Neural correlates of switching set as measured in fast, event-related functional magnetic resonance imaging

Cognitive inflexibility in obsessive-compulsive disorder and major depression is associated with distinct neural correlates

Obsessive-compulsive disorder (OCD) and major depressive disorder (MDD) are frequently co-morbid, and dysfunctional frontal-striatal circuits have been implicated in both disorders. Neurobiological distinctions between OCD and MDD are insufficiently clear, and comparative neuroimaging studies are extremely scarce. OCD and MDD may be characterized by cognitive rigidity at the phenotype level, and frontal-striatal brain circuits constitute the neural substrate of intact cognitive flexibility. In the present study, 18 non-medicated MDD-free patients with OCD, 19 non-medicated OCD-free patients with MDD, and 29 matched healthy controls underwent functional magnetic resonance imaging during performance of a self-paced letter/digit task switching paradigm. Results showed that both patient groups responded slower relative to controls during repeat events, but only in OCD patients slowing was associated with decreased error rates. During switching, patients with OCD showed increased activation of the putamen, anterior cingulate and insula, whereas MDD patients recruited inferior parietal cortex and precuneus to a lesser extent. Patients with OCD and MDD commonly failed to reveal anterior prefrontal cortex activation during switching. This study shows subtle behavioral abnormalities on a measure of cognitive flexibility in MDD and OCD, associated with differential frontal-striatal brain dysfunction in both disorders. These findings may add to the development of biological markers that more precisely characterize frequently co-morbid neuropsychiatric disorders such as OCD and MDD.

fMRI task parameters influence hemodynamic activity in regions implicated in mental set switching

Mental set switching is a complex executive function that is required when the focus of attention must be altered in order to adapt to a frequently-changing environment. While there is generally acceptance that switching is subserved by a fronto-parietal network, there is a considerable lack of consistency across studies as to other brain regions involved in executing mental set switches. This functional magnetic resonance imaging study sought to determine whether paradigmatic design aspects such as stimulus complexity, motor response complexity, and stimulus ordering could account for the differences in reporting of brain regions associated with mental set switching across previous studies. Several brain regions, including the striatum and anterior cingulate, previously associated with mental set switching were found to be related more to resolving intra-stimulus interference conferred by increased stimulus complexity and increased motor response complexity than to executing the mental set switch. In considering stimulus ordering, defined as the number of non-switch trials preceding a switch trial, brain activity was not observed in the fronto-parietal regions typically associated with switching but rather in regions in the anterior prefrontal cortex, sensorimotor cortex, and secondary visual cortices. Our results indicate that these important paradigm design aspects that are theoretically unrelated to set switching per se should be balanced and controlled for in future experiments, so as not to obscure clear identification of brain regions truly engaged in mental set switching.

Acute tryptophan depletion promotes an anterior-to-posterior fMRI activation shift during task switching in older adults

Studies have long reported that aging is associated with declines in several functions modulated by the prefrontal cortex, including executive functions like working memory, set shifting, and inhibitory control. The neurochemical basis to this is poorly understood, but may include the serotonergic system. We investigated the modulatory effect of serotonin using acute tryptophan depletion (ATD) during a cognitive switching task involving visual-spatial set shifting modified for a functional MRI environment. Ten healthy women over 55 years were tested on two separate occasions in this within-group double-blind sham-controlled crossover study to compare behavioral and physiological brain functioning following ATD and following a ("placebo") sham depletion condition. ATD did not significantly affect task performance. It did modulate brain functional recruitment. During sham depletion women significantly activated the expected task-relevant brain regions associated with the Switch task including prefrontal and anterior cingulate cortices. In contrast, following ATD participants activated posterior regions of brain more during switch than repeat trials. In addition to the main effects of depletion condition, a comparison of the ATD relative to the sham condition confirmed this anterior-to-posterior shift in activation. The posterior (increased) activation clusters significantly and negatively correlated with the reduced prefrontal activation clusters suggesting a compensation mechanism for reduced prefrontal activation during ATD. Thus, serotonin modulates an anterior-to-posterior shift of activation during cognitive switching in older adults. Neural adaptation to serotonin challenge during cognitive control may prove useful in determining cognitive vulnerability in older adults with a predisposition for serontonergic down-regulation (e.g., in vascular or late life depression).

Voxel and surface-based topography of memory and executive deficits in mild cognitive impairment and Alzheimer's disease

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) are associated with a progressive loss of cognitive abilities. In the present report, we assessed the relationship of memory and executive function with brain structure in a sample of 810 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants, including 188 AD, 396 MCI, and 226 healthy older adults (HC). Composite scores of memory (ADNI-Mem) and executive function (ADNI-Exec) were generated by applying modern psychometric theory to item-level data from ADNI's neuropsychological battery. We performed voxel-based morphometry (VBM) and surface-based association (SurfStat) analyses to evaluate relationships of ADNI-Mem and ADNI-Exec with grey matter (GM) density and cortical thickness across the whole brain in the combined sample and within diagnostic groups. We observed strong associations between ADNI-Mem and medial and lateral temporal lobe atrophy. Lower ADNI-Exec scores were associated with advanced GM and cortical atrophy across broadly distributed regions, most impressively in the bilateral parietal and temporal lobes. We also evaluated ADNI-Exec adjusted for ADNI-Mem, and found associations with GM density and cortical thickness primarily in the bilateral parietal, temporal, and frontal lobes. Within-group analyses suggest these associations are strongest in patients with MCI and AD. The present study provides insight into the spatially unbiased associations between brain atrophy and memory and executive function, and underscores the importance of structural brain changes in early cognitive decline.

Distinct prefrontal cortical regions negatively regulate evoked activity in nucleus accumbens subregions

Deficits in prefrontal cortical activity are consistent observations in a number of psychiatric diseases with two major regions consistently implicated being the medial prefrontal cortex (mPFC) and orbitofrontal cortex (OFC), regions that carry out independent, but complementary forms of cognitive processing in changing environmental conditions. Information from the prefrontal cortex is integrated in the nucleus accumbens (NAc) to guide goal-directed behaviour. Anatomical studies have demonstrated that distinct prefrontal cortical regions provide an overlapping but distinct innervation of NAc subregions; however, how information from these distinct regions regulates NAc output has not been conclusively demonstrated. Here we demonstrate that, while neurons receiving convergent glutamatergic inputs from the mPFC and OFC have a synergistic effect on single-spike firing, medium spiny neurons that receive a monosynaptic input from only one region are actually inhibited by activation of the complementary region. Therefore, the mPFC and OFC negatively regulate evoked activity within the lateral and medial regions of the NAc, respectively, and exist in a state of balance with respect to their influence on information processing within ventral striatal circuits.

