Reaction Time Variability in Children With ADHD Symptoms and/or Dyslexia

Reaction time (RT) variability on a Stop Signal task was examined among children with attention deficit hyperactivity disorder (ADHD) symptoms and/or dyslexia in comparison to typically developing (TD) controls. Children's go-trial RTs were analyzed using a novel ex-Gaussian method. Children with ADHD symptoms had increased variability in the fast but not the slow portions of their RT distributions compared to those without ADHD symptoms. The RT distributions of children with dyslexia were similar to those of TD-controls. It is argued that variability in responding may be underpinned by impairments in response preparation or timing during Stop Signal tasks.     

Prenatal alcohol exposure causes attention deficits in male rats

Children with fetal alcohol spectrum disorder (FASD) are often diagnosed with attention-deficit/ hyperactivity disorder (ADHD). These children show increases in reaction time (RT) variability and false alarms on choice reaction time (CRT) tasks. In this study, adult rats prenatally exposed to ethanol were trained to perform a CRT task. An analysis of the distribution of RTs obtained from the CRT task found that rats with a history of prenatal ethanol exposure had more variable RT distributions, possibly because of lapses of attention. In addition, it was found that, similar to children with FASD, the ethanol-exposed rats had more false alarms. Thus, rats with prenatal ethanol exposure show attention deficits that are similar to those of children with FASD and ADHD.     

Finger force enslaving and surplus in spinal cord injury patients

Developmental dyslexia is a reading disorder associated with impaired postural control. However, such deficits are also found in attention deficit hyperactivity disorder (ADHD), which is present in a substantial subset of dyslexia diagnoses. Very few studies of balance in dyslexia have assessed ADHD symptoms, thereby motivating the hypothesis that such measures can account for the group differences observed. In this study, we assessed adults with dyslexia and similarly aged controls on a battery of cognitive, literacy and attention measures, alongside tasks of postural stability. Displacements of centre of mass to perturbations of posture were measured in four experimental conditions using digital optical motion capture. The largest group differences were obtained in conditions where cues to the support surface were reduced. Between-group differences in postural sway and in sway variability were largely accounted for by co-varying hyperactivity and inattention ratings, however. These results therefore suggest that postural instability in dyslexia is more strongly associated with symptoms of ADHD than to those specific to reading impairment.     

Inhibition control and error processing in children with attention deficit/hyperactivity disorder: An event-related potentials study

We studied inhibitory control and error processing in a task requiring inhibition of a motor response. Behavioral and ERP indices were recorded in fourteen ADHD and fourteen healthy children aged between 6 and 10 years during the Stop signal task (SST). The ADHD group made more variable in RT and showed less accuracy, more omissions and choice errors. Also, the ADHD group had a tendency toward a lower probability of inhibition and a longer Stop signal reaction time. The ADHD group also displayed a flatter response inhibition slope compared to the control group. Smaller P1 in ADHD group reflected that the ADHD group has less efficient attention than the control group. Furthermore, the ADHD group showed normal ERN, reduced Pe (retrieved from response-locked epochs), and reduced LPW (retrieved from Stop signal-locked epochs), suggesting that they might be normal in early error monitoring process related to error detection, but show abnormal in later error monitoring process associated with a conscious evaluation of the error. Behavioral and ERP data of the present study show deficient selective attention, inhibitory control, and error processing in children of ADHD.     

Reaction time variability in ADHD: A meta-analytic review of 319 studies

Individuals with ADHD are characterized as ubiquitously slower and more variable than their unaffected peers, and increased reaction time (RT) variability is considered by many to reflect an etiologically important characteristic of ADHD. The present review critically evaluates these claims through meta-analysis of 319 studies of RT variability in children, adolescents, and adults with ADHD relative to typically developing (TD) groups, clinical control groups, and themselves (subtype comparisons, treatment and motivation effects). Random effects models corrected for measurement unreliability and publication bias revealed that children/adolescents (Hedges' g = 0.76) and adults (g = 0.46) with ADHD demonstrated greater RT variability relative to TD groups. This increased variability was attenuated by psychostimulant treatment (g = − 0.74), but unaffected by non-stimulant medical and psychosocial interventions. Individuals with ADHD did not evince slower processing speed (mean RT) after accounting for RT variability, whereas large magnitude RT variability deficits remained after accounting for mean RT. Adolescents and adults with ADHD were indistinguishable from clinical control groups, and children with ADHD were only minimally more variable than clinical control children (g = 0.25). Collectively, results of the meta-analysis indicate that RT variability reflects a stable feature of ADHD and other clinical disorders that is robust to systematic differences across studies.     

