Perceptual and motor inhibition in adolescents/young adults with childhood-diagnosed ADHD

Additive and Interactive Effects of Attention-Deficit/Hyperactivity Disorder and Tic Disorder on Brain Connectivity

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and persistent tic disorder (PTD) are two neurodevelopmental disorders that frequently co-occur. Contributions of each disorder to cognitive and behavioral deficits have been reported. In this paper, we tested 3 models of pathophysiology for the two disorders (additive, interactive, and phenotypic) using resting-state connectivity associated with each disorder separately and together.

METHODS

Participants were 148 children (55 with ADHD only, 33 with ADHD and PTD, 27 with PTD only, and 33 healthy control subjects) at ages 8 to 12 years. Following diagnostic interviews and behavioral assessment, participants underwent a 128-channel electroencephalography recording. Resting-state, cortical source-level effective connectivity was analyzed across the 4 groups using a 2 × 2 factorial design with factors of ADHD (with/without) and PTD (with/without).

RESULTS

ADHD diagnosis was the primary driver of cognitive and behavioral deficits, while deficits associated with PTD were primarily with thought problems and internalizing problems when compared with controls. Subadditive effects were observed in co-occurring ADHD+PTD for parent-rated behavioral problems and cognitive functions. Aberrant effective connectivity was primarily associated with ADHD, more specifically with lower posterior and occipital-frontal connectivity, while children with PTD exhibited greater left postcentral to precuneus connectivity. Weaker ADHD-related connectivity was associated with more severe behavioral problems, including internalizing behaviors, thought problems, and working memory deficits.

CONCLUSIONS

Similar to general behavioral deficits, aberrant resting-state neural connectivity in pediatric ADHD and PTD combines additively in co-occurring cases. The findings of this study support ADHD as a focus of treatment in comorbid cases, given the driving role of ADHD in both behavioral and neurophysiological deficits.

Predicting ADHD symptoms and diagnosis at age 14 from objective activity levels at age 7 in a large UK cohort

Hyperactivity is one of the three core symptoms in children with attention deficit hyperactivity disorder (ADHD). Diagnosing ADHD typically involves self-report, third party report and observations. Objective activity data can make a valuable contribution to the diagnostic process. Small actigraphy studies in clinical samples have shown that children with ADHD move more than children without ADHD. However, differences in physical activity between children with and without ADHD have not been assessed in large community samples or longitudinally. This study used data from the Millennium Cohort Study to test whether symptoms of ADHD (parent-rating Strengths and Difficulties Questionnaire) and ADHD diagnosis at age 14 (reported by parents) could be predicted from objective activity data (measured with actigraphs) at age 7 in N = 6675 children (final N = 5251). Regressions showed that less sedentary behavior at age 7 predicted more ADHD symptoms at age 14 (β =  - 0.002, CI  - 0.004 to  - 0.001). The result remained significant when controlled for ADHD symptoms at age 7, sex, BMI, month of birth, SES and ethnicity (β  =  - 0.001, CI  - 0.003 to  - 0.0003). ADHD diagnosis at age 14 was also significantly predicted by less sedentary behavior at age 7 (β  =  - 0.008). Our findings show that symptoms of ADHD can be predicted by objective activity data 5 years in advance and suggest that actigraphy could be a useful instrument aiding an ADHD diagnosis. Interestingly, the results indicate that the key difference between children with and without ADHD lies in reduced sedentary activity, i.e., times of rest.

