Executive processing and attention deficit hyperactivity disorder: an application of the supervisory attentional system

Inhibitory deficits and symptoms of attention-deficit hyperactivity disorder: How are they related to effortful control?

Separate studies with clinical and community-based samples have identified an association between symptoms of attention-deficit hyperactivity disorder (ADHD) and inhibitory control deficits and ADHD and weak effortful control. We tested whether differences in effortful control explained the associations between ADHD symptoms and inhibitory control deficits, controlling for conduct problems. In a community sample, parents rated ADHD symptoms, conduct problems, effortful control, surgency and negative affect in 77 4-7-year-olds (47 girls), who performed an inhibitory control task. ADHD symptoms, deficient inhibitory control and low effortful control were correlated. Controlling for conduct problems, path analysis showed the ADHD symptoms - inhibitory control link was mediated statistically by effortful control. This focuses attention on cognitive-energetic factors associated with ADHD-related executive deficits.

Assessment of executive functions in school-aged children: A narrative review

Introduction

In the past three decades, there has been increasing interest in assessing children's Executive Functions (EF). However, studies on the conceptualization and operationalization of this construct are incongruent and guidance for clinicians and researchers aiming to assess EF is insufficient due to measurement variability.

Aims

The purpose of this article was to examine current theories and models of EF in children, identify their assessment instruments, issues, and challenges, and discuss their impact on children's cognitive, behavioral, social and/or emotional development.

Methods

This narrative review reflected on English and French scholarly articles on EF assessment in children. References were identified through searches of PubMed, Medline, ScienceDirect, Google Scholar, and APA PsychNet throughout the last two decades up to June 2022.

Results

There are commonalities despite divergence in the definition and operationalization of EF. Assessment of EF requires psychometric tests as well as rating scales that must be integrated and interpreted considering the child's biological makeup, environmental background, and cultural specificities.

Conclusion

Current EF theories, assessment tools, issues, and challenges were discussed in addition to the impact of their components' dysfunctions on children's development. Further studies should be conducted to develop new measurement methods and technologies to improve the ecological and ethological validity of youth assessment, treatment, and interventions.

Do Executive Dysfunction, Delay Aversion, and Time Perception Deficit Predict ADHD Symptoms and Early Academic Performance in Preschoolers

Children with attention deficit/hyperactivity disorder (ADHD) are commonly observed to have learning difficulties. This study examined how three neuropsychological constructs—executive dysfunction, delay aversion, and time perception—were associated with ADHD symptoms and early academic performance in preschoolers at risk of ADHD. One hundred and thirty-one preschoolers (70 boys, 53%) aged 4 to 6 (M = 5.31 years) were assessed on their ADHD-related behaviors, neuropsychological functioning, word reading, and math abilities at two time points one year apart. Factor analysis indicated that inhibitory and attentional control deficit, delay aversion, and time perception/working memory deficit were three dissociable factors. Among the three factors, inhibitory and attentional control measured at Time 1 was the strongest predictor of ADHD symptoms at both Time 1 and Time 2. Time perception was closely related to working memory, and they predicted word reading and numeration across time most strongly among other neuropsychological constructs. Our findings suggested that inhibitory and attentional control, delay aversion, and time perception are dissociable neuropsychological deficits underlying ADHD symptoms in preschoolers. Poor time perception may serve as a marker for the early identification of preschoolers with potential learning problems, and a possible target of intervention for ADHD.

Dimensional structure of the BRIEF2 and its relations with ADHD symptoms and task performance on executive functions in Chinese children

This study examined the dimensional structure of the Behavior Rating Inventory of Executive Function, Second Edition (BRIEF2) in a Chinese sample of children with attention-deficit/hyperactivity disorder (ADHD)-related concerns and the correlations of the BRIEF2 with the children's ADHD symptoms and their performance on executive function (EF) tasks. Participants were 339 Chinese children aged 6-15 (M = 9.18 years, SD = 2.33; boys: 78.2%) recruited from 35 schools in Hong Kong. The results from confirmatory factor analyses revealed the best fit for a three-factor nine-scale model compared to a two-factor or single-factor model. Significant correlations were found between the BRIEF2 parent and teacher forms for the Behavioral Regulation Index and Cognitive Regulation Index, but not for the Emotion Regulation Index. Associations between performance on an EF task and the rating of the corresponding subscale on the BRIEF2 purportedly measuring the same EF construct were not consistently observed. Lastly, the BRIEF2 showed good convergent validity with the ratings of ADHD symptoms on the Swanson, Nolan, and Pelham Rating Scale Version IV (SNAP-IV). This study provided plausibly the first evidence on the dimensional structure of the BRIEF2 Parent and Teacher Forms in an Asian sample and confirmed the factorial validity of the Chinese version of the BRIEF2.

