A possible pathophysiologic substrate of attention deficit hyperactivity disorder

A Novel Rat Model of ADHD-like Hyperactivity/Impulsivity after Delayed Reward Has Selective Loss of Dopaminergic Neurons in the Right Ventral Tegmental Area

In attention deficit hyperactivity disorder (ADHD), hyperactivity and impulsivity occur in response to delayed reward. Herein we report a novel animal model in which male Sprague-Dawley rats exposed to repeated hypoxic brain injury during the equivalent of extreme prematurity were ADHD-like hyperactive/impulsive in response to delayed reward and attentive at 3 months of age. Thus, a unique animal model of one of the presentations/subtypes of ADHD was discovered. An additional finding is that the repeated hypoxia rats were not hyperactive in the widely used open field test, which is not ADHD specific. Hence, it is recommended that ADHD-like hyperactivity and ADHD-like impulsivity, specifically in response to delayed reward, be a primary component in the design of future experiments that characterize potential animal models of ADHD, replacing open field testing of hyperactivity. Unknown is whether death and/or activity of midbrain dopaminergic neurons contributed to the ADHD-like hyperactivity/impulsivity detected after delayed reward. Hence, we stereologically measured the absolute number of dopaminergic neurons in four midbrain subregions and the average somal/nuclear volume of those neurons. Repeated hypoxia rats had a significant specific loss of dopaminergic neurons in the right ventral tegmental area (VTA) at 2 weeks of age and 18 months of age, providing new evidence of a site of pathology. No dopaminergic neuronal loss occurred in three other midbrain regions. Fewer VTA dopaminergic neurons correlated with increased ADHD-like hyperactivity and impulsivity. Novel early intervention therapies to rescue VTA dopaminergic neurons and potentially prevent ADHD-like hyperactivity/impulsivity can now be investigated.

Peridontitis as a Risk Factor for Attention Deficit Hyperactivity Disorder: Possible Neuro-inflammatory Mechanisms

Periodontitis is a condition caused mostly by the creation of a biofilm by the bacterium P. gingivalis, which releases toxins and damages the tooth structure. Recent research studies have reported association between dental health and neuropsychiatric illnesses. Neuroinflammation triggered by the first systemic inflammation caused by the bacterium present in the oral cavities is a plausible explanation for such a relationship. Substantial amount of evidence supports the role of neuroinflammation and dysfunction of the dopaminergic system in the pathology of ADHD (Attention deficit hyperactivity disorders). Recent epidemiological, microbiological and inflammatory findings strengthen that, periodontal bacteria, which cause systemic inflammation can contribute to neuroinflammation and finally ADHD. Although both diseases are characterized by inflammation, the specific pathways and crosslink's between periodontitis and ADHD remain unknown. Here, the authors describe the inflammatory elements of periodontitis, how this dental illness causes systemic inflammation, and how this systemic inflammation contributes to deteriorating neuroinflammation in the evolution of ADHD. Therefore, the aim of this review is to present possible links and mechanisms that could confirm the evidence of this association.

Tetrahydrobiopterin and Its Multiple Roles in Neuropsychological Disorders

Tetrahydrobiopterin (BH4) is a multifunctional co-factor of various enzymes and a substantial amount of studies have shown BH4 as a key regulator in the synthesis of neurotransmitters such as serotonin, nor-epinephrine as well as dopamine. The imbalance of BH4 may affect neurotransmitter production which can lead to many abnormalities in CNS. This article reviews the role of BH4 in neurodegenerative and neurodevelopmental disorders. We focus on the therapeutic potential of BH4 in various brain diseases that involves neurotransmitters and attempt to address how the modulation of BH4 may provide a novel strategy in various neuropsychological conditions.

Frontal corticostriatal functional connectivity reveals task positive and negative network dysregulation in relation to ADHD, sex, and inhibitory control

Frontal corticostriatal circuits (FCSC) are involved in self-regulation of cognition, emotion, and motor function. While these circuits are implicated in attention-deficit/hyperactivity disorder (ADHD), the literature establishing FCSC associations with ADHD is inconsistent. This may be due to study variability in considerations of how fMRI motion regression was handled between groups, or study specific differences in age, sex, or the striatal subregions under investigation. Given the importance of these domains in ADHD it is crucial to consider the complex interactions of age, sex, striatal subregions and FCSC in ADHD presentation and diagnosis. In this large-scale study of 362 8-12 year-old children with ADHD (n = 165) and typically developing (TD; n = 197) children, we investigate associations between FCSC with ADHD diagnosis and symptoms, sex, and go/no-go (GNG) task performance. Results include: (1) increased striatal connectivity with age across striatal subregions with most of the frontal cortex, (2) increased frontal-limbic striatum connectivity among boys with ADHD only, mostly in default mode network (DMN) regions not associated with age, and (3) increased frontal-motor striatum connectivity to regions of the DMN were associated with greater parent-rated inattention problems, particularly among the ADHD group. Although diagnostic group differences were no longer significant when strictly controlling for head motion, with motion possibly reflecting the phenotypic variance of ADHD itself, the spatial distribution of all symptom, age, sex, and other ADHD group effects were nearly identical to the initial results. These results demonstrate differential associations of FCSC between striatal subregions with the DMN and FPN in relation to age, ADHD, sex, and inhibitory control.

Asymmetry in the Central Nervous System: A Clinical Neuroscience Perspective

Recent large-scale neuroimaging studies suggest that most parts of the human brain show structural differences between the left and the right hemisphere. Such structural hemispheric asymmetries have been reported for both cortical and subcortical structures. Interestingly, many neurodevelopmental and psychiatric disorders have been associated with altered functional hemispheric asymmetries. However, findings concerning the relation between structural hemispheric asymmetries and disorders have largely been inconsistent, both within specific disorders as well as between disorders. In the present review, we compare structural asymmetries from a clinical neuroscience perspective across different disorders. We focus especially on recent large-scale neuroimaging studies, to concentrate on replicable effects. With the notable exception of major depressive disorder, all reviewed disorders were associated with distinct patterns of alterations in structural hemispheric asymmetries. While autism spectrum disorder was associated with altered structural hemispheric asymmetries in a broader range of brain areas, most other disorders were linked to more specific alterations in brain areas related to cognitive functions that have been associated with the symptomology of these disorders. The implications of these findings are highlighted in the context of transdiagnostic approaches to psychopathology.