Time perception in children: a neurodevelopmental approach

In this review, we discuss behavioral studies on time perception in healthy children that suggest the existence of a primitive "sense" of time in infants as well as research that has revealed the changes in time judgments that occur throughout childhood. Moreover, a distinction is made between implicit and explicit time judgments in order to take account of the different types of temporal judgments that emerge across ages. On the basis of both the neurobiological model of the internal clock proposed by Matell and Meck (2000), and of results of imaging studies in human adults, we then try to identify which of the neural structures underlying this primitive sense of time mature faster and which mature more slowly in order to explain the age-related variance in time judgments. To this end, we also present the small number of timing studies conducted among typically and non-typically developing children that have used functional magnetic resonance imaging (fMRI) as well as those that have assessed the cognitive capacities of such children on the basis of various neuropsychological tests.

Meta-analytic evidence for a superordinate cognitive control network subserving diverse executive functions

Classic cognitive theory conceptualizes executive functions as involving multiple specific domains, including initiation, inhibition, working memory, flexibility, planning, and vigilance. Lesion and neuroimaging experiments over the past two decades have suggested that both common and unique processes contribute to executive functions during higher cognition. It has been suggested that a superordinate fronto-cingulo-parietal network supporting cognitive control may also underlie a range of distinct executive functions. To test this hypothesis in the largest sample to date, we used quantitative meta-analytic methods to analyze 193 functional neuroimaging studies of 2,832 healthy individuals, ages 18-60, in which performance on executive function measures was contrasted with an active control condition. A common pattern of activation was observed in the prefrontal, dorsal anterior cingulate, and parietal cortices across executive function domains, supporting the idea that executive functions are supported by a superordinate cognitive control network. However, domain-specific analyses showed some variation in the recruitment of anterior prefrontal cortex, anterior and midcingulate regions, and unique subcortical regions such as the basal ganglia and cerebellum. These results are consistent with the existence of a superordinate cognitive control network in the brain, involving dorsolateral prefrontal, anterior cingulate, and parietal cortices, that supports a broad range of executive functions.

The what and how components of cognitive control

In daily life, people show remarkable flexibility in adapting to novel circumstances. Although there is general agreement on which brain areas are involved in cognitive flexibility, little is known about the precise representational content of these cognitive control areas in different sub-processes involved in cognitive control. In the present study, we used an adaptation approach to differentiate the brain areas selectively representing the what and the how components of cognitive control in task preparation. When selectively repeating the task goal (the what component) without repeating the stimulus-response (S-R) mapping (the how component), task goal preferential adaptation was found in the left lateral prefrontal cortex, the medial prefrontal cortex and the left posterior parietal cortex. Within these areas, task goal specific adaptation was found in the left inferior frontal gyrus, the posterior part of the left inferior parietal lobule and the precuneus. Selectively repeating the S-R mapping, by contrast, resulted in S-R mapping preferential adaptation in the bilateral pre-central gyrus extending bilaterally to the intra-parietal lobule, indicating representation of the how component in these areas. Adaptation general to both task goal and S-R mapping was only found in Broca's area extending to the inferior frontal junction, suggesting that the what and the how components of cognitive control are similarly represented in this part of the brain.

Anterior cingulate cortex activation is related to learning potential on the WCST in schizophrenia patients

The remediation of executive function in patients with schizophrenia is important in rehabilitation because these skills affect the patient's capacity to function in the community. There is evidence that instructional techniques can improve deficits in the Wisconsin Card Sorting Test (WCST) in some schizophrenia patients. We used a standard test/training phase/standard test format of the WCST to classify 36 schizophrenia patients as high-achievers, learners or non-retainers. All healthy controls performed as high-achievers. An event-related fMRI design assessed neural activation patterns during post-training WCST performance. Patients showed a linear trend between set-shifting related activation in the anterior cingulate cortex and learning potential, i.e. increased activation in high-achievers, a trend for increased activation in learners, and no activation in non-retainers compared to controls. In addition, activation in the temporoparietal cortex was highest in patients classified as learners, whereas in non-retainers activation was increased in the inferior frontal gyrus compared to controls and high-achieving patients. These results emphasize the relevance of the ACC's neural integrity in learning set-shifting strategies for patients with schizophrenia. Also, our results support the hypothesis that compensatory neural activation in patients with schizophrenia helps them to catch up with healthy controls on cognitive tasks.

The many faces of preparatory control in task switching: reviewing a decade of fMRI research

A large body of behavioural research has used the cued task-switching paradigm to characterize the nature of trial-by-trial preparatory adjustments that enable fluent task implementation when demands on cognitive flexibility are high. This work reviews the growing number of fMRI studies on the same topic, mostly focusing on the central hypothesis that preparatory adjustments should be indicated by enhanced prefrontal and parietal BOLD activation in task switch when compared with task repeat trials under conditions that enable advance task preparation. The evaluation of this straight-forward hypothesis reveals surprisingly heterogeneous results regarding both the precise localization and the very existence of switch-related preparatory activation. Explanations for these inconsistencies are considered on two levels. First, we discuss methodological issues regarding (i) the possible impact of different fMRI-specific experimental design modifications and (ii) statistical uncertainty in the context of massively multivariate imaging data. Second, we discuss explanations related to the multidimensional nature of task preparation itself. Specifically, the precise localization and the size of switch-related preparatory activation might depend on the differential interplay of hierarchical control via abstract task goals and attentional versus action-directed preparatory processes. We argue that different preparatory modes can be adopted relying either on advance goal activation alone or on the advance resolution of competition within action sets or attentional sets. Importantly, while either mode can result in a reduction of behavioral switch cost, only the latter two are supposed to be associated with enhanced switch versus repeat BOLD activation in prepared trial conditions.

Task-specific effects of tDCS-induced cortical excitability changes on cognitive and motor sequence set shifting performance

In this study, we tested the effects of transcranial Direct Current Stimulation (tDCS) on two set shifting tasks. Set shifting ability is defined as the capacity to switch between mental sets or actions and requires the activation of a distributed neural network. Thirty healthy subjects (fifteen per site) received anodal, cathodal and sham stimulation of the dorsolateral prefrontal cortex (DLPFC) or the primary motor cortex (M1). We measured set shifting in both cognitive and motor tasks. The results show that both anodal and cathodal single session tDCS can modulate cognitive and motor tasks. However, an interaction was found between task and type of stimulation as anodal tDCS of DLPFC and M1 was found to increase performance in the cognitive task, while cathodal tDCS of DLPFC and M1 had the opposite effect on the motor task. Additionally, tDCS effects seem to be most evident on the speed of changing sets, rather than on reducing the number of errors or increasing the efficacy of irrelevant set filtering.

