Interference control, working memory, concept shifting, and verbal fluency in adults with attention-deficit/hyperactivity disorder (ADHD)

In this study, the authors aimed to examine 4 domains of executive functioning in adults with attention-deficit/hyperactivity disorder (ADHD)--namely interference control, concept shifting, verbal fluency, and verbal working memory. Four groups of participants were included: (a) adults diagnosed with ADHD (ADHD-super(-); n = 20), (b) adults diagnosed with both ADHD and 1 or more comorbid disorder(s) (ADHD-super(+); n = 22), (c) adults referred for ADHD because of ADHD symptomatology but not diagnosed as such (non-ADHD; n = 34), and (d) healthy controls (n = 136). ADHD-related deficits (independent of comorbidity) were revealed for concept shifting and verbal working memory. In addition, the ADHD-super(+) and non-ADHD groups displayed deficits in terms of general processing speed. Given that these deficits were not found in the ADHD-super(-) group, the authors contend that these deficits are likely attributable to comorbidity rather than ADHD itself. Contrary to the authors' expectations, these findings do not correspond with the cognitive subtype hypothesis.     

Time estimation and performance on reproduction tasks in subtypes of children with attention deficit hyperactivity disorder.

This study compared Hispanic children (ages 7 to 11) with combined type (CT, n=33) and inattentive type (IT, n=21) attention deficit hyperactivity disorder (ADHD) and a control group (n=25) on time-estimation and time-reproduction tasks. The ADHD groups showed larger errors in time reproduction but not in time estimation than the control group, and the groups did not differ from each other on their performance on this task. Individual differences could not be accounted for by oppositional-defiance ratings and low math or reading scores. Although various measures of executive functioning did not make significant unique contributions to time estimation performance, those of interference control and nonverbal working memory did so to the time-reproduction task. Findings suggest that ADHD is associated with a specific impairment in the capacity to reproduce rather than estimate time durations and that this may be related to the children's deficits in inhibition and working memory.     

The impact of specific language impairment on working memory in children with ADHD combined subtype.

The objective of this study was to examine the impact of comorbid specific language impairment (SLI) on verbal and spatial working memory in children with DSM-IV combined subtype Attention Deficit Hyperactivity Disorder (ADHD-C). Participants were a clinical sample of 812- to 1212-year-old children diagnosed with ADHD-C. A group of ADHD-C with SLI was compared to a group of ADHD-C without SLI, and a group of normal children, matched on age and nonverbal intelligence. The results show that ADHD-C children with SLI scored significantly lower than those without SLI and normal children, on verbal working memory measures only. Both ADHD groups performed normally on spatial working memory measures. It is concluded that working memory deficits are not a specific characteristic of ADHD but are associated with language impairments. The importance of screening for language disorders in studies of neuropsychological functioning in children with ADHD is emphasized.     

Neuropsychological performance deficits in adults with attention deficit/hyperactivity disorder.

Neuropsychological deficits in children diagnosed with attention deficit/hyperactivity disorder (ADHD) have been well documented utilizing various neuropsychological tests. Only recently has research begun to examine if similar deficits are present in adults with ADHD. A neuropsychological testing battery was constructed that assessed verbal learning and memory, psychomotor speed, and sustained attention--all demonstrated to be deficient in individuals with ADHD. Fifty-six self-referred nonmedicated adults with a DSM-IV diagnosis of ADHD and 38 normal comparison adults participated. ADHD adults demonstrated verbal and nonverbal memory deficits and decreased psychomotor speed compared to normal controls. Differences between ADHD and normal adults were not documented on traditional measures of executive functioning. A pattern of results emerged whereby ADHD adults' performance, particularly with regard to psychomotor speed, became more impaired as task complexity increased. This study's results largely corroborate similar neuropsychological testing results in ADHD children and recent ADHD adult findings, and support a frontal lobe dysfunction hypothesis of ADHD.     

Quantitative trait locus for reading disability on chromosome 6p is pleiotropic for attention‐deficit/hyperactivity disorder

Comorbidity is pervasive among both adult and child psychiatric disorders; however, the etiological mechanisms underlying the majority of comorbidities are unknown. This study used genetic linkage analysis to assess the etiology of comorbidity between reading disability (RD) and attention‐deficit hyperactivity disorder (ADHD), two common childhood disorders that frequently co‐occur. Sibling pairs (N = 85) were ascertained initially because at least one individual in each pair exhibited a history of reading difficulties. Univariate linkage analyses in sibling pairs selected for ADHD from within this RD‐ascertained sample suggested that a quantitative trait locus (QTL) on chromosome 6p is a susceptibility locus for ADHD. Because this QTL is in the same region as a well‐replicated QTL for reading disability, subsequent bivariate analyses were conducted to test if this QTL contributed to comorbidity between the two disorders. Analyses of data from sib pairs selected for reading deficits revealed suggestive bivariate linkage for ADHD and three measures of reading difficulty, indicating that comorbidity between RD and ADHD may be due at least in part to pleiotropic effects of a QTL on chromosome 6p. © 2002 Wiley‐Liss, Inc.     

