Controlled processing and vigilance in hyperactivity: time will tell

Is the deficit in attention-deficit/hyperactivity disorder a concentration deficit?

Attention-deficit/hyperactivity disorder (ADHD) is comprised of two behavioral clusters of symptoms, inattention and hyperactivity/impulsivity. Numerous studies have attempted to address the underlying neuropsychological mechanism of ADHD. However, there is still no uniform mechanism that can fully explain both inattention and hyperactivity/impulsivity symptoms. This review describes the research findings that have shifted the focus from cognitive selective attention to executive function deficits and notes that the prominence of the attention deficit remains unclear. As ADHD is not consistently explained by cognitive selective attention but rather with cognitive sustained attention/vigilance and executive function deficits, this review suggests that concentration deficit is likely the cause of inattention symptoms. Indeed, considering concentration deficit as the cause of inattention symptoms may better describe the underlying difficulties of maintaining and controlling attention in ADHD. In addition, as concentration, impulsivity, and hyperactivity may share a common cognitive deficit, this shift in focus may help in identifying a single mechanism for all ADHD symptoms.

Allostasis and metastasis: The yin and yang of childhood self-regulation

Most research has studied self-regulation by presenting experimenter-controlled test stimuli and measuring change between baseline and stimulus. In the real world, however, stressors do not flash on and off in a predetermined sequence, and there is no experimenter controlling things. Rather, the real world is continuous and stressful events can occur through self-sustaining interactive chain reactions. Self-regulation is an active process through which we adaptively select which aspects of the social environment we attend to from one moment to the next. Here, we describe this dynamic interactive process by contrasting two mechanisms that underpin it: the "yin" and "yang" of self-regulation. The first mechanism is allostasis, the dynamical principle underlying self-regulation, through which we compensate for change to maintain homeostasis. This involves upregulating in some situations and downregulating in others. The second mechanism is metastasis, the dynamical principle underling dysregulation. Through metastasis, small initial perturbations can become progressively amplified over time. We contrast these processes at the individual level (i.e., examining moment-to-moment change in one child, considered independently) and also at the inter-personal level (i.e., examining change across a dyad, such as a parent-child dyad). Finally, we discuss practical implications of this approach in improving the self-regulation of emotion and cognition, in typical development and psychopathology.

Circadian Effects on Attention and Working Memory in College Students With Attention Deficit and Hyperactivity Symptoms

Objective

Individuals with an evening chronotype prefer to sleep later at night, wake up later in the day and perform best later in the day as compared to individuals with morning chronotype. Thus, college students without ADHD symptoms with evening chronotypes show reduced cognitive performance in the morning relative to nighttime (i.e., desynchrony effect). In combination with symptoms presented in attention deficit hyperactivity disorder (ADHD), we predicted that having evening chronotype renders impairment in attention during the morning, when students require optimal performance, amplifying desynchrony.

Method

Four hundred college students were surveyed for evening chronotype and symptoms of ADHD. Of those surveyed, 43 students with evening chronotype (19 with ADHD symptoms) performed laboratory attention tasks and were queried about fatigue during morning and evening sessions.

Results

Students with ADHD symptoms demonstrated a greater decrement in sustained attentional vigilance when abstaining from stimulants and asked to perform cognitive tests at times misaligned with natural circadian rhythms in arousal compared to their non-ADHD counterparts with the same chronotype. While individuals with ADHD symptoms had slower reaction-times during sustained attention tasks in the morning session compared to those without symptoms, there was no significant group difference in working memory performance, even though both groups made more errors in the morning session compared to the evening session.

Conclusion

These findings suggest that evening chronotype students with ADHD symptoms are at a greater disadvantage when having to perform sustained attention tasks at times that are not aligned to their circadian rhythm compared to their neuro-typical peers. The implications of this finding may be useful for the provision of disability accommodations to college age students with ADHD when they are expected to perform tasks requiring sustained attention at times misaligned with their circadian rhythms.

It Takes Time: Vigilance and Sustained Attention Assessment in Adults with ADHD

Objectives: The present study compares the utility of eight different tests of vigilance and sustained attention in the neuropsychological examination of adults with Attention-deficit/hyperactivity disorder (ADHD). Methods: Thirty-one adults diagnosed with ADHD performed eight tests for vigilance and sustained attention, spread over three assessment days. Results: Adults with ADHD showed cognitive impairments in most tests and test variables, even though their sensitivity differed greatly. No specific type of test variable stands out to be the most sensitive, and no evidence for a differential deterioration of performance over time was observed. Conclusion: This study underscores the role of vigilance and sustained attention tests in the assessment of adult ADHD. It is further concluded that summary scores over the entire test duration are sufficient, but that all variables of a test should be considered. Finally, we hypothesize that reassessment on a different day may benefit a more accurate clinical assessment of adults with ADHD, in order to adequately take intraindividual fluctuations and limitations regarding test reliability into account.

Attention and Motor Learning in Adult Patients with Neurofibromatosis Type 1

OBJECTIVE

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder that is associated with cognitive disabilities, including attention and motor learning problems. These disabilities have been extensively studied in children with NF1 but limited studies have been performed in adults.

METHOD

Attention, motor learning and intellectual performance were studied with neuropsychological tasks in 32 adults with NF1 and 32 controls.

RESULTS

The NF1 and control group performed similarly on attention and motor learning tasks, although controls had shorter reaction times than adults with NF1 during the motor learning task (t[60] = -2.20, p = .03). Measures of attention or motor learning were not significantly associated with reduced intellectual performance in NF1.

