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.     

Aspects of social and emotional competence in adult attention-deficit/hyperactivity disorder

Social and emotional competence were evaluated using self-report and behavioral measures in adults with attention-deficit/hyperactivity disorder (ADHD) and controls. Adults with ADHD viewed themselves as less socially competent but more sensitive toward violations of social norms than controls. Films depicting emotional interactions were used to assess linguistic properties of free recall and perceived emotional intensity. Although adults with ADHD used more words to describe the scenes, they used fewer emotion-related words, despite rating the emotions depicted as more intense than did controls. In contrast, no group differences for words depicting social or cognitive processes were observed. Overall, adults with ADHD appear more aware of their problems in social versus emotional skills. Findings may have implications for improving the psychosocial functioning of these adults.     

Characteristic neurocognitive profile associated with adult attention-deficit/hyperactivity disorder

BACKGROUND: It is now accepted that attention-deficit/hyperactivity disorder (ADHD) often persists into adulthood. However, relative to the considerable literature concerning the profile of neurocognitive deficits associated with this disorder in childhood, equivalent investigations in adult populations have been less common. The current study examined cognitive function in adults diagnosed with ADHD employing well-validated neuropsychological tasks. METHOD: Nineteen adult patients who satisfied DSM-IV criteria for ADHD and 19 matched (gender, age and verbal IQ), non-clinical control subjects were recruited. Patients were either unmedicated or had abstained from a psychostimulant medication regime for at least 24 h prior to neurocognitive assessment. A functionally wide-ranging test battery was administered. RESULTS: Relative to controls, ADHD adults performed significantly worse on spatial working memory, planning, and attentional-set shifting tests and were significantly slower to respond to target stimuli on the go/no-go task. In contrast, the two subject groups performed equivalently on decision-making and pattern/spatial recognition memory assessments. CONCLUSIONS: The demonstration of neuropsychological dysfunction in the adult ADHD cohort provides some support for the validity of this diagnosis in adulthood. In particular, there is broad consistency between the cognitive profile revealed in the current investigation and that previously demonstrated in a study of medication-na?ve ADHD children. There is evidence that frontostriatal function is especially disrupted.     

Experienced emotion and affect recognition in adult attention-deficit hyperactivity disorder

Emotional competence and deficits that may disrupt interpersonal interactions were evaluated in 28 adults with attention-deficit hyperactivity disorder (ADHD) and 28 demographically equivalent controls. Participants completed tasks assessing affect recognition and experienced emotional intensity. Adults with ADHD performed worse in affect recognition than did adults without the disorder; however, the impairment was unrelated to gross perceptual processes, fundamental abilities in facial recognition, or attentional aspects of affect perception. Moreover, intensity of experienced emotion moderated affect recognition: Among controls, experienced emotion facilitated affect recognition. Among adults with ADHD, who reported significantly greater intensity, experienced emotion was inversely related to affect recognition. Results are consistent with theories of ADHD as a deficit in behavioral inhibition; yet, results may merely reflect a constellation of deficits associated with the disorder.     

Linkage study of catechol-O-methyltransferase and attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder is the most common child psychiatric disorder with a prevalence rate in an Ontario study of 9% in boys and 3% in girls [Szatmari et al., 1989]. This disorder is characterized by problems in the areas of attention, overactivity, impulse control, and distractibility. Strong evidence for a genetic component has been provided from twin, family, and adoption studies [for review see Levy et al., 1998] and molecular genetic studies are in progress by several groups worldwide. The Catechol-O-Methyltransferase (COMT) gene is an interesting candidate for ADHD as it is involved in the breakdown of dopamine and norepinephrine, neurotransmitters strongly implicated in the etiology of ADHD. In addition, children with velo-cardio-facial syndrome, a deletion syndrome of the chromosomal region 22q11 where the COMT gene has been localized, often have symptoms of ADHD suggesting this gene may have an etiological role in ADHD. In this study, we have tested for linkage in ADHD families using the functional polymorphism at codon 158 that determines COMT activity [Lachman et al., 1996] and analyzed the data with the transmission disequilibrium test (TDT). A total of 77 nuclear families collected from Toronto were genotyped. We find no evidence for linkage of this polymorphism and ADHD in our sample. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:710-713, 1999.     