Executive Function and Attention Performance in Children with ADHD: Effects of Medication and Comparison with Typically Developing Children

The emerging literature reports that children with Attention-Deficit/Hyperactivity Disorder (ADHD) show deficits in executive functioning. To date, the combination of drug therapy with certain evidence-based non-medication interventions has been proven to be the most effective treatment for ADHD. There is a gap in the literature regarding comparing the executive functions (EF) of treatment naïve and medicated children with ADHD with both each other and typically developing children. Altogether, 50 treatment naïve and 50 medicated children with ADHD and 50 typically developing children between the ages of six and 12 were enrolled. The Mini International Neuropsychiatric Interview for Children and Adolescents (Mini Kid) and the Test of Attentional Performance for Children (KiTAP) measures were employed. Treatment naïve children with ADHD showed weaker performance on most executive function measures (12 out of 15) than either the medicated ADHD group or the controls. There were no significant differences between the medicated ADHD children and typically developing children in most KiTAP parameters (10 out of 15). Executive function impairments were observable in treatment naïve ADHD children, which draws attention to the importance of treating ADHD. Future studies should focus on the specific effects of stimulant medication on executive functions.

Regional Brain Volumes and ADHD Symptoms in Middle-Aged Adults: The PATH Through Life Study

OBJECTIVE

We investigated whether volumetric differences in ADHD-associated brain regions are related to current symptoms of inattention and hyperactivity in healthy middle-aged adults and whether co-occurring anxiety/depression symptoms moderate these relationships.

METHOD

ADHD Self-Report Scale and Brief Patient Health Questionnaire were used to assess current symptoms of inattention, hyperactivity, anxiety, and depression in a population-based sample ( n = 269). Brain volumes, measured using a semi-automated method, were analyzed using multiple regression and structural equation modeling to evaluate brain volume-inattention/hyperactivity symptom relationships for selected regions.

RESULTS

Volumes of the left nucleus accumbens and a region overlapping the dorsolateral prefrontal cortex were positively associated with inattention symptoms. Left hippocampal volume was negatively associated with hyperactivity symptoms. The brain volume-inattention/hyperactivity symptom associations were stronger when anxiety/depression symptoms were controlled for.

CONCLUSION

Inattention and hyperactivity symptoms in middle-aged adults are associated with different brain regions and co-occurring anxiety/depression symptoms moderate these brain-behavior relationships.

Attention-Deficit/Hyperactivity Disorder: A Historical Neuropsychological Perspective

The behavior patterns of hyperactivity, impulsivity and inattention that would ultimately become recognized as Attention-Deficit Hyperactivity Disorder (ADHD) have been described for centuries. Nevertheless, in the past 35 years, advances in diagnostic methods, identification of biomarkers, and treatments have advanced at an exponential rate. ADHD is now recognized as the most common behavioral disorder of childhood, with risks extending well into adulthood for both males and females, leading to its identification as a significant public health issue. This historical neuropsychological review of ADHD emphasizes scientific highlights in the past 35 years related to ADHD, including the evolution of the diagnosis (from Hyperkinetic Reaction of Childhood to ADHD), influential theories (executive functions, cognitive-energetic, delay aversion), landmark treatment studies (Multimodal Treatment of ADHD [MTA] and Preschool ADHD Treatment Study [PATS]), and advances in brain mapping techniques (anatomic, functional, and resting state magnetic resonance imaging, diffusion tensor imaging). The review concludes by highlighting the challenges of studying and treating a heterogeneous neurodevelopmental disorder like ADHD, with emphasis on associated disorders and conditions (learning disabilities, sluggish cognitive tempo), special populations (girls, preschoolers, adults), and recommendations for scientific inquiry in the next 35 years. Neuropsychologists are well positioned to address the clinical and research challenges of the next generation of studies, especially involving advances in understanding the sexual dimor.phism, full developmental course, and dynamic risks associated with ADHD. (JINS, 2017, 23, 916-929).

Increased transient Na+ conductance and action potential output in layer 2/3 prefrontal cortex neurons of the fmr1-/y mouse

KEY POINTS

Layer 2/3 neurons of the prefrontal cortex display higher gain of somatic excitability, responding with a higher number of action potentials for a given stimulus, in fmr1^-/y mice. In fmr1^-/y L2/3 neurons, action potentials are taller, faster and narrower. Outside-out patch clamp recordings revealed that the maximum Na⁺ conductance density is higher in fmr1^-/y L2/3 neurons. Measurements of three biophysically distinct K⁺ currents revealed a depolarizing shift in the activation of a rapidly inactivating (A-type) K⁺ conductance. Realistic neuronal simulations of the biophysical observations recapitulated the elevated action potential and repetitive firing phenotype.

ABSTRACT

Fragile X syndrome is the most common form of inherited mental impairment and autism. The prefrontal cortex is responsible for higher order cognitive processing, and prefrontal dysfunction is believed to underlie many of the cognitive and behavioural phenotypes associated with fragile X syndrome. We recently demonstrated that somatic and dendritic excitability of layer (L) 5 pyramidal neurons in the prefrontal cortex of the fmr1^-/y mouse is significantly altered due to changes in several voltage-gated ion channels. In addition to L5 pyramidal neurons, L2/3 pyramidal neurons play an important role in prefrontal circuitry, integrating inputs from both lower brain regions and the contralateral cortex. Using whole-cell current clamp recording, we found that L2/3 pyramidal neurons in prefrontal cortex of fmr1^-/y mouse fired more action potentials for a given stimulus compared with wild-type neurons. In addition, action potentials in fmr1^-/y neurons were significantly larger, faster and narrower. Voltage clamp of outside-out patches from L2/3 neurons revealed that the transient Na⁺ current was significantly larger in fmr1^-/y neurons. Furthermore, the activation curve of somatic A-type K⁺ current was depolarized. Realistic conductance-based simulations revealed that these biophysical changes in Na⁺ and K⁺ channel function could reliably reproduce the observed increase in action potential firing and altered action potential waveform. These results, in conjunction with our prior findings on L5 neurons, suggest that principal neurons in the circuitry of the medial prefrontal cortex are altered in distinct ways in the fmr1^-/y mouse and may contribute to dysfunctional prefrontal cortex processing in fragile X syndrome.

