Biological contributions to the presentation and understanding of attention-deficit/hyperactivity disorder: a review

Front and center: Maturational dysregulation of frontal lobe functional neuroanatomic connections in attention deficit hyperactivity disorder

Frontal lobe function may not universally explain all forms of attention deficit hyperactivity disorder (ADHD) but the frontal lobe hypothesis described supports an internally consistent model for integrating the numerous behaviors associated with ADHD. The paper examines the developmental trajectories of frontal and prefrontal lobe development, framing ADHD as maturational dysregulation concluding that the cognitive, motor, and behavioral abilities of the presumptive majority of ADHD children may not primarily be disordered or dysfunctional but reflect maturational dysregulation that is inconsistent with the psychomotor and cognitive expectations for the child’s chronological and mental age. ADHD children demonstrate decreased activation of the right and middle prefrontal cortex. Prefrontal and frontal lobe regions have an exuberant network of shared pathways with the diencephalic region, also having a regulatory function in arousal as well as with the ascending reticular formation which has a capacity for response suppression to task-irrelevant stimuli. Prefrontal lesions oftentimes are associated with the regulatory breakdown of goal-directed activity and impulsivity. In conclusion, a presumptive majority of childhood ADHD may result from maturational dysregulation of the frontal lobes with effects on the direct, indirect and/or, hyperdirect pathways.

Detection of Executive Performance Profiles Using the ENFEN Battery in Children Diagnosed With Attention-Deficit Hyperactivity Disorder

Attention-deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders in children and adolescents. People who have this disorder are characterized by presenting difficulties in the processes of sustained attention, being very active, and having poor control of their impulses. Despite the high prevalence of this disorder and the existence of various tests used for its diagnosis, few data are available regarding the usefulness and diagnostic validity of these tools. Given the difficulties that these subjects present in executive functions, the aim of this study was to evaluate whether the Neuropsychological Assessment of Executive Functions battery for Children (ENFEN, for its acronym in Spanish, Portellano et al., 2009) allows to establish specific profiles of executive performance for people with attention-deficit hyperactivity disorder (ADHD). The sample was made up of 197 participants of both sexes, aged between 6 and 12 years age (134 with a clinical diagnosis and 63 without pathology). A nonexperimental design was followed, using a comparative descriptive study method. The results indicated that the scales of phonological fluency, color path, rings, and interference are the most associated with the diagnosis of ADHD, providing data on inhibition, mental flexibility, sustained and selective attention, planning, verbal fluency, and working memory, among others. The practical implication of these results is in line with providing support in the clinical diagnosis that is carried out in children's mental health units. In addition, the ENFEN tool can be valued as a suitable psychometric instrument in the psychoeducational field, helping professionals in a school environment to be more aware of the areas of cognitive development in which a student diagnosed with ADHD will have more difficulties and, in doing so, providing more adjusted and effective psychopedagogical measures when it comes to supporting students in their adaptation to the school environment.

Is the Theta/Beta EEG Marker for ADHD Inherently Flawed?

OBJECTIVE

Despite advances in our understanding of ADHD as a neurodevelopmental disorder, robust biomarkers are yet to be established in clinical practice. More than 40 years of electroencephalography (EEG)-based research has culminated in the recent Food and Drug Administration (FDA) approval of the theta/beta (EEG power) ratio (TBR) as a diagnostic marker of ADHD.

METHOD

This review article focuses on resting-state EEG power research in ADHD.

RESULTS

Inconsistent findings in the literature and suggestions of reduced specificity threaten the utility of TBR as a biomarker of ADHD. The use of fixed EEG bands may be a significant limitation, particularly in youth, and alternative approaches are needed.

CONCLUSION

We propose that a personalized theta-to-alpha cut point or "transition frequency" is a better frame of reference for the measurement of TBR. Such an approach is better placed to test maturational lag and cortical hypoarousal models of ADHD and may in turn have greater utility in supporting diagnosis.

Reductionism Revisited

Reductionism in psychology is often linked with the mind-body problem. This paper reviews the reductionism debate and concludes that many of its controversies can indeed be traced to the relation between reduction and the metaphysical mind-body problem. It is proposed that reductionism, by bridging different theories, rather should be considered as a scientific stance which favours interdisciplinary co-operation. This perspective on reductionism throws a new light on the classical model of reduction, which may capture important aspects of intertheoretic reductions if it is recognized that the bridges between theories do not need to comply completely with the classical conditions. These ideas are illustrated by analysing an example of reductionistic research concerning the psychology and neuropsychology of attention-deficit/hyperactivity disorder.