A developmental neuroimaging investigation of the change paradigm

This neuroimaging study examines the development of cognitive flexibility using the Change task in a sample of youths and adults. The Change task requires subjects to inhibit a prepotent response and substitute an alternative response, and the task incorporates an algorithm that adjusts task difficulty in response to subject performance. Data from both groups combined show a network of prefrontal and parietal areas that are active during the task. For adults vs. youths, a distributed network was more active for successful change trials versus go, baseline, or unsuccessful change trials. This network included areas involved in rule representation, retrieval (lateral PFC), and switching (medial PFC and parietal regions). These results are consistent with data from previous task-switching experiments and inform developmental understandings of cognitive flexibility.

"Cool" inferior frontostriatal dysfunction in attention-deficit/hyperactivity disorder versus "hot" ventromedial orbitofrontal-limbic dysfunction in conduct disorder: a review

Attention-deficit/hyperactivity disorder (ADHD) and conduct disorder overlap behaviorally, clinically, and cognitively. An important question of potential future clinical relevance is whether these two overlapping disorders are mediated by similar or distinct underlying brain substrates. This article reviews the modern neuroimaging literature on brain structure, function, and connectivity in both disorders, shaping out commonalities and differences. Findings show that ADHD is characterized predominantly by abnormalities in inferior frontal, striatal, parietotemporal, and cerebellar regions and networks that mediate "cool"-cognitive, i.e., inhibitory, attention and timing functions associated with the disorder. Conduct disorder, by contrast, has consistently been associated with abnormalities of the "hot" paralimbic system that regulates motivation and affect, comprising lateral orbital and ventromedial prefrontal cortices, superior temporal lobes, and underlying limbic structures, most prominently the amygdala. Direct comparisons in functional imaging show that these associations of cool inferior fronto-striato-cerebellar dysfunction in ADHD and of hot orbitofrontal-paralimbic dysfunction in conduct disorder are disorder-specific. There is, hence, evidence for dissociated underlying pathophysiologies for these two disorders that may have implications for future anatomy-based differential diagnosis and prevention and intervention.

Challenging a decade of brain research on task switching: brain activation in the task-switching paradigm reflects adaptation rather than reconfiguration of task sets

In daily life, we permanently need to adapt our behavior to new task situations, requiring cognitive control. Such adaptive processes are commonly investigated with the task-switching paradigm. Many fMRI studies have interpreted stronger activation for switch than repeat trials in fronto-parietal brain areas as reflecting an active reconfiguration process in switch trials, tuning the cognitive system for proper task execution. From the single cell literature, however, one could deduce the alternative interpretation that switch-specific activity reflects reduced brain activity in repeat trials due to adaptation. These alternative explanations cannot be distinguished by simply comparing brain activity in switch and repeat trials. Therefore, we used a parametric approach to examine which interpretation is more powerful to account for the data. In all areas of the fronto-parietal network, adaptation explained the data better than reconfiguration. Therefore, our results call the classical reconfiguration interpretation into question and provide first evidence for adaptation of abstract task representations.

Emotional processing and executive functions in major depressive disorder: dorsal prefrontal activity correlates with performance in the intra-extra dimensional set shift

Heinzel A, Northoff G, Boeker H, Boesiger P, Grimm S. Emotional processing and executive functions in major depressive disorder: dorsal prefrontal activity correlates with performance in the intra-extra dimensional set shift.

OBJECTIVE

Major depressive disorder (MDD) is characterised by predominately negatively valenced emotional symptoms that are often accompanied by cognitive impairments. We posited that cognitive impairments in MDD are related to altered emotional processing in prefrontal cortex.

METHODS

We compared 20 medication-free patients with MDD and 29 matched healthy controls. Both groups performed an emotional task during functional magnetic resonance imaging (fMRI). Furthermore, they completed the intra-extra dimensional set shift (IED) test probing for cognitive impairments. Then we correlated the results of the IED with the changes in fMRI BOLD signal in MDD patients and healthy subjects.

RESULTS

The subcategory of the IED applying extradimensional shift (EDS) showed a divergent performance of the MDD group committing significantly more errors than the control group. Correlating the EDS errors with fMRI signal changes, the healthy subjects showed a positive correlation with the right ventrolateral prefrontal cortex and the right orbitofrontal cortex. MDD subjects, in contrast, showed a positive correlation in right dorsolateral prefrontal cortex (DLPFC) and a negative correlation in the left dorsomedial prefrontal cortex (DMPFC).

CONCLUSION

We hypothesise that the differential correlation in healthy controls and MDD patients may reflect the use of different strategies in their performance. The impaired executive functions, as reflected by altered processing in right DLPFC and left DMPFC, may implicitly influence emotional processing in patients suffering from MDD.

Neural correlates of set-shifting: decomposing executive functions in schizophrenia

BACKGROUND

Although there is considerable evidence that patients with schizophrenia have impaired executive functions, the neural mechanisms underlying these deficits are unclear. Generation and selection is one of the basic mechanisms of executive functioning. We investigated the neural correlates of this mechanism by means of functional magnetic resonance imaging (fMRI) in patients with schizophrenia and healthy controls.

METHODS

We used the Wisconsin Card Sorting Test (WCST) in an event-related fMRI study to analyze neural activation patterns during the distinct components of the WCST in 36 patients with schizophrenia and 28 controls. We focused our analyses on the process of set-shifting. After participants received negative feedback, they had to generate and decide on a new sorting rule.

RESULTS

A widespread activation pattern encompassing the inferior and middle frontal gyrus, parietal, temporal and occipital cortices, anterior cingulate cortex (ACC), supplementary motor area, insula, caudate, thalamus and brainstem was observed in patients with schizophrenia after negative versus positive feedback, whereas in healthy controls, significant activation clusters were more confined to the cortical areas. Significantly increased activation in the rostral ACC after negative feedback and in the dorsal ACC during matching after negative feedback were observed in schizophrenia patients compared with controls. Controls showed activation in the bilateral dorsolateral prefrontal cortex (Brodmann area 46), whereas schizophrenia patients showed activation in the right dorsolateral prefrontal cortex only.

LIMITATIONS

All patients were taking neuroleptic medication, which has an impact on cognitive function as well as on dopaminergic and serotonergic prefrontal metabolism.