Peripheral Hypoarousal but Not Preparation-Vigilance Impairment Endures in ADHD Remission

Objective: This study investigates whether impairments associated with persistent ADHD-impaired attention allocation (P3 amplitude), peripheral hypoarousal (skin conductance level [SCL]), and adjustment in preparatory state (contingent negative variation [CNV])-reflect enduring deficits unrelated to ADHD outcome or are markers of ADHD remission. Method: Young people with childhood ADHD (73 persisters and 18 remitters) and 144 controls were compared on neurophysiological measures during two conditions (baseline and fast-incentive) of a four-choice reaction time task. Results: ADHD remitters differed from persisters, and were indistinguishable from controls, on baseline P3 amplitude and fast-incentive CNV amplitude (p ≤ .05). ADHD remitters differed from controls (p ≤ .01), and were indistinguishable from persisters (p > .05), on baseline SCL. Conclusion: Preparation-vigilance measures were markers of ADHD remission, confirming previous findings with other measures. Yet, SCL-measured peripheral hypoarousal emerges as an enduring deficit unrelated to ADHD improvement. Future studies should explore potential compensatory mechanisms that enable efficient preparation-vigilance processes in ADHD remitters.

In Quest of Pathognomonic/Endophenotypic Markers of Attention Deficit Hyperactivity Disorder (ADHD): Potential of EEG-Based Frequency Analysis and ERPs to Better Detect, Prevent and Manage ADHD

Attention deficit hyperactivity disorder (ADHD) is a chronic heritable developmental delay psychiatric disorder requiring chronic management, characterized by inattention, hyperactivity, hyperkinectivity and impulsivity. Subjective clinical evaluation still remains crucial in its diagnosis. Discussed are two key aspects in the “characterizing ADHD” and on the quest for objective “pathognomonic/endophenotypic diagnostic markers of ADHD”. The first aspect briefly revolves around issues related to identification of pathognomonic/endophenotypic diagnostic markers in ADHD. Issues discussed include changes in ADHD definition, remission/persistence and overlapping-symptoms cum shared-heritability with its co-morbid cross-border mental disorders. The second aspect discussed is neurobiological and EEG-based studies on ADHD. Given the neurobiological and temporal aspects of ADHD symptoms the electroencephalograph (EEG) like NeuralScan by Medeia appears as an appropriate tool. The EEGs appropriateness is further enhanced when coupled with suitable behavior/cognitive/motor/psychological tasks/paradigms yielding EEG-based markers like event-related-potential (ERPs like P3 amplitudes and latency), reaction time variability (RTV), Theta:Beta ratio (TBR) and sensorimotor rhythm (SMR). At present, these markers could potentially help in the neurobiological characterization of ADHD and either help in identifying or lay the groundwork for identifying pathognomonic and/or endophenotypic EEG-based markers enabling its diagnosis, treatment and management.

Live fast, die young? A review on the developmental trajectories of ADHD across the lifespan

Attention-deficit/hyperactivity disorder (ADHD) is highly heritable and the most common neurodevelopmental disorder in childhood. In recent decades, it has been appreciated that in a substantial number of cases the disorder does not remit in puberty, but persists into adulthood. Both in childhood and adulthood, ADHD is characterised by substantial comorbidity including substance use, depression, anxiety, and accidents. However, course and symptoms of the disorder and the comorbidities may fluctuate and change over time, and even age of onset in childhood has recently been questioned. Available evidence to date is poor and largely inconsistent with regard to the predictors of persistence versus remittance. Likewise, the development of comorbid disorders cannot be foreseen early on, hampering preventive measures. These facts call for a lifespan perspective on ADHD from childhood to old age. In this selective review, we summarise current knowledge of the long-term course of ADHD, with an emphasis on clinical symptom and cognitive trajectories, treatment effects over the lifespan, and the development of comorbidities. Also, we summarise current knowledge and important unresolved issues on biological factors underlying different ADHD trajectories. We conclude that a severe lack of knowledge on lifespan aspects in ADHD still exists for nearly every aspect reviewed. We encourage large-scale research efforts to overcome those knowledge gaps through appropriately granular longitudinal studies.

Can Methodological Considerations Challenge the Dissociation of the Perceptual and Motor Inhibitory Processes?

Using an original conflict task paradigm, Nassauer and Halperin (2003) argued that inhibition ability can be classified into two distinct perceptual and motor inhibitory processes. The current study examined the robustness of this paradigm by raising two major methodological points: the amount of information that needs to be processed and the task order (fixed vs. random). Sixty young adults performed the original or modified tasks. Overall, a decrease in the amount of information had the effect of removing the stimulus conflict on some subtests. Therefore, no more inhibition performance could be assessed. Even if the findings can be interpreted as a change in response-related complexity that relates reaction time performance to the informational processing load, the discrepancies in terms of the amount of information originally designed are necessary to induce inhibitory conflicts. Additionally, unlike previous recommendations, the fixed task order initially adopted cannot be considered an essential methodological requirement.

