Psychological heterogeneity in AD/HD--a dual pathway model of behaviour and cognition

What would Karl Popper say? Are current psychological theories of ADHD falsifiable?

Attention Deficit Hyperactivity Disorder (ADHD) is a common and highly heritable neurodevelopmental psychiatric disorder. Here, we critically review four major psychological theories of ADHD - the Executive Dysfunction, the State Regulation, the Delay Aversion and the Dynamic Developmental - on their abilities to explain all the symptoms of ADHD, their testability and their openness to falsification. We conclude that theoreticians should focus, to a greater extent than currently practiced, on developing refutable theories of ADHD.

Origins of altered reinforcement effects in ADHD

Attention-deficit/hyperactivity disorder (ADHD), characterized by hyperactivity, impulsiveness and deficient sustained attention, is one of the most common and persistent behavioral disorders of childhood. ADHD is associated with catecholamine dysfunction. The catecholamines are important for response selection and memory formation, and dopamine in particular is important for reinforcement of successful behavior. The convergence of dopaminergic mesolimbic and glutamatergic corticostriatal synapses upon individual neostriatal neurons provides a favorable substrate for a three-factor synaptic modification rule underlying acquisition of associations between stimuli in a particular context, responses, and reinforcers. The change in associative strength as a function of delay between key stimuli or responses, and reinforcement, is known as the delay of reinforcement gradient. The gradient is altered by vicissitudes of attention, intrusions of irrelevant events, lapses of memory, and fluctuations in dopamine function. Theoretical and experimental analyses of these moderating factors will help to determine just how reinforcement processes are altered in ADHD. Such analyses can only help to improve treatment strategies for ADHD.

Behavioural characterisation of high impulsivity on the 5-choice serial reaction time task: specific deficits in 'waiting' versus 'stopping'

Impulsivity is a core deficit of a number of neuropsychiatric disorders including attention-deficit hyperactivity disorder (ADHD), anti-social conduct disorder and drug addiction. Recent research has highlighted the multifaceted nature of impulsivity and the myriad of putative neural and psychological mechanisms thought to underpin behavioural syndromes of impaired self-control. Here we report a novel conceptualisation of impulsivity based on 'waiting' and 'stopping' efficiency with explanatory value in defining the psychological and neural basis of impulsivity and the high co-morbidity of brain disorders such as ADHD and drug addiction. Rats selected for high levels of impulsivity on a reaction time task analogous to the continuous performance test in humans exhibited correspondingly high levels of impulsive decision-making on a delay-of-reward task. The same rats, however, were unimpaired on a stop-signal task requiring inhibition of an already initiated motor response. The specific nature of this deficit in 'waiting impulsivity' was confirmed by unimpaired acquisition of appetitive Pavlovian conditioning, a putative ancillary measure of impulsive behaviour. These findings are significant in light of recent evidence linking impulsivity in rats to high levels of cocaine self-administration and development of compulsive cocaine seeking behaviour. We thus suggest that an inability to bridge delays to future rewards and reward-related stimuli is a candidate behavioural endophenotype that pre-disposes to clinical psychopathology.

Impulsivity as a determinant and consequence of drug use: a review of underlying processes

Impulsive behaviors are closely linked to drug use and abuse, both as contributors to use and as consequences of use. Trait impulsivity is an important determinant of drug use during development, and in adults momentary 'state' increases in impulsive behavior may increase the likelihood of drug use, especially in individuals attempting to abstain. Conversely, acute and chronic effects of drug use may increase impulsive behaviors, which may in turn facilitate further drug use. However, these effects depend on the behavioral measure used to assess impulsivity. This article reviews data from controlled studies investigating different measures of impulsive behaviors, including delay discounting, behavioral inhibition and a newly proposed measure of inattention. Our findings support the hypothesis that drugs of abuse alter performance across independent behavioral measures of impulsivity. The findings lay the groundwork for studying the cognitive and neurobiological substrates of impulsivity, and for future studies on the role of impulsive behavior as both facilitator and a result of drug use.

Neural hyporesponsiveness and hyperresponsiveness during immediate and delayed reward processing in adult attention-deficit/hyperactivity disorder

BACKGROUND

Dysfunctional reward processing, accompanied by a limited ability to tolerate reward delays, has been proposed as an important feature in attention-deficit/hyperactivity disorder (ADHD).

METHODS

Using functional magnetic resonance imaging (fMRI), brain activation in adult patients with ADHD (n=14) and healthy control subjects (n=12) was examined during a series of choices between two monetary reward options that varied by delay to delivery.

RESULTS

Compared with healthy control subjects, hyporesponsiveness of the ventral-striatal reward system was replicated in patients with ADHD and was evident for both immediate and delayed rewards. In contrast, delayed rewards evoked hyperactivation in dorsal caudate nucleus and amygdala of ADHD patients. In both structures, neural activity toward delayed rewards was significantly correlated with self-rated ADHD symptom severity.

CONCLUSIONS

The finding of ventral-striatal hyporesponsiveness during immediate and delayed reward processing in patients with ADHD further strengthens the concept of a diminished neural processing of rewards in ADHD. Hyperactivation during delayed reward processing, gradually increasing along the ventral-to-dorsal extension of the caudate nucleus, and especially the concomitant hyperactivation of the amygdala are in accordance with predictions of the delay aversion hypothesis.

Development of attentional processes in ADHD and normal children

Attention Deficit Hyperactivity Disorder (ADHD) is a developmental disorder. Typical development of attentional processes is rapid during early childhood. ADHD results in impairment in response inhibition, error monitoring, attentional disengagement, executive attention, and delay aversion and may effect the ongoing development of these processes during childhood. We examined the development of attentional processes in children with ADHD and normal children. Two hundred forty children (120 in each group) in the age range of 6-9 years participated in the study. Four tasks: Stop-Signal, attentional disengagement, attention network, and choice delay task were administered. Stop signal reaction time, switch costs, conflict effect, and percentage choice of short delay reward was higher in ADHD group compared to normal group. Post error of slowing was less in ADHD children. Endogenous orienting effect was more in normal children compared to ADHD children. Different developmental trajectories were observed for control functions in normal children. Major development in response inhibition occurred in 7-8 years, error monitoring in 6-9 years, and attentional disengagement in 7-9 years. Late development in alerting network was observed in normal children at age 9 years. No developmental changes occurred on these control functions in ADHD children aged 6-9 years. Age related changes were observed on delay aversion between 6 and 9 years in normal children, while it changed between 6 and 7 years in ADHD children. Performance was not changed on orienting and conflict attentional networks in both the children except conflict effect reduced between 7 and 9 years in ADHD children under double cue condition. Conflict network was interacted with the alerting and orienting network in normal children; specifically conflict network interacted with the orienting network in younger children (age 6 years) and with alerting network in older children (age 9 years). In ADHD group interaction between alerting and conflict network was observed only in the double cue condition. Together these results indicated that the deficits in control processes accumulate with age in ADHD children Present study favors the conceptual view of ADHD as a stable deficit in cognitive control functions, which are implicated in the pathology of ADHD. These results have theoretical implication for the theories of executive control and ADHD.