CONCLUSION

Our data suggest that, in patients with schizophrenia, set-shifting is associated with increased activation in the rostral and dorsal ACC, reflecting higher emotional and cognitive demands, respectively.

Neurocognitive performance in children aged 9-12 years who present putative antecedents of schizophrenia

BACKGROUND

We previously developed a novel method of identifying children aged 9-12 years who may be at elevated risk of developing schizophrenia and the spectrum disorders because they present a triad of putative antecedents of schizophrenia (ASz). The present study aimed to determine whether ASz children also present neurocognitive deficits that are commonly observed in patients with schizophrenia.

METHODS

Twenty-eight ASz children and 28 typically-developing (TD) children without the antecedents of schizophrenia completed a battery of neurocognitive tests assessing seven domains of function: General intelligence, scholastic achievement, verbal memory, visual memory, working memory, executive function (EF)-verbal fluency, and EF-inhibition.

RESULTS

Relative to TD children, the ASz group showed poorer performance on all neurocognitive tests (mean Cohen's d effect size=0.52). In linear regression analyses, group status (ASz vs. TD) significantly predicted scores on the general intelligence, verbal memory, working memory, and EF-inhibition domains (p<0.05). The severity of problems on each of the individual antecedents comprising the antecedent triad did not relate strongly to performance on the neurocognitive domains.

CONCLUSIONS

Children aged 9-12 years who present multiple antecedents of schizophrenia display poorer neurocognition than healthy peers on several domains showing pronounced deficits in schizophrenia, first-episode psychosis, and youth with prodromal symptoms. Longitudinal follow-up is necessary to determine the extent to which poorer neurocognitive performance is specific to those who develop schizophrenia.

Gray matter correlates of set-shifting among neurodegenerative disease, mild cognitive impairment, and healthy older adults

There is increasing recognition that set-shifting, a form of cognitive control, is mediated by different neural structures. However, these regions have not yet been carefully identified as many studies do not account for the influence of component processes (e.g., motor speed). We investigated gray matter correlates of set-shifting while controlling for component processes. Using the Design Fluency (DF), Trail Making Test (TMT), and Color Word Interference (CWI) subtests from the Delis-Kaplan Executive Function System (D-KEFS), we investigated the correlation between set-shifting performance and gray matter volume in 160 subjects with neurodegenerative disease, mild cognitive impairment, and healthy older adults using voxel-based morphometry. All three set-shifting tasks correlated with multiple, widespread gray matter regions. After controlling for the component processes, set-shifting performance correlated with focal regions in prefrontal and posterior parietal cortices. We also identified bilateral prefrontal cortex and the right posterior parietal lobe as common sites for set-shifting across the three tasks. There was a high degree of multicollinearity between the set-shifting conditions and the component processes of TMT and CWI, suggesting DF may better isolate set-shifting regions. Overall, these findings highlight the neuroanatomical correlates of set-shifting and the importance of controlling for component processes when investigating complex cognitive tasks.

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.

Structural and functional brain imaging in adult attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a childhood disorder that persists into adulthood. Nevertheless, there are far fewer imaging studies in adult compared with childhood ADHD. Here we review the imaging literature on brain structure, function and structural and functional connectivity in adult ADHD, as well as the effects of psychostimulants on brain dysfunctions. Importantly, we discuss similarities and differences between these deficit findings and those in childhood ADHD to address the key question of continuity of brain abnormalities into adulthood. Findings show strikingly similar but more inconsistent abnormalities in adult ADHD in key childhood ADHD deficit areas of frontostriatal, temporoparietal and cerebellar regions, presumably due to highly prevalent confounding factors in adult ADHD of elevated rates of comorbidity and medication history.

Is the behavior rating inventory of executive function more strongly associated with measures of impairment or executive function?

The Behavior Rating Inventory of Executive Function (BRIEF) is commonly used in the assessment of children and adolescents presenting with a wide range of concerns. It is unclear, however, whether the questionnaire is more closely related to general measures of behavioral disruption and impairment or to specific measures of executive function. In the present study, associations between the Behavioral Regulation Index and Metacognition Index of the BRIEF and cognitive, behavioral, and academic measures were examined in a sample of clinic-referred youth (n = 60) and healthy youth (n = 37) 6-15 years of age. Measures included ratings of inattentive and hyperactive-impulsive symptoms in youth, ratings of how well youth functioned in their everyday environments, youth's scores on measures of reading and math, and youth's scores on measures of inhibition, performance monitoring, and working memory. Although both BRIEF indices were strongly related to parent and teacher ratings of behavioral disruption and impairment, neither was associated with youth's scores on the performance-based tasks of executive function. These findings support the use of the BRIEF as a clinical tool for assessing a broad range of concerns, but raise questions about the relation of the BRIEF to performance-based tasks that are commonly used to assess executive function.

Executive functions and memory abilities in children with 22q11.2 deletion syndrome

OBJECTIVE

Velo-cardio-facial syndrome or 22q11.2 deletion syndrome (22q11DS) is the most common known microdeletion syndrome. One of the genes in the deleted region is the catechol-O-methyltransferase (COMT) gene, which is thought to have significant effects on cognition through its influence on dopamine metabolism. The aim of the present study was to better characterize the cognitive phenotype in a large cohort children with 22q11DS compared with sibling controls and to investigate if the cognitive deficits in 22q11DS were modulated by COMT expression.

METHOD

The memory, executive function and attentional abilities of children with 22q11DS (n = 50) compared to sibling controls (n = 31), were measured. Also, within children with 22q11DS, a preliminary exploration was carried out of the relationship between cognitive ability and COMT genotype.

RESULTS

Overall, the 22q11DS group had significantly reduced scores on tests of memory (especially in visual memory) and executive function (particularly in planning, working memory, and motor organization) compared with sibling controls. No association, however, was identified between COMT genotype and cognitive function.

CONCLUSIONS

Although 22q11DS children have specific cognitive deficits, differences in COMT do not account for these findings.

Disorder-specific dysfunction in right inferior prefrontal cortex during two inhibition tasks in boys with attention-deficit hyperactivity disorder compared to boys with obsessive-compulsive disorder

BACKGROUND

Inhibitory dysfunction is a key behavioral and cognitive phenotype of attention-deficit hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD). Both disorders show neuropsychological deficits and fronto-striatal dysfunction during tasks of motor response inhibition and cognitive flexibility. This study investigates differences and commonalities in functional neural networks mediating inhibitory control between adolescents with ADHD and those with OCD to identify disorder-specific neurofunctional markers that distinguish these two inhibitory disorders.

