive–impulsive ADHD symptoms in adolescents.

Method: Working individually, participants aged between 12 and 16 years (N = 118; 75 with ADHD) performed tests of cognitive EF (working memory, planning, flexibility, and inhibition), and parents and teachers completed a multi-informant assessment focusing on measures of ADHD symptoms and temperament dimensions (EC, S, and NA).

Results: There were significant differences between ADHD and control participants in EF and temperament dimensions. ADHD participants had lower scores than controls in working memory, planning, and inhibition EF; they also had lower scores in EC and higher scores in S and NA. Structural equation modeling indicated differential associations between EC, S, and NA temperament dimensions, and working memory, planning and inhibition EF, and ADHD symptoms. Mediation analysis suggested that EF exerted indirect effects on the inattentive and hyperactive–impulsive symptoms, via EC; higher EF abilities were related to higher levels of EC, which in turn were related to lower scores of inattentive and hyperactive–impulsive ADHD symptoms. S and NA did not mediate relations among EF and hyperactive–impulsive symptoms.

Conclusion: The findings expand on those of previous studies of the complex relationship between temperament dimensions and EF and confirm the differential association between impairments in some EF, low EC, and the expression of inattentive and hyperactive–impulsive symptoms in adolescents, which may account for the ADHD–control group differences.     

Reading comprehension in adolescents with ADHD: Exploring the poor comprehender profile and individual differences in vocabulary and executive functions

The overall objective of this study was to investigate reading comprehension in youth with and without a prior diagnosis of attention-deficit hyperactivity disorder (ADHD). The first goal was to determine whether youth with and without ADHD matched in word reading ability exhibited differences in reading comprehension proficiency. The next goal was to determine whether good and poor comprehenders within the ADHD subgroup differed from each other on language and academic achievement measures. The third objective was to examine whether word recognition or oral vocabulary knowledge mediated the effect of ADHD symptoms on reading comprehension performance. Youth with ADHD scored significantly lower than the comparison youth on a standardized measure of reading comprehension. Relative to good comprehenders with ADHD, poor comprehenders with ADHD exhibited weaknesses in expressive vocabulary, mathematical reasoning, written expression, and exhibited more executive function (EF) difficulties as reported by the teacher. Expressive vocabulary and word reading, but not teacher EF ratings, accounted for unique variance in reading comprehension performance and mediated the relationship between ADHD symptoms and reading comprehension. Implications for further research and educational practice are discussed.     

Behavior ratings of executive function among preschoolers with ADHD

The Behavior Rating Inventory of Executive Function-Preschool Version (BRIEF-P; Gioia, Espy, & Isquith, 2003) was developed to assess executive function (EF) behaviors in children aged 2 to 5 years. We compared parent ratings of 25 preschool children with ADHD to 25 age-, sex-, and SES-matched controls from the BRIEF-P standardization sample. Children with ADHD were rated significantly higher than controls (p < .01) on all five primary scales (Inhibit, Shift, Emotional Control, Working Memory, Plan/Organize), and on all four indices (Inhibitory Self Control, Flexibility, Emerging Metacognition, General Executive Composite). The largest effect size was on the Working Memory scale. All five BRIEF-P clinical scales were significantly intercorrelated in the control group, and seven of ten scale intercorrelations were significant in the ADHD group. Within the ADHD group, the BRIEF-P Index scores were significantly correlated with ratings on the Conners' Parent Rating Scale, but only moderately correlated with an estimate of Verbal IQ. The BRIEF-P had low, non-significant correlations with performance-based measures of EF, and patterns of correlations were not significantly different than those between the BRIEF-P and non-EF measures (sensorimotor, receptive vocabulary). Similar to its predecessor, the BRIEF-P is sensitive to symptoms of ADHD, but appears to measure different elements of EF than those tapped by performance-based measures.     