Computerspiele im Kindes- und Jugendalter unter besonderer Betrachtung von Suchtverhalten, ADHS und Aggressivität

Einleitung: Computerspiele gehören mittlerweile zu den beliebtesten Freizeitbeschäftigungen von Kindern und Jugendlichen und ersetzen in zunehmendem Maß traditionelle Spiel-und Interaktionsaktivitäten. Gesamt betrachtet sind mit dieser Entwicklung nicht nur emotionale oder soziale Entwicklungsrisiken verbunden und im pädagogisch-therapeutischen Bereich können sich mit der Nutzung von Computerspielen auch durchaus Förder- oder sogar therapeutische Möglichkeiten verbinden. Anderseits mehren sich Belege, dass die exzessive Nutzung von Computerspielen mit einem signifikant erhöhten Risiko zu nicht-stoffgebundenem Suchtverhalten einhergeht und die Prävalenzen hierfür altersübergreifend besorgniserregend hoch sind mit tendenzieller Zunahme. Zielsetzung: Der vorliegende Beitrag basiert auf einer Medlinerecherche. Die Zielsetzung besteht darin, zunächst motivationale und entwicklungspsychologische Besonderheiten von Computerspielen herauszuarbeiten, Prävalenzen und Risiken für eine Suchtentwicklung darzustellen und Verbindungen sowie Auswirkungen zu ausgewählten psychischen Störungen, nämlich Aufmerksamkeitsdefizitstörungen und aggressiven Verhaltensweisen darzustellen. Ergebnisse: Die vorliegenden Ergebnisse weisen aus, dass speziell von einer ADHS betroffene Kinder und Jugendliche aufgrund der neuropsychologischen Gegebenheiten dieses Störungsbildes vulnerabel sind für die Entwicklung einer Computerspielsucht. Zum anderen kann der exzessive Konsum gewalthaltiger Computerspiele ein wichtiges Bindeglied für das Zustandekommen vermehrt aggressiver Verhaltensweisen bedeuten bei Vorliegen von bereits vorbestehenden aggressiven Kognitionen und Verhaltensskripten. Schlussfolgerung: Angesichts der zunehmenden klinischen Relevanz von Suchtverhalten bei Computerspielen besteht dringend die Notwendigkeit zur Erarbeitung diagnostischer und therapeutischer Standards, wobei der Vernetzung mit ebenfalls mit der Materie befassten Fach- bzw. Arbeitsbereichen eine wichtige Bedeutung zukommt.

A review and analysis of the relationship between neuropsychological measures and DAT1 in ADHD

Meta-analyses indicate that the gene coding for the dopamine transporter (DAT1 or SLC6A3) is associated with an increased risk for ADHD. The mechanisms of this gene for ADHD are unclear. We systematically reviewed studies linking the VNTR in the 3' UTR of the DAT1 to neurophysiological and neuropsychological measures. In addition, a broad set of executive/cognitive and motor tests was administered to 350 children (5-11 years) and adolescents (11-19 years) with ADHD and 195 non-affected siblings. Two VNTRs (in intron 8 and the 3' UTR) and four SNPs (two 5' and two 3') in DAT1 were genotyped. The effect of the polymorphisms on neuropsychological functioning was studied. The review indicated that the majority of studies did not find a relation between DAT1 and neurophysiological or neuropsychological measures. In our sample, several of the polymorphisms of DAT1 were associated with ADHD and ADHD was associated with impaired neuropsychological functioning. However, none of the DAT1 polymorphisms was convincingly associated with neuropsychological dysfunctioning. This suggests that the effect of DAT1 on ADHD was not mediated by neuropsychological performance. However, since DAT1 is mainly expressed in the striatum and not the prefrontal cortex, it may influence striatum-related functions (such as delay aversion) more heavily than prefrontal related functions (such as executive functions). Associations of DAT1 with ADHD were only found in adolescents, which may suggest that DAT1 mainly exerts its effect in adolescence, and/or that having a more persistent form of ADHD may mark a more severe or homogeneous genetic form of the disorder.

Response inhibition and interference control in children with AD/HD: a visual ERP investigation

Children with Attention-deficit Hyperactivity Disorder (AD/HD) show deficits in executive inhibitory functions such as behavioral inhibition and interference control, but investigations of both of these domains in the same groups of children is scarce, especially with concurrent consideration of ERP indices of inhibitory processes. Twenty children with AD/HD and 20 matched controls aged between 8 and 14 years performed visual Go-Nogo (30% Nogo) and Flanker tasks while EEG was recorded. Results indicated that children with AD/HD traded off speed for accuracy in the Go-Nogo task, resulting in similar levels of response inhibition accuracy; in the Flanker task response speed and errors were at control levels, while misses were increased and showed an enhanced interference effect. In the Go-Nogo task, the AD/HD group showed reduced Go/Nogo P2, a reduced central N2 Nogo>Go effect, and a more anterior Go/Nogo P3 compared to controls. For the Flanker task, the AD/HD group showed delayed N1 and P2, dramatically reduced N2 to Incongruent stimuli, enhanced N2 to Neutral stimuli, as well as increased P3 to Incongruent stimuli, compared to controls. These results indicate that Go-Nogo behavioral inhibition and Flanker interference control were not equally impaired in children with AD/HD, and that factors such as effort, arousal and motivation require further investigation.

