A motor presetting study in hyperactive, learning disabled and control children

Impulsive and Omission Errors: Potential Temporal Processing Endophenotypes in ADHD

Temporal processing (TP) is associated with functions such as perception, verbal skills, temporal perspective, and future planning, and is intercorrelated with working memory, attention, and inhibitory control, which are highly impaired in individuals with attention deficit hyperactivity disorder (ADHD). Here we evaluate TP measures as potential endophenotypes in Caribbean families ascertained from probands affected by ADHD. A total of 232 individuals were recruited and clinically evaluated using an extensive battery of neuropsychological tasks and reaction time (RT)-based task paradigms. Further, the heritability (genetic variance underpinning phenotype) was estimated as a measure of the genetics apportionment. A predictive framework for ADHD diagnosis was derived using these tasks. We found that individuals with ADHD differed from controls in neuropsychological tasks assessing mental control, visual-verbal memory, verbal fluency, verbal, and semantic fluency. In addition, TP measures such as RT, errors, and variability were also affected in individuals with ADHD. Moreover, we determined that only omission and commission errors had significant heritability. In conclusion, we have disentangled omission and commission errors as possible TP endophenotypes in ADHD, which can be suitable to assess the neurobiological and genetic basis of ADHD. A predictive model using these endophenotypes led to remarkable sensitivity, specificity, precision and classification rate for ADHD diagnosis, and may be a useful tool for patients' diagnosis, follow-up, and longitudinal assessment in the clinical setting.

Methodological Problems With Online Concussion Testing

Reaction time testing is widely used in online computerized concussion assessments, and most concussion studies utilizing the metric have demonstrated varying degrees of difference between concussed and non-concussed individuals. The problem with most of these online concussion assessments is that they predominantly rely on consumer grade technology. Typical administration of these reaction time tests involves presenting a visual stimulus on a computer monitor and prompting the test subject to respond as quickly as possible via keypad or computer mouse. However, inherent delays and variabilities are introduced to the reaction time measure by both computer and associated operating systems that the concussion assessment tool is installed on. The authors hypothesized systems that are typically used to collect concussion reaction time data would demonstrate significant errors in reaction time measurements. To remove human bias, a series of experiments was conducted robotically to assess timing errors introduced by reaction time tests under four different conditions. In the first condition, a visual reaction time test was conducted by flashing a visual stimulus on a computer monitor. Detection was via photodiode and mechanical response was delivered via computer mouse. The second condition employed a mobile device for the visual stimulus, and the mechanical response was delivered to the mobile device's touchscreen. The third condition simulated a tactile reaction time test, and mechanical response was delivered via computer mouse. The fourth condition also simulated a tactile reaction time test, but response was delivered to a dedicated device designed to store the interval between stimulus delivery and response, thus bypassing any problems hypothesized to be introduced by computer and/or computer software. There were significant differences in the range of responses recorded from the four different conditions with the reaction time collected from visual stimulus on a mobile device being the worst and the device with dedicated hardware designed for the task being the best. The results suggest that some of the commonly used visual tasks on consumer grade computers could be (and have been) introducing significant errors for reaction time testing and that dedicated hardware designed for the reaction time task is needed to minimize testing errors.

Arousal and Executive Alterations in Attention Deficit Hyperactivity Disorder (ADHD)

Attention deficit hyperactivity disorder (ADHD) is the most common neurobehavioral disorder in childhood and can significantly affect a child's personal and social development and academic achievement. Taking into account the model of attentional networks proposed by Posner et al., the aim of the present study was to review the literature regarding two main explicative models of ADHD, i.e., the inhibition model and the cognitive-energetic model, by discussing behavioral and neurological evidence of both models and the limitations of each model. The review highlights evidence that favors the energetic model and points to an unstable arousal as a potential pathogenetic factor in ADHD.

An Accurate Measure of Reaction Time can Provide Objective Metrics of Concussion

There have been numerous reports of neurological assessments of post-concussed athletes and many deploy some type of reaction time assessment. However, most of the assessment tools currently deployed rely on consumer-grade computer systems to collect this data. In a previous report, we demonstrated the inaccuracies that typical computer systems introduce to hardware and software to collect these metrics with robotics (Holden et al, 2020). In that same report, we described the accuracy of a tactile based reaction time test (administered with the Brain Gauge) as approximately 0.3 msec and discussed the shortcoming of other methods for collecting reaction time. The latency errors introduced with those alternative methods were reported as high as 400 msec and the system variabilities could be as high as 80 msec, and these values are several orders of magnitude above the control values previously reported for reaction time (200-220msec) and reaction time variability (10-20 msec). In this report, we examined the reaction time and reaction time variability from 396 concussed individuals and found that there were significant differences in the reaction time metrics obtained from concussed and non-concussed individuals for 14-21 days post-concussion. A survey of the literature did not reveal comparable sensitivity in reaction time testing in concussion studies using alternative methods. This finding was consistent with the prediction put forth by Holden and colleagues with robotics testing of the consumer grade computer systems that are commonly utilized by researchers conducting reaction time testing on concussed individuals. The significant difference in fidelity between the methods commonly used by concussion researchers is attributed to the differences in accuracy of the measures deployed and/or the increases in biological fidelity introduced by tactile based reaction times over visually administered reaction time tests. Additionally, while most of the commonly used computerized testing assessment tools require a pre-season baseline test to predict a neurological insult, the tactile based methods reported in this paper did not utilize any baselines for comparisons. The reaction time data reported was one test of a battery of tests administered to the population studied, and this is the first of a series of papers that will examine each of those tests independently.  

Kinematic analysis of fast pen strokes in children with ADHD

In this study, we aimed to determine whether a new measure of fine motor skills, the Pen Stroke Test (PST), can discriminate between children with and without attention-deficit/hyperactivity disorder (ADHD). Twelve children with ADHD and 12 controls age 8-11 were asked to produce handwriting strokes on a digitizer. The sigma-lognormal model derived from the Kinematic Theory of rapid human movements was used to analyze the strokes. Standard measurements of fine motor skills and handwriting were also obtained. Children with ADHD demonstrated poorer motor planning (t₀, D) and execution (nbLog) and greater variability in motor control (SNR/nbLog) than did controls. Parameters extracted from the PST were significantly correlated with performance on other motor and handwriting measures. This study provides preliminary evidence that the PST may be useful as a tool for rapidly detecting motor skill problems in the context of ADHD.

Neurological soft signs are associated with attentional dysfunction in children with attention deficit hyperactivity disorder

INTRODUCTION

Inattention is one of the core symptoms of Attention Deficit Hyperactivity Disorder (ADHD). Most of patients with ADHD show motor impairment, consisting in the persistence of neurological soft signs (NSS). Our aim was to evaluate attentional and motor functioning in an ADHD sample and healthy children (HC) and possible link between attentional dysfunction and motor impairment in ADHD.

METHOD

Twenty-seven drug-naive patients with ADHD and 23 HC were tested with a test battery, measuring different aspects of attention. Motor evaluation has provided three primary variables: overflow movements (OM), dysrhythmia and total speed of timed activities.

RESULTS

Compared to HC, patients were impaired in a considerable number of attentional processes and showed a greater number of NSS. Significant correlations between disturbances of attention and motor abnormalities were observed in ADHD group.

CONCLUSION

Our findings suggest that attentional processes could be involved in the pathophysiology of the NSS and add scientific evidence to the predictive value of NSS as indicators of the severity of functional impairment in ADHD. Given the marked improvement or complete resolution of NSS following treatment with methylphenidate, we suggest that evaluation of NSS is useful to monitor the effectiveness of pharmacological treatment with MPH in ADHD.

