Impaired extra-dimensional shift performance in medicated and unmedicated Parkinson's disease: evidence for a specific attentional dysfunction

Improving response inhibition in Parkinson's disease with atomoxetine

BACKGROUND

Dopaminergic drugs remain the mainstay of Parkinson's disease therapy but often fail to improve cognitive problems such as impulsivity. This may be due to the loss of other neurotransmitters, including noradrenaline, which is linked to impulsivity and response inhibition. We therefore examined the effect of the selective noradrenaline reuptake inhibitor atomoxetine on response inhibition in a stop-signal paradigm.

METHODS

This pharmacological functional magnetic resonance imaging study used a double-blinded randomized crossover design with low-frequency inhibition trials distributed among frequent Go trials. Twenty-one patients received 40 mg atomoxetine or placebo. Control subjects were tested on no-drug. The effects of disease and drug on behavioral performance, regional brain activity, and functional connectivity were analyzed using general linear models. Anatomical connectivity was examined using diffusion-weighted imaging.

RESULTS

Patients with Parkinson's disease had longer stop-signal reaction times, less stop-related activation in the right inferior frontal gyrus (RIFG), and weaker functional connectivity between the RIFG and striatum compared with control subjects. Atomoxetine enhanced stop-related RIFG activation in proportion to disease severity. Although there was no overall behavioral benefit from atomoxetine, analyses of individual differences revealed that enhanced response inhibition by atomoxetine was associated with increased RIFG activation and functional frontostriatal connectivity. Improved performance was more likely in patients with higher structural frontostriatal connectivity.

CONCLUSIONS

This study suggests that enhanced prefrontal cortical activation and frontostriatal connectivity by atomoxetine may improve response inhibition in Parkinson's disease. These results point the way to new stratified clinical trials of atomoxetine to treat impulsivity in selected patients with Parkinson's disease.

Neuropsychological assessment in obsessive-compulsive disorder

BACKGROUND

Neuropsychological deficits in obsessive-compulsive disorder (OCD) have been encouraged by brain imaging studies suggesting a putative fron to- striatial biological basis of the condition. Studies of neuropsychological functions in OCD have documented deficits in several cognitive domains, particularly with regard to visuospatial abilities, executive functioning, motor speed and memory. The Aim of the present study was to assess neuropsychological profile of patients with OCD. Objectives of the study were to assess and compare the neuropsychological profile of patients with OCD and matched healthy controls.

MATERIALS AND METHODS

Twenty clinically stable outpatients with ICD-10 diagnosis of OCD and equal number of normal controls matched for age, education, gender and handedness were studied using a battery of neuropsychological tests. The tests consisted of verbal and performance tests of intelligence, memory, perceptual motor functions, set test and Wisconsin Card Sorting Test (WCST).

RESULTS

On perceptual-motor functions, verbal fluency, executive functions (WCST), intelligence and memory patients with OCD did not show impairments comparable to healthy controls. An attempt to correlate the test findings with the duration of illness, stability of illness and the average drug dose was made and it was found that there was no correlation between the two.

CONCLUSION

The present study does not provide evidence for a localized neuropsychological/cognitive impairment in OCD in cases that are stable for at least three months. Absence of impairments in perceptual-motor functions, verbal fluency, executive functions (WCST), intelligence, and memory does not agree with the results of other studies using these tests.

Strategy use, planning, and rule acquisition deficits in spinocerebellar ataxia type 2 patients

Our goal was to improve spinocerebellar ataxia type 2 (SCA2) cognitive profile characterization by testing the hypothesis that strategy, planning and rule acquisition capacities are affected in SCA2. Forty one patients with SCA2 were evaluated with the Spatial Working Memory (SWM), the Stockings of Cambridge (SOC), and the Intra-Extra Dimensional Shift (IED) tests of the Executive module of the Cambridge Neuropsychological Testing Automated Battery (CANTAB). Paired Associates Learning (PAL) and Delayed Matching to Sample (DMS) from the CANTAB memory module were also assessed to corroborate previous findings. Motor deterioration was measured using the Scale for the Assessment and Rating of Ataxia (SARA). We found significant SCA2 related deficits in strategy, planning, and rule acquisition. Our results also corroborated significant memory deficits in these patients with SCA2. Further analysis also showed that patients with large motor deterioration had poorer associative learning and spatial planning scores. Patients with SCA2 show strategy, planning, and rule acquisition deficits as revealed with the CANTAB battery. These deficits should be noted when planning an effective therapy for these patients.

