Frontostriatal connectivity and its role in cognitive control in parent-child dyads with ADHD

A distributed effects perspective of dimensionally defined psychiatric disorders: and convergent versus core deficit effects in ADHD

The focus of psychiatric and psychological research has arguably shifted from brain damage and psychosis to more common forms of psychopathology that reflect extremes variants of otherwise normal cognitive and behavioral characteristics. Now, in addition to trying to understand overtly damaged brain-function (flat tire effects), we are also seeking to understand liabilities associated with non-optimized, but otherwise intact, cognitive and behavioral abilities (poor tuning effects). This shift has pushed us to evolve our investigational strategies to more broadly consider whole-brain integrated brain systems, as well as seek to develop more specific quantifiable indicators of impoverished brain function and behavior. This paper discusses such challenges in relation to dimensionally defined psychiatric disorders and presents a novel whole-brain integrated perspective of ADHD brain function pathology.

Attention deficit hyperactivity disorder

Over the last two decades, there have been numerous technical and methodological advances available to clinicians and researchers to better understand attention deficit hyperactivity disorder (ADHD) and its etiology. Despite the growing body of literature investigating the disorder's pathophysiology, ADHD remains a complex psychiatric disorder to characterize. This chapter will briefly review the literature on ADHD, with a focus on its history, the current genetic insights, neurophysiologic theories, and the use of neuroimaging to further understand the etiology. We address some of the major concerns that remain unclear about ADHD, including subtype instability, heterogeneity, and the underlying neural correlates that define the disorder. We highlight that the field of ADHD is rapidly evolving; the descriptions provided here will hopefully provide a sturdy foundation for which to build and improve our understanding of the disorder.

Visual Network Asymmetry and Default Mode Network Function in ADHD: An fMRI Study

BACKGROUND

A growing body of research has identified abnormal visual information processing in attention-deficit hyperactivity disorder (ADHD). In particular, slow processing speed and increased reliance on visuo-perceptual strategies have become evident.

OBJECTIVE

The current study used recently developed fMRI methods to replicate and further examine abnormal rightward biased visual information processing in ADHD and to further characterize the nature of this effect; we tested its association with several large-scale distributed network systems.

METHOD

We examined fMRI BOLD response during letter and location judgment tasks, and directly assessed visual network asymmetry and its association with large-scale networks using both a voxelwise and an averaged signal approach.

RESULTS

Initial within-group analyses revealed a pattern of left-lateralized visual cortical activity in controls but right-lateralized visual cortical activity in ADHD children. Direct analyses of visual network asymmetry confirmed atypical rightward bias in ADHD children compared to controls. This ADHD characteristic was atypically associated with reduced activation across several extra-visual networks, including the default mode network (DMN). We also found atypical associations between DMN activation and ADHD subjects' inattentive symptoms and task performance.

CONCLUSION

The current study demonstrated rightward VNA in ADHD during a simple letter discrimination task. This result adds an important novel consideration to the growing literature identifying abnormal visual processing in ADHD. We postulate that this characteristic reflects greater perceptual engagement of task-extraneous content, and that it may be a basic feature of less efficient top-down task-directed control over visual processing. We additionally argue that abnormal DMN function may contribute to this characteristic.

White matter tract integrity of frontostriatal circuit in attention deficit hyperactivity disorder: association with attention performance and symptoms

The frontostriatal circuit has been postulated to account for the core symptoms such as inattention in attention deficit/hyperactivity disorder (ADHD). This study investigated the white matter integrity of frontostriatal fiber tracts using diffusion spectrum imaging (DSI) tractography and its correlations with measures of multi-dimensional aspects of inattention based on psychiatric interview and attention tasks in 25 children with ADHD and 25 matched typically developing (TD) children. All the subjects were assessed with comprehensive psychiatric interviews and the Conner's Continuous Performance Test (CCPT). DSI data were acquired on a 3-Tesla MRI system. The frontostriatal fiber pathways were reconstructed by deterministic tractography, and generalized fractional anisotropy values were measured along individual targeted tracts to investigate alterations in microstructure integrity. Children with ADHD performed worse than TD children in the dimensions of focused attention, sustained attention, impulsivity, and vigilance of the CCPT, and showed impaired integrity in four bilateral frontostriatal tracts, namely the dorsolateral-caudate, medial prefrontal-caudate, orbitofrontal-caudate, and ventrolateral-caudate tracts, and in global white matter as well. The integrity of the left orbitofronto-caudate tract was associated with the symptom of inattention in children with ADHD, compatible with the attention deficit and motivational dysfunction theories in ADHD. The integrity of the frontostriatal tracts was associated with the attention performance only in TD children, suggestive of possible recruitment of tracts other than the frontostriatal tracts implicated in attention deficits in children with ADHD. In conclusion, our results demonstrate the functional involvement of the frontostriatal circuit with respect to clinical symptoms and attention performance.

Neuroimaging and ADHD: fMRI, PET, DTI findings, and methodological limitations

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by pervasive and developmentally inappropriate levels of inattention, impulsivity, and hyperactivity. There is no conclusive cause of ADHD although a number of etiologic theories have been advanced. Research across neuroanatomical, neurochemical, and genetic disciplines collectively support a physiological basis for ADHD and, within the past decade, the number of neuroimaging studies concerning ADHD has increased exponentially. The current selective review summarizes research findings concerning ADHD using functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and diffusion tensor imaging (DTI). Although these technologies and studies offer promise in helping to better understand the physiologic underpinnings of ADHD, they are not without methodological problems, including inadequate sensitivity and specificity for psychiatric disorders. Consequently, neuroimaging technology, in its current state of development, should not be used to inform clinical practice.

White matter correlates of cognitive inhibition during development: a diffusion tensor imaging study

Inhibitory control and cognitive flexibility are two key executive functions that develop in childhood and adolescence, increasing one's capacity to respond dynamically to changing external demands and refrain from impulsive behaviors. These gains evolve in concert with significant brain development. Magnetic resonance imaging studies have identified numerous frontal and cingulate cortical areas associated with performance on inhibition tasks, but less is known about the involvement of the underlying anatomical connectivity, namely white matter. Here we used diffusion tensor imaging (DTI) to examine correlations between a DTI-derived parameter, fractional anisotropy (FA) of white matter, and performance on the NEPSY-II Inhibition test (Naming, Inhibition and Switching conditions) in 49 healthy children aged 5-16years (20 females; 29 males). First, whole brain voxel-based analysis revealed several clusters in the frontal projections of the corpus callosum, where higher FA was associated with worse inhibitory performance, as well as several clusters in posterior brain regions and one in the brainstem where higher FA was associated with better cognitive flexibility (in the Switching task), suggesting a dichotomous relationship between FA and these two aspects of cognitive control. Tractography through these clusters identified several white matter tracts, which were then manual traced in native space. Pearson's correlations confirmed associations between higher FA of frontal projections of the corpus callosum with poorer inhibitory performance (independent of age), though associations with Switching were not significant. Post-hoc evaluation suggested that FA of orbital and anterior frontal projections of the corpus callosum also mediated performance differences across conditions, which may reflect differences in self-monitoring or strategy use. These findings suggest a link between the development of inhibition and cognitive control with that of the underlying white matter, and may help to identify deviations of neurobiology in adolescent psychopathology.

