Association between response inhibition and working memory in adult ADHD: a link to right frontal cortex pathology?

The Wender Utah Rating Scale: Adult ADHD diagnostic tool or personality index?

OBJECTIVE

The Wender Utah Rating Scale (WURS) is used to retroactively assess ADHD symptoms. This study sought to determine whether the WURS actually functions as an index of dysfunctional personality traits.

METHOD

Five hundred twenty-two adult participants completed the WURS and at least one of the following measures: Wechsler Adult Intelligence Scale-III (WAIS-III), Trails Making Test (Forms A and B), Conners' Continuous Performance Test, d2 Test of Attention, and the Personality Assessment Inventory (PAI).

RESULTS

The WURS correlated significantly with all PAI clinical and treatment scales; however, of the neuropsychological measures, only the CPT significantly correlated with the WURS score. Multiple regression analyses revealed a significant model that included clinical and treatment scales from the PAI as well as working memory and processing speed indexes from the WAIS-III that accounted for 39% of the variance in WURS scores.

CONCLUSION

Performance on the WURS was more related to dysfunctional personality traits than to actual attentional performance in this young adult sample. (J. of Att. Dis. 2009; 13(1) 87-94).

Impaired conscious and preserved unconscious inhibitory processing in recent onset schizophrenia

BACKGROUND

Impairments in inhibitory function have been found in studies of cognition in schizophrenia. These have been linked to a failure to adequately maintain the task demands in working memory. As response inhibition is known to occur in both voluntary and involuntary processes, an important question is whether both aspects of response inhibition are specifically impaired in people with schizophrenia.

METHOD

The subjects were 33 patients presenting with a first episode of psychosis (27 with schizophrenia and six with schizo-affective disorder) and 24 healthy controls. We administered two motor response tasks: voluntary response inhibition was indexed by the stop-signal task and involuntary response inhibition by the masked priming task. We also administered neuropsychological measures of IQ and executive function to explore their associations with response inhibition.

RESULTS

Patients with schizophrenia compared to healthy controls showed significantly increased duration of the voluntary response inhibition process, as indexed by the stop-signal reaction time (SSRT). By contrast, there were no group differences on the pattern of priming on the masked priming task, indicative of intact involuntary response inhibition. Neuropsychological measures revealed that voluntary response inhibition is not necessarily dependent on working memory.

CONCLUSIONS

These data provide evidence for a specific impairment of voluntary response inhibition in schizophrenia.

Response disengagement on a spatial self-ordered sequencing task: effects of regionally selective excitotoxic lesions and serotonin depletion within the prefrontal cortex

Prefrontal cortex (PFC) is critical for self-ordered response sequencing. Patients with frontal lobe damage are impaired on response sequencing tasks, and increased blood flow has been reported in ventrolateral and dorsolateral PFC in subjects performing such tasks. Previously, we have shown that large excitotoxic lesions of the lateral PFC (LPFC) and orbitofrontal cortex FC (OFC), but not global prefrontal dopamine depletion, markedly impaired marmoset performance on a spatial self-ordered sequencing task (SSOST). To determine whether LPFC or OFC was responsible for the previously observed impairments and whether the underlying neural mechanism was modulated by serotonin, the present study compared the effects of selective LPFC and OFC excitotoxic lesions and 5,7-DHT-induced PFC serotonin depletions in marmosets on SSOST performance. Severe and long-lasting impairments in SSOST performance, including robust perseverative responding, followed LPFC but not OFC lesions. The deficit was ameliorated by task manipulations that precluded perseveration. Depletions of serotonin within LPFC and OFC had no effect, despite impairing performance on a visual discrimination reversal task, thus providing further evidence for differential monaminergic regulation of prefrontal function. In the light of the proposed attentional control functions of ventrolateral PFC and the failure of LPFC-lesioned animals to disengage from the immediately preceding response, it is proposed that this deficit may be due to a failure to attend to and register that a response has been made and thus should not be repeated. However, 5-HT does not appear to be implicated in this response inhibitory capacity.