Examination of reactive motor responses to Achilles tendon vibrations during an inhibitory stepping reaction time task

Inhibition is known to influence balance, step initiation and gait control. A specific subcomponent of inhibition, the perceptual inhibition process, has been suggested to be specifically involved in the integration of proprioceptive information that is necessary for efficient postural responses. This study aimed to investigate the inhibition requirements of planning and executing a choice step initiation task in young adults following experimental perturbation of proprioceptive information using Achilles tendon vibrations. We developed an inhibitory stepping reaction time task in which participants had to step in response to visual arrows that manipulated specific perceptual or motor inhibition according to two proprioceptive configurations: without or with application of vibrations. Performance of twenty-eight participants (mean age 21 years) showed that Achilles tendon vibrations induced an increase in attentional demands (higher reaction time and longer motor responses). Further, this increase in attentional demands did not affect specifically the different inhibitory processes tested in this reactive stepping task. It suggests that attentional demands associated with the vibratory perturbation to postural control do not lead to a shift from automatic to more attentional inhibition processes, at least in young adults.

Clinical, Sociobiological, and Cognitive Predictors of ADHD Persistence in Children Followed Prospectively Over Time

With increasing awareness that ADHD is chronically disabling, a burgeoning literature has examined childhood clinical indicators of ADHD persistence. This study investigates whether childhood factors reflecting biological risk and cognitive reserve have additive predictive value for the persistence of ADHD that is unique beyond childhood indicators of disorder severity. One-hundred thirty children with ADHD (mean age = 8.9 years, 75 % male) were followed into adolescence (mean age = 14.0 years). Childhood ADHD and co-morbidities were assessed via interviews with parents and teachers; parental psychopathology was assessed via parent interview; exposure to neurobiological and psychosocial adversity were indexed by parent questionnaire; and cognitive reserve was evaluated through children's performance on measures of IQ and executive functioning. Univariate analyses identified childhood inattention and hyperactivity-impulsivity, co-morbid oppositional defiant disorder, overall impairment, and paternal anxiety and depression as more prevalent amongst adolescents with persistent compared with remitted ADHD. Only child-level predictors remained significant in a final multivariate model. These results suggest that children who are most likely to experience persistent ADHD have a more severe clinical presentation in childhood, reflected by increased levels of inattention, oppositional behavior, and impairment. They also are more likely to have fathers with internalizing concerns, but these concerns do not uniquely predict ADHD persistence beyond child-level factors. Contrary to expectations, childhood adversity and cognitive functioning did not predict the course of ADHD.

Neurocognitive and Symptom Trajectories of ADHD from Childhood to Early Adolescence

OBJECTIVE

This longitudinal study investigated changes in neurocognitive functioning from childhood to early adolescence in a sample of children diagnosed with DSM-IV attention-deficit hyperactivity disorder (ADHD). It also compared the neurocognitive trajectories of children who continued to meet the diagnostic criteria for ADHD at follow-up and those in partial remission.

METHODS

Children diagnosed with ADHD (N = 55) were tested at baseline (M = 7.7 years, SD = 1.5) and 4 years later (M = 11.7 years, SD = 1.5) on measures of intellectual, academic, and executive functioning. Group and individual analyses were used to examine neurocognitive functioning over this period.

RESULTS

Intellectual function was stable over the 4-year interval. Reliable change analyses highlighted variability in academic performance. Approximately half the sample showed a reliable decline in at least 1 academic subject with almost a third showing reliable improvement. Executive functions generally followed a stable or improving course, with significant improvements on measures of information processing, attentional control, cognitive flexibility, and goal setting. There was some evidence of better neurocognitive performance in those with partial symptom remission at follow-up.