METHODS

Event-related fMRI was used to compare brain activation between 20 healthy boys, 18 (Stop task) or 12 boys (Switch task) with ADHD, and 10 boys with OCD during a tracking Stop task that measures inhibition and stopping failure and during a visual-spatial switching task measuring cognitive flexibility.

RESULTS

Both patient groups shared brain dysfunction compared to healthy controls in right orbitofrontal (successful inhibition) and left dorsolateral prefrontal cortices (failed inhibition). Right inferior prefrontal dysfunction, however, was disorder-specific to ADHD during both tasks. Left inferior prefrontal dysfunction during the Switch task was significant in children with ADHD relative to controls, but only reached a trend in patients with OCD. Patients with ADHD furthermore showed disorder-specific dysfunction in left basal ganglia and cingulate gyrus during the Switch task.

CONCLUSIONS

Patients with ADHD compared to those with OCD have both common and distinct dysfunctions during inhibitory control. The most consistently reported functional abnormality in children with ADHD in right inferior prefrontal cortex during inhibitory control appears to be disorder-specific when compared to patients with OCD and may be a specific neurofunctional biomarker of ADHD.

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.

A functional magnetic resonance imaging study of inhibitory control in obsessive-compulsive disorder

People with obsessive-compulsive disorder (OCD) have abnormalities in cognitive and motor inhibition, and it has been proposed that these are related to dysfunction of fronto-striatal circuits. However, nobody has investigated neuro-functional abnormalities during a range of inhibition tasks in adults with OCD. The aims of the study were to compare brain activation of people with OCD and controls during three tasks of inhibitory control. Ten unmedicated adults with OCD and 11 healthy controls performed three different tasks of motor and cognitive inhibitory control during event-related functional magnetic resonance imaging: a Go/No-go task (motor inhibition), a motor Stroop task (interference inhibition) and a Switch task (cognitive flexibility). People with OCD displayed significantly different patterns of brain activation compared to controls during all three tasks. During the Go/No-go and Switch experiments, people with OCD had underactivation in task-relevant orbitofrontal/dorsolateral prefrontal, striatal and thalamic regions. During the motor Stroop and Switch tasks, people with OCD also displayed underactivation in temporo-parietal areas. In the Go/No-go and motor Stroop tasks the OCD group showed increased activation compared to controls in cerebellum and predominantly posterior brain regions. OCD is associated with task-relevant fronto-striatal dysfunction during motor inhibition and cognitive switching. In addition, parieto-temporal dysfunction was observed during tasks with a higher attentional load.

Neuropsychological aspects of Tourette syndrome: a review

Tourette syndrome (TS) is assumed to result from frontostriatal dysfunction, which would be expected to result in impairments in neuropsychological functions. This possibility has been explored in a number of studies that have assessed the performance of patients with TS within major cognitive domains and on tests involving executive functioning. We aim to summarize the main findings of these studies while evaluating the influence of task limitations and potentially critical confounding factors such as the presence of comorbidity. Although there is clearly a need for improved study design, we tentatively suggest that there is considerable evidence for cognitive impairment in a subgroup of patients, and that some difficulties seem to be intrinsic to TS. These impairments may reflect dysfunction of the anterior cingulate network within the frontostriatal pathway.

Executive dysfunction and periventricular diffusion tensor changes in amnesic mild cognitive impairment and early Alzheimer's disease

Our aim in this study was to explore the neural substrates of executive function in frontal and nonfrontal white matter using diffusion tensor imaging (DTI). We studied the relationship between executive dysfunction and DTI measurements on 13 subjects with amnesic mild cognitive impairment (aMCI), 11 subjects with early Alzheimer's disease (AD), and 16 control subjects. All participants underwent an examination of their intelligence, memory, and executive function and were subjected to DTI. Both aMCI and early AD subjects showed executive function impairment with differential performance in frontal-related behaviors. Both aMCI and early AD subjects showed increased mean diffusivity in the genu of the corpus callosum and left frontal periventricular white matter (PVWM), whereas subjects with early AD showed an additional decrease in the fractional anisotropy of bilateral frontal PVWM and in the genu of the corpus callosum. The frontal PVWM was associated with performance on the Verbal Fluency Test, the Wisconsin Card Sorting Test (WCST), and Part B of the Trail Making Test. The parietal PVWM was associated with perseverative errors on the WCST and Part A of the Trail Making Test. In summary, executive function was impaired in subjects with aMCI and early AD and was associated with frontal and parietal PVWM changes. These changes may be due to early AD degeneration of the lateral cholinergic projections or to early change of the superior longitudinal fasciculus.

Executive Functions after Age 5: Changes and Correlates

Research and theorizing on executive function (EF) in childhood has been disproportionately focused on preschool age children. This review paper outlines the importance of examining EF throughout childhood, and even across the lifespan. First, examining EF in older children can address the question of whether EF is a unitary construct. The relations among the EF components, particularly as they are recruited for complex tasks, appear to change over the course of development. Second, much of the development of EF, especially working memory, shifting, and planning, occurs after age 5. Third, important applications of EF research concern the role of school-age children's EF in various aspects of school performance, as well as social functioning and emotional control. Future research needs to examine a more complete developmental span, from early childhood through late adulthood, in order to address developmental issues adequately.

Differential frontal-striatal and paralimbic activity during reversal learning in major depressive disorder and obsessive-compulsive disorder

BACKGROUND

Several lines of research suggest a disturbance of reversal learning (reward and punishment processing, and affective switching) in patients with major depressive disorder (MDD). Obsessive-compulsive disorder (OCD) is also characterized by abnormal reversal learning, and is often co-morbid with MDD. However, neurobiological distinctions between the disorders are unclear. Functional neuroimaging (activation) studies comparing MDD and OCD directly are lacking.

METHOD

Twenty non-medicated OCD-free patients with MDD, 20 non-medicated MDD-free patients with OCD, and 27 healthy controls performed a self-paced reversal learning task in an event-related design during functional magnetic resonance imaging (fMRI).

RESULTS

Compared with healthy controls, both MDD and OCD patients displayed prolonged mean reaction times (RTs) but normal accuracy. In MDD subjects, mean RTs were correlated with disease severity. Imaging results showed MDD-specific hyperactivity in the anterior insula during punishment processing and in the putamen during reward processing. Moreover, blood oxygen level-dependent (BOLD) responses in the dorsolateral prefrontal cortex (DLPFC) and the anterior PFC during affective switching showed a linear decrease across controls, MDD and OCD. Finally, the OCD group showed blunted responsiveness of the orbitofrontal (OFC)-striatal loop during reward, and in the OFC and anterior insula during affective switching.

