Reduced electrodermal response to errors predicts poor sustained attention performance in attention deficit hyperactivity disorder

Altered interaction of physiological activity and behavior affects risky decision-making in ADHD

Background

Adult attention-deficit/hyperactivity disorder (ADHD) is often associated with risky decision-making behavior. However, current research studies are often limited by the ability to adequately reflect daily behavior in a laboratory setting. Over the lifespan impairments in cognitive functions appear to improve, whereas affective functions become more severe. We assume that risk behavior in ADHD arises predominantly from deficits in affective processes. This study will therefore aim to investigate whether a dysfunction in affective pathways causes an abnormal risky decision-making (DM) behavior in adult ADHD.

Methods

Twenty-eight participants with ADHD and twenty-eight healthy controls completed a battery of questionnaires regarding clinical symptoms, self-assessment of behavior and emotional competence. Furthermore, skin conductance responses were measured during the performance in a modified version of the Balloon Analogue Risk Task. A linear mixed-effects model analysis was used to analyze emotional arousal prior to a decision and after feedback display.

Results

Results showed higher emotional arousal in ADHD participants before decision-making (β = -0.12, SE = 0.05, t = -2.63, p < 0.001) and after feedback display (β = -0.14, SE = 0.05, t = -2.66, p = 0.008). Although risky behavior was greater in HC than in ADHD, we found a significant interaction effect of group and anticipatory skin conductance responses regarding the response behavior (β = 107.17, SE = 41.91, t = 2.56, p = 0.011). Post hoc analyses revealed a positive correlation between anticipatory skin conductance responses and reaction time in HC, whereas this correlation was negative in ADHD. Self-assessment results were in line with the objective measurements.

Conclusion

We found altered changes in physiological activity during a risky decision-making task. The results confirm the assumption of an aberrant relationship between bodily response and risky behavior in adult ADHD. However, further research is needed with respect to age and gender when considering physiological activities.

Head Motion During MRI Predicted by out-of-Scanner Sustained Attention Performance in Attention-Deficit/Hyperactivity Disorder

Objective: To characterize head movements in children with ADHD using an ex-Gaussian distribution and examine associations with out-of-scanner sustained attention. Method: Fifty-six children with ADHD and 61 controls aged 9 to 11 years completed the Sustained Attention to Response Task (SART) and resting-state functional magnetic resonance imaging (fMRI). In-scanner head motion was calculated using ex-Gaussian estimates for mu, sigma, and tau in delta variation signal and framewise displacement. Sustained attention was evaluated through omission errors and tau in response time on the SART. Results: Mediation analysis revealed that out-of-scanner attention lapses (omissions during the SART) mediated the relationship between ADHD diagnosis and in-scanner head motion (tau in delta variation signal), indirect effect: B = 1.29, 95% confidence interval (CI) = [0.07, 3.15], accounting for 29% of the association. Conclusion: Findings suggest a critical link between trait-level sustained attention and infrequent large head movements during scanning (tau in head motion) and highlight fundamental challenges in measuring the neural basis of sustained attention.

Emotion Regulation via the Autonomic Nervous System in Children with Attention-Deficit/Hyperactivity Disorder (ADHD): Replication and Extension

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent disorder characterized by symptoms of inattention, hyperactivity, and/or impulsivity, as well as executive dysfunction. Recent work underlines the importance in understanding the role of emotion reactivity and regulatory deficits in the context of the disorder. One study (i.e., Musser et al. 2011) utilized a positive and negative emotion induction and suppression task, as well as indexes of autonomic nervous system reactivity, to examine emotional functioning in youth with ADHD. This study revealed inflexible parasympathetic-based regulation across emotion conditions among youth with ADHD compared to typically developing youth. The present study sought to replicate and extend these findings to a clinically recruited, diverse sample, while also examining sympathetic functioning. Two hundred fifty-nine participants (160 youth with ADHD), aged 5 to 13, completed the task utilized in Musser et al. 2011, while indexes of parasympathetic (i.e., respiratory sinus arrhythmia [RSA]) and sympathetic (i.e., pre-ejection period [PEP] and electrodermal activity [EDA]) reactivity were obtained. ADHD was associated with significantly elevated parasympathetic (i.e., augmented RSA) and sympathetic (as indexed by EDA) reactivity. Overall, results replicate and extend Musser et al. 2011, revealing sympathetic-linked disruptions in emotion reactivity and parasympathetic-linked disruptions in emotion regulation among youth with ADHD. Future studies of behavioral therapies for ADHD should consider the efficacy of adding an emotion regulation skills training component.

The Effect of Tactile Training on Sustained Attention in Young Adults

Sustained attention is crucial for higher-order cognition and real-world activities. The idea that tactile training improves sustained attention is appealing and has clinical significance. The aim of this study was to explore whether tactile training could improve visual sustained attention. Using 128-channel electroencephalography (EEG), we found that participants with tactile training outperformed non-trainees in the accuracy and calculation efficiency measured by the Math task. Furthermore, trainees demonstrated significantly decreased omission error measured by the sustained attention to response task (SART). We also found that the improvements in behavioral performance were associated with parietal P300 amplitude enhancements. EEG source imaging analyses revealed stronger brain activation among the trainees in the prefrontal and sensorimotor regions at P300. These results suggest that the tactile training can improve sustained attention in young adults, and the improved sustained attention following training may be due to more effective attentional resources allocation. Our findings also indicate the use of a noninvasive tactile training paradigm to improve cognitive functions (e.g., sustained attention) in young adults, potentially leading to new training and rehabilitative protocols.

Electrophysiological Correlates of Response Time Variability During a Sustained Attention Task

Individuals with Attention Deficit Hyperactivity Disorder (ADHD) tend to perform cognitive tasks with greater Response Time Variability (RTV). Greater RTV in ADHD may be due to inefficient functional connectivity of the brain during information processing. This study aimed to investigate the relationship between brain connectivity, RTV, and levels of ADHD symptoms. Twenty-eight children aged 9–12 years and 49 adolescents aged 15–18 years performed the Sustained Attention to Response Task (SART) while EEG was recorded. The participants’ levels of ADHD symptoms were measured using self- and parent-rated questionnaires. The ex-Gaussian analysis and The Fast Fourier Transform were used to measure multiple aspects of RTV. Functional connectivity between 64 electrodes was computed during task performance, and global efficiency and modularity were calculated, reflecting integration and segregation of the brain, respectively. There was a positive association between multiple RTV measures and the level of ADHD symptoms, where participants with higher levels of ADHD symptoms showed greater RTV, except for sigma from the ex-Gaussian analysis. More efficient brain network activity, measured by global efficiency, was associated with reduced RTV. Children showed greater RTV and less efficient brain network activity compared with the adolescents. These findings support the view that stable responses are achieved with more integrated (and efficient) brain connectivity.