The Third and Fourth Factors of the WISC-III: What they Don't Measure

Factor analysis of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) continues to demonstrate support for the Verbal, Performance, and Full Scale IQs, as well as for the Verbal Comprehension (VC) and Perceptual Organization (PO) factors. With the addition of the Symbol Search subtest, however, the factor analysis reported in the examiner's manual yielded two additional factors rather than just one. There is, however, no early evidence that the third and fourth factors are clinically interpretable. This study examined the relationship between the WISC-III third and four factors and other neuropsychological and behavioral measures. Results indicated that although Freedom From Distractibility (EFD) and Processing Speed (PS) correlated significantly with VC and PO factors, the FD and PS factors did not correlate significantly with any of the other measures of attention. The most robust correlations were between measures of immediate/working memory and FFD and PS. When comparing clinical groups (LD/no ADHD, ADHD Predominantly Inattentive, and ADHD Combined Type), no differences emerged on the FFD or PS factors. The clinical validity of these factors remains questionable. The significant relationship between WISC-III factors and measures of immediate/working memory is promising, but in need of additional research.

Caudate asymmetry is related to attentional impulsivity and an objective measure of ADHD-like attentional problems in healthy adults

Case-control studies comparing ADHD with typically developing individuals suggest that anatomical asymmetry of the caudate nucleus is a marker of attention deficit hyperactivity disorder (ADHD). However, there is no consensus on whether the asymmetry favors the right or left caudate nucleus in ADHD, or whether the asymmetry is increased or decreased in ADHD. The current study aimed to clarify this relationship by applying a dimensional approach to assessing ADHD symptoms that, instead of relying on clinical classification, utilizes the natural behavioral continuum of traits related to ADHD. Structural T1-weighted MRI was collected from 71 adults between 18 and 35 years and analyzed for caudate asymmetry. ADHD-like attentional symptoms were assessed with an objective measure of attentional problems, the ADHD score from the Test of Variables of Attention (TOVA). Impulsivity, a core feature in ADHD, was measured using the Barratt Impulsiveness Scale, a self-report measure that assesses attentional, non-planning, and motor features of impulsivity. We found that larger right relative to left caudate volumes correlated with both higher attentional impulsiveness and worse ADHD scores on the TOVA. Higher attentional impulsiveness also correlated with worse ADHD scores, establishing coherence between the objective measure and the self-report measure of attentional problems. These results suggest that a differential passage of information through frontal-striatal networks may produce instability leading to attentional problems. The findings also demonstrate the utility of a dimensional approach to understanding structural correlates of ADHD symptoms.

Disengagement and inhibition of visual-spatial attention are differently impaired in children with rolandic epilepsy and Panayiotopoulos syndrome

We assessed voluntary orientation and reorientation of visuospatial attention in 313 healthy 6- to 22-year-old participants, 30 children suffering from benign epilepsy with centrotemporal spikes (BECTS) and 13 children with Panayiotopoulos syndrome (PS). The developmental section highlights the late development of reorienting skills. Only children with BECTS-R showed a strong tendency toward a rightward bias in attentional orientation. Additionally, a unilateral deficit of disengagement characterizes the patients with BECTS-R and comorbid ADHD. Right rolandic spikes seem to aggravate subclinical reorienting difficulties. Finally, children with PS failed to diffuse inhibition, except in the nearest area outside the attentional focus. This deficit could be attributed to the typical occipital-to-frontal spreading of the spikes in PS. By showing distinct attentional deficiencies according to the epileptic syndrome and the epileptic focus lateralization in BECTS, the results provide new evidence for alterations of attentional mechanisms by interictal epileptic activity, which probably contribute to learning difficulties.

Sensory integration, sensory processing, and sensory modulation disorders: putative functional neuroanatomic underpinnings

This paper examines conditions that have variously been called sensory integration disorder, sensory processing disorder, and sensory modulation disorder (SID/SPD/SMD). As these conditions lack readily and consistently agreed-upon operational definitions, there has been confusion as to how these disorders are conceptualized. Rather than addressing various diagnostic controversies, we will instead focus upon explaining the symptoms that are believed to characterize these disorders. First, to clarify the overall context within which to view symptoms, we summarize a paradigm of adaptation characterized by continuous sensorimotor interaction with the environment. Next, we review a dual-tiered, integrated model of brain function in order to establish neuroanatomic underpinnings with which to conceptualize the symptom presentations. Generally accepted functions of the neocortex, basal ganglia, and cerebellum are described to illustrate how interactions between these brain regions generate both adaptive and pathological symptoms and behaviors. We then examine the symptoms of SID/SPD/SMD within this interactive model and in relation to their impact upon the development of inhibitory control, working memory, academic skill development, and behavioral automation. We present likely etiologies for these symptoms, not only as they drive neurodevelopmental pathologies but also as they can be understood as variations in the development of neural networks.