Postural control among children with and without attention deficit hyperactivity disorder in single and dual conditions

Given the known deficits in attention in attention deficit hyperactivity disorder (ADHD) and the evidence suggesting that postural control requires attention, this study aimed to investigate the mechanisms of postural control of children with and without ADHD in single-(ST) and dual-task (DT) conditions. Postural sway and stabilogram diffusion analysis (SDA) were performed on the Center of Pressure trajectories on 24 ADHD children and 17 age-gender-matched healthy controls. The subjects were instructed to stand as stable as possible on a force platform in two task conditions: (1) single task (ST) and (2) dual task (DT)-an auditory-memory attention-demanding cognitive task. During ST and DT conditions, the ADHD children showed significantly greater ML-sway, short- and long-term effective diffusion coefficients, and critical displacement of SDA compared with controls. The effects of DT were somewhat unexpected; the control group indicated a significant decrease in ML-sway, AP-sway, sway area, and critical displacement of SDA; the ADHD group showed a significant decrease in ML-sway range and critical displacement. It is concluded that a greater sway displacement before closed-loop mechanisms is called into play in ADHD children. The DT enhanced balance control by reinforcing balance automaticity and minimizing sway in both healthy and ADHD children.

Cognitive and electroencephalographic disturbances in children with attention-deficit/hyperactivity disorder and sleep problems: new insights

There is overlap between the behavioural symptoms and disturbances associated with Attention-Deficit/Hyperactivity Disorder (AD/HD) and sleep problems. The aim of this study was to examine the extent of overlap in cognitive and electrophysiological disturbances identified in children experiencing sleep problems and children with AD/HD or both. Four groups (aged 7-18) were compared: children with combined AD/HD and sleep problems (n=32), children with AD/HD (n=52) or sleep problems (n=36) only, and children with neither disorder (n=119). Electrophysiological and cognitive function measures included: absolute EEG power during eyes open and eyes closed, event-related potential (ERP) components indexing attention and working memory processes (P3), and a number of standard neuropsychological tests. Children with symptoms of both AD/HD and sleep problems had a different profile from those of children with either AD/HD or sleep problems only. These findings suggest it is unlikely that disturbances in brain and cognitive functioning associated with sleep problems also give rise to AD/HD symptomatology and consequent diagnosis. Furthermore, findings suggest that children with symptoms of both AD/HD and sleep problems may have a different underlying aetiology than children with AD/HD-only or sleep problems-only, perhaps requiring unique treatment interventions.

Understanding genes, environment and their interaction in attention-deficit hyperactivity disorder: is there a role for neuroimaging?

Attention-deficit hyperactivity disorder (ADHD) has an established heritable component, but identifying the genes involved has proven difficult. To date, the two most investigated risk genes in ADHD are the DRD4 and DAT1-genes. However, individual risk genes have only explained up to 1% of the variance in the phenotype, suggesting that they represent only relatively small risk factors for ADHD. As such, the role of environmental factors, gene-gene and gene-environment interactions are being investigated. However, studies have not always been able to address the neurobiological mechanisms by which environmental factors and interactions with genes exert their effect on the ADHD-phenotype. Neuroimaging is being used as a tool to investigate the neurobiological effects of individual risk genes. We suggest it could also be applied to investigate the mechanisms involved in environmental effects and interactions between genetic and environmental factors.

Converging methods in studying attention-deficit/hyperactivity disorder: what can we learn from neuroimaging and genetics?

This paper discusses how converging methods may form a powerful tool in unraveling the neurobiology of attention-deficit/hyperactivity disorder (ADHD). Integrating findings from multiple disciplines can inform us on how different neurobiological and cognitive mechanisms tie together in both typical and atypical development. Examples are discussed of this approach: combining family and genetic approaches with anatomical neuroimaging illustrates how mapping familial effects can bring us closer to understanding the neurobiology of ADHD. Functional neuroimaging has convincingly linked cognitive problems in this disorder with frontostriatal functioning, but also shows that other systems may be involved in some of the symptoms of ADHD. Combining these findings has suggested new avenues for investigation, such as the role of frontocerebellar networks. Furthermore, findings may have practical applications: this paper discusses an example of how converging evidence of striatal dysregulation in ADHD suggests possible directions for treatment that are now being explored in functional imaging studies.

