Attention deficit disorder without hyperactivity: a distinct behavioral and neurocognitive syndrome

Probe-caught spontaneous and deliberate mind wandering in relation to self-reported inattentive, hyperactive and impulsive traits in adults

Research has revealed a positive relationship between types of mind wandering and ADHD at clinical and subclinical levels. However, this work did not consider the relationship between mind wandering and the core symptoms of ADHD: inattention, hyperactivity and impulsivity. Given that the DMS-V attributes mind wandering to inattention only, and that only inattention is thought to result from impairment to the executive function linked to mind wandering, the present research sought to examine this relationship in 80 undiagnosed adults. Using both standard and easy versions of the Sustained Attention to Response Task (SART) we measured both spontaneous and deliberate mind wandering. We found that spontaneous mind wandering was related to self-reported inattentive traits when the task was cognitively more challenging (standard SART). However, hyperactive and impulsive traits were related to spontaneous mind wandering independent of task difficulty. The results suggest inattentive traits are not uniquely related to mind wandering; indeed, adults with hyperactive/impulsive traits were more likely to experience mind wandering, suggesting that mind wandering might not be useful diagnostic criteria for inattention.

Ulk4 deficiency leads to hypomyelination in mice

Brain nerve fibers are insulated by myelin which is produced by oligodendrocytes. Defects in myelination are increasingly recognized as a common pathology underlying neuropsychiatric and neurodevelopmental disorders, which are associated with deletions of the Unc-51-like kinase 4 (ULK4) gene. Key transcription factors have been identified for oligodendrogenesis, but little is known about their associated regulators. Here we report that Ulk4 acts as a key regulator of myelination. Myelination is reduced by half in the Ulk4^tm1a/tm1a hypomorph brain, whereas expression of axonal marker genes Tubb3, Nefh, Nefl and Nefm remains unaltered. Transcriptome analyses reveal that 8 (Gfap, Mbp, Mobp, Plp1, Slc1a2, Ttr, Cnp, Scd2) of the 10 most significantly altered genes in the Ulk4^tm1a/tm1a brain are myelination-related. Ulk4 is co-expressed in Olig2⁺ (pan-oligodendrocyte marker) and CC1⁺ (mature myelinated oligodendrocyte marker) cells during postnatal development. Major oligodendrogeneic transcription factors, including Olig2, Olig1, Myrf, Sox10, Sox8, Sox6, Sox17, Nkx2-2, Nkx6-2 and Carhsp1, are significantly downregulated in the mutants. mRNA transcripts enriched in oligodendrocyte progenitor cells (OPCs), the newly formed oligodendrocytes (NFOs) and myelinating oligodendrocytes (MOs), are significantly attenuated. Expression of stage-specific oligodendrocyte factors including Cspg4, Sox17, Nfasc, Enpp6, Sirt2, Cnp, Plp1, Mbp, Ugt8, Mag and Mog are markedly decreased. Indirect effects of axon caliber and neuroinflammation may also contribute to the hypomyelination, as Ulk4 mutants display smaller axons and increased neuroinflammation. This is the first evidence demonstrating that ULK4 is a crucial regulator of myelination, and ULK4 may therefore become a novel therapeutic target for hypomyelination diseases.

Double-Deficit Hypothesis in a Clinical Sample: Extension Beyond Reading

This study explored the double-deficit hypothesis (DDH) in a transparent orthography (Finnish) and extended the view from reading disabilities to comorbidity of learning-related problems in math and attention. Children referred for evaluation of learning disabilities in second through sixth grade (N = 205) were divided into four groups based on rapid automatized naming (RAN) and phonological awareness (PA) according to the DDH: the double-deficit group, the naming speed deficit-only group, the phonological deficit-only group, and the no-deficit group. The results supported the DDH in that the prevalence and severity of reading disability were greatest in the double-deficit group. Despite the greater prevalence of reading disabilities in single-deficit groups compared to the no-deficit group, the means of reading measures in the single-deficit groups were similar to those of the no-deficit group. The PA single-deficit group was poorer in spelling than the no-deficit group and single-naming-deficit group. Deficits in RAN or PA were primarily linked to reading disabilities but not with math or attention problems. The results supported the DDH partially and indicate that deficits in RAN and PA are specific to reading disabilities.