Efficacy and safety of dopamine agonists in traumatic brain injury: a systematic review of randomized controlled trials

In the intensive care unit, dopamine agonists (DA) have been used in traumatic brain injury (TBI) patients to augment or accelerate cognitive recovery and rehabilitation. However, the efficacy and safety of DA in this population is not well established. We conducted a systematic review of randomized controlled trials (RCTs) examining the clinical efficacy and safety of DA in patients with TBI. We searched MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials, comparing DA to either placebo, standard treatment, or another active comparator. There was no restriction for age, date, or language of publication. Sensitivity analyses were planned to evaluate the potential effect of timing of TBI, age, drugs, and year of publication on efficacy. Among the 790 citations identified, 20 RCTs evaluating methylphenidate, amantadine, and bromocriptine were eligible. Significant clinical heterogeneity was observed between and within studies, which precluded any pooling of data. Efficacy outcomes included mainly neuropsychological measures of cognitive functioning. A total of 76 different neuropsychological tests were used, but most of them (59%) only once. Only 5 studies systematically assessed safety. No trend could be drawn from the analysis of efficacy and safety. Important sources of bias in the studies were of major concern. Considering the absence of consensus regarding clinical outcome, the lack of safety assessment, and the high risk of bias in the included trials, more research is warranted before DA can be recommended in critically ill TBI patients.

Effects of DSP4 and methylphenidate on spatial memory performance in rats

In this experiment, we have investigated the spatial memory performance of rats following a central noradrenaline depletion induced by three different doses of the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) and following administration of three different doses of methylphenidate (MPH). The rats were required to find food pellets hidden on a holeboard. The sole administration of DSP4 induced only minor cognitive deficits. However, the treatment with MPH increased the reference memory error, the impulsivity and the motor activity of the DSP4-treated rats. Since the noradrenergic terminals in a DSP4-treated rat are significantly reduced, the administration of MPH has little effect on the noradrenergic system and increases dopaminergic rather than noradrenergic activity, resulting in an imbalance with relatively high dopaminergic and low noradrenergic activities. It is suggested that a reduction of noradrenaline and an increase of dopamine induce ADHD-related deficits and that the depletion of noradrenaline is not sufficient for an appropriate rat model of ADHD.

Differences in Performance of ADHD Children on a Visual and Auditory Continuous Performance Test according to IQ

OBJECTIVE

Continuous performance tests (CPTs) are frequently used in clinical practice to assess the attentiveness of ADHD children. Although most CPTs do not categorize T scores by intelligence, there is great diversity of opinion regarding the interrelation between intelligence and CPT performance. This study aimed to determine if ADHD children with superior IQs would perform better than ADHD children with average IQs. Additionally, we aimed to examine the need for CPTs' to categorize according to IQ.

METHODS

Participants were 326 outpatients, aged 5-15 years, diagnosed with ADHD. All participants completed the Wechsler Intelligence Scale for Children-Revised and a CPT. After excluding those who meet exclusion criteria, we had 266 patients for our analysis.

RESULTS

The "Highly Intelligent Group" (HIG), patients with IQs 120 and above, performed superiorly to the "Normally Intelligent Group" (NIG) patients, with IQs between 70 and 120, with regard to omission and commission errors on the visual-auditory CPT, even after controlling for age and gender. The HIG had higher ratios of subjects with T scores <65 on the visual and auditory CPT variables than the NIG did.

CONCLUSION

The results of this study suggest this CPT is not sensitive for discerning ADHD in children with superior IQs; thus, there is a need to standardize the variables based on IQ, as well as on age and gender. Moreover, clinicians need to pay attention to the effect of IQ in interpreting CPT scores; that is, a "normal" score does not rule out a diagnosis of ADHD.

Quantifying excessive mirror overflow in children with attention-deficit/hyperactivity disorder

OBJECTIVES

Qualitative observations have revealed that children with attention-deficit/hyperactivity disorder (ADHD) show increased overflow movements, a motor sign thought to reflect impaired inhibitory control. The goal of this study was to develop and implement methods for quantifying excessive mirror overflow movements in children with ADHD.

METHODS

Fifty right-handed children aged 8.2-13.3 years, 25 with ADHD (12 girls) and 25 typically developing (TD) control children (10 girls), performed a sequential finger-tapping task, completing both left-handed (LHFS) and right-handed finger sequencing (RHFS). Phasic overflow of the index and ring fingers was assessed in 34 children with video recording, and total overflow in 48 children was measured by calculating the total angular displacement of the index and ring fingers with electrogoniometer recordings.

RESULTS

Phasic overflow and total overflow across both hands were greater in children with ADHD than in TD children, particularly during LHFS. Separate gender analyses revealed that boys, but not girls, with ADHD showed significantly more total phasic overflow and total overflow than did their gender-matched control children.

CONCLUSIONS

The quantitative overflow measures used in this study support past qualitative findings that motor overflow persists to a greater degree in children with ADHD than in age-matched TD peers. The quantitative findings further suggest that persistence of mirror overflow is more prominent during task execution of the nondominant hand and reveal gender-based differences in developmental neural systems critical to motor control. These quantitative measures will assist future physiologic investigation of the brain basis of motor control in ADHD.

Parameterization-invariant shape comparisons of anatomical surfaces

We consider 3-D brain structures as continuous parameterized surfaces and present a metric for their comparisons that is invariant to the way they are parameterized. Past comparisons of such surfaces involve either volume deformations or nonrigid matching under fixed parameterizations of surfaces. We propose a new mathematical representation of surfaces, called q-maps, such that L² distances between such maps are invariant to re-parameterizations. This property allows for removing the parameterization variability by optimizing over the re-parameterization group, resulting in a proper parameterization-invariant distance between shapes of surfaces. We demonstrate this method in shape analysis of multiple brain structures, for 34 subjects in the Detroit Fetal Alcohol and Drug Exposure Cohort study, which results in a 91% classification rate for attention deficit hyperactivity disorder cases and controls. This method outperforms some existing techniques such as spherical harmonic point distribution model (SPHARM-PDM) or iterative closest point (ICP).

Effects of osmotic-release methylphenidate in attention-deficit/hyperactivity disorder as measured by event-related potentials

AIM

Attention-deficit/hyperactivity disorder (ADHD) is a relatively common central nervous system disorder in school-age children, which may involve a specific disorder in cognition and/or information processing. Event-related potentials (ERP) are commonly used as physiological measures of cognitive function as they are easily measured and non-invasive. Thus, in the present study, we examined the effects of osmotic-release methylphenidate (MPH) (Concerta), a common treatment for childhood attention-deficit/hyperactivity disorder (ADHD), in ADHD children as measured by ERP.