Executive functioning in individuals with intellectual disabilities and autism spectrum disorders

BACKGROUND

Executive functioning (EF) is important for adequate behavioural functioning and crucial for explaining symptoms of autism spectrum disorders (ASD) in individuals with normal intelligence, but is scarcely studied in individuals with ASD and intellectual disabilities (ID). We therefore study EF in an ID population by comparing performances on three frequently studied executive functions (shifting, inhibition and updating) between individuals with ASD and individuals without ASD. When studying ID populations, one should be aware of Spearman's Law of Diminishing Returns (SLODR), as it questions the possibility of measuring separate cognitive functions in ID populations.

METHODS

Six EF tasks were administered to 50 individuals with mild to borderline ID, of which half was diagnosed with ASD. In order to investigate the distinctness of the three executive functions in this ID sample, the results on the six EF tasks were subjected to principal components analysis (PCA). Subsequently, a multivariate analysis of variance (MANOVA) was performed to assess differences between the ASD and non-ASD group on shifting, inhibition and updating.

RESULTS

The PCA revealed the hypothesised EF trichotomy. MANOVA analysis showed no significant group differences on EF-performance.

CONCLUSIONS

Three separate executive functions were measured in this ID population, but despite much evidence that individuals with ASD display more behavioural problems and the proven relevance of EF in behavioural functioning, no significant group difference was found on shifting, inhibition or updating. After this first effort to achieve more insight into EF of individuals with ASD and ID the relation between behavioural problems and EF will require further study.

Cognitive function and health-related quality of life four years after cardiac arrest

AIM

Neuropsychological testing has uncovered cognitive impairment in cardiac arrest survivors with good neurologic outcome according to the cerebral performance categories. We investigated cognitive function and health-related quality of life four years after cardiac arrest.

METHODS

Thirty cardiac arrest survivors over the age of 18 in cerebral performance category 1 or 2 on hospital discharge completed the EQ-5D-5L and HADS questionnaires prior to cognitive testing using the Cambridge Neuropsychological Test Automated Battery. The results were compared with population norms.

RESULTS

Twenty-nine per cent of patients were cognitively impaired. The pattern of cognitive impairment reflects dysfunction in the medial temporal lobe, with impaired short-time memory and executive function slightly but distinctly affected. There was a significant reduction in quality of life on the EQ-VAS, but not on the EQ index.

CONCLUSION

Cognitive impairment four years after cardiac arrest affected more than one quarter of the patients. Short-term memory was predominantly affected.

Compensatory fronto-parietal hyperactivation during set-shifting in unmedicated patients with Parkinson's disease

Patients with Parkinson's disease (PD) often suffer from impairments in executive functions, such as mental rigidity, which can be measured as impaired set-shifting. Previous studies have shown that set-shifting deficits in patients with PD result from hypo-excitation of the caudate nucleus and lateral prefrontal cortices. The results of these studies may have been influenced by the inclusion of patients on dopaminergic medication, and by choosing set-shifting paradigms in which performance also depends on other cognitive mechanisms, such as matching-to-sample. To circumvent these potential confounding factors, we tested patients with PD that were not on dopamine replacement therapy, and we developed a new feedback-based paradigm to measure the cognitive construct set-shifting more accurately. In this case-control study, 18 patients with PD and 35 well-matched healthy controls performed the set-shifting task, while task-related neural activation was recorded using functional magnetic resonance imaging. Behaviourally, PD patients, compared with healthy controls, made more errors during repeat trials, but not set-shift trials. The patients, compared with controls, showed increased task-related activation of the bilateral inferior parietal cortex, and the right superior frontal gyrus, and decreased activation of the right ventrolateral prefrontal cortex during set-shift trials. Our findings suggest that, despite decreased task-related activation of the right ventrolateral prefrontal cortex, these early-stage unmedicated patients with PD do not yet suffer from set-shifting deficits due to compensatory hyperactivation in the inferior parietal cortex and the superior frontal gyrus.