Executive Functioning in Children with Asperger Syndrome,ADHD-Combined Type,ADHD-Predominately Inattentive Type,and Controls

The purpose of the study was to evaluate neuropsychological and behavioral rating measures of executive functions (EF) in children with two subtypes of ADHD, Asperger syndrome (AS), and controls. Relative to the control group, the clinical groups experienced more difficulty in EF. The AS group showed the most difficulty in emotional control, behavioral regulation, fluid reasoning, and planning compared to the ADHD groups. Number of symptoms of ADHD or AS was found to be significantly related to ratings of difficulty with behavior regulation, metacognition, and general behavioral regulation across the sample. These findings indicate that children with AS or ADHD may have a differing EF profile and thus, may respond differentially to interventions.     

A comparison of once-daily and divided doses of modafinil in children with attention-deficit/hyperactivity disorder: a randomized, double-blind, and placebo-controlled study

OBJECTIVE: This randomized, double-blind, placebo-controlled study assessed the efficacy and tolerability of several modafinil dosing regimens in children with attention-deficit/hyperactivity disorder (ADHD) to determine whether modafinil can be given once daily in pediatric ADHD. METHOD: Children and adolescents (age range, 6-13 years) (N = 248) with DSM-IV-defined ADHD were enrolled in a 4-week, double-blind, placebo-controlled study, conducted February-May 2002. The group was assigned to receive oral (100-mg tablets) modafinil 300 mg once daily (300 mg in the morning followed by placebo at midday), modafinil 300 mg as a divided dose (100/200 mg or 200/100 mg), or matching placebo. In children weighing > or = 30 kg, a higher dose of 400 mg (200/200 mg) was evaluated. Efficacy measures included the teacher-rated School Version and clinician-rated Home Version of the ADHD Rating Scale-IV and the parent-completed Conners' ADHD/DSM-IV Scales. RESULTS: 223 children completed the study. Those who received modafinil 300 mg once daily showed a significantly greater improvement (change from baseline) than those who received placebo in symptoms of ADHD across all rating scales and subscales (all p < .05). Divided 300-mg doses of modafinil provided some significant but inconsistent improvements in ADHD symptoms. In children weighing > or = 30 kg, modafinil 400 mg (200/200 mg) was significantly superior to placebo on clinician- and parent-completed scales (all p < .05). Insomnia was the only adverse event to occur with significantly greater frequency in a modafinil group (200/100) than in the placebo group (14% vs. 2%) (p = .03). CONCLUSION: Modafinil significantly improved ADHD symptoms in children. Once-daily dosing (300 mg) provided the most consistent improvement in symptoms. All dosing regimens of modafinil were well tolerated.     

Is there any incremental benefit to conducting neuroimaging and neurocognitive assessments in the diagnosis of ADHD in young children? A machine learning investigation

Given the negative trajectories of early behavior problems associated with ADHD, early diagnosis is considered critical to enable intervention and treatment. To this end, the current investigation employed machine learning to evaluate the relative predictive value of parent/teacher ratings, behavioral and neural measures of executive function (EF) in predicting ADHD in a sample consisting of 162 young children (ages 4–7, mean age 5.55, 82.6 % Hispanic/Latino). Among the target measures, teacher ratings of EF were the most predictive of ADHD. While a more extensive evaluation of neural measures, such as diffusion-weighted imaging, may provide more information as they relate to the underlying cognitive deficits associated with ADHD, the current study indicates that measures of cortical anatomy obtained in research studies, as well cognitive measures of EF often obtained in routine assessments, have little incremental value in differentiating typically developing children from those diagnosed with ADHD. It is important to note that the overlap between some of the EF questions in the BRIEF, and the ADHD symptoms could be enhancing this effect. Thus, future research evaluating the importance of such measures in predicting children’s functional impairment in academic and social areas would provide additional insight into their contributing role in ADHD.     

