On dysfunction and function in psychological theories of childhood disorder

Attention-deficit/hyperactivity disorder (ADHD) in cultural context II: a comparison of the links between ADHD symptoms and waiting-related responses in Hong Kong and UK

The concept of attention-deficit/hyperactivity disorder (ADHD) is considered to have cross-cultural validity, but direct comparisons of its psychological characteristics across cultures are limited. This study investigates whether preschool children's ADHD symptoms expressed in two cultures with different views about child behaviour and parenting, Hong Kong and the UK, show the same pattern of associations with their waiting-related abilities and reactions, an important marker of early self-regulation. A community sample of 112 preschoolers (mean age = 46.22 months; 55 from UK, 57 from HK) completed three tasks measuring different waiting elements - waiting for rewards, choosing the amount of time to wait, and having to wait unexpectedly when a task is interrupted. Participants' waiting-related behavioural and emotional reactions were coded. Parents rated their children's ADHD symptoms and delay aversion. Our findings revealed that the associations between ADHD symptoms and waiting-related responses were comparable in both UK and HK samples. This suggests that the core psychological characteristics of ADHD, particularly in relation to waiting behaviours, may exhibit similarity across cultural contexts. Future research can extend this cross-cultural analysis to other ADHD-related psychological domains and explore additional cultural settings.

Brain mechanisms of temporal processing in impulsivity: Relevance to attention-deficit hyperactivity disorder

In this article, we critique the hypothesis that different varieties of impulsivity, including impulsiveness present in attention-deficit hyperactivity disorder, encompass an accelerated perception of time. This conceptualisation provides insights into how individuals with attention-deficit hyperactivity disorder have the capacity to maximise cognitive capabilities by more closely aligning themselves with appropriate environmental contexts (e.g. fast paced tasks that prevent boredom). We discuss the evidence for altered time perception in attention-deficit hyperactivity disorder alongside putative underlying neurobiological substrates, including a distributed brain network mediating time perception over multiple timescales. In particular, we explore the importance of temporal representations across the brain for time perception and symptom manifestation in attention-deficit hyperactivity disorder, including a prominent role of the hippocampus and other temporal lobe regions. We also reflect on how abnormalities in the perception of time may be relevant for understanding the aetiology of attention-deficit hyperactivity disorder and mechanism of action of existing medications.

An experimental task to measure preschool children's frustration induced by having to wait unexpectedly: The role of sensitivity to delay and culture

The ability to manage frustration induced by having to wait for valued outcomes emerges across childhood and is an important marker of self-regulatory capacity. However, approaches to measure this capacity in preschool children are lacking. In this study, we introduced a new task, the Preschool Delay Frustration Task (P-DeFT), designed specifically to identify children's behavioral and emotional markers of waiting-induced frustration during the imposed wait period and after the release from waiting. We then explored how waiting-induced frustration relates to individual differences in delay sensitivity and whether it differs between two cultural groups thought to have different attitudes toward children's conduct and performance: Hong Kong (HK) and the United Kingdom (UK). A total of 112 preschool children (mean age = 46.22 months) completed the P-DeFT in a quiet laboratory. Each trial had two stages; first, a button press elicited a Go signal; second, this Go signal allowed children to go to a "supermarket" to pick a target toy. On most trials, the Go signal occurred immediately on the first press. On 6 trials, an unexpected/unsignaled 5- or 10-s pre-Go-signal period was imposed. Frustration was indexed by performance (button presses and press duration), behavioral agitation, and negative affect during the pre-Go-signal wait period and the post-Go-signal shopping task. Parents rated their children's delay sensitivity. Waiting-related frustration expressed during both the pre-Go-signal wait period and the post-Go-signal task varied with (a) the length of wait and (b) individual differences in parent-rated delay sensitivity. UK children displayed more negative affect during delay than their HK counterparts, although the relationship between delay sensitivity and frustration was culturally invariant.

The amygdala in adolescents with attention-deficit/hyperactivity disorder: Structural and functional correlates of delay aversion

OBJECTIVES

Recent magnetic resonance imaging (MRI) studies implicate structural alterations of amygdala, a brain region responsible for processing and experiencing negative emotions, in adolescents with attention-deficit/hyperactivity disorder (ADHD). Here we examined ADHD-related structural correlates of amygdala functional activity elicited during a functional MRI task designed to test behavioural and brain responses to the imposition of delay - an event known to both elicit amygdala hyperactivation and aversity in ADHD.

METHODS

Structural MRI scans from 28 right-handed male adolescents with combined type ADHD and 32 age-matched controls were analysed. Regional grey matter volumes of ADHD and control participants (P[FWE] < 0.05) were correlated with delay aversion self-ratings and neural activity in response to delay-related cues on the Escape Delay Incentive fMRI task.

RESULTS

ADHD was associated with significantly reduced volumes in bilateral amygdala, parahippocampal and temporal gyrus (P[FWE] < 0.05), greater basolateral amygdala activation to delay-related cues (P[FWE] < 0.05) and higher delay aversion self-ratings. Amygdala volume reductions were significantly correlated with, and statistically mediated the pathway from ADHD to, delay-cue-related amygdala hyperactivity (P < 0.01) and self-reported delay aversion (P < 0.01).

CONCLUSIONS

We provide the first evidence of the functional significance of reduced amygdala volumes in adolescents with ADHD by highlighting its relation to delay-induced brain activity that is linked to delay aversion.