Differential Validity of the BASC Student Observation System and the BASC Teacher Rating Scale

This study evaluated the differerrtial validity of the BASC Teacher Rating Scale (TRS) and the BASC Student Observation System (SOS) in the differentintion of nondisabled children from children with an ADHD diagnosis, and children with only an ADHD dingrrosis from children with ADHD and comorbid dingnoses. The results indicated that the TRS and SOS exhibited good differential validity. The group differences that were found were consistent with the definition of ADHD, and a good classification rate was found for the TRS and SOS (73%). The Predictive Discriminant Analysis also indicated, however, that the SOS does not contribute a sufficient amount of information above and beyond that obtained from the TRS alone.

Neurofeedback: A Comprehensive Review on System Design, Methodology and Clinical Applications

Neurofeedback is a kind of biofeedback, which teaches self-control of brain functions to subjects by measuring brain waves and providing a feedback signal. Neurofeedback usually provides the audio and or video feedback. Positive or negative feedback is produced for desirable or undesirable brain activities, respectively. In this review, we provided clinical and technical information about the following issues: (1) Various neurofeedback treatment protocols i.e. alpha, beta, alpha/theta, delta, gamma, and theta; (2) Different EEG electrode placements i.e. standard recording channels in the frontal, temporal, central, and occipital lobes; (3) Electrode montages (unipolar, bipolar); (4) Types of neurofeedback i.e. frequency, power, slow cortical potential, functional magnetic resonance imaging, and so on; (5) Clinical applications of neurofeedback i.e. treatment of attention deficit hyperactivity disorder, anxiety, depression, epilepsy, insomnia, drug addiction, schizophrenia, learning disabilities, dyslexia and dyscalculia, autistic spectrum disorders and so on as well as other applications such as pain management, and the improvement of musical and athletic performance; and (6) Neurofeedback softwares. To date, many studies have been conducted on the neurofeedback therapy and its effectiveness on the treatment of many diseases. Neurofeedback, like other treatments, has its own pros and cons. Although it is a non-invasive procedure, its validity has been questioned in terms of conclusive scientific evidence. For example, it is expensive, time-consuming and its benefits are not long-lasting. Also, it might take months to show the desired improvements. Nevertheless, neurofeedback is known as a complementary and alternative treatment of many brain dysfunctions. However, current research does not support conclusive results about its efficacy.

Assessing Attention Deficit by Binocular Rivalry

OBJECTIVE

To determine whether the frequency and duration of the periods of suppression of a percept in a binocular rivalry (BR) task can be used to distinguish between participants with ADHD and controls.

METHOD

A total of 122 participants (6-15 years) were assigned to three groups: ADHD-Combined (ADHD-C), ADHD-Predominantly Inattentive (ADHD-I), and controls. They each performed a BR task and two measures were recorded: alternation rate and duration of exclusive dominance periods.

RESULTS

ADHD-C group presented fewer alternations and showed greater variability than did the control group; results for the ADHD-I group being intermediate between the two. The duration of dominance periods showed a differential profile: In control group, it remained stable over time, whereas in the clinical groups, it decreased logarithmically as the task progressed.

CONCLUSION

The differences between groups in relation to the BR indicators can be attributed to the activity of involuntary inhibition.

Effects of methylphenidate on acute math performance in children with attention-deficit hyperactivity disorder

OBJECTIVE

Examine the short-term (acute) effects of methylphenidate (MPH) on math performance in children with attention-deficit hyperactivity disorder (ADHD) and what factors predict improvement in math performance.

METHOD

One hundred ninety-eight children with ADHD participated in a double-blind, placebo-controlled, randomized crossover MPH trial. Math response to MPH was determined through administration of math problems adjusted to their academic level during the Restricted Academic Situation Scale (RASS). Student t tests were conducted to assess change in math performance with psychostimulants. Correlation between change on the RASS and change on the math performance was also examined. Linear regression was performed to determine predictor variables.

RESULTS

Children with ADHD improved significantly in their math with MPH (P < 0.001). The degree of improvement on the RASS (which evaluates motor activity and orientation to task) and on math performance on MPH was highly correlated. A child's age at baseline and Wechsler Individual Achievement Test (WIAT)-Numerical Operations standard scores at baseline accounted for 15% of variances for acute math improvement.