The Emerging Neurobiology of Attention Deficit Hyperactivity Disorder: The Key Role of the Prefrontal Association Cortex

Attention deficit/hyperactivity disorder (ADHD) is characterized by symptoms of inattention, impulsivity, and locomotor hyperactivity. Recent advances in neurobiology, imaging, and genetics have led to a greater understanding of the etiology and treatment of ADHD. Studies have found that ADHD is associated with weaker function and structure of prefrontal cortex (PFC) circuits, especially in the right hemisphere. The prefrontal association cortex plays a crucial role in regulating attention, behavior, and emotion, with the right hemisphere specialized for behavioral inhibition. The PFC is highly dependent on the correct neurochemical environment for proper function: noradrenergic stimulation of postsynaptic alpha-2A adrenoceptors and dopaminergic stimulation of D1 receptors is necessary for optimal prefrontal function. ADHD is associated with genetic changes that weaken catecholamine signaling and, in some patients, with slowed PFC maturation. Effective pharmacologic treatments for ADHD all enhance catecholamine signaling in the PFC and strengthen its regulation of attention and behavior. Recent animal studies show that therapeutic doses of stimulant medications preferentially increase norepinephrine and, to a lesser extent, dopamine, in the PFC. These doses reduce locomotor activity and improve PFC regulation of attention and behavior through enhanced catecholamine stimulation of alpha-2A and D1 receptors. These findings in animals are consistent with improved PFC function in normal human subjects and, more prominently, in patients with ADHD. Thus, a highly cohesive story is emerging regarding the etiology and treatment of ADHD.

Rule violation errors are associated with right lateral prefrontal cortex atrophy in neurodegenerative disease

Good cognitive performance requires adherence to rules specific to the task at hand. Patients with neurological disease often make rule violation (RV) errors, but the anatomical basis for RV during cognitive testing remains debated. The present study examined the neuroanatomical correlates of RV errors made on tests of executive functioning in 166 subjects diagnosed with neurodegenerative disease or as neurologically healthy. Specifically, RV errors were voxel-wisely correlated with gray matter volume derived from high-definition magnetic resonance images using voxel-based morphometry implemented in SPM2. Latent variable analysis showed that RV errors tapped a unitary construct separate from repetition errors. This analysis was used to generate factor scores to represent what is common among RV errors across tests. The extracted RV factor scores correlated with tissue loss in the lateral middle and inferior frontal gyri and the caudate nucleus bilaterally. When a more stringent control for global cognitive functioning was applied using Mini Mental State Exam scores, only the correlations with the right lateral prefrontal cortex (PFC) remained significant. These data underscore the importance of right lateral PFC in behavioral monitoring and highlight the potential of RV error assessment for identifying patients with damage to this region.

Age-related grey matter volume correlates of response inhibition and shifting in attention-deficit hyperactivity disorder

BACKGROUND

Children with attention-deficit hyperactivity disorder (ADHD) have difficulties with executive function and impulse control which may improve with age.

AIMS

To map the brain correlates of executive function in ADHD and determine age-related changes in reaction times and brain volumes.

METHOD

Attention-deficit hyperactivity disorder and control groups were compared on the change task measures of response inhibition (stop signal reaction time, SSRT) and shifting (change response reaction time, CRRT). Voxel-wise magnetic resonance imaging (MRI) correlations of reaction times and grey matter volume were determined, along with bivariate correlations of reaction times, brain volumes and age.

RESULTS

Individuals in the ADHD group had longer SSRTs and CRRTs. Anterior cingulate, striatal and medial temporal volumes highly correlated with SSRT. Striatal and cerebellar volumes strongly correlated with CRRT. Older children had faster reaction times and larger regional brain volumes. In controls, orbitofrontal, medial temporal and cerebellar volumes correlated with CRRT but not SSRT. Neither reaction times nor regional brain volumes were strongly age-dependent.