Nutritional and dietary influences on attention deficit hyperactivity disorder

An abundance of research has investigated causes and treatments for attention deficit hyperactivity disorder (ADHD). The research includes identification of suboptimal levels of nutrients and sensitivities to certain foods and food additives. This review gives an overview of this research and provides an up-to-date account of clinical trials that have been conducted with zinc, iron, magnesium, Pycnogenol, omega-3 fatty acids, and food sensitivities. A literature search was conducted using PubMed, ISI Web of Knowledge, and Google Scholar and included studies published before April 2008. Although further research is required, the current evidence supports indications of nutritional and dietary influences on behavior and learning in these children, with the strongest support to date reported for omega-3s and behavioral food reactions.

Imaging genetics in ADHD: a focus on cognitive control

This paper evaluates neuroimaging of cognitive control as an endophenotype for investigating the role of dopamine genes in ADHD. First, this paper reviews both data-driven and theory-driven approaches from genetics and neuroimaging. Several viable candidate genes have been implicated in ADHD, including the dopamine DRD4 and DAT1 genes. Neuroimaging studies have resulted in a good understanding of the neurobiological basis of deficits in cognitive control in this disorder. Second, this paper discusses imaging genetics in ADHD. Papers to date have taken one of two approaches: whereas early papers investigated the effects of one or two candidate genes on many brain areas, later papers constrained regions of interest by gene expression patterns. These papers have largely focused on cognitive control and the dopamine circuits involved in this ability. The results show that neuroimaging of cognitive control is useful as an endophenotype in investigating dopamine gene effects in ADHD. Other avenues of investigation are suggested by a combination of data- and theory-driven approaches in both genetics and neuroimaging.

Who is at risk for special health care needs: findings from the National Survey of Children's Health

OBJECTIVE

A conceptual model of risk factors for special health care needs in childhood was presented previously. This article uses that conceptual model to identify candidate variables for an exploratory empirical examination of the effects of factors that may increase or decrease the risk of developing a special health care need.

METHODS

The National Survey of Children's Health was used for our analysis (N = 102 353). We used multilevel and multivariate analysis methods. We examined risk factors for special health care needs generally and for specific physical, developmental, behavioral, and emotional conditions cooccurring with special health care needs. Risk factors were grouped into 6 major domains, namely, predisposing characteristics, genetic endowment, physical environment, social environment, health-influencing behavior, and health care system characteristics. We examined preschool-aged and school-aged children separately.

RESULTS

Significant associations were found in 5 of 6 domains studied (no variables in the health care systems characteristics were significant). Individual variables found to decrease or to increase significantly the odds of experiencing special health care needs were expressed at the child level (eg, age and gender), family level (eg, family structure and family conflict), and neighborhood level (eg, perception of supportiveness of the neighborhood).

CONCLUSIONS

This analysis is the first to consider empirically a range of risk factors for special health care needs, using a population health model. Although provisional, the results of our analysis can help us to begin thinking about which characteristics of the child, family, and community are worthy of further exploration. Some of the variables we found to be significantly associated with special health care needs, such as age and ethnicity, are immutable. However, we found a number of significant correlates (ie, possible risk factors) that may be amenable to public health interventions, including breastfeeding practices, exposure to secondhand smoke, family closeness, and neighborhood cohesion.

Blinded, multi-center validation of EEG and rating scales in identifying ADHD within a clinical sample

Previous validation studies of attention deficit/hyperactivity disorder (ADHD) assessment by rating scales or EEG have provided Class-IV evidence per standards of the American Academy of Neurology. To investigate clinical applications, we collected Class-I evidence, namely from a blinded, prospective, multi-center study of a representative clinical sample categorized with a clinical standard. Participating males (101) and females (58) aged 6 to 18 had presented to one of four psychiatric and pediatric clinics because of the suspected presence of attention and behavior problems. DSM-IV diagnosis was performed by clinicians assisted with a semi-structured clinical interview. EEG (theta/beta ratio) and ratings scales (Conners Rating Scales-Revised and ADHD Rating Scales-IV) were collected separately in a blinded protocol. ADHD prevalence in the clinical sample was 61%, whereas the remainder had other childhood/adolescent disorders or no diagnosis. Comorbidities were observed in 66% of ADHD patients and included mood, anxiety, disruptive, and learning disorders at rates similar to previous findings. EEG identified ADHD with 87% sensitivity and 94% specificity. Rating scales provided sensitivity of 38-79% and specificity of 13-61%. While parent or teacher identification of ADHD by rating scales was reduced in accuracy when applied to a diverse clinical sample, theta/beta ratio changes remained consistent with the clinician's ADHD diagnosis. Because theta/beta ratio changes do not identify comorbidities or alternative diagnoses, the results do not support the use of EEG as a stand-alone diagnostic and should be limited to the interpretation that EEG may complement a clinical evaluation for ADHD.