CONCLUSION

In contrast to many studies in children with NF1, our findings did not provide evidence for presence of attention or motor learning problems in adults with NF1 in neuropsychological tasks. Our observations may be of clinical importance to determine treatment focus in adults with NF1.

In infancy, it's the extremes of arousal that are 'sticky': Naturalistic data challenge purely homeostatic approaches to studying self-regulation

Most theoretical models of arousal/regulatory function emphasise the maintenance of homeostasis; consistent with this, most previous research into arousal has concentrated on examining individuals' recovery following the administration of experimentally administered stressors. Here, we take a different approach: we recorded day-long spontaneous fluctuations in autonomic arousal (indexed via electrocardiogram, heart rate variability and actigraphy) in a cohort of 82 typically developing 12-month-old infants while they were at home and awake. Based on the aforementioned models, we hypothesised that extreme high or low arousal states might be more short-lived than intermediate arousal states. Our results suggested that, contrary to this, both low- and high-arousal states were more persistent than intermediate arousal states. The same pattern was present when the data were viewed over multiple epoch sizes from 1 s to 5 min; over 10-15-minute time-scales, high-arousal states were more persistent than low- and intermediate states. One possible explanation for these findings is that extreme arousal states have intrinsically greater hysteresis; another is that, through 'metastatic' processes, small initial increases and decreases in arousal can become progressively amplified over time. Rather than exclusively using experimental paradigms to study recovery, we argue that future research should also use naturalistic data to study the mechanisms through which states can be maintained or amplified over time.

Sustained attention in adult ADHD: time-on-task effects of various measures of attention

Neuropsychological research on adults with ADHD showed deficits in various aspects of attention. However, the majority of studies failed to explore the change of performance over time, so-called time-on-task effects. As a consequence, little is known about sustained attention performance of adults with ADHD. The aim of the present study was therefore to test the hypothesis of sustained attention deficits of adults with ADHD. Twenty-nine adults with ADHD and 30 healthy individuals were assessed on four 20-min tests of sustained attention, measuring alertness, selective attention, divided attention and flexibility. The deterioration of performance over time (time-on-task effects) was compared between patients with ADHD and healthy individuals to conclude on sustained attention performance. Compared to healthy individuals, patients with ADHD showed significant deficits of medium size in selective attention and divided attention. Furthermore, medium sustained attention deficits was observed in measures of alertness, selective attention and divided attention. This study supports the notion of sustained attention deficits of adults with ADHD.

A longitudinal examination of the developmental executive function hierarchy in children with externalizing behavior problems

OBJECTIVE

Using a 4-year longitudinal design, we evaluated two hypotheses based on developmental executive function (EF) hierarchy accounts in a sample of children with externalizing problems.

METHOD

The participants performed EF tasks when they were between 8 and 12 years (M = 9.93), and again approximately 4 years later when they were between 12 and 15 years (M = 13.36).

RESULTS

Inhibition in middle childhood predicted working memory (WM) 4 years later. Further, deficits in inhibition and sustained attention were more prominent in middle rather than late childhood, whereas poor WM was salient throughout these periods.

CONCLUSIONS

These findings support the hypotheses that EFs develop hierarchically and that EF deficits in ADHD are more prominent in actively developing EFs. They also emphasize ADHD as a developmental disorder.

Relations between response trajectories on the continuous performance test and teacher-rated problem behaviors in preschoolers

Although both the continuous performance test (CPT) and behavior rating scales are used in both practice and research to assess inattentive and hyperactive/impulsive behaviors, the correlations between performance on the CPT and teachers' ratings are typically only small-to-moderate. This study examined trajectories of performance on a low target-frequency visual CPT in a sample of preschool children and how these trajectories were associated with teacher-ratings of problem behaviors (i.e., inattention, hyperactivity/impulsivity [H/I], and oppositional/defiant behavior). Participants included 399 preschool children (mean age = 56 months; 49.4% female; 73.7% White/Caucasian). An attention deficit/hyperactivity disorder (ADHD) rating scale was completed by teachers, and the CPT was completed by the preschoolers. Results showed that children's performance across 4 temporal blocks on the CPT was not stable across the duration of the task, with error rates generally increasing from initial to later blocks. The predictive relations of teacher-rated problem behaviors to performance trajectories on the CPT were examined using growth curve models. Higher rates of teacher-reported inattention and H/I were uniquely associated with higher rates of initial omission errors and initial commission errors, respectively. Higher rates of teacher-reported overall problem behaviors were associated with increasing rates of omission but not commission errors during the CPT; however, the relation was not specific to 1 type of problem behavior. The results of this study indicate that the pattern of errors on the CPT in preschool samples is complex and may be determined by multiple behavioral factors. These findings have implications for the interpretation of CPT performance in young children.

Sluggish cognitive tempo and its neurocognitive, social and emotive correlates: a systematic review of the current literature

OBJECTIVES

Since the elimination of items associated with Sluggish Cognitive Tempo (SCT) during the transition from DSM-III to DSM-IV from the diagnostic criteria of Attention-deficit Hyperactivity Disorder (ADHD), interest in SCT and its associated cognitive as well as emotional and social consequences is on the increase. The current review discusses recent findings on SCT in clinical as well as community based ADHD populations. The focus is further on clinical correlates of SCT in populations different from ADHD, SCT's genetic background, SCT's association with internalizing and other behavioral comorbidities, as well as SCT's association with social functioning and its treatment efficacy.

METHOD

A systematic review of empirical studies on SCT in ADHD and other pathologies in PsycInfo, SocIndex, Web of Science and PubMed using the key terms "Sluggish Cognitive Tempo", "Cognitive Tempo", "Sluggish Tempo" was performed. Thirty-two out of 63 studies met inclusion criteria and are discussed in the current review.