CONCLUSIONS

MPH improves acute math performance in children with ADHD. Younger children with lower math scores (as assessed by the WIAT) improved most on math scores when given psychostimulants.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00483106.

WISC-IV profiles are associated with differences in symptomatology and outcome in children with ADHD

OBJECTIVE

The current study investigated the Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) cluster profiles of children with ADHD to examine the association between IQ profiles and diagnostic frequency, symptomatology, and outcome in this population.

METHOD

Hierarchical cluster analysis was conducted on 189 children with a diagnosis of ADHD-inattentive (ADHD-I) and ADHD-combined (ADHD-C) subtypes. Clusters were then compared across symptom rating scale factor scores, behavioral rating scales, and achievement scores.

RESULTS

A five-cluster solution was extracted. One cluster was identified to have reduced processing speed relative to other WISC-IV indexes and significantly higher ratings of inattention and incidence of ADHD-I diagnosis. A second cluster had impairments in processing speed and working memory and was associated with impaired behavioral functioning.

CONCLUSION

Findings support a relationship between reduced processing speed and inattention and provide evidence that WISC-IV profiles may be helpful in predicting symptomatology and outcome in children with ADHD.

Emergent literacy skills, behavior problems and familial antecedents of reading difficulties: a follow-up study of reading achievement from kindergarten to fifth grade

This study examined the relation between emergent literacy skills, teachers' reports of behavioral problems, and word reading achievement in a community sample of French students. Family background was investigated and included familial antecedents of reading difficulties (Fa/Rd) and parents' educational level. The analyses explored the pattern of concurrent relations between behavioral, familial and emergent literacy measures in a sample of 812 preschoolers, and their predictive power in explaining word reading achievement in a sub-sample of 150 children followed from kindergarten to fifth grade. Word reading at fifth grade was predicted by kindergarten measures of phonological awareness and letter knowledge. Teachers' reports of inattention symptoms at each grade level were associated with early reading skills and with subsequent word reading. Fa/Rd were concurrently and longitudinally associated with emergent literacy skills, teachers' reported inattention and word reading. These results indicate that children with a family history of reading difficulties are at increased risk for the co-occurrence of reading difficulties and attention problems from kindergarten onward. These findings confirm the shared influence of Fa/Rd on the comorbidity between inattention symptoms and reading difficulties in a non-diagnosed community sample of preschool children followed through late elementary school.

Processing speed weakness in children and adolescents with non-hyperactive but inattentive ADHD (ADD)

DSM-IV-TR defines ADHD-Predominantly Inattentive as allowing up to five symptoms of hyperactivity/impulsivity, while theories of the inattentive type usually assume a group that is hypoactive and characterized by processing speed and cognitive interference deficits. In a community-recruited sample of 572 children and adolescents, a pure inattentive subtype of ADHD (ADD) was defined as those who met DSM-IV-TR criteria for ADHD-PI but had two or fewer hyperactive/impulsive symptoms. Processing and output speeds of those with ADD were compared to those identified with DSM-IV-TR ADHD combined type and non-ADHD controls. These results were then contrasted with those found when DSM-IV-TR defined ADHD-PI was compared with ADHD-C and controls. Processing and output speed were assessed with the Trailmaking A and B and the Stroop Naming Tests. Cognitive interference control was assessed with the interference score from the Stroop Task. Slower cognitive interference speed was found in the ADD vs. ADHD-C and controls comparisons, but not the ADHD-PI versus ADHD-C and controls comparisons. On output speed measures, ADD exhibited the slowest performance, significantly different from controls and the effect size for the set-shifting speed contrast (Trailmaking B) was double that of the ADHD-PI vs. control comparison. ADHD-Inattentive type as defined by the DSM-IV-TR is a heterogeneous condition with a meaningful proportion of those affected exhibiting virtually no hyperactive/impulsive symptoms. This subgroup may represent a distinct inattentive condition characterized by poor cognitive interference control and slow processing or output speed.

