This fMRI study of 126 youth explored whether the neural mechanisms underlying the N-back task, commonly used to examine executive control over the contents of working memory, are associated with ...individual differences in academic achievement in reading and math. Moreover, the study explored whether these relationships occur regardless of the nature of the stimulus being manipulated in working memory (letters, numbers, nonsense shapes) or whether these relationships are specific to achievement domain and stimulus type (i.e., letters for reading and numbers for math). The results indicated that higher academic achievement in each of reading and math was associated with greater activation of dorsolateral prefrontal cortex in the N-back task regardless of stimulus type (i.e., did not differ for letters and numbers), suggesting that at least some aspects of the neural mechanisms underlying these academic domains are executive in nature. In addition, regardless of level of academic achievement, prefrontal regions were engaged to a greater degree for letters than numbers than nonsense shapes. In contrast, nonsense shapes yielded greater hippocampal activation than letters and numbers. Potential reasons for this pattern of findings are discussed.
Attention-deficit/hyperactivity disorder (ADHD) and reading disability (RD) are complex childhood disorders that frequently co-occur, but the etiology of this comorbidity remains unknown.
...Participants were 457 twin pairs from the Colorado Learning Disabilities Research Center (CLDRC) twin study, an ongoing study of the etiology of RD, ADHD, and related disorders. Phenotypic analyses compared groups with and without RD and ADHD on composite measures of six cognitive domains. Twin analyses were then used to test the etiology of the relations between the disorders and any cognitive weaknesses.
Phenotypic analyses supported the hypothesis that both RD and ADHD arise from multiple cognitive deficits rather than a single primary cognitive deficit. RD was associated independently with weaknesses on measures of phoneme awareness, verbal reasoning, and working memory, whereas ADHD was independently associated with a heritable weakness in inhibitory control. RD and ADHD share a common cognitive deficit in processing speed, and twin analyses indicated that this shared weakness is primarily due to common genetic influences that increase susceptibility to both disorders.
Individual differences in processing speed are influenced by genes that also increase risk for RD, ADHD, and their comorbidity. These results suggest that processing speed measures may be useful for future molecular genetic studies of the etiology of comorbidity between RD and ADHD.
Evidence-based practice in psychology (EBPP) has long focused on treatment, but evidence-based psychological assessment (EBPA) is also crucial given the important role of accurate and reliable ...diagnostic practices in treatment planning. In terms of the diagnosis of attention-deficit/hyperactivity disorder (ADHD), EBPA practices are well-established for children, and more recently for adults, but for college students in particular there are special considerations that warrant attention. College students with symptoms of ADHD have some challenges that are unique, and thus the assessment and diagnosis of ADHD in these students is unique. The aim of this review is not to cover all EBPA strategies for diagnosing ADHD in emerging adult college students; rather, we will focus on the unique considerations at play in college ADHD assessment. These include (a) conceptual matters such as the appropriateness of the DSM-5 criteria for college students, the limitations of our understanding of ADHD this population because of a lack of diversity in research studies, and the issue of late-identified ADHD; and (b) practical matters, such as specific documentation needs, how to gather and interpret self- and other-report of symptoms, how to assess impairment, and alternate explanations for ADHD-like symptoms in college students.
Purpose of Review
This review provides an overview of studies that used behavioral genetic methods to understand the genetic and environmental influences that lead to comorbidity, the co-occurrence ...of two or more developmental disorders in the same individual.
Recent Findings
Comorbidity is primarily explained by shared genetic influences for most pairs of disorders that have been studied, including attention-deficit hyperactivity disorder (ADHD) and learning disabilities, conduct disorder and ADHD, anxiety and depression, and anxiety and autism spectrum disorder (ASD). Molecular genetic studies indicate that the etiologies of developmental disorders are highly multifactorial, with dozens or even hundreds of genes acting in combination with environmental risk factors to lead to each individual disorder and the extensive comorbidity between disorders. Due to this complexity, current state-of-the-art studies are now combining molecular genetic data from multiple large samples to begin to achieve adequate statistical power to identify the specific genetic polymorphisms that lead to comorbidity.
Summary
An extensive literature demonstrates the pervasiveness and potential importance of comorbidity between developmental disorders, and results of family, twin, and molecular genetic studies indicate that these comorbidities may be largely explained by shared genetic influences. Additional studies are ongoing to identify the specific genetic polymorphisms that increase risk for each developmental disorder and comorbidity between disorders.
The current study utilized a large, unselected sample of adolescent twins to examine whether processing speed (PS) is an important shared predictor that accounts for covariance among reading, math, ...ADHD, and rapid naming (RN). The best fitting model included correlated but distinguishable latent measures of PS, RN, reading, math, inattention, hyperactivity/impulsivity, and academic fluency. PS was a shared predictor across all outcomes, while RN was uniquely associated with reading, fluency, and (albeit weakly) math. The results add to a growing literature suggesting that PS and RN may be important components of comprehensive neuropsychological models of academics, ADHD, and their covariation.