An open trial of adjunctive donepezil in attention-deficit/hyperactivity disorder

OBJECTIVE: Despite available pharmacotherapeutics, a number of youths with attentiondeficit/ hyperactivity disorder (ADHD) continue to experience residual symptoms and prominent executive function (EF) deficits resulting in impairment in multiple domains. We sought to determine if donepezil, used adjunctively to stimulant medication, would improve residual symptoms of ADHD and EF deficits. METHODS: In a 12-week open trial, we treated 7 children and 6 adults who had ADHD and evidence of further EF deficits with adjunctive donepezil. All subjects were stabilized on stimulants, at which time donepezil was initiated at 2.5 mg daily and increased to a maximum of 10 mg over the 12-week trial. RESULTS: Of 13 subjects receiving medication, 7 completed the trial. There was no clinically or statistically significant improvement in the ADHD Rating Scale and the Executive Function Checklist, our primary outcome measures. A majority of individuals experienced nonserious adverse events. CONCLUSIONS: Results of this small open study suggest that donepezil augmentation of stimulants is not well tolerated and does not appear useful for the treatment of residual ADHD and/or EF deficits.     

Associations Between Limbic System White Matter Structure and Socio-Emotional Functioning in Children with ADHD + ASD

Children with attention deficit/hyperactivity disorder (ADHD) combined with autism spectrum disorder (ASD) symptoms (ADHD?+?ASD) have poorer social and emotional functioning than those with ADHD alone. However, no studies have specifically examined the associations between ASD symptoms, measures of social and emotional functioning and limbic system white matter microstructure. Tractography on the cingulum, uncinate fasciculus and fornix were performed for 151 children with (N?=?78) and without (N?=?73) ADHD. Participants in the ADHD group who scored 11 or above on the Social Communication Questionnaire were classified as the ADHD?+?ASD group (N?=?16). Significant differences in mean cingulum FA were present between the control group and the ADHD (all) group, however, no significant differences were seen between the ADHD and ADHD?+?ASD groups. Despite this, significant associations were seen between mean FA of the left cingulum and emotional problems for the ADHD?+?ASD group. Results give greater insights into the specific biological basis of emotional problems in the ADHD?+?ASD group, indicating that the cingulum may play a role.

     

Cortical deficits of emotional face processing in adults with ADHD: its relation to social cognition and executive function

Although it has been shown that adults with attention-deficit hyperactivity disorder (ADHD) have impaired social cognition, no previous study has reported the brain correlates of face valence processing. This study looked for behavioral, neuropsychological, and electrophysiological markers of emotion processing for faces (N170) in adult ADHD compared to controls matched by age, gender, educational level, and handedness. We designed an event-related potential (ERP) study based on a dual valence task (DVT), in which faces and words were presented to test the effects of stimulus type (faces, words, or face-word stimuli) and valence (positive versus negative). Individual signatures of cognitive functioning in participants with ADHD and controls were assessed with a comprehensive neuropsychological evaluation, including executive functioning (EF) and theory of mind (ToM). Compared to controls, the adult ADHD group showed deficits in N170 emotion modulation for facial stimuli. These N170 impairments were observed in the absence of any deficit in facial structural processing, suggesting a specific ADHD impairment in early facial emotion modulation. The cortical current density mapping of N170 yielded a main neural source of N170 at posterior section of fusiform gyrus (maximum at left hemisphere for words and right hemisphere for faces and simultaneous stimuli). Neural generators of N170 (fusiform gyrus) were reduced in ADHD. In those patients, N170 emotion processing was associated with performance on an emotional inference ToM task, and N170 from simultaneous stimuli was associated with EF, especially working memory. This is the first report to reveal an adult ADHD-specific impairment in the cortical modulation of emotion for faces and an association between N170 cortical measures and ToM and EF.     

Functional impairment in adults positively screened for attention-deficit hyperactivity disorder: The role of symptom presentation and executive functioning

Background

While the number of symptoms of attention-deficit hyperactivity disorder (ADHD) decreases with age, a high proportion of adults with ADHD symptoms suffer from persistent functional impairment (Fi) linked to these symptoms. Our objective was to investigate the specific roles of two potentially important predictors of this Fi: the clinical symptom presentation and the deficit in executive functions (EFs).