CONCLUSIONS

Our evidence supports delayed brain maturation in ADHD and implies that some features of ADHD improve with age.

Task complexity enhances response inhibition deficits in childhood and adolescent attention-deficit/hyperactivity disorder: a meta-regression analysis

BACKGROUND

The ability to inhibit motor responses, as assessed by the stop-signal reaction time (SSRT), is impaired in children and adolescents with attention-deficit/hyperactivity disorder (ADHD). However, the between-study variation in effect sizes is large. The aim of this study was to investigate whether this variability can be explained by between-study variation in Go task complexity.

METHOD

Forty-one studies comparing children or adolescents diagnosed with ADHD to normal control subjects were incorporated in a random-effects meta-regression analysis. The independent variables were a global index of Go task complexity (i.e., mean reaction time in control subjects [RTc]) and a more specific index (i.e., spatial compatibility of the stimulus-response mapping). The dependent variable was the SSRT difference between ADHD and control subjects.

RESULTS

The SSRT difference increased significantly with increasing RTc. Moreover, the SSRT difference was significantly increased in studies that employed a noncompatible, that is, arbitrary, mapping compared with studies that incorporated a spatially compatible stimulus-response mapping.

CONCLUSIONS

These results indicate that inhibitory dysfunction in children and adolescents with ADHD varies with task complexity: inhibitory dysfunction in ADHD is most pronounced for spatially noncompatible responses. Explanations in terms of inhibition and working memory deficits and a tentative neurobiological explanation are briefly discussed.

Left inferior frontal gyrus is critical for response inhibition

Background

Lesion studies in human and non-human primates have linked several different regions of prefrontal cortex (PFC) with the ability to inhibit inappropriate motor responses. However, recent functional neuroimaging studies have specifically implicated right inferior PFC in response inhibition. Right frontal dominance for inhibitory motor control has become a commonly accepted view, although support for this position has not been consistent. Particularly conspicuous is the lack of data on the importance of the homologous region in the left hemisphere. To investigate whether the left inferior frontal gyrus (IFG) is critical for response inhibition, we used neuropsychological methodology with carefully characterized brain lesions in neurological patients.

Results

Twelve individuals with damage in the left IFG and the insula were tested in a Go/NoGo response inhibition task. In alternating blocks, the difficulty of response inhibition was easy (50% NoGo trials) or hard (10% NoGo trials). Controls showed the predicted pattern of faster reaction times and more false alarm errors in the hard condition. Left IFG patients had higher error rates than controls in both conditions, but were more impaired in the hard condition, when a greater degree of inhibitory control was required. In contrast, a patient control group with orbitofrontal cortex lesions showed intact performance.

Conclusion

Recent neuroimaging studies have focused on a highly specific association between right IFG and inhibitory control. The present results indicate that the integrity of left IFG is also critical for successful implementation of inhibitory control over motor responses. Our findings demonstrate the importance of obtaining converging evidence from multiple methodologies in cognitive neuroscience.

Entwicklungspsychopathologie der ADHS

Galt die ADHS vor einigen Jahren noch als eine Erkrankung des Kindes- und Jugendalters, so versteht man heute darunter ein Störungsbild über die Lebensspanne. Mit Beginn im Vorschulalter divergieren die Symptome in Abhängigkeit des Alters. Daraus lässt sich ein Modell ableiten, welches diese Veränderungen (Komorbiditäten, Alltagsbeeinträchtigungen) auf der Zeitachse dokumentiert und mit den jeweils gültigen diagnostischen Kriterien in Verbindung bringt. Ausgehend von einer genetischen Prädisposition und einer neurobiologischen Dysregulation sind Faktoren festzustellen, die über die Lebensspanne andauern, sich altersspezifisch verändern oder nur für einen bestimmten Entwicklungsabschnitt gültig sind. Es wird deutlich, dass das Vorschulalter und der Übergang in das Erwachsenenalter die Phasen darstellen, in denen sich die meisten qualitativen Veränderungen feststellen lassen. Dies hat Implikationen für die klinische Praxis, indem diese Veränderungen zu Zwecken der Prävention, des diagnostischen Prozesses und der Therapieplanung herangezogen werden können und somit sowohl dem Anwender eine Hilfestellung bieten, aber auch als Ausgangspunkt für weitere Studien herangezogen werden können.