Is the Brixton Spatial Anticipation Test sensitive to frontal dysfunction? Evidence from patients with frontal and posterior lesions

INTRODUCTION

The Brixton Spatial Anticipation Test is a widely used neuropsychological test, thought to assess executive functions and to be sensitive to frontal lobe lesions. Our aim was to investigate Brixton performance in patients with focal frontal or posterior lesions and healthy controls.

METHOD

We compared performance on the Brixton in a sample of 24 frontal patients, 18 posterior patients and 22 healthy controls. Both overall performance (total number of errors) and error types were analyzed.

RESULTS

We found no significant differences between frontal and posterior patients and healthy controls in overall Brixton performance. Moreover, our error analysis showed no difference between frontal patients, posterior patients and healthy controls. The only exception was that posterior patients had a greater tendency to guess and make more errors when following specific rules than healthy controls but this was no longer significant once fluid intelligence was controlled for. We also found no significant difference between the performance of patients with left lateral (n = 11), right lateral (n = 10) or superior medial (n = 18) frontal lesions and healthy controls.

CONCLUSIONS

The Brixton test is not sensitive to frontal lobe dysfunction. It is likely that the test draws on a range of cognitive abilities not specific to frontal lobe lesions. Hence, caution should be taken when drawing conclusions about its neural substrates.

Selective impairment of attentional set shifting in adults with ADHD

Background

Task switch protocols are frequently used in the assessment of cognitive control, both in clinical and non-clinical populations. These protocols frequently confound task switch and attentional set shift. The current study investigated the ability of adult ADHD patients to shift attentional set in the context of switching tasks.

Method

We tested 38 adults with ADHD and 39 control adults with an extensive diagnostic battery and a task switch protocol without proactive interference. The experiment combined orthogonally task-switch vs. repetition, and attentional set shift vs. no shift. Each experimental stimulus had global and local features (Hierarchical/“Navon” stimuli), associated with corresponding attentional sets.

Results

ADHD patients were slower than controls in task switch trials with a simultaneous shift of attention between global/local attentional sets. This also correlated significantly with diagnostic scales for ADHD symptoms. The patients had more variable reaction times, but when the attentional set was kept constant neither were they significantly slower nor showed higher task switch costs.

Conclusion

ADHD is associated with a deficit in flexible deployment of attention to varying sources of stimulus information.

Disrupted Control-Related Functional Brain Networks in Drug-Naive Children with Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disease featuring executive control deficits as a prominent neuropsychological trait. Executive functions are implicated in multiple sub-networks of the brain; however, few studies examine these sub-networks as a whole in ADHD. By combining resting-state functional MRI and graph-based approaches, we systematically investigated functional connectivity patterns among four control-related networks, including the frontoparietal network (FPN), cingulo-opercular network, cerebellar network, and default mode network (DMN), in 46 drug-naive children with ADHD and 31 age-, gender-, and intelligence quotient-matched healthy controls (HCs). Compared to the HCs, the ADHD children showed significantly decreased functional connectivity that primarily involved the DMN and FPN regions and cross-network long-range connections. Further graph-based network analysis revealed that the ADHD children had fewer connections, lower network efficiency, and more functional modules compared with the HCs. The ADHD-related alterations in functional connectivity but not topological organization were correlated with clinical symptoms of the ADHD children and differentiated the patients from the HCs with a good performance. Taken together, our findings suggest a less-integrated functional brain network in children with ADHD due to selective disruption of key long-range connections, with important implications for understanding the neural substrates of ADHD, particularly executive dysfunction.

Development of the Brazilian version of the Child Hayling Test

Abstract Introduction: The Hayling Test assesses the components of initiation, inhibition, cognitive flexibility and verbal speed by means of a sentence completion task. This study presents the process of developing the Brazilian version of the Child Hayling Test (CHT) and reports evidence of its content validity. Methods: 139 people took part in the study. The adaptation was performed by seven translators and 12 specialist judges. An initial sample of 92 healthy children was recruited to test a selection of sentences adapted from previous adult and pediatric versions of the instrument, and a sample of 28 healthy children was recruited for pilot testing of the final version. The instrument was developed in seven stages: 1) translation, 2) back-translation, 3) comparison of translated versions, 4) preparation of new stimuli, 5) data collection with healthy children to analyze comprehension of the stimuli and analyses by the authors against the psycholinguistic criteria adopted, 6) analyses conducted by judges who are specialists in neuropsychology or linguistics, and 7) the pilot study. Results: Twenty-four of the 72 sentences constructed were selected on the basis of 70-100% agreement between judges evaluating what they assessed and level of comprehensibility. The pilot study revealed better performance by older children, providing evidence of the instrument's sensitivity to developmental factors. Conclusions: Future studies employing this version of CHT with clinical pediatric populations who have frontal lesions and dysfunctions and in related areas are needed to test functional and differential diagnoses of preserved or impaired executive functions.