Long-term moderate alcohol consumption does not exacerbate age-related cognitive decline in healthy, community-dwelling older adults

Recent census data has found that roughly 40% of adults 65 years and older not only consume alcohol but also drink more of it than previous generations. Older drinkers are more vulnerable than younger counterparts to the psychoactive effects of alcohol due to natural biological changes that occur with aging. This study was specifically designed to measure the effect of long-term moderate alcohol consumption on cognitive health in older adult drinkers. An extensive battery of validated tests commonly used in aging and substance use literature was used to measure performance in specific cognitive domains, including working memory and attention. An age (young, old) (*) alcohol consumption (light, moderate) factorial study design was used to evaluate the main effects of age and alcohol consumption on cognitive performance. The focus of the study was then limited to light and moderate older drinkers, and whether or not long-term moderate alcohol consumption exacerbated age-related cognitive decline. No evidence was found to support the idea that long-term moderate alcohol consumption in older adults exacerbates age-related cognitive decline. Findings were specific to healthy community dwelling social drinkers in older age and they should not be generalized to individuals with other consumption patterns, like heavy drinkers, binge drinkers or ex-drinkers.

Attentional Set-Shifting Across Species

Attentional set-shifting, as a measure of executive flexibility, has been a staple of investigations into human cognition for over six decades. Mediated by the frontal cortex in mammals, the cognitive processes involved in forming, maintaining and shifting an attentional set are vulnerable to dysfunction arising from a number of human neurodegenerative diseases (such as Alzheimer's, Parkinson's and Huntington's diseases) and other neurological disorders (such as schizophrenia, depression, and attention deficit/hyperactivity disorder). Our understanding of these diseases and disorders, and the cognitive impairments induced by them, continues to advance, in tandem with an increasing number of tools at our disposal. In this chapter, we review and compare commonly used attentional set-shifting tasks (the Wisconsin Card Sorting Task and Intradimensional/Extradimensional tasks) and their applicability across species. In addition to humans, attentional set-shifting has been observed in a number of other animals, with a substantial body of literature describing performance in monkeys and rodents. We consider the task designs used to investigate attentional set-shifting in these species and the methods used to model human diseases and disorders, and ultimately the comparisons and differences between species-specific tasks, and between performance across species.

Self-Disorders, Neurocognition and Rationality in Schizophrenia: A Preliminary Study

BACKGROUND/AIMS

Although the very idea that the generative disorder in schizophrenia is a disturbance of the self is as old as the schizophrenia concept itself, empirical studies have only recently emerged, documenting that anomalous self-experiences (i.e. self-disorders, SDs) aggregate in schizophrenia spectrum disorders but not in other mental disorders. The aim of this study is to explore potential associations between SDs, neurocognitive performance, rationality and IQ in patients with schizophrenia.

METHODS

The sample comprises 31 patients diagnosed with schizophrenia (DSM-IV). All patients underwent comprehensive evaluation. SDs were assessed with the Examination of Anomalous Self-Experience scale. Neurocognitive performance was measured with 4 PC-implemented subtests from the Cambridge Neuropsychological Test Automated Battery. Rationality was measured using syllogism tests. The IQ was indexed by a summary score of 4 IST-2000-R computerized subtests.

RESULTS

No correlation was found between SDs and neurocognitive performance or between SDs and IQ. SDs were found to correlate with rationality. Neurocognitive performance correlated with rationality, and both correlated with IQ, respectively.