Reward sensitivity and electrodermal responses to actions and outcomes in a go/no-go task

Skin conductance response (SCR) is used in psychophysiological research to measure the reactions of the autonomic nervous system to reward and punishment. While there is consistent evidence that SCR increases to both aversive and appetitive stimuli, it remains unclear whether SCR simply represents a general index of arousal to motivationally significant outcomes or may also differentiate action or inhibition of action that lead to such outcomes. Furthermore, individual differences in trait sensitivity to reward and punishment can influence physiological arousal during approach and avoidance behaviors. Yet, their inter-relationships have not been examined. To address these gaps, we employed a reward go/no-go task with ⅔ go and ⅓ no-go trials and an individually titrated go response window. Correct go and no-go responses were rewarded while incorrect responses were penalized. We examined whether SCR varied with outcome (win vs. loss), action (go vs. no-go), and individual differences in reward sensitivity (SR) and sex. The results showed greater SCRs to loss vs. win, to go vs. no-go success, and to go success in positive correlation with SR. Further, SCR mediated the relationship between SR and go success rate. In sex differences, men exhibited greater SCR which was more predictive of go success rate relative to women. In contrast, SCR was more predictive of no-go success rate in women. Thus, SCR varies according to behavioral contingency, outcome, sex, and reward sensitivity. These findings add to the literature by characterizing the individual and behavioral factors that may influence physiological arousal in response to salient events.

Autonomic arousal profiles in adolescents and young adults with ADHD as a function of recording context

A recent study (James et al. 2016) found that attention-deficit/hyperactivity disorder (ADHD) was associated with hypo-arousal, indexed by low electrodermal activity, during a low-demand reaction-time task, which normalized in a fast-incentive condition. We now investigate if (1) autonomic arousal in individuals with ADHD changes over a long testing session and (2) across time, to clarify if arousal profiles are context-dependent. We also examine (3) how autonomic arousal relates to each ADHD symptom domain, and specificity of arousal profiles to ADHD, by controlling for oppositional defiant/conduct disorder (ODD/CD) symptoms. Skin conductance level and non-specific fluctuations were measured during four successive resting-state and cognitive conditions (Resting-state time 1, Continuous Performance Task, Fast Task: Baseline and Fast-Incentive conditions, Resting-state time 2) from 71 adolescents/young adults with ADHD and 140 controls. Lower arousal was observed in individuals with ADHD only during a slow, low-demanding task, and more fluctuating arousal was observed towards the end of assessment. Both inattentive and hyperactive-impulsive symptoms were associated with arousal levels and fluctuations, independently from ODD/CD. Overall, we extend previous findings showing that under-arousal, but also fluctuating arousal, are context-specific rather than stable impairments in ADHD.

The origin of the centrality deficit in individuals with attention-deficit/hyperactivity disorder

INTRODUCTION

Studies have shown that skilled and disabled readers recall central ideas, which are important to the overall comprehension of the text, to a greater extent than peripheral, less important ideas after reading. However, readers with attention-deficit/hyperactivity disorder (ADHD) recall significantly fewer central ideas than skilled readers. The present study was designed to examine whether difficulties in identifying, attending, and/or retrieving central ideas underlie their centrality deficit.

METHOD

28 adult university students with ADHD and 27 control students read three expository texts (successively) to summarize their central ideas, while their eye-movements were recorded. After reading, the participants recalled, recognized, and estimated the centrality level of all text ideas, which were divided into central and peripheral based on pretest ratings.

RESULTS

The participants with ADHD recalled fewer central ideas than controls, although they recognized and estimated their centrality to the same extent as controls. Moreover, the participants with ADHD invested more time in rereading central ideas than peripheral ones, to a greater extent than controls.

CONCLUSIONS

The eye-movement data suggest that our university students with ADHD were aware of the reading task requirements, their difficulties, and the appropriate strategies for coping with them (i.e., rereading central ideas). More importantly, the present findings suggest that readers with ADHD have specific difficulty in retrieving central ideas that are available in their long-term memory. It supports the hypothesis that readers with ADHD establish fewer connections between text ideas during reading, and consequently benefit from a reduced number of retrieval cues after reading.

Simple, Transparent, and Flexible Automated Quality Assessment Procedures for Ambulatory Electrodermal Activity Data

OBJECTIVE

Electrodermal activity (EDA) is a noninvasive measure of sympathetic activation often used to study emotions, decision making, and health. The use of "ambulatory" EDA in everyday life presents novel challenges-frequent artifacts and long recordings-with inconsistent methods available for efficiently and accurately assessing data quality. We developed and validated a simple, transparent, flexible, and automated quality assessment procedure for ambulatory EDA data.

METHODS

A total of 20 individuals with autism (5 females, 5-13 years) provided a combined 181 h of EDA data in their home using the Affectiva Q Sensor across 8 weeks. Our procedure identified invalid data using four rules: First, EDA out of range; second, EDA changes too quickly; third, temperature suggests the sensor is not being worn; and fourth, transitional data surrounding segments identified as invalid via the preceding rules. We identified invalid portions of a pseudorandom subset of our data (32.8 h, 18%) using our automated procedure and independent visual inspection by five EDA experts.

RESULTS

Our automated procedure identified 420 min (21%) of invalid data. The five experts agreed strongly with each other (agreement: 98%, Cohen's κ: 0.87) and, thus, were averaged into a "consensus" rating. Our procedure exhibited excellent agreement with the consensus rating (sensitivity: 91%, specificity: 99%, accuracy: 92%, κ: 0.739 [95% CI = 0.738, 0.740]).

CONCLUSION

We developed a simple, transparent, flexible, and automated quality assessment procedure for ambulatory EDA data.

SIGNIFICANCE

Our procedure can be used beyond this study to enhance efficiency, transparency, and reproducibility of EDA analyses, with free software available at http://www.cbslab.org/EDAQA.

Time-on-task effects in children with and without ADHD: depletion of executive resources or depletion of motivation?