Developmental Trajectory of Rule Detection in Four- to Six-Year-Old Children

Children younger than three years old are able to detect hidden rules in numerical sequences, and this ability matches that of adults by age seven. However, the developmental trajectory of this ability during the ages of four to six remains unknown. The present study adopted a modified Brixton task to address this issue. In this task, children were presented with sequences of moving circles and were asked to predict which circle would next turn blue based on hidden rules that were either simple (e.g. + 2) or complex (e.g. + 2 – 1). Results suggested that (a) four-year-olds were only able to detect comparably few simple rules, whereas children older than 4.5 years were able to successfully detect most of the simple rules hidden in number sequences; (b) although all children performed significantly poorer when attempting to identify complex rules as compared with simple rules, rule detection (RD) ability improved rapidly with age, and children older than five were able to identify most complex rules. These findings extended previous work on rule learning by revealing the developmental trajectory of RD among preschoolers.

Are Individual Differences in Arithmetic Fact Retrieval in Children Related to Inhibition?

Although it has been proposed that inhibition is related to individual differences in mathematical achievement, it is not clear how it is related to specific aspects of mathematical skills, such as arithmetic fact retrieval. The present study therefore investigated the association between inhibition and arithmetic fact retrieval and further examined the unique role of inhibition in individual differences in arithmetic fact retrieval, in addition to numerical magnitude processing. We administered measures of cognitive inhibition (i.e., numerical and non-numerical stroop tasks) and a complementary, more ecologically valid measure of children’s inhibition in the classroom (i.e., teacher questionnaire), as well as numerical magnitude processing (i.e., symbolic and non-symbolic numerical magnitude comparison) and arithmetic fact retrieval (i.e., two verification tasks) in 86 typically developing third graders. We used a correlation, a regression and a Bayesian analysis. This study failed to observe a significant association between inhibition and arithmetic fact retrieval. Consequently, our results did not reveal a unique contribution of inhibition to arithmetic fact retrieval in addition to numerical magnitude processing. On the other hand, symbolic numerical magnitude processing turned out to be a very powerful predictor of arithmetic fact retrieval, as indicated by both frequentist and Bayesian approaches.

Age-Related Performance on the Brixton Spatial Anticipation Test in Healthy Child and Adolescent Girls: A Preliminary Evaluation

The Brixton Spatial Anticipation Test assesses individuals' cognitive flexibility in terms of rule detection and attainment. It has been used to assess executive functioning in both clinical and nonclinical adult samples. However, little is currently known about the suitability of this task for younger populations. The current study therefore aimed to provide an initial exploration of this task's suitability for young people. Brixton responses from a healthy sample of children and adolescents were presented to investigate performance in both rule detection and rule attainment, respectively. A convenience sample of 72 female participants (Mage = 14.95 years, SD = 1.53 years, range = 11-17 years; MIQ = 103.76, SD = 10.81) was studied. The sample was divided according to age into four groups (11-12 years, 13-14 years, 15 years, and 16-17 years) to allow for developmental trajectory. No significant age performance differences were found. Small effect sizes between age groups lend support to the null findings. The current study suggests that the Brixton task norms are suitable for use with individuals aged 11 to 17 years old. However, normative work is still needed in this area, incorporating an adult sample for comparison, to comment upon the developmental trajectory specific to this task.

[An international neuropsychological assessment tool for children, adolescents, and adults with anorexia nervosa – the German adaptation of the Ravello Profile]

OBJECTIVE

Adults with anorexia nervosa (AN) show weaknesses in several cognitive functions before and after weight restoration. There is a great demand for standardized examinations of executive functioning in the field of child and adolescent AN. Previous studies exhibited methodological inconsistencies regarding test selection and operationalization of cognitive functions, making the interpretation of their findings difficult. In order to overcome these inconsistencies, a neuropsychological assessment tool, the "Ravello Profile," was developed, though previously not available in German. This paper presents a German adaptation of the Ravello Profile and illustrates its applicability in children and adolescents via three case descriptions.

METHODS

The Ravello Profile was adapted for the German-speaking area. The applicability of the Ravello Profile was evaluated in three children and adolescents with AN.