CONCLUSION

Study findings emphasize the importance of monitoring academic performance in children with ADHD, including examination of change at the individual level. Declines in academic performance were observed, despite stable intellectual and improving executive function. Early cognitive functioning did not predict symptom remission; however, reduced symptoms at follow-up were associated with better executive function.

Prefrontal and parietal correlates of cognitive control related to the adult outcome of attention-deficit/hyperactivity disorder diagnosed in childhood

The protracted and highly variable development of prefrontal cortex regions that support cognitive control has been purported to shape the adult outcome of attention-deficit/hyperactivity disorder (ADHD). This neurodevelopmental model was tested in a prospectively followed sample of 27 adult probands who were diagnosed with ADHD in childhood and 28 carefully matched comparison subjects aged 21-28 years. Probands were classified with persistent ADHD or remitted ADHD. Behavioral and neural responses to the Stimulus and Response Conflict Task (SRCT) performed during functional magnetic resonance imaging (fMRI) were compared in probands and comparison subjects and in probands with persistent and remitted ADHD. Response speed and accuracy for stimulus, response, and combined conflicts did not differ across groups. Orbitofrontal, inferior frontal and parietal activation was lower in probands than comparison subjects, but only for combined conflicts, when demand for cognitive control was highest. Reduced activation for combined conflicts in probands was almost wholly attributable to the persistence of ADHD; orbitofrontal, inferior frontal, anterior cingulate and parietal activation was lower in probands with persistent ADHD than both probands with remitted ADHD and comparison subjects, but did not differ between probands with remitted ADHD and comparison subjects. These data provide the first evidence that prefrontal and parietal activation during cognitive control parallels the adult outcome of ADHD diagnosed in childhood, with persistence of symptoms linked to reduced activation and symptom recovery associated with activation indistinguishable from adults with no history of ADHD.

Attention-Deficit/Hyperactivity Disorder Remission Is Linked to Better Neurophysiological Error Detection and Attention-Vigilance Processes

BACKGROUND

The processes underlying persistence and remission of attention-deficit/hyperactivity disorder (ADHD) are poorly understood. We examined whether cognitive and neurophysiological impairments on a performance-monitoring task distinguish between ADHD persisters and remitters.

METHODS

On average 6 years after initial assessment, 110 adolescents and young adults with childhood ADHD (87 persisters, 23 remitters) and 169 age-matched control participants were compared on cognitive-performance measures and event-related potentials of conflict monitoring (N2) and error processing (error-related negativity and positivity) from an arrow flanker task with low-conflict and high-conflict conditions. ADHD outcome was examined with parent-reported symptoms and functional impairment measures using a categorical (DSM-IV) and a dimensional approach.

RESULTS

ADHD persisters were impaired compared with controls on all cognitive-performance and event-related potential measures (all p < .05). ADHD remitters differed from persisters and were indistinguishable from control participants on the number of congruent (low-conflict) errors, reaction time variability, error-related negativity, and error-related positivity (all p ≤ .05). Remitters did not differ significantly from the other groups on incongruent (high-conflict) errors, mean reaction time, and N2. In dimensional analyses on all participants with childhood ADHD, ADHD symptoms and functional impairment at follow-up were significantly correlated with congruent errors, reaction time variability, and error-related positivity (r = .19-.23, p ≤ .05).

CONCLUSIONS

Cognitive and neurophysiological measures of attention-vigilance and error detection distinguished ADHD remitters from persisters. These results extend our previous findings with other tasks and indicate that such measures are markers of remission and candidates for the development of nonpharmacological interventions.

Atomoxetine could improve intra-individual variability in drug-naïve adults with attention-deficit/hyperactivity disorder comparably with methylphenidate: A head-to-head randomized clinical trial

OBJECTIVE

Intra-individual variability in reaction time (IIV-RT) is common in individuals with attention-deficit/hyperactivity disorder (ADHD). It can be improved by stimulants. However, the effects of atomoxetine on IIV-RT are inconclusive. We aimed to investigate the effects of atomoxetine on IIV-RT, and directly compared its efficacy with methylphenidate in adults with ADHD.