CONCLUSIONS

The lack of correlation between SDs and neurocognitive performance is consistent with the results from the only previous study exploring this issue, suggesting that SDs depict something essential to schizophrenia, whereas neurocognitive impairment does not. The correlation between SDs and rationality indicates that the syllogism tests reflect something central for schizophrenia, but the result needs further corroboration from larger, empirical studies.

Cognitive deficits in Parkinson's disease: a cognitive neuroscience perspective

Progress in characterization of the nature, neural basis, and treatment of cognitive deficits in Parkinson's disease is reviewed from the perspective of cognitive neuroscience. An initial emphasis on fronto-striatal executive deficits is surveyed along with the discoveries of disruption as well as remediation of certain impairments by dopaminergic mediation and their association with theories of reinforcement learning. Subsequent focus on large cohorts has revealed considerable heterogeneity in the cognitive impairments as well as a suggestion of at least two distinct syndromes, with the dopamine-dependent fronto-striatal deficits being somewhat independent of other signs commonly associated with Parkinson's disease dementia. The utility is proposed of a new, integrated cognitive neuroscience approach based on combining genetic and neuroimaging methodologies with neuropsychological and, ultimately, psychopharmacological approaches.

Clinical Practice Regarding Dopamine-Agonist Use and Driving in Parkinson's Disease

Background:

Current Health Canada instructions for use of the dopamine agonists (DA), pramipexole and ropinirole, state that Parkinson's disease (PD) patients should be told not to drive. The objective was to assess neurologists' actual clinical practice concerning driving advice they give to PD patients starting a DA.

Methods:

An online survey was created consisting of 4 items regarding demographics, 5 regarding PD and driving, and 9 regarding DA use and driving. The survey was distributed to 563 neurologists.

Results:

In total 96 neurologists (17.9%) responded. 4.4% tell patients with PD not to drive, solely because they are taking a DA. Respondents assess the patient's tendency for excessive daytime sleepiness and sleep attacks after starting a DA more frequently than after starting other dopaminergic drugs (p<0.001).

Discussion:

A minor proportion of the clinicians responding to our survey advise PD patients not to drive, solely because they use a DA. Such being the case, we propose that current Health Canada guidelines need revision.

Subjective deficits of attention, cognition and depression in patients with narcolepsy

OBJECTIVE

Patients with narcolepsy often complain about attention deficits in everyday situations. In comparison with these subjective complaints, deficits in objective testing are subtler. The present study assessed the relationships between subjective complaints, objectively measured cognitive performance, disease-related variables, and mood.

PATIENTS/METHODS

A total of 51 patients with narcolepsy and 35 healthy controls responded to questionnaires regarding subjectively perceived attention deficits, sleepiness, anxiety and depression. Moreover, they performed an extensive neuropsychological assessment tapping into attention, executive functions, and memory.

RESULTS

Patients rated their level of attention in everyday situations to be relatively poor. In an objective assessment of cognitive functioning, they showed only slight attention and executive function deficits. The subjective ratings of attention deficits significantly correlated with ratings of momentary sleepiness, anxiety, and depression, but not with objectively measured cognitive performance. Momentary sleepiness and depression predicted almost 39% of the variance in the ratings of subjectively perceived attention deficits.

CONCLUSION

The present study showed that sleepiness and depression, more than objective cognitive deficits, might play a role in the subjectively perceived attention deficits of patients with narcolepsy. The results suggested that when counselling and treating patients with narcolepsy, clinicians should pay attention to potential depression because subjective cognitive complaints may not relate to objective cognitive impairments.

Attentional set-shifting in Parkinson's disease patients with freezing of gait-acquisition and discrimination set learning deficits at the background?