Prefrontal activation during inhibitory control measured by near-infrared spectroscopy for differentiating between autism spectrum disorders and attention deficit hyperactivity disorder in adults

The differential diagnosis of autism spectrum disorders (ASDs) and attention deficit hyperactivity disorder (ADHD) based solely on symptomatic and behavioral assessments can be difficult, even for experts. Thus, the development of a neuroimaging marker that differentiates ASDs from ADHD would be an important contribution to this field. We assessed the differences in prefrontal activation between adults with ASDs and ADHD using an entirely non-invasive and portable neuroimaging tool, near-infrared spectroscopy. This study included 21 drug-naïve adults with ASDs, 19 drug-naïve adults with ADHD, and 21 healthy subjects matched for age, sex, and IQ. Oxygenated hemoglobin concentration changes in the prefrontal cortex were assessed during a stop signal task and a verbal fluency task. During the stop signal task, compared to the control group, the ASDs group exhibited lower activation in a broad prefrontal area, whereas the ADHD group showed underactivation of the right premotor area, right presupplementary motor area, and bilateral dorsolateral prefrontal cortices. Significant differences were observed in the left ventrolateral prefrontal cortex between the ASDs and ADHD groups during the stop signal task. The leave-one-out cross-validation method using mean oxygenated hemoglobin changes yielded a classification accuracy of 81.4% during inhibitory control. These results were task specific, as the brain activation pattern observed during the verbal fluency task did not differentiate the ASDs and ADHD groups significantly. This study therefore provides evidence of a difference in left ventrolateral prefrontal activation during inhibitory control between adults with ASDs and ADHD. Thus, near-infrared spectroscopy may be useful as an auxiliary tool for the differential diagnosis of such developmental disorders.

Challenges in the transition of care for adolescents with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is often considered a childhood disorder. However, in those diagnosed with ADHD as children, inattention, impulsivity, and hyperactivity can persist into adulthood, causing significant functional impairment and emotional distress, even if the condition no longer meets diagnostic criteria. This review examines the developmental and psychosocial factors to consider in adolescents with ADHD and the strategies that facilitate the transition from pediatric to adult care. Our findings are based on PubMed database searches conducted on November 29, 2011, that identified articles pertaining to ADHD and continuity or transition in medical care for adolescents published in English within the 5-year period preceding this date. Adolescents with ADHD face specific burdens associated with transitioning into adulthood that can impede the achievement of academic and occupational goals. The main finding of the literature review was that ADHD treatment rates decline sharply from childhood through young adulthood, despite the fact that functional impairment often persists. Moreover, although psychosocial therapy can play an important role in resolving functional difficulties and encouraging patient adherence to pharmacotherapy, the existing literature focuses mainly on pharmacotherapy as first-line treatment for ADHD. Therefore, careful, advanced planning to ensure continuity of medical and psychiatric care is essential. This planning involves the pediatric service that has been providing care, the adult service that will assume the responsibility of providing care, the young person with ADHD, and the family. Although recommendations for planning initiatives have been developed by a variety of professional organizations, they do not seem to be routinely implemented for the transition of ADHD care. Such careful advanced transition planning can ensure continuity of treatment, encourage treatment adherence, and help young individuals adjust to new life circumstances and avoid negative educational, social, and vocational results. Guidelines designed to facilitate this transition of care may be helpful.

Proactive and reactive control of movement are differently affected in Attention Deficit Hyperactivity Disorder children

Attention-Deficit/Hyperactivity Disorder children are impaired in the ability to interrupt an ongoing action in relation to a sudden change in the environment (reactive control, measured by stop signal reaction time, SSRT). Less investigated is the ability to control the response when it is known in advance that it will be required to stop (proactive control, measured by change in Reaction time, RT). The study is aimed at exploring both the reactive and the proactive inhibitory control in a group of ADHD children compared to a group of age-matched controls. ADHD children (N=28) and Controls (N=28) performed 4 tasks: 2 tasks required to respond to the appearance of the go-signals (go task and nostop task) and 2 tasks to respond to the go signals in a context in which sometimes a restrain or suppression of the response was required (go-nogo task and stop task). ADHD children showed a longer SSRT compared to controls. Both groups showed an increment in RT by comparing the go-nogo to the go task and an increment in RT and SD by comparing the stop to the nostop task. ADHD children showed higher intra-individual variability (SD) compared to controls only in the stop and nostop task. ADHD children showed impaired reactive control but preserved proactive control, and the physical appearance of the go signal affected their reaction times intra-individual variability. A comparison between the reactive and proactive controls helps in defining neuropsychological profiles of ADHD children and can inspires therapeutic behavioral-cognitive strategies for response control.

Probabilistic diffusion tractography and graph theory analysis reveal abnormal white matter structural connectivity networks in drug-naive boys with attention deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD), which is characterized by core symptoms of inattention and hyperactivity/impulsivity, is one of the most common neurodevelopmental disorders of childhood. Neuroimaging studies have suggested that these behavioral disturbances are associated with abnormal functional connectivity among brain regions. However, the alterations in the structural connections that underlie these behavioral and functional deficits remain poorly understood. Here, we used diffusion magnetic resonance imaging and probabilistic tractography method to examine whole-brain white matter (WM) structural connectivity in 30 drug-naive boys with ADHD and 30 healthy controls. The WM networks of the human brain were constructed by estimating inter-regional connectivity probability. The topological properties of the resultant networks (e.g., small-world and network efficiency) were then analyzed using graph theoretical approaches. Nonparametric permutation tests were applied for between-group comparisons of these graphic metrics. We found that both the ADHD and control groups showed an efficient small-world organization in the whole-brain WM networks, suggesting a balance between structurally segregated and integrated connectivity patterns. However, relative to controls, patients with ADHD exhibited decreased global efficiency and increased shortest path length, with the most pronounced efficiency decreases in the left parietal, frontal, and occipital cortices. Intriguingly, the ADHD group showed decreased structural connectivity in the prefrontal-dominant circuitry and increased connectivity in the orbitofrontal-striatal circuitry, and these changes significantly correlated with the inattention and hyperactivity/impulsivity symptoms, respectively. The present study shows disrupted topological organization of large-scale WM networks in ADHD, extending our understanding of how structural disruptions of neuronal circuits underlie behavioral disturbances in patients with ADHD.

Targeting glia cells: novel perspectives for the treatment of neuropsychiatric diseases

Neuropsychiatric disorders are devastating mental illnesses with a high economic burden. The additional morbidity associated with social issues that arises along with the course of these diseases increases the need for a clear understanding of their etiopathogenesis to allow an implementation of novel pharmacological strategies. Yet a poor knowledge about interactions occurring at the glia-neuron interface in health and disease still hampers innovative discoveries, despite the fact that glia cells have been long described to actively participate in the regulation of brain circuits.

The purpose of this review was to collect the scattered literature on the involvement of glia cells in neuropsychiatric disorders and to describe how also these cells besides neurons might be responsive to current pharmacological interventions. We hope thereby to offer alternative approaches for investigations that may open avenues to search for new potential targets for drug discovery.