METHODS

An 8-10 week, open-label, head-to-head, randomized clinical trial was conducted in 52 drug-naïve adults with ADHD, who were randomly assigned to two treatment groups: immediate-release methylphenidate (n=26) thrice daily (10-20 mg per dose) and atomoxetine once daily (n=26) (0.5-1.2 mg/kg/day). IIV-RT, derived from the Conners' continuous performance test (CCPT), was represented by the Gaussian (reaction time standard error, RTSE) and ex-Gaussian models (sigma and tau). Other neuropsychological functions, including response errors and mean of reaction time, were also measured. Participants received CCPT assessments at baseline and week 8-10 (60.4±6.3 days).

RESULTS

We found comparable improvements in performances of CCPT between the immediate-release methylphenidate- and atomoxetine-treated groups. Both medications significantly improved IIV-RT in terms of reducing tau values with comparable efficacy. In addition, both medications significantly improved inhibitory control by reducing commission errors.

CONCLUSION

Our results provide evidence to support that atomoxetine could improve IIV-RT and inhibitory control, of comparable efficacy with immediate-release methylphenidate, in drug-naïve adults with ADHD. Shared and unique mechanisms underpinning these medication effects on IIV-RT awaits further investigation.

A four-year follow-up controlled study of stress response and symptom persistence in Brazilian children and adolescents with attention deficit disorder and hyperactivity (ADHD)

This study evaluated children and adolescents with Attention Deficit Disorder andHyperactivity Disorder (ADHD), reassessing them at a four-year follow-up. Their cortisol response to a stress stimulus was measured twice. ADHD symptom persistence, development of comorbidities, and psychostimulant usage were also reassessed. The initial sample consisted of 38 ADHD patients and 38 healthy controls, age ranging 6-14. At the follow-up, there were 37 ADHD patients and 22 healthy controls, age ranging 10-18. ADHD was classified as persistent if the patients fulfilled all DSM IV criteria for syndromic or subthreshold or had functional impairment. Salivary cortisol samples were collected prior to the application of a cognitive stressor (Continuous Performance Test - CPT), and at three time intervals afterwards at baseline and at the follow-up. Their reassessment showed that 75% had persistent symptoms, psychiatric comorbidities (oppositional defiant and behavioral disorders), functional and academic impairement. Only seven patients were on medication. The ADHD group's cortisol levels were lower than those measured four years earlier, but cortisol concentrations were similar for both ADHD and control groups at the four-year follow-up. The cortisol results suggest that HPA axis reactivity could be a marker differentiating ADHD from ADHD with comorbidities.

The executive control network and symptomatic improvement in attention-deficit/hyperactivity disorder

BACKGROUND

One neurodevelopmental theory hypothesizes remission of attention-deficit/hyperactivity disorder (ADHD) to result from improved prefrontal top-down control, while ADHD, independent of the current diagnosis, is characterized by stable non-cortical deficits (Halperin & Schulz, 2006). We tested this theory using resting state functional MRI (fMRI) data in a large sample of adolescents with remitting ADHD, persistent ADHD, and healthy controls.

METHODS

Participants in this follow-up study were 100 healthy controls and 129 adolescents with ADHD combined type at baseline (mean age at baseline 11.8 years; at follow-up 17.5 years). Diagnostic information was collected twice and augmented with magnetic resonance imaging (MRI) scanning at follow-up. We used resting state functional connectivity (RSFC) of the executive control network to investigate whether improved prefrontal top-down control was related to a developmental decrease in ADHD symptoms. In addition, we tested whether non-cortical RSFC, i.e., cerebellar and striatal RSFC, was aberrant in persistent and/or remittent ADHD compared to controls.

RESULTS

Higher connectivity within frontal regions (anterior cingulate cortex) of the executive control network was related to decreases in ADHD symptoms. This association was driven by change in hyperactive/impulsive symptoms and not by change in inattention. Participants with remitting ADHD showed stronger RSFC than controls within this network, while persistent ADHD cases exhibited RSFC strengths intermediate to remittent ADHD cases and controls. Cerebellar and subcortical RSFC did not differ between participants with ADHD and controls.

