Towards a neuroscience of attention-deficit/hyperactivity disorder: Fractionating the phenotype

Response inhibition and emotional cognition improved by atomoxetine in children and adolescents with ADHD: The ACTION randomized controlled trial

Although the non-stimulant medication atomoxetine is effective for attention-deficit hyperactivity disorder (ADHD) in children and adolescents, there are still significant gaps in our knowledge about whether atomoxetine improves anxiety symptoms or cognition in children. Furthermore, while cognition has been proposed as an intermediate phenotype for ADHD dysfunction, the relationships between clinical and cognitive outcomes are not yet understood. We addressed these knowledge gaps in a controlled trial using objective assessments of both general and emotional cognitive functions implicated in ADHD and in anxiety, which commonly co-occurs with ADHD. A total of 136 children and adolescents with ADHD (ages 6-17years; 80% male; 31.6% with a comorbid anxiety disorder) were enrolled in a randomized double-blind, placebo-controlled, cross-over trial of 6-weeks treatment with atomoxetine. Of these, 109 completed the second cross-over phase. Selected cognitive domains associated with ADHD and anxiety disorders (Sustained attention, response inhibition and fearful face identification) were assessed using a normed, computerized test battery. Symptom outcomes were assessed by parent reports on the ADHD Rating Scale-IV and Conners' Anxious-Shy subscale. For completers, atomoxetine caused a greater improvement in the primary cognitive outcomes of response inhibition and fear identification compared to placebo, but not in sustained attention. Atomoxetine also improved ADHD and anxiety symptoms. Anxiety symptoms improved most for ADHD and anxiety disorder combined, but presence of an anxiety disorder did not moderate any other outcomes. Changes in cognitive and clinical outcomes were not correlated. These findings contribute to the foundations of measurement-based treatment planning and offer targets for probing the mechanisms of atomoxetine action.

Identification of biotypes in Attention-Deficit/Hyperactivity Disorder, a report from a randomized, controlled trial

Attention-Deficit/Hyperactivity Disorder (ADHD) is a heterogeneous disorder. Current subtypes lack longitudinal stability or prognostic utility. We aimed to identify data-driven biotypes using multiple cognitive measures, then to validate these biotypes using EEG, ECG, and clinical response to atomoxetine as external validators. Study design was a double-blind, randomized, placebo-controlled crossover trial of atomoxetine including 116 subjects ages 6 through 17 with diagnosis of ADHD and 56 typically developing controls. Initial features for unsupervised machine learning included a cognitive battery with 20 measures affected in ADHD. External validators included baseline mechanistic validators (using electroencephalogram/EEG and electrocardiogram/ECG) and clinical response (ADHD Rating Scale and correlation with cognitive change). One biotype, labeled impulsive cognition, was characterized by increased errors of commission and shorter reaction time, had greater EEG slow wave (theta/delta) power and greater resting heart rate. The second biotype, labeled inattentive cognition, was characterized by longer/more variable reaction time and errors of omission, had lower EEG fast wave (beta) power, resting heart rate that did not differ from controls, and a strong correlation (r = -0.447, p < 0.001) between clinical response to atomoxetine and improvement in verbal memory immediate recall. ADHD comprises at least two biotypes that cut across current subtype criteria and that may reflect distinct arousal mechanisms. The findings provide evidence that further investigation of cognitive subtypes may be at least as fruitful as symptom checklist-based subtypes for development of biologically-based diagnostics and interventions for ADHD.

Gifted students with a coexisting disability: The twice exceptional

The twice exceptional are students who have both high ability and a disability or disorder. The ability can be in any culturally-valued domain, including high intelligence, academics, the visual or performing arts, and athletics. The co-existing disability can be physical, medical, or psychological. There is a growing literature of scholarly opinion about twice exceptionality; however, there are few well-designed empirical investigations of gifted students with anxiety, depression, bipolar disorder, attention-deficit/hyperactivity disorder, eating disorders, conduct problems, or medical, physical or sensory disabilities. This article examines a few key issues about the twice exceptional student and then discusses what we know about the gifted students with attention-deficit hyperactivity disorder and gifted students with learning disabilities. The article also provides a brief discussion on suicide and the gifted student.