Children with attention-deficit/hyperactivity disorder (ADHD) are characterized by deficits in their executive functioning and motivation. In addition, these children are characterized by a decline in performance as time-on-task increases (i.e., time-on-task effects). However, it is unknown whether these time-on-task effects should be attributed to deficits in executive functioning or to deficits in motivation. Some studies in typically developing (TD) adults indicated that time-on-task effects should be interpreted as depletion of executive resources, but other studies suggested that they represent depletion of motivation. We, therefore, investigated, in children with and without ADHD, whether there were time-on-task effects on executive functions, such as inhibition and (in)attention, and whether these were best explained by depletion of executive resources or depletion of motivation. The stop-signal task (SST), which generates both indices of inhibition (stop-signal reaction time) and attention (reaction time variability and errors), was administered in 96 children (42 ADHD, 54 TD controls; aged 9-13). To differentiate between depletion of resources and depletion of motivation, the SST was administered twice. Half of the participants was reinforced during second task performance, potentially counteracting depletion of motivation. Multilevel analyses indicated that children with ADHD were more affected by time-on-task than controls on two measures of inattention, but not on inhibition. In the ADHD group, reinforcement only improved performance on one index of attention (i.e., reaction time variability). The current findings suggest that time-on-task effects in children with ADHD occur specifically in the attentional domain, and seem to originate in both depletion of executive resources and depletion of motivation. Clinical implications for diagnostics, psycho-education, and intervention are discussed.

Pupil-size asymmetry is a physiologic trait related to gender, attentional function, and personality

A small difference in the size of the two pupils is common in healthy individuals, a condition termed benign or physiologic anisocoria (BA). Past research indicates that BA is probably caused by asymmetry in sympathetic nervous system (SNS) function [e.g., Rosenberg (2008). Physiologic anisocoria: A manifestation of a physiologic sympathetic asymmetry. Neuro-Ophthalmology, 32, 147-149]. This study is the first to show that BA varies with psychological factors linked to brain asymmetry and autonomic arousal, including gender, attention, and personality. Males exhibited a more directional BA than females, consistent with greater hemispheric lateralization in males. BA also varied with a self-report measure of attentional function, consistent with evidence of hemispheric asymmetry in visuospatial attention networks. Finally, BA varied with personality traits linked to autonomic arousal. Individuals exhibiting higher Meanness and Boldness, and lower Empathy scores tended to show more directional BA. This link between personality traits and BA may be related to brain asymmetries in autonomic arousal and emotion-related processing. If future studies employing direct measures of lateralized brain activity confirm the link between BA and SNS asymmetries, this new metric may prove useful in discovering new relationships between brain organization and psychological function, and how these relationships vary across individuals.

Modifiable Arousal in Attention-Deficit/Hyperactivity Disorder and Its Etiological Association With Fluctuating Reaction Times

Background

Cognitive theories of attention-deficit/hyperactivity disorder (ADHD) propose that high within-subject fluctuations of cognitive performance in ADHD, particularly reaction time (RT) variability (RTV), may reflect arousal dysregulation. However, direct evidence of arousal dysregulation and how it may account for fluctuating RTs in ADHD is limited. We used skin conductance (SC) as a measure of peripheral arousal and aimed to investigate its phenotypic and familial association with RTV in a large sample of ADHD and control sibling pairs.

Methods

Adolescents and young adults (N = 292), consisting of 73 participants with ADHD and their 75 siblings, and 72 controls and their 72 siblings, completed the baseline (slow, unrewarded) and fast-incentive conditions of a RT task, while SC was simultaneously recorded.

Results

A significant group-by-condition interaction emerged for SC level (SCL). Participants with ADHD had decreased SCL, compared with controls, in the baseline condition but not the fast-incentive condition. Baseline SCL was negatively associated with RTV, and multivariate model fitting demonstrated that the covariance of SCL with RTV, and of SCL with ADHD, was mostly explained by shared familial effects.

Conclusions

ADHD is associated with decreased, but modifiable, tonic peripheral arousal. A shared familial cause underlies the relationship between arousal and RTV and between arousal and ADHD. Given the malleability of SCL, if our findings are replicated, it warrants further exploration as a potential treatment target for ADHD.

Tonic and phasic co-variation of peripheral arousal indices in infants

Tonic and phasic differences in peripheral autonomic nervous system (ANS) indicators strongly predict differences in attention and emotion regulation in developmental populations. However, virtually all previous research has been based on individual ANS measures, which poses a variety of conceptual and methodlogical challenges to comparing results across studies. Here we recorded heart rate, electrodermal activity (EDA), pupil size, head movement velocity and peripheral accelerometry concurrently while a cohort of 37 typical 12-month-old infants completed a mixed assessment battery lasting approximately 20 min per participant. We analysed covariation of these autonomic indices in three ways: first, tonic (baseline) arousal; second, co-variation in spontaneous (phasic) changes during testing; third, phasic co-variation relative to an external stimulus event. We found that heart rate, head velocity and peripheral accelerometry showed strong positive co-variation across all three analyses. EDA showed no co-variation in tonic activity levels but did show phasic positive co-variation with other measures, that appeared limited to sections of high but not low general arousal. Tonic pupil size showed significant positive covariation, but phasic pupil changes were inconsistent. We conclude that: (i) there is high covariation between autonomic indices in infants, but that EDA may only be sensitive at extreme arousal levels, (ii) that tonic pupil size covaries with other indices, but does not show predicted patterns of phasic change and (iii) that motor activity appears to be a good proxy measure of ANS activity. The strongest patterns of covariation were observed using epoch durations of 40s per epoch, although significant covariation between indices was also observed using shorter epochs (1 and 5s).

A Componential Analysis of Visual Attention in Children With ADHD

OBJECTIVE

Inattentive behaviour is a defining characteristic of ADHD. Researchers have wondered about the nature of the attentional deficit underlying these symptoms. The primary purpose of the current study was to examine this attentional deficit using a novel paradigm based upon the Theory of Visual Attention (TVA).

METHOD

The TVA paradigm enabled a componential analysis of visual attention through the use of a mathematical model to estimate parameters relating to attentional selectivity and capacity. Children's ability to sustain attention was also assessed using the Sustained Attention to Response Task. The sample included a comparison between 25 children with ADHD and 25 control children aged 9-13.

RESULTS

Children with ADHD had significantly impaired sustained attention and visual processing speed but intact attentional selectivity, perceptual threshold and visual short-term memory capacity.

