Rozmin Halari

A review of fronto-striatal and fronto-cortical brain abnormalities in children and adults with Attention Deficit Hyperactivity Disorder (ADHD) and new evidence for dysfunction in adults with ADHD during motivation and attention.

Attention Deficit Hyperactivity Disorder (ADHD) has long been associated with abnormalities in frontal brain regions. In this paper we review the current structural and functional imaging evidence for abnormalities in children and adults with ADHD in fronto-striatal, fronto-parieto-temporal, fronto-cerebellar and fronto-limbic regions and networks. While the imaging studies in children with ADHD are more numerous and consistent, an increasing number of studies suggests that these structural and functional abnormalities in fronto-cortical and fronto-subcortical networks persist into adulthood, despite a relative symptomatic improvement in the adult form of the disorder. We furthermore present new data that support the notion of a persistence of neurofunctional deficits in adults with ADHD during attention and motivation functions. We show that a group of medication-naïve young adults with ADHD behaviours who were followed up 20 years from a childhood ADHD diagnosis show dysfunctions in lateral fronto-striato-parietal regions relative to controls during sustained attention, as well as in ventromedial orbitofrontal regions during reward, suggesting dysfunctions in cognitive-attentional as well as motivational neural networks. The lateral fronto-striatal deficit findings, furthermore, were strikingly similar to those we have previously observed in children with ADHD during the same task, reinforcing the notion of persistence of fronto-striatal dysfunctions in adult ADHD. The ventromedial orbitofrontal deficits, however, were associated with comorbid conduct disorder (CD), highlighting the potential confound of comorbid antisocial conditions on paralimbic brain deficits in ADHD. Our review supported by the new data therefore suggest that both adult and childhood ADHD are associated with brain abnormalities in fronto-cortical and fronto-subcortical systems that mediate the control of cognition and motivation. The brain deficits in ADHD therefore appear to be multi-systemic and to persist throughout the lifespan.

Disorder-Specific Dissociation of Orbitofrontal Dysfunction in Boys With Pure Conduct Disorder During Reward and Ventrolateral Prefrontal Dysfunction in Boys With Pure ADHD During Sustained Attention

OBJECTIVE Among children, attention deficit hyperactivity disorder (ADHD) and conduct disorder are often comorbid and overlap clinically. Neuropsychological evidence suggests that children with conduct disorder demonstrate more prominent motivational problems and children with ADHD demonstrate more prominent attention deficits relative to healthy comparison subjects. The purpose of the present study was to investigate disorder-specific abnormalities in the neurobiological correlates of motivation and sustained attention in children and adolescents with pure conduct disorder and children and adolescents with pure ADHD. METHOD Participants were male pediatric patients, ages 9-16 years, with noncomorbid conduct disorder (N=14) and noncomorbid ADHD, combined hyperactive-inattentive subtype (N=18), as well as age- and IQ-matched healthy comparison subjects (N=16). Both patient groups were medication naive. Event-related functional magnetic resonance imaging (fMRI) was used to compare brain activation during a rewarded continuous performance task that measured sustained attention as well as the effects of reward on performance. RESULTS During the sustained attention condition, patients with noncomorbid ADHD showed significantly reduced activation in the bilateral ventrolateral prefrontal cortex and increased activation in the cerebellum relative to patients with noncomorbid conduct disorder and healthy comparison subjects. Patients with noncomorbid conduct disorder showed decreased activation in paralimbic regions of the insula, hippocampus, and anterior cingulate as well as the cerebellum relative to patients with noncomorbid ADHD and healthy comparison subjects. However, during the reward condition, patients with noncomorbid conduct disorder showed disorder-specific underactivation in the right orbitofrontal cortex, while patients with noncomorbid ADHD showed disorder-specific dysfunction in the posterior cingulate gyrus. CONCLUSIONS The findings revealed a process-related dissociation of prefrontal dysfunction in ADHD and conduct disorder patients. Attention-related dysfunction in the ventrolateral prefrontal cortex was seen in ADHD patients, and reward-related dysfunction in the orbitofrontal cortex was seen in conduct disorder patients. These findings, together with the pattern of paralimbic dysfunction demonstrated among children with conduct disorder during sustained attention, support theories of abnormalities in orbitofrontal-paralimbic motivation networks in individuals with conduct disorder and, in contrast, ventrolateral fronto-cerebellar attention network dysfunction in individuals with ADHD.

