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PubMed1997

Behavioral inhibition, sustained attention, and executive functions: constructing a unifying theory of ADHD.

Attention deficit hyperactivity disorder (ADHD) comprises a deficit in behavioral inhibition. A theoretical model is constructed that links inhibition to 4 executive neuropsychological functions that appear to depend on it for their effective execution: (a) working memory, (b) self-regulation of affect-motivation-arousal, (c) internalization of speech, and (d) reconstitution (behavioral analysis and synthesis). Extended to ADHD, the model predicts that ADHD should be associated with secondary impairments in these 4 executive abilities and the motor control they afford. The author reviews evidence for each of these domains of functioning and finds it to be strongest for deficits in behavioral inhibition, working memory, regulation of motivation, and motor control in those with ADHD. Although the model is promising as a potential theory of self-control and ADHD, far more research is required to evaluate its merits and the many predictions it makes about ADHD.

Affect↗

PubMed2001

Is ADHD a disinhibitory disorder?

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

Anxiety Disorders↗

PubMed2006

Single dissociation findings of ADHD deficits in vigilance but not anterior or posterior attention systems.

Following a distributed network model of visuospatial attention, the authors used an A-X version of the Continuous Performance Test and a covert orienting paradigm to examine the vigilance, anterior, and posterior attention systems. Compared with control participants without attention-deficit/hyperactivity disorder (ADHD), children with the predominantly inattentive (ADHD-I) and combined (ADHD-C) subtypes had lower sensitivity (d') to detect targets from nontargets. Children with ADHD-C, but not ADHD-I, additionally had a highly activated response style (lnbeta). Performance for both subtypes decreased to a greater extent over time in a manner consistent with problems in sustained attention. Together, these results suggest the presence of vigilance system deficits in participants with both ADHD subtypes. However, consistent with previous meta-analytic work, there was no evidence for anterior or posterior system orienting dysfunctions in either subtype.

Attention↗

PubMed2003

A multitrait-multisource confirmatory factor analytic approach to the construct validity of ADHD rating scales.

Confirmatory factor analysis was used to model a multitrait-multisource design to evaluate the construct validity of attention-deficit/hyperactivity disorder (ADHD) rating scales. The 2 trait factors were the ADHD inattention and hyperactivity/impulsivity dimensions. The 2 source factors were parents and teachers. In Study 1, parents and teachers rated 1,475 Australian elementary school children on the ADHD symptoms. In Study 2, parents and teachers rated 285 Brazilian elementary school children on the ADHD symptoms. Similar results occurred in both studies with most of the ADHD symptoms containing more source than trait variance, thus providing weak evidence for the convergent and discriminant validity of the symptoms as measured by rating scales. The study outlines the implications of such strong source effects for understanding ADHD.

Attention Deficit Disorder with Hyperactivity↗

PubMed2006

Measurement and structural invariance of parent ratings of ADHD and ODD symptoms across gender for American and Malaysian children.

The purpose of this study was to examine the measurement (configural, metric, scalar, and residual) and structural (factor variance, factor covariance, and factor means) invariance of parent ratings of the attention-deficit/hyperactivity disorder - inattention (ADHD-IN), ADHD - hyperactivity/impulsivity (ADHD-HI), and oppositional defiant disorder (ODD) symptoms as described in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) across boys and girls. In an American pediatric sample (N = 1,015) and a Malaysian elementary school-age sample (N = 928), there was strong support for configural, metric, scalar, residual, factor variance, and covariance invariance across gender within each sample. Both American and Malaysian boys had significantly higher scores on the ADHD-IN and ADHD-HI factor means than did girls, whereas only in the American sample did boys score significantly higher on the ODD factor than did girls. The implications of the results for the study of gender, ethnic, and cultural differences associated with ADHD and ODD are discussed.

Attention Deficit Disorder with Hyperactivity↗

PubMed2000

Evidence for the serotonin HTR2A receptor gene as a susceptibility factor in attention deficit hyperactivity disorder (ADHD).