Current State and Model for Development of Technology-Based Care for Attention Deficit Hyperactivity Disorder

INTRODUCTION

Care (i.e., evaluation and intervention) delivered through technology is used in many areas of mental health services, including for persons with attention deficit hyperactivity disorder (ADHD). Technology can facilitate care for individuals with ADHD, their parents, and their care providers. The adoption of technological tools for ADHD care requires evidence-based studies to support the transition from development to integration into use in the home, school, or work for persons with the disorder. The initial phase, which is development of technological tools, has begun in earnest; however, the evidence base for many of these tools is lacking. In some instances, the uptake of a piece of technology into home use or clinical practice may be further along than the research to support its use.

METHODS

In this study, we review the current evidence regarding technology for ADHD and also propose a model to evaluate the support for other tools that have yet to be tested.

RESULTS

We propose using the Research Domain Criteria as a framework for evaluating the tools' relationships to dimensions related to ADHD.

CONCLUSION

This article concludes with recommendations for testing new tools that may have promise in improving the evaluation or treatment of persons with ADHD.

Extra-Task Stimulation on Mathematics Performance in Children with and without ADHD

The optimal stimulation theory developed by Zentall (1975) holds that children with Attention Deficit Hyperactivity Disorder (ADHD) will demonstrate high levels of activity when faced with a task or situation of low arousal or stimulation. Both Zentall's early work and more recent research have supported the theory. The present study aimed to add to this literature by comparing children with and without ADHD on an academic task under two counterbalanced stimulation conditions. The first required children to do mathematics problems in silence, and the second required doing the problems with their favourite music playing. Twenty-two children with ADHD and 20 children without ADHD, with a mean age of 9.75 years, were hypothesised to perform significantly differently under the two conditions. Mathematics performance was scored as Correct, Number attempted, and Accurate (number correct divided by number attempted). A repeated measures ANOVA demonstrated that generally no main effects for group (ADHD and non-ADHD) nor condition (music and silence) were observed. The only significant finding was that Accuracy (the complex mathematical calculation) improved for both the ADHD and non-ADHD groups, an effect not influenced by order of task presentation. This finding supports the optimal stimulation theory for all children under both order conditions, and is not specific to ADHD.

Altered response-preparation in patients with adult ADHD: A high-density ERP study

Aberrations in early-developing bottom-up processes, such as stimulus-driven response preparation, are thought to play a critical role in the onset of ADHD, and in its persistence over time. Electrophysiology offers a unique tool to gain insight into response preparation, since response preparation has been associated with distinctive ERP changes, including negative potential-shifts which occur predominantly over frontal brain areas. We examined response-preceding negative potential shifts (RPNS) as a probe of response-preparation in adult ADHD patients by obtaining high-density event-related potentials from 33 ADHD and 29 matched healthy subjects during a Go/Nogo task using a 128-channel BioSemi recording-system. Compared to controls, ADHD patients showed enhancement of the RPNS in fronto-central brain regions in the Go condition during correct responses. This change was associated with poor performance in the Stroop incongruency-task: the greater the enhancement, the higher the proportion of errors. Moreover, the ERP-enhancement showed association with the severity of ADHD-symptoms; and with heightened response-variability. Thus, ADHD patients demonstrate neurophysiological alterations in response-preparation and response-preceding brain activity, suggestive of excessive activation of prefrontal neural circuits. Given the correlation with neuropsychological and psychopathological measures, these changes may constitute a pathway for core symptoms of ADHD, including premature and impaired response-preparation and motor-hyperactivity.

The Unique and Combined Effects of Reinforcement and Methylphenidate on Temporal Information Processing in Attention-Deficit/Hyperactivity Disorder

Temporal information processing and reward sensitivity are neurocognitive impairments key to attention-deficit/hyperactivity disorder (ADHD). The aim of this study was to examine the unique and combined impact of reinforcement and methylphenidate (MPH) on temporal information processing in children with ADHD. We predicted that both monetary reinforcement and MPH would ameliorate temporal information processing deficits in ADHD, and we expected that the combined effect of reinforcement and MPH would be most beneficial. Forty children (23 with ADHD and 27 typical controls, aged 8-12 y) performed a time production task under 3 conditions: reward, response cost, and feedback only. Children with ADHD also performed the task (in random order) with placebo, a low, a medium, and a high dose of MPH. Dependent variables were time production accuracy and variability. At baseline, children with ADHD displayed poor internal clock functioning compared with controls, as reflected by greater underestimations of the 1-second interval, and they showed poor motor output as reflected by increased timing variability. Reward and response cost improved motor output (timing variability), with similar effects for both groups. Methylphenidate increased performance (timing variability) compared with placebo, with a higher dose showing greater effects. Effect sizes of reinforcement and medication were medium to large. Contrary to expectations, MPH did not add to the reinforcement effect. The results of this study confirm the value of reward and response cost being similar to that of MPH to optimize (timing) performance of children with ADHD.

Prefrontal cortical α2A-adrenoceptors and a possible primate model of attention deficit and hyperactivity disorder

Attention deficit and hyperactivity disorder (ADHD), a prevalent syndrome in children worldwide, is characterized by impulsivity, inappropriate inattention, and/or hyperactivity. It seriously afflicts cognitive development in childhood, and may lead to chronic under-achievement, academic failure, problematic peer relationships, and low self-esteem. There are at least three challenges for the treatment of ADHD. First, the neurobiological bases of its symptoms are still not clear. Second, the commonly prescribed medications, most showing short-term therapeutic efficacy but with a high risk of serious side-effects, are mainly based on a dopamine mechanism. Third, more novel and efficient animal models, especially in nonhuman primates, are required to accelerate the development of new medications. In this article, we review research progress in the related fields, focusing on our previous studies showing that blockade of prefrontal cortical α2A-adrenoceptors in monkeys produces almost all the typical behavioral symptoms of ADHD.

Hyperactivity and Motoric Activity in ADHD: Characterization, Assessment, and Intervention

The aim of the present literature review is threefold. (1) We will review theories, models, and studies on symptomatic hyperactivity and motoric activity in attention-deficit/hyperactivity disorder (ADHD). (2) Another focus will be on assessment methods that have been proven to be effective in the detection of hyperactivity and motoric activity in children, adolescents, and adults with and without ADHD and emerging areas of research in the field of ADHD. We will compare subjective methods (i.e., rating scales) and objective methods (i.e., accelerometers). (3) Finally, physical activity intervention studies aiming at a modification of activity and overactive behavior will be summarized that seem to be promising candidates for alleviating hyperactivity symptoms in children, adolescents, and adults with ADHD.

Kinematic performance of fine motor control in attention-deficit/hyperactivity disorder: the effects of comorbid developmental coordination disorder and core symptoms

BACKGROUND

The aims of this study were: (i) to determine whether differences exist in the fine motor fluency and flexibility of three groups (children with attention-deficit/hyperactivity disorder [ADHD], children in whom ADHD is comorbid with developmental coordination disorder [DCD] [denoted as ADHD+DCD], and a typically developing control group); and (ii) to clarify whether the degree of severity of core symptoms affects performance.

METHODS

The Peabody Picture Vocabulary Test-Revised, the Beery-Buktenica Development Test of Visual-Motor Integration and the Movement Assessment Battery for Children were used as prescreening tests. The Integrated Visual and Auditory+Plus test was utilized to assess subjects' attention. The redesigned fine motor tracking and pursuit tasks were administered to evaluate subjects' fine motor performance.