Impulsiveness as a timing disturbance: neurocognitive abnormalities in attention-deficit hyperactivity disorder during temporal processes and normalization with methylphenidate

We argue that impulsiveness is characterized by compromised timing functions such as premature motor timing, decreased tolerance to delays, poor temporal foresight and steeper temporal discounting. A model illustration for the association between impulsiveness and timing deficits is the impulsiveness disorder of attention-deficit hyperactivity disorder (ADHD). Children with ADHD have deficits in timing processes of several temporal domains and the neural substrates of these compromised timing functions are strikingly similar to the neuropathology of ADHD. We review our published and present novel functional magnetic resonance imaging data to demonstrate that ADHD children show dysfunctions in key timing regions of prefrontal, cingulate, striatal and cerebellar location during temporal processes of several time domains including time discrimination of milliseconds, motor timing to seconds and temporal discounting of longer time intervals. Given that impulsiveness, timing abnormalities and more specifically ADHD have been related to dopamine dysregulation, we tested for and demonstrated a normalization effect of all brain dysfunctions in ADHD children during time discrimination with the dopamine agonist and treatment of choice, methylphenidate. This review together with the new empirical findings demonstrates that neurocognitive dysfunctions in temporal processes are crucial to the impulsiveness disorder of ADHD and provides first evidence for normalization with a dopamine reuptake inhibitor.

The relationship of structural alterations to cognitive deficits in schizophrenia: a voxel-based morphometry study.

BACKGROUND Region of interest studies have identified a number of structure-cognition associations in schizophrenia and revealed alterations in structure-cognition relationship in this population. METHODS We examined the relationship of structural brain alterations, identified using voxel-based morphometry, to cognitive deficits in 45 schizophrenia patients relative to 43 healthy control subjects and tested the hypothesis that structure-cognition relationship is altered in schizophrenia. RESULTS Patients had smaller total brain, gray matter, and white matter volumes. Regional alterations were left-hemisphere specific, including: gray matter reduction of inferior frontal, lingual, and anterior superior temporal gyri; white matter reduction of posterior and occipital lobes; and gray matter increase of the putamen and the precuneus. Smaller whole brain and gray matter volumes were associated with lower premorbid intelligence quotient (IQ) and poorer performance on IQ-dependent cognitive measures in patients and to a similar extent in control subjects. Larger precuneus was associated with better immediate verbal memory in patients, whereas verbal and nonverbal memory were positively associated with inferior frontal gyrus volume in control subjects. Smaller occipital white matter volume was associated with slower information processing speed in patients but not in control subjects. CONCLUSIONS Regional volume alterations are associated with specific cognitive deficits in schizophrenia. Some structure-cognition relationships differentiate this population from healthy control subjects.

Reduced activation and inter-regional functional connectivity of fronto-striatal networks in adults with childhood Attention-Deficit Hyperactivity Disorder (ADHD) and persisting symptoms during tasks of motor inhibition and cognitive switching

Attention-Deficit Hyperactivity Disorder (ADHD) in children has been associated with fronto-striatal functional abnormalities during tasks of inhibitory control. In adults with ADHD, however, hardly any functional magnetic resonance imaging (fMRI) studies have investigated the neurofunctional correlates of the most compromised cognitive functions of motor response inhibition and no study has investigated cognitive flexibility. In this study we used fMRI to compare brain function and task-relevant inter-regional functional connectivity between 11 medication-naïve adults with persistent inattentive/hyperactive behaviours, followed up from childhood when they had been diagnosed with ADHD, and 14 age-matched healthy controls during a Stop and a cognitive Switch tasks. Whole-brain regression MR analyses were conducted within patients to correlate symptoms with brain activation. Despite comparable task performance, adults with childhood ADHD showed reduced activation compared to controls in bilateral inferior prefrontal cortex, caudate and thalamus during both tasks, as well as in left parietal lobe during the Switch task. Within patients, the severity of the behavioural symptoms was negatively correlated with more extensive activation of similar regions in fronto-striatal, parietal and cerebellar brain areas. In the Stop task, patients showed reduced inter-regional functional connectivity between right inferior fronto-frontal, fronto-striatal and fronto-parietal neural networks. The findings demonstrate that adults with childhood ADHD and persisting behavioural symptoms show strikingly similar patterns of fronto-striatal and parietal dysfunction to those observed in childhood ADHD during the same tasks of inhibitory control. This suggests that neuro-functional abnormalities in ADHD patients are likely to continue between childhood and early adulthood.