Evaluating the role of prefrontal and parietal cortices in memory-guided response with repetitive transcranial magnetic stimulation

The dorsolateral prefrontal cortex (dlPFC) plays an important role in working memory, including the control of memory-guided response. In this study, with 24 subjects, we used high frequency repetitive transcranial magnetic stimulation (rTMS) to evaluate the role of the dlPFC in memory-guided response to two different types of spatial working memory tasks: one requiring a recognition decision about a probe stimulus (operationalized with a yes/no button press), another requiring direct recall of the memory stimulus by moving a cursor to the remembered location. In half the trials, randomly distributed, rTMS was applied to the dlPFC and in a separate session, the superior parietal lobule (SPL), a brain area implicated in spatial working memory storage. A 10-Hz (3s, 110% of motor threshold) train of TMS was delivered at the onset of the response period. We found that only dlPFC rTMS significantly affected performance, with rTMS of right dlPFC decreasing accuracy on delayed-recall trials, and rTMS of left and right dlPFC decreasing and enhancing accuracy, respectively, on delayed-recognition trials. These findings confirm that the dlPFC plays an important role in memory-guided response, and suggest that the nature of this role varies depending on the processes required for making a response.

Poor response inhibition: at the nexus between substance abuse and attention deficit/hyperactivity disorder

The co-morbidity between attention deficit hyperactivity disorder (ADHD) and substance abuse and dependence disorders may have multiple causes and consequences. In this review, we will describe neurobehavioral, genetic and animal model studies that support the notion that a common, genetically determined failure of response inhibition function is an endophenotype for both disorders. Through an impairment in the ability to cognitively control pre-potent behaviors, subjects can exhibit a collection of ADHD-like traits (impulsivity and hyperactivity), as well as susceptibility for the initiation of drug taking and its ultimate progression to an inflexible, uncontrollable form. At the neural level, dysfunction within circuitry that includes the ventrolateral frontal and cingulate cortices, as well as in associated basal ganglia zones, contributes to a common pattern of behavioral impairment, explaining aspects of co-morbidity. Animal models of substance abuse/dependence and ADHD that exhibit deficits in response inhibition have substantiated the role of this endophenotype in both disorders and their co-morbidity and should provide a testing ground for interventions targeting it. New directions for research that will further explore this hypothesis and begin to reveal the underlying biological mechanisms will be proposed.

Role of Dopamine in the Motivational and Cognitive Control of Behavior

Brain dopamine has often been implicated in impulsive and/or inflexible behaviors, which may reflect failures of motivational and/or cognitive control. However, the precise role of dopamine in such failures of behavioral control is not well understood, not least because they implicate paradoxical changes in distinct dopamine systems that innervate dissociable neural circuits. In addition, there are large individual differences in the response to dopaminergic drugs with some individuals benefiting from and others being impaired by the same drug. This complicates progress in the understanding of dopamine's role in behavioral control processes, but also provides a major problem for neuropsychiatry, where some individuals are disproportionately vulnerable to the adverse effects of dopamine-enhancing drugs on motivation and cognition. Recent progress is reviewed from cognitive and behavioral neuroscience research on motivation and cognitive control, which begins to elucidate the factors that mediate the complex roles of mesolimbic, mesocortical, and nigrostriatal dopamine in behavioral control. NEUROSCIENTIST 14(4):381–395, 2008. DOI: 10.1177/1073858408317009