RESULTS

No significant difference was found when comparing the performance of the Children with ADHD and the typically developing group. Significant differences existed between children in whom ADHD is comorbid with DCD and typically developing children.

CONCLUSIONS

Children with ADHD demonstrated proper fine motor fluency and flexibility, and deficient performance occurred when ADHD was comorbid with developmental coordination disorder. Children with ADHD had more difficulty implementing closed-loop movements that required higher levels of cognitive processing than those of their typically developing peers. Also, deficits in fine motor control were more pronounced when ADHD was combined with movement coordination problems. The severity of core symptoms had a greater effect on children with ADHD's fine motor flexibility than did fluency performance. In children with pure ADHD, unsmooth movement performance was highly related to the severity of core symptoms.

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.

HFA and ADHD: A direct comparison on state regulation and response inhibition

This study examined whether children with high-functioning autism (HFA) are easily overaroused/activated and whether children with attention-deficit/hyperactivity disorder (ADHD) are easily underaroused/activated. This double dissociation was tested using a go/no-go paradigm with computer-paced fast and slow conditions and a self-paced condition. In the HFA group, a performance decline in the fast condition and slow performance in the self-paced condition were expected. In the ADHD group, a performance decline in the slow condition and fast performance in the self-paced condition were expected. No difference was found between groups for state regulation and response inhibition. Findings are discussed in the light of development, comorbidity, and subtypes.

Event rate and event-related potentials in ADHD

BACKGROUND

It has been repeatedly found that performance of children with attention deficit hyperactivity disorder (ADHD) is more impaired when a long inter-stimulus interval (ISI) is used than when a short ISI is used. According to the cognitive-energetic model, this may reflect difficulty in remaining in an optimal motor activation state because of insufficient effort allocation.

METHOD

Event-related potentials (ERPs) were evaluated during a Go/No-Go task that incorporates a condition with a fast and a slow presentation rate.

RESULTS

ADHD, whether or not comorbid with oppositional defiant/conduct disorder (ODD/CD), was associated with a steeper increase in reaction time (RT) from the fast to the slow condition accompanied by a missing increment of the parietal P3. Speed of responding was found to be correlated with P3 amplitude. In the fast condition, children with ADHD made more errors of commission, accompanied by a smaller No-Go N2, a component thought to be related to inhibition; however, after controlling for ODD/CD these differences disappeared.

CONCLUSIONS

The association between the steeper increase in RT and reduced parietal P3s may indicate that the children with ADHD did not allocate enough extra effort to adjust to a potentially under-activated state. However, the event rate effects could not account for all of the differences between groups and also early automatic information processing stages seem disturbed in this disorder as indexed by larger P2 amplitudes. Alternative explanations are discussed.

Attentional functioning in children with ADHD - predominantly hyperactive-impulsive type and children with ADHD - combined type

Although particular importance has been attributed to attention deficits in attention deficit hyperactivity disorder (ADHD), there is no consensus as to the exact nature of inattention in ADHD or which components of attention are affected. The present study was based on a neuropsychological model of attention and assessed various components of attention in 23 children with ADHD/predominantly hyperactive-impulsive type (ADHD-H), 32 children with ADHD/combined type (ADHD-C) and healthy children (N(1) = 23 and N(2) = 32). A computerized test battery consisting of reaction time tasks of low complexity was used for the assessment of attention (alertness task, vigilance task, divided attention task, visual scanning task, incompatibility task, test of crossmodal integration, flexibility task). In comparison to healthy participants, patient groups were impaired in measures of vigilance, divided attention, selective attention and flexibility but not in measures of alertness. Analysis of the test performance of patient groups revealed no differences between children with ADHD-H and children with ADHD-C. The results of the present study suggest that both children with ADHD-H and children with ADHD-C are seriously impaired in attentional functioning. Children with ADHD-H and children with ADHD-C produced comparable results in measures of attention.

ADHD and DCD: A relationship in need of research

Although the connection between attention deficit hyperactivity disorder (ADHD) and developmental coordination disorder (DCD) has been recognized for several decades, little research has examined the relationship between these two disorders. This paper draws attention to the contribution the cognitive-energetic model (CEM) can make in determining the specific nature of these two disorders. An information processing approach such as the CEM is a useful model to identify specific and overlapping mechanisms that are disrupted in these two disorders. This paper describes the CEM and reviews the research so-far in relation to the model. The CEM has several advantages over other models: First, it predicts which task variables will be independent or may interact, thus enabling the investigator to determine the success/failure of the task manipulation(s) and identify spurious findings. Second, the CEM links energetic factors to task variables and predicts both additive and interactive effects. Third, the CEM enables executive processes such as selective attention, working memory and inhibition to be related to both energetic and lower level processes. Fourth, by employing the CEM in clinical research, taxonomy of deficits can be derived enabling further insight into the nature of the disorders and their specific neuropsychological dysfunction. Suggestions are made for future research into the neuropsychological deficits associated with ADHD and DCD.

Tapping and anticipation performance in attention deficit hyperactivity disorder

The objective of this study was to examine the precise timing of a motor response in a sample of adolescents with ADHD and comparison participants. 46 participants with ADHD (M age=15.6, SD=1.4; 40 boys) and 44 control participants (M age=15.3, SD=1.4; 40 boys) were recruited through a metropolitan hospital. Participants were administered a tapping task and an anticipation task. Adolescents with ADHD displayed significantly more intra-individual variability on the visual 1000-msec. frequency interval of the tapping task and displayed lower accuracy on the cued and uncued trials of the anticipation task than comparison participants. Intra-individual variability on the tapping task was correlated with intra-individual variability on the anticipation task within both the ADHD and control groups. These findings suggest that adolescents with ADHD have impairments in both the cognitive representation and motor production of the precise timing of a motor response.

Modeling attention-deficit/hyperactivity disorder: a critical appraisal of the cognitive-energetic model

A number of theoretical models of attention-deficit/hyperactivity disorder (ADHD) have emerged in recent years that may be used as systematic guides for clinical research. The cognitive-energetic model (CEM) proposes that the overall efficiency of information processing is determined by the interplay of three levels: computational mechanisms of attention, state factors, and management/executive function (EF). The CEM encompasses both top-down and bottom-up processes and draws attention to the fact that ADHD causes defects at all three levels. These include cognitive mechanisms, such as response output; energetic mechanisms, such as activation and effort; and management/EF deficits. Increasing evidence suggests that inhibition deficits associated with ADHD may, at least in part, be explained in terms of an energetic dysfunction. The activation and effort energetic pools appear most relevant to ADHD, being directly related to response organization; however, further testing of CEM is critically dependent on the development of direct measures of these energetic pools. The CEM is a comprehensive model of ADHD but is not without limitations. In particular, further research is required to define more specifically the relationship between process dysfunction and state dysregulation in ADHD.

Abnormal brain activity related to performance monitoring and error detection in children with ADHD

Brain electrical activity associated with inhibitory control was recorded in ten ADHD and ten healthy children using high density event related potentials (ERPs) during the Stop Signal Task (SST). SST is a two-choice reaction time (RT) paradigm, in which subjects are required, on 25% of the trials, to withdraw their response upon presentation of a "Stop Signal". In the healthy children, the ERP evoked by the Stop Signal differed for successful inhibitions (SI) compared to failed inhibitions (FI), with greater amplitude of a positive wave peaking around 320 msec over anterior medial frontal scalp (P3a). Such success-related P3a activity was significantly reduced in amplitude in the ADHD group. In addition, the error related negativity (ERN), a sharp negative wave that is present selectively on error trials in choice RT experiments, peaking 100 ms after motor onset, and distributed over anterior medial frontal scalp, was also markedly reduced in the ADHD group. The scalp distribution of the group differences in P3a and the ERN is consistent with a reduction of activity of sources in dorsal anterior cingulate cortex (dACC), suggesting a global deficit in cognitive control operations subserved by dACC in ADHD.