Methods

A total of 158 subjects from a community sample positively screened for ADHD were classified into two groups: those with and without Fi. Following a detailed diagnostic process, participants were administered a self-rating scale for ADHD symptoms as well as a neuropsychological test battery containing tests of EF and attention relevant as potential cognitive endophenotypes for ADHD.

Results

The overall number as well as the number of inattentive, hyperactive and impulsive symptoms, confirmed both by examiner and self-report, were significantly higher among Fi subjects. The highest odds ratio for Fi was associated with impulsive symptoms. Additionally, self-reported complaints of problems with self-concept were significantly higher among Fi subjects. No significant relationship between Fi and neuropsychological measures of EF and attention was detected.

Conclusions

This study revealed that the number of symptoms, in particular that of impulsivity, had a significant impact on Fi in adults with symptoms of ADHD. Furthermore, our results underline the importance of assessing complaints and behaviors related to self-concept, which are not included in DSM-IV diagnostic criteria of ADHD but nonetheless may be associated with functional outcome of the disorder.     

Treatment effects of methylphenidate on behavioral adjustment in children with mental retardation and ADHD

OBJECTIVE: The effects of stimulant medication treatment were investigated in children with mental retardation (MR) and attention-deficit/hyperactivity disorder (ADHD). METHOD: Parent and teacher behavioral ratings and reports of side effects were obtained for children (N = 24, mean age = 10.9 years, SD = 2.4) during a placebo-controlled, double-blind, crossover treatment trial with 0.15 mg/kg, 0.30 mg/kg, and 0.60 mg/kg b.i.d. dosages of methylphenidate. RESULTS: The most significant improvements occurred at the 0.60 mg/kg methylphenidate dose for teacher ratings of inattention (p =.024), hyperactivity (p <.001), aggression (p <.001), and asocial behavior (p =.009). No significant improvements, relative to placebo, occurred at the 0.15 mg/kg dosage. Of interest, nearly all significant medication-related behavioral improvements were detected by teachers. However, parents were sensitive raters of side effects, noting more sleeping problems and loss of appetite at the 0.60 mg/kg dose compared with placebo. CONCLUSIONS: These results suggest that symptoms of ADHD can be treated successfully in children with ADHD/MR, and consistent with MTA study results, higher doses were most effective. Furthermore, these improvements were not accompanied by increases in symptoms such as staring, social withdrawal, or anxiety.     

Testing for neuropsychological endophenotypes in siblings discordant for attention-deficit/hyperactivity disorder.

BACKGROUND: Neurocognitive deficits associated with attention-deficit/hyperactivity disorder (ADHD) might be useful intermediate endophenotypes for determining specific genetic pathways that contribute to ADHD. METHODS: This study administered 17 measures from prominent neuropsychological theories of ADHD (executive function, processing speed, arousal regulation and, motivation/delay aversion) in dizygotic (DZ) twin pairs discordant for ADHD and control twin pairs (ages 8-18 years) to compare performance between twins affected with ADHD (n = 266), their unaffected co-twins (n = 228), and control children from twin pairs without ADHD or learning difficulties (n = 332). RESULTS: The ADHD subjects show significant impairment on executive function, processing speed, and response variability measures compared with control subjects. Unaffected co-twins of ADHD subjects are significantly impaired on nearly all the same measures as their ADHD siblings, even when subclinical symptoms of ADHD are controlled. CONCLUSIONS: Executive function, processing speed, and response variability deficits might be useful endophenotypes for genetic studies of ADHD.     