CONCLUSIONS

This study shows frontal-striatal and (para)limbic functional abnormalities during reversal learning in MDD, in the context of generic psychomotor slowing. These data converge with currently influential models on the neuropathophysiology of MDD. Moreover, this study reports differential neural patterns in frontal-striatal and paralimbic structures on this task between MDD and OCD, confirming previous findings regarding the neural correlates of deficient reversal learning in OCD.

Dissociation of frontal and medial temporal lobe activity in maintenance and binding of sequentially presented paired associates

Substructures of the prefrontal cortex (PFC) and the medial-temporal lobe are critical for associating objects presented over time. Previous studies showing frontal and medial-temporal involvement in associative encoding have not addressed the response specificity of these regions to different aspects of the task, which include instructions to associate and binding of stimuli. This study used a novel paradigm to temporally separate these two components of the task by sequential presentation of individual images with or without associative instruction; fMRI was used to investigate the temporal involvement of the PFC and the parahippocampal cortex in encoding each component. Although both regions showed an enhanced response to the second stimulus of a pair, only the PFC had increased activation during the delay preceding a stimulus when associative instruction was given. These findings present new evidence that prefrontal and medial-temporal regions provide distinct temporal contributions during associative memory formation.

Sex-dependent age modulation of frontostriatal and temporo-parietal activation during cognitive control

Developmental functional imaging studies of cognitive control show progressive age-related increase in task-relevant fronto-striatal activation in male development from childhood to adulthood. Little is known, however, about how gender affects this functional development. In this study, we used event related functional magnetic resonance imaging to examine effects of sex, age, and their interaction on brain activation during attentional switching and interference inhibition, in 63 male and female adolescents and adults, aged 13 to 38. Linear age correlations were observed across all subjects in task-specific frontal, striatal and temporo-parietal activation. Gender analysis revealed increased activation in females relative to males in fronto-striatal areas during the Switch task, and laterality effects in the Simon task, with females showing increased left inferior prefrontal and temporal activation, and males showing increased right inferior prefrontal and parietal activation. Increased prefrontal activation clusters in females and increased parietal activation clusters in males furthermore overlapped with clusters that were age-correlated across the whole group, potentially reflecting more mature prefrontal brain activation patterns for females, and more mature parietal activation patterns for males. Gender by age interactions further supported this dissociation, revealing exclusive female-specific age correlations in inferior and medial prefrontal brain regions during both tasks, and exclusive male-specific age correlations in superior parietal (Switch task) and temporal regions (Simon task). These findings show increased recruitment of age-correlated prefrontal activation in females, and of age-correlated parietal activation in males, during tasks of cognitive control. Gender differences in frontal and parietal recruitment may thus be related to gender differences in the neurofunctional maturation of these brain regions.

IQ-related fMRI differences during cognitive set shifting

This event-related functional magnetic resonance imaging study compared neural correlates of executive function (cognitive set-shifting) in 28 healthy participants with either high (HIQ) or average (AIQ) intelligence. Despite comparable behavioral performance (except for slower reactions), the AIQ participants showed greater (especially prefrontal) activation during response selection; the HIQ participants showed greater activation (especially parietal) during feedback evaluation. HIQ participants appeared to engage cognitive resources to support more efficient strategies (planning during feedback in preparation for the upcoming response) which resulted in faster responses and less need for response inhibition and conflict resolution. Whether greater intelligence is associated with more or less brain activity (the “neural efficiency” debate) depends therefore on the specific component of the task being examined as well as the brain region recruited. One implication is that caution must be exercised when drawing conclusions from differences in activation between groups of individuals in whom IQ may differ (e.g., psychiatric vs. control samples).

Neuropsychological assessment of impulsive behavior in abstinent alcohol-dependent subjects

OBJECTIVE: Poor impulse control is thought to be one of the characteristics of alcohol addiction. The capacity to remain abstinent may be linked to cognitive bias related to three dimensions of impulsivity: motor, non-planning, and attentional impulsivity. The aim of this study was to evaluate the neuropsychological profile related to these impulsivity dimensions in alcohol-dependent patients within 15 -120 days of abstinence. METHOD: We compared 31 alcohol-dependent patients to 30 matched healthy controls regarding their performances on the Continuous Performance Task, the Iowa Gambling Test, and the Wisconsin Card Sorting Test, each of which is thought to tax primarily one of the three dimensions of impulsivity just outlined. RESULTS: When compared to controls, alcohol-dependent patients presented more commission errors on the Continuous Performance Task; made more disadvantageous choices on the Iowa Gambling Test; and made more perseverative errors on the Wisconsin Card Sorting Test. There was no significant correlation between performance on these tests and the length of abstinence. CONCLUSIONS: These results suggest that deficits related to motor, non-planning and attentional components of impulsivity exist in alcohol-dependent patients, in the period immediately after acute alcohol withdrawal. These results may help guide interventions designed to prevent the risk of relapse in alcohol-abstinent patients.

Corpus callosum volume and neurocognition in autism

The corpus callosum has recently been considered as an index of interhemispheric connectivity. This study applied a novel volumetric method to examine the size of the corpus callosum in 32 individuals with autism and 34 age-, gender- and IQ-matched controls and to investigate the relationship between this structure and cognitive measures linked to interhemispheric functioning. Participants with autism displayed reductions in total corpus callosum volume and in several of its subdivisions. Relationships were also observed between volumetric alterations and performance on several cognitive tests including the Tower of Hanoi test. These findings provide further evidence for anatomical alterations in the corpus callosum in autism, but warrant additional studies examining the relationship of this structure and specific measures of interhemispheric connectivity.

The paradox of cognitive flexibility in autism

We present an overview of current literature addressing cognitive flexibility in autism spectrum disorders. Based on recent studies at multiple sites, using diverse methods and participants of different autism subtypes, ages and cognitive levels, no consistent evidence for cognitive flexibility deficits was found. Researchers and clinicians assume that inflexible everyday behaviors in autism are directly related to cognitive flexibility deficits as assessed by clinical and experimental measures. However, there is a large gap between the day-to-day behavioral flexibility and that measured with these cognitive flexibility tasks. To advance the field, experimental measures must evolve to reflect mechanistic models of flexibility deficits. Moreover, ecologically valid measures are required to be able to resolve the paradox between cognitive and behavioral inflexibility.