RESULTS AND CONCLUSIONS

The cases presented confirm the feasible implementation of this adaptation of the Ravello Profile, both in children and adolescents. Hence, it enables a methodologically consistent examination of executive functioning in German-speaking children, adolescents, and adults with AN. Using the Ravello Profile, the role of cognitive functions in the development of AN can be systematically examined over a broad age range.

Componentes atencionais e de funções executivas em meninos com TDAH: dados de uma bateria neuropsicológica flexível

OBJETIVO: Comparar o desempenho de sete meninos com diagnóstico comprovado de TDAH (G1) e 14 controles saudáveis (G2) em tarefas neuropsicológicas. MÉTODO: G1 e G2 foram pareados por sexo, idade e escolaridade em tarefas atencionais e executivas (Fluência Verbal e Discurso Narrativo da Bateria MAC, Teste de Cancelamento dos Sinos - versão infantil, Geração Aleatória de Números, Go-no Go do NEUPSILIN-Inf e N-Back auditivo). RESULTADOS: Destacaram-se diferenças entre os grupos quanto à atenção concentrada seletiva, à memória de trabalho, ao automonitoramento, à iniciação e à inibição. CONCLUSÃO: Foi possível verificar contribuições incipientes para um raciocínio de relações intercomponentes das FE e atencionais em pacientes com TDAH.

Cognitive neuroscience from a behavioral perspective: A critique of chasing ghosts with geiger counters

Cognitive neuroscience is a growing new discipline concerned with relating complex behavior to neuroanatomy. Relatively new advances in the imaging of brain function, such as positron emission tomography (PET), have generated hundreds of studies that have demonstrated a number of interesting but also potentially problematic brain-behavior relations. For example, cognitive neuroscientists largely favor interpretations of their data that rely on unobserved hypothetical mechanisms. Their reports often contain phraseology such as central executive, willed action, and mental imagery. As B. F. Skinner argued for decades, cognitive constructs of neurological data may yield nothing more than a conceptual nervous system.

Reduced lateral prefrontal activation in adult patients with attention-deficit/hyperactivity disorder (ADHD) during a working memory task: a functional near-infrared spectroscopy (fNIRS) study

Near-infrared spectroscopy (NIRS) is an optical imaging method, which allows non-invasive in vivo measurements of changes in the concentration of oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin in cortical tissue. For the present study, we examined 13 adult ADHD patients and 13 age- and gender-matched healthy controls by means of multi-channel NIRS (Optical Topography; ETG-100, Hitachi Medical Co., Japan) during performance of a working memory (n-back) paradigm. Compared to the healthy control group, ADHD patients showed reduced task-related increases in the concentration of O2Hb in NIRS channels located over the ventro-lateral prefrontal cortex, indicating reduced activation during performance of the n-back task in this part of the brain. This finding was particularly apparent for the task condition with high working memory load (2-back), and was accompanied by a statistical trend towards an increased number of omission errors in the patient group. The data confirm previous findings of working memory deficits and prefrontal cortex dysfunction in patients suffering from ADHD, and are discussed in the light of imaging findings and theoretical models of working memory function.

O conceito de executivo central e suas origens

O interesse no Executivo Central (EC) cresce a cada dia em vista da observação de disfunção executiva em patologias como o transtorno do déficit de atenção. Entretanto, embora existam referências a esse conceito na literatura nacional, não há nenhum estudo dedicado a um detalhamento teórico a seu respeito. Este trabalho apresenta o conceito de Executivo Central e suas origens teóricas. O EC se caracteriza como um coordenador das operações mentais. A concepção desse sistema remonta à dicotomia entre processos controlados e automáticos. O EC foi explorado na Psicologia soviética e, no contexto da teoria do processamento da informação, seu funcionamento foi explicitado no modelo composto por um Sistema Atencional Supervisor e um organizador pré-programado. Conhecer as origens do conceito de Executivo Central pode trazer novas idéias sobre o seu desenvolvimento normal ou patológico.

Gait in attention deficit hyperactivity disorder

BACKGROUND

Cognitive function and the loading of attention presumably play an important role in gait as well as in fall risk, but previous work has not demonstrated this in any cause-and-effect way.

OBJECTIVES

To gain insight into the relationship between gait and cognitive function, we sought: (1) To compare the gait rhythmicity (stride time variability) of children with attention deficit hyperactivity disorder (ADHD) to controls, (2) To test the hypothesis that dual tasking leads to increased stride-to-stride variability in ADHD, and (3) To test whether pharmacological treatment that relieves ADHD symptoms reduces stride-to-stride variability.