CONCLUSION

The results of this study lend support to the notion of differential impairment of attentional functions in children with ADHD.

Withholding and canceling a response in ADHD adolescents

BACKGROUND

Deficient response inhibition in situations involving a trade-off between response execution and response stopping is a hallmark of attention deficit hyperactive disorder (ADHD). There are two key components of response inhibition; reactive inhibition where one attempts to cancel an ongoing response and prospective inhibition is when one withholds a response pending a signal to stop. Prospective inhibition comes into play prior to the presentation of the stop signal and reactive inhibition follows the presentation of a signal to stop a particular action. The aim of this study is to investigate the neural activity evoked by prospective and reactive inhibition in adolescents with and without ADHD.

METHODS

Twelve adolescents with ADHD and 12 age-matched healthy controls (age range 9-18) were imaged while performing the stop signal task (SST).

RESULTS

Reactive inhibition activated right inferior frontal gyrus (IFG) in both groups. ADHD subjects activated IFG bilaterally. In controls, prospective inhibition invoked preactivation of the same part of right IFG that activated during reactive inhibition. In ADHD subjects, prospective inhibition was associated with deactivation in this region. Controls also deactivated the medial prefrontal cortex (MPFC) during prospective inhibition, whereas ADHD subjects activated the same area.

DISCUSSION

This pattern of activity changes in the same structures, but in opposite directions, was also evident across all phases of the task in various task-specific areas like the superior and middle temporal gyrus and other frontal areas.

CONCLUSION

Differences between ADHD and control participants in task-specific and default mode structures (IFG and MPFC) were evident during prospective, but not during reactive inhibition.

Women are more sensitive than men to prior trial events on the Stop-signal task

Sexual dimorphism in the brain and cognition is a topic of widespread interest. Many studies of sex differences have focused on visuospatial and verbal abilities, but few studies have investigated sex differences in executive functions. We examined two key components of executive function - response inhibition and response monitoring - in healthy men (n = 285) and women (n = 346) performing the Stop-signal task. In this task, participants are required to make a key press to a stimulus, unless a tone is presented at some delay following the initial stimulus presentation; on these infrequent trials, participants are instructed to inhibit their planned response. Response inhibition was assessed with an estimate of the latency needed to inhibit a response (stop-signal reaction time), and response monitoring was measured by calculating the degree to which participants adjusted their reaction times based on the immediately preceding trial (e.g., speeding following correct trials and slowing following errors). There were no sex differences in overall accuracy or response inhibition, but women showed greater sensitivity to trial history. Women sped up more than men following correct 'Go' trials, and slowed down more than men following errors. These small but statistically significant effects (Cohen's d = 0.25-0.3) suggest more flexible adjustments in speed-accuracy trade-offs in women and greater cognitive flexibility associated with the responsive control of action.

Enhancing SART Validity by Statistically Controlling Speed-Accuracy Trade-Offs

Numerous studies focused on elucidating the correlates, causes, and consequences of inattention/attention-lapses employ the Sustained Attention to Response Task (SART), a GO-NOGO task with infrequent withholds. Although the SART has become popular among inattention researchers, recent work has demonstrated its susceptibility to speed-accuracy trade-offs (SATOs), rendering its assessment of inattention problematic. Here, we propose and illustrate methods to statistically control for the occurrence of SATOs during SART performance. The statistical solutions presented here can be used to correct standard SART-error scores, including those of already-published data, thereby allowing researchers to re-examine existing data, and to more sensitively evaluate the validity of earlier conclusions.

Preliminary evidence for reduced posterror reaction time slowing in hyperactive/inattentive preschool children

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) has been associated with deficits in self-regulatory cognitive processes, some of which are thought to lie at the heart of the disorder. Slowing of reaction times (RTs) for correct responses following errors made during decision tasks has been interpreted as an indication of intact self-regulatory functioning and has been shown to be attenuated in school-aged children with ADHD. This study attempted to examine whether ADHD symptoms are associated with an early-emerging deficit in posterror slowing.

METHOD

A computerized two-choice RT task was administered to an ethnically diverse sample of preschool-aged children classified as either "control" (n = 120) or "hyperactive/inattentive" (HI; n = 148) using parent- and teacher-rated ADHD symptoms. Analyses were conducted to determine whether HI preschoolers exhibit a deficit in this self-regulatory ability.

RESULTS

HI children exhibited reduced posterror slowing relative to controls on the trials selected for analysis. Supplementary analyses indicated that this may have been due to a reduced proportion of trials following errors on which HI children slowed rather than due to a reduction in the absolute magnitude of slowing on all trials following errors.

CONCLUSIONS

High levels of ADHD symptoms in preschoolers may be associated with a deficit in error processing as indicated by posterror slowing. The results of supplementary analyses suggest that this deficit is perhaps more a result of failures to perceive errors than of difficulties with executive control.

Synergistic tonic and phasic activity of the locus coeruleus norepinephrine (LC-NE) arousal system is required for optimal attentional performance

A certain level of arousal is required for an individual to perform optimally, and the locus coeruleus norepinephrine (LC-NE) system plays a central role in optimizing arousal. Tonic firing of LC-NE neurons needs to be held within a narrow range of 1-3 Hz to facilitate phasic firing of the LC-NE neurons; these two modes of activity act synergistically, to allow the individual to perform attentional tasks optimally. How this information can be applied to further our understanding of psychiatric disorders has not been fully elucidated. Here we propose two models of altered LC-NE activity that result in attentional deficits characteristic of psychiatric disorders: 1) 'hypoaroused' individuals with e.g. attention-deficit/hyperactivity disorder (ADHD) have decreased tonic firing of the LC-NE system, resulting in decreased cortical arousal and poor attentional performance and 2) 'hyperaroused' individuals with e.g. anxiety disorders have increased tonic firing of the LC-NE system, resulting in increased cortical arousal and impaired attentional performance. We argue that hypoarousal (decreased tonic firing of LC-NE neurons) and hyperarousal (increased tonic firing of LC-NE neurons) are suboptimal states in which phasic activity of LC-NE neurons is impeded. To further understand the neurobiology of attentional dysfunction in psychiatric disorders a translational approach that integrates findings on the LC-NE arousal system from animal models and human imaging studies may be useful.