Cognitive control and attentional selection in adolescents with ADHD versus ADD

An important research question is whether Attention Deficit Hyperactivity Disorder (ADHD) is related to early- or late-stage attentional control mechanisms and whether this differentiates a nonhyperactive subtype (ADD). This question was addressed in a sample of 145 ADD/ADHD and typically developing comparison adolescents (aged 13-17). Attentional blink and antisaccade tasks were used to assay early- and late-stage control, respectively. ADD was defined using normative cutoffs to ensure low activity level in children who otherwise met full criteria for ADHD. The ADD group had an attenuated attentional blink versus controls and ADHD-combined. The effect was not produced using DSM--IV definition of ADHD-primarily inattentive type or DSM symptom counts. ADHD-combined showed greater weakness in response inhibition, as manifest in the antisaccade task. Combining tasks yielded an interaction differentiating group performance on the two tasks.

ADHD subtypes and co-occurring anxiety, depression, and oppositional-defiant disorder: differences in Gordon diagnostic system and Wechsler working memory and processing speed index scores

OBJECTIVE

Wechsler Intelligence Scale for Children Freedom-from-Distractibility/Working Memory Index (FDI/WMI), Processing Speed Index (PSI), and Gordon Diagnostic System (GDS) scores in ADHD children were examined as a function of subtype and coexisting anxiety, depression, and oppositional-defiant disorder.

METHOD

Participants were 587 children with ADHD combined type (alone, with oppositional-defiant disorder, and with anxiety or depression) and ADHD inattentive type (alone and with anxiety or depression).

RESULTS

Attention scores (FDI/WMI and GDS Vigilance and Distractibility) were similar and low for all groups. ADHD combined groups had greater impulsivity (GDS Delay) than ADHD inattentive groups, and ADHD inattentive groups had slower processing speed (PSI) than ADHD combined groups. Comorbidity did not affect test performance. Scores differentiated ADHD subtypes with 72% accuracy.

CONCLUSION

Findings support the validity of DSM-IV ADHD combined and inattentive subtypes and the validity of the GDS, FDI/WMI, and PSI in assessing attention, impulsivity, and processing speed in children with ADHD.

Prevalence rates of attention deficit/hyperactivity disorder in a school sample of Venezuelan children

A total of 1,535 4-12 year-old children were screened with the Conners' rating scales, followed by diagnostic confirmation by the diagnostic interview schedule for children-IV-parent version. The prevalence of ADHD was estimated to be 10.03%, and only 3.9% of children had received medication for the treatment of ADHD symptoms. Prevalence rates and demographic profile of Venezuelan children with ADHD are very similar to those found in samples from other countries. Authorities need to develop public health policies to correctly identify and treat affected subjects. Furthermore, clinicians must actively search for children with ADHD in order to provide the best-available treatment.

ADHD subtypes and comorbid anxiety, depression, and oppositional-defiant disorder: differences in sleep problems

OBJECTIVE

Sleep problems were analyzed in children with ADHD (Attention-deficit hyperactivity disorder).

METHODS

Scales were completed by parents of 135 control children and 681 children with ADHD combined type (ADHD-C) or inattentive type (ADHD-I) with or without comorbid oppositional defiant disorder (ODD), anxiety, or depression.

RESULTS

Children with ADHD-I alone had the fewest sleep problems and did not differ from controls. Children with ADHD-C had more sleep problems than controls and children with ADHD-I. Comorbid anxiety/depression increased sleep problems, whereas ODD did not. Daytime sleepiness was greatest in ADHD-I and was associated with sleeping more (not less) than normal. Medicated children had greater difficulty falling asleep than unmedicated children.

CONCLUSIONS

Differences in sleep problems were found as a function of ADHD subtype, comorbidity, and medication.

Dysfunction of right-hemisphere attentional networks in attention deficit hyperactivity disorder

Although differential right-hemisphere dysfunction has been implicated in attention deficit hyperactivity disorder (ADHD) for more than 15 years, this relation remains controversial. Neuroimaging studies suggest asymmetric dysfunction, but neuropsychological evidence in support of this is rather inconsistent. This study examined attentional asymmetry in ADHD adults with a psychophysical extinction task. The interference from right- or left-hemifield distractors with contralateral orientation sensitivity was determined. In a previous study using this paradigm, right brain-damaged patients with left neglect displayed asymmetric distractor interference, meaning a significant interference from a right distractor with left-hemifield orientation sensitivity but no interference from a left distractor with right-hemifield orientation sensitivity. A similar but less pronounced asymmetry was observed in a group of ADHD adults (n = 16). These results indicate dysfunction of right-hemisphere attentional circuits in ADHD.