Dissociated Functional Brain Abnormalities of Inhibition in Boys With Pure Conduct Disorder and in Boys With Pure Attention Deficit Hyperactivity Disorder

OBJECTIVE Inhibitory dysfunction may be a transdiagnostic etiopathophysiology of disruptive behavior disorders. Functional magnetic resonance imaging (fMRI) of inhibitory control has only been investigated in patients with attention deficit hyperactivity disorder (ADHD), including comorbidity with conduct disorder, showing frontal-striatal dysfunction. This study investigates differences and commonalities in functional neural networks mediating inhibitory control between medication-naive adolescents with pure conduct disorder and those with pure ADHD to identify biological markers that distinguish these clinically overlapping disorders. METHOD Event-related fMRI was used to compare brain activation of 13 boys with noncomorbid conduct disorder, 20 with noncomorbid ADHD, and 20 normal boys during an individually adjusted tracking stop task that measures the neural substrates of inhibition and stopping failure. RESULTS During successful inhibition, only patients with ADHD showed reduced activation in the left dorsolateral prefrontal cortex in relation to comparison subjects and patients with conduct disorder. During inhibition failures compared to go responses, both patient groups shared underactivation in the posterior cingulate gyrus in relation to comparison subjects. Patients with conduct disorder showed reduced activation in bilateral temporal-parietal regions compared to the other groups, which did not differ in this measure. CONCLUSIONS Patients with pure ADHD or pure conduct disorder show qualitative differences in their brain abnormality patterns during inhibitory control. Inhibition-mediating prefrontal regions appear to be specifically reduced in ADHD, whereas posterior temporal-parietal, performance monitoring networks are specifically dysfunctional in conduct disorder. The findings provide pioneering evidence that distinct neurobiological abnormalities may be underlying the overlapping behavioral phenotype of the two disruptive disorders.

Methylphenidate Normalizes Fronto-Striatal Underactivation During Interference Inhibition in Medication-Naïve Boys with Attention-Deficit Hyperactivity Disorder

Youth with attention deficit hyperactivity disorder (ADHD) have deficits in interference inhibition, which can be improved with the indirect catecholamine agonist methylphenidate (MPH). Functional magnetic resonance imaging was used to investigate the effects of a single dose of MPH on brain activation during interference inhibition in medication-naïve ADHD boys. Medication-naïve boys with ADHD were scanned twice, in a randomized, double-blind design, under either a single clinical dose of MPH or placebo, while performing a Simon task that measures interference inhibition and controls for the oddball effect of low-frequency appearance of incongruent trials. Brain activation was compared within patients under either drug condition. To test for potential normalization effects of MPH, brain activation in ADHD patients under either drug condition was compared with that of healthy age-matched comparison boys. During incongruent trials compared with congruent–oddball trials, boys with ADHD under placebo relative to controls showed reduced brain activation in typical areas of interference inhibition, including right inferior prefrontal cortex, left striatum and thalamus, mid-cingulate/supplementary motor area, and left superior temporal lobe. MPH relative to placebo upregulated brain activation in right inferior prefrontal and premotor cortices. Under the MPH condition, patients relative to controls no longer showed the reduced activation in right inferior prefrontal and striato-thalamic regions. Effect size comparison, furthermore, showed that these normalization effects were significant. MPH significantly normalized the fronto-striatal underfunctioning in ADHD patients relative to controls during interference inhibition, but did not affect medial frontal or temporal dysfunction. MPH therefore appears to have a region-specific upregulation effect on fronto-striatal activation.