Symptoms of ADHD Affect Intrasubject Variability in Youths with Autism Spectrum Disorder: An Ex-Gaussian Analysis

Increased intrasubject variability in reaction times (RT-ISV) is frequently found in individuals with autism spectrum disorder (ASD). However, how dimensional attention deficit/hyperactivity disorder (ADHD) symptoms impact RT-ISV in individuals with ASD remains elusive. We assessed 97 high-functioning youths with co-occurring ASD and ADHD (ASD+ADHD), 124 high-functioning youths with ASD only, 98 youths with ADHD only, and 249 typically developing youths, 8–18 years of age, using the Conners Continuous Performance Test (CCPT). We compared the conventional CCPT parameters (omission errors, commission errors, mean RT and RT standard error (RTSE) as well as the ex-Gaussian parameters of RT (mu, sigma, and tau) across the four groups. We also conducted regression analyses to assess the relationships between RT indices and symptoms of ADHD and ASD in the ASD group (i.e., the ASD+ADHD and ASD-only groups). The ASD+ADHD and ADHD-only groups had higher RT-ISV than the other two groups. RT-ISV, specifically RTSE and tau, was significantly associated with ADHD symptoms rather than autistic traits in the ASD group. Regression models also revealed that sex partly accounted for RT-ISV variance in the ASD group. A post hoc analysis showed girls with ASD had higher tau and RTSE values than their male counterparts. Our results suggest that RT-ISV is primarily associated with co-occurring ADHD symptoms/diagnosis in children and adolescents with ASD. These results do not support the hypothesis of response variability as a transdiagnostic phenotype for ASD and ADHD and warrant further validation at a neural level.     

Do motivational incentives reduce the inhibition deficit in ADHD?

The primary goal of this study was to test three competing theories of ADHD: the inhibition theory, the motivational theory, and a dual deficit theory. Previous studies have produced conflicting findings about the effects of incentives on executive processes in ADHD. In the present study of 25 children with ADHD and 30 typically developing controls, motivation was manipulated within the Stop Task. Stop signal reaction time was examined, as well as reaction time, its variability, and the number of errors in the primary choice reaction time task. Overall, the pattern of results supported the inhibition theory over the motivational or dual deficit hypotheses, as main effects of group were found for most key variables (ADHD group was worse), whereas the group by reward interaction predicted by the motivational and dual deficit accounts was not found. Hence, as predicted by the inhibition theory, children with ADHD performed worse than controls irrespective of incentives.     

Cognitive predictors of sequential motor impairments in children with dyslexia and/or attention deficit/hyperactivity disorder

This study examined cognitive predictors of sequential motor skills in 215 children with dyslexia and/or attention deficit/hyperactivity disorder (ADHD). Visual working memory and math fluency abilities contributed significantly to performance of sequential motor abilities in children with dyslexia (N = 67), ADHD (N = 66) and those with a comorbid diagnosis (N = 82), generally without differentiation between groups. In addition, primary diagnostic features of each disorder, such as reading and inattention, did not contribute to the variance in motor skill performance of these children. The results support a unifying framework of motor impairment in children with neurodevelopmental disorders such as dyslexia and ADHD.     

Variability of Response Time as a Predictor of Methylphenidate Treatment Response in Korean Children with Attention Deficit Hyperactivity Disorder

Purpose

Methylphenidate (MPH) is an effective medication for the treatment of attention deficit hyperactivity disorder (ADHD). However, about 30% of patients do not respond to or are unable to tolerate MPH. Based on previous findings, we hypothesized that great variability in response time (RT) among Korean children with ADHD on a computerized continuous performance attention test would be related to poor MPH treatment response.