RESULTS/CONCLUSION

From the current literature, it can be concluded that SCT is a psychometrically valid construct with additive value in the clinical field of ADHD, oppositional defiant disorder (ODD), internalizing disorders and neuro-rehabilitation. The taxonomy of SCT has been shown to be far from consistent across studies; however, the impact of SCT on individuals' functioning (e.g., academic achievement, social interactions) seems remarkable. SCT has been shown to share some of the genes with ADHD, however, related most strongly to non-shared environmental factors. Future research should focus on the identification of adequate SCT measurement to promote symptom tailored treatment and increase studies on SCT in populations different from ADHD.

Video game performances are preserved in ADHD children compared with controls

OBJECTIVE

Although ADHD and excessive video game playing have received some attention, few studies have explored the performances of ADHD children when playing video games. The authors hypothesized that performances of ADHD children would be as good as those of control children in motivating video games tasks but not in the Continuous Performance Test II (CPT II).

METHOD

The sample consisted of 26 ADHD children and 16 control children. Performances of ADHD and control children were compared on three commercially available games, on the repetition of every game, and on the CPT II.

RESULTS

ADHD children had lower performances on the CPT II than did controls, but they exhibited equivalent performances to controls when playing video games at both sessions and on all three games.

CONCLUSION

When playing video games, ADHD children present no difference in inhibitory performances compared with control children. This demonstrates that cognitive difficulties in ADHD are task dependent.

Annual research review: Reaction time variability in ADHD and autism spectrum disorders: measurement and mechanisms of a proposed trans-diagnostic phenotype

BACKGROUND

Intraindividual variability in reaction time (RT) has received extensive discussion as an indicator of cognitive performance, a putative intermediate phenotype of many clinical disorders, and a possible trans-diagnostic phenotype that may elucidate shared risk factors for mechanisms of psychiatric illnesses.

SCOPE AND METHODOLOGY

Using the examples of attention deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD), we discuss RT variability. We first present a new meta-analysis of RT variability in ASD with and without comorbid ADHD. We then discuss potential mechanisms that may account for RT variability and statistical models that disentangle the cognitive processes affecting RTs. We then report a second meta-analysis comparing ADHD and non-ADHD children on diffusion model parameters. We consider how findings inform the search for neural correlates of RT variability.

FINDINGS

Results suggest that RT variability is increased in ASD only when children with comorbid ADHD are included in the sample. Furthermore, RT variability in ADHD is explained by moderate to large increases (d = 0.63-0.99) in the ex-Gaussian parameter τ and the diffusion parameter drift rate, as well as by smaller differences (d = 0.32) in the diffusion parameter of nondecision time. The former may suggest problems in state regulation or arousal and difficulty detecting signal from noise, whereas the latter may reflect contributions from deficits in motor organization or output. The neuroimaging literature converges with this multicomponent interpretation and also highlights the role of top-down control circuits.

CONCLUSION

We underscore the importance of considering the interactions between top-down control, state regulation (e.g., arousal), and motor preparation when interpreting RT variability and conclude that decomposition of the RT signal provides superior interpretive power and suggests mechanisms convergent with those implicated using other cognitive paradigms. We conclude with specific recommendations for the field for next steps in the study of RT variability in neurodevelopmental disorders.

Effects of Methylphenidate on Attention Skills in Children With Attention Deficit/Hyperactivity Disorder

This study aimed to investigate the effects of methylphenidate on children with Attention Deficit Hyperactivity Disorder (ADHD). The study employed a conceptual framework of attention, consistent with contemporary theory, and including the following components: sustained attention, selective attention, divided attention, shifting attention, and speed of information processing. Fifteen children (12 boys and 3 girls) of normal intelligence, with a diagnosis of ADHD according to the DSM-IV criteria, and ranging in age from 8 to 11 years participated in the study. Children's attentional abilities were evaluated using the Test of Everyday Attention for Children (TEA-Ch: Manly, Roberston, Anderson, & Nimmo-Smith, 1999). A double-blind counterbalanced repeated-measures design approach was employed to tap on–off medication effects, and deviations from normal. Results showed that comparisons between on–off medication conditions generally detected few differences with respect to sustained and selective attention measures and simple processing speed. In contrast, for higher-level attention domains, including shifting and divided attention, children on medication demonstrated a speed–accuracy trade-off, exhibiting greater accuracy, but slower completion times. When data from the ADHD group were compared to controls a consistent pattern emerged, with children with ADHD in the medication condition being more accurate across all attention domains on all measures. While these children also tended to record slower completion times, group differences and effect sizes were of smaller magnitude. The findings of this study suggest a possible speed–accuracy trade-off effect for children with ADHD on medication.

Methylphenidate, interstimulus interval, and reaction time performance of children with attention deficit/hyperactivity disorder: a pilot study

Thirteen children with attention deficit/hyperactivity disorder (ADHD: DSM-IV-TR) participated in the pilot study. They carried out a Go/No-Go test with a short (2 seconds) and long (6 seconds) interstimulus interval (ISI) when on placebo and a therapeutic dose of methylphenidate (MPH). For the long-ISI placebo condition the responses were slow and inaccurate. This pattern of response may be due to underactivation of the readiness-to-respond state that is not fully controlled by effort allocation. Speed of response and accuracy were enhanced during the short-ISI placebo condition and the long-ISI MPH condition. However, the combined effect (short ISI and MPH) resulted in a fast but inaccurate response style. This pattern of response may be due to overactivation of the readiness-to-respond state. The data of the pilot study support the stimulus shift hypothesis: MPH administration result in deterioration on tests on which children had previously done well (short ISI plus placebo versus short ISI plus MPH). In addition, the data support the idea that ADHD is associated with poor state regulation rather than motivational (delay aversion) theories or temporal-processing/time-estimation theories of ADHD. The pilot study defined empirically an issue for further study with the larger controlled sample.