Disorder-specific inferior prefrontal hypofunction in boys with pure attention-deficit/hyperactivity disorder compared to boys with pure conduct disorder during cognitive flexibility

Background. Problems with cognitive flexibility have been observed in patients with attention deficit hyperactivity disorder (ADHD) and in patients with conduct disorder (CD), characterized by the violation of societal rules and the rights of others. Functional magnetic resonance imaging (fMRI) of cognitive switching, however, has only been investigated in patients with ADHD, including comorbidity with CD, finding frontostriatal and temporoparietal underactivation. This study investigates disorder‐specific functional abnormalities during cognitive flexibility between medication‐naïve children and adolescents with noncomorbid CD and those with noncomorbid ADHD compared to healthy controls. Methods. Event‐related fMRI was used to compare brain activation of 14 boys with noncomorbid, childhood‐onset CD, 14 boys with noncomorbid ADHD, and 20 healthy comparison boys during a visual–spatial Switch task. Results. Behaviorally, children with ADHD compared to children with CD had significantly slower reaction times to switch compared to repeat trials. The fMRI comparison showed that the patients with ADHD compared to both controls and patients with CD showed underactivation in right and left inferior prefrontal cortex. No disorder‐specific brain underactivation was observed in patients with CD. Only when compared with controls alone, the disruptive behavior group showed reduced activation in bilateral temporoparietal and occipital brain regions. Conclusions. The findings extend previous evidence for disorder‐specific underactivation in patients with ADHD compared to patients with CD in inferior prefrontal cortex during tasks of inhibitory control to the domain of cognitive flexibility. Inferior prefrontal underactivation thus appears to be a disorder‐specific neurofunctional biomarker for ADHD when compared with patients with CD. Hum Brain Mapp, 2010.

Methylphenidate Normalizes Frontocingulate Underactivation During Error Processing in Attention-Deficit/Hyperactivity Disorder

Background Children with attention-deficit/hyperactivity disorder (ADHD) have deficits in performance monitoring often improved with the indirect catecholamine agonist methylphenidate (MPH). We used functional magnetic resonance imaging to investigate the effects of single-dose MPH on activation of error processing brain areas in medication-naive boys with ADHD during a stop task that elicits 50% error rates. Methods Twelve medication-naive boys with ADHD were scanned twice, under either a single clinical dose of MPH or placebo, in a randomized, double-blind design while they performed an individually adjusted tracking stop task, designed to elicit 50% failures. Brain activation was compared within patients under either drug condition. To test for potential normalization effects of MPH, brain activation in ADHD patients under either drug condition was compared with that of 13 healthy age-matched boys. Results During failed inhibition, boys with ADHD under placebo relative to control subjects showed reduced brain activation in performance monitoring areas of dorsomedial and left ventrolateral prefrontal cortices, thalamus, cingulate, and parietal regions. MPH, relative to placebo, upregulated activation in these brain regions within patients and normalized all activation differences between patients and control subjects. During successful inhibition, MPH normalized reduced activation observed in patients under placebo compared with control subjects in parietotemporal and cerebellar regions. Conclusions MPH normalized brain dysfunction in medication-naive ADHD boys relative to control subjects in typical brain areas of performance monitoring, comprising left ventrolateral and dorsomedial frontal and parietal cortices. This could underlie the amelioration of MPH of attention and academic performance in ADHD.

Effects of age and sex on developmental neural networks of visual-spatial attention allocation

Compared to our understanding of the functional maturation of brain networks underlying complex cognitive abilities, hardly anything is known of the neurofunctional development of simpler cognitive abilities such as visuo-spatial attention allocation. Furthermore, nothing is known on the effect of gender on the functional development of attention allocation. This study employed event related functional magnetic resonance imaging to investigate effects of age, sex, and sex by age interactions on the brain activation of 63 males and females, between 13 to 38years, during a visual-spatial oddball task. Behaviourally, with increasing age, speed was traded for accuracy, indicative of a less impulsive performance style in older subjects. Increasing age was associated with progressively increased activation in typical areas of selective attention of lateral fronto-striatal and temporo-parietal brain regions. Sex difference analysis showed enhanced activation in right-hemispheric inferior frontal and superior temporal regions in females, and in left-hemispheric inferior temporo-parietal regions in males. Importantly, the age by sex interaction findings showed that these sex-dimorphic patterns of brain activation may be the result of underlying sex differences in the functional maturation of these brain regions, as females had sex-specific progressive age-correlations in the same right inferior fronto-striato-temporal areas, while male-specific age-correlations were in left medial temporal and parietal areas. The findings demonstrate progressive functional maturation of fronto-striato-parieto-temporal networks of the relatively simple function of attention allocation between early adolescence and mid-adulthood. They furthermore show that sex-dimorphic patterns of enhanced reliance on right inferior frontal, striatal and superior temporal regions in females and of left temporo-parietal regions in males during attention allocation may be the result of underlying sex differences in the functional maturation of these brain regions.