Deficient post-error slowing in children with ADHD is limited to the inattentive subtype

Post-error slowing (i.e., slowing of a response on correct trials following an error) is thought to reflect adaptive behavior that may be impaired in Attention-Deficit/Hyperactivity Disorder (ADHD). The current study examined post-error slowing in children with ADHD and typically developing controls on two cognitive tasks. Fifty-one ADHD-Combined type, 53 ADHD-Inattentive type, and 47 controls completed a Choice Discrimination and Stop Signal Task with incentive and event rate manipulations. Linear mixed models were used to examine reaction times surrounding errors (trial-by-trial). Pre-error speeding and pre- to post-error slowing occurred on both tasks. Impaired post-error slowing was only present on the Choice Discrimination Task for the ADHD-Inattentive type. Post-error slowing is impaired in children with ADHD-Inattentive type, but not ADHD-Combined type, on a simple attention task. These findings highlight the importance of considering task demands and ADHD subtype when examining post-error slowing and also provide a novel approach to quantifying post-error slowing.

Altered cortical morphology in sensorimotor processing regions in adolescents and adults with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that is common in children and frequently persists into adulthood. While ADHD is characterized by developmentally inappropriate, persistent and impairing levels of inattention, impulsiveness and hyperactivity, it is also associated with sensorimotor deficits and altered neural processing of somatosensory stimuli, as well as with executive function deficits. The latter are associated with thinning of frontal lobe structures in ADHD; however, few structural neuroimaging studies have focused on changes in brain morphology in sensorimotor regions in this population. Moreover, little is known about morphological changes that occur in these regions throughout the developmental trajectory into adulthood. In this preliminary cross-sectional study, we examined cortical thickness with a focus on brain regions involved in sensorimotor processing in adolescents and adults with ADHD compared to neurotypical cohorts. Compared to controls, adolescents with ADHD showed significant increased cortical thickness in the pre-supplementary motor area (SMA) and adults with ADHD showed increased thickness in the primary somatosensory cortex (SI). Based on these differences, we collated the data from the adolescents and adults and examined possible age×group interaction effects on cortical thickness. A significant interaction effect was found in SI where healthy participants showed decreased thickness in this region at older ages, whereas the ADHD cohort showed little change. Results suggest that sensorimotor brain regions are altered in ADHD and these changes may not dissipate in adolescence, but rather persist into adulthood.

Electrophysiological markers of genetic risk for attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder with complex genetic aetiology. The identification of candidate intermediate phenotypes may facilitate the detection of susceptibility genes and neurobiological mechanisms underlying the disorder. Electroencephalography (EEG) is an ideal neuroscientific approach, providing a direct measurement of neural activity that demonstrates reliability, developmental stability and high heritability. This systematic review evaluates the utility of a subset of electrophysiological measures as potential intermediate phenotypes for ADHD: quantitative EEG indices of arousal and intraindividual variability, and functional investigations of attention, inhibition and performance monitoring using the event-related potential (ERP) technique. Each measure demonstrates consistent and meaningful associations with ADHD, a degree of genetic overlap with ADHD and potential links to specific genetic variants. Investigations of the genetic and environmental contributions to EEG/ERP and shared genetic overlap with ADHD might enhance molecular genetic studies and provide novel insights into aetiology. Such research will aid in the precise characterisation of the clinical deficits seen in ADHD and guide the development of novel intervention and prevention strategies for those at risk.

Deficient cardiovascular stress reactivity predicts poor executive functions in adults with attention-deficit/hyperactivity disorder

Associations between cardiovascular stress markers, subjective stress reactivity, and executive functions were studied in 60 adults (30 with attention-deficit/hyperactivity disorder, ADHD, and 30 controls) using the Paced Auditory Serial Addition Test (PASAT, a test of executive functions) as a cognitive stressor. Despite higher self-perceived stress, the adults with ADHD showed lower or atypical cardiovascular stress reactivity, which was associated with poorer performance on PASAT. Using cardiovascular stress markers, subjective stress, and results on PASAT as predictors in a logistic regression, 83.3% of the ADHD group and 86.9% of the controls could be classified correctly.

Variants of the SLC6A3 (DAT1) polymorphism affect performance monitoring-related cortical evoked potentials that are associated with ADHD

Although the 10-repeat (10R) variant of the dopamine transporter gene (DAT1 or SLC6A3) is suggested to be a risk allele for Attention Deficit Hyperactivity Disorder (ADHD) no relationships between DAT1 and measures of cognition in children with ADHD have yet been demonstrated. We studied neurophysiological correlates of performance monitoring during a feedback-based learning task by measuring cortical event-related potentials (ERPs) in a group of 65 10-13-year-old children half of whom were diagnosed as ADHD. The first part of the study investigates correlations between parent-reported behaviour problems and several performance monitoring components, while the second part investigates the relationship between DAT1 and these components. Specifically ADHD problems correlated significantly with an error-related positivity (Pe) and a feedback-anticipatory negativity (the SPN). Only these two components discriminated between the DAT1 10/10R and 9R carriers. The 10/10R carriers showed a smaller Pe to errors and a smaller SPN in anticipation of negative feedback, particularly with learning.

Physiological and behavioral differences in sensory processing: a comparison of children with autism spectrum disorder and sensory modulation disorder

A high incidence of sensory processing difficulties exists in children with Autism Spectrum Disorder (ASD) and children with Sensory Modulation Disorder (SMD). This is the first study to directly compare and contrast these clinical disorders. Sympathetic nervous system markers of arousal and reactivity were utilized in a laboratory paradigm that administered a series of sensory challenges across five sensory domains. The Short Sensory Profile, a standardized parent-report measure, provided a measure of sensory-related behaviors. Physiological arousal and sensory reactivity were lower in children with ASD whereas reactivity after each sensory stimulus was higher in SMD, particularly to the first stimulus in each sensory domain. Both clinical groups had significantly more sensory-related behaviors than typically developing children, with contrasting profiles. The ASD group had more taste/smell sensitivity and sensory under-responsivity while the SMD group had more atypical sensory seeking behavior. This study provides preliminary evidence distinguishing sympathetic nervous system functions and sensory-related behaviors in Autism Spectrum Disorder and Sensory Modulation Disorder. Differentiating the physiology and sensory symptoms in clinical groups is essential to the provision of appropriate interventions.

The restless brain: attention-deficit hyperactivity disorder, resting-state functional connectivity, and intrasubject variability

OBJECTIVES

To highlight recent advances in the conceptualization of attention-deficit hyperactivity disorder (ADHD) emerging from neuroimaging and endophenotypic approaches.