Long-term far-transfer effects of working memory training in children with ADHD: a randomized controlled trial

ADHD affects working memory (WM) and other executive functions (EFs) and thereby negatively impacts school performance, clinical symptoms and functional impairment. The main aim of this study was to analyse the efficacy of computerized WM training (CWMT) on EF rating scales. A secondary objective was to assess its efficacy on performance-based measures of EF (PBMEF), learning, clinical symptoms and functional impairment. 66 children with combined-type ADHD between 7 and 12 years of age from the Child and Adolescent Psychiatric Unit (Spain) were included in this randomized, double-blind, placebo-controlled, parallel-group clinical trial. The participants were randomized (1:1) to an experimental group (EG) (CWMT) (n = 36) or a control group (CG) (placebo training). Assessments were conducted at baseline (T0), 1–2 weeks (T1), and 6 months post-intervention (T2) with the administration of EF rating scales, PBMEF, measures of academic achievement, and questionnaires regarding clinical symptoms and functional impairment. Participants, parents, teachers and professionals who performed the cognitive assessments were blinded. Adjusted multiple linear regression analysis showed significant improvements in EF scales-parent version, from T1 to T2, on the metacognition index [p = 0.03, d′ = ?0.78 (95 % CI ?1.28 to ?0.27)] and on WM (also significant at T2–T0) and plan/organize subscales. Significant improvements were also noted in EF scales-teacher version, from T0 to T1 and T2, on the metacognitive index [p = 0.05, d′ = ?0.37 (95 % CI ?0.86 to 0.12) T1–T0, p = 0.02, d’ = ?0.81 (95 % CI ?1.31 to ?0.30) T2–T0] and on the initiate, WM, monitor and shift subscales. There were also significant improvements in PBMEF, ADHD symptoms, and functional impairment. CWMT had a significant impact on ADHD deficits by achieving long-term far-transfer effects.     

Cognitive variability in adults with ADHD and AS: Disentangling the roles of executive functions and social cognition

Attention-deficit/hyperactivity disorder (ADHD) and Asperger's Syndrome (AS) share a heterogeneous cognitive profile. Studies assessing executive functions (EF) and social cognition in both groups have found preserved and impaired performances. These inconsistent findings would be partially explained by the cognitive variability reported in these disorders. First, the present study explored the inter-individual variability in EF and social cognition in both patient groups. Second, we compared differential characteristics and commonalities in the cognitive profiles of EF and social cognition between ADHD, AS and control adults. We assessed 22 patients with ADHD, 23 adults with AS and 21 matched typically developing subjects using different measures of EF (working memory, cognitive flexibility and multitasking) and social cognition (theory of mind and decision-making). Group comparisons and multiple case series analyses (MCSA) were conducted. The between-group comparisons showed an EF deficit in working memory in ADHD and a theory of mind (ToM) impairment in AS. The MCSA evidenced that, compared to controls, ADHD patients had a higher inter-individual variability in EF, while individuals with AS had a more heterogeneous profile in social cognition tasks compared to both groups. Finally, the AS and ADHD groups presented higher task-related variability compared to controls and shared a common heterogeneous profile in EF. This is the first study to compare variability in EF and social cognition profiles of ADHD and AS. We propose that heterogeneity in EF performance is a link between ADHD and AS which may explain the overlap of symptomatology between both diagnoses. In addition, patients with AS seem to show a unique heterogeneous profile in ToM which may explain the low probability of finding AS symptoms in patients with ADHD.     

A meta-analysis of working memory impairments in children with attention-deficit/hyperactivity disorder