Materials and Methods

Children (ages 6-18 years) with ADHD were recruited for a prospective 12-week, open-labeled, multicenter study to examine optimal dosage of OROS methylphenidate. Of the 144 subjects selected, 28 dropped out due to adverse events, medication noncompliance, or follow-up loss, and an additional 26 subjects with comorbid disorders were excluded from statistical analyses. We defined ''responders'' as subjects who received a score of less than 18 on the attention deficit hyperactivity disorder rating scale (ARS; Korean version, K-ARS) and a score of 1 or 2 on the Clinical Global Impression-Improvement scale (CGI-I). RT variability was assessed with the ADHD diagnostic system (ADS).

Results

Fifty-nine (67%) subjects responded to MPH treatment. The non-responders showed greater RT variability at baseline (Mann Whitney U = 577.0, p < 0.01). Baseline RT variability was a significant predictor of MPH response (Nagelkerke R² = 0.136, p < 0.01). It predicted 94.9% of responder, 17.2% of non-responder and 69.3% of overall group.

Conclusion

High RT variability may predict poor response to MPH treatment in children with ADHD.     

Reaction time performance in ADHD: improvement under fast-incentive condition and familial effects

BACKGROUND: Reaction time (RT) variability is one of the strongest findings to emerge in cognitive-experimental research of attention deficit hyperactivity disorder (ADHD). We set out to confirm the association between ADHD and slow and variable RTs and investigate the degree to which RT performance improves under fast event rate and incentives. Using a group familial correlation approach, we tested the hypothesis that there are shared familial effects on RT performance and ADHD. METHOD: A total of 144 ADHD combined-type probands, 125 siblings of the ADHD probands and 60 control participants, ages 6-18, performed a four-choice RT task with baseline and fast-incentive conditions. RESULTS: ADHD was associated with slow and variable RTs, and with greater improvement in speed and RT variability from baseline to fast-incentive condition. RT performance showed shared familial influences with ADHD. Under the assumption that the familial effects represent genetic influences, the proportion of the phenotypic correlation due to shared familial influences was estimated as 60-70%. CONCLUSIONS: The data are inconsistent with models that consider RT variability as reflecting a stable cognitive deficit in ADHD, but instead emphasize the extent to which energetic or motivational factors can have a greater effect on RT performance in ADHD. The findings support the role of RT variability as an endophenotype mediating the link between genes and ADHD.     

Electrophysiological correlates of response inhibition in children and adolescents with ADHD: influence of gender, age, and previous treatment history

Deficits in response inhibition may be at the core of the cognitive syndrome in ADHD. Here, inhibitory control mechanisms were studied in 36 ADHD-combined type and 30 healthy children by exploring the event-related brain activity during the Stop Signal task. The influence of age, gender, and previous treatment history was evaluated. The ADHD group showed reduced N200 wave amplitudes. For successful inhibitions, the N200 reduction was greatest over right inferior frontal scalp, and only the control group showed a success-related enhancement of such right frontal N200. Source analysis identified a source of the N200 group effect in right dorsolateral prefrontal cortex. Finally, a late positive wave to failed inhibitions was selectively reduced only in treatment-naïve ADHD children, suggesting that chronic stimulants may normalize late conscious error recognition. Both effects were independent of gender and age.     

The intermediate visual and auditory continuous performance test as a neuropsychological measure.

The Intermediate Visual and Auditory (IVA) Continuous Performance Test (CPT) and Neuropsychological Impairment Scale (NIS) were completed with adults diagnosed with mild traumatic brain injury (mTBI), adults diagnosed with Attention Deficit Hyperactivity Disorder (ADHD), and controls. On the IVACPT, the mTBI and ADHD groups performed significantly lower on the full and secondary scales for attention and response accuracy. For individual scales, the mTBI and ADHD groups showed lower performance on measures of reaction time, inattention, impulsivity, and variability of RT. The mTBI and ADHD groups showed similar patterns of performance on the IVA. On the NIS, the mTBI and ADHD groups reported more neuropsychological symptoms than the control group and the mTBI group reported more neuropsychological symptoms than the ADHD group. The results are discussed in regard to changes in cognitive processing and sustained attention in individuals diagnosed with mTBI and ADHD.     

The Integrated Visual and Auditory Continuous Performance Test as a neuropsychological measure.