Comparison of a standard psychiatric evaluation to rating scales and EEG in the differential diagnosis of attention-deficit/hyperactivity disorder

The objective was to investigate the effectiveness of rating scales and electroencephalography (EEG) in detecting the presence of attention-deficit/hyperactivity disorder (ADHD) within a diverse clinical sample. A standard psychiatric evaluation was used to assess 26 children/adolescents who presented to a clinic because a parent suspected the presence of ADHD. EEG data was collected in a blinded protocol, and rating scales were collected as well. Although all subjects had presented with ADHD-like symptoms, only 62% were diagnosed with ADHD, while the remaining 38% had other disorders or no diagnosis. Rating scales readily classified inattentive, impulsive, and/or hyperactive symptoms as being due to ADHD, regardless of the actual underlying disorder, leading to a sensitivity of 81% and a specificity of 22%. Previous studies have observed that there is an EEG marker that identifies ADHD vs. controls, and this marker was present in 15 out of 16 of the ADHD subjects (sensitivity=94%) and in none of the subjects with ADHD-like symptoms due to other disorders (specificity=100%). In the detection of ADHD in a diverse clinical sample, rating scales and EEG were both sensitive markers, whereas only EEG was specific. These results may have important implications to ADHD differential diagnosis.

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.

A murine model of hyperdopaminergic state displays altered respiratory control

The dopamine transporter (DAT) protein plays an important role in the termination of dopamine signaling. We addressed the hypothesis that loss of DAT function would result in a distinctive cardiorespiratory phenotype due to the significant role of dopamine in the control of breathing, especially with respect to chemical control, metabolism, and thermoregulation. The DAT knockout mouse (DAT-/-) displays a state of functional hyperdopaminergia characterized by marked novelty driven hyperactivity. Certain behavioral and drug responses in these mice are reminiscent of endophenotypes of individuals with attention deficit hyperactivity disorders (ADHD). We performed experiments on conscious, unrestrained DAT-/- mice (KO) and littermate DAT+/+ wild-type (WT) controls. Ventilation was measured by the barometric technique during normoxia, hypoxia, or hypercapnia. We measured core body temperature and CO2 production as an index of metabolism. DAT-/- mice displayed a significantly lower respiratory frequency than WT mice, reflecting a prolonged inspiratory time. DAT-/- mice exhibited a reduced ventilatory response to hypoxia characterized by an attenuation of both the respiratory frequency and tidal volume responses. Both groups showed similar metabolic responses to hypoxia. Circadian measurements of body temperature were significantly lower in DAT-/- mice than WT mice during inactive periods. We conclude that loss of the DAT protein in this murine model of altered dopaminergic neurotransmission results in a significant respiratory and thermal phenotype that has possible implications for understanding of conditions associated with altered dopamine regulation.

A meta-analysis of quantitative EEG power associated with attention-deficit hyperactivity disorder

A meta-analysis was performed on quantitative EEG (QEEG) studies that evaluated attention-deficit hyperactivity disorder (ADHD) using the criteria of the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th edition). The nine eligible studies (N = 1498) observed QEEG traits of a theta power increase and a beta power decrease, summarized in the theta/beta ratio with a pooled effect size of 3.08 (95% confidence interval, 2.90, 3.26) for ADHD versus controls (normal children, adolescents, and adults). By statistical extrapolation, an effect size of 3.08 predicts a sensitivity and specificity of 94%, which is similar to previous results 86% to 90% sensitivity and 94% to 98% specificity. It is important to note that the controlled group studies were often with retrospectively set limits, and that in practice the sensitivity and specificity results would likely be more modest. The literature search also uncovered 32 pre-DSM-IV studies of ADHD and EEG power, and 29 of the 32 studies demonstrated results consistent with the meta-analysis. The meta-analytic results are also supported by the observation that the theta/beta ratio trait follows age-related changes in ADHD symptom presentation (Pearson correlation coefficient, 0.996, P = 0.004). In conclusion, this meta-analysis supports that a theta/beta ratio increase is a commonly observed trait in ADHD relative to normal controls. Because it is known that the theta/beta ratio trait may arise with other conditions, a prospective study covering differential diagnosis would be required to determine generalizability to clinical applications. Standardization of the QEEG technique is also needed, specifically with control of mental state, drowsiness, and medication.