Prenatal alcohol exposure causes attention deficits in male rats

Children with fetal alcohol spectrum disorder (FASD) are often diagnosed with attention-deficit/ hyperactivity disorder (ADHD). These children show increases in reaction time (RT) variability and false alarms on choice reaction time (CRT) tasks. In this study, adult rats prenatally exposed to ethanol were trained to perform a CRT task. An analysis of the distribution of RTs obtained from the CRT task found that rats with a history of prenatal ethanol exposure had more variable RT distributions, possibly because of lapses of attention. In addition, it was found that, similar to children with FASD, the ethanol-exposed rats had more false alarms. Thus, rats with prenatal ethanol exposure show attention deficits that are similar to those of children with FASD and ADHD.

Equating tasks and sustaining attention in children and adults: The methodological and theoretical utility ofd’ matching

The present study develops a method to create task equivalency for children and adults in vigilance research. Experiment 1 employed the signal detection index of perceptual sensitivity (d') to calibrate vigilance tasks for 32 children (ages 7-8) and 32 adults. The results of Experiment 1 suggest that task equivalency across groups can be attained, and a vigilance decrement was observed for children. In Experiment 2, the task parameter of event rate was manipulated across two vigils. Again, 32 children (ages 7-8) and 32 adults participated. The results suggest that a reverse event rate effect emerged for both children and adults. In addition, developmental differences in response to the event rate manipulation and with respect to the vigilance decrement emerged: Children benefited less from the manipulation and were more likely to demonstrate a vigilance decrement than were adults. No developmental differences emerged for the sensitivity decrement. The results are explained with reference to how task demands interact with participant arousal, and implications for development and for future research are discussed.

Relationship between motor proficiency, attention, impulse, and activity in children with ADHD

The aim of this study was to investigate the relationship between motor performance, attention deficit, impulsiveness, and hyperactivity in children with attention-deficit--hyperactivity disorder (ADHD). Participants were 42 school-aged children with ADHD (36 males, 6 females; mean age 8 years 2 months, SD 1 year 2 months; range 6 years to 11 years), and 42 age- and sex-matched children without ADHD (mean age 8 years 3 months, SD 1 year 1 month; range 6 years to 11 years). Motor abilities were assessed with the Bruininks-Oseretsky Test of Motor Proficiency. Attention and impulse control were measured with the Gordon Diagnostic System, and assessment of activity level was based on two Activity Level Rating Scales that were completed by parents and teachers. Analysis by t-test revealed a significant difference between children with and without ADHD in fine and gross motor skills, impulse control, and attention. Stepwise regression indicated that attention, impulse control, and parent ratings of activity level were the three best predictors of gross motor skills for children with ADHD, accounting for 55.9% of the variance. Attention and impulse control were the two best predictors of fine motor skills, accounting for 45.7% of the variance. Attention and impulse control were consistently found to be important predictors of both fine and gross motor skills in children with ADHD. However, the fact that activity level was a predictor for gross motor proficiency but not for fine motor tasks suggests that different behavioral processes are involved in fine and gross motor performance to different extents.

Motor timing deficits in community and clinical boys with hyperactive behavior: the effect of methylphenidate on motor timing

In a previous paper we showed that community children with hyperactive behavior were more inconsistent than controls in the temporal organization of their motor output. In this study we investigated: (1) various aspects of motor timing processes in 13 clinically diagnosed boys with attention deficit hyperactivity disorder (ADHD) who were compared to 11 community boys with hyperactive behavior and to a control group and (2) the effect of methylphenidate on the motor timing processes in the clinical group with ADHD in a double blind, cross-over, medication-placebo design, including 4 weeks of medication. The clinical group with ADHD, like the community group with hyperactivity, showed greater variability in sensorimotor synchronization and in sensorimotor anticipation relative to controls. The clinical group was also impaired in time perception, which was spared in the community group with hyperactivity. The persistent, but not the acute dose, of methylphenidate reduced the variability of sensorimotor synchronization and anticipation, but had no effect on time perception. This study shows that motor timing functions are impaired in both clinical and community children with hyperactivity. It is the first study to show the effectiveness of persistent administration of methylphenidate on deficits in motor timing in ADHD children and extends the use of methylphenidate from the domain of attentional and inhibitory functions to the domain of executive motor timing.

Association of ADHD and conduct disorder--brain electrical evidence for the existence of a distinct subtype

BACKGROUND

To evaluate the impact of psychopathological comorbidity with oppositional defiant/conduct disorder (ODD/CD) on brain electrical correlates in children with attention deficit hyperactivity disorder (ADHD) and to study the pathophysiological background of comorbidity of ADHD+ODD/CD.

METHOD

Event-related potentials (ERPs) were recorded during a cued continuous performance test (CPT-A-X) in children (aged 8 to 14 years) with ICD-10 diagnoses of either hyperkinetic disorder (HD; n = 15), hyperkinetic conduct disorder (HCD; n = 16), or ODD/CD (n = 15) and normal children (n = 18). HD/HCD diagnoses in all children were fully concordant with the DSM-IV diagnosis of ADHD-combined type. ERP-microstates, i.e., time segments with stable brain electrical map topography were identified by adaptive segmentation. Their characteristic parameters and behavioral measures were further analyzed.

RESULTS

Children with HD but not comorbid children showed slower and more variable reaction times compared to control children. Children with HD and ODD/CD-only but not comorbid children displayed reduced P3a amplitudes to cues and certain distractors (distractor-X) linked to attentional orienting. Correspondingly, global field power of the cue-CNV microstate related to anticipation and preparation was reduced in HD but not in HCD. Topographical alterations of the HD occurred already in the cue-P2/N2 microstate. In sum, the comorbid group was less deviant than both the HD-group and the ODD/CD-group.

CONCLUSIONS

The findings suggest that HD children (ADHD-combined type without ODD/CD) suffer from a more general deficit (e.g., suboptimal energetical state regulation) including deficits of attentional orienting and response preparation than just a responseinhibitory deficit, backing the hypothesis of an involvement of a dysregulation of the central noradrenergic networks. The results contradict the hypothesis that ADHD+ODD/CD represents an additive co-occurrence of ADHD and ODD/CD and strongly suggest that it represents a separate pathological entity as considered in the ICD-10 classification system, which differs from both HD and ODD/CD-only.