Understanding comorbidity: a twin study of reading disability and attention-deficit/hyperactivity disorder.

A community sample of twins in which at least one member of each pair exhibited significant reading difficulties (99 monozygotic and 80 dizygotic pairs) or symptoms of attention-deficit/hyperactivity disorder (ADHD; 83 monozygotic and 78 dizygotic pairs) was used to test the etiology of comorbidity between reading disability (RD) and ADHD. Univariate analyses revealed moderate to high heritability for all measures of reading difficulty and ADHD. Subsequent bivariate analyses indicated that the relation between reading difficulties and inattention symptoms is primarily attributable to common genetic influences, whereas bivariate heritability estimates were not significant for hyperactivity-impulsivity and any of the reading measures. Reading difficulties and ADHD symptoms were more highly heritable if the proband met criteria for both disorders versus RD or ADHD alone, suggesting that future molecular genetic analyses of comorbid RD + ADHD may facilitate the identification of susceptibility genes for RD, ADHD, and their comorbidity.     

Cortical excitability in adult patients with attention-deficit/hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is more and more focused on, and the awareness of adult patients with ADHD increases. Deficits in inhibitory processes in cortical brain areas are discussed as possible causes for ADHD. An easy measurement of these processes is provided by transcranial magnetic stimulation (TMS). We applied single- and double-pulse TMS to the left motor cortex while an electromyogram (EMG) was taken at the abductor pollicis brevis muscle (APB) of the right hand. Intracortical inhibition (SICI) and facilitation (ICF) were measured in ten adult ADHD patients and ten healthy participants using inter-pulse intervals of 2 and 3ms (SICI), and 8 and 15ms (ICF). Furthermore, resting motor threshold (RMT) and latency of the motor evoked potential (MEP) following magnetic stimulation were compared. t-Tests were calculated for statistical analysis. TMS measurements resulted in impaired inhibition in ADHD patients, whereas there were no differences in facilitation, RMT and MEP-latency between groups. Large variability in the patient group was found. This study expands the findings of deficits in inhibition described in earlier studies in children to an adult population, which could be a hint for similar neurophysiological mechanisms underlying ADHD symptomatology in children and adults.     

Stroop interference and attention-deficit/hyperactivity disorder: a review and meta-analysis

Previous reviews and meta-analyses that addressed abnormal Stroop interference in attention-deficit/hyperactivity disorder (ADHD) yielded mixed results. The authors of the present study argue that the inconsistencies may reflect the problematic nature of 2 frequently used methods to quantify Stroop interference-the difference score and Golden's method (C. J. Golden, 1978). Golden's method correction for base-word reading is inadequate, and the difference score is sensitive to the nature of the outcome variable. The latter can be remedied with a ratio score. Contrasting previous meta-analyses, this meta-analysis covers all age groups and all Stroop test variants, and it excludes studies using the Golden quantification method. Mean effect sizes for interference in ADHD as quantified by difference scores relative to control scores were 0.24 across all studies but 1.11 for time-per-item studies; outcome variable was a significant moderator variable, reflecting the sensitivity of the difference score to this variable. Consistency analysis of ratio scores across 19 studies reveals more interference for the ADHD groups relative to the control groups. It is concluded that interference control is consistently compromised in individuals with ADHD.     