Attention-deficit/hyperactivity disorder without comorbidity is associated with distinct atypical patterns of cerebral microstructural development

Differential core symptoms and treatment responses are associated with the pure versus comorbid forms of attention-deficit/hyperactivity disorder (ADHD). However, comorbidity has largely been unaccounted for in neuroimaging studies of ADHD. We used diffusional kurtosis imaging to investigate gray matter (GM) and white matter (WM) microstructure of children and adolescents with ADHD (n = 22) compared to typically developing controls (TDC, n = 27) and examined whether differing developmental patterns are related to comorbidity. The ADHD group (ADHD-mixed) consisted of subgroups with and without comorbidity (ADHD-comorbid, n = 11; ADHD-pure, n = 11, respectively). Age-related changes and group differences in cerebral microstructure of the ADHD-mixed group and each ADHD subgroup were compared to TDC. Whole-brain voxel-based analyses with mean kurtosis (MK) and mean diffusivity (MD) metrics were conducted to probe GM and WM. Tract-based spatial statistics analyses of WM were performed with MK, MD, fractional anisotropy, and directional (axial, radial) kurtosis and diffusivity metrics. ADHD-pure patients lacked significant age-related changes in GM and WM microstructure that were observed globally in TDC and had significantly greater WM microstructural complexity than TDC in bilateral frontal and parietal lobes, insula, corpus callosum, and right external and internal capsules. Including ADHD patients with diverse comorbidities in analyses masked these findings. A distinct atypical age-related trajectory and aberrant regional differences in brain microstructure were detected in ADHD without comorbidity. Our results suggest that different phenotypic manifestations of ADHD, defined by the presence or absence of comorbidity, differ in cerebral microstructural markers.

The impact of acute tryptophan depletion on attentional performance in adult patients with ADHD

OBJECTIVE

To date, the impact of the neurotransmitter serotonin (5-HT) on different neuropsychological functions in adults with attention deficit hyperactivity disorder (ADHD) is underinvestigated. We aimed to examine the effects of acute tryptophan depletion (ATD) and the resulting reduction in central nervous 5-HT synthesis on target/non-target discrimination ability and sustained attention in adults with ADHD using an AX-Continuous Performance Test (AX-CPT).

METHOD

Twenty male patients with ADHD (age: M = 30.25 SD = 9.37) and twenty male healthy controls (age: M = 27.90 SD = 6.01) received ATD on one day and a tryptophan-balanced control condition (BAL) on another day in a double-blind within-subject crossover design. A continuous performance test (AX-CPT) with three conditions (AX, AY, and BX) was administered on both days under depleted and sham-depleted conditions.

RESULTS

In patients omissions increased after ATD when compared with BAL. Patient's reaction time decreased after ATD when compared with BAL, which was contrasted by opposite effects in controls. Patients showed fewer correct responses (AX condition) and showed a higher rate of errors (condition AXE ) independent of ATD or BAL intake.

CONCLUSION

The present preliminary results are indicative of the contribution of serotonergic neurotransmission to attentional processes in adults with ADHD.

Dimensional change card sort performance associated with age-related differences in functional connectivity of lateral prefrontal cortex

The Dimensional Change Card Sort (DCCS) is a standard procedure for assessing executive functioning early in development. In the task, participants switch from sorting cards one way (e.g., by color) to sorting them a different way (e.g., by shape). Traditional accounts associate age-related changes in DCCS performance with circumscribed changes in lateral prefrontal cortex (lPFC) functioning, but evidence of age-related differences in the modulation of lPFC activity by switching is mixed. The current study therefore tested for possible age-related differences in functional connectivity of lPFC with regions that comprise a larger cognitive control network. Functional magnetic resonance imaging (fMRI) data collected from children and adults performing the DCCS were analyzed by means of independent components analysis (ICA). The analysis revealed several important age-related differences in functional connectivity of lPFC. In particular, lPFC was more strongly connected with the anterior cingulate, inferior parietal cortex, and the ventral tegmental area in adults than in children. Theoretical implications are discussed.

Impact of socio-emotional context, brain development, and pubertal maturation on adolescent risk-taking

While there is little doubt that risk-taking is generally more prevalent during adolescence than before or after, the underlying causes of this pattern of age differences have long been investigated and debated. One longstanding popular notion is the belief that risky and reckless behavior in adolescence is tied to the hormonal changes of puberty. However, the interactions between pubertal maturation and adolescent decision making remain largely understudied. In the current review, we discuss changes in decision making during adolescence, focusing on the asynchronous development of the affective, reward-focused processing system and the deliberative, reasoned processing system. As discussed, differential maturation in the structure and function of brain systems associated with these systems leaves adolescents particularly vulnerable to socio-emotional influences and risk-taking behaviors. We argue that this asynchrony may be partially linked to pubertal influences on development and specifically on the maturation of the affective, reward-focused processing system.

Disturbed microstructural integrity of the frontostriatal fiber pathways and executive dysfunction in children with attention deficit hyperactivity disorder

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is recognized as an early-onset neuropsychiatric disorder with executive dysfunctions and neurobiological deficits. The authors compared executive functions and microstructural integrity of the frontostriatal circuit in children with ADHD and typically developing children. Method We assessed 25 children with ADHD and 25 age-, sex-, handedness- and intelligence-matched typically developing children by using psychiatric interviews, the Wechsler Intelligence Scale for Children - third edition, and the tasks involving executive functions in the Cambridge Neuropsychological Test Automated Battery. The frontostriatal tracts were reconstructed by diffusion spectrum imaging tractography and were subdivided into four functionally distinct segments, including dorsolateral, medial prefrontal, orbitofrontal and ventrolateral tracts. Tract-specific and matched case-control analyses were used and generalized fractional anisotropy values were computed.

RESULTS

Children with ADHD had lower generalized fractional anisotropy of all the bilateral frontostriatal fiber tracts and poorer performance in verbal and spatial working memory, set-shifting, sustained attention, cognitive inhibition and visuospatial planning. The symptom severity of ADHD and the executive functioning performance significantly correlated with integrity of the frontostriatal tracts, particularly the left orbitofrontal and ventrolateral tracts. Children with ADHD also demonstrated loss of the leftward asymmetry in the dorsolateral and medial prefrontal tracts that was present in typically developing children.

CONCLUSIONS

Our findings demonstrate disturbed structural connectivity of the frontostriatal circuitry in children with ADHD and add new evidence of associations between integrity of the frontostriatal tracts and measures of core symptoms of ADHD and a wide range of executive dysfunctions in both groups.