CONCLUSIONS

In line with the neurodevelopmental theory, symptom recovery in ADHD was related to stronger integration of prefrontal regions in the executive control network. The pattern of RSFC strength across remittent ADHD, persistent ADHD, and healthy controls potentially reflects the presence of compensatory neural mechanisms that aid symptomatic remission.

Childhood predictors of adolescent and young adult outcome in ADHD

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) often persists into adulthood, but it remains unclear which childhood factors predict future outcome.

AIM

To identify childhood predictors of ADHD outcome using both dimensional and categorical approaches.

METHODS

116 adolescents and young adults with childhood ADHD were followed up on average 6.6 years later. ADHD outcome variables were interview-based parent-reported ADHD symptoms and impairment. Childhood predictors included parent- and teacher-rated ADHD symptoms and co-occurring behaviours; actigraph measures of activity level; socio-economic status (SES); and cognitive measures previously associated with ADHD.

RESULTS

Of the sample, 79% continued to meet clinical criteria of ADHD in adolescence and young adulthood. Higher parent-rated ADHD symptoms and movement intensity in childhood, but not teacher-rated symptoms, predicted ADHD symptoms at follow up. Co-occurring symptoms of oppositional behaviours, anxiety, social and emotional problems were also significant predictors, but these effects disappeared after controlling for ADHD symptoms. IQ and SES were significant predictors of both ADHD symptoms and impairment at follow up, but no other cognitive measures significantly predicted outcome.

CONCLUSIONS

SES and IQ emerge as potential moderators for the prognosis of ADHD. Childhood severity of ADHD symptoms, as measured by parent ratings and actigraph movement intensity, also predicts later ADHD outcome. These factors should be considered when identifying ADHD children at most risk of poor long-term outcomes and for the development of interventions to improve prognosis.

A longitudinal examination of neuropsychological and clinical functioning in boys with attention deficit hyperactivity disorder (ADHD): improvements in executive functioning do not explain clinical improvement

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) often, but not always, persists into adulthood. Investigations of the associations between clinical and biological markers of persistence can shed light on causal pathways. It has been proposed that compensatory improvements in executive neuropsychological functioning are associated with clinical improvements. This is the first study to test this hypothesis prospectively.

METHOD

The clinical and neuropsychological functioning of 17 boys with ADHD (mean age 10.45 years at time 1; 14.65 years at time 2) and 17 typically developing (TYP) boys (mean age 10.39 years at time 1; 14.47 years at time 2) was tested on two occasions, 4 years apart. This was done using a battery of standardized neuropsychological tests that included tasks with high and low executive demands.

RESULTS

Clinical improvements were observed over time. Neuropsychological performance improvements were also evident, with ADHD boys developing with a similar pattern to TYP boys, but with a developmental lag. Whilst there was an association between reduced symptoms and superior performance at retest for one task with a high executive demand (spatial working memory), this was not seen with two further high executive demand tasks [Stockings of Cambridge and intra-dimensional extra-dimensional (ID/ED) set shifting]. Also, there was no association between change in executive functioning and change in symptoms. Baseline performance on the ID/ED set-shifting task predicted better clinical outcome. Only change in performance on the low executive demand delayed matching-to-sample task predicted better clinical outcome.

CONCLUSIONS

These data highlight the importance of longitudinal measurements of cognition, symptoms and treatment response over time in children and adolescents with ADHD.

The persistence of cognitive deficits in remitted and unremitted ADHD: a case for the state-independence of response inhibition

BACKGROUND

Response inhibition, working memory, and response variability are possible endophenotypes of ADHD based on their association with the disorder and evidence of heritability. One of the critical although rarely studied criteria for a valid endophenotype is that it persists despite waxing and waning of the overt manifestations of the disorder, a criterion known as state-independence. This study examined whether these aspects of cognition exhibit state-independence in ADHD.