COMT Val108/158Met polymorphism and the modulation of task-oriented behavior in children with ADHD

It has been suggested that the symptoms of attention-deficit/hyperactivity disorder (ADHD), including inattention and/or hyperactivity/impulsivity, translate into deficits in task-oriented behavior or problem-focused activity. The frontosubcortical dopamine pathway has been implicated in ADHD. One of the key modulators of extracellular dopamine levels in the prefrontal cortex is catechol-O-methyltransferase (COMT). The objective of this study was to examine the association of the COMT Val(108/158)Met polymorphism with (1) task-oriented behavior in children with ADHD, and (2) response of this behavior given methylphenidate (MPH) treatment. Children of Caucasian ethnicity, having ADHD (n=188), were assessed using the Restricted Academic Situation Scale (RASS). The RASS uses a simulated academic environment within the research clinic, to assess the child's ability for independent, sustained orientation to an assignment of math problems. Each child was administered placebo and MPH (0.5 mg/kg in a divided b.i.d. dose), each for a 1-week period, in a randomized, double-blind, crossover trial. On day 3 of the respective treatment week, the child was administered placebo/MPH in the clinic, and the acute change in behavior (before and 1 h after treatment) was evaluated on the RASS. Analysis was carried out using mixed model analysis of variance. Significant main effects of COMT genotype (F(2,184)=5.12, p=0.007) and treatment (F(1,184)=44.26, p<0.001) on task-oriented behavior were observed. However, no genotype by treatment interaction was observed. These results suggest that the COMT Val(108/158)Met polymorphism modulates task-oriented behavior, but it does not modulate the response of this behavior with MPH treatment.

Neurodevelopmental basis of bipolar disorder: a critical appraisal

Neurodevelopmental factors have been implicated in the pathophysiology of mental disorders. However, the evidence regarding their role in bipolar disorder is controversial. We reviewed the pertinent literature searching for evidence regarding a neurodevelopmental origin of bipolar disorder. Findings from clinical, epidemiological, neuroimaging, and post-mortem studies are discussed, as well as the implications of the available data for a better understanding of the mechanisms involved in the genesis of bipolar disorder. While some evidence exists for developmental risk factors in bipolar disorder, further research is needed to determine the precise extent of their contribution to pathogenesis. The timing and course of such developmentally mediated neurobiological alterations also need to be determined. Of particular importance for further study is the possibility that bipolar disorder may be mediated by an abnormal maturation of brain structures involved in affect regulation.

Delay Aversion in Attention Deficit/Hyperactivity Disorder: an empirical investigation of the broader phenotype

BACKGROUND

Delay-related motivational processes are impaired in children with Attention Deficit/Hyperactivity Disorder (ADHD). Here we explore the impact of ADHD on the performance of three putative indices of Delay Aversion (DAv): (i) the choice for immediate over delayed reward; (ii) slower reaction times following delay; and (iii) increased delay-related frustration-to see whether these tap into a common DAv construct that differentiates ADHD cases from controls and shows evidence of familiality.

METHOD

Seventy seven male and female individuals (age range 6-17) with a research diagnosis combined type ADHD, 65 of their siblings unaffected by ADHD and 50 non-ADHD controls completed three delay tasks.

RESULTS

As predicted the size of the correlation between tasks was small but a common latent component was apparent. Children with ADHD differed from controls on all tasks (d=.4-.7) and on an overall DAv index (d=.9): The battery as a whole demonstrated moderate sensitivity and specificity. In general, deficits were equally marked in childhood and adolescence and were independent of comorbid ODD. IQ moderated the effect on the MIDA. Scores on the DAv factor co-segregated within ADHD families.

DISCUSSION

There is value in exploring the broader DAv phenotype in ADHD. The results illustrate the power of multivariate approaches to endophenotypes. By highlighting the significant, but limited, role of DAv in ADHD these results are consistent with recent accounts that emphasize neuropsychological heterogeneity.

What's in a game: the effect of social motivation on interference control in boys with ADHD and autism spectrum disorders

BACKGROUND

Children with attention deficit hyperactivity disorder (ADHD) and with autism spectrum disorders (ASD) are known to have cognitive control deficits. Some studies suggest that such deficits may be reduced when motivation is increased through tangible reinforcers. Whether these deficits can also be modulated by non-tangible reinforcers has hardly been studied.

METHODS

Therefore, the effect of social motivation on the ability to suppress irrelevant information (i.e., interference control) was investigated in 22 ADHD boys, 22 ASD boys, and 33 typically developing (TD) boys. An adapted Eriksen Flanker task was administered under a motivational condition in which the boys were told that they were competing with peers, and under a neutral condition in which standard instructions were given.

RESULTS

In comparison with TD boys, boys with ADHD were impaired even when no interference was present, while this was not the case for the ASD boys. All groups benefited from the motivation manipulation, i.e., their performance increased when they thought they were competing with peers. Although the boys with ADHD were still slower than TD boys when motivated, they performed as accurately as TD boys. Children with ASD also improved slightly in accuracy and response speed, but this did not reach significance.

CONCLUSION

Children with ADHD are able to exert sufficient cognitive control when they are motivated, which is in line with the current models of ADHD. However, motivation seems to have a general effect on performance and is not solely related to cognitive control abilities. In contrast, this effect was not obtained in children with ASD.

The effects of incentives on visual-spatial working memory in children with attention-deficit/hyperactivity disorder

Working memory is one of several putative core neurocognitive processes in attention-deficit/hyperactivity disorder (ADHD). The present work seeks to determine whether visual-spatial working memory is sensitive to motivational incentives, a laboratory analogue of behavioral treatment. Participants were 21 children (ages 7-10) with a diagnosis of ADHD-combined type. Participants completed a computerized spatial span task designed to assess storage of visual-spatial information (forward span) and manipulation of the stored information (backward span). The spatial span task was completed twice on the same day, once with a performance-based incentive (trial-wise feedback and points redeemable for prizes) and once without incentives. Participants performed significantly better on the backward span when rewarded for correct responses, compared to the no incentive condition. However, incentives had no effect on performance during the forward span. These findings may suggest the use of motivational incentives improved manipulation, but not storage, of visual-spatial information among children with ADHD. Possible explanations for the differential incentive effects are discussed, including the possibility that incentives prevented a vigilance decrement as task difficulty and time on task increased.

Research review: dopamine transfer deficit: a neurobiological theory of altered reinforcement mechanisms in ADHD

This review considers the hypothesis that changes in dopamine signalling might account for altered sensitivity to positive reinforcement in children with ADHD. The existing evidence regarding dopamine cell activity in relation to positive reinforcement is reviewed. We focus on the anticipatory firing of dopamine cells brought about by a transfer of dopamine cell responses to cues that precede reinforcers. It is proposed that in children with ADHD there is diminished anticipatory dopamine cell firing, which we call the dopamine transfer deficit (DTD). The DTD theory leads to specific and testable predictions for human and animal research. The extent to which DTD explains symptoms of ADHD and effects of pharmacological interventions is discussed. We conclude by considering the neural changes underlying the etiology of DTD.