Neuropsychological and academic functioning in preschool boys with attention deficit hyperactivity disorder

We compared 34 preschool boys with attention deficit hyperactivity disorder (ADHD) to 30 community comparison boys without behavioral problems on a battery of neuropsychological and academic achievement tests along with behavioral observations. The battery of 25 measures was reduced to 4 dimensions through dimensional (factor) analysis. Comparison of the 2 groups revealed that boys with ADHD performed more poorly than comparison boys on 2 of the 4 dimensions, these being motor control and working memory‐persistence. No differences were found on the dimensions of verbal learning‐memory or picture identification‐factual knowledge. The results suggest that achievement problems are evident early in development in clinic‐referred children with ADHD and may be related to deficiencies in more fundamental neuropsychological functions. These early deficits in motor control and working memory seem to be an inherent part of ADHD, supporting both the neuromaturational nature of the disorder and current efforts to more broadly conceptualize it as involving deficits in executive functions beyond the core problems in behavioral inhibition and sustained attention.     

Identical neural risk factors predict cognitive deficit in dyslexia and schizophrenia

In previous work, the authors found that an anatomical risk index created from the combination of 7 neuroanatomical measures predicted reading and oral language skills in individuals with learning disabilities. Individuals with small auditory brain structures and reduced asymmetry had more deficits than those with large structures and exaggerated asymmetry. In the present study, the same anatomical index predicted reading and other cognitive abilities in 45 individuals with chronic schizophrenia. The anatomical risk index was significantly associated with broad cognitive ability (Pearson r = .53, p < .0001), reading comprehension (r = .58, p < .0001), and a measure of nonverbal reasoning (r = .39, p < .01), but not with age, parental socioeconomic status, symptom measures, alcohol use, or processing speed. These findings support the prediction that reduced size and asymmetry in temporal lobe auditory cortex and cerebellum may not be specific risk factors for schizophrenia but for cognitive deficits that characterize a broad spectrum of developmental disorders.     

Time Estimation and Performance on Reproduction Tasks in Subtypes of Children With Attention Deficit Hyperactivity Disorder

This study compared Hispanic children (ages 7 to 11) with combined type (CT, n = 33) and inattentive type (IT, n = 21) attention deficit hyperactivity disorder (ADHD) and a control group (n = 25) on time-estimation and time-reproduction tasks. The ADHD groups showed larger errors in time reproduction but not in time estimation than the control group, and the groups did not differ from each other on their performance on this task. Individual differences could not be accounted for by oppositional-defiance ratings and low math or reading scores. Although various measures of executive functioning did not make significant unique contributions to time estimation performance, those of interference control and nonverbal working memory did so to the time-reproduction task. Findings suggest that ADHD is associated with a specific impairment in the capacity to reproduce rather than estimate time durations and that this may be related to the children's deficits in inhibition and working memory.     

Visual versus verbal mnemonic training effects on memory‐deficient and language‐deficient subgroups of children with reading disability

This study compared the effectiveness of two different memory strategies for memory‐deficit, reading‐disabled (RD) children with different cognitive patterns. Forty learning‐disabled children 7 to 13 years old were divided into two groups based on whether they showed general language disorder (GLD) or specific memory disorder (SMD) without a language deficit. Each child was then given training in one of two memory strategies: visual mapping or cumulative verbal rehearsal. Subsequent memory performance of the two RD subgroups was compared over the two treatment conditions. There was a significant interaction in the effectiveness of the two treatments for the two groups’ memory performance after treatment. GLD children made significantly greater gains from pretesting to posttesting on the visual mapping treatment than on the cumulative verbal rehearsal treatment, whereas the SMD children demonstrated significantly greater gains on cumulative verbal rehearsal than on visual mapping. The findings suggest that there is a relation between an RD child's cognitive strengths and deficits and ability to employ a given memory strategy effectively.     