Activation in ventral prefrontal cortex is sensitive to genetic vulnerability for attention-deficit hyperactivity disorder

BACKGROUND

Attention-deficit hyperactivity disorder (ADHD) is a heritable neuropsychiatric disorder, associated with atypical patterns of brain activation in functional imaging studies. Neuroimaging measures may serve as an intermediate phenotype in genetic studies of ADHD, as they are putatively more closely linked to gene expression than a clinical diagnosis.

METHODS

We used rapid, mixed-trial, event-related functional magnetic resonance imaging (fMRI) to investigate changes in brain activation during a go no-go task in boys with ADHD, their unaffected siblings, and matched control subjects.

RESULTS

On the hardest inhibitory trials in our task, children and adolescents with ADHD had lower accuracy than control subjects, whereas their unaffected siblings did not. Control subjects activated a network of regions, including ventral prefrontal and inferior parietal cortex. Both children and adolescents with ADHD and their unaffected siblings showed decreased activation in these areas, as well as fewer correlations between performance and activation.

CONCLUSIONS

These findings suggest that the magnitude of activation during successful inhibitions is sensitive to genetic vulnerability for ADHD in a number of regions, including ventral prefrontal cortex. If this can be replicated in future studies, this suggests that neuroimaging measures related to inhibitory control may be suitable as intermediate phenotypes in studies investigating gene effects in ADHD.

Children at risk for special health care needs

OBJECTIVE

Despite the widespread use of the Maternal and Child Health Bureau definition of children with special health care needs, no published studies have considered the "at-risk" component of the definition. The purpose of this article is to present a conceptual model of risk for special health care needs.

METHODOLOGY

The conceptual model presented here was developed based on a comprehensive review of the literature on the determinants of population health and the etiologic literature for selected representative childhood chronic conditions.

RESULTS

Our conceptual model is built on 5 key pillars derived from the literature. First, determinants of health have been demonstrated to include genetic endowment, the physical and social environment, health-related behaviors, and the health care system. Second, the model recognizes that the relative importance of each of these domains in contributing to the presence of a special health care need is likely to vary across the major chronic conditions experienced by children. Third, these domains can be conceptualized as acting at the child, family, community, or societal level. Fourth, the model recognizes the presence of a complex interplay of causal factors influencing the development of chronic conditions and associated special health care needs. Fifth, the model incorporates a temporal aspect to the development of special health care needs.

CONCLUSIONS

The conceptual model presented here represents a starting point for thinking about the risk factors that influence the occurrence and severity of a special health care need. The model incorporates many of the important breakthroughs by social epidemiologists over the past 25 years by including a broad range of genetic, social, and environmental risk factors; multiple pathways by which they operate; a time dimension; the notion of differential susceptibility and resilience; and a multilevel approach to considering risk. Nevertheless, we recognize that the conceptual model represents an oversimplification of reality. The study of risk factors for special health care needs remains largely in its infancy and is ripe for additional development.

Integrative neuroscience approach to predict ADHD stimulant response

Despite high rates of prescription, little is known about the long-term consequences of stimulant medication therapy for attention-deficit hyperactivity disorder (ADHD) sufferers. Historically, the clinical use of stimulants for ADHD has been based on trial and error before optimal therapy is reached. Concurrently, scientific research on the mechanism of action of stimulants has influenced neurobiological models of ADHD, but has not always informed their prescription. Whilst the two main stimulant types (methylphenidate and dexamphetamine) have numerous similarities, they also differ (slightly) in mechanism and possibly individual response. A further issue relates to differences in cost and availability compounded by the expectation for stimulants to be effective in ameliorating a broad spectrum of ADHD-related symptoms. Thus, there is an increasing need for treating clinicians to prescribe not only the most effective drug, but also the most appropriate dose with the associated release mechanism and schedule for each ADHD patient presented. In this regard, the field is witnessing an emergence of the personalized medicine approach to ADHD, in which treatment decisions are tailored to each individual. This shift requires a new approach to research into treatment response prediction. Given the heterogeneity of ADHD, a profile of information may be required to capture the most sensitive predictors of treatment response in individuals. These profiles will also benefit from the integration of data from clinical rating scales with more direct measures of cognition and brain function. In conclusion, there is a need to establish a more robust normative framework as the baseline for treatment, as well as diagnostic decisions, and as discussed, the growth of integrated neuroscience databases will be important in this regard.