Common and unique components of inhibition and working memory: an fMRI, within-subjects investigation

Behavioural findings indicate that the core executive functions of inhibition and working memory are closely linked, and neuroimaging studies indicate overlap between their neural correlates. There has not, however, been a comprehensive study, including several inhibition tasks and several working memory tasks, performed by the same subjects. In the present study, 11 healthy adult subjects completed separate blocks of 3 inhibition tasks (a stop task, a go/no-go task and a flanker task), and 2 working memory tasks (one spatial and one verbal). Activation common to all 5 tasks was identified in the right inferior frontal gyrus, and, at a lower threshold, also the right middle frontal gyrus and right parietal regions (BA 40 and BA 7). Left inferior frontal regions of interest (ROIs) showed a significant conjunction between all tasks except the flanker task. The present study could not pinpoint the specific function of each common region, but the parietal region identified here has previously been consistently related to working memory storage and the right inferior frontal gyrus has been associated with inhibition in both lesion and imaging studies. These results support the notion that inhibitory and working memory tasks involve common neural components, which may provide a neural basis for the interrelationship between the two systems.

Dissociable roles of prefrontal subregions in self-ordered working memory performance

The anatomical segregation of executive control processes within the prefrontal cortex remains poorly defined. The present study focused on strategy implementation on two working memory tasks: the CANTAB spatial working memory task and a visuospatial sequence generation task. These measures were administered to a group of frontal lesion patients and a comparison group of healthy subjects. Frontal patients with damage to the right inferior frontal gyrus were impaired on the CANTAB spatial working memory task, compared with healthy controls and patients without damage to this region. This deficit was most strongly related to the pars opercularis subregion (BA44) and was accompanied by poor strategy usage. On the sequence generation task, frontal lesion patients were impaired on a strategy-training phase when the working memory demands of the task were reduced, but had relatively intact performance on other phases of the task. Performance on the training phase was correlated with the amount of damage to the dorsolateral prefrontal cortex (DLPFC: BA46/9). These results support theoretical notions of prefrontal cortical function that emphasise its contribution to executive processes such as mnemonic strategies and monitoring over its role as a short-term memory store. Moreover, we provide evidence for the first time that such functions are dependent on dissociable brain regions within the prefrontal cortex.

Visual fields in children with attention-deficit / hyperactivity disorder before and after treatment with stimulants

PURPOSE

This study aimed to evaluate visual function in children with attention-deficit/hyperactivity disorder (ADHD), to correlate these data with the morphology of the optic nerve, and to find out if and how psychostimulant medication affects visual functions.

METHODS

The visual acuity (VA) and visual fields (VFs) of 18 children with ADHD (two girls and 16 boys), aged 6-17 years, were examined before and after treatment with psychostimulants. A control group, consisting of 24 children (nine girls and 15 boys), aged 7-18 years, were examined twice to evaluate the repeatability of the tests and the learning effect. Fundus photographs were analysed by digital planimetry.

RESULTS

Visual acuity increased significantly (p = 0.0039) in the ADHD group after treatment. The difference between the two VF examinations was significantly larger in the ADHD group compared with the control group (p = 0.036). Significantly more ADHD subjects had subnormal VF results without stimulants, compared with controls (p = 0.0043), but with stimulants the difference was no longer significant.

CONCLUSIONS

Children with ADHD showed better VA and VF results with than without psychostimulant medication.