Working toward a neurobiological account of ADHD: commentary on Gail Tripp and Jeff Wickens, dopamine transfer deficit

The dopamine transfer deficit model of attention deficit hyperactivity disorder (ADHD) is compared and contrasted with the existing dynamic developmental theory and the extended temporal difference (TD) model. The first two both identify learning deficits as a key problem in ADHD, but this mechanism would seem at least as likely to cause other neurodevelopmental disorders. Learning deficits also do not provide a natural account of ADHD performance worsening in longer trials, nor of stimulant action, nor of the high rate of test-retest inconsistency. The extended TD model is based on the quite different premise that there are very many underlying causes for the disorder, and computational simulation of it has supported the existence of two subtypes that involve no dopamine transfer deficit, as well as several subtypes that do. The three models have markedly different ways of accounting for key aspects of ADHD, including intra-individual variability, stimulant effects, and extinction deficits. The most important shortcoming of all the models is their limited treatment of state-regulation processes, which are very important in ADHD; this is partially addressed by the extended TD model's proposed dopamine appetite.

Decision-making in ADHD: sensitive to frequency but blind to the magnitude of penalty?

BACKGROUND

Decision-making and reinforcement sensitivity were investigated in 23 children with ADHD and 20 healthy controls using a gambling paradigm.

METHODS

Children were required to choose between three alternatives that carried (A) small rewards and small penalties (advantageous), (B) large rewards and increasing penalties and (C) small rewards and increasing penalties (both disadvantageous). Penalties increased either in frequency or magnitude in two independent conditions. Heart rate (HR) and skin conductance (SC) were measured to examine whether impaired decision-making was accompanied by autonomic abnormalities.

RESULTS

Children with ADHD showed a maladaptive response style compared to controls by demonstrating a smaller preference for the advantageous alternative, when penalties increased in magnitude. When penalties increased in frequency, children with ADHD performed like controls. Group differences in decision-making attenuated after the task was administered twice. Compared to controls, performance of children with ADHD in the magnitude condition was accompanied by increased HR acceleration following reward. In this condition, the post-selection SC of children with ADHD was larger for advantageous than for disadvantageous alternatives, in contrast to controls who showed an opposite SC pattern.

CONCLUSIONS

The current findings suggest that during decision-making, children with ADHD may be sensitive to the frequency but blind to the magnitude of penalty.

Inhibitory performance, response speed, intraindividual variability, and response accuracy in ADHD

OBJECTIVE

To determine the potential of inhibitory performance, response speed, and response accuracy and variability, measures central to the conceptualization of attention-deficit/hyperactivity disorder (ADHD), in distinguishing children with ADHD from healthy controls (HCs).

METHOD

The stop signal paradigm was administered to 38 children with ADHD and 31 NCs. The stop signal reaction time (SSRT), mean reaction time (MRT), intraindividual coefficient of variation (ICV), and number of errors were used to predict diagnostic status.

RESULTS

Univariate tests showed that the ADHD group performed worse than NCs on all of the dependent variables. Exploratory univariate analyses showed that oppositional defiant disorder comorbidity and ADHD type did not influence results except for the ICV, the effect for this variable (more variability in the ADHD group) being less pronounced for the Predominantly Inattentive type than for the Hyperactive-Impulsive and Combined types. A logistic regression model of the MRT, ICV, and number of errors combined showed best predictive performance, with the MRT contributing the most to group classification (56% of the variance). The final model (MRT, ICV, and number of errors) predicted 87% of the sample in the correct diagnostic category. Operating characteristics showed excellent sensitivity and specificity of 89.5% and 83.9%, respectively.

CONCLUSIONS

Our results contrast with theoretical accounts emphasizing inhibitory control as the pivotal measure characterizing cognitive performance in ADHD. Results are discussed in the context of a delay aversion perspective of ADHD.

Attention deficit/hyperactivity disorder and video games: a comparative study of hyperactive and control children

INTRODUCTION

This study describes and compares the behavior of hyperactive and control children playing video games.

SUBJECTS AND METHODS

The sample consisted of 29 ADHD children and 21 controls aged between 6 and 16 years playing video games. We used the Child Behavior Checklist and the Problem Videogame Playing scale (PVP scale). This instrument gives objective measures of problem use, which can be considered as an indication of addictive videogame playing. We designed a questionnaire for the parents, eliciting qualitative information about their child's videogame playing. There were no significant differences concerning frequency or duration of play between ADHD children and controls but differences were observed on the PVP scale. None of the controls scored above four whereas 10 hyperactive children answered affirmatively to five or more questions. These children presented a greater intensity of the disorder than the other ADHD children.

CONCLUSION

While no differences concerning video game use were found, ADHD children exhibited more problems associated with videogame playing. It seems that a subgroup of ADHD children could be vulnerable to developing dependence upon video games.

Attention impairment in rolandic epilepsy: systematic review

PURPOSE

Conflicting evidence about impairment of attention systems and the absence of a working model of attention has contributed to lack of clarity about comorbidity of attention problems in rolandic epilepsy (RE). Impairments in distributed attention systems may inform a disease model for RE, as well as direct interventions.

METHODS

We used a systematic review of the relevant literature published in English from 1990 to 2006 to evaluate impairment in attention in RE. The Mirsky and Posner models of attention were evaluated for applicability, and studies were reviewed for design, instrumentation, and congruence with the Posner model of attention.

RESULTS

Fourteen studies were identified: seven using a cross-sectional design (six active EEG abnormalities; one EEG remission) and seven longitudinal studies (abnormal EEGs and follow-up until normalized). According to the Posner model of attention, 12 studies employed measures that tapped the alerting network, 11 studies the orienting network, and eight the executive network. Nearly all controlled studies demonstrated impairments in all tested attention networks. In contrast, uncontrolled studies uniformly did not demonstrate impairments. Follow-up studies demonstrated complete or near complete resolution of attention impairments.

DISCUSSION

The weight of evidence, defined as the majority of studies evaluated, suggests that all three attention systems are impaired in children with active centrotemporal spikes (CTS), implying a more widespread functional cortical disturbance in RE than previously held. These impairments resolve upon EEG remission, suggesting a common pathological basis to the autosomal dominant CTS trait. Sources of methodological variation are discussed with recommendations for future investigations.