METHODS

We selectively reviewed recent published literature on the phenomena of resting-state functional connectivity, intrasubject variability, and diffusion tensor imaging pertaining to ADHD.

RESULTS

Recent advances based on the novel approach of resting-state functional connectivity appear to be highly promising and likely to link to studies of intrasubject variability.

CONCLUSIONS

Endophenotypic fractionation may offer a means of addressing the complex heterogeneity of ADHD on the path to testable models of pathophysiology. Such models focusing on intrasubject variability, intrinsic brain activity, and reward-related processing are progressing rapidly.

Different behavioral and eye movement patterns of dyslexic readers with and without attentional deficits during single word reading

Comorbidity of learning disabilities is a very common phenomenon which is intensively studied in genetics, neuropsychology, prevalence studies and causal deficit research. In studies on the behavioral manifestation of learning disabilities, however, comorbidity is often neglected. In the present study, we systematically examined the reading behavior of German-speaking children with dyslexia, of children with attentional problems, of children with comorbid dyslexia and attentional problems and of normally developing children by measuring their reading accuracy, naming latencies and eye movement patterns during single word reading. We manipulated word difficulty by contrasting (1) short vs. long words with (2) either low or high sublexical complexity (indexed by consonant cluster density). Children with dyslexia only (DYS) showed the expected reading fluency impairment of poor readers in regular orthographies but no accuracy problem. In contrast, comorbid children (DYS+AD) had significantly higher error rates than all other groups, but less of a problem with reading fluency than DYS. Concurrently recorded eye movement measures revealed that DYS made the highest number of fixations, but exhibited shorter mean single fixations than DYS+AD. Word length had the strongest effect on dyslexic children, whereas consonant cluster density affected all groups equally. Theoretical implications of these behavioral and eye movement patterns are discussed and the necessity for controlling for comorbid attentional deficits in children with reading deficits is highlighted.

Anatomy of an error: a bidirectional state model of task engagement/disengagement and attention-related errors

We present arguments and evidence for a three-state attentional model of task engagement/disengagement. The model postulates three states of mind-wandering: occurrent task inattention, generic task inattention, and response disengagement. We hypothesize that all three states are both causes and consequences of task performance outcomes and apply across a variety of experimental and real-world tasks. We apply this model to the analysis of a widely used GO/NOGO task, the Sustained Attention to Response Task (SART). We identify three performance characteristics of the SART that map onto the three states of the model: RT variability, anticipations, and omissions. Predictions based on the model are tested, and largely corroborated, via regression and lag-sequential analyses of both successful and unsuccessful withholding on NOGO trials as well as self-reported mind-wandering and everyday cognitive errors. The results revealed theoretically consistent temporal associations among the state indicators and between these and SART errors as well as with self-report measures. Lag analysis was consistent with the hypotheses that temporal transitions among states are often extremely abrupt and that the association between mind-wandering and performance is bidirectional. The bidirectional effects suggest that errors constitute important occasions for reactive mind-wandering. The model also enables concrete phenomenological, behavioral, and physiological predictions for future research.

Physiological and psychological stress responses in adults with attention-deficit/hyperactivity disorder (ADHD)

According to self-report and unsystematic observational data adult patients with attention-deficit/hyperactivity disorder suffer from increased vulnerability to daily life stressors. The present study examined psychological and physiological stress responses in adult ADHD subjects in comparison to healthy controls under laboratory conditions. Thirty-six subjects (18 patients with DSM-IV ADHD diagnosis, 18 sex- and age-matched healthy controls) underwent the Trier Social Stress Test (TSST; Kirschbaum, C., Pirke, K.-M., Hellhammer, D.H., 1993. The "Trier Social Stress Test"--a tool for investigating psychobiological stress responses in a laboratory setting. Neuropsychobiology 28, 76-81), a standardized psychosocial stress protocol which contains a stress anticipation phase and a stress phase with a free speech assignment and subsequent performance of a mental arithmetic. Physiological stress measures were salivary cortisol as an indicator of the HPA axis, heart rate (HR), and time- and frequency-domain heart rate variability (HRV) parameters. Subjective stress experience was measured via self-report repeatedly throughout the experimental session. In line with previous theoretical and empirical work in the field of childhood ADHD, it was hypothesized that the ADHD and control group would exhibit comparable baseline levels in all dependent variables. For ADHD subjects, we expected attenuated responses of the physiological parameters during anticipation and presence of the standardized stressor, but elevated subjective stress ratings. Hypotheses were confirmed for the baseline condition. Consistent with our assumptions in regard to the psychological stress response, the ADHD group experienced significantly greater subjective stress. The results for the physiological variables were mixed. While ADHD subjects revealed an attenuated HR during the stress phase, no significant group differences were found for the other parameters, although a trend was observed for both the low frequency/high frequency (LF/HF) ratio of the HRV power spectral analysis and salivary cortisol (the latter possibly indicating generally lower cortisol levels in ADHD subjects). In summary, the present findings are the first to demonstrate a significant alteration of a specific physiological stress measure (HR) and, more clearly, of psychological aspects of the stress response in adults suffering from ADHD. In regard to the physiological stress response, it is recommended that future studies employ larger sample sizes and a more comprehensive range of physiological stress parameters. Additionally, the issue of transferability of laboratory results to real life stressors needs to be addressed.

Arousal and continuous attention during Ramadan intermittent fasting

During the month of Ramadan, practicing Muslims abstain from eating and drinking from sunrise to sunset. We aimed to investigate the effect of Ramadan fasting on arousal and continuous attention. The electrodermal activity and cancellation test of students were measured in fasting and non-fasting conditions after the conclusion of the Ramadan fast period. The skin conductance level of the fasting group was no different from the non-fasting group. In non-fasting group, the skin conductance response amplitude to an auditory stimulus was higher and the skin conductance response onset latency was lower than in the fasting group. Cancellation test results: the fasting group had a lower total number of marked targets (TNTM) but a higher total number of missed targets (TNMT) and length of time for the subject to complete the test (LTCT) than the non-fasting group. Ramadan fasting did not change arousal, but the reaction time to an auditory stimulus increased during the Ramadan intermittent fasting. Both reaction amplitude and continuous attention also decreased in the fasting condition.