OBJECTIVE: To determine the empirical evidence for deficits in working memory (WM) processes in children and adolescents with attention-deficit/hyperactivity disorder (ADHD). METHOD: Exploratory meta-analytic procedures were used to investigate whether children with ADHD exhibit WM impairments. Twenty-six empirical research studies published from 1997 to December, 2003 (subsequent to a previous review) met our inclusion criteria. WM measures were categorized according to both modality (verbal, spatial) and type of processing required (storage versus storage/manipulation). RESULTS: Children with ADHD exhibited deficits in multiple components of WM that were independent of comorbidity with language learning disorders and weaknesses in general intellectual ability. Overall effect sizes for spatial storage (effect size = 0.85, CI = 0.62 - 1.08) and spatial central executive WM (effect size = 1.06, confidence interval = 0.72-1.39) were greater than those obtained for verbal storage (effect size = 0.47, confidence interval = 0.36-0.59) and verbal central executive WM (effect size = 0.43, confidence interval = 0.24-0.62). CONCLUSION: Evidence of WM impairments in children with ADHD supports recent theoretical models implicating WM processes in ADHD. Future research is needed to more clearly delineate the nature, severity, and specificity of the impairments to ADHD.     

Do cognitive interventions for preschoolers improve executive functions and reduce ADHD and externalizing symptoms? A meta-analysis of randomized controlled trials

Many interventions targeting executive function (EF) development in the preschool period, where malleability might be particularly high, have been created and evaluated. We conducted a meta-analysis of randomized controlled trials (RCTs) on the effects of these interventions on (a) EFs in preschool children from the general population as well as preschool children with (symptoms of) attention-deficit hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD), and (b) ADHD and ODD symptoms in preschool children with ADHD/ODD (symptoms). Literature search yielded 35 RCTs. Risk of bias of the individual studies was assessed. A random-effects model was used. Moderator effects were tested using mixed model analyses. The overall effects on EFs were: d = 0.46 (95% CI 0.30–0.61) for working memory (WM), d = 0.30 (95% CI 0.21–0.38) for inhibitory control (IC), d = 0.33 (95% CI − 0.04 to 0.71) for reward-related IC, and d = 0.47 (95% CI 0.28–0.66) for flexibility. In children with ADHD/ODD, mean effects were d = 0.64 (95% CI 0.31–0.96) for WM and d = 0.46 (95% CI 0.07–0.84) for IC. Studies on reward-related IC and FL were lacking. Effects on ODD and ADHD symptoms were d = 0.40 (95% CI − 0.23 to 1.03) and d = 0.28 (95% CI − 0.08 to 0.64), respectively. Interventions targeting multiple EFs and using interpersonal cognitive scaffolding approaches showed large and statistically significant effects on ADHD and ODD symptoms. In preschool children of the general population and in those with ADHD/ODD (symptoms), interventions led to an improvement of EF performance. In children with ADHD and ODD, cognitive scaffolding interventions were most effective in terms of reducing ADHD and ODD symptoms. However, more well-controlled studies need to be conducted before any firm conclusions can be drawn.

     

Etiology and neuropsychology of comorbidity between RD and ADHD: The case for multiple-deficit models

Introduction

Attention-deficit/hyperactivity disorder (ADHD) and reading disability (RD) are complex childhood disorders that frequently co-occur, but the etiology of this comorbidity remains unknown.

Method

Participants were 457 twin pairs from the Colorado Learning Disabilities Research Center (CLDRC) twin study, an ongoing study of the etiology of RD, ADHD, and related disorders. Phenotypic analyses compared groups with and without RD and ADHD on composite measures of six cognitive domains. Twin analyses were then used to test the etiology of the relations between the disorders and any cognitive weaknesses.

Results

Phenotypic analyses supported the hypothesis that both RD and ADHD arise from multiple cognitive deficits rather than a single primary cognitive deficit. RD was associated independently with weaknesses on measures of phoneme awareness, verbal reasoning, and working memory, whereas ADHD was independently associated with a heritable weakness in inhibitory control. RD and ADHD share a common cognitive deficit in processing speed, and twin analyses indicated that this shared weakness is primarily due to common genetic influences that increase susceptibility to both disorders.

Conclusions

Individual differences in processing speed are influenced by genes that also increase risk for RD, ADHD, and their comorbidity. These results suggest that processing speed measures may be useful for future molecular genetic studies of the etiology of comorbidity between RD and ADHD.