The Integrated Visual and Auditory (IVA) Continuous Performance Test (CPT) and Neuropsychological Impairment Scale (NIS) were completed by adults diagnosed with mild traumatic brain injury (mTBI), adults diagnosed with attention deficit hyperactivity disorder (ADHD), and controls. On the IVA CPT, the mTBI and ADHD groups performed significantly lower on the full and secondary scales for attention and response accuracy. For individual scales, the mTBI and ADHD groups showed lower performance on measures of reaction time, inattention, impulsivity, and variability of RT. The mTBI and ADHD groups showed similar patterns of performance on the IVA. On the NIS, the mTBI and ADHD groups reported more neuropsychological symptoms than the control group, and the mTBI group reported more neuropsychological symptoms than the ADHD group. The results are discussed in regard to changes in cognitive processing and sustained attention in individuals diagnosed with mTBI and ADHD.     

Stopping and changing in adults with ADHD

BACKGROUND: A lack of inhibitory control has been suggested to be the core deficit in children with attention deficit hyperactivity disorder (ADHD). This means that a primary deficit in behavioral inhibition mediates a cascade of secondary deficits in other executive functions, such as arousal regulation. Clinical observations have revealed that with increasing age symptoms of hyperactivity and impulsivity decline at a higher rate than those of inattention. This might imply that a deficit in attention rather than a lack of inhibitory control is the major feature in adult ADHD. METHOD: To study whether an attentional or inhibitory deficit predominates, the stop-signal task and the stop-change task were presented to 24 adults with ADHD combined subtype and 24 controls. RESULTS: Relative to controls, the stop-signal reaction time (SSRT) was significantly more prolonged than the go-stimulus reaction time (RT) in patients with ADHD. This disproportionate elongation of the SSRT was comparable across tasks, even though the stop-change task exerted more complex (or at least different) demands on the inhibitory system than the stop-signal task. ADHD patients had a higher proportion of choice errors, possibly reflecting more premature responses. Specifically in the stop-change task, patients had more variable choice responses and made more inappropriate change responses, which may also reflect enhanced impulsivity. CONCLUSIONS: The results support a core deficit in behavioral inhibition in adults with ADHD. We further suggest that there is more evidence for a critical role of deficient inhibitory control in adults than in children with ADHD.     

The development of stop-signal and Go/Nogo response inhibition in children aged 7-12 years: performance and event-related potential indices.

The present study examined the development of response inhibition during the Stop-signal and Go/Nogo tasks in children using performance and ERP measures. Twenty-four children aged 7 to 12 years completed both tasks, each with an auditory Nogo/Stop-signal presented on 30% of trials. On average, response inhibition was more difficult in the Stop-signal than Go/Nogo task. Response inhibition performance did not develop significantly across the age range, while response execution varied significantly in a task dependent manner (Go/Nogo: increasing accuracy and reducing response variability with age; Stop-signal: reducing Go mean reaction time and response variability with age). The N1, P2, N2 and P3 components showed different scalp distributions, with N1 and P2 peaking earlier, and P3 later, in Nogo compared to Stop stimuli. N2 and P3 amplitude were positively correlated with successful inhibition probability in the Go/Nogo task only. N2 amplitude and latency to both Nogo and successful Stop stimuli decreased linearly with age, but not in the frontal regions. N1 and P3 amplitude in the parietal region increased with age for Stop-signals. An age-related reduction in P3 latency to Nogo stimuli correlated significantly with reduced RT and variability in Go responding, indicating a relationship between efficient Nogo and Go processing. Together the behavioural and ERP results suggest little development of the response inhibition process as measured via the Stop-signal and Go/Nogo tasks across the 7 to 12 year age range, while response execution processes develop substantially.     

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

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

The Relation Between Disinhibition and Emotion Regulation in Boys With Attention Deficit Hyperactivity Disorder

This study examined group differences of 49 boys ages 6 to 11 years with and without attention deficit hyperactivity disorder (ADHD) in emotion regulation during frustrating peer competition. Half of all boys in each group were explicitly instructed to hide their feelings if they became upset during the competition. Behavioral inhibition, both before and after the competitive task, was examined using the Stop Signal Task (SST), and emotion regulation was assessed via structured observation data. Effect sizes indicated that impulsive ADHD boys displayed greater disinhibition and were less effective at emotion regulation than comparison boys. In addition, boys with ADHD were unsuccessful in masking their emotions even when instructed to do so. In contrast, comparison boys were more successful at emotion regulation when given instruction to self-regulate, and these regulatory attempts predicted later inhibitory control. Findings are discussed in the context of current ADHD-related theories of inhibitory deficit, and suggestions for future research are provided.     