Attention problems and hyperactivity as predictors of college grade point average

OBJECTIVE

This study examined the relative contributions of measures of attention problems and hyperactivity to the prediction of college grade point average (GPA).

METHOD

A sample of 316 students enrolled in introductory psychology and sociology classes at a southeastern university completed the BASC-2 Self-Report of Personality College Form. Scores on the attention problems scale and the hyperactivity scale of the BASC-2 were entered into a regression equation as predictors of cumulative GPA.

RESULTS

Each of the independent variables made a significant contribution to the prediction of GPA. Attention problem scores alone explained 7% of the variability in GPAs. The addition of hyperactivity scores to the equation produced a 2% increase in explanatory power.

CONCLUSION

The implications of these results for assessing symptoms of inattention and hyperactivity in college students are discussed.

ADHD subtype differences in motivational responsivity but not inhibitory control: evidence from a reward-based variation of the stop signal paradigm

In this study we examined prepotent motor inhibition and responsiveness to reward using a variation of the stop signal reaction time (SSRT) task in clinic- and community-recruited children ages 7 to 12 with attention-deficit/hyperactivity disorder-inattentive type (ADHD-I), ADHD-combined type (ADHD-C), and non-ADHD controls. Contrary to theoretical expectations, we found evidence for inhibitory weaknesses in ADHD-I. We also found evidence that although children with ADHD-I were able to improve their inhibitory control given reward-based motivation, the improvement depended on the order of reward conditions. Results suggest that the 2 primary subtypes of ADHD share similar neuropsychological weaknesses in inhibitory control but that there are subtype differences in response to success and failure that contribute to a child's ultimate level of performance.

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.

Antisocial behaviors moderate the deviant peer pathway to substance use in children with ADHD

This study evaluated the interplay of attention deficit hyperactivity disorder (ADHD) symptom severity, deviant peer group affiliation, oppositional defiant disorder (ODD), and conduct disorder (CD) as risk factors among 142 adolescents with childhood ADHD. Deviant peer affiliation mediated the relation between childhood ADHD symptoms and 6 substance use and abuse variables. Moreover, moderated mediation analyses found that for children with high levels of ODD and CD symptoms, the mediated effect of ADHD through deviant peer affiliation was significant; however, for children with low levels of ODD and CD symptoms, this mediated effect was weak and nonsignificant. Results suggest that children with severe ADHD symptomatology and comorbid antisocial behavior are at highest risk for peer-mediated substance use in adolescence.

Attentional versus motor inhibition in adults with attention-deficit/hyperactivity disorder

Faulty inhibition is theorized to be a central feature in attention-deficit/hyperactivity disorder (ADHD), but it remains unclear whether inhibitory impairments encompass both motoric and attentional domains. Further, characterization of inhibitory deficits in adults with ADHD is needed. We experimentally assessed adults who met diagnostic criteria for ADHD and a subgroup who had partially remitted. Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) subtype effects were also examined. Motoric inhibition was assessed with the antisaccade task, and attentional inhibition was assessed with the attentional blink (AB) task. Antisaccade results replicated prior findings of extended latencies and increased anticipatory saccades in ADHD. Errors, however, appeared to be epiphenomenal to ADHD as they were absent when symptoms had partially remitted. Anticipatory saccades appeared as potential core problems that remained even when symptoms had improved. Differential response patterns were found for predominantly inattentive and combined subtypes, with the latter showing increasing anticipatory movements with increasing fixation time. In the AB task, ADHD groups committed more errors but showed no convincing evidence of an abnormal blink. These results demonstrate clear effects on motoric inhibition but not attentional inhibition in adults with ADHD.

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.

Subtypes of attention-deficit/hyperactivity disorder (ADHD): distinct or related disorders across measurement levels?