Exploring the Variability in Reaction Times of Preschoolers at Risk of Attention-Deficit/Hyperactivity Disorder: an ex-Gaussian Analysis

Reaction times (RTs) are typically slower and more variable in individuals with attention-deficit/hyperactivity disorder (ADHD). Analysis of the ex-Gaussian RT distribution, which is described by mu, sigma (mean and standard deviation, respectively, of the normal distribution) and tau (that of exponential distribution), reveals that individuals with ADHD do not display overall slower RTs but have a high proportion of extremely slow RTs, represented by a high tau value. Although this is a vital component for describing ADHD-related RT variability in school-aged children, adolescents, and adults, it has not been thoroughly studied at the preschool age. We assessed 65 preschoolers at risk of ADHD and 98 typically developing preschoolers with the Conners' Kiddie Continuous Performance Test (K-CPT) and parental and teacher reports of ADHD symptoms. We found that preschoolers at risk of ADHD had greater values for RT standard deviation, sigma, and tau than typically developing preschoolers at long inter-stimulus intervals (ISIs) (3 s), but not at short ISIs (1.5 s). This suggests that attention problems in preschool children may only be apparent in the tasks with a relatively slow event rate. Our study demonstrates that the ex-Gaussian tau value is essential for describing the inattentive component of task performance in preschoolers with heightened ADHD symptoms. Furthermore, the fact that the tau effect was modulated by ISI suggests that the longer duration (3 s vs. 1.5 s) is a non-optimal energetic state in preschoolers at risk of ADHD, and that this might account for the subtle attentional flaw in task performance.

The reinforcing value of delay escape in attention deficit/hyperactivity disorder: An electrophysiological study

The delay aversion hypothesis argues that the tendency for impulsive choice (preference for smaller sooner over larger later rewards) is motivated by the escape of negative affective states associated with delay. This model predicts that individuals with ADHD find the imposition of delay before an outcome or event especially aversive and its escape reinforcing. Consistent with this, fMRI studies show that ADHD is associated with amygdala hyper-sensitivity to cues of delay. However, evidence that delay escape is reinforcing is lacking. Here we extend fMRI research by using electrophysiological methods to study the reinforcing properties of delay-escape in ADHD. Thirty controls and 25 adolescents with ADHD aged 10–15 years performed the Escape Delay Incentive (EDI) task- in which pre-target cues indicated three conditions: i) CERTAIN DELAY: delay would follow a response irrespective of response speed ii) CONDITIONAL DELAY: delay would only follow if the response was too slow and iii) NO DELAY: delay would follow the response whatever the speed. We focused on the Contingent Negative Variation (CNV), a cue-evoked marker of motivated response preparation, across two time windows (CNV1 and CNV2). We took measures of parent, teacher and self-rated ADHD symptoms, task performance (RT) and self-rated delay aversion. We isolated CNV components and compared these between ADHD and controls. Adolescents with ADHD displayed a larger CNV2 to the CONDITIONAL DELAY than the CERTAIN DELAY cues compared to controls. However, this effect was not mirrored at the performance level and was unrelated to self-reported delay aversion. Our study provides the first ERP evidence that delay escape differentially reinforcers neural activation of attention preparation in ADHD cases. Future studies should examine the impact of varying cognitive load on task EDI performance.

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Individuals with ADHD find cues predicting the imposition of delay aversive but evidence that delay escape is reinforcing is lacking

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We used the Escape-Delay Incentive Task to isolate the CNV, reflecting motivated attention preparation to escape delay cues

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Adolescents with ADHD displayed larger CNV2 to cues signalling the possibility to escape delay

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Results provide the first ERP evidence of the reinforcing value of delay escape in ADHD

Development of the frontal lobe

Development of the frontal lobe is critical to acquisition, execution, and control of a wide range of functions, from basic motor response to complex decision-making. These functions are influenced by contingency-based (e.g., reward and response-cost/punishment) feedback that is mediated through the adaptive integration of fronto-subcortical neural circuitry. The frontal lobe manages incoming information and chooses the appropriate action based on one's goals in a particular context. This aspect of frontal function, while only one component, is crucial to development and maintenance of approach and avoidance behavior central to all human (and animal) behavior. Furthermore, disruptions in fronto-subcortical circuitry governing motivated behavior appear to contribute to a range of developmental disorders, including attention-deficit/hyperactivity disorder (ADHD), and confer vulnerability for psychopathology more broadly. The particular deficits that manifest in altered behavior depend upon the specific circuitry that is compromised due to the functional specificity of distinct regions of the frontal lobe and its interconnections with subcortical structures. Neurobiologic models of motivated behavior provide a valuable framework for characterizing developmental disorders from a transdiagnostic dimensional systems perspective. Improved characterization of approach and avoidance motivation across neurodevelopmental disorders has the potential to inform the development of novel interventions and personalized medicine.

ADHD-related sex differences in fronto-subcortical intrinsic functional connectivity and associations with delay discounting

Background

Attention-deficit/hyperactivity disorder (ADHD) is associated with atypical fronto-subcortical neural circuitry and heightened delay discounting, or a stronger preference for smaller, immediate rewards over larger, delayed rewards. Recent evidence of ADHD-related sex differences in brain structure and function suggests anomalies in fronto-subcortical circuitry may differ among girls and boys with ADHD. The current study examined whether the functional connectivity (FC) within fronto-subcortical neural circuitry differs among girls and boys with ADHD compared to same-sex typically developing (TD) controls and relates to delay discounting.

Methods

Participants include 8–12-year-old children with ADHD (n = 72, 20 girls) and TD controls (n = 75, 21 girls). Fronto-subcortical regions of interest were functionally defined by applying independent component analysis to resting-state fMRI data. Intrinsic FC between subcortical components, including the striatum and amygdala, and prefrontal components, including ventromedial prefrontal cortex (vmPFC), anterior cingulate cortex (ACC), and anterior dorsolateral prefrontal cortex (dlPFC), was compared across diagnostic groups overall and within sex. Correlations between intrinsic FC of the six fronto-subcortical pairs and delay discounting were also examined.