PATIENTS AND METHODS

Gait was quantified in children with ADHD and in age-matched healthy controls under single task and dual task conditions on three occasions: off medications (both groups) and, in the ADHD group, after double blinded, randomized administration of methylphenidate (MPH) or placebo.

RESULTS

At baseline, children with ADHD tended to walk with increased stride-to-stride variability compared to the controls during the single task condition (p = 0.09). During dual task walking, stride time variability was significantly reduced in the children with ADHD (p < 0.004), but not in the controls. In the children with ADHD, the placebo did not significantly affect stride-to-stride variability or the dual tasking response. In contrast, stride time variability was significantly reduced on MPH (p < 0.001) such that dual tasking no longer affected variability.

CONCLUSIONS

The present findings demonstrate alterations in the gait of children with ADHD, support a cause and effect link between cognitive function and gait, and suggest that enhancement of attention abilities may, in certain populations, improve gait rhythmicity.

Disfunção executiva como uma medida de funcionalidade em adultos com TDAH

Este artigo aborda a presença e a apresentação clínica da disfunção executiva em pacientes com TDAH. Na medida em que sintomas de disfunção executiva determinam as alterações de funcionamento desses pacientes nas atividades do dia-a-dia, torna-se relevante o estudo das relações entre alterações em testes neuropsicológicos formais de funções executivas e a ocorrência desses sintomas. A constatação relativamente recente do papel da disfunção executiva no TDAH tem impulsionado a pesquisa neuropsicológica, mas os dados até agora disponíveis são ainda pouco consistentes. Uma visão atualizada dessas questões sugere que a semiologia neuropsicológica disponível ainda não alcança plenamente a constelação de sintomas práticos do TDAH no dia-a-dia, mostrando a necessidade de avanços na pesquisa dessas relações.

Interference effects in a numerical Stroop paradigm in 9- to 12-year-old children with ADHD-C

Attention deficit hyperactivity disorder (ADHD) is characterized by deficient self-regulation, poor attentional control, and poor response inhibition. To date, however, the extent to which these deficits affect basic interference control remains a matter of controversy. Secondly, ADHD has been reported to be associated with arithmetic deficits. It remains unclear whether such deficits are a secondary consequence of the above-mentioned characteristics of ADHD or whether basic numerical magnitude representations are also affected. In the present study we attempted to investigate these issues using a basic numerical interference paradigm. Nine- to twelve-year-old children with ADHD-C (attention-deficit hyperactivity-disorder combined type) and control children without ADHD (each n = 16) were presented with two digits of possibly different physical sizes (e.g., 3 7). This numerical Stroop task requires subjects to make a magnitude classification concerning either the physical or the numerical stimulus dimension. The irrelevant dimension can be congruent (same response), incongruent (different response), or neutral (no response association). Children with ADHD-C performed worse than control children in most analyses. The most important finding was a significant interaction of congruity effects with group in the numerical comparison task. Children with ADHD-C tended to show larger congruity and interference effects than controls, and these were not attributable to a speed-accuracy trade-off. The results might reflect differential processing speeds, or a different degree of automatic activation of physical and numerical magnitudes in children with and without ADHD-C. Alternative explanations, such as insufficient inhibition of selective (domain-specific) attention are also discussed.

Conduct Problems in Adolescence: Three Domains of Inhibition and Effect of Gender

Behavioral and neuropsychological evidence has often shown that children with conduct disorder drawn from clinical populations show problems with impulsivity and are impaired in motor tasks of inhibitory control. We explored the relation between conduct problems and inhibitory deficits in a community sample. Three domains of inhibition were explored in 54 adolescents with conduct problems compared to 53 age, IQ, sex, school, and ethnicity matched controls in 2 geographical areas. Motor response inhibition was assessed using the Stop task, verbal inhibition using the Hayling Sentence Completion test, and cognitive interference inhibition using the Stroop task. Adolescents with conduct problems showed deficits in executive and inhibitory processes of the motor response inhibition task, but were unimpaired in cognitive or verbal inhibitory control. No sex differences were observed and impairments were independent of IQ or geographical location. Findings suggest that motor deficits, rather than higher cognitive forms of inhibitory control, are a specific deficit in children with conduct problems, that girls are as affected as boys, and that motor impulsiveness is a dimensional trait associated with conduct problems, as it is also observed in the community.