Self-Alert Training: volitional modulation of autonomic arousal improves sustained attention

The present study examines a new alertness training strategy (Self-Alert Training, SAT) designed to explore the relationship between the top-down control processes governing arousal and sustained attention. In order to maximally target frontal control systems SAT combines a previously validated behavioural self-alerting technique [Robertson, I. H., Tegner, R., Tham, K., Lo, A., & Nimmo-Smith, I. (1995). Sustained attention training for unilateral neglect: Theoretical and rehabilitation implications. Journal of Clinical and Experimental Neuropsychology, 17, 416-430] with an autonomic arousal biofeedback protocol in which participants learn to modulate their own arousal levels. The SAT protocol was first validated with a group of 23 neurologically healthy participants and then independently tested in a group of 18 adults with ADHD to determine its clinical utility. Half of the participants in each group were assigned to a placebo condition to control for non-specific effects. All participants performed the sustained attention to response task (SART) during pre- and post-training testing sessions to assess training effects on sustained attention. By the end of SAT all participants were able to modulate their own arousal levels without external prompting. Comparison of pre- and post-training baseline data indicated that, as predicted, SAT was associated with increased levels of autonomic arousal accompanied by improved accuracy on the SART. In contrast, participants in the placebo condition exhibited a gradual reduction in arousal over time and increased reaction time variability indicative of a vigilance decrement. These data demonstrate that the recruitment of top-down control processes during volitional modulation of arousal leads to improved sustained attention. These findings have important implications for the rehabilitation of attention deficits arising from frontal dysfunction.

Modulation of response timing in ADHD, effects of reinforcement valence and magnitude

The present study investigated the impact of reinforcement valence and magnitude on response timing in children with ADHD. Children were required to estimate a 1-s interval, and both the median response time (response tendency) and the intrasubject-variability (response stability) were investigated. In addition, heart rate and skin conductance were measured to examine the autonomic responses to reinforcement. Feedback-only trials were compared to low response cost trials (response cost for incorrect responses), low reward trials (reward for correct responses), high response cost and high reward trials. In feedback-only trials, children with ADHD underestimated more severely the interval and responded more variably than controls. Children with ADHD, unlike controls, were unaffected by the reinforcement conditions in terms of time underestimations. The variability of responding, on the other hand, decreased under conditions of reinforcement to a larger extent in children with ADHD than controls. There were no indications that children with ADHD were abnormally affected by the valence or magnitude of reinforcement. Furthermore, skin conductance responses increased when feedback was coupled with reinforcement, an effect which was larger in children with ADHD than controls. This could be interpreted as demonstrating that children with ADHD suffer from a diminished awareness of the significance of feedback in the feedback-only condition. The current study suggests that children with ADHD suffer from motivation problems when reinforcement was not available, at least when variability in responding was measured. Underestimations of time may reflect more stable deficits in ADHD.

Time perception deficit in children with ADHD

Time perception deficit has been demonstrated in children with attention deficit hyperactivity disorder (ADHD) by using time production and time reproduction tasks. The impact of motor demand, however, has not yet been fully examined. The current study, which is reported herein, aimed to investigate the pure time perception of Chinese children with ADHD by using a duration discrimination task. A battery of tests that were specifically designed to measure time perception and other related abilities, such as inhibition, attention, and working memory, was administered to 40 children with ADHD and to 40 demographically matched healthy children. A repeated measure MANOVA indicated that children with ADHD showed significantly higher discrimination thresholds than did healthy controls, and there was an interaction effect between group and duration. Pairwise comparison indicated that children with ADHD were less accurate in discriminating duration at either target duration. Working memory (Corsi blocks task) was related to the discrimination threshold at a duration of 800 ms after controlling for full-scale IQ (FIQ) in the ADHD group, but this did not survive the Bonferroni correction. The results indicated that children with ADHD may have perceptual deficits in time discrimination. They needed a greater difference between the comparison and target intervals to discriminate the short, median, and long durations reliably. This study provides further support for the existence of a generic time perception deficit, which is probably due to the involvement of a dysfunctional fronto-striato-cerebellar network in this capacity, especially the presence of deficits in basic internal timing mechanisms.

The effects of lorazepam on skin conductance responses to aversive stimuli in healthy subjects

BACKGROUND

Autonomic responses to aversive stimuli are widely used to model anxiolytic drug effects in healthy humans. Benzodiazepine anxiolytics dose dependently attenuate autonomic responses to aversive stimuli by their anxiolytic as well as sedative action. The present study aimed to examine the effects of non-sedative doses of lorazepam on skin cutaneous responses to aversive stimuli and subjective mood.

METHODS

A randomized, double blind, cross over study of 12 healthy male volunteers aged 24 years (23-32; median; range) was carried out. Subjects received single oral doses of 0.5 and 1.0 mg lorazepam as well as placebo on three different occasions with at least 5 days in-between. Skin conductance responses (SCRs) to unpleasant pictures and noises, pupillary unrest index as well as subjective levels of anxiety were measured repeatedly before and after drug administration.

RESULTS

SCRs were found significantly lower 2 hours following ingestion of 0.5 mg lorazepam as well as 1, 2 and 3 hours after 1.0 mg lorazepam were given as compared to baseline conditions. By contrast, administration of placebo did not influence SCRs to a significant extent. Both doses of lorazepam did not change pupillary unrest index nor subjective mood.

CONCLUSIONS

Lorazepam may attenuate SCRs to aversive stimuli without affecting vigilance nor subjective mood. Attenuation of autonomic responses to aversive stimuli may not be specific for an anxiolytic effect.

Cognitive remediation in ADHD: effects of periodic non-contingent alerts on sustained attention to response

Few studies have attempted direct cognitive remediation of attention deficits in attention-deficit hyperactivity disorder (ADHD). The present study investigated the efficacy of periodic non-informative alerting cues for improving sustaining attention in ADHD. This technique is known to improve sustained attention in right frontal injury patients and may be effective in ADHD, given that this disorder has also been linked with right frontal dysfunction. Fifteen children with ADHD and 15 matched controls completed four blocks of a modified version of the Sustained Attention to Response Task (SART). Eight random non-contingent alerts were introduced on two of these blocks as a cue for participants to adopt a more supervisory stance to their performance. While the alerting cues did not alter the total number of commission errors committed by ADHD children over a task block, they did produce a significant short-term reduction in commission errors in the period immediately following an alerting cue. Our data demonstrate that sustained attention performance can be enhanced in children with ADHD using a simple cognitive training strategy. Methods from the field of cognitive rehabilitation may be viably applied to the remediation of attention deficits in ADHD.