Results

Both girls and boys with ADHD show atypical FC between vmPFC and subcortical regions including the striatum (stronger positive FC in ADHD) and amygdala (weaker negative FC in ADHD), with the greatest diagnostic effects among girls. In addition, girls with ADHD show atypical intrinsic FC between the striatum and dlPFC components, including stronger positive FC with ACC and stronger negative FC with dlPFC. Further, girls but not boys, with ADHD, show heightened real-time delay discounting. Brain–behavior correlations suggest (1) stronger negative FC between the striatal and dlPFC components correlated with greater money delay discounting across all participants and (2) stronger FC between the amygdala with both the dlPFC and ACC components was differentially related to heightened real-time discounting among girls and boys with and without ADHD.

Conclusions

Our findings suggest fronto-subcortical functional networks are affected in children with ADHD, particularly girls, and relate to delay discounting. These results also provide preliminary evidence of greater disruptions in fronto-subcortical FC among girls with ADHD that is not due to elevated inattention symptom severity, intellectual reasoning ability, age, or head motion.

Electronic supplementary material

The online version of this article (10.1186/s11689-018-9254-9) contains supplementary material, which is available to authorized users.

Delay Aversion and Executive Functioning in Adults With Attention-Deficit/Hyperactivity Disorder: Before and After Stimulant Treatment

BACKGROUND

Attention deficit hyperactivity disorder is a heterogeneous disorder, associated with deficits in motivation (e.g., delay aversion) and cognition. Methylphenidate is recommended as a first line treatment for attention deficit hyperactivity disorder symptoms, but little is known about its nonacute effects on motivational and cognitive deficits, particularly in adults with attention deficit hyperactivity disorder.

METHODS

We utilized a prospective, non-randomized, non-blinded, 6-week follow-up design with 42 initially stimulant medication-naïve adult patients with moderate to severe attention deficit hyperactivity disorder, and 42 age- and parental education-matched healthy controls. Delay aversion and executive functioning were assessed with 2 questionnaires and 5 performance-based tests.

RESULTS

At baseline, patients and controls differed significantly on performance-based measures (moderate to large effect sizes), and self-report of delay aversion and executive functioning (very large effect sizes). Treatment with methylphenidate medication (mean dose 65.54 mg/d, SD=10.39) was not associated with improvements in performance-based measures of delay aversion and executive functioning compared to controls, although improvements in self-report executive functioning and delay aversion were found. Self-reported delay aversion was most consistently associated with ADHD symptomatology at baseline and after medication.

CONCLUSION

Methylphenidate treatment does not have an effect on performance-based measures of delay aversion and executive functioning, but may have significant effects on self-reported delay aversion and executive functioning. The latter finding should be interpreted cautiously, given the subjective nature of these measures and design limitations. Self-reported delay aversion is most consistently associated with attention deficit hyperactivity disorder symptomatology.

Delay aversion in attention deficit/hyperactivity disorder is mediated by amygdala and prefrontal cortex hyper-activation

BACKGROUND

Experimental research supports delay aversion as a motivational feature of attention deficit/hyperactivity disorder (ADHD). To investigate the neurobiology of delay aversion in ADHD, this study examined whether adolescents with ADHD display an unusually strong activation in affective brain regions in response to cues predicting forthcoming delay and whether these effects are (a) delay-dose dependent and (b) statistically mediate the association between ADHD and self-reported delay aversion.

METHODS

Twenty-nine right-handed male adolescents with combined type ADHD and 32 typically developing controls (ages 10-18 years) performed a reaction time task in an MRI scanner. Pretarget cues indicated delay-related response consequences. One indicated that delay would follow the response irrespective of response speed (CERTAIN DELAY), a second that delay would only follow if the response was too slow (CONDITIONAL DELAY), and a third that no delay would follow the response whatever its speed (NO DELAY). Delay levels were 2, 6, or 14 s. Participants also rated their own delay aversion in everyday life.

RESULTS

Individuals with ADHD rated themselves as more delay averse than controls. Significantly greater activation to CERTAIN DELAY cues relative to NO DELAY cues was found in participants with ADHD compared to controls (bilaterally) in amygdala, anterior insula, temporal pole, dorsolateral prefrontal cortex (DLPFC), and ventromedial prefrontal cortex. Amygdala and DLPFC activation strength were strongly and delay-dose dependently correlated with delay aversion ratings, and statistically mediated the relationship between ADHD status and delay aversion.

CONCLUSIONS

When presented with cues predicting impending delay, adolescents with ADHD, relative to controls, displayed a delay-related increase in activation in amygdala and DLPFC, regions known to be implicated in the processing of aversive events. Future studies should examine the specificity of these effects to delay aversion compared to aversive events in general.

Overlapping and disease specific trait, response, and reflection impulsivity in adolescents with first-episode schizophrenia spectrum disorders or attention-deficit/hyperactivity disorder

BACKGROUND

Schizophrenia and attention-deficit/hyperactivity disorder (ADHD) are developmental disorders with shared clinical characteristics such as cognitive impairments and impulsivity. Impulsivity is a core feature of ADHD and an important factor in aggression, violence, and substance use in schizophrenia. Based on the hypothesis that schizophrenia and ADHD represent a continuum of neurodevelopmental impairments, the aim was to identify overlapping and disease specific forms of impulsivity.

METHODS

Adolescents between 12 and 17 years of age were assessed with the Schedule for Affective Disorders and Schizophrenia for School-aged Children - Present and Lifetime Version. Subjects with early-onset, first-episode schizophrenia spectrum disorders (EOS) (N = 29) or ADHD (N = 29) and healthy controls (N = 45) were compared on two performance measures (Information Sampling Task, Stop Signal Task) and a subjective personality trait measure of impulsivity (Barratt Impulsiveness Scale, Version 11 (BIS-11)).

RESULTS

Significantly increased reflection impulsivity was observed in ADHD but not in the EOS group. No significant response inhibition deficits (stop signal reaction time) were found in the two clinical groups. The ADHD and the EOS group showed significantly increased motor, attentional, and non-planning subtraits of impulsivity.

