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.     

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.     

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.     

Executive Function and Theory of Mind in 2 Year Olds: A Family Affair?

This study aimed to enhance our understanding of neuropsychological functioning in children with early-treated phenylketonuria (PKU) and assess the relative impact of white matter abnormalities (WMA) and neurotransmitter deficiencies on cognitive functions in this population. The study consisted of 33 children with early-treated PKU and 34 healthy control children aged between 7 to 18 years. All children had a neuropsychological evaluation that included measures of general intelligence, attention, processing speed, memory and learning, executive function, and academic achievement. Children in the PKU group also had a magnetic resonance (MR) brain scan. When compared with the control group, the PKU group exhibited global cognitive impairment including lower IQ, attention problems, slow information processing, reduced learning capacity, mild executive impairments, and educational difficulties. Children in the PKU group with extensive WMA (n = 14) displayed significant impairments across all cognitive domains. Metabolic control correlated weakly to moderately with attention, executive, and memory/learning factors. Within the PKU group, regressions revealed that executive function and attention factors were independently related to severity of WM pathology and age, while the memory and learning factor was independently related to metabolic control and age. It is concluded that children with early-treated PKU exhibit a global pattern of impairment, with a particular deficit in processing speed. WM pathology extending into frontal and subcortical regions correlates with the greatest deficits and a profile of impairment consistent with diffuse WM damage. Our findings also offer some support for dopamine depletion in the prefrontal cortex, however adverse consequences as a result of norepinephrine and serotonin deficiencies should not be discounted.     

Are neuropsychological impairments in children with early-treated phenylketonuria (PKU) related to white matter abnormalities or elevated phenylalanine levels?

This study aimed to enhance our understanding of neuropsychological functioning in children with early-treated phenylketonuria (PKU) and assess the relative impact of white matter abnormalities (WMA) and neurotransmitter deficiencies on cognitive functions in this population. The study consisted of 33 children with early-treated PKU and 34 healthy control children aged between 7 to 18 years. All children had a neuropsychological evaluation that included measures of general intelligence, attention, processing speed, memory and learning, executive function, and academic achievement. Children in the PKU group also had a magnetic resonance (MR) brain scan. When compared with the control group, the PKU group exhibited global cognitive impairment including lower IQ, attention problems, slow information processing, reduced learning capacity, mild executive impairments, and educational difficulties. Children in the PKU group with extensive WMA (n = 14) displayed significant impairments across all cognitive domains. Metabolic control correlated weakly to moderately with attention, executive, and memory/learning factors. Within the PKU group, regressions revealed that executive function and attention factors were independently related to severity of WM pathology and age, while the memory and learning factor was independently related to metabolic control and age. It is concluded that children with early-treated PKU exhibit a global pattern of impairment, with a particular deficit in processing speed. WM pathology extending into frontal and subcortical regions correlates with the greatest deficits and a profile of impairment consistent with diffuse WM damage. Our findings also offer some support for dopamine depletion in the prefrontal cortex, however adverse consequences as a result of norepinephrine and serotonin deficiencies should not be discounted.     

Genetic analyses of the stability of executive functioning during childhood

Executive functioning is an umbrella term for several related cognitive functions like selective- and sustained attention, working memory, and inhibition. Little is known about the stability of executive functioning during childhood. In this study the longitudinal stability of executive functioning was examined in young twins. The twin design enables to investigate genetic and environmental contributions to (the stability of) executive functioning. Computerized reaction time tasks on working memory, selective- and sustained attention were collected in twins at age 5 years (N=474 children) and at age 12 (N=346 children). The longitudinal correlations of processing speed on all tasks were substantial ( approximately 0.38). For slope (i.e., the delay caused by higher memory load) and fluctuation in tempo the longitudinal correlations were 0.08 and 0.26, respectively. The results hinted at genetic factors being an important mediator of stability of executive functioning over time. Also, genetic variation was the most important explanation for individual differences in executive functioning at both ages.     