Executive functioning in hyperactive children as young adults: attention, inhibition, response perseveration, and the impact of comorbidity

Tests of several executive functions (EFs) as well as direct observations of symptoms of attention deficit hyperactivity disorder (ADHD) during testing were collected at the young adult follow-up (M = 20 years) on a large sample of hyperactive (H; N = 147) and community control (CC; N = 71) children. The EF tasks included tests of attention, inhibition, and response perseveration. The H group was subdivided into those with and without ADHD (+ or w/o) at follow-up. The H+ADHD group made significantly more inhibition errors than the CC group on a Continuous Performance Test (CPT) and showed more ADHD symptoms while performing the CPT. The H+ADHD group also displayed more ADHD symptoms during a letter cancellation task than did both the hyperactive w/o ADHD and CC groups. Both H groups showed slower reaction times during a Card Playing Task. That subset of hyperactive probands with Conduct Disorder (CD) displayed significantly more perseverative responding on that task than did those without CD, but otherwise it did not differ on any other measures. Current level of anxiety contributed adversely to both CPT commission errors and ADHD behavior during the CPT. Comorbid depression did not contribute to any group differences on these tests. Although developmental improvements were found in both the H and the CC groups in their CPT inattention and inhibition scores since adolescence, the H groups remained distinguishable from the CC groups over this period. We conclude that formerly hyperactive children manifest greater EF deficits at follow-up in the areas of inattention, disinhibition, and slowed reaction time and greater ADHD behavior during testing, but these problems are mostly confined to those with current ADHD. Response perseveration, however, was limited to those hyperactive children with CD by follow-up, consistent with Quay's theory of these two disorders.     

The relation between disinhibition and emotion regulation in boys with attention deficit hyperactivity disorder.

This study examined group differences of 49 boys ages 6 to 11 years with and without attention deficit hyperactivity disorder (ADHD) in emotion regulation during frustrating peer competition. Half of all boys in each group were explicitly instructed to hide their feelings if they became upset during the competition. Behavioral inhibition, both before and after the competitive task, was examined using the Stop Signal Task (SST), and emotion regulation was assessed via structured observation data. Effect sizes indicated that impulsive ADHD boys displayed greater disinhibition and were less effective at emotion regulation than comparison boys. In addition, boys with ADHD were unsuccessful in masking their emotions even when instructed to do so. In contrast, comparison boys were more successful at emotion regulation when given instruction to self-regulate, and these regulatory attempts predicted later inhibitory control. Findings are discussed in the context of current ADHD-related theories of inhibitory deficit, and suggestions for future research are provided.     

Behavioural Treatment Increases Activity in the Cognitive Neuronal Networks in Children with Attention Deficit/Hyperactivity Disorder

Response cost and token approach (RCT) within the scope of a summer camp training is an effective treatment program for attention deficit hyperactivity disorder (ADHD). It is likely that intensive RCT training influences networks responsible for ADHD symptoms. Functional magnetic resonance imaging (fMRI) was carried out in 12 children with ADHD before and after the RCT program and in 12 healthy control children twice. For fMRI, a Go/No-go paradigm was used to investigate the influence of RCT training on attention and impulsivity. The No-go condition revealed only weak activation in the dorsal part of the anterior cingulate cortex (ACC), parietal and dorsolateral prefrontal cortex (DLPFC) before the training in children with ADHD compared to healthy children. However, this activation in these brain regions was significantly more pronounced after the training. This increase in hemodynamic response cannot be attributed merely to repetition of the measurement since the effect was not observed in healthy children. The increase in hemodynamic response in the ACC and right DLPFC was significantly associated with a reduction in response time variability and clinical symptoms in ADHD patients. After the RCT training, the children with ADHD demonstrated more pronounced activation of cortical structures which are typically related to response monitoring and self-control. It seems likely that children with ADHD learned more cognitive control in a continuous performance task as was revealed by both neuropsychological outcome and fMRI.