Attention-deficit disorder (attention-deficit/ hyperactivity disorder without hyperactivity): a neurobiologically and behaviorally distinct disorder from attention-deficit/hyperactivity disorder (with hyperactivity)

Most studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the combined type and emphasized a core problem in response inhibition. It is proposed here that the core problem in the truly inattentive type of ADHD (not simply the subthreshold combined type) is in working memory. It is further proposed that laboratory measures, such as complex-span and dual-task dichotic listening tasks, can detect this. Children with the truly inattentive type of ADHD, rather than being distractible, may instead be easily bored, their problem being more in motivation (underarousal) than in inhibitory control. Much converging evidence points to a primary disturbance in the striatum (a frontal-striatal loop) in the combined type of ADHD. It is proposed here that the primary disturbance in truly inattentive-type ADHD (ADD) is in the cortex (a frontal-parietal loop). Finally, it is posited that these are not two different types of ADHD, but two different disorders with different cognitive and behavioral profiles, different patterns of comorbidities, different responses to medication, and different underlying neurobiologies.

Impairment of Executive Functions in Boys with Attention Deficit/Hyperactivity Disorder

The main aim of the present study is to compare the efficiency of executive control processes in 24 boys with attention deficit/hyperactivity disorder (ADHD) and 58 normal controls of similar age (between 8 and 11 years). Three reaction time (RT) paradigms were utilized: a dual task that requires coordination of two tasks responses, a shift task that makes it necessary to disengage attention from one task and engage into another one, and a stimulus-response spatial compatibility task that requires participants to inhibit a prepotent response. Another purpose of the study is to examine whether Barkley's (1997) executive dysfunction or Sergeant et al.'s (1999) resource allocation/arousal model best account for the behavioral deficits associated with ADHD. Examination of raw RT data showed significantly poorer performance in ADHD children with respect to age-matched controls on both the higher-level cognitive functions of executive control and on lower-level abilities (e.g., speed of processing) of all tasks of this study. However, using proportional transformations of raw RT data, we could demonstrate that, in addition to differences in processing speed, also executive control processes were significantly impaired in children with ADHD.

Attention-deficit disorder (attention-deficit/ hyperactivity disorder without hyperactivity): a neurobiologically and behaviorally distinct disorder from attention-deficit/hyperactivity disorder (with hyperactivity)

Most studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the combined type and emphasized a core problem in response inhibition. It is proposed here that the core problem in the truly inattentive type of ADHD (not simply the subthreshold combined type) is in working memory. It is further proposed that laboratory measures, such as complex-span and dual-task dichotic listening tasks, can detect this. Children with the truly inattentive type of ADHD, rather than being distractible, may instead be easily bored, their problem being more in motivation (underarousal) than in inhibitory control. Much converging evidence points to a primary disturbance in the striatum (a frontal-striatal loop) in the combined type of ADHD. It is proposed here that the primary disturbance in truly inattentive-type ADHD (ADD) is in the cortex (a frontal-parietal loop). Finally, it is posited that these are not two different types of ADHD, but two different disorders with different cognitive and behavioral profiles, different patterns of comorbidities, different responses to medication, and different underlying neurobiologies.

Are endophenotypes based on measures of executive functions useful for molecular genetic studies of ADHD?

BACKGROUND

Behavioral genetic studies provide strong evidence that attention-deficit/hyperactivity disorder (ADHD) has a substantial genetic component. Yet, due to the complexity of the ADHD phenotype, questions remain as to the specific genes that contribute to this condition as well as the pathways from genes to behavior. Endophenotypes, or phenotypes that are more closely linked to the neurobiological substrate of a disorder, offer the potential to address these two issues simultaneously (Freedman, Adler, & Leonard, 1999). Thus far, potential endophenotypes for ADHD have not been systematically studied.

METHOD

The current paper reviews evidence supporting the use of deficits on neurocognitive measures of executive functions for this purpose.

RESULTS

Such deficits are a correlate of ADHD and show preliminary evidence of heritability and association with relevant candidate genes. Nonetheless, studies that have assessed the familial and genetic overlap of neurocognitive impairments with ADHD have yielded inconsistent results.

CONCLUSIONS

In order for executive function deficits to be used as an endophenotype for ADHD, we recommend greater attention to the neurocognitive heterogeneity of this disorder and to the precision of measurement of the neuropsychological tests employed. We also discuss empirical strategies that may be necessary to allow such research to progress prior to full resolution of the pathophysiological basis of ADHD.