Neuropsychological correlates of ADHD symptoms in preschoolers

The authors examined the neuropsychological status of 22 preschoolers at risk for attention-deficit/hyperactivity disorder (ADHD) and 50 matched control children, using measures of nonverbal working memory, perceptual and motor inhibition, and memory for relative time. All tasks included paired control conditions, which allowed for the isolation of discrete executive function constructs. Group differences were evident on several measures of neuropsychological functioning; however, after accounting for nonexecutive abilities, no deficits could be attributed to specific functions targeted by the tasks. Performance on executive measures was not related to objective indices of activity level or ratings of ADHD symptoms. Yet, the fact that at-risk preschoolers were highly symptomatic casts doubt on whether executive function deficits and/or frontostriatal networks contribute etiologically to early behavioral manifestations of ADHD.     

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.     

Exploring the roles of the visual‐spatial sketch pad and central executive in children's arithmetical skills: Views from cognition and developmental neuropsychology

Short‐term memory has often been found to play a major role in children's arithmetical skills. However, Bull and Johnston (1997) found that when differences in reading skills were controlled for, short‐term memory, specifically the functioning of the articulatory loop, did not represent a fundamental deficit for children of low mathematical ability. This study examined the role of other working‐memory mechanisms in arithmetical skills, namely the central executive, using the Wisconsin Card Sorting Test (WCST), and the visual‐spatial sketch pad, using the Corsi Blocks. Results showed that children of high and low mathematics ability differed significantly on WCST measures after controlling for differences in reading ability and IQ but did not differ in visual sequential memory. Correlation analyses revealed a significant correlation between arithmetic performance and perseveration measures from the WCST. The implications of this result are discussed in terms of central‐executive functioning and related cognitive and behavioral difficulties.     

Comparative efficiency of a discrepancy analysis for the classification of Attention-Deficit/Hyperactivity Disorder in adults.

The present study evaluated an alternative method of neuropsychological test interpretation for the classification of Attention-Deficit/Hyperactivity Disorder (ADHD) in adults. Specifically, an intra-individual discrepancy analysis was implemented in which differences between intellectual functioning and performance on a battery of six frontal/executive tests were examined within a homogeneous group of ADHD adults and matched normal controls. Significant group differences were identified between the ADHD adults and control sample on each of the dependent measures, with moderate diagnostic efficiency rates for the individual measures and a Discrepancy Impairment Index (DII). The discrepancy analysis approach generated significantly greater sensitivity in detecting the presence of ADHD as compared to a level of performance interpretive approach. Overall, these results provide support for the consideration of discrepancies between intellectual ability and frontal/executive functioning for the assessment of adult ADHD.     

The construct of problem solving in higher level neuropsychological assessment and rehabilitation.

Three inter-related studies examine the construct of problem solving as it relates to the assessment of deficits in higher level outpatients with traumatic brain injury (TBI). Sixty-one persons with TBI and 58 uninjured participants completed measures of problem solving and conceptually related constructs, which included neuropsychological tests, self-report inventories, and roleplayed scenarios. In Study I, TBI and control groups performed with no significant differences on measures of memory, reasoning, and executive function, but medium to large between-group differences were found on timed attention tasks. The largest between-group differences were found on psychosocial and problem-solving self-report inventories. In Study II, significant-other (SO) ratings of patient functioning were consistent with patient self-report, and for both self-report and SO ratings of patient problem solving, there was a theoretically meaningful pattern of correlations with timed attention tasks. In Study III, a combination of self-report inventories that accurately distinguished between participants with and without TBI, even when cognitive tests scores were in the normal range, was determined. The findings reflect intrinsic differences in measurement approaches to the construct of problem solving and suggest the importance of using a multidimensional approach to assessment.     

Executive functioning in children with attention-deficit/hyperactivity disorder: combined type with and without a stimulant medication history

Behavioral and neuropsychological functioning in unmedicated children with attention-deficit/hyperactivity disorder (ADHD) who have a history of medication treatment (Rx) versus those who are treatment na?ve (TN) has, to our knowledge, not been previously studied. Ninety-four children in four groups (ADHD/Rx, ADHD/TN, learning disabilities [LD], and controls) were evaluated, while unmedicated, on measures of achievement, neuropsychological functioning, and behavior. The ADHD/Rx group performed significantly better than the TN group on writing, Stroop interference, and measures of attention, and performed as well as the control group on executive functioning, verbal working memory, and academics. Behaviorally, the ADHD groups showed more difficulty with mood and externalizing behaviors compared with the LD and control groups, with the ADHD/TN performing the most poorly. Findings suggest that the ADHD/Rx group shows better executive and academic functioning even when unmedicated.     