Executive dysfunction and delay aversion in attention deficit hyperactivity disorder: nosologic and diagnostic implications

In this article the authors reflect on the role of executive function (EF) deficits and delay aversion (DAv) in the diagnosis of attention deficit hyperactivity disorder (ADHD). The authors, empirical review shows clearly that EF deficits and DAv are implicated in ADHD, although neither is necessary for ADHD nor specific to it. The constructs are somewhat dissociable from one another so that each may represent a distinctive feature associated with an ADHD subsample. The authors argue that neither EF deficits nor DAv add much value to the diagnosis of ADHD as it is currently conceptualized, but may be crucial in helping to partition heterogeneity in the condition, leading to the refinement of ADHD nosology.

Attention deficit hyperactivity disorder and substance use disorders

Attention deficit hperactivity disorder (ADHD) is highly prevalent among adolescents who have substance use disorder (SUD). Several lines of evidence, although not conclusive, suggest that ADHD might have an independent effect on SUD liability. It is still to be determined, however, whether this association is mediated by conduct disorder. This article reviews ADHD and SUD.

Electrophysiological evidence of atypical motivation and reward processing in children with attention-deficit hyperactivity disorder

Behavioral and neurophysiological evidence suggest that attention-deficit hyperactivity disorder (ADHD) is characterized by the impact of abnormal reward prediction error signals carried by the midbrain dopamine system on frontal brain areas that implement cognitive control. To investigate this issue, we recorded the event-related brain potential (ERP) from typical children and children with ADHD as they navigated a "virtual maze" to find monetary rewards, and physically gave them their accumulated rewards halfway through the task and at the end of the experiment. We found that the amplitude of a reward-related ERP component decreased somewhat for typical children after they received their first payment, but increased for children with ADHD following the payment. This result indicates that children with ADHD are unusually sensitive to the salience of reward and suggests that such sensitivity may be mediated in part by the midbrain dopamine system.

Modulation of response timing in ADHD, effects of reinforcement valence and magnitude

The present study investigated the impact of reinforcement valence and magnitude on response timing in children with ADHD. Children were required to estimate a 1-s interval, and both the median response time (response tendency) and the intrasubject-variability (response stability) were investigated. In addition, heart rate and skin conductance were measured to examine the autonomic responses to reinforcement. Feedback-only trials were compared to low response cost trials (response cost for incorrect responses), low reward trials (reward for correct responses), high response cost and high reward trials. In feedback-only trials, children with ADHD underestimated more severely the interval and responded more variably than controls. Children with ADHD, unlike controls, were unaffected by the reinforcement conditions in terms of time underestimations. The variability of responding, on the other hand, decreased under conditions of reinforcement to a larger extent in children with ADHD than controls. There were no indications that children with ADHD were abnormally affected by the valence or magnitude of reinforcement. Furthermore, skin conductance responses increased when feedback was coupled with reinforcement, an effect which was larger in children with ADHD than controls. This could be interpreted as demonstrating that children with ADHD suffer from a diminished awareness of the significance of feedback in the feedback-only condition. The current study suggests that children with ADHD suffer from motivation problems when reinforcement was not available, at least when variability in responding was measured. Underestimations of time may reflect more stable deficits in ADHD.

Review of cognitive, cognitive-behavioral, and neural-based interventions for Attention-Deficit/Hyperactivity Disorder (ADHD)

Primary evidence-based treatment approaches for ADHD involve pharmacological and behavioral treatments. However, there continue to be investigations of cognitive-behavioral, cognitive, and neural-based intervention approaches that are not considered evidence-based practice. These particular treatments are summarized, as they all involve training in cognitive skills or cognitive strategies. We identified 26 studies (six cognitive-behavioral, six cognitive, and 14 neural-based), and calculated effect sizes where appropriate. Overall, our analysis suggests that further research is needed to determine the efficacy of these approaches on both cognitive and behavioral outcome measures, but that some of these methods show promise for treating ADHD. We discuss some important conceptual and methodological issues that need to be taken into account for future research in order to evaluate the clinical efficacy of these approaches.

Do delay aversion and executive function deficits make distinct contributions to the functional impact of ADHD symptoms? A study of early academic skill deficits

BACKGROUND

The present study examined the distinct properties of executive functioning in relation to ADHD symptoms, as well as functional outcomes associated with ADHD. In line with the dual-pathway model of ADHD, executive functioning and delay aversion were expected to show independent effects on ADHD symptoms. Furthermore, relations to early academic skills were examined, and it was hypothesized that the two processes of the dual-pathway model can be differentiated in terms of their effect on academic skill deficits, such that EF deficits, but not delay aversion, mediate the link between ADHD and academic functioning.

RESULTS

As hypothesized, both EF deficits and delay aversion were independently related to ADHD symptoms. However, when conducting separate analyses for the two ADHD symptom domains, only the effect of EF deficits was independently related to symptoms of inattention, whereas only the effect of delay aversion was independently related to symptoms of hyperactivity/impulsivity. The mediation analysis showed that EF deficits, but not delay aversion, act as a mediator in the relation between symptoms of inattention and both mathematics and language skills. In addition, there was also a significant direct effect of inattention on early academic skills.

CONCLUSIONS

The findings of the present study are of importance for current models of heterogeneity in ADHD as they 1) provide further support for the notion that EF deficits and delay aversion are two possible pathways to ADHD, 2) add new interesting knowledge by showing that EF deficits and delay aversion can be differentiated in terms of their relations to the two ADHD symptom domains, and 3) indicate that the two processes of the dual-pathway model can also be differentiated in terms of their effect on functional impairments associated with ADHD.

Hot and cool forms of inhibitory control and externalizing behavior in children of mothers who smoked during pregnancy: an exploratory study

This study examined whether children exposed to prenatal smoking show deficits in “hot” and/or “cool” executive functioning (EF). Hot EF is involved in regulation of affect and motivation, whereas cool EF is involved in handling abstract, decontextualized problems. Forty 7 to 9-year-old children (15 exposed to prenatal smoking, 25 non-exposed) performed two computerized tasks. The Sustained Attention Dots (SA-Dots) Task (as a measure of “cool” inhibitory control) requires 400 non-dominant hand and 200 dominant hand responses. Inhibitory control of the prepotent response is required for dominant hand responses. The Delay Frustration Task (DeFT) (as a measure of “hot” inhibitory control) consists of 55 simple maths exercises. On a number of trials delays are introduced before the next question appears on the screen. The extent of response-button pressing during delays indicates frustration-induced inhibitory control. Prenatally exposed children showed poorer inhibitory control in the DeFT than non-exposed children. A dose–response relationship was also observed. In addition, prenatally exposed children had significantly higher (dose-dependent) conduct problem- and hyperactivity-inattention scores. There were no significant group differences in inhibitory control scores from the SA-Dots. These results indicate that children exposed to prenatal smoking are at higher risk of hot but not cool executive function deficits.