Cognitive loading aggravates the freezing of gait (FoG), which is observed in approximately 50% of patients with Parkinson's disease (PD) in the advanced stages. To investigate whether a specific pattern of executive deficits, that is, attentional set-shifting and/or inhibitory control, are associated with FoG in PD, 30 PD patients with FoG (PD-FoG+) and 36 PD patients without FoG (PD-FoG-) and 22 control healthy subjects were examined with a comprehensive neuropsychological battery. Intra-Extra Dimensional Set shifting Test (IED) and Stop Signal Task (SST), selected from the Cambridge Automated Neuropsychological Battery (CANTAB battery), were administered to analyze set-shifting and motor inhibition, respectively. The IED task was significantly sensitive for differentiating between PD-FoG+ and PD-FoG- groups (p<.01), as well Adenbrook's clock drawing task (p=.033). By contrast, no differences emerged on any aspect of the SST task and other cognitive tasks. The attrition rate during the IED task showed that the problem in the PD-FoG+ group appeared at the pre-ID level, on the discrimination-learning set; the 32% PD-FoG+ subjects did not achieve the ID level of the task in comparison to negligible 4% of the PD-FoG- patients (p=.011). The logistic regression analysis, indicated the higher the IED stage successfully completed, the less likely presence of FoG in PD subjects. These results demonstrate that the complex cognitive-motor interplay might be responsible for FoG in PD and have had real life implication for the patients.

Cortical and subcortical contributions to state- and strength-based perceptual judgments

Perceptual judgments can be made on the basis of different kinds of information: state-based access to specific details that differentiate two similar images, or strength-based assessments of relational match/mismatch. We explored state- and strength-based perception in eleven right-hemisphere stroke patients, and examined lesion overlap images to gain insight into the neural underpinnings of these different kinds of perceptual judgments. Patients and healthy controls were presented with pairs of scenes that were either identical or differed in that one scene was slightly expanded or contracted relative to the other. Same/different confidence judgments were used to plot receiver-operating characteristics and estimate the contributions of state- and strength-based perception. The patient group showed a significant and selective impairment of strength-based, but not state-based, perception. This finding was not an artifact of reduced levels of overall performance, because matching perceptual discriminability levels between controls and patients revealed a double dissociation, with higher state-based, and lower strength-based, perception in patients vs.

CONTROLS

We then conducted exploratory follow-up analyses on the patient group, based on the observation of substantial individual differences in state-based perception - differences that were masked in analyses based on the group mean. Patients who were relatively spared in state-based perception (but impaired in strength-based perception) had damage that was primarily in temporo-parietal cortical regions. Patients who were relatively impaired in both state- and strength-based perception had overlapping damage in the thalamus, putamen, and adjacent white matter. These patient groups were not different in any other measure, e.g., presence of spatial neglect symptoms, age, education, lesion volume, or time since stroke. These findings shed light on the different roles of right hemisphere regions in high-level perception, suggesting that the thalamus and basal ganglia play a critical role in state- and strength-based perception, whereas temporo-parietal cortical regions are important for intact strength-based perception.

Shifting impairment and aggression in intellectual disability and autism spectrum disorder

Aggressive behaviour is a major problem in individuals with an intellectual disability (ID) as well as in individuals with an Autism Spectrum Disorder (ASD). There are indications that suggest a link between cognitive shifting and aggression. In this study, reports of aggressive incidents of adolescents and young adults with different clinical diagnoses (ID, ID+ASD, ASD) were collected during 1 year, using the Staff Observation Aggression Scale-Revised. Whether they were diagnosed with ID, ASD or both; individuals who displayed aggression were found to face more cognitive shifting difficulties than non-aggressive individuals, while no significant differences were found on severity of ASD symptoms. Study results support the assumption that a cognition-based model for aggression may be more adequate than a diagnose-based model.

Set shifting in children and adolescents with anorexia nervosa: an exploratory systematic review and meta-analysis

OBJECTIVE

Set shifting inefficiencies in adults with anorexia nervosa (AN) are established, however the neurocognitive profile of children and adolescents with AN is less clear. This study aimed to provide a review of the literature.

METHOD

Electronic databases were used to search for manuscripts.