CONCLUSIONS

Impaired pre-decisional information gathering appeared to be specific for ADHD while the information gathering was not significantly reduced in subjects with EOS. Neither the ADHD nor EOS group showed impaired response inhibition but shared increased personality subtraits of attentional, non-planning, and motor impulsivity although the latter was significantly more pronounced in ADHD. These increased subtraits of impulsivity may reflect diagnostic non-specific neurodevelopmental impairments in ADHD and EOS in adolescence.

The Impact of Idle Time in the Classroom: Differential Effects on Children With ADHD

OBJECTIVE

Studies have identified an exacerbation of ADHD deficits under specific laboratory conditions. Less is known about the significance of such contextual factors in relation to everyday functioning in naturalistic settings.

METHOD

This study investigated the differential impact of classroom "idle time"--periods when students are not actively engaged or waiting for a task--on the behavior of 31 children with ADHD (25 boys and 6 girls; aged 6-12 years) and 31 sex- and age-matched typically developing classmates, who were simultaneously observed in their normal classroom during two school days.

RESULTS

Both groups experienced the same amount of idle time (12% of the time). During idle time, however, levels of hyperactivity and noisiness increased significantly more in children with ADHD than in their classmates (p < .05).

CONCLUSION

Findings highlight the differential susceptibility of ADHD children to classroom idle time. Classroom interventions might consider targeting specifically these periods to reduce disruptive behavior in these children.

Neuroeconomics of attention-deficit/hyperactivity disorder: differential influences of medial, dorsal, and ventral prefrontal brain networks on suboptimal decision making?

Psychiatric neuroeconomics offers an alternative approach to understanding mental disorders by studying the way disorder-related neurobiological alterations constrain economic agency, as revealed through decisions about choices between future goods. In this article, we apply this perspective to understand suboptimal decision making in attention-deficit/hyperactivity disorder (ADHD) by integrating recent advances in the neuroscience of decision making and studies of the pathophysiology of ADHD. We identify three brain networks as candidates for further study and develop specific hypotheses about how these could be implicated in ADHD. First, we postulate that altered patterns of connectivity within a network linking medial prefrontal cortex and posterior cingulate cortex (i.e., the default mode network) disrupts ordering of utilities, prospection about desired future states, setting of future goals, and implementation of aims. Second, we hypothesize that deficits in dorsal frontostriatal networks, including the dorsolateral prefrontal cortex and dorsal striatum, produce executive dysfunction-mediated impairments in the ability to compare outcome options and make choices. Third, we propose that dopaminergic dysregulation in a ventral frontostriatal network encompassing the orbitofrontal cortex, ventral striatum, and amygdala disrupts processing of cues of future utility, evaluation of experienced outcomes (feedback), and learning of associations between cues and outcomes. Finally, we extend this perspective to consider three contemporary themes in ADHD research.

Childhood Obesity and Impulsivity: An Investigation With Performance-Based Measures

The study investigated whether obese children are more impulsive than lean children, taking into account the multidimensionality of the construct. Responses of 41 overweight children were compared to those of 40 lean children. The Stop Task, Circle Drawing Task and Opposite Worlds Task were administered to measure executive inhibitory control, and the Maudsley Index of Childhood Delay Aversion and the Door Opening Task were administered to measure motivational inhibitory control. On the Stop Task, the overweight children showed less inhibitory control. On the Opposite Worlds task, we found no significant difference, whereas on the Circle Drawing Task an unexpected group difference was found. Although on the Door Opening Task the overweight children showed greater reward sensitivity, they were equally motivated to wait on the Maudsley Index of Childhood Delay. We conclude that the findings were different depending on the measure used, but that they suggest that overweight children can be characterised by a decrease in executive and motivational inhibitory control.

Linking ADHD, impulsivity, and drug abuse: a neuropsychological perspective

In this chapter, we consider the relevance of impulsivity as both a psychological construct and endophenotype underlying attention-deficit/hyperactivity disorder (ADHD) and drug addiction. The case for executive dysfunction in ADHD and drug addiction is critically reviewed in the context of dissociable cognitive control processes mediated by the dorsolateral prefrontal cortex (DLPFC), the orbital and ventral medial prefrontal cortex (VMPFC). We argue that such neuroanatomical divisions within the prefrontal cortex are likely to account for the multidimensional basis of impulsivity conceptually categorized in terms of "motoric" and "choice" impulsivity. The relevance of this distinction for the etiology of ADHD and drug addiction is integrated within a novel theoretical framework. This scheme embraces animal learning theory to help explain the heterogeneity of impulse control disorders, which are exemplified by ADHD as a vulnerability disorder for drug addiction.

The quick delay questionnaire: a measure of delay aversion and discounting in adults

Individuals with ADHD often display an altered response to delay. To date, assessment of this has typically involved neuropsychological testing-however, such tests are designed specifically for children and may not be suitable for adults. They are also relatively time-consuming and expensive. In the current paper, we describe the initial validation of a short questionnaire to assess delay-related behaviour in adults. The Quick Delay Questionnaire (QDQ) is a 10-item scale. The questionnaire was administered to 575 participants from the normal population (ranging in age from 18 to 77 years). Forty of the original sample were selected at random and tested 1 week later. Data on ADHD, anxiety and depression were also collected. There were two five-item scales-(1) delay aversion; and (2) delay discounting. These had internal consistency and had good reliability. Subscales were differentially associated with ADHD, anxiety and depression. The QDQ is a potentially valuable way of assessing response to delay in adults. Further work is required to validate the scale against direct observation and neuropsychological assessment in clinically ascertained samples.