Attentional and processing skills following traumatic brain injury in early childhood

PRIMARY OBJECTIVE

Attentional deficits are common following TBI in adults. This study examined whether these skills are also vulnerable following early childhood injury, when such skills are rapidly developing.

RESEARCH DESIGN

This study investigated attention 30 months post-TBI in pre-schoolers (n=56) and age-matched controls (n=26). TBI children were divided into mild, moderate and severe injury groups.

METHODS AND PROCEDURE

Pre-injury data were collected at time of injury. Assessment of attention included the Continuous Performance Test, Wechsler Intelligence Scale and Personality Inventory for Children.

MAIN OUTCOMES AND RESULTS

Severe TBI was associated with reduced accuracy and slowed processing, particularly on complex motor responses. Sustained attention was more intact. Parental reports indicate internalized behavioural problems and somatic complaints.

CONCLUSIONS

Young children with severe TBI are at risk for severe, persisting attentional impairments. Children with mild and moderate TBI show better outcome, with pre-injury behaviour and age also predictive of attentional skills at 30 months post-injury.

Vigilance and sustained attention in children and adults with ADHD

OBJECTIVE

The present article tests the hypothesis of a sustained attention deficit in children and adults suffering from ADHD.

METHOD

Vigilance and sustained attention of 52 children with ADHD and 38 adults with ADHD were assessed using a computerized vigilance task. Furthermore, the attentional performance of healthy children (N = 52) and healthy adults (N = 38) was examined.

RESULTS

Children and adults with ADHD performed significantly less well in the vigilance task than healthy participants (main effect for group). Furthermore, children and adults showed a significant decrease of performance over time (time-on-task effects). However, there was no greater decrement of performance with the passage of time in patient groups than in control groups (group-by-time interaction).

CONCLUSION

The present results do not support the hypothesis of a sustained attention deficit in children and adults with ADHD.

Intelligence and Specific Cognitive Abilities in Children

This community-based study investigated the relationships between measures of specific cognitive functions (such as working memory [WM] and interference control) and intelligence in 283 8- to 11-year-old children, including 124 children who fulfilled criteria for a psychiatric diagnosis. A hierarchical regression analysis was used to overcome issues of overlapping predictor constructs. The results generally showed that measures of processing speed, WM, as well as inhibitory interference control entered in the order of presentation, each contributed uniquely to the explanation of fluid intelligence performance. The results for crystallized intelligence performance generally showed that the measures of processing speed, short-term memory (STM), WM, and sustained attention – entered in that order – made significant independent contributions. While effect sizes varied somewhat for contributions in the whole sample compared with the subgroup not meeting criteria for a psychiatric diagnosis, there were no significant differences. The findings therefore should be broadly representative in indicating that the unique aspects of these cognitive functions are important in the explanation of intelligence. The findings also demonstrate important independent features of the functions used as predictors.

Sustained and focused attention deficits in adult ADHD

OBJECTIVE

To examine the specificity of deficits in focused attention and sustained attention in adults with ADHD and to evaluate the effect of comorbidity.

METHOD

Twenty-eight adults with ADHD without comorbidity were compared with 28 ADHD outpatients with comorbidity. Two control groups were used: 68 adults referred for ADHD but with another psychopathology rather than ADHD (non-ADHD) and 28 healthy controls. All participants completed attention tests of the Amsterdam Neuropsychological Tasks program.

RESULTS

Both ADHD groups demonstrated a sustained attention deficit relative to the control groups, as indicated by a disproportionate deterioration of speed fluctuation with time-on-task reflecting temporal lapses in attention. Only the ADHD+ group showed focused attention deficits in that they were less able to ignore irrelevant information.

CONCLUSION

These findings show that adults with ADHD have specific deficits in sustained attention. Additional deficits in focused attention are confined to outpatients with ADHD and comorbidity.

Cognitive switching processes in young people with attention-deficit/hyperactivity disorder

Patients with attention-deficit/hyperactivity disorder (ADHD) can be slow at switching between stimuli, or between sets of stimuli to control behaviour appropriate to changing situations. We examined clinical and experimental parameters that may influence the speed of such processes measured in the trail-making (TMT) and switch-tasks in cases with ADHD combined type, their non-affected siblings and unrelated healthy controls. The latency for completion of the trail-making task controlling for psychomotor processing (TMT-B-A) was longer for ADHD cases, and correlated with Conners' ratings of symptom severity across all subjects. The effect decreased with age. Switch-task responses to questions of "Which number?" and "How many?" between sets of 1/111 or 3/333 elicited differential increases in latency with condition that affected all groups. But there was evidence for increased symptom-related intra-individual variability among the ADHD cases, and across all subjects. Young siblings showed familiality for some measures of TMT and switch-task performance but these were modest. The potential influences of moderator variables on the efficiency of processing stimulus change rather than the speed of processing are discussed.