Thyrotoropin receptor knockout changes monoaminergic neuronal system and produces methylphenidate-sensitive emotional and cognitive dysfunction

Attention deficit/hyperactivity disorder (ADHD) has been reported in association with resistance to thyroid hormone, a disease caused by a mutation in the thyroid hormone receptor β (TRβ) gene. TRβ is a key protein mediating down-regulation of thyrotropin (TSH) expression by 3,3',5-tri-iodothyronine (T3), an active form of thyroid hormone. Dysregulation of TSH and its receptor (TSHR) is implicated in the pathophysiology of ADHD but the role of TSHR remains elusive. Here, we clarified a novel role for TSHR in emotional and cognitive functions related to monoaminergic nervous systems. TSHR knockout mice showed phenotypes of ADHD such as hyperactivity, impulsiveness, a decrease in sociality and increase in aggression, and an impairment of short-term memory and object recognition memory. Administration of methylphenidate (1, 5 and 10mg/kg) reversed impulsiveness, aggression and object recognition memory impairment. In the knockout mice, monoaminergic changes including decrease in the ratio of 3-methoxy-4-hydroxyphenylglycol/noradrenaline and increase in the ratio of homovanillic acid/dopamine were observed in some brain regions, accompanied by increase in the expression of noradrenaline transporter in the frontal cortex. When TSH was completely suppressed by the supraphysiological administration of T3 to the adult mice, some behavioral and neurological changes in TSHR KO mice were also observed, suggesting that these changes were not due to developmental hypothyroidism induced by the inactivation of TSHR but to the loss of the TSH-TSHR pathway itself. Taken together, the present findings suggest a novel role for TSHR in behavioral and neurological phenotypes of 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.

[Emotional dysfunctions in attention deficit hyperactivity disorder]

Inattention, motor instability, and impulsivity, associated in varying degrees of severity depending on the clinical subtype, constitute the key symptoms of attention deficit/hyperactivity disorder (ADHD). However, emotional symptoms are frequent in patients with ADHD and may, in some cases, be responsible for a major part of the negative impact on functioning and outcome. Emotional problems have been described in ADHD even in the absence of characterized comorbid conditions such as depressive or anxiety disorders. They can manifest acutely in the form of severe tantrums and aggressive behaviour, generally in reaction to an environmental trigger, or show a more chronic course of irritable or labile mood. Symptoms of emotional undercontrol seem to occur more frequently when ADHD is associated with oppositional defiant behaviour, but they are not specific and may contribute to difficulties in making a differential diagnosis, especially with bipolar disorder and prodromal symptoms of personality disorders. The frequency and negative impact of emotional symptoms and the need to differentiate them from bipolar disorder has led some authors to the description of a novel clinical entity called "severe mood dysregulation" or "temper dysregulation with dysphoria." This article aims to review the recent literature on emotional symptoms associated with ADHD and to discuss relevant clinical and biological issues. Current research highlights the links between emotional self-regulation and executive functions and possible involvement of motivational systems. The role of environmental factors in the development of emotional regulation and self-control is another important issue, especially because environmental modification is the major focus of current preventive and therapeutic 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.

Attention-deficit/hyperactivity disorder: a neuropsychological perspective towards DSM-V

Neuropsychological methods and techniques have much to offer in the evaluation of the individual suspected as having Attention-Deficit/Hyperactivity Disorder (ADHD). After a review of the historical evolution of the ADHD concept, incidence and prevalence, and DSM-IV criteria for diagnosis, especially as regards omission related to gender differences, and other associated cultural, familial, socioenvironmental, and subject influences, this paper describes a number of dilemmas and obstacles encountered in clinical practice. Included are the confounds associated with the wide range of possible comorbidities, the insufficiency of current DSM-IV criteria, the emergence of subtype differentiation and its impact on diagnosis and treatment. The complex relationship between neuropsychological constructs and ADHD, and obstacles to valid assessment are also addressed. The complexities associated with a thorough ADHD evaluation are viewed within an impressive and expansive existing scientific framework and recommendations are made for future directions.

The role of abnormal neural oscillations in the pathophysiology of co-occurring Tourette syndrome and attention-deficit/hyperactivity disorder

OBJECTIVE

To examine the role of aberrant neural oscillatory activity in the pathophysiology of co-occurring Tourette Syndrome (TS) and Attention-Deficit/Hyperactivity Disorder (ADHD).

METHOD

Neural oscillations refer to periodic variations in the recording of neural activity. The temporal synchronization of oscillations represents a mechanism of neural communication implicated in normal brain functioning as well as psychopathology. We reviewed physiological, imaging, and neuropsychological evidence that tics and symptoms of ADHD may result from abnormal oscillatory activity in the brain.

RESULTS

Structural and functional abnormalities in the cortical-striatal-thalamo-cortical circuits may result in the disruption of oscillatory activity within the basal ganglia of individuals with TS and lead to transient hyperpolarization of selected thalamocortical regions. Extended to TS plus ADHD this or similar mechanisms, in turn, would lead to the dysrhythmia of particular vulnerable cortical regions and give rise to various deficits in motor control (TS + ADHD) as well as impulsivity and attention (ADHD). Compensatory systems within the prefrontal cortex could be activated and trained to modulate the misguided striatal and thalamocortical oscillations.

CONCLUSIONS

Although it is highly likely that abnormal neural oscillations have a prominent role in co-occurrence of TS + ADHD, its final relevance in this case deserves further differentiated research (i.e. oscillatory networks disentangled from other neuropsychiatric disorders).