METHODS

Ten ADHD children participated after giving consent. Based on the guidelines for evoked potential measurement, mismatch negativity (MMN) and P300 were obtained by auditory odd-ball tasks. We measured both MMN and P300 in the drug-naive condition and after intake of osmotic-release MPH.

RESULTS

  The MMN amplitudes after intake of osmotic-release MPH were significantly greater than those in the drug-naive situation at Pz and C4. The P300 amplitudes after intake of osmotic-release MPH were significantly greater than those in the drug-naive situation at Cz and Pz.

CONCLUSION

MMN and P300 are sensitive tools for measuring the pharmacological effects of osmotic-release MPH in ADHD children.

Clinical correlations of grey matter reductions in the caudate nucleus of adults with attention deficit hyperactivity disorder

BACKGROUND

Magnetic resonance imaging (MRI) studies have shown decreased caudate volumes in individuals with attention deficit hyperactivity disorder (ADHD). However, most of these studies have been carried out in male children. Very little research has been done in adults, and the results obtained in children are difficult to extrapolate to adults. We sought to compare the volume of the caudate of adults with ADHD with that of healthy controls; we also compared these volumes between men and women.

METHODS

We performed an MRI scan on 20 adults with ADHD (10 men and 10 women) aged 25-35 years and 20 healthy controls matched by age and sex. We used voxel-based morphometry with the DARTEL algorithm for image analyses. We used the specifically designed Friederichsen, Almeida, Serrano, Cortes Test (FASCT) to measure the severity of ADHD; both the self-reported (FASCT-SR) and the observer (FASCT-O) versions were used.

RESULTS

The statistical parametric map showed a smaller region with low grey matter volume and a smaller concentration of grey matter in this region of the right caudate in ADHD patients than in health controls, both in the entire sample and within each sex. There was a significant correlation between the volume of this region of the caudate with the number of DSM IV-TR criteria, as well as with the total scores and most of the factors of the FASCT-SR and FASCT-O scales. A separate correlation analysis by sex gave similar results.

LIMITATIONS

The study design was cross-sectional.

CONCLUSION

The region of the right caudate with low grey matter volume was smaller in adults with ADHD in both sexes and was correlated with ADHD severity.

ADHD familial loading and abnormal EEG alpha asymmetry in children with ADHD

OBJECTIVE

Abnormal brain laterality (ABL) is indicated in ADHD. ADHD and brain laterality are heritable. Genetic factors contributing to lateralization of brain function may contribute to ADHD. If so, increased ADHD family loading should be associated with greater ABL. Previous studies have shown increased rightward alpha asymmetry in ADHD. We tested whether this was more pronounced in ADHD children with increased ADHD family loading.

METHODS

We compared EEG alpha asymmetry at rest and during the Conner's Continuous Performance Test (CPT) in ADHD children with and without ADHD affected parents, and replicated our findings in a second larger sample. The replication study additionally stratified the parent-affected sample by parental persistent versus non-persistent ADHD status, increased spatial resolution of EEG measures, and assessed low versus high-alpha.

RESULTS

Study-1: the parent-affected group showed increased rightward asymmetry across frontal and central regions and reduced rightward parietal asymmetry during an eyes closed (EC) condition, as well as increasing rightward parietal asymmetry with advancing age during the CPT. Study-2 replicated these findings and further delineated influences of low versus high-alpha, recording site, and effects of parental persistent versus non-persistent ADHD status.

CONCLUSION

Increased ADHD familial loading was associated with increased rightward frontal asymmetry. In contrast, increased rightward parietal asymmetry was associated with reduced ADHD family loading. Frontal results are consistent with an ADHD endophenotype. Parietal results suggest an ADHD adaptive trait prevalent with less ADHD family loading. Age effects indicate a unique developmental course among ADHD children whose parents have non-persistent ADHD.

Case-control study of six genes asymmetrically expressed in the two cerebral hemispheres: association of BAIAP2 with attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset neuropsychiatric disease that persists into adulthood in at least 30% of patients. There is evidence suggesting that abnormal left-right brain asymmetries in ADHD patients may be involved in a variety of ADHD-related cognitive processes, including sustained attention, working memory, response inhibition and planning. Although mechanisms underlying cerebral lateralization are unknown, left-right cortical asymmetry has been associated with transcriptional asymmetry at embryonic stages and several genes differentially expressed between hemispheres have been identified.

METHODS

We selected six functional candidate genes showing at least 1.9-fold differential expression between hemispheres (BAIAP2, DAPPER1, LMO4, NEUROD6, ATP2B3, and ID2) and performed a case-control association study in an initial Spanish sample of 587 ADHD patients (270 adults and 317 children) and 587 control subjects.

RESULTS

The single- and multiple-marker analysis provided evidence for a contribution of BAIAP2 to adulthood ADHD (p = .0026 and p = .0016, respectively). We thus tested BAIAP2 for replication in two independent adult samples from Germany (639 ADHD patients and 612 control subjects) and Norway (417 ADHD cases and 469 control subjects). While no significant results were observed in the Norwegian sample, we replicated the initial association between BAIAP2 and adulthood ADHD in the German population (p = .0062).

CONCLUSIONS

Our results support the participation of BAIAP2 in the continuity of ADHD across life span, at least in some of the populations analyzed, and suggest that genetic factors potentially influencing abnormal cerebral lateralization may be involved in this disorder.

Randomized controlled trial of atomoxetine for cognitive dysfunction in early Huntington disease

BACKGROUND

Cognitive symptoms are associated with functional disability in Huntington disease; yet, few controlled trials have examined cognitive treatments that could improve patient independence and quality of life. Atomoxetine is a norepinephrine reuptake inhibitor approved for treatment of attention-deficit/hyperactivity disorder.

METHODS

Twenty participants with mild Huntington disease who complained of inattention were randomized to receive atomoxetine (80 mg/d) or placebo in a 10-week double-blind crossover study. Primary outcome measures were self-reported attention and attention and executive neuropsychological composite scores. Secondary outcomes were psychiatric and motor symptom scores.