Causal models of attention-deficit/hyperactivity disorder: from common simple deficits to multiple developmental pathways

Until recently, causal models of attention-deficit/hyperactivity disorder (ADHD) have tended to focus on the role of common, simple, core deficits. One such model highlights the role of executive dysfunction due to deficient inhibitory control resulting from disturbances in the frontodorsal striatal circuit and associated mesocortical dopaminergic branches. An alternative model presents ADHD as resulting from impaired signaling of delayed rewards arising from disturbances in motivational processes, involving frontoventral striatal reward circuits and mesolimbic branches terminating in the ventral striatum, particularly the nucleus accumbens. In the present article, these models are elaborated in two ways. First, they are each placed within their developmental context by consideration of the role of person x environment correlation and interaction and individual adaptation to developmental constraint. Second, their relationship to one another is reviewed in the light of recent data suggesting that delay aversion and executive functions might each make distinctive contributions to the development of the disorder. This provides an impetus for theoretical models built around the idea of multiple neurodevelopmental pathways. The possibility of neuropathologic heterogeneity in ADHD is likely to have important implications for the clinical management of the condition, potentially impacting on both diagnostic strategies and treatment options.

Dopamine, learning, and impulsivity: a biological account of attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) affects up to 10% of school-age children. The impulsivity which is seen as its core feature persists over years, yet experimental measures of impulsivity can be altered in a single session. In this study, we tested the theory that both the persistence and the variability of impulsivity could be the result of abnormalities in learning mechanisms and environment.

METHOD

We extended an existing model of the role of dopamine in operant conditioning to address the delayed response time task, which is one of the standard tests for impulsivity in ADHD. In this task, subjects choose between immediate responding for a small reinforcer and later responding for a larger one. We studied the influence on impulsivity of four key parameters of the model: The learning rate, discount factor, brittleness, and action bias.

RESULTS

The behavior of the model is broadly comparable with electrophysiological (monkey) and behavioral (ADHD and normal) data. Variations in any of the parameters can cause impulsivity. All parameters except the discount factor show inverted U-shaped curves for their effects on impulsivity, suggesting, for example, how either hyper- or hypofunctioning of dopamine can cause impulsivity. The model suggests how decision making can be affected by environmental unpredictability, and thus offers an account of one aspect of the natural history of ADHD.

CONCLUSIONS

Some types of ADHD may be caused by specific deficits in reinforcement learning and in the use of learned lessons. Environmental factors can interact with these deficits to delay maturation.

Diminished prefrontal brain function in adults with psychopathology in childhood related to attention deficit hyperactivity disorder

The aim of the present study was to investigate prefrontal brain function and cognitive response control in patients with personality disorders who either suffered or did not suffer from psychopathology related to attention deficit hyperactivity disorder (ADHD) during childhood. For this purpose, 36 psychiatric out-patients with personality disorders--24 of whom showed ADHD-related psychopathology during childhood assessed by the German short form of the Wender Utah Rating Scale--and 24 healthy controls were investigated electrophysiologically by means of a cued Go-NoGo task (Continuous Performance Test). Topographical analyses were conducted to individually quantify the NoGo anteriorisation (NGA), a neurophysiological correlate of prefrontal response control that has been suggested to reflect activation of the anterior cingulate cortex. ADHD patients exhibited a significantly reduced mean NGA and diminished amplitudes of the Global Field Power, as well as a reduced increase of fronto-central P300 amplitudes, in NoGo-trials compared with the healthy controls, whereas patients with personality disorders alone did not differ from the control group in any of the electrophysiological parameters. The results indicate that ADHD-related psychopathology is associated with prefrontal brain dysfunction, probably related to processes of response inhibition and/or cognitive response control.

Altered response control and anterior cingulate function in attention-deficit/hyperactivity disorder boys

OBJECTIVE

To investigate mechanisms and structures underlying prefrontal response control and inhibition in boys suffering from attention-deficit/hyperactivity disorder (ADHD).

METHOD

Sixteen boys with ADHD and 19 healthy controls were investigated electrophysiologically during performance of a visual Go-Nogo task (Continuous Performance Test, CPT). An electrophysiological source localization method was employed to further analyze the data.

RESULTS

The ADHD boys showed a significantly diminished central Nogo-P3, due to a lack of Nogo-related frontalization of the positive brain electrical field in this group. This two-dimensional effect was associated with a significantly reduced activation of the anterior cingulate cortex (ACC) in the ADHD boys in the Nogo condition of the CPT. Both groups did not significantly differ regarding the amplitude of the Nogo-N2.

CONCLUSIONS

The results indicate deficits in prefrontal response control in unmedicated ADHD boys that do not seem to be specifically inhibitory in nature. A supposed dysfunction of the ACC in ADHD was confirmed.

AD/HD and the capture of attention by briefly exposed delay-related cues: evidence from a conditioning paradigm

BACKGROUND

The selective attention of children with attention deficit/hyperactivity disorder (AD/HD) to briefly exposed delay-related cues was examined in two experiments using a dot-probe conditioning paradigm.

METHOD

Colour cues were paired with negatively (i.e., imposition of delay) and positively valenced cues (i.e., escape from or avoidance of delay) during a conditioning phase. These cues were presented alongside neutral cues in a subsequent dot-probe detection phase.