RESULTS

Meta-analysis was performed on seven studies using two neuropsychological tests (Trail Making Task, TMT; Wisconsin Card Sorting Task, WCST). The mean difference in outcome between AN and healthy control (HC) groups was standardized by calculating Cohen's d. Meta-analysis of TMT studies showed a nonsignificant negative, pooled standardized mean difference of -0.005 (95% C.I. -0.416 to 0.406, z = 0.02, p = .98). WCST studies revealed a nonsignificant pooled effect size of d = 0.196 (95% C.I. -0.091-0.483, z = 1.34, p = .18). Studies which did not allow for a calculation of effect size typically showed a nonsignificant, worse performance by the AN groups.

DISCUSSION

The inefficiencies in set shifting that are apparent in the adult AN literature do not appear to be as pronounced in children. This may suggest that set shifting difficulties in adult AN are the result of starvation or indicative of longer duration of illness. Larger studies are needed to confirm these impressions.

Cognitive performance in irritable bowel syndrome: evidence of a stress-related impairment in visuospatial memory

BACKGROUND

Central nervous system (CNS) dysfunction is a prominent feature of the functional gastrointestinal (GI) disorder, irritable bowel syndrome (IBS). However, the neurobiological and cognitive consequences of key pathophysiological features of IBS, such as stress-induced changes in hypothalamic-pituitary-adrenal (HPA)-axis functioning, is unknown. Our aim was to determine whether IBS is associated with cognitive impairment, independently of psychiatric co-morbidity, and whether cognitive performance is related to HPA-axis function.

METHOD

A cross-sectional sample of 39 patients with IBS, a disease control group of 18 patients with Crohn's disease (CD) in clinical remission and 40 healthy age- and IQ-matched control participants were assessed using the Paired Associates Learning (PAL), Intra-Extra Dimensional Set Shift (IED) and Spatial Working Memory (SWM) tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) and a computerized Stroop test. HPA-axis function was determined by measuring the cortisol awakening response (CAR).

RESULTS

IBS patients exhibited a subtle visuospatial memory deficit at the PAL six- pattern stage (p = 0.03), which remained after psychiatric co-morbidity was controlled for (p = 0.04). Morning cortisol levels were lower in IBS (p = 0.04) and significantly associated with visuospatial memory performance within IBS only (p = 0.02).

CONCLUSIONS

For the first time, altered cognitive function on a hippocampal-mediated test of visuospatial memory, which was related to cortisol levels and independent of psychiatric co-morbidity, has been identified in IBS. Visuospatial memory impairment may be a common, but currently neglected, component of IBS. Further elucidation of the nature of this impairment may lead to a greater understanding of the underlying pathophysiology of IBS, and may provide novel therapeutic approaches.

Cognitive effects of pregabalin in the treatment of long-term benzodiazepine-use and dependence

OBJECTIVE

Long-term benzodiazepine (BDZ) use and dependence affect cognitive functioning adversely and partly irreversibly. Emerging evidence suggests that pregabalin (PGB) might be a safe and efficacious treatment of long-term BDZ use. The aim of the present study was to investigate the changes in several core cognitive functions after successful treatment of long-term BDZ use and dependence with PGB.

METHODS

Fourteen patients with long-term BDZ use (mean duration >15 years) underwent neuropsychological assessment with the mini-mental state examination and four tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) battery before the initiation of PGB treatment and at a two months follow-up after the cessation of BDZs. Patients' CANTAB percentile score distributions were compared with normative CANTAB data.

RESULTS

Patients improved on cognitive measures of global cognitive functioning, time orientation, psychomotor speed, and visuospatial memory and learning with strong effect sizes. By contrast, they failed to improve on measures of attentional flexibility. Despite their significant improvement, patients' scores on most tests remained still at the lower percentiles of CANTAB normative scores.

CONCLUSIONS

Although preliminary, our findings suggest that successful treatment of long-term BDZ use with PGB is associated with a substantial, though only partial, recovery of BDZ-compromised neuropsychological functioning, at least at a 2-month follow-up.