METHODS

One hundred and seventy-nine children diagnosed with ADHD in a rigorous baseline assessment were contacted for follow-up assessment in adolescence. Of this sample, 130 (73%) were reascertained. At follow-up, children previously diagnosed with ADHD were identified as remittent (n = 24), persistent (n = 64), or in partial remission (n = 42) based on symptoms and impairment of the disorder. Response inhibition, working memory, and response variability were assessed both in childhood (baseline) and adolescence (follow-up) and were compared with age-matched controls (40 children and 28 adolescents) seen at either time point.

RESULTS

Relative to controls, ADHD children showed baseline deficits in response inhibition, working memory, and response variability. Only the group difference in response inhibition remained significant in adolescence. In general, cognitive performance among ADHD participants improved with age and did so regardless of changes in ADHD symptoms and impairment. Within the ADHD group, however, cognitive performance in childhood and in adolescence did not differ amongst those with persistent, remittent, and partially remittent forms of the disorder.

CONCLUSIONS

Results demonstrate that response inhibition not only distinguishes ADHD children from their unaffected peers but is also state-independent, such that deficits remain present irrespective of changes in the disease phenotype. In other words, inhibitory deficits measured in childhood persist into adolescence even when the ADHD phenotype remits. These findings provide further evidence that the ability to stop prepotent actions is an endophenotype of ADHD.

Neuropsychological functioning and severity of ADHD in early childhood: a four-year cross-lagged study

Children with attention deficit/hyperactivity disorder (ADHD) have poorer neuropsychological functioning relative to their typically developing peers. However, it is unclear whether early neuropsychological functioning predicts later ADHD severity and/or the latter is longitudinally associated with subsequent neuropsychological functioning; and whether these relations are different in children with and without early symptoms of ADHD. This study aimed to examine the longitudinal associations between ADHD severity and neuropsychological functioning among children at high and low risk of developing ADHD. Hyperactive/Inattentive (H/I; n = 140) and Typically developing (TD; n = 76) preschoolers (age 3-4 years) were recruited (BL) and followed annually for 3 years (F1, F2, and F3). Teachers rated the children's ADHD severity and impairment using the Behavior Assessment System for Children-2 and the Children's Problem Checklist, respectively. Parent reports of children's ADHD severity were obtained using the Kiddie-Schedule for Affective Disorders and Schizophrenia - Present and Lifetime version. Neuropsychological functioning was assessed using the NEPSY. In the full sample, there were bidirectional longitudinal associations between neuropsychological functioning and ADHD severity between F1 and F3. Among H/I children, neuropsychological functioning at F1 and F2 predicted ADHD severity at F2 and F3, respectively. In contrast, among TD children the only significant relationship observed was that elevated ADHD symptoms at F2 were associated with poorer neuropsychological functioning at F3. Improved neuropsychological functioning may attenuate ADHD symptoms and associated impairment among H/I children during the early school years. Interventions designed to improve neuropsychological functioning among young H/I children may be beneficial in reducing their ADHD severity.

Association between variation in neuropsychological development and trajectory of ADHD severity in early childhood

OBJECTIVE

This longitudinal study examined if changes in neuropsychological functioning were associated with the trajectory of symptoms related to attention deficit hyperactivity disorder (ADHD) and impairment between preschool and school age.

METHOD

The sample consisted of 3- and 4-year-old children (N=138) who were identified as being at risk for ADHD based on parent and teacher reports. Neuropsychological functioning was measured annually using the NEPSY at four time points (mean ages, 4.19, 5.36, 6.35, and 7.35 years). ADHD symptoms and impairment were assessed with semiannual parent and teacher reports using the ADHD Rating Scale-IV and the Children's Problems Checklist at 10 time points (mean ages at baseline and final assessment, 4.19 and 8.81 years, respectively). Hierarchical linear modeling was used to assess the trajectories of change in neuropsychological functioning and ADHD severity as well as the association of change in neuropsychological functioning with change in ADHD severity over time.