RESULTS

In experiment 1 teacher-identified children with AD/HD (N = 12), but not controls (N = 12), displayed an attentional bias towards both positively and negatively valenced cues. In experiment 2 children with a diagnosis of hyperkinetic disorder (N = 15), but not controls (N = 15), displayed a bias towards delay-related cues. However, this effect was largely carried by the response to positively valenced cues.

CONCLUSIONS

These results confirm the dot-probe conditioning paradigm as a useful test of motivational influence on attention. They provide the first evidence of qualitative differences in the attentional style of children with AD/HD and give further support to those theories that highlight the motivational significance of delay in AD/HD.

The dual pathway model of AD/HD: an elaboration of neuro-developmental characteristics

The currently dominant neuro-cognitive model of Attention Deficit Hyperactivity Disorder (AD/HD) presents the condition as executive dysfunction (EDF) underpinned by disturbances in the fronto-dorsal striatal circuit and associated dopaminergic branches (e.g. meso-cortical). In contrast, motivationally-based accounts focus on altered reward processes and implicate fronto-ventral striatal reward circuits and those meso-limbic branches that terminate in the ventral striatum especially the nucleus accumbens. One such account, delay aversion (DEL), presents AD/HD as a motivational style-characterised by attempts to escape or avoid delay-arising from fundamental disturbances in these reward centres. While traditionally regarded as competing, EDF and DEL models have recently been presented as complimentary accounts of two psycho-patho-physiological subtypes of AD/HD with different developmental pathways, underpinned by different cortico-striatal circuits and modulated by different branches of the dopamine system. In the current paper we describe the development of this model in more detail. We elaborate on the neuro-circuitry possibly underpinning these two pathways and explore their developmental significance within a neuro-ecological framework.

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

Psychological accounts have characterised attention-deficit/hyperactivity disorder (AD/HD) as either a neuro-cognitive disorder of regulation or a motivational style. Poor inhibitory control is thought to underpin AD/HD children's dysregulation while delay aversion is a dominant characteristic of their motivational style. A recent 'head to head' study of these two accounts suggest that delay aversion and poor inhibitory control are independent co-existing characteristics of AD/HD (combined type). In the present paper we build on these findings to propose a dual pathway model of AD/HD that recognises two quite distinct sub-types of the disorder. In one AD/HD is the result of the dysregulation of action and thought resulting from poor inhibitory control associated with the meso-cortical branch of the dopamine system projecting in the cortical control centres (e.g. pre-frontal cortex). In the other AD/HD is a motivational style characterised by an altered delay of reward gradient linked to the meso-limbic dopamine branch associated with the reward circuits (e.g. nucleus accumbens). The two pathways are further distinguished at the levels of symptoms, cognitive and motivation profiles and genetic and non-genetic origins.

Methylphenidate effects on task-switching performance in attention-deficit/hyperactivity disorder

OBJECTIVE

To examine the specificity of methylphenidate effects on the processes that support the ability to rapidly and accurately coordinate the performance of multiple tasks in children with attention-deficit hyperactivity disorder (ADHD).

METHOD

Twenty children with ADHD performed the task-switching paradigm while on and off medication. The paradigm involves switching between two different tasks, discriminating the value of a number presented on a computer screen and deciding how many numbers were present on the screen. The children also performed single-task control conditions.

RESULTS

Analyses of variance indicated the medication selectively enhanced the children's ability to rapidly and accurately switch between tasks and to focus attention on the currently relevant response set.

CONCLUSIONS

This study helps to elucidate the nature of methylphenidate effects on the cognitive processes which support the ability to coordinate the performance of multiple tasks. Medication appears to selectively enhance inhibitory processes which support task-switching.

Is ADHD a disinhibitory disorder?

Attention deficit hyperactivity disorder (ADHD) is widely theorized to stem from dysfunctional inhibitory processes. However, the definition of inhibition is imprecisely distinguished across theories. To clarify the evidence for this conception, the author relies on a heuristic distinction between inhibition that is under executive control and inhibition that is under motivational control (anxiety or fear). It is argued that ADHD is unlikely to be due to a motivational inhibitory control deficit, although suggestions are made for additional studies that could overturn that conclusion. Evidence for a deficit in an executive motor inhibition process for the ADHD combined type is more compelling but is not equally strong for all forms of executive inhibitory control. Remaining issues include specificity to ADHD, whether inhibitory problems are primary or secondary in causing ADHD, role of comorbid anxiety and conduct disorder, and functional deficits in the inattentive ADHD subtype.