Altered functional brain connectivity in a non-clinical sample of young adults with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is characterized by symptoms of inattention and hyperactivity/impulsivity that often persist in adulthood. There is a growing consensus that ADHD is associated with abnormal function of diffuse brain networks, but such alterations remain poorly characterized. Using resting-state functional magnetic resonance imaging, we characterized multivariate (complex network measures), bivariate (network-based statistic), and univariate (regional homogeneity) properties of brain networks in a non-clinical, drug-naive sample of high-functioning young men and women with ADHD (nine males, seven females) and a group of matched healthy controls. Data from our sample allowed the isolation of intrinsic functional connectivity alterations specific to ADHD diagnosis and symptoms that are not related to developmental delays, general cognitive dysfunction, or history of medication use. Multivariate results suggested that frontal, temporal, and occipital cortices were abnormally connected locally as well as with the rest of the brain in individuals with ADHD. Results from the network-based statistic support and extend multivariate results by isolating two brain networks comprising regions between which inter-regional connectivity was significantly altered in the ADHD group; namely, a frontal amygdala-occipital network and a frontal temporal-occipital network. Brain behavior correlations further highlighted the key role of altered orbitofrontal-temporal and frontal-amygdala connectivity for symptoms of inattention and hyperactivity/impulsivity. All univariate properties were similar between groups. Taken together, results from this study show that the diagnosis and the two main symptom dimensions of ADHD are related to altered intrinsic connectivity in orbitofrontal-temporal-occipital and fronto-amygdala-occipital networks. Accordingly, our findings highlight the importance of extending the conceptualization of ADHD beyond segregated fronto-striatal alterations.

White matter microstructure in subjects with attention-deficit/hyperactivity disorder and their siblings

OBJECTIVE

Previous voxel-based and regions-of-interest (ROI)-based diffusion tensor imaging (DTI) studies have found above-normal mean diffusivity (MD) and below-normal fractional anisotropy (FA) in subjects with attention-deficit/hyperactivity disorder (ADHD). However, findings remain mixed, and few studies have examined the contribution of ADHD familial liability to white matter microstructure.

METHOD

We used refined DTI tractography methods to examine MD, FA, axial diffusivity (AD), and radial diffusivity (RD) of the anterior thalamic radiation, cingulum, corticospinal tract, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, forceps major, forceps minor, superior longitudinal fasciculus, and uncinate fasciculus in children and adolescents with ADHD (n = 56), unaffected siblings of ADHD probands (n = 31), and healthy controls (n = 17).

RESULTS

Subjects with ADHD showed significantly higher MD than controls in the anterior thalamic radiation, forceps minor, and superior longitudinal fasciculus. Unaffected siblings of subjects with ADHD displayed similar differences in MD as subjects with ADHD. Although none of the tested tracts showed a significant effect of FA, the tracts with elevated MD likewise displayed elevated AD both in subjects with ADHD and in unaffected siblings. Differences in RD between subjects with ADHD, unaffected siblings, and controls were not as widespread as differences in MD and AD.

CONCLUSION

Our findings suggest that disruptions in white matter microstructure occur in several large white matter pathways in association with ADHD and indicate a familial liability for the disorder. Furthermore, MD may reflect these abnormalities more sensitively than FA.

Attention and internalizing behaviors in relation to white matter in children born preterm

OBJECTIVE

Diffusion tensor imaging (DTI) is a magnetic resonance imaging technique that provides quantitative characterization of white matter tracts in the brain. This study used DTI to examine the degree of association between parent-rated scores of attention, internalizing behaviors including anxiety symptoms, and externalizing behaviors and white matter fractional anisotropy (FA) in children born preterm.

METHODS

Participants were aged 9 to 16 years; 25 were born at <36 weeks of gestation (mean = 28.6 wk, birth weight = 1191 g) and 20 were full term. The authors analyzed the results using Tract-Based Spatial Statistics, a technique that generates a skeleton representing the core of white matter tracts throughout the brain. The authors examined the correlations between behavior scores and FA of (1) the whole skeleton and (2) the specific regions of interest.

RESULTS

In preterm children, scores on attention and internalizing behavior scales were each associated with whole skeleton FA and several regions of interest; unfavorable scores were consistently associated with lower FA. Externalizing behaviors were not associated with whole skeleton FA, but significant associations were found within a few regions of interest. The network of significant regions for attention and internalizing symptoms was widely distributed and overlapping. In full-term children, no associations of FA and behavior were significant.

CONCLUSIONS

Attention and internalizing behaviors in preterm children were associated with FA in a widely distributed overlapping network of white matter tracts, suggesting common underlying neurobiology. DTI contributes to understanding individual differences in attention and behavior characteristics in children born preterm.

White matter tract abnormalities between rostral middle frontal gyrus, inferior frontal gyrus and striatum in first-episode schizophrenia

BACKGROUND

Previous studies have shown that frontostriatal networks, especially those involving dorsolateral prefrontal cortex (DLPFC) and ventrolateral prefrontal cortex (VLPFC) mediate cognitive functions some of which are abnormal in schizophrenia. This study examines white matter integrity of the tracts connecting DLPFC/VLPFC and striatum in patients with first-episode schizophrenia (FESZ), and their associations with cognitive and clinical correlates.

METHODS

Diffusion tensor and structural magnetic resonance images were acquired on a 3T GE Echospeed system from 16 FESZ and 18 demographically comparable healthy controls. FreeSurfer software was used to parcellate regions of interest. Two-tensor tractography was applied to extract fibers connecting striatum with rostral middle frontal gyrus (rMFG) and inferior frontal gyrus (IFG), representing DLPFC and VLPFC respectively. DTI indices, including fractional anisotropy (FA), trace, axial diffusivity (AD) and radial diffusivity (RD), were used for group comparisons. Additionally, correlations were evaluated between these diffusion indices and the Wisconsin Card Sorting Task (WCST) and the Brief Psychiatric Rating Scale (BPRS).

RESULTS

FA was significantly reduced in the left IFG-striatum tract, whereas trace and RD were significantly increased in rMFG-striatum and IFG-striatum tracts, bilaterally. The number of WCST categories completed correlated positively with FA of the right rMFG-striatum tract, and negatively with trace and RD of right rMFG-striatum and right IFG-striatum tracts in FESZ. The BPRS scores did not correlate with these indices.

CONCLUSIONS

These data suggest that white matter tract abnormalities between rMFG/IFG and striatum are present in FESZ and appear to be significantly associated with executive dysfunction but not with symptom severity.

Adjusting behavior to changing environmental demands with development

Plasticity refers to changes in the brain that enable an organism to adapt its behavior in the face of changing environmental demands. The evolutionary role of plasticity is to provide the cognitive flexibility to learn from experiences, to monitor the world based on learned predictions, and adjust actions when these predictions are violated. Both progressive (myelination) and regressive (synaptic pruning) brain changes support this type of adaptation. Experience-driven changes in neural connections underlie the ability to learn and update thoughts and behaviors throughout life. Many cognitive and behavioral indices exhibit nonlinear life-span trajectories, suggesting the existence of specific sensitive developmental periods of heightened plasticity. We propose that age-related differences in learning capabilities and behavioral performance reflect the distinct maturational timetable of subcortical learning systems and modulatory prefrontal regions. We focus specifically on the developmental transition of adolescence, during which individuals experience difficulty flexibly adjusting their behavior when confronted with unexpected and emotionally salient events. In this article, we review the findings illustrating this phenomenon and how they vary by individual.

Genetics of impulsive behaviour

Impulsivity, defined as the tendency to act without foresight, comprises a multitude of constructs and is associated with a variety of psychiatric disorders. Dissecting different aspects of impulsive behaviour and relating these to specific neurobiological circuits would improve our understanding of the etiology of complex behaviours for which impulsivity is key, and advance genetic studies in this behavioural domain. In this review, we will discuss the heritability of some impulsivity constructs and their possible use as endophenotypes (heritable, disease-associated intermediate phenotypes). Several functional genetic variants associated with impulsive behaviour have been identified by the candidate gene approach and re-sequencing, and whole genome strategies can be implemented for discovery of novel rare and common alleles influencing impulsivity. Via deep sequencing an uncommon HTR2B stop codon, common in one population, was discovered, with implications for understanding impulsive behaviour in both humans and rodents and for future gene discovery.