Timing and force control in boys with attention deficit hyperactivity disorder: subtype differences and the effect of comorbid developmental coordination disorder

This study examined the motor and performance outcomes of boys with subtypes of attention deficit hyperactivity disorder (ADHD) (DSM-IV, [American Psychiatric Association, Diagnostic and statistical manual of mental disorders, 4th ed., Washington, DC, 1994]). It also examined the differences between boys with a single diagnosis of ADHD versus those who have the dual categorisation of ADHD and developmental coordination disorder (DCD). The participants were 157 boys, aged 7.70-12.98 years recruited from a community sample. Parent report was used to classify 143 boys into either a comparison group or one of the three DSM-IV ADHD subtypes. Participants were given a battery of tests that included the Movement Assessment Battery for Children [Movement Assessment Battery for Children, Psychological Corporation/Harcourt Brace-Jovanovich, New York, 1992], the Wechsler Intelligence Scales for Children--Third Edition [Manual for the Wechsler Intelligence Scale for Children, Psychological Corporation, New York, 1992] and a finger tapping task targeting motor processing, preparation, and execution. Boys with subtypes that included inattentive symptomatology had significant difficulties with timing, force output and showed greater variability in motor outcomes. Boys with the comorbid condition (i.e., ADHD and DCD) had particular difficulty with force control. These outcomes identify a need for increased recognition of the clinical and research implications of the relationship between ADHD and motor dysfunction. This potentially impacts on assessment, intervention, theoretical modelling and the general interpretation of cognitive abilities research with children with ADHD.

Evidence for a pure time perception deficit in children with ADHD

BACKGROUND

Deficits have been found previously in children with ADHD on tasks of time reproduction, time production and motor timing, implicating a deficit in temporal processing abilities, which has been interpreted as either secondary or primary to core executive dysfunctions. The aim of this study was to explore further the abilities of hyperactive children in skills of time estimation, using a range of time perception tasks in different temporal domains.

METHOD

Time estimation was tested in a verbal estimation task of 10 seconds. Time reproduction was also acquired for two time intervals of 5 and 12 seconds. A temporal discrimination task aimed to determine the idiosyncratic threshold of minimum time interval (in milliseconds) necessary to distinguish two intervals differing by approximately 300 milliseconds. Twenty-two children diagnosed with ADHD were compared to 22 healthy children, matched for age, handedness and working memory skills.

RESULTS

Children with ADHD were significantly impaired in their time discrimination threshold: on average, time intervals had to be 50 ms longer for the hyperactive children in order to be discriminated when compared with controls. Children with ADHD also responded earlier on a 12-second reproduction task, which however only approached significance after controlling for IQ and short-term memory. No group differences were found for the 5-second time reproduction or verbal time estimation tasks.

CONCLUSIONS

The findings suggest that children with ADHD perform poorly on time reproduction tasks which load heavily on impulsiveness and attentional processes and they also suggest that these children may have a perceptual deficit of time discrimination, which may only be detectable in brief durations which differ by several hundred milliseconds. A temporal perception deficit in the range of milliseconds in ADHD may impact upon other functions such as perceptual language skills and motor timing.

The dynamic approach to neurodevelopmental psychiatric disorders: use of fMRI combined with neuropsychology to elucidate the dynamics of psychiatric disorders, exemplified in ADHD and schizophrenia

The paper discusses the application of fMRI in combination with neuropsychology to neurodevelopmental psychiatric disorders, exemplified on the case of attention deficit hyperactivity disorder (ADHD) in comparison with schizophrenia. The view is presented that ADHD, rather than being a compound of unrelated co-existing deficits, is a pervasive disorder of impulsiveness, which manifests at the motor, emotional, social and cognitive domain. Neuropsychology needs to refine the psychological measurements of these impulsivity symptoms and, in combination with fMRI, provide new insights into the interrelationship between brain and dysfunction and its bi-directional causalities. The suitability of the dynamic technique of functional MRI to assess the dynamic nature of developmental neuropsychiatric disorders is discussed. Brain activation can inform about strategy and compensatory mechanisms at a neuroanatomical level, which are not observable at a psychological level, providing insight into the underlying neurocognitive mechanisms of psychiatric disorders. Data are presented and discussed on opposing neurocognitive activation patterns for patients with ADHD and those with schizophrenia while performing a stop task. Comparisons between patient groups will be essential to address the specificity of neurocognitive mechanisms corresponding to specific neurodevelopmental psychiatric disorders.

Impaired metabolic capacity in the perirhinal and posterior parietal cortex lead to dissociation between attentional, motivational and spatial components of exploration in the Naples High-Excitability rat

This study aimed at investigating the neural substrates of spatial and non-spatial Behavioural components of exploration to novelty by a neurogenetic approach. Thus, functional imaging and Behavioural analysis were carried out in the Naples High-Excitability (NHE) rats, a model of hyperactivity and attention-deficit. Quantitative cytochrome oxidase (C.O.) histochemistry was used to measure the basal metabolic capacity of different forebrain structures. In parallel experiments, exploration in an 8-arm radial maze (Olton-maze) with extra-maze cues was used to measure attentional, motivational and spatial components of Behaviour after feeding rats' ad-libitum or at a reduced diet. Functional imaging analysis: brains from naive rats were stained for quantitative C.O. histochemistry along with standards. NHE rats showed lower C.O. activity in perirhinal and posterior-parietal cortex (all layers) and cortical amygdala, and greater activity in entorhinal cortex (superficial layers). The outer granular cell layer of the dentate gyrus had greater activity in NHE. Behavioural analysis: at low and high motivational level, maze exploration was reinforced during shaping throughout and then only a single arm. The Behaviour was monitored by a CCD camera and videotaped. (i) There was no line difference in working memory during non reinforced maze exploration, independent of the motivational level; (ii) during shaping with all baited arms, there was no line difference in working memory, but NHE rats showed a very low or lower food consumption at low and high motivational level, respectively; (iii) rats showed a higher working memory in finding the single baited arm at high motivational level; (iv) NHE rats paid little attention towards reinforcement upon visiting the baited arm only at low motivational level. Thus, Behavioural and functional neuroimaging analysis suggests the neural substrates of spatial and non-spatial components of exploration to be underlined by different network operations in the neocortical and limbic cortices in the NHE rat lines. Therefore, they appear as an useful tool to the understanding of Attention-Deficit Hyperactivity Disorder (ADHD) in children.

A morphometric evidence for a hyperfunctioning mesolimbic system in an animal model of ADHD

The hyperfunctioning dopamine hypothesis in the mesocorticolimbic (MCL) system has been addressed by a neurogenetic approach in model systems. Thus, a morphometric analysis was carried out on neurons of origin of Substantia Nigra (SN) and Ventral Tegmental Area (VTA) dopamine systems of the Naples High-Excitability (NHE), Low-Excitability (NLE) and control lines. Male adult rats were tested in a spatial novelty for indices of activity and non-selective attention. Mesencephalic coronal sections were processed for tyrosine hydroxylase (TH) immunohistochemistry and cytochromoxidase (C.O.) histochemistry. Image analysis in the rostro-caudal plane showed (i) a higher neuron size of TH+ elements in the VTA of NHE and NLE, across the entire structure in the NHE, and only in the middle portion in the NLE; (ii) a higher expression of TH in the neuropil of the VTA in NHE; (iii) a lower C.O. activity in both NLE and NHE; (iv) no differences in the SN. The larger neuron size in both NHE and NLE rats as compared with control rats, along with higher TH expression mainly in the NHE, in absence of any relevant alteration in the SN, reveals an unbalance between the two dopamine systems and a subsequent alteration in limbic (reward, motivation, sustained attention) functions. The decreased C.O. activity might be due to reduced feedback inhibition by striatal GABA neurons and interneurons leading to increased DA neuron firing. In conclusion, the increased behavioral activity and impaired attention observed in the NHE rats are associated to hyperfunctioning MCL system in this genetic model of Attention-Deficit Hyperactivity Disorder (ADHD).