Naming and verbal memory skills in adults with Attention Deficit Hyperactivity Disorder and Reading Disability

Research suggests that children with Attention Deficit Hyperactivity Disorder (ADHD) and Reading Disability (RD) can be differentiated based on their performance on measures of naming and verbal memory. It is not known whether this same pattern characterizes adults with these disorders. In this study, adults with and without ADHD and RD were compared on naming and verbal memory abilities. Results did not support the hypothesis that adults with ADHD and RD are significantly different from each other, or from a contrast group, on naming and verbal memory measures after controlling for Full-Scale IQ (FSIQ). These results were replicated across two sets of classification criteria used to identify diagnostic groups. Factors that could account for the inconsistency in research findings with children and adult subjects are discussed.     

Executive functioning in boys with ADHD: primarily an inhibition deficit?

This study was aimed at: (1) testing whether boys with Attention Deficit/Hyperactivity Disorder (ADHD) demonstrate a deficit in response inhibition and deficits in other executive functions (EF), or alternatively, demonstrate a deficit in only response inhibition; (2) investigating which role associated factors, such as IQ, age, and performance on non-EF tasks play in EF in ADHD; (3) studying the association between the three different forms of inhibition studied here. Boys with ADHD were compared with normal control (NC) boys on five domains of executive functioning: inhibition (inhibition of a prepotent response, inhibition of an ongoing response, and interference control), planning, set-shifting, working memory, and verbal fluency. Boys with ADHD demonstrated deficits in interference control, inhibition of an ongoing response, planning, and letter fluency. After controlling for age, IQ, and non-EF measures, none of the EF deficits in ADHD remained. Finally, correlations between different inhibition measures were generally low, and correlations within domains of inhibition were not higher than correlations between domains of inhibition. This calls into question the distinctiveness of the different forms of response inhibition.     

Quantitative trait locus for reading disability on chromosome 6p is pleiotropic for attention-deficit/hyperactivity disorder

Comorbidity is pervasive among both adult and child psychiatric disorders; however, the etiological mechanisms underlying the majority of comorbidities are unknown. This study used genetic linkage analysis to assess the etiology of comorbidity between reading disability (RD) and attention-deficit hyperactivity disorder (ADHD), two common childhood disorders that frequently co-occur. Sibling pairs (N = 85) were ascertained initially because at least one individual in each pair exhibited a history of reading difficulties. Univariate linkage analyses in sibling pairs selected for ADHD from within this RD-ascertained sample suggested that a quantitative trait locus (QTL) on chromosome 6p is a susceptibility locus for ADHD. Because this QTL is in the same region as a well-replicated QTL for reading disability, subsequent bivariate analyses were conducted to test if this QTL contributed to comorbidity between the two disorders. Analyses of data from sib pairs selected for reading deficits revealed suggestive bivariate linkage for ADHD and three measures of reading difficulty, indicating that comorbidity between RD and ADHD may be due at least in part to pleiotropic effects of a QTL on chromosome 6p.     

Which neuropsychological functions predict various processing speed components in children with and without attention-deficit/hyperactivity disorder?

We identified statistical predictors of four processing speed (PS) components in a sample of 151 children with and without attention-deficit/hyperactivity disorder (ADHD). Performance on perceptual speed was predicted by visual attention/short-term memory, whereas incidental learning/psychomotor speed was predicted by verbal working memory. Rapid naming was predictive of each PS component assessed, and inhibition predicted all but one task, suggesting a shared need to identify/retrieve stimuli rapidly and inhibit incorrect responding across PS components. Hence, we found both shared and unique predictors of perceptual, cognitive, and output speed, suggesting more specific terminology should be used in future research on PS in ADHD.     

Attention deficit hyperactivity disorder and executive dysfunction

To evaluate the relationship between attention deficit hyperactivity disorder (ADHD) and executive functioning (EF) a sample of ADHD children (N = 48) with above average IQs (median = 117.5) was administered a battery of standardized norm‐referenced tests sensitive to EF. Below average performance was found on the Wisconsin Card Sorting Test and continuous performance test (Test of Variables of Attention, TOVA) but not on Word Fluency or the Rey Complex Figure. Significant intraindividual discrepancies were found for a selected pair of content‐matched tests that differed in EF task demands. Pennington, Groisser, and Welsh's (1993) “double dissociation” of ADHD and reading disability (RD) was tested by examining the EF performance of ADHD with and without RD. No significant differences between ADHD/No‐RD and ADHD/RD were found on any of the EF measures.     