Automatic diagnosis of ADHD based on multichannel nonlinear analysis of actimetry registries

Attention-Deficit Hyperactivity Disorder (ADHD) is the most common mental health problem in childhood and adolescence. It is commonly diagnosed by means of subjective methods which tend to overestimate the severity of the pathology. A number of objective methods also exist, but they are either expensive or time-consuming. Some recent proposals based on nonlinear processing of activity registries have deserved special attention. Since they rely on actigraphy measurements, they are both inexpensive and non-invasive. Among these methods, those shown to have higher reliability are based on single-channel complexity assessment of the activity patterns. This way, potentially useful information related to the interaction between the different channels is discarded. In this paper we propose a new methodology for ADHD diagnosis based on joint complexity assessment of multichannel activity registries. Results on real data show that the proposed method constitute a useful diagnostic aid tool reaching 87:10% sensitivity and 84.38% specificity. The combination of ADHD indicators extracted with the proposed method with single-channel complexity-based indices previously proposed lead to sensitivity and specifity values above 90%.

Altered gene expression in the prefrontal cortex of young rats induced by the ADHD drug atomoxetine

Atomoxetine (ATX), a selective norepinephrine reuptake inhibitor, is a non-stimulant approved for the treatment of attention deficit/hyperactivity disorder (ADHD). Little is known about the molecular basis for its therapeutic effect. The objective of this animal study was to determine alterations in gene expression patterns in the prefrontal cortex after long-term administration of atomoxetine. Rats were treated for 21 days during childhood and early adolescent stages of development with a once-daily oral application of 0.05 g/kg atomoxetine, which resulted in plasma levels similar to those described in children. A whole genome RNA-microarray of rat prefrontal cortical gene expression after administration of atomoxetine versus sterile water revealed an mRNA increase in 114 genes (≥2-fold) while 11 genes were down-regulated (≤0.5-fold). By applying quantitative real-time PCR (qRT-PCR) and Western Blot we confirmed a significant increase in the expression of GABA A receptor subunits as well as ubiquinol-cytochrome c reductase complex core protein 2 (Uqcrc2). SNAP-25 (synaptosomal-associated protein of 25 kDa), which is an ADHD candidate gene and an important vesicle protein involved in axonal growth, synaptic plasticity and regulation of neurotransmitter release was also significantly upregulated on RNA- and protein level after atomoxetine treatment. In summary, we could show that long-term treatment with the ADHD drug atomoxetine induces the regulation of several genes in the prefrontal cortex of young rats. Especially the increased expression of SNAP-25 and GABA-A receptor subunits may indicate additional active therapeutic mechanisms for atomoxetine.

Temperamental exuberance and executive function predict propensity for risk taking in childhood

The present study utilized a multilevel approach to examine developmental trajectories in risk-taking propensity. We examined the moderating role of specific executive function components, attention shifting and inhibitory control, on the link between exuberant temperament in infancy and propensity for risk taking in childhood. Risk taking was assessed using a task previously associated with sensation seeking and antisocial behaviors. Two hundred ninety-one infants were brought into the lab and behaviors reflecting exuberance were observed at 4, 9, 24, and 36 months of age. Executive function was assessed at 48 months of age. Risk-taking propensity was measured when children were 60 months of age. The results indicated that exuberance and attention shifting, but not inhibitory control, significantly interacted to predict propensity for risk taking. Exuberance was positively associated with risk-taking propensity among children who were relatively low in attention shifting but unrelated for children high in attention shifting. These findings illustrated the multifinality of developmental outcomes for temperamentally exuberant young children and pointed to the distinct regulatory influences of different executive functions for children of differing temperaments. Attention shifting likely affords a child the ability to consider both positive and negative consequences and moderates the relation between early exuberance and risk-taking propensity.

Abnormal anatomical connectivity between the amygdala and orbitofrontal cortex in conduct disorder

OBJECTIVE

Previous research suggested that structural and functional abnormalities within the amygdala and orbitofrontal cortex contribute to the pathophysiology of Conduct Disorder (CD). Here, we investigated whether the integrity of the white-matter pathways connecting these regions is abnormal and thus may represent a putative neurobiological marker for CD.

METHODS

Diffusion Tensor Imaging (DTI) was used to investigate white-matter microstructural integrity in male adolescents with childhood-onset CD, compared with healthy controls matched in age, sex, intelligence, and socioeconomic status. Two approaches were employed to analyze DTI data: voxel-based morphometry of fractional anisotropy (FA), an index of white-matter integrity, and virtual dissection of white-matter pathways using tractography.

RESULTS

Adolescents with CD displayed higher FA within the right external capsule relative to controls (T = 6.08, P<0.05, Family-Wise Error, whole-brain correction). Tractography analyses showed that FA values within the uncinate fascicle (connecting the amygdala and orbitofrontal cortex) were abnormally increased in individuals with CD relative to controls. This was in contrast with the inferior frontal-occipital fascicle, which showed no significant group differences in FA. The finding of increased FA in the uncinate fascicle remained significant when factoring out the contribution of attention-deficit/hyperactivity disorder symptoms. There were no group differences in the number of streamlines in either of these anatomical tracts.

CONCLUSIONS

These results provide evidence that CD is associated with white-matter microstructural abnormalities in the anatomical tract that connects the amygdala and orbitofrontal cortex, the uncinate fascicle. These results implicate abnormal maturation of white-matter pathways which are fundamental in the regulation of emotional behavior in CD.

Brain Activity in ADHD Patients Performing the Counting Stroop Task: A Social Neuroscience Approach

Attention Deficit/Hyperactivity Disorder (ADHD) symptoms are manifested in social dynamics. In this study, the brain activity of eight child and adolescent patients diagnosed with ADHD was examined while they performed the Counting Stroop task and results were interpreted using social neuroscience premises. Brain activity was identified in frontal, parietal, and temporal regions related to the orienting system of attention and with linguistic, facial recognition, and mnemonic processes. Consistent with previous reports, these patients showed no activation in prefrontal and anterior cingulate cortices related to the executive system of attention. Also, they manifested activation in the insular cortex involving interoceptive processes that may be associated with impulsiveness. Global brain activity involves a network formed during early development and includes experiential components such as learning of rules, reward systems, empathy, and decision making. An integrative assessment of ADHD should consider psychosocial and neurobiological causes integrated into an individual's own experiences assembled throughout life.