Attention and executive functions in adolescents with spina bifida

OBJECTIVE: This study was designed to examine attention processes and executive functioning in adolescents with spina bifida, and to explore whether impairment in these domains contributes to problems with social adjustment. METHODS: A sample of adolescents with spina bifida (n = 68) and a matched comparison group (n = 68) and their families were followed longitudinally. All participants completed questionnaires, and the adolescent participants underwent neurocognitive testing. RESULTS: The spina bifida sample showed greater impairment on objective and subjective measures of attention and executive functioning, even when differences in intellectual functioning were controlled. Additionally, attention and executive deficits were found to be predictive of social adjustment difficulties. A mediational analysis suggested the neurocognitive deficits mediate associations between spina bifida status and social adjustment difficulties. CONCLUSIONS: Adolescents with spina bifida appear to exhibit clear impairment in attention and executive functioning and this impairment may contribute to their well-established social difficulties.     

Executive functions in children aged 6 to 13: a dimensional and developmental study

A cross-sectional study using 92 children aged 6 to 13 years investigated the dimensionality and the development of executive functioning. The measures were drawn from developmentally relevant conceptualizations of executive functioning and included a go/no-go task, a verbal fluency task, a continuous performance task, a Stroop-like task, a hand movements task, and a digit span task. Analyses revealed 3 dimensions interpreted as Disinhibition, Speed/arousal, and Working memory/Fluency. Age and sex differences were analyzed for the delineated functions, which means that the results may be taken to represent age effects at the level of specific processes within the executive domain rather than on single tests. Age-dependent changes in children's performance on all 3 dimensions were demonstrated, with 3 particularly active stages of maturation: early childhood (6-8 years of age), middle childhood (9-12 years of age), and during early adolescence. Sex differences were only found for the speed/arousal dimension. The results are discussed in terms of 2 developmental executive function frameworks (Barkley, 1997b; Roberts & Pennington, 1996), where inhibition and the interaction between inhibition and working memory, respectively, are seen as key in the development of executive functioning.     

Cognitive performance and electrophysiological indices of cognitive control: a validation study of conflict adaptation

Psychiatric and neurologic disorders are associated with deficits in the postconflict recruitment of cognitive control. The primary aim of this study was to validate the relationship between cognitive functioning and indices of conflict adaptation. Event-related potentials were obtained from 89 healthy individuals who completed an Eriksen flanker task. Neuropsychological domains tested included memory, verbal fluency, and attention/executive functioning. Behavioral measures and N2 amplitudes showed significant conflict adaptation (i.e., previous-trial congruencies influenced current-trial measures). Higher scores on the attention/executive functioning and verbal fluency domains were associated with larger incongruent-trial N2 conflict adaptation; measures of cognitive functioning were not related to behavioral indices. This study provides initial validation of N2 conflict adaptation effects as cognitive function-related aspects of cognitive control.     

Does Brief Loss of Consciousness Affect Cognitive Functioning After Mild Head Injury?

Loss of consciousness often is considered an important variable when estimating head injury severity. The purpose of this study was to determine if brief loss of consciousness had any effect on the neuropsychological test performance of patients in acute recovery from an uncomplicated mild head injury (N = 195). Three groups of 65 patients were given a brief battery of neuropsychological tests within one week of sustaining a mild head injury. The groups, sorted on the basis of loss of consciousness (i.e., positive, negative, or equivocal), did not differ in age or education. There were no significant differences among the groups on any of the measures of attention, learning, memory, language, or executive functioning.     

Long-term neuropsychological impact of brief occupational exposure to organic solvents.