This study investigated the association between reading disability (RD) and internalizing
and externalizing psychopathology in a large community sample of twins with (N = 209) and
without RD (N = ...192). The primary goals were to clarify the relation between RD and
comorbid psychopathology, to test for gender differences in the behavioral correlates of RD,
and to test if common familial influences contributed to the association between RD and
other disorders. Results indicated that individuals with RD exhibited significantly higher
rates of all internalizing and externalizing disorders than individuals without RD. However,
logistic regression analyses indicated that RD was not significantly associated with symptoms
of aggression, delinquency, oppositional defiant disorder, or conduct disorder after
controlling for the significant relation between RD and ADHD. In contrast, relations
between RD and symptoms of anxiety and depression remained significant even after
controlling for comorbid ADHD, suggesting that internalizing difficulties may be specifically
associated with RD. Analyses of gender differences indicated that the significant relation
between RD and internalizing symptoms was largely restricted to girls, whereas the
association between RD and externalizing psychopathology was stronger for boys. Finally,
preliminary etiological analyses suggested that common familial factors predispose both
probands with RD and their non-RD siblings to exhibit externalizing behaviors, whereas
elevations of internalizing symptomatology are restricted to individuals with RD.
Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criteria for attention deficit/hyperactivity disorder (ADHD) specify two dimensions of inattention and ...hyperactivity−impulsivity symptoms that are used to define three nominal subtypes: predominantly hyperactive−impulsive type (ADHD-H), predominantly inattentive type (ADHD-I), and combined type (ADHD-C). To aid decision making for DSM-5 and other future diagnostic systems, a comprehensive literature review and meta-analysis of 546 studies was completed to evaluate the validity of the DSM-IV model of ADHD. Results indicated that DSM-IV criteria identify individuals with significant and persistent impairment in social, academic, occupational, and adaptive functioning when intelligence, demographic factors, and concurrent psychopathology are controlled. Available data overwhelmingly support the concurrent, predictive, and discriminant validity of the distinction between inattention and hyperactivity−impulsivity symptoms, and indicate that nearly all differences among the nominal subtypes are consistent with the relative levels of inattention and hyperactivity−impulsivity symptoms that define the subtypes. In contrast, the DSM-IV subtype model is compromised by weak evidence for the validity of ADHD-H after first grade, minimal support for the distinction between ADHD-I and ADHD-C in studies of etiological influences, academic and cognitive functioning, and treatment response, and the marked longitudinal instability of all three subtypes. Overall, we conclude that the DSM-IV ADHD subtypes provide a convenient clinical shorthand to describe the functional and behavioral correlates of current levels of inattention and hyperactivity−impulsivity symptoms, but do not identify discrete subgroups with sufficient long-term stability to justify the classification of distinct forms of the disorder. Empirical support is stronger for an alternative model that would replace the subtypes with dimensional modifiers that reflect the number of inattention and hyperactivity−impulsivity symptoms at the time of assessment.
Individual differences in children’s math performance have been associated with math anxiety, attention problems, working memory (WM), and reading skills, but the mechanisms by which these factors ...jointly contribute to children’s math achievement are unknown. Here, we use structural equation modeling to characterize the relation between these factors and their influence on non-verbal Numerical Operations (NO) and verbal Math Reasoning (MR) in 330 children (M=8.34years). Our findings indicate that WM plays a central role in both non-verbal NO and verbal MR, whereas math anxiety and reading comprehension have unique and more pronounced influences on MR, compared to NO. Our study elucidates how affective and cognitive factors distinctly influence non-verbal and verbal mathematical problem solving.
Previous studies have shown that Attention-Deficit/Hyperactivity disorder (ADHD) is marked by impairments in academic functioning in reading, writing, and mathematics. Yet, virtually no studies have ...examined academic functioning in terms of both basic skills (e.g., word recognition, handwriting/spelling, arithmetic calculations) and more complex advanced skills (e.g., reading comprehension, writing composition, and mathematical problem-solving) within the same sample. In the present study, 518 children with ADHD were compared to a control group of 851 children without ADHD (ages 8-18) and assessed on a comprehensive battery of reading, writing, and math assessments. It was hypothesized that ADHD diagnostic status would uniquely predict performance on advanced skill measures even after controlling for performance on basic skills in that academic domain. ADHD status was associated with worse performance across all academic tests. Results also indicated that ADHD independently predicted performance for measures of writing composition and one measure of reading comprehension, even after controlling for performance on basic skills in those domains. However, ADHD did not independently predict mathematical problem-solving performance. These findings add to the literature on ADHD and academic functioning and indicate that inattention may weaken skills necessary for effective reading comprehension and writing composition.
Background Neurocognitive deficits associated with attention-deficit/hyperactivity disorder (ADHD) might be useful intermediate endophenotypes for determining specific genetic pathways that ...contribute to ADHD. Methods This study administered 17 measures from prominent neuropsychological theories of ADHD (executive function, processing speed, arousal regulation and, motivation/delay aversion) in dizygotic (DZ) twin pairs discordant for ADHD and control twin pairs (ages 8–18 years) to compare performance between twins affected with ADHD (n = 266), their unaffected co-twins (n = 228), and control children from twin pairs without ADHD or learning difficulties (n = 332). Results The ADHD subjects show significant impairment on executive function, processing speed, and response variability measures compared with control subjects. Unaffected co-twins of ADHD subjects are significantly impaired on nearly all the same measures as their ADHD siblings, even when subclinical symptoms of ADHD are controlled. Conclusions Executive function, processing speed, and response variability deficits might be useful endophenotypes for genetic studies of ADHD.
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