The neurobiology and genetics of Attention-Deficit/Hyperactivity Disorder (ADHD): what every clinician should know

This review, addressed mainly to clinicians, considers commonly asked questions related to the neuroimaging, neurophysiology, neurochemistry and genetics of Attention-Deficit/Hyperactivity Disorder (ADHD). It provides answers based on the most recent meta-analyses and systematic reviews, as well as additional relevant original studies. Empirical findings from neurobiological research into ADHD reflect a shift in the conceptualisation of this disorder from simple theoretical views of a few isolated dysfunctions to more complex models integrating the heterogeneity of the clinical manifestations of ADHD. Thus, findings from structural and functional neuroimaging suggest the involvement of developmentally abnormal brain networks related to cognition, attention, emotion and sensorimotor functions. Brain functioning alterations are confirmed by neurophysiological findings, showing that individuals with ADHD have elevated theta/beta power ratios, and less pronounced responses and longer latencies of event-related potentials, compared with controls. At a molecular level, alterations in any single neurotransmitter system are unlikely to explain the complexity of ADHD; rather, the disorder has been linked to dysfunctions in several systems, including the dopaminergic, adrenergic, serotoninergic and cholinergic pathways. Genetic studies showing a heritability of ∼60-75% suggest that a plethora of genes, each one with a small but significant effect, interact with environmental factors to increase the susceptibility to ADHD. Currently, findings from neurobiological research do not have a direct application in daily clinical practice, but it is hoped that in the near future they will complement the diagnostic process and contribute to the long-term effective treatment of this impairing condition.

Subcortical and cortical structural central nervous system changes and attention processing deficits in preschool-aged children with prenatal methamphetamine and tobacco exposure

OBJECTIVE

To examine the independent contributions of prenatal methamphetamine exposure (PME) and prenatal tobacco exposure (PTE) on brain morphology among a sample of nonalcohol-exposed 3- to 5-year-old children followed prospectively since birth.

STUDY DESIGN

The sample included 20 children with PME (19 with PTE) and 15 comparison children (7 with PTE), matched on race, birth weight, maternal education and type of insurance. Subcortical and cortical volumes and cortical thickness measures were derived through an automated segmentation procedure from T1-weighted structural magnetic resonance images obtained on unsedated children. Attention was assessed using the computerized Conners' Kiddie Continuous Performance Test Version 5 (K-CPT™ V.5). PME effects on subcortical and cortical brain volumes and cortical thickness were tested by general linear model with type III sum of squares, adjusting for PTE, prenatal marijuana exposure, age at time of scan, gender, handedness, pulse sequence and total intracranial volume (for volumetric outcomes). A similar analysis was done for PTE effects on subcortical and cortical brain volumes and thickness, adjusting for PME and the above covariates.

RESULTS

Children with PME had significantly reduced caudate nucleus volumes and cortical thickness increases in perisylvian and orbital-frontal cortices. In contrast, children with PTE showed cortical thinning in perisylvian and lateral occipital cortices and volumetric increases in frontal regions and decreases in anterior cingulate. PME was positively related and caudate volume was inversely related to K-CPT reaction time by inter-stimulus interval, a measure of the ability to adjust to changing task demands, suggesting that children with PME may have subtle attentional deficits mediated by caudate volume reductions.

CONCLUSIONS

Our results suggest that PME and PTE may have distinct differential cortical effects on the developing central nervous system. Additionally, PME may be associated with subtle deficits in attention mediated by caudate volume reductions.

Decreased frontostriatal microstructural organization in attention deficit/hyperactivity disorder

Frontostriatal brain areas have been implicated in the neurobiology of attention deficit/hyperactivity disorder (ADHD), but little work has directly addressed the white matter connections between these regions. The present study investigates the microstructural organization and myelination of frontostriatal white matter in children with ADHD and controls. Diffusion tensor imaging and magnetization transfer imaging scans were acquired in 30 children with ADHD and 34 controls. A study specific volume of interest (VOI) of frontostriatal white matter was created using a tractography based statistical group map. Fractional anisotropy (FA, indexing microstructural organization) and magnetization transfer ratio (MTR, indexing macromolecular content, myelin in particular) were computed for the frontostriatal VOI and for total cerebral white matter. Exploratory analyses were conducted investigating the effect of stimulant use on these measures. Frontostriatal FA but not MTR was decreased in ADHD compared with controls. There were no differences in FA or MTR for total cerebral white matter. Frontostriatal FA correlated negatively with teacher-rated attention problems in controls but not children with ADHD. The duration of stimulant use did not affect the main results. Changes in frontostriatal connectivity in ADHD appear to be related to changes in microstructural organization rather than myelination per se. A correlation with attention problems for controls suggests that frontostriatal organization is relevant to ADHD-related behaviors.

Training cognition in ADHD: current findings, borrowed concepts, and future directions

With both its high prevalence and myriad of negative outcomes, Attention-Deficit/Hyperactivity Disorder (ADHD) demands a careful consideration of the efficacy of its treatment options. Although the benefits of medication have a robust empirical background, nonpharmaceutical interventions evoke particular interest, as they are often viewed more favorably by parents. This review pays special attention to the use of working memory and recent cognitive training attempts in ADHD, describing its cognitive, behavioral, and biological effects in relation to current neurological theory of the disorder. While these treatments have demonstrated positive effects on some measures, there are limitations, as studies have failed to demonstrate generalization to critical measures, such as teacher-rated classroom behaviors, and have provided limited but growing evidence of functionally significant improvements in behavior. There is also a clear lack of research on the effects of training on reward systems and self-control. These limitations may be addressed by broadening the scope and procedures of the training and incorporating research concepts from other fields of study. First, it is important to consider the developmental trajectories of brain regions in individuals with the disorder, as they may relate to the effectiveness of cognitive training. Notions from behavioral economics, including delay discounting and framing (i.e., context) manipulations that influence present orientation, also have applications in the study of cognitive training in ADHD. In considering these other domains, we may find new ways to conceptualize and enhance cognitive training in ADHD and, in turn, address current limitations of interventions that fall in this category.

Biomarkers for attention-deficit/hyperactivity disorder (ADHD). A consensus report of the WFSBP task force on biological markers and the World Federation of ADHD

OBJECTIVE

Psychiatric "nosology" is largely based on clinical phenomenology using convention-based diagnostic systems not necessarily reflecting neurobiological pathomechanisms. While progress has been made regarding its molecular biology and neuropathology, the phenotypic characterization of ADHD has not improved. Thus, validated biomarkers, more directly linked to the underlying pathology, could constitute an objective measure for the condition.

METHOD

The task force on biological markers of the World Federation of Societies of Biological Psychiatry (WFSBP) and the World Federation of ADHD commissioned this paper to develop a consensus report on potential biomarkers of ADHD. The criteria for biomarker-candidate evaluation were: (1) sensitivity >80%, (2) specificity >80%, (3) the candidate is reliable, reproducible, inexpensive, non-invasive, easy to use, and (4) confirmed by at least two independent studies in peer-reviewed journals conducted by qualified investigators.

RESULTS

No reliable ADHD biomarker has been described to date, but some promising candidates (e.g., olfactory sensitivity, substantial echogenicity) exist. A problem in the development of ADHD markers is sample heterogeneity due to aetiological and phenotypic complexity and age-dependent co-morbidities.

CONCLUSIONS

Most likely, no single ADHD biomarker can be identified. However, the use of a combination of markers may help to reduce heterogeneity and to identify homogeneous subtypes of ADHD.