Reward anticipation and outcomes in adult males with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) has been suggested to involve deficits in reward processing. We used functional magnetic resonance imaging (fMRI) to compare the neural responses to reward anticipation and outcomes in 10 adults with ADHD and 10 controls as they played a monetary incentive delay task. Adults with ADHD were unmedicated, and groups were matched for age, verbal IQ and smoking habits. Adults with ADHD showed decreased activation in the ventral striatum during the anticipation of gain, but increased activation of the orbitofrontal cortex in response to gain outcomes. Ventral striatal activation in adults with ADHD during gain anticipation was negatively correlated with self-rated symptoms of hyperactivity and impulsivity. These findings suggest that male adults with ADHD show neural signs of abnormal reward processing. Future studies will have to investigate whether these dysfunctional patterns might be normalized by treatment.

Behavioural and ERP indices of response inhibition during a Stop-signal task in children with two subtypes of Attention-Deficit Hyperactivity Disorder

Previous research has shown that children with Attention-Deficit Hyperactivity Disorder of the Combined Type (AD/HDcom) have problems with response inhibition, with poorer task performance and atypical inhibition-related ERPs relative to control subjects, while little is known about response inhibition in children with Attention-deficit Hyperactivity Disorder of the Predominantly Inattentive Type (AD/HDin). In this study children with AD/HDin (N=12), AD/HDcom (N=13) and age-matched controls (N=13) aged between 8 and 14 years completed a Stop-signal task, with visual Go and auditory Stop-signal stimuli, while EEG was recorded. The results indicated that the groups did not differ on any inhibitory task performance measure, but the AD/HD groups showed more errors of omission to Go stimuli than controls. ERPs to the visual Go stimuli differed between children with AD/HDin and controls (increased central N1 and N2, decreased central P2 and increased parietal P3), while the AD/HDcom group showed only minor scalp distribution differences for N2 and P3. The AD/HDin group showed amplitude differences from controls to Stop signals (larger central N1 and parietal P3; reduced midline N2) and did not show a Successful vs. Failed inhibition effect for P3. The AD/HDcom group showed reduced parietal P3 to Stop signals, with the Trial Type effect present for N2 but not P3. These data suggest that the apparent atypical inhibitory processing at N2 and P3 may stem, at least in part, from atypical early sensory/alerting processing of all stimuli in children with AD/HDin.

ADHD subtype differences in motivational responsivity but not inhibitory control: evidence from a reward-based variation of the stop signal paradigm

In this study we examined prepotent motor inhibition and responsiveness to reward using a variation of the stop signal reaction time (SSRT) task in clinic- and community-recruited children ages 7 to 12 with attention-deficit/hyperactivity disorder-inattentive type (ADHD-I), ADHD-combined type (ADHD-C), and non-ADHD controls. Contrary to theoretical expectations, we found evidence for inhibitory weaknesses in ADHD-I. We also found evidence that although children with ADHD-I were able to improve their inhibitory control given reward-based motivation, the improvement depended on the order of reward conditions. Results suggest that the 2 primary subtypes of ADHD share similar neuropsychological weaknesses in inhibitory control but that there are subtype differences in response to success and failure that contribute to a child's ultimate level of performance.

Temporal reward discounting and ADHD: task and symptom specific effects

This study investigated a new aspect of the association between ADHD symptoms and delay aversion. Participants were 55 undergraduate Psychology students with varying levels of self-reported ADHD symptoms. Various delay aversion tasks were used, including real and hypothetical temporal discounting tasks previously used in the field of ADHD. ADHD symptoms, specifically hyperactivity/impulsivity, were associated with steep discounting, but only when rewards and delays were real. These data suggest that (1) real temporal discounting tasks are more sensitive to ADHD-related delay aversion than hypothetical ones; (2) delay aversion may be a causal mechanism specifically associated with ADHD-Combined and Hyperactive/Impulsive Types but not Inattentive Type. These findings may help refine behavioral treatment approaches and models of ADHD.

Heart rate and reinforcement sensitivity in ADHD

BACKGROUND

Both theoretical and clinical accounts of attention-deficit/hyperactivity disorder (ADHD) implicate a dysfunctional reinforcement system. This study investigated heart rate parameters in response to feedback associated with reward and response cost in ADHD children and controls aged 8 to 12.

METHODS

Heart rate responses (HRRs) following feedback and heart rate variability (HRV) in the low frequency band (.04-.08 Hz), a measure of mental effort, were calculated during a time production paradigm. Performance was coupled to monetary gain, loss or feedback-only in a cross-over design.

RESULTS

Children with ADHD exhibited smaller HRRs to feedback compared to controls. HRV of children with ADHD decreased when performance was coupled to reward or response cost compared to feedback-only. HRV of controls was similar across conditions.

CONCLUSIONS

Children with ADHD were characterised by (a) possible abnormalities in feedback monitoring and (b) motivational deficits, when no external reinforcement is present.

Attention-deficit/hyperactivity disorder: a neuropsychological perspective towards DSM-V

Neuropsychological methods and techniques have much to offer in the evaluation of the individual suspected as having Attention-Deficit/Hyperactivity Disorder (ADHD). After a review of the historical evolution of the ADHD concept, incidence and prevalence, and DSM-IV criteria for diagnosis, especially as regards omission related to gender differences, and other associated cultural, familial, socioenvironmental, and subject influences, this paper describes a number of dilemmas and obstacles encountered in clinical practice. Included are the confounds associated with the wide range of possible comorbidities, the insufficiency of current DSM-IV criteria, the emergence of subtype differentiation and its impact on diagnosis and treatment. The complex relationship between neuropsychological constructs and ADHD, and obstacles to valid assessment are also addressed. The complexities associated with a thorough ADHD evaluation are viewed within an impressive and expansive existing scientific framework and recommendations are made for future directions.