Neurobiological substrates of social cognition impairment in attention-deficit hyperactivity disorder: gathering insights from seven structural and functional magnetic resonance imaging studies

Social cognitive neuroscience is beginning to unravel a neuroanatomy of social cognition, networks of brain regions especially involved in social cognition and social functioning. It is widely acknowledged that social functioning and social cognition are impaired in attention-deficit hyperactivity disorder (ADHD). Although an impressive amount of neuroscientific research has been conducted in ADHD, little effort has been made to link those deficits in social cognition and functioning to the well-known brain abnormalities detected in structural and functional neuroimaging studies. We review seven functional and magnetic resonance studies conducted at our laboratory in ADHD samples during the last 5 years in order to scrutinize whether the putative neuroanatomic regions underpinning social cognition are affected in ADHD. The orbitofrontal cortex (OFC), the caudate nucleus, the ventral striatum, and the cerebellum are among those regions that displayed functional or morphometric abnormalities in our ADHD samples. The OFC is clearly involved in social cognition, and several features of OFC dysfunction may be related to the social cognition and function impairment in ADHD. In contrast to the OFC, the role of the caudate nucleus, the ventral striatum, and the cerebellum is elusive. However, on one hand, there is converging evidence from human and animal neuropsychology, neuroscience, and psychiatry that support the role of such areas in social cognition, mainly through its involvement in emotional processing. On the other hand, the morphometric and functional ADHD abnormalities in these regions could account for the impoverished social functioning and the deficient social cognition skills of ADHD children.

What would Karl Popper say? Are current psychological theories of ADHD falsifiable?

Attention Deficit Hyperactivity Disorder (ADHD) is a common and highly heritable neurodevelopmental psychiatric disorder. Here, we critically review four major psychological theories of ADHD - the Executive Dysfunction, the State Regulation, the Delay Aversion and the Dynamic Developmental - on their abilities to explain all the symptoms of ADHD, their testability and their openness to falsification. We conclude that theoreticians should focus, to a greater extent than currently practiced, on developing refutable theories of ADHD.

Neuropsychological deficits in relation to symptoms of ADHD: independent contributions and interactions

The aim of the present study was to investigate possible independent and combined effects of inhibitory control, delay aversion, and RT variability in relation to symptoms of hyperactivity/impulsivity and inattention. A community-based sample of school children (N = 111) completed neuropsychological tasks designed to measure inhibitory control, delay aversion, and RT variability. Behavioral symptoms were measured through parental and teacher ratings of the DSM-IV criteria for ADHD and ODD. The results showed that inhibitory control and RT variability were primarily related to symptoms of inattention rather than hyperactivity/impulsivity. Further, out of the three neuropsychological factors studied, only inhibitory control contributed uniquely to the variance of ADHD symptoms. However, significant interaction effects of delay aversion and RT variability on symptoms of both hyperactivity/impulsivity and inattention were found. This study shows the importance of searching for possible combined effects of neuropsychological factors to learn more about the different pathways that lead to ADHD symptoms in children.

Delay Aversion in Attention Deficit/Hyperactivity Disorder: an empirical investigation of the broader phenotype

BACKGROUND

Delay-related motivational processes are impaired in children with Attention Deficit/Hyperactivity Disorder (ADHD). Here we explore the impact of ADHD on the performance of three putative indices of Delay Aversion (DAv): (i) the choice for immediate over delayed reward; (ii) slower reaction times following delay; and (iii) increased delay-related frustration-to see whether these tap into a common DAv construct that differentiates ADHD cases from controls and shows evidence of familiality.

METHOD

Seventy seven male and female individuals (age range 6-17) with a research diagnosis combined type ADHD, 65 of their siblings unaffected by ADHD and 50 non-ADHD controls completed three delay tasks.

RESULTS

As predicted the size of the correlation between tasks was small but a common latent component was apparent. Children with ADHD differed from controls on all tasks (d=.4-.7) and on an overall DAv index (d=.9): The battery as a whole demonstrated moderate sensitivity and specificity. In general, deficits were equally marked in childhood and adolescence and were independent of comorbid ODD. IQ moderated the effect on the MIDA. Scores on the DAv factor co-segregated within ADHD families.

DISCUSSION

There is value in exploring the broader DAv phenotype in ADHD. The results illustrate the power of multivariate approaches to endophenotypes. By highlighting the significant, but limited, role of DAv in ADHD these results are consistent with recent accounts that emphasize neuropsychological heterogeneity.

Puppets, robots, critics, and actors within a taxonomy of attention for developmental disorders

This review proposes a new taxonomy of automatic and controlled attention. The taxonomy distinguishes among the role of the attendee (puppet and robot, critic and actor), the attention process (stimulus orienting vs. response control), and the attention operation (activation vs. inhibition vs. adjustment), and identifies cognitive phenotypes by which attention is overtly expressed. We apply the taxonomy to four childhood attention disorders: attention deficit hyperactivity disorder, spina bifida meningomyelocele, traumatic brain injury, and acute lymphoblastic leukemia. Variations in attention are related to specific brain regions that support normal attention processes when intact, and produce disordered attention when impaired. The taxonomy explains group differences in behavioral inattention, hyperactivity, and impulsiveness, as well as medication response. We also discuss issues relevant to theories of the cognitive and neural architecture of attention: functional dissociations within and between automatic and controlled attention; the relative importance of type of brain damage and developmental timing to attention profile; cognitive-energetic models of attention and white matter damage; temporal processing deficits, attention deficits and cerebellar damage; and the issue of cognitive phenotypes as candidate endophenotypes.

Enhanced resting-state brain activities in ADHD patients: a fMRI study

Resting-state functional MRI (fMRI) could be an advantageous choice for clinical applications by virtue of its clinical convenience and non-invasiveness. Without explicit stimulus, resting-state brain activity patterns cannot be obtained using any model-driven method. In this study, we advanced a measure named resting-state activity index (RSAI) to evaluate the resting-state brain activities. Using RSAI, we first investigated the resting-state brain activity patterns in normal adolescents to test the validity of this RSAI measure. Then we compared the resting-state brain activity patterns of Attention deficit hyperactivity disorder (ADHD) patients to those of their matched controls. According to the resultant brain activity patterns, we suggest that RSAI could be an applicable measure to evaluate resting-state brain activities. As compared to the controls, the ADHD patients exhibited more significant resting-state activities in basic sensory and sensory-related cortices. This finding was in accordance with ADHD symptoms of inattention.