Changes of the brain electrical fields during the continuous performance test in attention-deficit hyperactivity disorder-boys depending on methylphenidate medication

OBJECTIVE

The continuous performance test (CPT) is successfully applied to evaluate attentional performance in attention-deficit hyperactivity disorder (ADHD)-children. The aim of the present study was to investigate the changes of the topographic P300-features in relation to methylphenidate-medication and to different attentional processes in primer- and distractor-conditions.

METHODS

Twenty-one-channel-ERPs of 17 ADHD-boys were analyzed with reference-independent methods. Four quasi stable microstates within the time frames of conventional P100, P200, P3a and P3b components were identified by means of a data-driven segmentation procedure.

RESULTS

In segment 3 topographical assessment yielded a significant occipital and right-shift of the positive centroid, longer centroid distance and higher amplitudes in primer- than in distractor conditions. MPH increased the amplitude and distance in primer and distractor-condition, without changing the topography. In segment 4 the electric field strength of distractor-conditions collapsed, whereas the primer condition showed a strong fronto-parietally oriented potential-field. There was a tendency to higher amplitudes due to MPH-medication.

CONCLUSIONS

These results indicate a robust neurophysiologic differentiation of cognitive processes. MPH activates an early (P3a) covert attention process indicated by increased amplitudes and centroid. No effects were seen in later processes. Based on these effects, we propose to use the amplitude- and distance-increase in microstate 3 as an indicator of MPH efficacy in ADHD-boys.

Evaluation of sensorimotor training in children with ADHD

Reduced ability to regulate motor behavior seems to be an essential aspect of Attention-Deficit Hyperactivity Disorder (ADHD) and may reflect deficits in behavioral response inhibition. In this respect, pragmatic clinical experience over the last two decades, in daily practice, training of motor control has played an important role within multimodal treatment approaches, although an adequate proof of its efficacy is still lacking. Therefore, to examine the efficacy of sensorimotor training, 12 children with ADHD (two groups of six) were treated with both sensorimotor training and (as control) cognitive behavioral training using a within-subject cross-over design. Each treatment had a duration of 4 months (20 sessions), yielding a total of 40 sessions for the completed cross-over design. Results showed that Sensorimotor Training improved sensorimotor coordination slightly, while Cognitive Behavioral Training ameliorated cognitive impulse control. Hyperactivity and anxious-depressive/aggressive behavior were markedly reduced by Sensorimotor Training but not by Cognitive Behavioral Training. In conclusion, a combined treatment may be recommended since compensation and regulation of inhibitory deficits in ADHD come into play within the framework of both kinds of training.

Hypertrophic A10 dopamine neurones in a rat model of attention-deficit hyperactivity disorder (ADHD)

To clarify whether a hypo or hyperfunctioning mesocorticolimbic system is the neural substrate of Attention-Deficit Hyperactivity Disorder (ADHD), we carried out a morphometric analysis on an animal model, the Naples high excitability rat (NHE). Male adult NHE and control rats were used for tyrosine hydroxylase (TH) immunocytochemistry in the ventral tegmental area and substantia nigra in coronal cryostat sections. PC-assisted image analysis showed larger DA neurones in the ventral tegmental area but not in the substantia nigra of NHE rats than in controls, associated with a higher expression of TH in the neuropil. Thus, the increased activity and impaired attention of NHE rats are associated with a hyperfunctioning mesocorticolimbic system in this ADHD model.

Attention deficit/hyperactivity disorder: characteristics, interventions and models

An epidemiological study of Attention Deficit/Hyperactivity Disorder (ADHD) suggests that the prevalence may be two to three times higher than the figure of 3-5% often cited. In addition, the data suggest that both underdiagnosis and overdiagnosis occur frequently. Rodent animal models of ADHD, like the Spontaneously Hypertensive Rat (SHR) and other rat models such as those with chemical and radiation-induced brain lesions and cerebellar stunting, and the Coloboma mouse model exhibit clear similarities with several aspects of the human disorder and should prove useful in studying specific traits. Operant behavioral tasks that model learning, short-term memory and simple discriminations are sensitive to ADHD and methylphenidate has been shown to normalize ADHD performance in a short-term memory task. Recent findings challenge not only the current postulate that response inhibition is a unique deficit in ADHD, but also the concepts of ADHD and its treatment, which presume intact perceptual abilities. Time perception deficits may account, in part, for the excessive variability in motor response times on speeded reaction time tasks, motor control problems and motor clumsiness associated with ADHD. The Multimodality Treatment Study of ADHD (MTA) provided data suggesting that pharmacological interventions that included systematic and frequent follow-up with parents and teachers, with or without psychosocial interventions, are superior to psychosocial interventions or standard community care alone. Additionally, the MTA was one of the first studies to demonstrate benefits of multimodal and pharmacological interventions lasting longer than 1 year. Imaging studies have demonstrated differences in brain areas in children with ADHD: anterior corpus callosum, right anterior white matter, and cerebellar volumes are all decreased in children with ADHD and there is less brain asymmetry in ADHD subjects. Additionally, functional imaging studies, coupled with pharmacological manipulations, suggest decreased blood flow and energy utilization in prefrontal cortex and striatum and the dysregulation of catecholamine systems in persons with ADHD.

Inhibitory control in children with attention-deficit/hyperactivity disorder: event-related potentials identify the processing component and timing of an impaired right-frontal response-inhibition mechanism

BACKGROUND

A core deficit in inhibitory control may account for a wide range of dysfunctional behaviors in attention-deficit/hyperactivity disorder (ADHD).

METHODS

Event-related potentials were measured in 10 children with ADHD and 10 healthy children during a task specifically involving response inhibition (Stop signal task).

RESULTS

In response to all Stop signals, control participants produced a large negative wave at 200 msec (N200) over right inferior frontal cortex, which was markedly reduced in ADHD children. The N200 amplitude was significantly correlated across subjects with response-inhibition performance. In response to the Go stimuli, ADHD children showed a reduced slow positive wave (250-500 msec) in anticipation of failed inhibitions over right frontal scalp regions.

CONCLUSIONS

ADHD children appear to have an abnormality in an early-latency, right inferior frontal processing component critical to the initiation of normal response-inhibition operations. They also appear to have a right frontal abnormality associated to the covert processing of Go stimuli preceding failed inhibitions. By providing timing and processing component specificity, these results extend the findings of recent functional MRI studies of inhibitory control reporting right frontal abnormalities in ADHD.

Klinische Validität der computerunterstützten TAP bei Kindern mit Aufmerksamkeits-/Hyperaktivitätsstörungen

Zusammenfassung: Die Studie diente der klinischen Validierung der Testbatterie zur Aufmerksamkeitsprüfung (TAP) bei Kindern mit Aufmerksamkeits-/Hyperaktivitätsstörungen. Die Stichprobe bestand aus 20 Jungen mit Aufmerksamkeits-/Hyperaktivitätsstörungen und 20 männlichen Kontrollkindern im Alter von 7;5-13;5 Jahren. Die beiden Gruppen wurden bezüglich spezifischer und allgemeiner Aufmerksamkeitsfunktionen verglichen. Allgemein zeigte die Gruppe der Kinder mit Aufmerksamkeits-/Hyperaktivitätsstörungen im Vergleich zur Kontrollgruppe mehr Fehler und Auslassungen und erhöhte intraindividuelle Streuungen der Reaktionszeiten in verschiedenen Subtests. Die Untersuchung der diskriminativen Validität der TAP-Tests ergab, dass durch zwei Testmaße und unter Berücksichtigung des Testalters 90 % der Kinder beider Gruppen richtig klassifiziert werden konnten. Ein spezifisches Aufmerksamkeitsdefizit der Kinder mit Aufmerksamkeits-/Hyperaktivitätsstörungen wurde nur in einem Subtest, in dem das Tempo der Reizdarbietung nicht vorgegeben war, d. h. in einer zeitlich wenig strukturierten Aufgabe, festgestellt. Die Untersuchung spricht für die klinische Validität der TAP-Testbatterie zur Untersuchung von Kindern mit Aufmerksamkeits-/Hyperaktivitätsstörungen.