Attention-deficit hyperactivity disorder in girls: epidemiology and management

Attention-deficit hyperactivity disorder (ADHD) in girls is a topic of growing research and clinical interest. For many years, girls with ADHD have been ignored and overshadowed by hyperkinetic and impulsive boys, but they are now attracting interest in an effort to understand the similarities and differences in the prevalence, symptoms, familial risk, comorbidities and treatment of ADHD in the two sexes. A review of past and current literature finds that the symptoms of ADHD are not sex specific, but that identification of girls with ADHD is hampered by parental and teacher bias, and confusion. Girls are more likely to be inattentive without being hyperactive or impulsive, compared with boys. Girls and boys share the same familial risk patterns, as well as similar, although not identical, comorbidity or impairment patterns. The risk of non-treatment is as great in girls as it is in boys; up to 70-80% of identified children will have persistent symptoms and impairment that extends into adolescence and adulthood. Treatment modalities are equally effective in girls and boys. Stimulants, non-stimulants and behavioural modalities are the mainstays of effective treatment.

The relations between DISC-IV DSM diagnoses of ADHD and multi-informant CBCL-AP syndrome scores

BACKGROUND

Previous studies have examined the relation between attention problems (APs) obtained with the Child Behavior Checklist (CBCL) and attention deficit hyperactivity disorder (ADHD) assessed with the Diagnostic and Statistical Manual of Mental Disorders (DSM). We will examine this relation across sex using multi-informant data.

METHODS

Parents of 12538 twins, aged 7, 10, and 12 years, and teachers of twins, aged 10 years, completed the questionnaires. The mothers of a sample of 283 boys and 291 girls who scored either low or high on longitudinal maternal CBCL-AP were interviewed.

RESULTS

Children with a low AP score obtained a negative ADHD diagnosis in 96% of cases. Children with a high AP score obtained a positive diagnosis in 36% (girls) and 59% (boys) of cases. The association between paternal and maternal AP ratings and ADHD was the same, whereas the association between teacher AP ratings and ADHD was low.

CONCLUSIONS

The association between AP and ADHD is higher in boys than girls, possibly because of a bias toward the male manifestation of ADHD.

Online measurement of motivational processes: introducing the Continuous Delay Aversion Test (ConDAT)

The Continuous Delay Aversion Test (ConDAT), a new computer task for online monitoring and continuously measuring delay aversion (DA), is introduced. DA is a motivational style related to a shortened delay gradient which is proposed as a major endophenotype of attention deficit hyperactivity disorder (ADHD). It is characterised by avoiding or escaping from delay-rich situations despite the prospects of a reward. In each ConDAT trial the rapidly diminishing reward/delay ratio, which tends asymptotically towards zero, is visually presented on the computer screen. The test subject is permanently confronted with the question whether to quit or to continue the trial in the face of the deteriorating reward/time ratio. An elaborated control of stimuli and responses, including the sending of trigger codes to external recording devices, makes the task useful for neurophysiological or brain imaging experiments. Compared to existing tasks, the ConDAT is more flexible and sensitive due to its asymptotic open-ended trials and the interval-scaled output measure. Pilot data give evidence for satisfactory reliability and external validity of the task.

Bildgebende Darstellung neurokognitiver Dysfunktionen bei der Aufmerksamkeitsdefizit-/Hyperaktivit�tsst�rung

Attention Deficit Hyperactivity Disorder (ADHD) is a neurobiological disorder of early childhood onset. Defining symptoms are chronic impairments of attention, impulse control and motor hyperactivity that frequently persist until adulthood. Miscellaneous causes of the disorder have been discussed. Accumulating evidence from imaging- and molecular genetic studies strengthened the theory of ADHS being a predominantly inherited disorder of neurobiological origin. In the last 15 years, non-invasive brain imaging methods were successfully implemented in pediatric research. Functional magnetic resonance imaging studies gave major insight into the neurobiological correlates of executive malfunction, inhibitory deficits and psychomotoric soft signs. These findings are in good accordance with brain morphometric data indicating a significant volumetric decrease of major components of striato-thalamo-cortical feedback loops, primarily influencing prefrontal executive functioning (e.g. basal ganglia). Empirical evidence points to a broad array of associated behavioral disturbances like deficient visuomotor abilities and oculomotor dysfunctions. This paper reviews the current empirical evidence derived from prior imaging studies. Special emphasis is given to the relevance of oculomotor dysfunctions in clinical and research settings, as well as their assessment in the MR environment.