The aim of this literature review is to assess the current state of knowledge regarding differences and similarities between the inattentive (IA) and combined (C) subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) in order to detail challenges concerning further conceptualization, diagnostics, and treatment. The literature on ADHD-IA and ADHD-C was reviewed and contrasted across genetic, neuroanatomical, neurophysiological/ neurochemical, neuro(psycho)logical, and clinical psychiatric measurement levels. It was found that the more fundamental the measurement level, the less unambiguous evidence is found for subtype differences. Only on the clinical psychiatric diagnostic level, do more or less clear-cut differences in cognitive, social, academic, and behavioural functioning emerge. In conclusion, fundamental research that compares ADHD-IA and ADHD-C is relatively rare. At this point, only irrefutable phenomenological evidence of subtype differences seems to be available, even in attention problems which are presumed to be identical. The question as to whether both subtypes should be considered as two independent disorders was not adequately resolved.

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.

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.

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.

Deficient attention is hard to find: applying the perceptual load model of selective attention to attention deficit hyperactivity disorder subtypes

BACKGROUND

Whether selective attention is a primary deficit in childhood Attention Deficit Hyperactivity Disorder (ADHD) remains in active debate.

METHODS

We used the perceptual load paradigm to examine both early and late selective attention in children with the Primarily Inattentive (ADHD-I) and Combined subtypes (ADHD-C) of ADHD.

RESULTS

No evidence emerged for selective attention deficits in either of the subtypes, but sluggish cognitive tempo was associated with abnormal early selection.

CONCLUSIONS

At least some, and possibly most, children with DSM-IV ADHD have normal selective attention. Results support the move away from theories of attention dysfunction as primary in ADHD-C. In ADHD-I, this was one of the first formal tests of posterior attention network dysfunction, and results did not support that theory. However, ADHD children with sluggish cognitive tempo (SCT) warrant more study for possible early selective attention deficits.

Larger deficits in brain networks for response inhibition than for visual selective attention in attention deficit hyperactivity disorder (ADHD)

BACKGROUND

Brain activation differences between 12 control and 12 attention deficit hyperactivity disorder (ADHD) children (9- to 12-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI).

METHOD

Visual selective attention was measured with the visual search of a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go/no-go task.

RESULTS

There were limited group differences in the selective attention task, with control children showing significantly greater intensity of activation in a small area of the superior parietal lobule region of interest. There were large group differences in the response inhibition task, with control children showing significantly greater intensity of activation in fronto-striatal regions of interest including the inferior, middle, superior and medial frontal gyri as well as the caudate nucleus and globus pallidus.

CONCLUSION

The widespread hypoactivity for the ADHD children on the go/no-go task is consistent with the hypothesis that response inhibition is a specific deficit in attention deficit hyperactivity disorder.

Developmental timing of exposure to elevated levels of phenylalanine is associated with ADHD symptom expression

This study addresses attention deficit hyperactivity disorder (ADHD), with a focus on how the timing of a known biological insult affects ADHD symptom expression. The sample consists of children exposed to elevated levels of phenylalanine, either postnatally as in Phenylketonuria (PKU; n = 46) or prenatally as in Maternal PKU (MPKU; n = 15). Non-hyperphenylalaninemic siblings of children with PKU (n = 18) serve as controls. Results indicate that elevated levels of phenylalanine are associated with ADHD symptoms. The manifestations of the symptom expression are dependent on exposure timing: prenatal exposure is associated with a higher likelihood of expressing hyperactive/impulsive symptoms and postnatal exposure is associated with a higher likelihood of expressing inattentive symptoms. This toxicity is dose-dependent and higher levels of phenylalanine appear more detrimental.

A chart review study of the inattentive and combined types of ADHD

Studies of the clinical correlates of the subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) have identified differences in the representation of age, gender, prevalence, comorbidity, and treatment. We report retrospective chart review data detailing the clinical characteristics of the Inattentive (IA) and Combined (C) subtypes of ADHD in 143 cases of ADHD-IA and 133 cases of ADHD-C. The children with ADHD-IA were older, more likely to be female, and had more comorbid internalizing disorders and learning disabilities. Individuals in the ADHD-IA group were two to five times as likely to have a referral for speech and language problems. The children with ADHD-IA were rated as having less overall functional impairment, but did have difficulty with academic achievement. Children with ADHD-IA were less likely to be treated with stimulants. One eighth of the children with ADHD-IA still had significant symptoms of hyperactivity/impulsivity, but did not meet the DSM-IV threshold for diagnosis of ADHD-Combined Type. The ADHD-IA subtype includes children with no hyperactivity and children who still manifest clinically significant hyperactive symptomatology but do not meet DSM-IV criteria for Combined Type. ADHD-IA children are often seen as having speech and language problems, and are less likely to receive medication treatment, but respond to medical treatment with improvement both in attention and residual hyperactive/impulsive symptoms.