Network operations revealed by brain metabolic mapping in a genetic model of hyperactivity and attention deficit: the naples high- and low-excitability rats

Genetic rat models are important for research on the neural networks of attention and emotionality. Naples-High Excitability (NHE) rats and Naples Low-Excitability (NLE) rats were investigated with random-bred (NRB) rats as controls. These rat lines were named for their respective behavior on spatial novelty tasks. Quantitative cytochrome oxidase (CO) histochemistry has been demonstrated to reflect long-lasting changes in tissue metabolic capacity. CO metabolic differences between the NLE and NHE were found in the granular cell layer of the outer blade of the dentate gyrus. In addition, NLE showed greater CO activity than NRB in medial frontal cortex, and lower activity in perirhinal cortex (dorsal region). NHE showed greater CO activity than NRB in entorhinal cortex (superficial layers) and lower activities in perirhinal cortex and cortical amygdala. These data support the hypothesis that NLE/NHE rats may be an appropriate model for studying genetically altered limbic regions related to impaired emotional processing. The results support the involvement of limbic circuits in attentive processes and impulsiveness, and support the use of the NLE and NHE strains as animal models of Attention Deficit Hyperactivity Disorder (ADHD) in children.

Non-selective attention in a rat model of hyperactivity and attention deficit: subchronic methylphenydate and nitric oxide synthesis inhibitor treatment

The involvement of dopamine (DA) and nitric oxide (NO) in the process of non-selective attention (NSA) to environmental stimuli has been investigated in the juvenile Spontaneously Hypertensive rat (SHR). To this aim the frequency and duration of rearing episodes in a novelty situation, which is thought to monitor NSA, have been measured in male SHR and Wistar-Kyoto (WKY) control rats following subchronic treatment with methylphenidate (MP; 3 mg/kg) or the nitric oxide synthase (NOS) inhibitor L-Nitro-arginine-methylester (L-NAME; 1 mg/kg) or vehicle daily for two weeks. Different groups were tested at 0.5 h or 24 h after the last injection in a Làt-maze. Tests were repeated twice at a 24 h interval and lasted 10 min each. Upon first exposure, there was a differential drug effect only in the SHR. In fact, MP and L-NAME yielded a shift to the left and to the right, i.e. towards episodes of lower or higher duration, respectively. This shift was more pronounced in the group tested 0.5 h after the last injection. In contrast, both drugs produced a significant lengthening of the rearing episodes in the SHR only in comparison with the vehicle-treated rats over days of testing. Therefore both MP and L-NAME appear to shear a similar effect on non-selective attention, although the effect of L-NAME is somewhat paradoxical. The latter is likely to be due to increased arginine selective uptake due to negative feedback with the NO production. The consequent increased arginine availability displaces the NOS inhibitor, thus leading to increased NO production. In conclusion, dopamine and nitric oxide play a role in non-selective attention by synaptic and extrasynaptic mechanisms, respectively, in a rat model of hyperactivity and attention-deficits.

Motor control and state regulation in children with ADHD: a cardiac response study

The goal of the current study was to investigate whether poor motor control in children with Attention-Deficit Hyperactivity Disorder (ADHD) was associated with a state regulation deficit. For this purpose, 28 ADHD and 22 healthy children carried out two Go No-Go tests: one with a fast stimulus presentation rate, and the other with a slow stimulus presentation rate. Groups were compared on RT performance and on specific cardiac measures, reflecting arousal, motor activation/inhibition, and effort allocation. No group difference in the arousal measure (mean heart rate) was found. Further, groups did not differ with respect to response inhibition: in both the fast and slow condition, ADHD children made comparable numbers of errors of commission to the control group, and the groups did not differ with respect to the heart rate deceleration after the onset of the No-Go signal, reflecting motor inhibition. Group differences were found with respect to motor activation and effort allocation in the condition with a slow presentation rate. In this condition: (1) ADHD children reacted more slowly to Go signals than control children, suggesting poor motor activation; (2) the heart rate deceleration before the onset of Go signals, which is believed to reflect motor preparation, was less pronounced in the ADHD children; (3) after Go signals, where a response was given, the cardiac shift from deceleration to acceleration, indicating response initiation, was delayed in ADHD children; and (4) ADHD children had greater heart rate variability (0.10 Hz component) than the control group, indicating that less effort was allocated. No group differences in motor activation and effort allocation were found in the condition with a fast presentation rate of stimuli. We conclude, therefore, that a slow presentation rate of stimuli brings the ADHD child in a non-optimal activation state.

The cognitive-energetic model: an empirical approach to attention-deficit hyperactivity disorder

Attention Deficit/Hyperactivity Disorder (ADHD) is a childhood psychiatric disorder which when carefully defined, affects around 1% of the childhood population [Swanson JM, Sergeant JA, Taylor E, Sonuga-Barke EJS, Jensen PS, Canwell DP. Attention-deficit hyperactivity disorder and hyperkinetic disorder. Lancet 1998;351:429-433]. The primary symptoms: distractibility, impulsivity and overactivity vary in degree and association in such children, which led DSM IV to propose three subgroups. Only one of these subgroups, the combined subtype: deficits in all three areas, meets the ICD-10 criteria. Since the other two subtypes are used extensively in North America (but not in Europe), widely different results between centres are to be expected and have been reported. Central to the ADHD syndrome is the idea of an attention deficit. In order to investigate attention, it is necessary to define what one means by this term and to operationalize it in such a manner that others can test and replicate findings. We have advocated the use of a cognitive-energetic model [Sanders, AF. Towards a model of stress and performance. Acta Psychologica 1983;53: 61-97]. The cognitive-energetic model of ADHD approaches the ADHD deficiency at three distinct levels. First, a lower set of cognitive processes: encoding, central processing and response organisation is postulated. Study of these processes has indicated that there are no deficits of processing at encoding or central processing but are present in motor organisation [Sergeant JA, van der Meere JJ. Convergence of approaches in localizing the hyperactivity deficit. In Lahey BB, Kazdin AE, editors. Advancements in clinical child psychology, vol. 13. New York: Plenum press, 1990. p. 207-45; Sergeant, JA, van der Meere JJ. Additive factor methodology applied to psychopathology with special reference to hyperactivity. Acta Psychologica 1990;74:277-295]. A second level of the cognitive-energetic model consists of the energetic pools: arousal, activation and effort. At this level, the primary deficits of ADHD are associated with the activation pool and (to some extent) effort. The third level of the model contains a management or executive function system. Barkley [Barkley RA, Behavioral inhibition, sustained attention, and executive functions: constructing a unifying theory of ADHD. Psychological Bulletin 1997;121:65-94] reviewed the literature and concluded that executive function deficiencies were primarily due to a failure of inhibition. Oosterlaan, Logan and Sergeant [Oosterlaan J, Logan GD, Sergeant JA. Response inhibition in ADHD, CD, comorbid ADHD + CD, anxious and normal children: a meta-analysis of studies with the stop task. Journal of Child Psychology and Psychiatry 1998;39:411-426] demonstrated that this explanation was not specific to ADHD but also applied to children with the associated disorders of oppositional defiant and conduct disorder. Other executive functions seem to be intact, while others, are deficient. It is argued here that the cognitive-energetic model is a useful guide for determining not only ADHD deficiencies and associated disorders but also linking human cognitive neuroscience studies with neurobiological models of ADHD using animals [Sadile AG. Multiple evidence of a segmental defect in the anterior forebrain of an animal model of hyperactivity and attention deficits. Neuroscience and Biobehavioral Reviews, in press; Sagvolden T, Sergeant JA. Attention-deficit hyperactivity disorder: from brain dysyfunctions to behaviour. Behavioural Brain Research 1998;94:1-10]. A plea for an integrated attack on this research problem is made and the suggestion that conceptual refinement between levels of analysis is essential for further fundamental work to succeed is offered here.