High antenatal maternal anxiety is related to impulsivity during performance on cognitive tasks in 14- and 15-year-olds

This study prospectively investigated the influence of antenatal maternal anxiety, measured with the State Trait Anxiety Inventory at 12-22, 23-31 and 32-40 postmenstrual weeks of pregnancy, on cognitive functioning in 57 adolescents (mean age 15 years). ANCOVAs showed effects of State anxiety at 12-22 weeks, after controlling for influences of State anxiety in later pregnancy and postnatal maternal Trait anxiety. Adolescents of high anxious pregnant women reacted impulsively in the Encoding task; they responded faster but made more errors than adolescents of low anxious women. They also scored lower on two administered WISC-R subtests. In the Stop task no differences in inhibiting ongoing responses were found between adolescents of high and low anxious pregnant women. We suspect that high maternal anxiety in the first half of pregnancy may negatively affect brain development of the fetus, reflected by impulsivity and lower WISC-R scores at 14-15 years.

Genetic and environmental contributions to stability and change of ADHD symptoms between 8 and 13 years of age: a longitudinal twin study

OBJECTIVE

To study the genetic and environmental contributions to stability and change of attention-deficit/hyperactivity disorder (ADHD) symptoms between 8 and 9 and 13 and 14 years of age.

METHOD

The sample included 1,480 twin pairs born in Sweden between May 1985 and December 1986. At wave 1 in 1994, when twins were 8-9 years old, 1,106 (75%) of the parents responded to a mailed questionnaire, and at wave 2 when the twins were 13-14 years old, 1,063 (73%) responded. A checklist with 14 items based on the 14 DSM-III-R symptoms for ADHD was completed. Structural equation modeling was used to analyze the data.

RESULTS

A relatively high stability of ADHD symptoms over this 5-year period was found. This continuity was mainly due to the same genetic effects operating at both points in time. Change in symptoms between childhood and early adolescence was to a large extent due to new genetic effects in early adolescence but also due to new nonshared environmental effects that became important during adolescence.

CONCLUSIONS

The genetic stability highlights the importance of the continuing search for genes and endophenotypes of ADHD.

High Antenatal Maternal Anxiety Is Related to ADHD Symptoms, Externalizing Problems, and Anxiety in 8- and 9-Year-Olds

Associations between antenatal maternal anxiety, measured with the State Trait Anxiety Inventory, and disorders in 8- and 9-year-olds were studied prospectively in 71 normal mothers and their 72 firstborns. Clinical scales were completed by the mother, the child, the teacher, and an external observer. Hierarchical multiple regression analyses showed that maternal state anxiety during pregnancy explained 22%, 15%, and 9% of the variance in cross-situational attention deficit hyperactivity disorder symptoms, externalizing problems, and self-report anxiety, respectively, even after controlling for child's gender, parents' educational level, smoking during pregnancy, birth weight, and postnatal maternal anxiety. Anxiety at 12 to 22 weeks postmenstrual age turned out to be a significant independent predictor whereas anxiety at 32 to 40 weeks was not. Results are consistent with a fetal programming hypothesis.

Magnetic resonance imaging of boys with attention-deficit/hyperactivity disorder and their unaffected siblings

OBJECTIVE

To study the influence of increased familial risk for attention-deficit/hyperactivity disorder (ADHD) on brain morphology.

METHOD

Volumetric cerebral measures based on whole brain magnetic resonance imaging scans from 30 boys with ADHD, 30 of their unaffected siblings, and 30 matched controls were compared.

RESULTS

Both subjects with ADHD and their unaffected siblings displayed reductions in right prefrontal gray matter and left occipital gray and white matter of up to 9.1% (p < 0.05). Right cerebellar volume was reduced by 4.9% in subjects with ADHD (p = 0.026) but not in their unaffected siblings (p = 0.308). A 4.0% reduction in intracranial volume was found in subjects with ADHD (p = 0.031), while a trend was observed in their unaffected siblings (p = 0.068).

CONCLUSIONS

The volumetric reductions in cortical gray and white matter in subjects with ADHD are also present in their unaffected siblings, suggesting that they are related to an increased familial risk for the disorder. In contrast, the cerebellum is unaffected in siblings, suggesting that the reduction in volume observed in subjects with ADHD may be more directly related to the pathophysiology of this disorder.