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.

ADHD and delay aversion: the influence of non-temporal stimulation on choice for delayed rewards

BACKGROUND

Delay aversion, the motivation to escape or avoid delay, results in preference for small immediate over large delayed rewards. Delay aversion has been proposed as one distinctive psychological process that may underlie the behavioural symptoms and cognitive deficits of attention deficit/hyperactivity disorder (ADHD). Furthermore, the delay aversion hypothesis predicts that ADHD children's preference for immediate small over large delayed rewards will be reduced when stimulation, which makes time appear to pass more quickly, is added to the delay interval. The current paper tests these predictions.

METHODS

A group of children with a diagnosis of ADHD (with or without oppositional defiant disorder (ODD)), a group with a diagnosis of high-functioning autism (HFA), and a normal control group were compared on an experimental paradigm giving repeated choices between small immediate and large delayed rewards (Maudsley Index of Delay Aversion-MIDA) under two conditions (stimulation and no stimulation).

RESULTS

As predicted, ADHD children displayed a stronger preference than the HFA and control children for the small immediate rewards under the no-stimulation condition. The ADHD children preferences were normalised under the stimulation condition with no differences between the groups. This pattern of results was the same whether the ADHD children had comorbid ODD or not.

DISCUSSION

The findings from the MIDA are consistent with the delay aversion hypothesis of ADHD in showing that preference for small immediate rewards over large delayed rewards is a specific feature of ADHD and that this preference can be reduced by the addition of stimulation. Further research is required to better understand the emotional and motivational mechanisms underpinning delay aversion.

A computerized test of self-control predicts classroom behavior

We assessed choices on a computerized test of self-control (CTSC) for a group of children with features of attention deficit hyperactivity disorder (ADHD) and a group of controls. Thirty boys participated in the study. Fifteen of the children had been rated by their parents as hyperactive and inattentive, and 15 were age- and gender-matched controls in the same classroom. The children were observed in the classroom for three consecutive mornings, and data were collected on their activity levels and attention. The CTSC consisted of two tasks. In the delay condition, children chose to receive three rewards after a delay of 60 s or one reward immediately. In the task-difficulty condition, the children chose to complete a difficult math problem and receive three rewards or complete an easier problem for one reward. The children with ADHD features made more impulsive choices than their peers during both conditions, and these choices correlated with measures of their activity and attention in the classroom.

State regulation in adult ADHD: an event-related potential study

The state regulation hypothesis postulates that poor task performance of children with ADHD is related to poor energetical state control. The current study aimed to investigate whether such a deficit persists in adult ADHD. Event-related potentials (ERPs) were recorded during administration of a Go/No-Go task that incorporated the stressor presentation rate of stimuli. It was found that males with ADHD responded slower than control males in the slow condition, which was accompanied by smaller parietal P3s, suggesting less effort allocation. No group differences were found with respect to the response inhibition measures (errors of commission and the N2 effect). In conclusion, problems in state regulation seem to persist in male adults with ADHD.

Neuropsychological functioning in people with ADHD across the lifespan

ADHD is defined by behavioral characteristics similar to neuropsychological disorders of executive dysfunction. This paper is a literature review of the neurocognitive characteristics of ADHD from early childhood through adulthood. The author addresses the development of the concept of attention and executive function (EF) deficits in ADHD, clinical neuropsychological studies of pre-teenage children, teenagers and adults with ADHD, gender and the role of psychiatric co-morbidity including the relationship of learning disabilities to ADHD, heterogeneity of neuropsychological dysfunctions, experimental neuropsychological studies, the relationship of brain structure to function, psychopharmacology of ADHD, and clinical neuropsychological assessment. The group data clearly supports the hypothesis that executive dysfunctions are correlates of ADHD regardless of gender and age, and these EF deficits are exacerbated by co-morbidity with learning disabilities such as dyslexia. However, there is limited data on children under the age of 5, teenagers from age 13-18, and adults with ADHD over the age of 40. Studies of individual classification of people with ADHD compared to healthy, non-psychiatric controls do not support the use of neuropsychological tests for the clinical diagnosis of ADHD, and indicate that not all persons with ADHD have EF deficits. Some persons with ADHD may have deficits in brain reward systems that are relatively independent of EF impairments. Future research should clarify the multiple sources of ADHD impairments, continue to refine neuropsychological tools optimized for assessment, and incorporate longitudinal, developmental designs to understand ADHD across the lifespan.

Neuropsychological functioning in girls with attention-deficit/hyperactivity disorder with and without learning disabilities

The authors' goal was to assess neuropsychological performance in girls with attention-deficit/hyperactivity disorder (ADHD) and evaluate the role of comorbid learning disabilities (LDs). Participants were 140 girls with ADHD and 122 girls without ADHD, ages 6-17 years. Neuropsychological performance was measured in a standardized manner, blind to clinical status. LD was defined by a combined regression-based and low-achievement classification. ADHD was associated with modest, but significant, neuropsychological impairment, as measured with an aggregate measure of performance and with the Stroop Color-Word Test, independent of age, social class, IQ, and psychiatric comorbidity. Neuropsychological deficits were most pronounced in girls with both ADHD and an LD and in those without medications. These results extend to females the previously documented association of LDs with neuropsychological functioning in males with ADHD.