RESULTS

The rate of reported adverse effects while on atomoxetine was 56% (vs 35% on placebo), which most commonly included dry mouth (39%), loss of appetite (22%), insomnia (22%), and dizziness (17%). There were no serious adverse events related to atomoxetine. There were statistically significant, although mild, increases in heart rate and diastolic blood pressure on atomoxetine, consistent with other studies and not requiring medical referral. There were no significant improvements while on atomoxetine compared with placebo on primary outcomes. However, there was evidence of significant placebo effects on self-reported attention and psychiatric functions. There were no group differences on the Unified Huntington's Disease Rating total motor score.

CONCLUSIONS

Atomoxetine demonstrated no advantages over placebo for primary or secondary outcomes. Although atomoxetine was not effective at improving attention at this dose, its safety and tolerability were similar to other studies.

Abnormal spatial asymmetry of selective attention in ADHD

BACKGROUND

Evidence for a selective attention abnormality in children with attention deficit hyperactivity disorder (ADHD) has been hard to identify using conventional methods from cognitive science. This study tested whether the presence of selective attention abnormalities in ADHD may vary as a function of perceptual load and target lateralisation. Given evidence of right-hemisphere dysfunction in ADHD we predicted increased interference effects for right, but not left-sided target displays, particularly under low perceptual load.

METHOD

Fourteen children with ADHD-C and 14 typically developing children were tested on a modified flanker task under low and high perceptual load. We also sought evidence for our hypothesis in a re-analysis of an independent data set (42 ADHD; 34 typically developing) in which load effects on selective attention in ADHD were previously examined (Huang-Pollock, Nigg, & Carr, 2005).

RESULTS

As predicted, all children showed evidence of greater interference by flankers under low compared with high perceptual load conditions. Crucially, however, children with ADHD showed the greatest interference effect for right-sided target displays under low but not high perceptual load. In contrast, typically developing children showed the greatest interference for left-sided target displays. The magnitude of interference for right-sided targets was also positively correlated with ADHD symptom levels. Re-analysis of an independent data set (Huang-Pollock et al., 2005) further confirmed our findings.

CONCLUSIONS

This study demonstrates that interference effects in children with ADHD and typically developing children are spatially asymmetrical but opposite in direction. The pattern of right-sided interference effects in children with ADHD suggests disruption within right hemisphere attentional networks in ADHD.

Executive functioning differences between adults with attention deficit hyperactivity disorder and autistic spectrum disorder in initiation, planning and strategy formation

Executive functioning deficits characterize the neuropsychological profiles of the childhood neurodevelopmental disorders of attention deficit hyperactivity disorder (ADHD) and autistic spectrum disorder (ASD). This study sought to determine whether similar impairments exist in adults with ADHD (N = 53) and ASD (N = 45) in comparison with a healthy control group (N = 31), whether the two disorders can be distinguished on the basis of their executive functioning features, and whether these impairments are related to symptom severity. Both clinical groups were found to exhibit executive functioning deficits. The ADHD group had difficulty withholding a response, with relative preservation of initiation and planning abilities. In contrast, the ASD group exhibited significant impairments in initiation, planning and strategy formation. The specific executive functioning deficits were related to severity of response inhibition impairments in ADHD and stereotyped, repetitive behaviours in ASD. These findings suggest the pattern of executive functioning deficits follows a consistent trajectory into adulthood.

Manual MRI parcellation of the frontal lobe

The ability to examine associations between neuropsychiatric conditions and functionally relevant frontal lobe sub-regions is a fundamental goal in neuropsychiatry, but methods for identifying frontal sub-regions in MR (magnetic resonance) images are not well established. Prior published techniques have principally defined gyral regions that do not necessarily correspond to known functional divisions. We present a method in which sulcal-gyral landmarks are used to manually delimit functionally relevant regions within the frontal lobe: primary motor cortex, anterior cingulate, deep white matter, premotor cortex regions (supplementary motor complex (SMC), frontal eye field and lateral premotor cortex) and prefrontal cortex (PFC) regions (medial PFC, dorsolateral PFC (DLPFC), inferior PFC, lateral orbitofrontal cortex (OFC) and medial OFC). Feasibility was tested by applying the protocol to brain MR data from 15 boys with attention-deficit/hyperactivity disorder (ADHD) and 15 typically developing controls, 8-12 years old. Intra- and inter-rater intraclass correlation coefficients were calculated using parcellation volumes from a subset of that group. Inter-rater results for the 22 hemisphere specific sub-regions ranged from 0.724 to 0.997, with all but seven values above 0.9. Boys with ADHD showed significantly smaller left hemisphere SMC and DLPFC volumes after normalization for total cerebral volume. These findings support the method as a reliable and valid technique for parcellating the frontal lobe into functionally relevant sub-regions.

Atypical alpha asymmetry in adults with ADHD

INTRODUCTION

A growing body of literature suggests atypical cerebral asymmetry and interhemispheric interaction in ADHD. A common means of assessing lateralized brain function in clinical populations has been to examine the relative proportion of EEG alpha activity (8-12 Hz) in each hemisphere (i.e., alpha asymmetry). Increased rightward alpha asymmetry has been associated with ADHD-like traits such as reduced reward responsiveness, a lack of inhibition toward aversive experience, and increased approach behaviors, and previous work has indicated increased rightward alpha asymmetry in children with ADHD. The current study explores whether increased rightward alpha asymmetry is also evident in adults with ADHD.

METHOD

We assessed low (8-10 Hz) and high (10-12 Hz) alpha asymmetry in adults with ADHD (n=29) versus controls (n=62) during baseline and cognitive activation conditions for nine homologous electrode pairs along the anterior-posterior axis.

RESULT

Seven results emerged (p<.05) showing increased rightward alpha asymmetry in adults with ADHD. This occurred in three specific electrode pairs across two testing conditions, and five of six results occurred in the lower alpha band. Finally, post hoc analysis indicated that increased rightward alpha asymmetry was generally associated with greater numbers of ADHD symptoms--with a possible parietal association for inattentive and a fronto-temporal association for hyperactivity symptoms.