Preadolescent girls with attention-deficit/hyperactivity disorder: II. Neuropsychological performance in relation to subtypes and individual classification

This study examined executive functions, motor speed, and language processing in a diverse, preadolescent sample of 93 girls with attention-deficit/hyperactivity disorder (ADHD) combined type, 47 ADHD inattentive type, and 88 age- and ethnicity-matched comparison girls. Testing was performed without stimulant medication. All 10 neuropsychological variables showed significant omnibus subgroup differences, with 8 of 10 combined versus comparison contrasts significant (average effect size medium) and 6 of 10 inattentive versus comparison contrasts significant (average effect size small to medium), but only 2 of 10 combined versus inattentive contrasts significant (average effect size small). Results were robust to statistical control of demographic variables, comorbidities, and IQ. Discriminant function analysis revealed relatively high sensitivity but only modest specificity in predicting ADHD from comparison status from test performance; classification of the inattentive type was extremely poor.

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

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

A randomized double-blind, placebo-controlled study of the effects of supplementation with highly unsaturated fatty acids on ADHD-related symptoms in children with specific learning difficulties

(1) The authors tested the prediction that relative deficiencies in highly unsaturated fatty acids (HUFAs) may underlie some of the behavioral and learning problems associated with attention-deficit/hyperactivity disorder (ADHD) by studying the effects of HUFA supplementation on ADHD-related symptoms in children with specific learning difficulties (mainly dyslexia) who also showed ADHD features. (2) Forty-one children aged 8-12 years with both specific learning difficulties and above-average ADHD ratings were randomly allocated to HUFA supplementation or placebo for 12 weeks. (3) At both baseline and follow-up, a range of behavioral and learning problems associated with ADHD was assessed using standardized parent rating scales. (4) At baseline, the groups did not differ, but after 12 weeks mean scores for cognitive problems and general behavior problems were significantly lower for the group treated with HUFA than for the placebo group; there were significant improvements from baseline on 7 out of 14 scales for active treatment, compared with none for placebo. Group differences in change scores all favored HUFA, reaching conventional significance levels for 3 out of 14 scales. (5) HUFA supplementation appears to reduce ADHD-related symptoms in children with specific learning difficulties. Given the safety and tolerability of this simple treatment, results from this pilot study strongly support the case for further investigations.

Interhemispheric asymmetry of regional cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder

The prefrontal cortex is asymmetric in both structure and function. In normal subjects, the right prefrontal cortex is activated more than the left during response inhibition. Patients with attention deficit hyperactivity disorder (ADHD) have impaired response inhibition and altered structural interhemispheric asymmetry. This study was conducted to examine the functional interhemispheric asymmetry during response inhibition in children with ADHD. Subjects were divided into three groups according to the level of motor hyperactivity. Blood flow tracer (99m)Tc-ethyl cysteinate dimer was injected while subjects were performing a response inhibition task (RIT), followed by single photon emission computerized tomography (SPECT). After three-dimensional reconstruction, filtering and smoothing, individual scans were morphed to a template. Three average group images were created from individual scans. Each average group image was subtracted voxel-by-voxel from its mirror image to compare the regional cerebral blood flow (rCBF) in the right and left cerebral hemispheres, yielding images of significant interhemispheric rCBF asymmetry. The severe hyperactivity group exhibited most prefrontal left>right rCBF asymmetry and left>right occipitoparietal asymmetry. Reversal of functional prefrontal asymmetry in boys with severe motor hyperactivity supports the hypothesis of right prefrontal cortex dysfunction in ADHD.