Probing the limits of delay intolerance: preliminary young adult data from the Delay Frustration Task (DeFT)

Delay intolerance/aversion is one amongst a number of candidate neuropsychological endophenotypes for ADHD. Pilot data suggest that, because of potential ceiling effects, simple choice measures of delay tolerance used for children are probably not appropriate for adolescents and adults. The Delay Frustration Task (DeFT) is a new measure of delay intolerance, designed to be used in a similar form with adolescents and adults as well as children. In it delay frustration is indexed as the number and duration of responses made on a response key during a series of unpredictable and unsignalled delay periods, which interrupt the completion of a simple computer-based tests. The aim of this study was to provide preliminary data on the applicability of the task in a sample of young adults. The DeFT was administered to 49 male and female undergraduate students selected from a normal population-base. Their mean age was 23.14 (S.D.=1.54). Three measures of delay frustration were recorded across time intervals during the response window; the number of responses, their duration and their combined product (total time button was pressed) was calculated for each second interval bin during the post-response delay period. The AARS and HADS were used as screening questionnaires for ADHD and anxiety behaviour, respectively. The results indicated that young adults with high-ADHD symptoms scores pressed the button more than those with low ADHD scores during the post-response delay condition. While both groups increased responding across time within intervals this was significantly more marked in the high-ADHD symptom group. These effects became more pronounced when anxiety was controlled. Young adults with high-ADHD symptoms appear to be more sensitive to the imposition of unscheduled and unsignalled delay during a simple maths test. DeFT may provide a useful index of delay tolerance in young adults with ADHD. Future research needs to examine DeFT performance in different age groups and in clinical and non-clinical populations.

Activity in children with ADHD during waiting situations in the classroom: a pilot study

BACKGROUND

According to the optimal stimulation theory and the delay aversion hypothesis, children with attention deficit hyperactivity disorder (ADHD) experience difficulties when they are confronted with low levels of stimulation and delay, respectively.

AIM

This study investigated the activity level of children with ADHD during waiting situations in the classroom. Three series of hypothesis were made: (1) with respect to the comparison between waiting and non-waiting intervals, (2) with respect to the effects of non-temporal stimulation, and (3) with respect to the effects of temporal stimulation on behaviour during waiting.

SAMPLE AND METHOD

The activity level of 14 children with ADHD and 14 control children between the ages of 6 and 11 years was observed during two non-waiting class situations and three waiting situations: without any stimulation, in the presence of nontemporal stimulation and in the presence of temporal stimulation.

RESULTS

Both groups of children obtained higher activity scores for all behavioural dimensions during waiting compared with non-waiting situations. The results further revealed additive effects of waiting and diagnostic group on behaviour. Additional nontemporal stimulation during waiting affected the behaviour of all children for most behavioural characteristics. For noisiness, additive effects were also found for diagnostic group and either non-temporal stimulation or temporal stimulation. For restlessness, a trend for an interaction effect between diagnostic group and nontemporal stimulation was found.

CONCLUSION

The findings have clear implications for school observations within an assessment protocol.

Causal models of attention-deficit/hyperactivity disorder: from common simple deficits to multiple developmental pathways

Until recently, causal models of attention-deficit/hyperactivity disorder (ADHD) have tended to focus on the role of common, simple, core deficits. One such model highlights the role of executive dysfunction due to deficient inhibitory control resulting from disturbances in the frontodorsal striatal circuit and associated mesocortical dopaminergic branches. An alternative model presents ADHD as resulting from impaired signaling of delayed rewards arising from disturbances in motivational processes, involving frontoventral striatal reward circuits and mesolimbic branches terminating in the ventral striatum, particularly the nucleus accumbens. In the present article, these models are elaborated in two ways. First, they are each placed within their developmental context by consideration of the role of person x environment correlation and interaction and individual adaptation to developmental constraint. Second, their relationship to one another is reviewed in the light of recent data suggesting that delay aversion and executive functions might each make distinctive contributions to the development of the disorder. This provides an impetus for theoretical models built around the idea of multiple neurodevelopmental pathways. The possibility of neuropathologic heterogeneity in ADHD is likely to have important implications for the clinical management of the condition, potentially impacting on both diagnostic strategies and treatment options.

AD/HD and the capture of attention by briefly exposed delay-related cues: evidence from a conditioning paradigm

BACKGROUND

The selective attention of children with attention deficit/hyperactivity disorder (AD/HD) to briefly exposed delay-related cues was examined in two experiments using a dot-probe conditioning paradigm.

METHOD

Colour cues were paired with negatively (i.e., imposition of delay) and positively valenced cues (i.e., escape from or avoidance of delay) during a conditioning phase. These cues were presented alongside neutral cues in a subsequent dot-probe detection phase.

RESULTS

In experiment 1 teacher-identified children with AD/HD (N = 12), but not controls (N = 12), displayed an attentional bias towards both positively and negatively valenced cues. In experiment 2 children with a diagnosis of hyperkinetic disorder (N = 15), but not controls (N = 15), displayed a bias towards delay-related cues. However, this effect was largely carried by the response to positively valenced cues.

CONCLUSIONS

These results confirm the dot-probe conditioning paradigm as a useful test of motivational influence on attention. They provide the first evidence of qualitative differences in the attentional style of children with AD/HD and give further support to those theories that highlight the motivational significance of delay in AD/HD.

The dual pathway model of AD/HD: an elaboration of neuro-developmental characteristics

The currently dominant neuro-cognitive model of Attention Deficit Hyperactivity Disorder (AD/HD) presents the condition as executive dysfunction (EDF) underpinned by disturbances in the fronto-dorsal striatal circuit and associated dopaminergic branches (e.g. meso-cortical). In contrast, motivationally-based accounts focus on altered reward processes and implicate fronto-ventral striatal reward circuits and those meso-limbic branches that terminate in the ventral striatum especially the nucleus accumbens. One such account, delay aversion (DEL), presents AD/HD as a motivational style-characterised by attempts to escape or avoid delay-arising from fundamental disturbances in these reward centres. While traditionally regarded as competing, EDF and DEL models have recently been presented as complimentary accounts of two psycho-patho-physiological subtypes of AD/HD with different developmental pathways, underpinned by different cortico-striatal circuits and modulated by different branches of the dopamine system. In the current paper we describe the development of this model in more detail. We elaborate on the neuro-circuitry possibly underpinning these two pathways and explore their developmental significance within a neuro-ecological framework.