A recent study demonstrated that treatment of hyperactive mice with psychostimulants and serotonergic agents produced a calming effect that was dependent on serotonergic neurotransmission and was not associated with any changes in extracellular dopamine levels. The complex interaction between the serotonergic and dopaminergic neurotransmitter systems suggests that a balance between the two systems may be necessary for mediating hyperactive behaviour. Defects in serotonin system genes, therefore, may disrupt normal brain serotonin function causing an imbalance between these neurotransmitter systems leading to the development of attention deficit hyperactivity disorder (ADHD). Using the transmission disequilibrium test (TDT), the current study assesses for linkage disequilibrium between polymorphisms in the serotonin HTR2A receptor gene and ADHD. One hundred and fifteen families with a total of 143 children diagnosed with ADHD (DSM-IV) were genotyped for the His452 Tyr and the T102C polymorphisms in the serotonin HTR2A receptor gene. TDT analysis revealed a preferential transmission of the 452Tyr allele to the affected offspring (P = 0.03), suggesting linkage disequilibrium of this polymorphism with ADHD. This may open a new door in ADHD molecular genetics research, expanding the existing view of a catecholaminergic hypothesis to include a serotonergic hypothesis and should help elucidate the complex interplay among the neurotransmitter systems in the etiology of ADHD.

Adolescent↗

PubMed2002

Serotonergic system and attention deficit hyperactivity disorder (ADHD): a potential susceptibility locus at the 5-HT(1B) receptor gene in 273 nuclear families from a multi-centre sample.

Attention deficit hyperactivity disorder (ADHD) is a highly heritable and heterogeneous disorder, which usually becomes apparent during the first few years of childhood. Imbalance in dopamine neurotransmission has been suggested as a factor predisposing to ADHD. However, evidence has suggested an interaction between dopamine and serotonin systems in the pathophysiology of the disorder. Studies using selective agonists of the different 5-HT receptors microinjected into selected brain structures have shown a positive modulating effect on the functional activities of the mesotelencephalic dopaminergic system. This suggests that some of the genetic predisposition to ADHD might be due to DNA variation at serotonin system genes. In this study, we investigated polymorphisms in HTR(1B) and HTR(2A) (which encode the serotonin receptors 5-HT(1B) and 5-HT(2A) respectively) in a European ADHD sample. Using haplotype based haplotype relative risk (HHRR) and transmission disequilibrium test (TDT) analyses, we observed significant preferential transmission of the allele 861G of the HTR(1B) in the total sample (for HHRR; chi(2) = 7.4, P = 0.0065 and TDT; (chi(2) = 6.4, P = 0.014). Analysis of HTR(2A) failed to reveal evidence of association or linkage between the His452Tyr polymorphism and ADHD in the total sample. However, a significantly increased transmission of the allele 452His was observed in the Irish sample alone (chi(2) = 4.9, P = 0.026). These preliminary data suggest an important role for the serotonin system in the development of ADHD. Further studies, preferentially including different ethnic groups are required to substantiate these findings.

Attention Deficit Disorder with Hyperactivity↗

PubMed2003

Attention deficit hyperactivity disorder: review of ADHD in learning disability: the Diagnostic Criteria for Psychiatric Disorders for Use with Adults with Learning Disabilities/Mental Retardation[DC-LD] criteria for diagnosis.

BACKGROUND: Attention deficit hyperactivity disorder [ADHD)]is believed to be common among people with learning disabilities. Classification systems in current use have presented diagnostic difficulties in this area, when used for people with learning disability (particularly adults). METHODS: A literature search using electronic databases was undertaken, and journals were hand-searched for articles relevant to the diagnosis of mental disorders in adults with intellectual disabilities. RESULTS: There is preliminary evidence that ADHD is more common in this population than among the non-learning-disabled population, and indeed that rates of hyperactivity increase with increasing severity of learning disability. There are also associations between ADHD and certain causal syndromes of learning disability. CONCLUSION: While available evidence suggests that ADHD may be common among children and adults with learning disabilities, research has been hindered by deficits in currently used diagnostic classification systems. With the recent development of criteria for the diagnosis of ADHD in learning-disabled adults, and the publication of these in Diagnostic Criteria for Learning Disabilities/Mental Retardation[DC-LD] there is scope for an increase in the level of interest in the study of ADHD among adults with learning disabilities.