Comorbidade em crianças e adolescentes com transtorno do déficit de atenção: resultados preliminares

Trinta e quatro crianças e adolescentes com idades entre 6 e 16 anos, com diagnóstico de transtorno do déficit de atenção com hiperatividade (TDAH) segundo a DSM-IV, foram examinadas e avaliadas quanto a comorbidade com outros transtornos psiquiátricos através do questionário padronizado P-CHIPS aplicado aos pais. Observou-se expressiva ocorrência de transtornos comórbidos (85,7%), sendo o transtorno opositivo-desafiador (20,6%) e o transtorno de conduta (39,2%) os mais comuns. Pelo menos dois outros diagnósticos que não o de TDAH puderam ser observados em 57% da amostra. A depressão maior pode ser diagnosticada em quatro casos e quadros ansiosos (transtorno de ansiedade generalizada, ansiedade de separação e fobias) foram observados em 34,3% da amostra. A presença de comorbidade altera de modo significativo o prognóstico da enfermidade e pode sugerir estratégias terapêuticas específicas dependendo de cada caso. A comorbidade frequente também pode sugerir a necessidade do uso de entrevistas diagnósticas que contemplam outros transtornos psiquiátricos.

Symptom properties as a function of ADHD type: an argument for continued study of sluggish cognitive tempo

Inconsistent alertness and orientation (sluggishness, drowsiness, daydreaming) were reported to accompany Attention Deficit Disorder (ADD) without Hyperactivity in DSM-III. Such Sluggish Cognitive Tempo items were tested in the DSM-IV Field Trial for ADHD, but were discarded from the Inattention symptom list because of poor negative predictive power. Using 692 children referred to a pediatric subspecialty clinic for ADHD, Sluggish Tempo items were re-evaluated. When Hyperactivity-Impulsivity was absent (i.e., using only cases of Inattentive Type plus clinic controls), Sluggish Tempo items showed substantially improved utility as symptoms of Inattention. Factor analyses distinguished a Sluggish Tempo factor from an Inattention factor. When DSM-IV ADHD types were compared, Inattentive Type was uniquely elevated on Sluggish Tempo. These findings suggest that (a) Sluggish Tempo items are adequate symptoms for Inattentive Type, or (b) Sluggish Tempo may distinguish two subtypes of Inattentive Type. Either conclusion is incompatible with ADHD nosology in DSM-IV.

Multimethod assessment of psychopathology among DSM-IV subtypes of children with attention-deficit/hyperactivity disorder: self-, parent, and teacher reports

Using data based on self-, parent, and teacher reports, we assessed various aspects of psychopathology in a large sample of control children and those with ADHD. Confirmatory factor analysis was employed to extract response bias from latent constructs of aggression, anxiety, attention problems, depression, conduct disorder, and hyperactivity. These latent constructs were then entered into logistic regression equations to predict membership in control versus ADHD groups, and to discriminate between ADHD subtypes. Results of the regression equations showed that higher levels of attention problems and aggression were the best predictors of membership in the ADHD group relative to controls. Logistic regression also indicated that a higher degree of aggression was the only significant predictor of membership in the ADHD-Combined group compared to the ADHD-Inattentive group. However, when comorbid diagnoses of Oppositional Defiant Disorder and Conduct Disorder were controlled for in the logistic regression, greater hyperactivity rather than aggression was the sole variable with which to distinguish the ADHD-Combined from the ADHD-Inattentive subtype. Results are discussed in the context of the DSM-IV ADHD nosology and the role of instrument and source bias in the diagnosis of ADHD.

Inattentive behavior in childhood: epidemiology and implications for development

Poor concentration is a relatively common childhood problem. The current North American psychiatric diagnostic classification system (Diagnostic and Statistical Manual of Mental Disorders, fourth edition; DSM-IV), American Psychological Association, 1994) differentiates children whose problems are distinguished primarily by symptoms of inattention (ADHD-I) from those whose difficulties are characterized by overactive, impulsive behavior by providing various subtypes within a broad diagnostic category. Yet, comparatively little is known about children who exhibit purely inattentive behavior. This study aims to redress this issue by using a large, community-based, epidemiological sample of 7-year-old children to compare the developmental functioning, social, and environmental backgrounds of children with pure inattentive behavior to that of children with pure overactive behavior and combined problems of inattentive and overactive behavior. Five hypotheses, centered on the validity of distinguishing inattentive behavior from overactivity, are tested. Children with pure inattentive behavior were more likely to have general cognitive delays, particularly in the area of language development, and were more likely to come from a family in which the father was of low occupational status. The results are discussed in relation to the implications for research and the identification of needs and intervention with children who exhibit pure inattentive behavior.