Optimal sustained attention is linked to the spectral content of background EEG activity: greater ongoing tonic alpha (∼10 Hz) power supports successful phasic goal activation

Efficient executive control frequently requires the timely activation or re-activation of a task-goal to enable purposeful behaviour. Additionally, more generalized factors such as alertness or neurological health will influence the efficiency with which control can be implemented. Goal-directed processes have been investigated by examining event-related potentials (ERPs), but much less is known about the involvement of background or 'tonic' processes reflected in the ongoing electroencephalogram (EEG), and how these affect the phasic processes expressed in the broad-band ERP. Here, we investigate the relationship between a key attention-sensitive tonic process--the alpha rhythm--and relevant phasic processes observed during a sustained attention paradigm in neurologically healthy subjects. We report that subjects with relatively higher tonic alpha power (approximately 10 Hz) show a larger-amplitude late positive ERP component that is thought to index goal activation and has been found to predict good sustained attention performance as defined by correct response patterns. Source localization results suggest that the neural generators responsible for oscillatory alpha activity, which are found primarily in the parietal and occipital lobes, are distinct from those giving rise to the late positive component. The results are discussed in terms of increased alpha synchrony facilitating goal-directed behaviour.

The cognitive genetics of attention deficit hyperactivity disorder (ADHD): sustained attention as a candidate phenotype

Here we describe the application of cognitive genetics to the study of attention deficit hyperactivity disorder (ADHD). Cognitive genetics owes much to the pioneering work of cognitive neuropsychologists such as John Marshall, whose careful observations of cognitive dissociations between brain-lesioned patients greatly advanced the theoretical understanding of normal cognitive function. These theories have in turn helped to constrain linkages between candidate genes and cognitive processes and thus help to drive the relatively new field of cognitive genetics in a hypothesis-driven fashion. We examined the relationship between sustained attention deficits in ADHD and genetic variation in a catecholamine-related gene, dopamine beta hydroxylase (DbetaH). DBH encodes the enzyme that converts dopamine to noradrenaline and is crucial to catecholamine regulation. A polymorphism with the DBH gene has been associated with ADHD. In fifty-two children with ADHD, we examined whether variation in the Taq I DBH gene polymorphism was related to sustained attention performance. Participants performed the Sustained Attention to Response Test (SART). Performance on the SART discriminates ADHD from control children, and in imaging work, is associated with right frontoparietal activation. A significant effect of DBH genotype was found on SART performance measures. Children possessing two copies of the ADHD-associated risk allele (A2) had significantly poorer sustained attention than those ADHD children who did not possess this allele or a non-genotyped control group. The DBH gene may contribute to the susceptibility for ADHD, in part because of its varying effects on the development of brain mechanisms mediating sustained attention.

Response variability in attention deficit hyperactivity disorder: evidence for neuropsychological heterogeneity

Response time (RT) variability is a common finding in ADHD research. RT variability may reflect frontal cortex function and may be related to deficits in sustained attention. The existence of a sustained attention deficit in ADHD has been debated, largely because of inconsistent evidence of time-on-task effects. A fixed-sequence Sustained Attention to Response Task (SART) was given to 29 control, 39 unimpaired and 24 impaired-ADHD children (impairment defined by the number of commission errors). The response time data were analysed using the Fast Fourier Transform, to define the fast-frequency and slow-frequency contributions to overall response variability. The impaired-ADHD group progressively slowed in RT over the course of the 5.5min task, as reflected in this group's greater slow-frequency variability. The fast-frequency trial-to-trial variability was also significantly greater, but did not differentially worsen over the course of the task. The higher error rates of the impaired-ADHD group did not become differentially greater over the length of the task. The progressive slowing in mean RT over the course of the task may relate to a deficit in arousal in the impaired-ADHD group. The consistently poor performance in fast-frequency variability and error rates may be due to difficulties in sustained attention that fluctuate on a trial-to-trial basis.

Altered resting-state functional connectivity patterns of anterior cingulate cortex in adolescents with attention deficit hyperactivity disorder

Dorsal anterior cingulate cortex (dACC) has been found to function abnormally in attention deficit hyperactivity disorder (ADHD) patients in several former functional MRI (fMRI) studies. Resting-state low-frequency fluctuations (LFFs) of blood oxygen level-dependent (BOLD) fMRI signals have been proved to be quite informative. This study used resting-state LFFs to investigate the resting-state functional connectivity pattern differences of dACC in adolescents with and without ADHD. As compared to the controls, the ADHD patients exhibited more significant resting-state functional connectivities with the dACC in bilateral dACC, bilateral thalamus, bilateral cerebellum, bilateral insula and bilateral brainstem (pons). No brain region in the controls was found to exhibit more significant resting-state functional connectivity with the dACC. We suggest these abnormally more significant functional connectivities in the ADHD patients may indicate the abnormality of autonomic control functions in them.

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.

Capture by misleading information and its false acceptance in patients with traumatic brain injury

Exposure to misleading information, presented after a critical episode, can alter or impair memory reports about that episode. Here, we examine vulnerability to misleading information in patients with traumatic brain injury (TBI). The ability to initiate an effective retrieval strategy and inhibit irrelevant or interfering information requires participation from the prefrontal cortices, which are susceptible to damage following brain injury. We report that TBI patients are more prone to interference effects produced by misleading information during a cued-recall task and are more likely to accept this information as the product of 'remembering' compared with healthy controls. The results are consistent with a model proposing that patients are captured by highly accessible responses eliminating their opportunity to engage in recollection. Correlations between the cued-recall interference task and other executive measures helped elucidate the processes underlying 'capture'. In TBI patients, reduced recollection produced by a misleading prime was associated with impaired prospective remembering when engaged in a background task. A common functional deficit that may underlie poor performance on both tasks is the failure to inhibit previously relevant but currently irrelevant information. Subjective reports pertaining to the subject's cued-recall response were indexed by electrodermal activity. In control subjects, larger skin conductance responses (SCRs) were associated with a greater frequency of guess reports, suggesting that SCRs provide a marker for uncertainty regarding the candidacy of a selected response. TBI patients did not show this relationship, suggesting that impairments of post-retrieval evaluation might also underlie greater false acceptance of misinformation. Discussion focuses on the role of the prefrontal cortex and cognitive processes that mediate the selection and evaluation of memories.