Performance of C57BL/6J and DBA/2J mice on a touchscreen-based attentional set-shifting task

Attentional set-shifting deficits are a feature of multiple psychiatric disorders. However, the neurogenetic mechanisms underlying these deficits are largely unknown. In the present study we assessed performance of C57BL/6J and DBA/2J mice on a touchscreen-based attentional set-shifting task similar to those used with humans and non-human primates. In experiment 1, mice discriminated simple white lines followed by compound stimuli composed of white lines superimposed on grey shapes. Although performance of the two strains was largely equivalent during early stages of the task, DBA/2J mice committed significantly more errors compared to C57BL/6J mice on the extra-dimensional shift. Additionally, performance of mice as a group declined across the three compound discrimination reversals. In experiment 2 we assessed salience of the shapes and lines dimensions and determined if dimensional salience, a variable previously shown to affect set-shifting abilities in humans and non-human primates, could be systematically manipulated. Findings from experiment 2 suggested that strain differences during the extra-dimensional shift in experiment 1 were most parsimoniously explained by a consistently impaired ability in DBA/2J mice to discriminate a subset of the compound stimuli. Additionally, unlike maze-based tasks, the relative salience of the two dimensions could be manipulated by systematically altering the width of lines exemplars while retaining other potentially-relevant attributes of the compound stimuli. These findings reveal unique and in some cases strain-dependent phenomena related to discriminations of simple and multidimensional visual stimuli which may facilitate future efforts to identify and fully characterize visual discrimination, reversal learning, and attentional set-shifting deficits in mice.

A head-to-head randomized clinical trial of methylphenidate and atomoxetine treatment for executive function in adults with attention-deficit hyperactivity disorder

Results regarding the effects of methylphenidate and atomoxetine on executive functions were inconsistent and no study has directly compared the efficacy of these two medications in improving executive functions in adults with attention-deficit hyperactivity disorder (ADHD). We conducted an 8-10 wk, open-label, head-to-head, randomized clinical trial involving adults with a clinical diagnosis of ADHD confirmed by psychiatric interview. The two treatment arms were immediate-release methylphenidate (IR-methylphenidate) (n = 31) and atomoxetine once daily (n = 32). Executive functions were assessed by the Cambridge Neuropsychological Test Automated Battery (CANTAB), including spatial working memory, spatial span, intra-extra dimensional set shifts, rapid visual information processing and Stockings of Cambridge (SOC). In addition to the symptom assessments at baseline (week 0), visit 2 (week 4-5) and visit 3 (week 8–10), they received CANTAB assessments at baseline and visit 3 (60.4 ± 6.3 d). Compared to baseline, adults treated with atomoxetine showed significant improvement in spatial working memory, spatial short-term memory, sustained attention and spatial planning at visit 3; adults treated with IR-methylphenidate showed significant improvement in spatial working memory at visit 3. Comparing the magnitude of improvement in executive functions between these two medications, the effect was generally similar for the two groups, although atomoxetine might have significantly greater efficacy than IR-methylphenidate in terms of improving spatial planning (SOC). Our results provide evidence to support that both IR-methylphenidate and atomoxetine improved various executive functions in adults with ADHD with greater improvement in atomoxetine than IR-methylphenidate in spatial planning.