Do executive deficits and delay aversion make independent contributions to preschool attention-deficit/hyperactivity disorder symptoms?

OBJECTIVE

To test whether deficits in executive function and delay aversion make independent contributions to levels of attention-deficit/hyperactivity disorder (ADHD) symptoms exhibited by preschool children.

METHOD

One hundred fifty-six children between 3 and 5.5 years old (78 girls and 78 boys) selected from the community completed an age-appropriate battery of tests measuring working memory, set shifting, planning, delay of gratification, and preference for delayed rewards. Parents completed a clinical interview about their children's ADHD symptoms.

RESULTS

Analysis of test performance revealed two factors: executive dysfunction and delay aversion. Multivariate analysis demonstrated that when other factors (i.e., age, IQ, and conduct problems) were controlled, executive dysfunction and delay aversion each made significant independent contributions to predictions of ADHD symptoms.

CONCLUSIONS

Preschool ADHD symptoms are psychologically heterogeneous. Executive dysfunction and delay aversion may represent two distinct and early appearing neurodevelopmental bases for ADHD symptoms.

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

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

Stimulation seeking and hyperactive behavior in children with ADHD: a re-analysis

To examine the stimulation-seeking function of hyperactivity in children with ADHD, Antrop and colleagues analyzed the behavior of 30 hyperactive and 30 nonhyperactive children during a waiting situation, either with or without extra stimulation. The behavior was assessed by frequency measures. In their study it was hypothesized that children with ADHD would show a greater decrease in activity in the presence of stimulation than control children. Since confirmation for this hypothesis was only found for 2 of 25 target behaviors, the present re-analysis included other behavioral measures to assess two relationships: first, how hyperactivity varies under fixed time conditions, using measures of duration and intensity of behavior instead of frequency measures, and second, how the perceived duration of waiting time affects behavior. Analysis indicated that children with ADHD showed a greater decrease in behavior in the presence of stimulation for touching objects and movements of trunk, as reported. Further, children who underestimated the waiting period were more apt to seek additional stimulation in its absence than those who overestimated the waiting period.

Interval length and time-use by children with AD/HD: a comparison of four models

Predictions made by 4 competing models of time use by children with AD/HD were tested using a computerized version of the Matching Familiar Figures Test in 2 studies. In Study 1 teacher-identified AD/HD children (N = 10) and non-AD/HD controls (N = 10) completed the task under 3 different trial duration conditions (5, 10, and 15 s). In Study 2 the same task was completed by a group of children with a diagnosis of Hyperkinetic Disorder (N = 12) and controls (N = 12). In both studies AD/HD children performed poorly on trials of both 5- and 15-s duration but as well as controls on the 10-s trials. This quadratic function provided support for the State Regulation Deficit model of time use in AD/HD. The value of tailoring the temporal features of learning contexts to the conceptual style of AD/HD children is discussed.

Psychological heterogeneity in AD/HD--a dual pathway model of behaviour and cognition

Psychological accounts have characterised attention-deficit/hyperactivity disorder (AD/HD) as either a neuro-cognitive disorder of regulation or a motivational style. Poor inhibitory control is thought to underpin AD/HD children's dysregulation while delay aversion is a dominant characteristic of their motivational style. A recent 'head to head' study of these two accounts suggest that delay aversion and poor inhibitory control are independent co-existing characteristics of AD/HD (combined type). In the present paper we build on these findings to propose a dual pathway model of AD/HD that recognises two quite distinct sub-types of the disorder. In one AD/HD is the result of the dysregulation of action and thought resulting from poor inhibitory control associated with the meso-cortical branch of the dopamine system projecting in the cortical control centres (e.g. pre-frontal cortex). In the other AD/HD is a motivational style characterised by an altered delay of reward gradient linked to the meso-limbic dopamine branch associated with the reward circuits (e.g. nucleus accumbens). The two pathways are further distinguished at the levels of symptoms, cognitive and motivation profiles and genetic and non-genetic origins.

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.

The role of interval underestimation in hyperactive children's failure to suppress responses over time

The relationship between response inhibition and time estimation abilities was investigated in a group of hyperactive and non-hyperactive children. Children performed a discrete trials intertemporal response task under two conditions. Under both conditions children had to respond within a 2 s window, which was delayed for a set period (either 5 or 15 s). In condition one (signalled condition), these response requirements were signalled by changes in the expression of a face drawn on a computer screen. In condition two (unsignalled condition), always presented on the trial following the signalled condition, these changes in expression were obscured by a hand drawn over the mouth of the face so that effective performance depended on the childs ability to estimate the point at which the facial expression changed on the preceding trial. Both groups of children had little difficulty inhibiting responses when the response requirements were signalled. All children made far more errors under the unsignalled condition. Hyperactive children displayed a systematic tendency to respond before the response window occurred. Taken together, these data give no support to the idea that hyperactivity is essentially a problem of disinhibition and raise interesting questions about the role of time mis-estimation in the disorder.

Test of two views of impulsivity in hyperactive and conduct-disordered children

The nature of impulsivity in hyperactive and conduct-disordered children was examined in two experiments, one involving a priming task, the other a delayed reaction time task. Four groups of children, aged 7 to 8 years and with IQs in the normal range, were recruited for study: (1) a pure hyperactive group (HA), (2) a hyperactive/conduct-disordered group (HA+CD), (3) a pure conduct-disordered group (CD), and (4) a normal control group (N). When the stimulus configuration and presentation were simple and well organized, none of the three clinical groups displayed any sign of impulsivity at the input/perceptual stage; there was no tendency to rush responding before adequate consideration of the relevant stimuli, i.e. a trading of accuracy for speed. Instead, the HA children were found to be disinhibited at the output/motor stage, i.e. failing to temporarily withhold activated responses. This deficit was found to be specific to the HA children; it was not observed in the CD and HA+CD children.