CONCLUSIONS

Increased rightward alpha asymmetry previously observed in children with ADHD appears to be a developmentally persistent feature of ADHD.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Abnormal cerebral cortex structure in children with ADHD

OBJECTIVE

Examination of cerebral cortical structure in children with Attention-Deficit/Hyperactivity Disorder (ADHD) has thus far been principally limited to volume measures. In the current study, an automated surface-based analysis technique was used to examine the ADHD-associated differences in additional morphologic features of cerebral cortical gray matter structure, including surface area, thickness, and cortical folding.

METHODS

MPRAGE images were acquired from 21 children with ADHD (9 girls) and 35 typically developing controls (15 girls), aged 8-12 years. Statistical difference maps were used to compare mean cortical thickness between groups along the cortical surface. Cortical volume, surface area, mean thickness, and cortical folding were measured within regions of interest, including the right/left hemispheres, frontal, temporal, parietal, and occipital lobes within each hemisphere, and sub-lobar regions.

RESULTS

Children with ADHD showed a decrease in total cerebral volume and total cortical volume of over 7 and 8%, respectively; volume reduction was observed throughout the cortex, with significant reduction in all four lobes bilaterally. The ADHD group also showed a decrease in surface area of over 7% bilaterally, and a significant decrease in cortical folding bilaterally. No significant differences in cortical thickness were detected.

CONCLUSIONS

Results from the present study reveal that ADHD is associated with decreased cortical volume, surface area, and folding throughout the cerebral cortex. The findings suggest that decreased cortical folding is a key morphologic feature associated with ADHD. This would be consistent with onset early in neural development and could help to identify neurodevelopmental mechanisms that contribute to ADHD.

Basal ganglia volume and shape in children with attention deficit hyperactivity disorder

OBJECTIVE

Volumetric abnormalities of basal ganglia have been associated with attention deficit hyperactivity disorder (ADHD), especially in boys. To specify localization of these abnormalities, large deformation diffeomorphic metric mapping (LDDMM) was used to examine the effects of ADHD, sex, and their interaction on basal ganglia shapes.

METHOD

The basal ganglia (caudate, putamen, globus pallidus) were manually delineated on magnetic resonance imaging from 66 typically developing children (35 boys) and 47 children (27 boys) with ADHD. LDDMM mappings from 35 typically developing children were used to generate basal ganglia templates. Shape variations of each structure relative to the template were modeled for each subject as a random field using Laplace-Beltrami basis functions in the template coordinates. Linear regression was used to examine group differences in volumes and shapes of the basal ganglia.

RESULTS

Boys with ADHD showed significantly smaller basal ganglia volumes compared with typically developing boys, and LDDMM revealed the groups remarkably differed in basal ganglia shapes. Volume compression was seen bilaterally in the caudate head and body and anterior putamen as well as in the left anterior globus pallidus and right ventral putamen. Volume expansion was most pronounced in the posterior putamen. No volume or shape differences were revealed in girls with ADHD.

CONCLUSIONS

The shape compression pattern of basal ganglia in boys with ADHD suggests that ADHD-associated deviations from typical brain development involve multiple frontal-subcortical control loops, including circuits with premotor, oculomotor, and prefrontal cortices. Further investigations employing brain-behavior analyses will help to discern the task-dependent contributions of these circuits to impaired response control that is characteristic of ADHD.

Support for an independent familial segregation of executive and intelligence endophenotypes in ADHD families

BACKGROUND

Impairments in executive functioning (EF) and intelligence quotient (IQ) are frequently observed in children with attention deficit hyperactivity disorder (ADHD). The aim of this paper was twofold: first, to examine whether both domains are viable endophenotypic candidates for ADHD and second to investigate whether deficits in both domains tend to co-segregate within families.

METHOD

A large family-based design was used, including 238 ADHD families (545 children) and 147 control families (271 children). Inhibition, visuospatial and verbal working memory, and performance and verbal IQ were analysed.

RESULTS

Children with ADHD, and their affected and non-affected siblings were all impaired on the EF measures and verbal IQ (though unimpaired on performance IQ) and all measures correlated between siblings. Correlations and sibling cross-correlations were not significant between EF and IQ, though they were significant between the measures of one domain. Group differences on EF were not explained by group differences on IQ and vice versa. The discrepancy score between EF and IQ correlated between siblings, indicating that siblings resembled each other in their EF-IQ discrepancy instead of having generalized impairments across both domains. Siblings of probands who had an EF but not IQ impairment, showed a comparable disproportionate lower EF score in relation to IQ score. The opposite pattern was not significant.

CONCLUSIONS

The results supported the viability of EF and IQ as endophenotypic candidates for ADHD. Most findings support an independent familial segregation of both domains. Within EF, similar familial factors influenced inhibition and working memory. Within IQ, similar familial factors influenced verbal and performance IQ.

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

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

Evidence that response inhibition is a primary deficit in ADHD

The present study examined response inhibition in children with attention deficit hyperactivity disorder (ADHD; n = 58) and controls (n = 84) using three go/no-go tests -- one with high working memory demand (cognitive), one with low working memory demand (simple), and one with rewards and response costs (motivation linked) in which emphasis was on reward for responding to "go" stimuli. Results of a repeated measure analysis of variance showed a significant effect of diagnosis for errors of commission for the simple, cognitive, and motivation-linked go/no-go tests, such that children with ADHD made significantly more errors than controls. Furthermore, a significant effect of test was noted across groups, such that both children in the ADHD and control groups performed worse on the cognitive and motivation-linked tests than they did on the simple test. The diagnosis by test interaction was not significant, suggesting that ADHD participants showed a similar degree of impairment to that of controls, regardless of the degree of working memory load or feedback provided in the test. In children with ADHD, response inhibition appears to be a primary deficit that is observed even when executive function demands of tasks are minimal. Although increasing working memory demand appears to impede response inhibition, this effect is similar in ADHD and typically developing children.