儿童家长对注意缺陷多动障碍的知晓率与治疗态度

目的:了解儿童家长对注意缺陷多动障碍(ADHD)的知晓率和治疗态度,为制定ADHD的健康教育和社区干预策略提供依据。方法:抽取6～13岁小学生的家长867名,采用自编儿童注意缺陷多动障碍知晓率调查问卷完成调查,问卷内容围绕一个ADHD典型案例的描述设置15个问题,了解家长对ADHD案例的识别能力、发展趋势与影响程度估计及治疗态度。结果:家长对ADHD的识别率为36.9%;全体家长中,有60.7%的家长认为ADHD对儿童健康造成明显影响,有53.6%的家长认为不需要看医生,61.0%的家长不赞同药物治疗。男性儿童的家长对ADHD的识别率(46.6%vs.58.2%)和认为需要看医生的比例(40.3%vs.50.6%)均低于女性儿童的家长(均P0.05);父亲对ADHD的识别率(44.7%vs.56.2%,61.4%)和影响估计(55.2%vs.65.9%,61.9%)低于母亲或其他长辈(均P0.05),而母亲对药物治疗的接受性低于父亲或其他长辈(33.0%vs.42.3%,50.0%;P0.05)。受教育程度为高中的家长对ADHD的识别率高于初中及以下或大学及以上程度的家长(60.4%vs.48.1%,49.6%;P0.05)。结论:小学生家长对ADHD有关问题的认识还有很多误解或不足,不同家长对ADHD的知晓率和治疗态度也存在差异,有必要开展针对性的ADHD相关知识的健康教育。     

Neuropsychological performance in adult attention-deficit hyperactivity disorder: meta-analysis of empirical data.

Attention-deficit hyperactivity disorder (ADHD) is increasingly recognized not only in children but also in adults. Neuropsychological tests are important tools to quantify the attentional and/or cognitive deficits of patients compared to controls. The present meta-analysis integrates 24 empirical studies reporting results of at least one of 50 standard neuropsychological tests comparing adult ADHD patients with controls. The 50 tests were categorized into the following 10 functional domains: verbal ability, figural problem solving, abstract problem solving, executive function, fluency, simple attention, sustained attention, focused attention, verbal memory, figural memory. For each domain a pooled effect size d' was calculated. Complex attention variables and verbal memory discriminated best between ADHD patients and controls. Effect sizes for these domains were homogeneous and of moderate size (d' between 0.5 and 0.6). In contrast to results reported in children, executive functions were not generally reduced in adult ADHD patients.     

Set shifting in a rodent model of attention-deficit/hyperactivity disorder

Two experiments compared spontaneously hypertensive rats (SHRs; a rodent model of attention-deficit/hyperactivity disorder) and Wistar rats (a normoactive control strain), on the acquisition of a set-shifting strategy. In Experiment 1, SHRs and Wistar rats were equivalent in trials to criterion to learn a brightness or a texture discrimination but SHRs were faster than Wistar rats in shifting to the opposite discrimination when there was 1 or 2 days between the initial discrimination and the shift. In Experiment 2, SHRs and Wistar rats were equivalent in shifting when the shift between discriminations occurred immediately after a criterion had been met in the first discrimination. The results are discussed in terms of a failure of SHRs to store or retrieve an initial discrimination and/or latent inhibition over a delay, leading to faster acquisition of a set-shift. This failure in storage or retrieval may be the result of a hypoactive dopamine system in the prefrontal cortex and nucleus accumbens shell as well as abnormalities in entorhinal cortex in SHRs.     

Conditioned inhibition in a rodent model of attention-deficit/hyperactivity disorder

A deficit in inhibition may underlie some of the symptoms of attention-deficit/hyperactivity disorder (ADHD), particularly impulsivity. However, the data on inhibitory deficits in children with ADHD are mixed. Moreover, there has been little characterization of inhibitory processes in animal models of ADHD. Pavlov's conditioned inhibition procedure allows a direct assessment of the inhibitory status of a stimulus via summation and retardation tests. Therefore, in the current study, we examined conditioned inhibition in spontaneously hypertensive rats (SHRs), the most well-validated animal model of ADHD. SHRs and Wistar rats were trained in a simultaneous feature-negative discrimination in eyeblink conditioning. Each session consisted of a mixture of 2 trial types: a tone paired with a periocular stimulation (A+) or a tone and light presented simultaneously without a periocular stimulation (XA-). Both SHRs and Wistars were able to discriminate A+ from XA- trials. In subsequent summation (X presented simultaneously with a different conditioned excitor, B) and retardation (X paired with the periocular stimulation) tests, the presence of inhibition to X was confirmed in both SHRs and Wistars: X reduced responding to B, and X was slow to develop excitation when paired with periocular stimulation. These results are the first to demonstrate Pavlovian conditioned inhibition in SHRs and to use summation and retardation tests to confirm X as a conditioned inhibitor. The data indicate that conditioned inhibition is intact in SHRs; thus, inhibitory processes that do not require prefrontal cortex or cerebellum may be normal in this strain.     