Attentional functions in children and adolescents with attention-deficit/hyperactivity disorder with and without comorbid tic disorder

Although the coexistence of attention-deficit/hyperactivity disorder (ADHD) and tic disorder (TD) is common, the nature of association is yet not fully understood. Thus, the aim of the present study was to explore attentional dysfunction in children with pure ADHD compared to children with comorbid ADHD + TD. Three groups of 20 children each, aged 8-15 years with either ADHD, ADHD + chronic tic disorder or Tourette syndrome (ADHD + TD) and a healthy control group were compared in their performance on three computerized attention tasks. Tasks of sustained attention, selective attention and interference control were employed. In addition, parental ratings of ADHD symptom severity and behaviour problems were obtained. Both clinical groups were rated as equally inattentive, however, externalising symptoms were more severe in the ADHD group. Objective measures of attentional performance revealed differences between the groups: whereas the ADHD group was markedly impaired in sustaining attention and selective attention/inhibitory control, the ADHD + TD group only showed marginal deficits in selective attention/inhibitory control. Possible explanations for the superior performance of the comorbid group are discussed: In particular, the results may indicate that in some patients, the tic disorder produces behavioural symptoms of ADHD, but not the broad neurocognitive deficits that usually are associated with ADHD. Alternatively, compensatory neural mechanisms of TD patients may result in a better neuropsychological performance of comorbid patients relative to patients suffering from pure ADHD.

Attention-Deficit/Hyperactivity Disorder and Working Memory: A Task Switching Paradigm

This study investigated working memory (WM) in children with Attention-Deficit/Hyperactivity Disorder (ADHD) using a task switching paradigm with Stroop color-word stimuli which required participants to switch from color-naming to word-reading. High and low WM load conditions were compared by manipulation of task reminders as a tempo cue. The sample comprised 83 children with ADHD and 29 normal children comparable in age (aged 7 to 13). Within the ADHD group, participants were divided according to the presence or absence of Learning Disability (LD). Results indicated that children with ADHD had slower response times and less accurate responses in general, however, the ADHD groups were not consistently slower in the high WM load condition. Instead, an impairment in adjusting response speed to cope with higher task demands (i.e., high WM load condition) was found. These results do not support the previously documented association between ADHD and a primary deficit in WM for task switching. However, children with ADHD do demonstrate a specific difficulty in slowing down for a demanding task. Present findings suggest that earlier proposals of under-arousal and poor state regulation in ADHD deserve renewed attention.

The Development of Sustained Attention in Children: The Effect of Age and Task Load

This study explored how children's sustained attention develops and the effect of manipulating task parameters on sustained attention. The sample comprised 57 children (5-12 years) who completed CogState and Score! (Test of Everyday Attention for Children). Novel variability and traditional indices indicated rapid development from 5-6 to 8-9 years on all measures and a developmental plateau from 8-9 to 11-12, with growth evident on some measures. Findings suggest that sustained attention improves to age 10, then plateaus with only minor improvements. Further, performance was generally poorer on high load tasks compared to low load, with the same developmental pattern uncovered.

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.

Methylphenidate-induced improvements of various measures of attention in adults with attention deficit hyperactivity disorder

The present study examined the effect of the stimulant medication methylphenidate (MPH) on attentional functioning of adults with ADHD. Sixteen adults with a diagnosed ADHD without comorbidity were assessed twice, at baseline off MPH and following MPH treatment. The assessment battery consisted of reaction time tasks of low complexity, including measures of alertness--subdivided into tonic and phasic alertness, vigilance, divided attention, flexibility and such aspects of selective attention as including focused attention, inhibition and integration of sensory information. In addition, 16 healthy participants who were matched to adults with ADHD according to sex, age, education level and intellectual functions were also assessed twice using the same test battery. The results of the present study suggest that adults with ADHD off stimulant medication are seriously impaired in various components of attention including vigilance, divided attention, selective attention and flexibility. These impairments of attention were observed primarily in regard to reaction time and its variability. Treatment of adults with ADHD using individually tailored doses of MPH has a positive effect on measures of alertness, vigilance, selective attention, divided attention and flexibility. However, even on MPH adults with ADHD displayed considerable deficits in vigilance and integration of sensory information. The present findings indicate that adults with ADHD are not differentially impaired in attentional processes but may suffer from a more global deficit of attention. Although MPH treatment has been found to be effective in the treatment of the attention deficit of adults with ADHD, additional treatment appears to be necessary.

Dissecting the attention deficit hyperactivity disorder (ADHD) phenotype: sustained attention, response variability and spatial attentional asymmetries in relation to dopamine transporter (DAT1) genotype

ADHD is a childhood-onset behavioural disorder with a heterogeneous profile of neuropsychological impairment. Neuropsychological heterogeneity may, in part, reflect underlying genetic differences. Here we examined sustained attention, response variability and spatial attentional asymmetries in a sample of children and adolescents with ADHD (n=22) in relation to dopamine transporter genotype (DAT1) and also controls (n=20). Participants performed the sustained attention to response task (SART) (testing sustained attention and response variability) and the greyscales task (a perceptual measure of attentional bias). The latter has previously been shown to yield a robust leftward attentional asymmetry in healthy subjects. The 10-repeat allele of the DAT1 gene has been associated with ADHD in a number of studies and appears to have biological significance. The ADHD group was sub-divided into those individuals with two copies of the "high-risk" 10-repeat allele (high-risk DAT1) versus those with one or no copies of this allele (low-risk DAT1). The high-risk DAT1 ADHD group displayed greater response variability on the SART than either the low-risk DAT1 group or healthy controls, whereas the latter two groups did not differ. Further, the high-risk DAT1 group showed an attenuated spatial asymmetry, relative to the low-risk DAT1 ADHD group, who showed the typical leftward attentional asymmetry. Our results suggest that the 10-repeat DAT1 allele may mediate neuropsychological impairment in ADHD. The application of molecular genetics may help to define neuropsychological impaired subgroups of ADHD.