Synchronization, anticipation, and consistency in motor timing of children with dimensionally defined attention deficit hyperactivity behaviour

We tested the hypothesis that children with hyperactive behaviour are impaired in the temporal organization of their motor output. The performance of 11 boys, scoring above a cut-off on standard scales of overactivity and inattention, was compared to that of controls in progressively more complex Motor-timing tasks. The tasks administered required self-paced and externally paced Sensorimotor Synchronization and Sensorimotor Anticipation. Deficits at a perceptual level were investigated with a Time-discrimination task. As hypothesized, we found that hyperactive children had no deficits in their perception of time but were impaired in timing their motor output. Hyperactive children were more inconsistent than controls in maintaining a freely chosen tapping rhythm, in synchronizing and in anticipating their motor response to external visual stimulation.

Relations of age to cognitive and motivational elements of impulse control in boys with and without externalizing behavior problems

In a cross-sectional study of 83 unmedicated boys, 6 to 16 years of age (M = 10.6, SD = 2.1), attending public (N = 48) and therapeutic schools for behaviorally disturbed children (N = 35), we examined relations of externalizing psychopathology to age-dependent change in performance on cognitive and motivational dimensions of impulse control assessed by laboratory tasks. When we controlled for internalizing symptoms and IQ or school achievement, all children showed improving competence with increasing age on both dimensions over the age range of the sample. Children with externalizing problems performed more poorly on both dimensions at all ages than children without such problems. Comparing age-dependent competence for the two groups, a model of convergent maturation in cognitive aspects of impulse control, and a model depicting a stable deficit in motivational aspects of impulse control in those children with externalizing behavior problems, relative to those without such problems, emerged. Studies of individual growth in impulse control, together with correlates of growth, are needed to validate these observations.

What is attention-deficit/hyperactivity disorder?

ADHD is a highly prevalent condition with the core symptoms of functionally impairing limitations in sustained attention and impulsivity/overactivity. Other frequent symptoms include overemotionality or overreactivity, academic underachievement, low self-esteem, and interpersonal difficulties. The assessment for and diagnosis of ADHD are complicated by the lack of a specific test or marker for the disorder, the occurrence of symptoms along a continuum in the population, and its frequent association with other neurodevelopmental and psychiatric disorders. Due to the often pervasive effects of these symptoms and their chronicity, treatment generally must be multifaceted and prolonged. Neuropsychological studies suggest that individuals with ADHD may have their most salient difficulties in the areas of organizing, preparing, and inhibiting responses. Neurobiologic studies suggest that the circuitry involving frontal cortical-basal ganglia connections may be structurally or functionally different in individuals with ADHD, although the specificity of these findings has not been researched thoroughly. ADHD symptoms are highly, although not entirely, heritable. Many questions remain as to the specifics of etiology and best treatment practices.

Die Aufmerksamkeitsleistungen von 6-10-jährigen Kindern in der TAP

Attentional Performance of 6-10-Year-Old Children on the TAP

Abstract: The aim of the study was to establish norms for the Attention Test Battery (TAP) for children aged 6 to 10. The effects of the age, gender and computer experience of the children were analyzed and order effects were investigated. The factor structure of the test results was explored. The sample was comprised of 79 girls and 71 boys. In most of the subtests, older children showed a nonspecific reduction of their reaction times and a specific improvement in their controlled information processing abilities compared with the younger children. In some subtests, gender effects were found: Boys had faster reaction times, and made more errors. These results are compatible with the well known differences between boys and girs in the early school years in the development of attention. Therefore, it would make sense to establish separate norms for boys and girls. Computer experience had no effect on the test results of the children. The factore analysis provided evidence that it is possible even in children to differenciate between various aspects of attention. The test results showed order effects. Therefore it would be important to conduct the subtests in a standardized order.

Attention-deficit hyperactivity disorder and developmental right-hemisphere syndrome: congruence and incongruence of cognitive and behavioral aspects of attention

We studied clinical aspects of attention in three groups: children with developmental right-hemisphere syndrome and attention-deficit hyperactivity disorder (ADHD), children with ADHD only, and normal controls. The three groups (N = 54) were case-matched for age, sex, IQ, hand dominance, and socioeconomic status. ADHD was diagnosed clinically using the Diagnostic and Statistical Manual of Mental Disorders-III-Revised criteria and the Conners' Abbreviated Teacher Questionnaire. Additional aspects of attention and behavior were measured by the Child Behavior Checklist, a low-cognitive-load continuous performance task, and the visual target cancellation test (paper and pencil). Although the Child Behavior Checklist profile of attentional deficits in the two clinical groups was similar, we found that the developmental right-hemisphere syndrome group was more severely impaired on parameters of attention measured by the continuous performance task and visual target cancellation test than the children with ADHD. We conclude that the profile of attentional deficits in developmental right-hemisphere syndrome is different than that seen in children with ADHD only, possibly reflecting disparate neurologic underpinnings for the two syndromes.

Non-selective attention and nitric oxide in putative animal models of Attention-Deficit Hyperactivity Disorder

Non-selective attention (NSA) to environmental stimuli has been measured in putative animal models of Attention-Deficit Hyperactivity Disorder (ADHD), such as the Spontaneously Hypertensive (SHR) and the Naples High-Excitability (NHE) rat lines. A series of experiments has been carried out on male juvenile SHR and Wistar-Kyoto (WKY) controls (experiment 1) and on the NHE and two controls, i.e. the Naples Low-Excitability (NLE) and a random-bred (NRB) line (experiment 2). It was done under basal conditions or following a single injection of the nitric oxide synthase (NOS) inhibitor L-nitro-arginine-methylester (L-NAME: 0.1-10 mg/kg, i.p.), or vehicle, 30 min before testing on day 1 and vehicle alone before testing on days 2 and 3 in SHR/WKY (experiment 3) and the Naples lines (experiment 4). The behavior in a Lát maze during three consecutive 10-min exposures at 24-h intervals was monitored by a CCD video camera and analyzed off-line for frequency and duration of rearings on hindlimbs per 1-min blocks. The results demonstrated that both SHR and NHE rats showed a higher frequency of rearings of shorter duration than controls. With time of testing, the duration of rearings tended to increase in the WKY but not the SHR. In the Naples lines the duration tended to increase in all but mostly in the NHE rats. The acute inhibition of NOS by L-NAME significantly increased the duration of rearing episodes both in SHR and NHE rats only at 10 mg/kg in the second part of the testing period. Therefore, NSA, as indexed by the duration of rearings, is defective in both hyperactivity models against different genetic backgrounds. In addition, this impairment is dependent upon nitric oxide (NO), which appears to play a significant role in these processes.