Attention-deficit/hyperactivity disorder and behavioral inhibition: a meta-analytic review of the stop-signal paradigm

Deficient behavioral inhibition (BI) processes are considered a core feature of attention deficit/hyperactivity disorder (ADHD). This meta-analytic review is the first to examine the potential influence of a wide range of subject and task variable moderator effects on BI processes--assessed by the stop-signal paradigm--in children with ADHD relative to typically developing children. Results revealed significantly slower mean reaction time (MRT), greater reaction time variability (SDRT), and slower stop-signal reaction time (SSRT) in children with ADHD relative to controls. The non-significant between-group stop-signal delay (SSD) metric, however, suggests that stop-signal reaction time differences reflect a more generalized deficit in attention/cognitive processing rather than behavioral inhibition. Several subject and task variables served as significant moderators for children's mean reaction time.

Attention-Deficit/Hyperactivity Disorder and Behavioral Inhibition: A Meta-Analytic Review of the Stop-signal Paradigm

Deficient behavioral inhibition (BI) processes are considered a core feature of attention deficit/hyperactivity disorder (ADHD). This meta-analytic review is the first to examine the potential influence of a wide range of subject and task variable moderator effects on BI processes--assessed by the stop-signal paradigm--in children with ADHD relative to typically developing children. Results revealed significantly slower mean reaction time (MRT), greater reaction time variability (SDRT), and slower stop-signal reaction time (SSRT) in children with ADHD relative to controls. The non-significant between-group stop-signal delay (SSD) metric, however, suggests that stop-signal reaction time differences reflect a more generalized deficit in attention/cognitive processing rather than behavioral inhibition. Several subject and task variables served as significant moderators for children's mean reaction time.

Listen to the noise: noise is beneficial for cognitive performance in ADHD

BACKGROUND

Noise is typically conceived of as being detrimental to cognitive performance. However, given the mechanism of stochastic resonance, a certain amount of noise can benefit performance. We investigate cognitive performance in noisy environments in relation to a neurocomputational model of attention deficit hyperactivity disorder (ADHD) and dopamine. The Moderate Brain Arousal model (MBA; Sikström & Söderlund, 2007) suggests that dopamine levels modulate how much noise is required for optimal cognitive performance. We experimentally examine how ADHD and control children respond to different encoding conditions, providing different levels of environmental stimulation.

METHODS

Participants carried out self-performed mini tasks (SPT), as a high memory performance task, and a verbal task (VT), as a low memory task. These tasks were performed in the presence, or absence, of auditory white noise.

RESULTS

Noise exerted a positive effect on cognitive performance for the ADHD group and deteriorated performance for the control group, indicating that ADHD subjects need more noise than controls for optimal cognitive performance.

CONCLUSIONS

The positive effect of white noise is explained by the phenomenon of stochastic resonance (SR), i.e., the phenomenon that moderate noise facilitates cognitive performance. The MBA model suggests that noise in the environment, introduces internal noise into the neural system through the perceptual system. This noise induces SR in the neurotransmitter systems and makes this noise beneficial for cognitive performance. In particular, the peak of the SR curve depends on the dopamine level, so that participants with low dopamine levels (ADHD) require more noise for optimal cognitive performance compared to controls.

Multidisciplinary perspectives on attention and the development of self-regulation

During infancy and early childhood, children develop their ability to regulate their own emotions and behavior. This development of self-regulatory mechanisms has been considered to be the crucial link between genetic predisposition, early experience, and later adult functioning in society. This paper brings together the updated empirical findings related to the role of attention and the maturation of brain frontal areas in self-regulation. It reviews viewpoints and evidence of disciplines such as developmental psychology, cognitive neuroscience, social psychology, and neurobiology. It examines the causes of individual differences in self-regulation and the effects of those differences on the social and academic functioning of the individual. The consequences of failure in self-regulation are illustrated by focusing on the attention deficit/hyperactivity disorder (ADHD), including a detailed review of the animal models related to this disorder. Finally, some initial evidence suggesting the possibility of fostering self-regulation through training of attention is presented.

Effects of the cannabinoid CB1 receptor antagonist rimonabant on distinct measures of impulsive behavior in rats

RATIONALE

Pathological impulsivity is a prominent feature in several psychiatric disorders, but detailed understanding of the specific neuronal processes underlying impulsive behavior is as yet lacking.

OBJECTIVES

As recent findings have suggested involvement of the brain cannabinoid system in impulsivity, the present study aimed at further elucidating the role of cannabinoid CB(1) receptor activation in distinct measures of impulsive behavior.

MATERIALS AND METHODS

The effects of the selective cannabinoid CB(1) receptor antagonist, rimonabant (SR141716A) and agonist WIN55,212-2 were tested in various measures of impulsive behavior, namely, inhibitory control in a five-choice serial reaction time task (5-CSRTT), impulsive choice in a delayed reward paradigm, and response inhibition in a stop-signal paradigm.

RESULTS

In the 5-CSRTT, SR141716A dose-dependently improved inhibitory control by decreasing the number of premature responses. Furthermore, SR141716A slightly improved attentional function, increased correct response latency, but did not affect other parameters. The CB(1) receptor agonist WIN55,212-2 did not change inhibitory control in the 5-CSRTT and only increased response latencies and errors of omissions. Coadministration of WIN55,212-2 prevented the effects of SR141716A on inhibitory control in the 5-CSRTT. Impulsive choice and response inhibition were not affected by SR141716A at any dose, whereas WIN55,212-2 slightly impaired response inhibition but did not change impulsive choice.

CONCLUSIONS

The present data suggest that particularly the endocannabinoid system seems involved in some measures of impulsivity and provides further evidence for the existence of distinct forms of impulsivity that can be pharmacologically dissociated.

Is attention-deficit/hyperactivity disorder associated with illicit substance use disorders in male adolescents? A community-based case-control study

AIMS

This study aims at evaluating the association between attention-deficit/hyperactivity disorder (ADHD) and illicit substance use disorders (SUD) (marijuana, cocaine and inhalants), controlling for the association with conduct disorder (CD), in a community-based sample of adolescents.

DESIGN

Case-control, community-based study.

SETTING

A delimited geographical area in the South of Brazil, served by four public health clinics.

PARTICIPANTS

A total of 968 male adolescents (15-20 years of age) were screened for SUD in their households. Of the subjects who were screened positive, we selected 61 cases with illicit SUD. For each case we selected, from the group which was screened negative, three controls without illicit or alcohol SUD, matched by age and proximity with the case's household.