RESULTS

Baseline neuropsychological functioning was not significantly associated with the slope of change in ADHD severity. However, the magnitude of change in neuropsychological functioning was linearly associated with the trajectory of ADHD symptom severity and impairment, such that individuals with greater neuropsychological growth over time had a greater diminution of ADHD severity and impairment. Family socioeconomic status at baseline was significantly associated with initial ADHD severity and impairment, but not with change over time.

CONCLUSIONS

Interventions that enhance neuropsychological functioning at an early age may be beneficial in attenuating long-term ADHD severity and impairment.

Protection from genetic diathesis in attention-deficit/hyperactivity disorder: possible complementary roles of exercise

OBJECTIVE

The degree of functional impairment and adverse developmental outcomes in individuals with attention-deficit/hyperactivity disorder (ADHD) likely reflect interplay between genes and environment. To establish whether physical exercise might reduce the level of ADHD symptoms or ADHD-related impairments, we conducted a comprehensive review of the effect of exercise in children with ADHD. Findings on the impact of exercise in animals and typically developing human beings, and an overview of putative mechanisms involved, are also presented to provide the context in which to understand this review.

METHOD

The electronic databases PubMed, OVID, and Web of Knowledge were searched for all studies investigating the effect of exercise in children and adolescents with ADHD, as well as animal models of ADHD behaviors (available in January 2013). Of 2,150 initially identified records, 16 were included.

RESULTS

Animal studies indicate that exercise, especially early in development, may be beneficial for ADHD symptom reduction. The limited research investigating the effect of exercise in children and adolescents with ADHD suggests that exercise may improve executive functioning and behavioral symptoms associated with ADHD. Although animal research suggests that brain-derived neurotrophic factor (BDNF) and catecholamines (CAs) play a role in mediating these effects, the association between BDNF and ADHD remains unclear in human beings.

CONCLUSIONS

The potential protective qualities of exercise with regard to reducing symptoms and impairments commonly associated with ADHD may hold promise for the future. Further research is needed to firmly establish whether there are clinically significant effects of exercise on the severity of ADHD symptoms, impairments, and associated developmental outcomes.

Emerging support for a role of exercise in attention-deficit/hyperactivity disorder intervention planning

Recent years have seen an expansion of interest in non-pharmacological interventions for attention-deficit/hyperactivity disorder (ADHD). Although considerable treatment development has focused on cognitive training programs, compelling evidence indicates that intense aerobic exercise enhances brain structure and function, and as such, might be beneficial to children with ADHD. This paper reviews evidence for a direct impact of exercise on neural functioning and preliminary evidence that exercise may have positive effects on children with ADHD. At present, data are promising and support the need for further study, but are insufficient to recommend widespread use of such interventions for children with ADHD.

Preventive interventions for ADHD: a neurodevelopmental perspective

It is proposed that the time is ripe for the development of secondary preventive interventions for attention-deficit/hyperactivity disorder (ADHD). By targeting preschool children, a developmental stage during which ADHD symptoms first become evident in most children with the disorder, many of the adverse long-term consequences that typify the trajectory of ADHD may be avoided. A dynamic/interactive model of the biological and environmental factors that contribute to the emergence and persistence of ADHD throughout the lifespan is proposed. Based on this model, it is argued that environmental influences and physical exercise can be used to enhance neural growth and development, which in turn should have an enduring and long-term impact on the trajectory of ADHD. Central to this notion are 2 hypotheses: 1) environmental influences can facilitate structural and functional brain development, and 2) changes in brain structure and function are directly related to ADHD severity over the course of development and the degree to which the disorder persists or remits with time. We present experimental and correlational data supporting the first hypothesis and longitudinal data in individuals with ADHD supporting the second. The case is made for initiating such an intervention during the preschool years, when the brain is likely to be more "plastic" and perhaps susceptible to lasting modifications, and before complicating factors, such as comorbid psychiatric disorders, academic failure, and poor social and family relationships emerge, making successful treatment more difficult. Finally, we review recent studies in young children with ADHD that might fall under the umbrella of secondary prevention.