White matter abnormalities associated with disruptive behavior disorder in adolescents with and without attention-deficit/hyperactivity disorder

Disruptive behavior disorders (DBD) are among the most commonly diagnosed mental disorders in children and adolescents. Some important characteristics of DBD vary based on the presence or absence of comorbid attention-deficit/hyperactivity disorder (ADHD), which may affect the understanding of and treatment decision-making related to the disorders. Thus, identifying neurobiological characteristics of DBD with comorbid ADHD (DBD+ADHD) can provide a basis to establish a better understanding of the condition. This study aimed to assess abnormal white matter microstructural alterations in DBD+ADHD as compared to DBD alone and healthy controls using diffusion tensor imaging (DTI). Thirty-three DBD (19 with comorbid ADHD) and 46 age-matched healthy adolescents were studied using DTI. Fractional anisotropy (FA), and mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) were analyzed using tract-based spatial statistics (TBSS). Significantly lower FA and higher MD, RD and AD in many white matter fibers were found in adolescents with DBD+ADHD compared to controls. Moreover, lower FA and higher RD were also found in the DBD+ADHD versus the DBD alone group. Alterations of white matter integrity found in DBD patients were primarily associated with ADHD, suggesting that ADHD comorbidity in DBD is reflected in greater abnormality of microstructural connections.

White matter abnormalities and their impact on attentional performance in adult attention-deficit/hyperactivity disorder

Inattention is the most important behavioral feature of adult patients with attention-deficit/hyperactivity disorder (ADHD). Neuroimaging studies in ADHD have demonstrated abnormalities primarily in the frontostriatal circuitry and were mostly conducted in children. We investigated white matter (WM) integrity in adult ADHD patients and the correlation of WM microstructure and neuropsychological parameters in 37 (21 men) never-medicated adult ADHD patients and 34 age- and gender-matched healthy controls. All subjects underwent clinical interviews, rating scales, and neuropsychological tests of attentional performance. Diffusion tensor imaging (DTI) was acquired, and 12 WM regions-of-interest (ROIs) within the attentional network were chosen. Group differences of mean fractional anisotropy (FA) and mean diffusivity (MD) values were calculated for each ROI, and patients' DTI measures were then correlated with measures of attentional performance. FA values in ADHD patients were significantly reduced in the left inferior longitudinal fasciculus (ILF), while MD values were significantly increased in ADHD patients in the frontal portion of the left frontooccipital fasciculus (IFO). In ADHD patients, MD values were negatively correlated with attentional performance in the left ILF. Our findings provide further support for disturbed frontostriatal structural connectivity and also point to an involvement of the left temporal white matter with an impact on attentional performance.

Diffusion tensor imaging reveals white matter abnormalities in Attention-Deficit/Hyperactivity Disorder

The specific brain structures or neural mechanisms underlying dysfunction in individuals with Attention-Deficit/Hyperactivity Disorder (ADHD) are not well established, particularly in regard to white matter (WM). Diffusion tensor imaging (DTI) was used to investigate WM in 12 adolescent males diagnosed with ADHD only and 12 typically developing controls (group matched; mean age=15.64 years, SD=1.15). In addition to fractional anisotropy (FA), we also examined axial and radial diffusivity (AD and RD) in an effort to help elucidate conflicting findings suggesting that both lower and higher FA values are characteristic of ADHD. Tract-based spatial statistics and voxel-wide analyses were conducted on the data utilizing a pre-frontal mask to enable focus on fronto-striatal and prefrontal pathways. Adolescents with ADHD had significantly higher FA and AD values in fronto-striatal pathways compared with controls. No differences were observed for RD. These results contribute to the growing literature implicating prefrontal WM variations in neuropsychiatric disorders, and are consistent with findings suggesting a role for fronto-striatal pathways in ADHD pathophysiology.

Possible effect of norepinephrine transporter polymorphisms on methylphenidate-induced changes in neuropsychological function in attention-deficit hyperactivity disorder

Background

Dysregulation of noradrenergic system may play important roles in pathophysiology of attention-deficit/hyperactivity disorder (ADHD). We examined the relationship between polymorphisms in the norepinephrine transporter SLC6A2 gene and attentional performance before and after medication in children with ADHD.

Methods

Fifty-three medication-naïve children with ADHD were genotyped and evaluated using the continuous performance test (CPT). After 8-weeks of methylphenidate treatment, these children were evaluated by CPT again. We compared the baseline CPT measures and the post-treatment changes in the CPT measures based on the G1287A and the A-3081T polymorphisms of SLC6A2.

Results

There was no significant difference in the baseline CPT measures associated with the G1287A or A-3081T polymorphisms. After medication, however, ADHD subjects with the G/G genotype at the G1287A polymorphism showed a greater decrease in the mean omission error scores (p = 0.006) than subjects with the G/A or A/A genotypes, and subjects with the T allele at the A-3081T polymorphism (T/T or A/T) showed a greater decrease in the mean commission error scores (p = 0.003) than those with the A/A genotypes.

Conclusions

Our results provide evidence for the possible role of the G1287A and A-3081T genotypes of SLC6A2 in methylphenidate-induced improvement in attentional performance and support the noradrenergic hypothesis for the pathophysiology of ADHD.

Loss of striatal cannabinoid CB1 receptor function in attention-deficit / hyperactivity disorder mice with point-mutation of the dopamine transporter

Abnormal dopamine (DA) transmission in the striatum plays a pivotal role in attention-deficit/hyperactivity disorder (ADHD). As striatal DA signalling modulates the endocannabinoid system (ECS), the present study was aimed at investigating cannabinoid CB1 receptor (CB1R) function in a model of ADHD obtained by triple point-mutation in the dopamine transporter (DAT) gene in mice, making them insensitive to cocaine [DAT cocaine-insensitive (DAT-CI) mice]. DAT-CI mice had a marked hyperactive phenotype, and neurophysiological recordings revealed that the sensitivity of CB1Rs controlling GABA-mediated synaptic currents [CB1Rs((GABA)) ] in the striatum was completely lost. In contrast, CB1Rs modulating glutamate transmission [CB1Rs((Glu)) ], and GABA(B) receptors were not affected in this model of ADHD. In DAT-CI mice, the blockade of CB1R((GABA)) function was complete even after cocaine or environmental manipulations activating the endogenous DA-dependent reward system, which are known to sensitize these receptors in control animals. Conversely, the hedonic property of sucrose was intact in DAT-CI mice, indicating normal sweet perception in these animals. Our results point to CB1Rs as novel molecular players in ADHD, and suggest that therapeutic strategies aimed at interfering with the ECS might prove effective in this disorder.