The prefrontal cortex and the executive control of attention

We review two studies aimed at understanding the role of prefrontal cortex (PFC) in the control of attention. The first study examined which attentional functions are critically dependent on PFC by removing PFC unilaterally and transecting the forebrain commissures in two macaques. The monkeys fixated a central cue and discriminated the orientation of a colored target grating presented among colored distracter gratings in either the hemifield affected by the PFC lesion or the normal control hemifield. When the cue was held constant for many trials, task performance in the affected hemifield was nearly normal. However, performance was severely impaired when the cue was switched frequently across trials. The monkeys were unimpaired in a pop-out task with changing targets that did not require top-down attentional control. Thus, the PFC lesion resulted in selective impairment in the monkeys' ability to switch top-down control. In the second study, we used fMRI to investigate the neural correlates of top-down control in humans performing tasks identical to those used in the monkey experiments. Several fronto-parietal and posterior visual areas showed enhanced activation when attention was switched, which was greater on color cueing (top-down) trials relative to pop-out trials. Taken together, our findings indicate that both frontal and parietal cortices are involved in generating top-down control signals for attentive switching, which may then be fed back to visual processing areas. The PFC in particular plays a critical role in the ability to switch attentional control on the basis of changing task demands.

Reduced activation in right lateral prefrontal cortex and anterior cingulate gyrus in medication-naïve adolescents with attention deficit hyperactivity disorder during time discrimination

BACKGROUND

Patients with attention deficit hyperactivity disorder (ADHD) under-perform when discriminating between durations differing by several hundred milliseconds. This function involves right prefrontal and anterior cingulate (AC) brain regions, which are structurally and functionally compromised in this patient group during executive tasks. We investigated the neuro-anatomical substrates mediating fine temporal discrimination in adolescents with ADHD compared with controls, using functional magnetic resonance imaging (fMRI).

METHODS

Twenty-one male medication-naïve adolescents aged 10-15 years with a DSM-IV diagnosis of ADHD (combined subtype) and without comorbid Axis I disorders (except conduct disorder) were compared to a group of 17 age- and IQ-matched healthy adolescents. Using fMRI on a 1.5T scanner, we compared brain activation and performance between adolescents with ADHD and controls during a time discrimination task contrasted with a temporal order task.

RESULTS

Despite comparable performance, patients with ADHD showed decreased activation in right dorsolateral and inferior prefrontal cortex and AC during time discrimination compared with controls.

CONCLUSIONS

Right hemispheric fronto-cingulate abnormalities in ADHD, previously observed during inhibitory and executive functions, are also associated with temporal perception. Furthermore, recruitment of medication-naïve patients precludes the possibility that deficits are attributable to stimulant exposure.

Inattentive/overactive children with histories of profound institutional deprivation compared with standard ADHD cases: a brief report

BACKGROUND

The Inattention/Overactivity/Impulsiveness (I/OA) behavioural cluster diagnostic of ADHD is recognized as a characteristic outcome of early institutional care.

METHODS

We compared the symptom and neuropsychological profiles of children with a history of I/OA and early severe deprivation (D-I/OA: n=13) with standard clinical ADHD cases (S-ADHD; N=20) and children who had experienced deprivation but were not pervasively I/OA (ERA-controls; n=22). The mean age of testing was around 13 years. D-I/OA and ERA-controls were selected from the English and Romanian Adoptees (ERA) study and had spent their early lives in the extremely depriving Romanian institutions of the Ceausescu regime and were later adopted into UK families.

RESULTS

ADHD symptoms for male D-I/OA and S-ADHD cases showed marked similarities across symptom domains. In contrast, girls with D-I/OA were more similar to ERA controls than to ADHD cases. Longitudinal data suggested that this was due to a remission of symptoms in D-I/OA girls. Neuropsychological profiles of males and females with D-I/OA, however, were similar: both were more impaired than S-ADHD and ERA controls.

DISCUSSION

Children with D-I/OA were more neuropsychologically impaired than S-ADHD despite the fact that only boys showed a persistent pattern of ADHD symptoms. These results need replication in a larger sample with groups matched for gender.

A mouse model of fragile X syndrome exhibits heightened arousal and/or emotion following errors or reversal of contingencies

This study was designed to further assess cognitive and affective functioning in a mouse model of Fragile X syndrome (FXS), the Fmr1(tm1Cgr) or Fmr1 "knockout" (KO) mouse. Male KO mice and wild-type littermate controls were tested on learning set and reversal learning tasks. The KO mice were not impaired in associative learning, transfer of learning, or reversal learning, based on measures of learning rate. Analyses of videotapes of the reversal learning task revealed that both groups of mice exhibited higher levels of activity and wall-climbing during the initial sessions of the task than during the final sessions, a pattern also seen for trials following an error relative to those following a correct response. Notably, the increase in both behavioral measures seen early in the task was significantly more pronounced for the KO mice than for controls, as was the error-induced increase in activity level. This pattern of effects suggests that the KO mice reacted more strongly than controls to the reversal of contingencies and pronounced drop in reinforcement rate, and to errors in general. This pattern of effects is consistent with the heightened emotional reactivity frequently described for humans with FXS.

Shifting set about task switching: behavioral and neural evidence for distinct forms of cognitive flexibility

Task switching is an important aspect of cognitive control and understanding its underlying mechanisms is the focus of considerable research. In this paper, we contrast two different kinds of task switching paradigms and provide evidence that different cognitive mechanisms underlie switching behavior depending on whether the switch is between sets of rules (rule switch) or sets of features presented simultaneously (perceptual switch). In two experiments, we demonstrate that behavioral effects (Experiment 1) and neural recruitment (Experiment 2) vary with the type of switch performed. While perceptual switch costs occurred when the alternative feature set was physically present, rule switch costs were observed even in their absence. Rule switching was also characterized by larger target repetition effects and by greater engagement of the dorsolateral prefrontal cortex. In contrast, perceptual switching was associated with greater recruitment of the parietal cortex. These results provide strong evidence for multiple forms of switching and suggest the limitations of generalizing results across shift types.

Endogenous testosterone levels, mental rotation performance, and constituent abilities in middle-to-older aged men

Evidence from both human and animal studies suggests that gonadal steroids, such as testosterone, exert activational effects on adult spatial behavior. Endogenous testosterone levels decline gradually but variably as men age; it remains to be shown whether these decreases are associated with age-related declines in visuo-spatial performance or constituent abilities indicative of generalized age-related cognitive decline. Ninety-six healthy, community dwelling men aged between 38 and 69 years completed the Vandenberg and Kuse Mental Rotation Test (MRT) together with a battery of tests including processing speed, executive function, perceptual discrimination, working memory, and reaction time measures. Significant main effects of tertiles of calculated free testosterone levels (cEFT) were found on composite measures of processing speed, executive function, and perceptual discrimination ability in a subset of men aged over 50 years in age and crystallized intelligence controlled analyses; higher cEFT levels were associated with poorer performance. Hierarchical multiple regression and path analyses on the whole data set showed that cEFT levels negatively moderated processing speed performance, which in turn predicted both working memory and MRT performance with aging. Together these data suggest that age-related declines in endogenous testosterone levels in healthy middle-to-older aged men are not associated with generalized age-related cognitive decline.