Dimensions of impulsivity are associated with poor spatial working memory performance in monkeys

Impulsive behavior and novelty seeking are dimensions of temperament that are behavioral determinants of risk for attention deficit/hyperactivity disorder and its neurocognitive endophenotypes, and variation in the dopamine D4 receptor gene (DRD4) explains at least a portion of the variance in the traits. To further characterize the dimensional phenotype associated with impulsiveness, adolescent male monkeys were evaluated using ecologically valid tests of impulsive approach and aggression in response to social or nonsocial stimuli; subsequently, a delayed response task was implemented to assess spatial working memory performance. Subjects were selected into this study based on their response to the social challenge task or by DRD4 genotype, resulting in three groups: low-impulsivity/common DRD4 allele, high-impulsivity/common DRD4 allele, or rare DRD4 allele. All animals acquired the delayed response task and could perform at near ceiling levels when a approximately 0 s delay version was imposed, but as delays were lengthened, high-impulsive animals, regardless of DRD4 genotype, made fewer correct responses than did low-impulsive subjects; an inverse relationship existed for working memory and impulsivity. Notably, impulsive behavior evoked by social and nonsocial stimuli explained overlapping and independent portions of the variance in working memory performance. CSF levels of monoamine metabolites did not significantly differentiate the high- and low-impulsive animals, although monkeys carrying the DRD4 rare allele tended to exhibit higher monoamine turnover. These data indicate that dimensions of impulsivity may impact on working memory performance in qualitatively similar ways but through different mechanisms.

Impulsivity as a vulnerability marker for substance-use disorders: review of findings from high-risk research, problem gamblers and genetic association studies

There is a longstanding association between substance-use disorders (SUDs) and the psychological construct of impulsivity. In the first section of this review, personality and neurocognitive data pertaining to impulsivity will be summarised in regular users of four classes of substance: stimulants, opiates, alcohol and 3,4-methylenedioxymethamphetamine (MDMA). Impulsivity in these groups may arise via two alternative mechanisms, which are not mutually exclusive. By one account, impulsivity may occur as a consequence of chronic exposure to substances causing harmful effects on the brain. By the alternative account, impulsivity pre-dates SUDs and is associated with the vulnerability to addiction. We will review the evidence that impulsivity is associated with addiction vulnerability by considering three lines of evidence: (i) studies of groups at high-risk for development of SUDs; (ii) studies of pathological gamblers, where the harmful consequences of the addiction on brain structure are minimised, and (iii) genetic association studies linking impulsivity to genetic risk factors for addiction. Within each of these three lines of enquiry, there is accumulating evidence that impulsivity is a pre-existing vulnerability marker for SUDs.

Homovanillic acid (HVA) plasma levels inversely correlate with attention deficit-hyperactivity and childhood neglect measures in addicted patients

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) seems to be a risk condition for substance use disorders, possibly in relationship to common neurobiological changes, underlying both addictive and externalising behaviour susceptibility. Although this vulnerability has been primarily attributed to gene variants, previous studies suggest that also adverse childhood experiences may influence neurotransmission, affecting in particular brain dopamine (DA) system and possibly concurring to the development of behavioural disorders. Therefore, we decided to investigate ADHD symptoms and plasma concentrations of the DA metabolite homovanillic acid (HVA) in abstinent addicted patients, in comparison with healthy control subjects, evaluating whether ADHD scores were related with HVA levels, as expression of DA turnover, and whether HVA values, in turn, were associated with childhood emotional neglect.

METHODS

Eighty-two abstinent drug dependent patients, and 44 normal controls, matched for age and sex, completed the Wender Utah Rating Scale (WURS), measuring ADHD symptoms, and the Childhood Experience of Care and Abuse Questionnaire (CECA-Q). Blood samples were collected to determine HVA plasma levels.

RESULTS

Addicted individuals showed significantly higher ADHD scores and lower HVA levels respect to control subjects. ADHD scores at WURS in addicted patients negatively correlated with plasma HVA values. In turn, plasma HVA levels were inversely associated with childhood neglect measures, reaching statistical significance with "mother-antipathy" and "mother neglect" scores.

CONCLUSIONS

These findings suggest the possibility that childhood experience of neglect and poor mother-child attachment may have an effect on central dopamine function as an adult, in turn contributing to both ADHD and substance abuse neurobiological vulnerability.