A review of the biological bases of ADHD: what have we learned from imaging studies?

Attention Deficit Hyperactivity Disorder (ADHD) is a common and impairing neuropsychiatric disorder with onset at preschool age. Although a significant amount of progress has been made investigating the neurobiology of this disorder, its precise etiology still remains unclear. Converging evidence from studies of the neuropharmacology, genetics, neuropsychology, and neuroimaging of ADHD imply the involvement of fronto-striatal circuitry in ADHD. However, while it does appear that poor inhibitory control and the deficits in fronto-striatal circuitry associated with it are central, there is evidence to suggest that more posterior cerebral areas are also implicated in this disorder. Anatomical studies suggest widespread reductions in volume throughout the cerebrum and cerebellum, while functional imaging studies suggest that affected individuals activate more diffuse areas than controls during the performance of cognitive tasks. The future impact of new MR imaging methodologies on the field is discussed.

Animal models of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) involves clinically heterogeneous dysfunctions of sustained attention, with behavioral overactivity and impulsivity, of juvenile onset. Experimental models, in addition to mimicking syndromal features, should resemble the clinical condition in pathophysiology, and predict potential new treatments. One of the most extensively evaluated animal models of ADHD is the spontaneously hypertensive rat. Other models include additional genetic variants (dopamine transporter gene knock-out mouse, coloboma mouse, Naples hyperexcitable rat, acallosal mouse, hyposexual rat, and population-extreme rodents), neonatal lesioning of dopamine neurons with 6-hydroxydopamine, and exposure to other neurotoxins or hippocampal irradiation. None is fully comparable to clinical ADHD. The pathophysiology involved varies, including both deficient and excessive dopaminergic functioning, and probable involvement of other monoamine neurotransmitters. Improved models as well as further testing of their ability to predict treatment responses are required.

Altered cortical activity in children with attention-deficit/hyperactivity disorder during attentional load task

OBJECTIVE

To evaluate whether cortical activity recorded during attentional load in children with ADHD is different compared with controls.

METHOD

Quantitative electroencephalography (QEEG) was performed at open eyes and during performance of the Continuous Performance Task.

RESULTS

Children with ADHD showed an altered pattern of QEEG activity, especially during the attentional load task, with increased slow cortical activity (mainly over the frontal areas) and decreased fast cortical activity.

CONCLUSIONS

The findings indicate a different arousal level in children with ADHD, which could be due to a delay in functional cortical maturation. To evaluate the clinical importance of these findings, a longitudinal follow-up will be conducted.

LY404187: a novel positive allosteric modulator of AMPA receptors

LY404187 is a selective, potent and centrally active positive allosteric modulator of AMPA receptors. LY404187 preferentially acts at recombinant human homomeric GluR2 and GluR4 versus GluR1 and GluR3 AMPA receptors. In addition, LY404187 potentiates the flip splice variant of these AMPA receptors to a greater degree than the flop splice variant. In both recombinant and native AMPA receptors, potentiation by LY404187 displays a unique time-dependent growth that appears to involve a suppression of the desensitization process of these ion channels. LY404187 has been shown to enhance glutamatergic synaptic transmission both in vitro and in vivo. This augmentation of synaptic activity is due to the direct potentiation of AMPA receptor function, as well as an indirect recruitment of voltage-dependent NMDA receptor activity. Enhanced calcium influx through NMDA receptors is known to be a critical step in initiating long-term modifications in synaptic function (e.g., long-term potentiation, LTP). These modifications in synaptic function may be substrates for certain forms of memory encoding. Consistent with a recruitment of NMDA receptor activity, LY404187 has been shown to enhance performance in animal models of cognitive function requiring different mnemonic processes. These data suggest that AMPA receptor potentiators may be therapeutically beneficial for treating cognitive deficits in a variety of disorders, particularly those that are associated with reduced glutamatergic signaling such as schizophrenia. In addition, LY404187 has been demonstrated to be efficacious in animal models of behavioral despair that possess considerable predictive validity for antidepressant activity. Although the therapeutic efficacy of AMPA receptor potentiators in these and other diseases will ultimately be determined in the clinic, evidence suggests that the benefit of these compounds will be mediated by multiple mechanisms of action. These mechanisms include direct enhancement of AMPA receptor function, secondary mobilization of intracellular signaling cascades, and prolonged modulation of gene expression.