This case series describes the cognitive functioning of 10 individuals who were briefly exposed to a mixture of organic solvents as a result of an industrial accident. Data were obtained 10 years after the exposure on measures of intellect, memory, attention, and executive functioning, using standardised neuropsychological measures including WAIS III, WMS III, Hayling and Brixton Tests, The Trail Making Test, Controlled Oral Word Association, Rey-Osterrieth Complex Figure Test, and The Speed and Capacity of Language-Processing Test. The group performed in the average range across the majority of measures but deficits (z > 1.0 S.D.) were observed on tests that measure speed of information processing, memory, attention, and verbal fluency. Discrepancy scores between the NART and the WAIS suggest subtle but statistically significant decline in performance IQ following solvent exposure.     

Executive Functions in Children Aged 6 to 13: A Dimensional and Developmental Study

A cross-sectional study using 92 children aged 6 to 13 years investigated the dimensionality and the development of executive functioning. The measures were drawn from developmentally relevant conceptualizations of executive functioning and included a go/no-go task, a verbal fluency task, a continuous performance task, a Stroop-like task, a hand movements task, and a digit span task. Analyses revealed 3 dimensions interpreted as Disinhibition, Speed/arousal, and Working memory/Fluency. Age and sex differences were analyzed for the delineated functions, which means that the results may be taken to represent age effects at the level of specific processes within the executive domain rather than on single tests. Age-dependent changes in children's performance on all 3 dimensions were demonstrated, with 3 particularly active stages of maturation: early childhood (6-8 years of age), middle childhood (9-12 years of age), and during early adolescence. Sex differences were only found for the speed/arousal dimension. The results are discussed in terms of 2 developmental executive function frameworks (Barkley, 1997b; Roberts & Pennington, 1996), where inhibition and the interaction between inhibition and working memory, respectively, are seen as key in the development of executive functioning.     

Digit Span components as predictors of attention problems and executive functioning in children.

This study examined the extent to which digits forward (DF) or digits backward (DB) account for variance in parent ratings of attention and executive function in children. The sample (n=90) included children with no diagnosis and children with a range of clinical problems, including attention deficit hyperactivity disorder (ADHD). Clinical groups differed from the No Diagnosis group on cognitive ability as well as achievement. Once cognitive ability was controlled, no group differences emerged for Digit Span or digits forward; notably, the ADHD-Predominantly Inattentive group was able to recall significantly more digits backward than the ADHD-Combined Type group. Regression analyses indicated that Full Scale IQ explained significant variance in parent ratings of attention and executive function; DF emerged as a significant predictor only for one measure of attention. When only children with ADHD were considered, DF no longer was a significant predictor. Results support the notion that DF and DB are differing constructs, as well as highlighting the importance of controlling for cognitive ability in consideration of group differences on behavioral measures.     

Sex Differences in Cognitive Functioning in Velocardiofacial Syndrome (VCFS)

Sex differences in cognitive functioning were investigated in children with velocardiofacial syndrome (VCFS), a genetic defect caused by a microdeletion on chromosome 22q.11. The study population consisted of six groups: 50 boys with VCFS (M = 11.1, SD = 2.7), 40 girls with VCFS (M = 10.8, SD = 2.5), 13 male siblings of the participant with VCFS (M = 12.3, SD = 1.9), 17 female siblings of the participant with VCFS (M = 12.2, SD = 1.9), and a race- and gender-ratio-matched sample of 28 boy community control participants (M = 10.7, SD =2.4) and 19 girl community control participants (M = 9.2, SD =2.3). Each participant received a psychological assessment including intellectual and academic achievement as well as structural magnetic resonance imaging of his or her brain. Our results indicate that boys with VCFS may be more cognitively affected than girls. In addition, and although cross-sectional in nature, our results document a negative association between age and cognitive functioning in girls with VCFS but not in boys. Sex differences in frontal lobe volume are generally seen in the general population between boys and girls (boys > girls) and across all three samples, this trend emerged. Relative to boys with VCFS, girls with VCFS may be less cognitively affected, although age is negatively associated with cognitive functioning in girls with VCFS but not boys, suggesting that girls with VCFS may fail to maintain this cognitive advantage over boys.