Adult↗

PubMed2001

An investigation of prospective memory in children with ADHD.

Prospective memory, defined as the ability to follow through on intended behavior, is believed to be subserved by a number of neuroanatomical substrates, but particularly dependent, at least in part, on the frontal lobes. Children with Attention-Deficit Hyperactivity Disorder (ADHD) traditionally have difficulty on tasks dependent on frontal lobe structures. The present study attempted to determine whether children with ADHD are impaired in prospective memory function. Two studies are described that use a new measure of time-based prospective memory, the CyberCruiser (Kerns, 2000), to compare children with ADHD to a control group consisting of participants who were matched in respect to age, gender, and IQ. The results document prospective memory deficits in ADHD. Prospective memory performance correlated significantly with clinical measures of ADHD as assessed by the Conners' Parent Rating Scale (Conners, 1990) Hyperactivity Index, but was unrelated to intellectual ability. Though psychometric measures of attention correlated with prospective memory performance, they did not account for the differences in prospective memory that were observed between the ADHD and control groups.

Adolescent↗

PubMed2001

Working memory interference control deficit in children referred by teachers for ADHD symptoms.

It has been hypothesised that children with Attention Deficit/Hyperactivity Disorder (ADHD) present memory problems, including working memory deficits. This research is aimed at finding clearer evidence of a working memory deficit in these children. In the first study 22 children that had been referred by teachers as having ADHD symptoms were compared with a control group. Their performance on a listening span test, drawn up by De Beni, Palladino, Pazzaglia, and Cornoldi (1998), was investigated. In this task the subjects were asked to select the names of animals in word strings and to remember the last word in each string. In a second study, 34 children with ADHD symptoms and 50 control children were presented with a visuospatial working memory task mirroring the verbal task used in Study 1. In both studies, the children with ADHD symptoms had difficulty in remembering the last item in the string and had a higher number of intrusions when memorising items that were not in the final position. The results were interpreted that children with ADHD symptoms have working memory problems because they are not capable of suppressing information that initially has to be processed, and subsequently excluded from memory. This particular difficulty can be interpreted as an inhibitory processing deficit. The implications of the results in understanding learning difficulties in children with ADHD are discussed.

Attention↗

PubMed2001

The Test of Everyday Attention for Children (TEA-Ch): patterns of performance in children with ADHD and clinical controls.

The present study explores the utility of the Test of Everyday Attention for Children (TEA-Ch) as a measure of the attentional impairments displayed by children with Attention Deficit Hyperactivity Disorder (ADHD). Sixty-three children with ADHD and 23 non-ADHD Clinical Control children were compared on subtests of the TEA-Ch reflecting three attentional domains: sustained, selective, and attentional control. Results show that children with ADHD performed significantly worse than clinical controls on subtests of sustained attention and attentional control. The groups did not differ, however, on subtests of selective attention. These findings suggest that the TEA-Ch is sensitive to attentional deficits unique to ADHD and holds promise as a useful tool in the assessment of ADHD. Performance patterns and future directions are discussed.

Adjustment Disorders↗

PubMed2004

Duration judgments in children with ADHD suggest deficient utilization of temporal information rather than general impairment in timing.