The neurophysiology of attention-deficit/hyperactivity disorder.

Recent reviews of the neurobiology of Attention-Deficit/Hyperactivity Disorder (AD/HD) have concluded that there is no single pathophysiological profile underlying this disorder. Certainly, dysfunctions in the frontal/subcortical pathways that control attention and motor behavior are implicated. However, no diagnostic criteria or behavioral/neuroimaging techniques allow a clear discrimination among subtypes within this disorder, especially when problems with learning are also considered. Two major Quantitative EEG (QEEG) subtypes have been found to characterize AD/HD. Here we review the major findings in the neurophysiology of AD/HD, focusing on QEEG, and briefly present our previous findings using a source localization technique called Variable Resolution Electromagnetic Tomography (VARETA). These two techniques represent a possible objective method to identify specific patterns corresponding to EEG-defined subtypes of AD/HD. We then propose a model representing the distribution of the neural generators in these two major AD/HD subtypes, localized within basal ganglia and right anterior cortical regions, and hippocampal, para-hippocampal and temporal cortical regions, respectively. A comprehensive review of neurochemical, genetic, neuroimaging, pharmacological and neuropsychological evidence in support of this model is then presented. These results indicate the value of the neurophysiological model of AD/HD and support the involvement of different neuroanatomical systems, particularly the dopaminergic pathways.     

Neuropsychology of adults with attention-deficit/hyperactivity disorder: a meta-analytic review

A comprehensive, empirically based review of the published studies addressing neuropsychological performance in adults diagnosed with attention-deficit/hyperactivity disorder (ADHD) was conducted to identify patterns of performance deficits. Findings from 33 published studies were submitted to a meta-analytic procedure producing sample-size-weighted mean effect sizes across test measures. Results suggest that neuropsychological deficits are expressed in adults with ADHD across multiple domains of functioning, with notable impairments in attention, behavioral inhibition, and memory, whereas normal performance is noted in simple reaction time. Theoretical and developmental considerations are discussed, including the role of behavioral inhibition and working memory impairment. Future directions for research based on these findings are highlighted, including further exploration of specific impairments and an emphasis on particular tests and testing conditions.     

Controlled visuomotor preparation deficits in attention-deficit/hyperactivity disorder

To the best of the authors' knowledge, there are no published reports on visuomotor preparation in attention-deficit/hyperactivity disorder (ADHD). This is unfortunate, because research suggests that ADHD is an output-related deficit, and suboptimal execution of tasks may be the result of incomplete visuomotor preparation. The authors compared 19 children with ADHD with 124 healthy and 120 pathological controls in terms of their performance (speed, speed variability, and accuracy) on the finger precuing test, a test measuring (automatic and controlled) visuomotor preparation. The data implied that children with ADHD have an impaired ability to engage in effortful, controlled visuomotor preparation activities. Fast, automatic response preparation was not affected by ADHD. In addition, children with ADHD showed more variability in overall test performance than other children. No group differences were found in response accuracy.     

Planning ability in adults with attention-deficit/hyperactivity disorder

Planning ability was investigated in 26 patients diagnosed with attention-deficit/hyperactivity disorder in adulthood and in 27 control participants, with groups matched for age, predicted IQ, and social class. They were tested using the 3-dimensional computerized Tower of London Test (Morris, Ahmed, Syed, & Toone, 1993; Morris, Rushe, Woodruffe, & Murray, 1995), which measures planning latencies as well as accuracy, with problems increasing in graded difficulty. For the control group, planning latencies increased systematically with task difficulty, with the participants slowing their initial responses to ensure accuracy. For those with attention-deficit/hyperactivity disorder, there was no increase in planning time and a corresponding diminution in accuracy on the most difficult problems. This pattern of impairment is interpreted as resulting from failure to inhibit responses when confronted with problem solving, leading to reduced planning activity.