Sustained attention and response inhibition in young children at risk for Attention Deficit/Hyperactivity Disorder

BACKGROUND

Studies of school-aged children, adolescents, and adults with Attention Deficit/Hyperactivity Disorder (ADHD) have variably shown ADHD-related impairment in both inhibitory control and sustained attention. However, few studies have examined ADHD-associated patterns of performance on these tasks among younger children (below age 7 years).

METHODS

A combined continuous performance test and go/no-go task (CPT/GNG) and the Day-Night Stroop Task (DNST) were administered to an ethnically diverse sample of 3.44- to 6.95-year-old children rated by parents and teachers as being either high risk or low risk for ADHD. All children performed the DNST (N = 71) and a subset of the sample (N = 44) performed the CPT/GNG. Analyses assessed task validity as well as the effects of age and risk status.

RESULTS

Significant main effects for age and risk status were found on all tasks. In addition, age x condition interactions were found for the CPT and DNST, which suggest that the tasks were sensitive to age-related changes in sustained attention and inhibitory control respectively. No significant risk status x condition interactions were found, suggesting that young children at risk for ADHD do not exhibit specific deficits in either inhibitory control or sustained attention. The most consistent effect related to risk status across tasks was the greater number of errors and longer and more variable reaction times on the part of children at risk for ADHD irrespective of condition.

CONCLUSIONS

ADHD-associated decrements in performance on these tasks appear to be attributable either to generalized behavioral dysregulation or poor state regulation rather than to deficient inhibitory control.

Varieties of attention-deficit/hyperactivity disorder-related intra-individual variability

Intra-individual variability in behavior and functioning is ubiquitous among children with attention-deficit/hyperactivity disorder (ADHD), but it has not been systematically examined or integrated within causal models. This article seeks to provide a conceptual, methodologic, and analytic framework as a foundation for future research. We first identify five key research questions and methodologic issues. For illustration, we examine the periodic structure of Eriksen Flanker task reaction time (RT) data obtained from 24 boys with ADHD and 18 age-matched comparison boys. Reaction time variability in ADHD differed quantitatively from control subjects, particularly at a modal frequency around .05 Hz (cycle length approximately 20 sec). These oscillations in RT were unaffected by double-blind placebo and were suppressed by double-blind methylphenidate. Together with converging lines of basic and clinical evidence, these secondary data analyses support the speculative hypothesis that the increased power of multisecond oscillations in ADHD RT data, and by inference, in attentional performance, represents a catecholaminergic deficit in the ability to appropriately modulate such oscillations in neuronal activity. These results highlight the importance of retaining time-series data and quantitatively examining intra-subject measures of variability as a putative endophenotype for ADHD.

Searching for the attention deficit in attention deficit hyperactivity disorder: the case of visuospatial orienting

We review all 14 extant studies of covert visuospatial attention in attention deficit hyperactivity disorder (ADHD) (total N=248). Metaanalysis showed that intriguing but isolated findings of alerting or posterior disengage deficits were too small to reliably detect with the sample sizes typically employed. Posterior move and engage operations and the vigilance sustained attention process were normal in ADHD. For exogenous cues, effect sizes for group differences were homogeneously small across all repeated-measures conditions, as were calculations of cost, benefit, and validity effects. For endogenous cues, effect sizes were heterogeneous; however, calculations of cost, benefit, and validity effects were small and homogenous. The most parsimonious conclusion may be that ADHD is not characterized by significant visual orienting dysfunction, but questions remain about the extent of anterior lateralized effects in the combined subtype and about attentional functioning in the inattentive subtype.

Exploring selective attention in ADHD: visual search through space and time

BACKGROUND

In order to examine the mechanisms mediating selective attention in Attention Deficit Hyperactivity Disorder (ADHD), this study compared the performance of children diagnosed with ADHD to non-clinical controls on a visual search task in three conditions.

METHOD

In the single feature condition, the target differed from distractors in terms of shape only, whilst in the conjunction baseline, the target was defined by shape and colour relative to distractors. In the preview condition, the conjunction stimuli were segmented over time, so that one set of distractors appeared first, followed 1000 ms later by the second set with the target.

RESULTS

Although children with ADHD were slower overall than controls, RTs revealed no difference in search mechanisms between groups; for all children, search was more efficient in the single feature and preview conditions than in the conjunction baseline. However, children with ADHD made more errors, especially in the conjunction and preview conditions.

CONCLUSIONS

Children with ADHD were not impaired in their mechanisms of visual search relative to controls, but their error patterns implied the adoption of a premature response deadline in the conjunction search condition, and an occasional failure to inhibit old items in the preview condition.

Sustained performance and regulation of effort in clinical and non-clinical hyperactive children

OBJECTIVE

To study sustained performance and its relation to regulation of effort among four different groups of children: two clinical subgroups of children diagnosed with attention-deficit hyperactivity disorder (ADHD)--one with and one without comorbid oppositional defiant disorder (ODD); a control sample of children without a diagnosis of ADHD but with parental reports of hyperactivity; and a normal control sample.

METHODS

Sustained performance was studied (n=64) using a choice reaction time task with long interstimulus intervals, and hyperactive behaviour and regulation of effort was rated throughout the task.

RESULTS

The clinical sample differed from the normal controls regarding all measures of overall, but not initial, performance. When studying performance over time, the ADHD group was shown to differ from the normal controls with regard to omissions, mean reaction time and regulation of effort. No significant differences were found between the ADHD children with or without comorbid ODD. The non-clinical hyperactive children differed from the normal controls with regard to reaction time, initially and overall, and regulation of effort overall.