The effects of frontal lobe functioning and age on veridical and false recall

Older adults' heightened susceptibility to false memories has been linked to compromised frontal lobe functioning as estimated by Glisky and colleagues' (Glisky, Polster, & Routhieaux, 1995) neuropsychological battery (e.g., Butler, McDaniel, Domburg, Price, & Roediger, 2004). This conclusion, however, rests on the untested assumption that young adults have uniformly high frontal functioning. We tested this assumption, and we correlated younger and older adults' frontal scores with veridical and false recall probabilities with prose materials. Substantial variability in scores on the Glisky battery occurred for younger (and older) adults. However, frontal scores and age were independent contributors to recall probabilities. Frontal functioning is not the sole cause of older adults' heightened susceptibility to false memories.

Role of the serotonin system in ADHD: treatment implications

A limited number of studies have considered whether the activity of serotonin (5-hydroxytryptamine [5-HT]) contributes to the problems experienced by youngsters with attention-deficit/hyperactivity disorder (ADHD). The aim of this article is to review this work and propose interpretations. Peripheral measures of 5-HT and its metabolite do not point to a widespread association with the diagnosis. However, separate consideration of the major domains of dysfunction (motor activity, inattention and impulsivity) support a more differentiated assessment. The marked innervation of motor regions of the brain by 5-HT projections and the clear involvement of 5-HT systems in the control of locomotion in animals suggests a likely node for dysfunction in ADHD. The few relevant studies do not show evidence of this, but more attention should be accorded to the issue. The situation is different for attention-related processes; here, there are deficiencies in perceptual sensitivity and the appropriate designation of saliency to stimulation. These are attributable, in part, to altered 5-HT activity. Marked and opposite changes of 5-HT responsivity are associated with behavioral and cognitive impulsivity. There is also a growing series of studies demonstrating preferential transmission of various genetic markers for 5-HT receptors that are expressed in ADHD. Currently, the heterogeneity of methods in this young discipline restricts the possibilities of definition of these markers and the types of ADHD in which they are expressed.

Top down attentional deficits in macaques with lesions of lateral prefrontal cortex

Brain imaging, electrical stimulation, and neurophysiological studies have all implicated the prefrontal cortex (PFC) in the top-down control of attention. Specifically, feedback from PFC has been proposed to bias activity in visual cortex in favor of attended stimuli over irrelevant distracters. To identify which attentional functions are critically dependent on PFC, we removed PFC unilaterally in combination with transection of the corpus callosum and anterior commissure in two macaques. In such a preparation, the ipsilesional hemisphere is deprived of top-down feedback from PFC to visual cortex, and the contralesional hemisphere can serve as an intact normal control. Monkeys were trained to fixate a central cue and discriminate the orientation of a colored target grating presented among colored distracter gratings in either the hemifield affected by the PFC lesion or the normal control hemifield. Locations of the targets and distracters were varied, and the color of the central cue specified the color of the target on each trial. The behavioral response was a bar release, and thus attentional impairments could be distinguished from impaired oculomotor control. When the cue was held constant for many trials, task performance in the affected hemifield was nearly normal. However, the monkeys were severely impaired when the cue was switched frequently across trials. The monkeys were unimpaired in a pop-out task with changing targets that did not require top-down attentional control. The PFC thus appears to play a critical role in the ability to flexibly reallocate attention on the basis of changing task demands.

Temporal lobe dysfunction in medication-naïve boys with attention-deficit/hyperactivity disorder during attention allocation and its relation to response variability

BACKGROUND

Patients with attention-deficit/hyperactivity disorder (ADHD) typically show fronto-striatal abnormalities during functions of cognitive control. In this study we investigate whether medication-naïve children with ADHD are impaired in temporo-parietal neural networks that mediate purely perceptual attention allocation to a behaviorally neutral oddball task. Furthermore, we explore the relationship between the neural substrates of attention allocation and response variability, typically increased in patients.

METHOD

Event-related functional magnetic resonance imaging was used to compare brain activation of 17 medication-naïve boys with ADHD with that of 18 handedness- and IQ-matched healthy comparison boys during a visual oddball task that required the same response to oddball and standard trials. Furthermore, to explore the relationship between behavioral dispersion and attention networks, regression analyses were conducted between response variability and brain activation networks.

RESULTS

Patients showed significantly reduced brain activation in left and right superior temporal lobes, basal ganglia, and posterior cingulate during the oddball versus standard contrast. The activation differences in superior temporal lobes correlated inversely with response variability in control subjects but not in patients with ADHD.

CONCLUSIONS

Brain abnormalities in patients with ADHD are not confined to fronto-striatal networks mediating executive functions but are also observed in temporo-striatal and cingulate regions during perceptive visual attention processes. Furthermore, temporal lobe dysfunction in the context of perceptual attention might be related to their behavioral problems with response variability.

Neurobiological underpinnings of insight deficits in schizophrenia

Impaired insight into illness is commonly observed across various psychiatric illnesses, but is most frequent in patients with schizophrenia. The clinical relevance and public health impact of poor insight is reflected by its close association with important clinical outcome measures, such as treatment non-adherence, lower psychosocial functioning, poor prognosis, involuntary hospitalization, and higher utilization of emergency services. Although the neurobiology of insight has not been determined, data from neurocognitive and a few structural imaging studies provide some understanding of the neurobiological underpinnings of insight function in schizophrenia. Using published and preliminary data, we propose a hypothetical model of insight that may help initiate neurobiological investigations in this complex area.

Performance of children with attention deficit hyperactivity disorder (ADHD) on a test battery of impulsiveness

Children with ADHD were compared to healthy controls on a task battery of cognitive control, measuring motor inhibition (Go/No-Go and Stop tasks), cognitive inhibition (motor Stroop and Switch tasks), sustained attention and time discrimination. Children with ADHD showed an inconsistent and premature response style across all 6 tasks. In addition they showed task-specific impairments in measures of sustained attention, time discrimination, and motor inhibition, but spared cognitive inhibition. Measures of impairment correlated with behavioral hyperactivity and with each other, suggesting that they measure interrelated aspects of a multifaceted construct of cognitive impulsiveness. The task battery as a whole showed 76% correct discrimination of cases and controls.