Processing speed, working memory, and IQ: a developmental model of cognitive deficits following cranial radiation therapy

IQ decrements following cranial radiation therapy (CRT) for acute lymphoblastic leukemia (ALL) are most apparent years after treatment. The authors examined a developmental model for delayed deficits by evaluating the relationship between processing speed, working memory, and IQ in long-term survivors of childhood ALL (n = 27) compared with demographically matched controls (n = 27). The ALL group treated with CRT showed deficits in IQ, working memory, and processing speed relative to controls. Differences in IQ between the CRT group and controls were mediated by differences in working memory. Processing speed did not fully account for the working memory deficit in the CRT group. Participants with ALL treated only with chemotherapy showed similar working memory and processing speed as matched controls. Data suggest that deficits in processing speed and working memory following CRT may underlie declines in IQ.     

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.     

Functional Impairments in Attention Deficit Hyperactivity Disorder: The Mediating Role of Neuropsychological Functioning

Attention deficit hyperactivity disorder (ADHD) is associated with multiple neuropsychological deficits and the present study aimed to investigate to what extent these deficits are related to the functional impairments associated with the disorder. The results showed that all executive functioning deficits and reaction time variability acted as mediators in the relation between ADHD and academic achievement. However, only the effect of working memory for language skills, and the effects of reaction time variability and working memory for mathematics, remained significant when studying independent effects. Regulation of anger was a significant mediator for peer problems. Gender or symptoms of oppositional defiant disorder (ODD) or conduct disorder (CD) did not moderate these findings.     

Behavioral inhibition,self-regulation of motivation,and working memory in children with attention deficit hyperactivity disorder

We examined 3 aspects of Barkley's (1997) recent model of Attention Deficit Hyperactivity Disorder (ADHD)-behavioral inhibition, self-regulation of motivation, and working memory utilizing 152 elementary school children ages 7 to 12. Seventy-six children with ADHD and 76 children without a psychiatric diagnosis completed the stop-signal task, a computerized Digit Span Task requiring concurrent storage and processing, and the Kaufman Brief Intelligence Test during a 1-hr testing session. Parent and teacher ratings were also obtained on the Conners Parent Rating Scale-Revised: Long Version (Conners, 1997), and the Conners Teacher Rating Scale-Revised: Long Version (Conners, 1997), respectively. Results indicated that children with ADHD had deficits in inhibitory control, working memory, and short-term memory relative to children without the disorder. Contrary to our prediction, the groups did not differ in their responsiveness to external reinforcement. In addition, children with and without ADHD had similar self-perceptions of their performances during the experimental session. Future directions for specifying childhood difficulties in inhibitory control and memory processes are discussed.     

Executive functioning and olfactory identification in young adults with attention deficit-hyperactivity disorder

Young adults with attention deficit-hyperactivity disorder (ADHD; N = 105) were compared with a control group (N = 64) on 14 measures of executive function and olfactory identification using a 2 (group) X 2 (sex) design. The ADHD group performed significantly worse on 11 measures. No Group X Sex interaction was found on any measures. No differences were found in the ADHD group as a function of ADHD subtype or comorbid oppositional defiant disorder. Comorbid depression influenced the results of only 1 test (Digit Symbol). After IQ was controlled for, some group differences in verbal working memory, attention, and odor identification were no longer significant, whereas those in inhibition, interference control, nonverbal working memory, and other facets of attention remained so. Executive function deficits found in childhood ADHD exist in young adults with ADHD and are largely not influenced by comorbidity but may be partly a function of low intelligence.     

Abnormal executive function in attention deficit hyperactivity disorder: the effect of stimulant medication and age on spatial working memory

OBJECTIVE: This study sought to examine the factors associated with spatial working memory and the use of strategies to impairments in spatial working memory in children with attention deficit hyperactivity disorder (ADHD). The developmental trajectories for spatial working memory in medicated and medication na?ve children with ADHD were investigated. In addition, the effect of psychostimulant medication on deficits in spatial working memory was examined. METHOD: A cross-sectional study compared performance between 21 psychostimulant medicated children with ADHD, 27 medication na?ve children with ADHD and 26 matched control subjects on computerized tests of spatial memory and spatial working memory. RESULTS: Compared with the controls, performance in medication na?ve children with ADHD was significantly worse on the spatial working memory task. There was no difference in performance between the medicated children with ADHD and the control subjects on this same task, despite the ongoing symptoms of ADHD in the former group. The pattern of normal and abnormal performance in the ADHD groups was age-independent. CONCLUSIONS: Deficits in executive functions related to spatial working memory do occur in children with ADHD, although the magnitude of these deficits is not related to the child's age or the level of ADHD symptoms. These deficits were not present in the current sample of children who were receiving psychostimulant medication.