CONCLUSIONS

Deficits in sustained performance among ADHD children appear to be evident when long interstimulus intervals are used, and these deficits are related to poor regulation of effort. Further, the observed differences between ADHD children and normal controls do not appear to be a result of comorbid conduct problems. The non-clinical hyperactive children were more similar to the control group than to the ADHD group.

Handlungskontrolldefizite und störungsspezifische Zielintentionen bei der Hyperkinetischen Störung

Zusammenfassung. Theoretischer Hintergrund: In diesem Beitrag wird innerhalb der Rubikontheorie der Handlungsphasen eine integrative Beschreibung hyperkinetischer Verhaltensauffälligkeiten entwickelt. Fragestellung: Es wird geprüft, ob sich auf diese Weise verschiedene vorliegende Erklärungsansätze unter einer einheitlichen Rahmenkonzeption zusammenführen lassen. Methode: Mithilfe der Handlungsphasentheorie lässt sich einerseits ein motivationaler Erkärungsansatz für die Hyperkinetische Störung elaborieren, der störungsspezifische stimulationsbezogene Zielintentionen als Grundlage hyperkinetischer Verhaltensauffälligkeiten postuliert. Andererseits kann ein volitionaler Erklärungsansatz formuliert werden, der Handlungskontrolldefizite bei der Abschirmung von Zielintentionen in den Vordergrund stellt. Ergebnisse: Auf der Grundlage dieses theoretischen Ansatzes lassen sich empirische Hypothesen ableiten, die die Rolle verschiedener möglicher Teilursachen der hyperkinetischen Störung bei der Entstehung störungsspezifischer Verhaltensauffälligkeiten betreffen. Schlussfolgerung: Das zugrundegelegte handlungspsychologische Rahmenmodell ist damit sowohl zur Integration von Erklärungsansätzen als auch zur Ableitung neuer empirischer Vorhersagen geeignet.

Brain mapping of bilateral interactions in attention deficit hyperactivity disorder and control boys

OBJECTIVES

Children with attention deficit hyperactivity disorder (ADHD) are thought to have deficits in attentional control, whereas the status of deficits at visual and pre-motor processing stages is unclear.

METHODS

The timing of such deficits was examined with event-related potential (ERP) microstates (stimulus- and response-related) and continuous force recordings in 15 ADHD and 16 control boys in a choice reaction time task. Unilateral and bilateral stimulus and response conditions were used to assess bilateral interactions at visual, central, and pre-motor stages.

RESULTS

ADHD boys showed poorer performance, particularly in the bilateral conditions. In the visual P1 microstates, they exhibited less suppression of visual evoked potential (VEP) amplitudes but similar speeding of VEP latencies in the bilateral compared to the summed unilateral condition. The central P3 and pre-/post-response microstates were attenuated and topographically altered in ADHD boys. The attenuation was most pronounced in the bilateral condition and was similar for stimulus- and response-related averages. The lateralized readiness potential was also reduced in ADHD boys; this was most pronounced for the left hand responses.

CONCLUSIONS

Brain mapping during uni- and bilateral stimulus and response conditions thus indicates multilevel deficits in ADHD boys affecting visuo-attentional, central, and pre-motor processes.

Neurobiological models of attention-deficit/hyperactivity disorder: a brief review of the empirical evidence

Attention-deficit/hyperactivity disorder (ADHD) is a psychiatric disorder characterized by inattention, impulsivity, and overactivity that begins in childhood. While considerable research has focused on the neurobiological substrates of this disorder, the specific nature of the brain dysfunction in ADHD has remained elusive. However, early data from pharmacological treatment studies, as well as from basic research in animals and humans, initially led several investigators to develop neurobiological models of ADHD. These models of ADHD and more recent evidence from neuropsychological, neuroimaging, neurochemical, and genetic research are briefly reviewed. While not completely consistent, the empirical data suggest that dysfunction in prefrontal-striatal neural circuits, as well as in brain stem catecholamine systems that innervate these circuits, may underlie the executive function deficits in ADHD.

Neurocognitive functioning in adults with attention-deficit/hyperactivity disorder

The performance of nine adults with attention-deficit/hyperactivity disorder (ADHD) was compared with the performance of 23 normal controls on computerized measures of target orientation, sustained attention, encoding speed, and motor output/response organization to determine the nature of the neurocognitive deficits of adults with ADHD. While the groups' performances on measures of sustained attention and encoding speed did not differ, significant group differences were seen on a task that targeted motor output/response organization. These data suggest that the neurocognitive difficulties of ADHD adults are not related to a primary deficit in sustained attentional functioning. Rather, the deficient information processing in ADHD adults is related to difficulties with motor output/response organization.

Visual sustained attention in a child psychiatric population

OBJECTIVE

To increase knowledge of the diversity and specificity of sustained attention deficits in children with attention-deficit hyperactivity disorder (ADHD), with special reference to the issue of distinguishing between children with ADHD and children with other psychiatric diagnoses.

METHOD

A visual sustained attention task was used to compare 52 boys with ADHD with 55 normal controls, 29 boys with oppositional defiant disorder or conduct disorder (ODD/CD), 29 boys with anxiety or dysthymia (ANX/DYS), 43 boys with pervasive developmental disorder, 24 boys with ADHD plus ODD/CD, and 14 boys with ADHD plus ANX/DYS.

RESULTS

Compared with normal controls, children with ADHD were slower, were more inaccurate, were more impulsive, were less responsive to feedback, and showed less perceptual sensitivity and stability of performance, resulting in a marked decrease in vigilance over time. Unresponsiveness to feedback and the extent of the decrease in vigilance during time on task were found to be the only factors that distinguished children with ADHD from children with other diagnoses.