The role of simple emotion recognition skills among school aged boys at risk of ADHD

Poor social skills and behavioral problems are a major component of ADHD. The different explanations offered so far, such as cognitive deficits and deficient self regulation, have not been able fully to account for the various aspects of the social dysfunction, suggesting that other mechanisms might underlay this impairment. Our study sought to assess the emotion recognition of Israeli boys at risk of ADHD, and to evaluate its associations with their social skills. A group of 111 boys (grades 4 and 5) were assigned to an At-risk (n=50) and a control (n=61) group based on their scores in an ADHD symptoms questionnaire. The two groups were matched on age, socio-economic status and class and school environment. Group comparisons revealed that compared to their non-At-risk counterparts, At-risk boys have impaired emotion recognition. Finally, multiple groups Structural Equation Modeling analyses (SEM) demonstrated that emotion misrecognition plays a significant role in the At-risk children's social functioning and behavioral problems compared to its role in the social competence and behavioral problems among the comparison group. Implications for the understanding and treatment of social skills problems among children at risk of ADHD are proposed.

Interaction of attention and graphomotor functions in children with attention deficit hyperactivity disorder

The present article provides a review of a series of studies in children with attention deficit hyperactivity disorder (ADHD) concerning (1) the effects of methylphenidate on various attentional functions, (2) the stimulant-induced changes of both qualitative and quantitative (i.e. kinematic) aspects of handwriting, (3) the interaction between conscious control of handwriting and fluency of handwriting movements, and (4) possible therapeutic approaches to graphomotor disturbances. Children with ADHD showed impairments in various aspects of attentional functioning. Pharmacological treatment of ADHD children with methylphenidate resulted in marked improvements of various components of attentional functioning. In comparison to the performance following the withdrawal of methylphenidate, children with ADHD on methylphenidate displayed a significant improvement in task accuracy in the areas of vigilance, divided attention, selective attention (inhibition, focused attention and integration of sensory information) and flexibility. However, the comparison with healthy children revealed considerable deficits regarding vigilance, divided attention, flexibility and selective attention (focused attention and integration of sensory information) in children with ADHD on methylphenidate. The comparison of writing movements of children on and off methylphenidate revealed that medication resulted in a better handwriting, but a deterioration in handwriting fluency as assessed by kinematic analysis. Children with ADHD may use their increased attentional capacities to focus on skills (e.g. handwriting) that are independent of conscious control or may even be disturbed by attention. The findings summarized in this paper indicate, therefore, that administration of methylphenidate alone is insufficient in the treatment of children with ADHD. Children with ADHD may benefit from instructions on how to best use their improved attentional capacities.

Revisiting the role of the prefrontal cortex in the pathophysiology of attention-deficit/hyperactivity disorder

Most neural models for the pathophysiology of attention-deficit/hyperactivity disorder (ADHD) have centered on the prefrontal cortex and its interconnections with the striatum and other subcortical structures. However, research only partially supports these models, and they do not correspond with the development of the prefrontal cortex and its interrelated neurocircuitry. The neural and functional development of the prefrontal cortex more closely parallels recovery from ADHD as indicated by the developmental remission of symptomatology. The authors hypothesize that ADHD is due to noncortical dysfunction that manifests early in ontogeny, remains static throughout the lifetime, and is not associated with the remission of symptomatology. Data supporting this neurodevelopmental model of prefrontal cortex function in ADHD are reviewed. Research and treatment implications are discussed.

Hemispheric functioning in children with subtypes of attention-deficit/hyperactivity disorder

OBJECTIVE

The authors investigated line bisection performance in children with Attention-Deficit/Hyperactivity Disorder (AD/HD) subtypes. Previous research with neurotypical children found a rightward bias with right-hand use and a leftward bias with left-hand use; however, research with AD/HD participants has failed to similarly measure the effects of hand use, which was the focus of this study.

METHOD

Line bisection was used to measure differences in right hemisphere functioning in children (7 to 12 years) with AD/HD-I and AD/HD-C.

RESULTS

Initial AD/HD group findings (without subtype differentiation) replicated previous research. However, further subtype analyses showed that the ADHD-I and ADHD-C groups perform significantly differently. Specifically, the ADHD-I group showed a leftward bias, irrespective of hand use, and the ADHD-C group showed a rightward bias, irrespective of hand use.

CONCLUSION

These findings suggest that the subtypes represent two distinct disorders and that, unlike ADHD-C, ADHD-I may not be the result of right hemisphere dysfunction.

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

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

Effects of methylphenidate on multiple components of attention in children with attention deficit hyperactivity disorder

RATIONALE

Methylphenidate (MPH) has been shown to be effective in the treatment of attention deficits in children with attention deficit hyperactivity disorder (ADHD). Although a variety of studies have been performed, there is little available information as to which components of attentional functioning are disturbed in ADHD.

OBJECTIVES

The aim of the present study was to monitor the effect of MPH on various measures of attention in children with ADHD.

METHODS

In a double-blind, placebo-controlled, crossover study, the attentional functioning of 58 children diagnosed with ADHD without psychiatric comorbidity was examined. Assessment of attention was performed on their usual MPH treatment and following withdrawal of the drug. Furthermore, the attentional performance of 58 healthy children was assessed. The test battery consisted of reaction time tasks, including measures of alertness, vigilance, divided attention, flexibility, and aspects of selective attention such as focused attention, inhibition, and integration of sensory information.

RESULTS

In comparison to the test performance of healthy children, children with ADHD displayed impairments of vigilance, divided attention, flexibility, and aspects of selective attention including focused attention, inhibition, and integration of sensory information. Statistical comparison of attentional functioning of children with ADHD on and off MPH treatment revealed that the medication resulted in an improved task accuracy regarding vigilance, divided attention, inhibition, focused attention, integration of sensory information, and flexibility.

CONCLUSION

The present findings indicate that various aspects of attention are markedly impaired in children with ADHD. Treatment with MPH was accompanied by improvements in attention functions of small to moderate sizes. Although MPH-induced improvements were observed in a broad range of attention measures, children with ADHD who were on MPH treatment nevertheless displayed serious deficits in a number of components of attention.