Sex, ADHD symptoms, and smoking outcomes: an integrative model

Both females and individuals with Attention-Deficit/Hyperactivity Disorder (ADHD) have been found to be at increased risk for a range of smoking outcomes, and recent empirical findings have suggested that women with ADHD may be particularly vulnerable to nicotine dependence. On a neurobiological level, the dopamine reward processing system may be implicated in the potentially unique interaction of nicotine with sex and with ADHD status. Specifically, nicotine appears to mitigate core ADHD symptoms through interaction with the dopamine reward processing system, and ovarian hormones have been found to interact with nicotine within the dopamine reward processing system to affect neurotransmitter release and functioning. This article synthesizes data from research examining smoking in women and in individuals with ADHD to build an integrative model through which unique risk for cigarette smoking in women with ADHD can be systematically explored. Based upon this model, the following hypotheses are proposed at the intersection of each of the three variables of sex, ADHD, and smoking: (1) individuals with ADHD have altered functioning of the dopamine reward system, which diminishes their ability to efficiently form conditioned associations based on environmental contingencies; these deficits are partially ameliorated by nicotine; (2) nicotine interacts with estrogen and the dopamine reward system to increase the positive and negative reinforcement value of smoking in female smokers; (3) in adult females with ADHD, ovarian hormones interact with the dopamine reward system to exacerbate ADHD-related deficits in the capacity to form conditioned associations; and (4) during different phases of the menstrual cycle, nicotine and ovarian hormones may interact differentially with the dopamine reward processing system to affect the type and value of reinforcement smoking provides for women with ADHD. Understanding the bio-behavioral mechanisms underlying cigarette addiction in specific populations will be critical to developing effectively tailored smoking prevention and cessation programs for these groups. Overall, the goal of this paper is to examine the interaction of sex, smoking, and ADHD status within the context of the dopamine reward processing system not only to elucidate potential mechanisms specific to female smokers with ADHD, but also to stimulate consideration of how the examination of such individual differences can inform our understanding of smoking more broadly.

Nonlinear analysis of actigraphic signals for the assessment of the attention-deficit/hyperactivity disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral disorder in children and adolescents; however, its etiology is still unknown, which hinders the existence of reliable, fast and inexpensive standard diagnostic methods. In this paper, we propose a novel methodology for automatic diagnosis of the combined type of ADHD based on nonlinear signal processing of 24h-long actigraphic registries. Since it relies on actigraphy measurements, it constitutes an inexpensive and non-invasive objective diagnostic method. Our results on real data reach 96.77% sensitivity and 84.38% specificity by means of multidimensional classifiers driven by combined features from different time intervals. Our analysis also reveals that, if features from a single time interval are used, the whole 24-h interval is the only one that yields classification figures with practical diagnostic capabilities. Overall, our figures overcome those obtained by actigraphy-based methods reported and are comparable with others based on more expensive (and not so convenient) adquisition methods.

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.

Laboratory snack food intake, negative mood, and impulsivity in youth with ADHD symptoms and episodes of loss of control eating. Where is the missing link?

To compare laboratory food intake, negative mood and trait impulsivity and their association with attention deficit hyperactivity disorder (ADHD) and loss of control (LOC) eating in youth (middle childhood to early adolescence). Ninety 10-14 year old youths with symptoms of ADHD, symptoms of LOC eating, and control participants took part in a laboratory snack food meal after having rated trait impulsivity. Negative mood was self-reported pre and post snack food meal, while representativeness of eating behavior and liking of the food was assessed post laboratory snack food meal. The ADHD group consumed more snack food than the other groups. Food intake was not influenced by negative mood or trait impulsivity. All groups exhibited a decrease in negative mood from pre to post food intake that was not accounted for by level of hunger or liking of the food. The greater food intake of the ADHD group compared to the other groups may contribute to the development of overweight and therefore be in accordance with the high co-morbidity reported between ADHD and obesity in youth. The influence of impulsivity and negative mood on food intake could not be shown, which corroborates a recent review on the association of negative mood and bingeing in adults but needs further assessment, particularly in the younger age groups.

Neural and behavioral endophenotypes in ADHD

In recent years, descriptive symptom-based approaches of attention deficit hyperactivity disorder (ADHD) have been increasingly replaced by more sophisticated endophenotype-based strategies, better suited to investigate its pathophysiological basis, which is inherently heterogeneous. Measurements derived from neuroimaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) constitute endophenotypes of growing interest, capable of providing unprecedented windows on neurochemical and neuroanatomical components of psychiatric conditions. This chapter reviews the current state of knowledge regarding putative neural and behavioral endophenotypes of ADHD, across the lifespan. To this end, recent evidence drawn from molecular and structural neuroimaging studies are discussed in the light of widely accepted neuropsychological and pharmacological models of ADHD.

The functional connectivity of the human caudate: an application of meta-analytic connectivity modeling with behavioral filtering

Meta-analysis based techniques are emerging as powerful, robust tools for developing models of connectivity in functional neuroimaging. Here, we apply meta-analytic connectivity modeling to the human caudate to 1) develop a model of functional connectivity, 2) determine if meta-analytic methods are sufficiently sensitive to detect behavioral domain specificity within region-specific functional connectivity networks, and 3) compare meta-analytic driven segmentation to structural connectivity parcellation using diffusion tensor imaging. Results demonstrate strong coherence between meta-analytic and data-driven methods. Specifically, we found that behavioral filtering resulted in cognition and emotion related structures and networks primarily localized to the head of the caudate nucleus, while perceptual and action specific regions localized to the body of the caudate, consistent with early models of nonhuman primate histological studies and postmortem studies in humans. Diffusion tensor imaging (DTI) revealed support for meta-analytic connectivity modeling's (MACM) utility in identifying both direct and indirect connectivity. Our results provide further validation of meta-analytic connectivity modeling, while also highlighting an additional potential, namely the extraction of behavioral domain specific functional connectivity.

Increased regional fractional anisotropy in highly screened attention-deficit hyperactivity disorder (ADHD)

Diffusion tensor imaging data were collected at 3.0 Tesla from 16 children with attention-deficit hyperactivity disorder (ADHD) and 16 typically developing controls, ages 9 to 14 years. Fractional anisotropy images were calculated and normalized by linear transformation. Voxel-wise and atlas-based region-of-interest analyses were performed. Using voxel-wise analysis, fractional anisotropy was found to be significantly increased in the attention-deficit hyperactivity disorder group in the right superior frontal gyrus and posterior thalamic radiation, and left dorsal posterior cingulate gyrus, lingual gyrus, and parahippocampal gyrus. No regions showed significantly decreased fractional anisotropy in attention-deficit hyperactivity disorder. Region-of-interest analysis revealed increased fractional anisotropy in the left sagittal stratum, that is, white matter that connects the temporal lobe to distant cortical regions. Only fractional anisotropy in the left sagittal stratum was significantly associated with attention-deficit hyperactivity disorder symptom severity. Several recent studies have reported pathological increases in fractional anisotropy in other conditions, highlighting the relevance of diffusion tensor imaging in identifying atypical white matter structure associated with neurodevelopmental processes.

The attenuation of dysfunctional emotional processing with stimulant medication: an fMRI study of adolescents with ADHD

Functional neuroimaging studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the neural correlates of cognitive control. However, for many youths with ADHD, emotional lability is an important clinical feature of the disorder. We aimed to identify the neural substrates associated with emotional lability that were distinct from impairments in cognitive control and to assess the effects that stimulants have on those substrates. We used functional magnetic resonance imaging (fMRI) to assess neural activity in adolescents with (N=15) and without (N=15) ADHD while they performed cognitive and emotional versions of the Stroop task that engage cognitive control and emotional processing, respectively. The participants with ADHD were scanned both on and off stimulant medication in a counterbalanced fashion. Controlling for differences in cognitive control, we found that during the emotional Stroop task, adolescents with ADHD as compared with controls demonstrated atypical activity in the medial prefrontal cortex (mPFC). Stimulants attenuated activity in the mPFC to levels comparable with controls.