CONCLUSION

Although only children with ADHD are characterized primarily by "attention deficit," sustained attention deficit is common to a certain extent to all children with psychiatric disorders.

Differential measures of 'sustained attention' in children with attention-deficit/hyperactivity or tic disorders: relations to monoamine metabolism

Controversy exists on whether the constructs tested by paper/pencil and computerized continuous-performance tests (CPT) are similar, and the deficits recorded in children with attention-deficit/hyperactivity symptoms (ADHD) are comparable. Signal-detection measures were recorded on four such tests of 'sustained attention', with increasing working-memory requirements in healthy children (14; mean 10 years), and those with ADHD (14; mean 10 years) or a tic syndrome (TS, 11; mean 11 years). Clinical associations were sought from 24-h urinary measures of monoamine activity. The cancellation paper/pencil test revealed no group differences for errors or signal detection measures. On the CPT, ADHD children made more omission and commission errors than control subjects, but TS children made mostly omissions. This reflected the poor perceptual sensitivity (d-prime, d') for ADHD and conservative response criteria (beta) for TS children. This group difference extended to the CPTax, which was shown on a regression analysis to test for putative working-memory-related abilities as well as concentration. In all children, immediate response-feedback reduced omissions, and modestly improved d'. CPTax performance related negatively to dopamine metabolism in control subjects and to serotonin metabolism in the ADHD group. But comparisons between the metabolites in the ADHD group suggest that increased serotonin and decreased noradrenaline, with respect to dopamine metabolism, may detract from CPT performance in terms of d'. CPT tasks demonstrated a perceptual-based impairment in ADHD and response conservatism in TS patients independent of difficulty. Catecholamine activity was implicated in the promotion of perceptual processing in normal and ADHD children, but serotonin activity may contribute to poor CPTax (working-memory) performance in ADHD patients.

Hyperactivity in children: a focus on genetic research and psychological theories

Hyperactivity has attracted a large amount of research interest in recent years. Here we review developments in genetic research and in research testing psychological theories of the condition. Family, adoptee and twin studies indicate a strong role for genetic factors in the etiology of hyperactivity. Evidence is emerging also from molecular genetic studies, implicating specific genes that may be involved. At the level of cognitive functioning, a divided, focused or sustained attention deficit does not seem to be a 'core' deficit in hyperactivity. Although children with hyperactivity often perform poorly on certain executive function tasks, there is disagreement about the interpretation of these findings. The association reported in some studies between a slow inhibitory process and hyperactivity may reflect a generally slow, variable in speed and inaccurate pattern of responding. Hypotheses about psychological mechanisms such as state regulation or delay aversion provide alternative, and particularly encouraging, interpretations of the findings. We discuss the possible integration of the two lines of research--those of genetic research and research on psychological mechanisms.

Motor control and state regulation in children with ADHD: a cardiac response study

The goal of the current study was to investigate whether poor motor control in children with Attention-Deficit Hyperactivity Disorder (ADHD) was associated with a state regulation deficit. For this purpose, 28 ADHD and 22 healthy children carried out two Go No-Go tests: one with a fast stimulus presentation rate, and the other with a slow stimulus presentation rate. Groups were compared on RT performance and on specific cardiac measures, reflecting arousal, motor activation/inhibition, and effort allocation. No group difference in the arousal measure (mean heart rate) was found. Further, groups did not differ with respect to response inhibition: in both the fast and slow condition, ADHD children made comparable numbers of errors of commission to the control group, and the groups did not differ with respect to the heart rate deceleration after the onset of the No-Go signal, reflecting motor inhibition. Group differences were found with respect to motor activation and effort allocation in the condition with a slow presentation rate. In this condition: (1) ADHD children reacted more slowly to Go signals than control children, suggesting poor motor activation; (2) the heart rate deceleration before the onset of Go signals, which is believed to reflect motor preparation, was less pronounced in the ADHD children; (3) after Go signals, where a response was given, the cardiac shift from deceleration to acceleration, indicating response initiation, was delayed in ADHD children; and (4) ADHD children had greater heart rate variability (0.10 Hz component) than the control group, indicating that less effort was allocated. No group differences in motor activation and effort allocation were found in the condition with a fast presentation rate of stimuli. We conclude, therefore, that a slow presentation rate of stimuli brings the ADHD child in a non-optimal activation state.

Factor analysis of the continuous performance test and parent-teacher reports of attention deficit disorder

The relationships between a computerized measure of attention deficit disorder and scores from two commonly used parent-teacher reports were investigated. A factor analysis of the raw omission and commission scores provided by the Continuous Performance Test and Conners' Parent Rating Scale and the ADD-H Comprehensive Teacher Rating Scale indicated that for a sample of 54 children the Continuous Performance Test was most closely associated with measures of impulsivity and hyperactivity provided by the Conners' rating. This finding was congruent with the use of the Continuous Performance Test in the evaluation as a measure of Attention Deficit Hyperactivity Disorder and suggestive of a positive and significant relation between this computerized measure of behavior and parents' perception of behavior. Little association was detected between scores on the teachers' scale and omission and commission scores.

Heart rate variability and sustained attention in ADHD children

The major goal of the current study was to investigate the association between continuous performance tests (CPTs) and the heart rate variability (HRV) of attention deficit hyperactivity disorder (ADHD) children. The HRV, specifically the 0.10-Hz component, may be considered to be a psychophysiological index of effort allocation (motivation): The less effort the subject allocates, the greater the 0.10-Hz component. Results indicated that, compared to controls, ADHD subjects had a greater 0.10-Hz component, which was associated with poor test performance over time. Thus, using a psychophysiological measure, we were able to confirm the clinical concept of ADHD from a motivational perspective.