MEASUREMENTS

The screening instrument was the Alcohol Smoking and Substance Screening Test (ASSIST). SUD diagnoses were assessed by the drug section of the Mini International Neuropsychiatry Interview (MINI). Other psychiatric diagnoses were based on semistructured (Schedule for Affective Disorders and Schizophrenia for School-Age Children-epidemiological version; MINI) and clinical interviews.

FINDINGS

Adolescents with ADHD presented a significantly higher odds ratio (OR) for illicit SUD than youths without ADHD, even after adjusting for potential confounders (CD, ethnicity, religion and estimated IQ) (OR = 9.12; 95% CI = 2.84-29.31, P < 0.01).

CONCLUSIONS

Our results suggest an association between ADHD and illicit SUD in Brazilian adolescents that is not mediated by CD. These findings are potentially important from a prevention perspective because treatments are available for ADHD.

Methylphenidate can reduce selectivity in associative learning in an aversive trace conditioning task

There are good grounds to expect that methylphenidate (MP) should enhance cognitive function. However, experimental evidence on this point is scant. The present study therefore examined the effects of MP on learning the association between a conditioned stimulus (CS, in this case, noise) and an unconditioned stimulus (UCS, in this case, footshock) in an aversive variant of a trace conditioning procedure. Learning was measured off-the-baseline as conditioned suppression of drinking (both latencies to drink, expressed as suppression ratios, and the amount drunk, expressed as the number of licks, in the presence of the CS). In addition to the measures of discrete cue conditioning, MP effects on contextual conditioning were measured as suppression to apparatus cues and an experimental background stimulus. MP was administered at 1 or 5 mg/kg prior to conditioning sessions. As attention deficit hyperactivity disorder (ADHD) has been characterized as involving a ;wide attentional window' (e.g. Shalev and Tsal, 2003), it was predicted that MP, as the treatment of choice for ADHD, should increase selectivity (narrowing the attentional window). This outcome would show as reduced levels of conditioning (compared to control rats) to less informative trace and contextual cues present during conditioning. Contrary to prediction, both 1 and 5 mg/kg MP increased learning about all the available stimuli, including the less informative trace CS and the background stimulus. These findings are consistent with reduced rather than increased selectivity in learning (because of increased rather than decreased conditioning to weak cues) under MP.

Association between response inhibition and working memory in adult ADHD: a link to right frontal cortex pathology?

BACKGROUND

We sought to assess the relationship between response inhibition and working memory in adult patients with attention-deficit/hyperactivity disorder (ADHD) and neurosurgical patients with frontal lobe damage.

METHODS

The stop-signal reaction time (SSRT) test and a spatial working memory (SWM) task were administered to 20 adult patients with ADHD and a group of matched controls. The same tasks were administered to 21 patients with lesions to right frontal cortex and 19 patients with left frontal lesions.

RESULTS

The SSRT test, but not choice reaction time, was significantly associated with search errors on the SWM task in both the adult ADHD and right frontal patients. In the right frontal patients, impaired performance on both variables was correlated with the volume of damage to the inferior frontal gyrus.

CONCLUSIONS

Response inhibition and working memory impairments in ADHD may stem from a common pathologic process rather than being distinct deficits. Such pathology could relate to right frontal-cortex abnormalities in ADHD, consistent with prior reports, as well as with the demonstration here of a significant association between SSRT and SWM in right frontal patients.

Validating psychiatric endophenotypes: inhibitory control and attention deficit hyperactivity disorder

ADHD is a heritable condition of childhood for which several risk alleles have been identified. However, observed effect sizes have been small and few replicated polymorphisms have been identified. There are many reasons for the lack of one-to-one correspondence between genotype and phenotype in ADHD. Endophenotypes are non-clinical markers of genetic risk which may facilitate gene discovery in complex disorders like ADHD. The most common endophenotypes under consideration in ADHD are neuropsychological measures of executive function, although a range of psychological, physiological and neuroanatomical endophenotypes have been proposed. If carefully chosen, endophenotypes have the potential to increase the power of genetic research to identify susceptibility genes. If not carefully selected, endophenotypes may generate false negative and false positive results. This paper reviews the theoretical rationale for endophenotypes and proposes a priori criteria by which ADHD endophenotypes should be selected and validated. The literature on motor response inhibition is reviewed to illustrate the validation process which is recommended in the selection of other candidate endophenotypes.

Impulsive personality predicts dopamine-dependent changes in frontostriatal activity during component processes of working memory

Dopaminergic drugs affect a variety of cognitive processes, but the direction and extent of effects vary across individuals and tasks. Paradoxical effects are observed, by which the same drug causes cognitive enhancing as well as adverse effects. Here, we demonstrate that individual differences in impulsive personality account for the contrasting effects of dopaminergic drugs on working memory and associated frontostriatal activity. We observed that the dopamine D2 receptor agonist bromocriptine improved the flexible updating (switching) of relevant information in working memory in high-impulsive subjects, but not in low-impulsive subjects. These behavioral effects in high-impulsive subjects accompanied dissociable effects on frontostriatal activity. Bromocriptine modulated the striatum during switching but not during distraction from relevant information in working memory. Conversely, the lateral frontal cortex was modulated by bromocriptine during distraction but not during switching. The present results provide a key link between dopamine D2 receptor function, impulsivity, and frontostriatal activity during component processes of working memory.

Multicomponent attention deficits in attention deficit hyperactivity disorder

The aim of this study was to examine the specific aspects of attention, such as selective attention, sustained attention, and short-term memory in children with attention deficit hyperactivity disorder, combined subtype (ADHD-C). A total of 40 children with a diagnosis of ADHD from the 4th edition of the Diagnostic and Statistical Manual, aged 6-11 years old were compared with 40 controls matched for age and gender on a battery of tests. Short-term memory span and attention was measured by Visual Aural Digit Span Test-Revised. Stroop test and the Turkish version of Cancellation Test were used to assess selective and sustained attention, respectively. In order to check for factor structure in two groups on the test scores, principal component analysis was conducted for both groups separately. Relative to the comparison children, children with ADHD showed significant deficits on tests that are related to different aspects of attention. The results are consistent with the theories explaining the biological basis of ADHD by scattered attention networks in the brain, which have reciprocal dynamic interactions. Further comparative studies are needed to elucidate whether the cognitive processes that are known to be assessed by these tests are specific to ADHD.