Clinicians, parents, and teachers alike have noted that individuals with ADHD often have difficulties with "time management," which has led some to suggest a primary deficit in time perception in ADHD. Previous studies have implicated the basal ganglia, cerebellum, and frontal lobes in time estimation and production, with each region purported to make different contributions to the processing and utilization of temporal information. Given the observed involvement of the frontal-subcortical networks in ADHD, we examined judgment of durations in children with ADHD (N = 27) and age- and gender-matched control subjects (N = 15). Two judgment tasks were administered: short duration (550 ms) and long duration (4 s). The two groups did not differ significantly in their judgments of short interval durations; however, subjects with ADHD performed more poorly when making judgments involving long intervals. The groups also did not differ on a judgment-of-pitch task, ruling out a generalized deficit in auditory discrimination. Selective impairment in making judgments involving long intervals is consistent with performance by patients with frontal lobe lesions and suggests that there is a deficiency in the utilization of temporal information in ADHD (possibly secondary to deficits in working memory and/or strategy utilization), rather than a problem involving a central timing mechanism.

Adolescent↗

PubMed2006

Functional connectivity of frontal cortex in healthy and ADHD children reflected in EEG coherence.

Abnormal functional brain connectivity is a candidate factor in developmental brain disorders associated with cognitive dysfunction. We analyzed a substantial (10 min per subject) record of dense array electroencephalography with spectral power and coherence methods in attention-deficit hyperactivity disorder (ADHD) (n = 42) and control (n = 21) 10- to 13-year-old children. We found topographically distinct narrow band coherence differences between subject groups: ADHD subjects showed elevated coherence in the lower alpha (8 Hz) band and reduced coherence in the upper alpha (10-11 Hz) band. The 8-Hz ADHD elevation and a 2- to 6-Hz control group coherence elevation were independent of stimulus presentation. In response to visual stimulation, the ADHD group exhibited reduced evoked potential power and elevated frontal coherence. Only the upper alpha band control group coherence elevation discriminated according to ADHD group medication status. The findings suggest a static state of deficient connectivity in ADHD and a stimulus-induced state of overconnectivity within and between frontal hemispheres.

Adolescent↗

PubMed2006

Increased prevalence of ADHD in Turner syndrome with no evidence of imprinting effects.

BACKGROUND: Turner syndrome (TS) results from the loss of part or all of one X chromosome in females. It can result in short stature, various dysmorphic findings, and difficulties with psychosocial adjustment. Girls with TS have previously been found to exhibit increased levels of hyperactivity and inattention. However, no studies have assessed whether individuals with TS meet strict (DSM-IV) criteria for attention-deficit/hyperactivity disorder (ADHD). OBJECTIVE: We looked at the prevalence of ADHD in girls with TS and evaluated the contribution of imprinting on cognitive performance (IQ) and ADHD. METHODS: We tested 50 girls with TS for ADHD, IQ, academic performance, and parental origin of the X chromosome. RESULTS: We report an 18-fold increase in the prevalence of ADHD in girls with TS (24%) compared with girls in the general population (1.3%) (p < .01) and a 4.8 fold increase when compared with boys and girls in the general population (5%) (p < .05). In contrast to previous reports, our molecular studies in females with 45,X also showed no association between IQ scores and the parental origin of the intact X chromosome. CONCLUSIONS: We find an increased prevalence of ADHD in girls with TS but no evidence for imprinting effects for cognitive performance.

Adolescent↗

PubMed1995

Differential effects of methylphenidate on working memory in ADHD children with and without comorbid anxiety.

OBJECTIVE: To examine the effects of methylphenidate (MPH) on working memory and behavior in anxious and nonanxious children with attention-deficit hyperactivity disorder (ADHD). METHOD: A total of 40 ADHD children (22 nonanxious, 18 anxious) completed a randomized, double-blind, placebo-controlled, crossover trial with three doses (0.3, 0.6, 0.9 mg/kg) of MPH. A serial addition task was used to assess working memory; direct observation of motor activity indexed behavior. RESULTS: MPH improved working memory in the nonanxious ADHD group but not in the comorbidity anxious group. By contrast, MPH reduced activity level in both groups. The presence of concurrent learning disabilities did not influence stimulant response. CONCLUSIONS: The presence of comorbid anxiety in children with ADHD predicts a less robust response to stimulant treatment and suggests that ADHD with anxiety may constitute a distinct and clinically meaningful subtype of ADHD.

Anxiety Disorders↗

PubMed1996

Behavioral distinctions in children with reading disabilities and/or ADHD.

OBJECTIVE: To investigate behavioral distinctions between children with reading disabilities (RD) and attention-deficit hyperactivity disorder (ADHD). METHOD: A four-group mixed design consisting of children with reading disabilities only (RD only), reading disabilities and ADHD (RD/ADHD), ADHD only, and a comparison group was used. Differences between parent reports, from age 5 to 15 years, and teacher reports, from age 5 to 13 years, were examined on measures of hyperactive and antisocial behaviors. RESULTS: The analyses indicated that, at home, children from the ADHD only and RD/ADHD groups exhibited significantly more hyperactive behaviors than children from the RD only and comparison groups. At school, children from the RD only, ADHD only, and RD/ADHD groups typically exhibited significantly more hyperactive and antisocial behaviors than children from the comparison group. With regard to antisocial behaviors, children from the RD/ADHD group exhibited significantly more antisocial behaviors than children from any other group. CONCLUSIONS: The results of the study indicate that children from these groups may exhibit either a "pervasive" or "situational" presentation of behavioral problems, a finding which suggests that in conducting an evaluation of ADHD it is important to obtain both parent and teacher reports of problem behaviors.

Adolescent↗

PubMed1998

Diagnostic continuity between child and adolescent ADHD: findings from a longitudinal clinical sample.

OBJECTIVE: To determine whether there are differences in the clinical expression and correlates of attention-deficit hyperactivity disorder (ADHD) between children and adolescents. METHOD: Subjects were 6- to 17-year old Caucasian, non-Hispanic boys with and without ADHD. DSM-III-R structured diagnostic interviews, psychometric measures, and blind raters assessed psychiatric diagnoses, intellectual performance, social disability, school failure, and family functioning. RESULTS: Children and adolescents with ADHD had an almost identical pattern of correlates in multiple domains of assessment including psychosocial adversity and comorbidity with conduct, mood, and anxiety disorders. Although the rate of substance abuse differed in comparison between child and adolescent subjects, this was independent of ADHD status. CONCLUSIONS: These findings document the diagnostic continuity of ADHD between childhood and adolescence and support the inclusion of adolescent samples in ADHD research protocols.

Adolescent↗

PubMed1998

Latent class and factor analysis of DSM-IV ADHD: a twin study of female adolescents.

OBJECTIVE: In an attempt to validate the current DSM-IV criteria for attention-deficit/hyperactivity disorder (ADHD) in females and to determine whether symptoms are continuously distributed or categorically discrete, the authors performed factor and latent class analysis on ADHD symptom data from a large general population of adolescent female twins (1,629 pairs). METHOD: A structured diagnostic assessment of DSM-IV ADHD was completed with at least one parent of 1,629 pairs by telephone. ADHD symptoms from 1,549 pairs were subjected to latent class and factor analysis. RESULTS: Latent class and factor analyses were consistent with the presence of separate continuous domains of inattention (ATT), hyperactivity-impulsivity (H-I), and combined ATT with H-I problems. Severe latent classes corresponding to the predominantly inattentive, predominantly hyperactive-impulsive, and combined types were identified with lifetime prevalence estimates of 4.0%, 2.2%, and 3.7%, respectively. Membership in the severe ATT class predicted academic problems, family problems, and referral to health care providers. Membership in the H-I and combined classes also predicted impaired social relationships. CONCLUSIONS: These results suggest that DSM-IV ADHD subtypes can be thought of as existing on separate continua of inattention, hyperactivity-impulsivity, and combined type problems. Membership in any of there severe ADHD latent classes did not preclude academic excellence, but it was associated with different types of impairment and health care-seeking behavior. These data have implications in the areas of diagnosis, classification, treatment, and research.

Adolescent↗