Understanding cognitive deficits in Parkinson's disease: lessons from preclinical animal models

Parkinson's disease (PD) has been, until recently, mainly defined by the presence of characteristic motor symptoms, such as rigidity, tremor, bradykinesia/akinesia, and postural instability. Accordingly, pharmacological and surgical treatments have so far addressed these motor disturbances, leaving nonmotor, cognitive deficits an unmet clinical condition. At the preclinical level, the large majority of studies aiming at defining mechanisms and testing novel therapies have similarly focused on the motor aspects of PD. Unfortunately, deterioration of the executive functions, such as attention, recognition, working memory, and problem solving, often appear in an early, premotor phase of the disease and progressively increase in intensity, negatively affecting the quality of life of ∼50%-60% of PD patients. At present, the cellular mechanisms underlying cognitive impairments in PD patients are largely unknown and an adequate treatment is still missing. The preclinical research has recently developed new animal models that may open new perspectives for a more integrated approach to the treatment of both motor and cognitive symptoms of the disease. This review will provide an overview on the cognitive symptoms occurring in early PD patients and then focus on the rodent and nonhuman primate models so far available for the study of discriminative and spatial memory attention and learning abilities related to this pathological condition.

Applications of technology in neuropsychological assessment

Most neuropsychological assessments include at least one measure that is administered, scored, or interpreted by computers or other technologies. Despite supportive findings for these technology-based assessments, there is resistance in the field of neuropsychology to adopt additional measures that incorporate technology components. This literature review addresses the research findings of technology-based neuropsychological assessments, including computer- and virtual reality-based measures of cognitive and functional abilities. We evaluate the strengths and limitations of each approach, and examine the utility of technology-based assessments to obtain supplemental cognitive and behavioral information that may be otherwise undetected by traditional paper-and-pencil measures. We argue that the potential of technology use in neuropsychological assessment has not yet been realized, and continued adoption of new technologies could result in more comprehensive assessment of cognitive dysfunction and in turn, better informed diagnosis and treatments. Recommendations for future research are also provided.

Cognitive deficits of executive functions and decision-making in obsessive-compulsive disorder

The nature of cognitive deficits in obsessive-compulsive disorder (OCD) is characterized by contradictory findings in terms of specific neuropsychological deficits. Selective impairments have been suggested to involve visuospatial memory, set shifting, decision-making and response inhibition. The aim of this study was to investigate cognitive deficits in decision-making and executive functioning in OCD. It was hypothesized that the OCD patients would be less accurate in their responses compared to the healthy controls in rational decision-making on a version of the Cambridge gambling task (CGT) and on the color-word interference test and on a version of the Tower of Hanoi test (tower test) of executive functioning. Thirteen participants with OCD were compared to a group of healthy controls (n = 13) matched for age, gender, education and verbal IQ. Results revealed significant differences between the OCD group and the healthy control group on quality of decision-making on the CGT and for achievement score on the tower test. On these two tasks the OCD group performed worse than the healthy control group. The symptom-dimension analysis revealed performance differences where safety checking patients were impaired on the tower test compared to contamination patients. Results are discussed in the framework of cognition and emotion processing and findings implicate that OCD models should address, specifically, the interaction between cognition and emotion. Here the emotional disruption hypothesis is forwarded to account for the dysfunctional behaviors in OCD. Further implications regarding methodological and inhibitory factors affecting cognitive information processing are highlighted.

Learning and switching between stimulus-saccade associations in Parkinson's disease

Making flexible associations between what we see and what we do is important for many everyday tasks. Previous work in patients with focal lesions has shown that the control of saccadic eye movements in such contexts relies on a network of areas in the frontal cerebral cortex. These regions are reciprocally connected with structures in the basal ganglia although the contribution of these sub-cortical structures to oculomotor control in complex tasks is not well understood. We report the performance of patients with idiopathic Parkinsons disease (PDs) in a test which required learning and switching between arbitrary cue-saccade rules. In Experiment 1 feedback was given following each response which reliably indicated which of the two possible rules was correct. PDs were slower to learn the first cue-saccade association presented, but did not show increased error or reaction time switch costs when switching between two rules within blocks. In a follow up experiment the feedback given by the computer was adjusted to be probabilistic such that executing a response based upon the "correct" rule only resulted in positive feedback on 80% of trials. Under these conditions patients were impaired in terms of response latencies and number of errors. In all conditions PDs showed multi-stepping/hypometria of saccades consistent with a motoric deficit in executing actions based on cognitive cues. The findings are consistent with a role for the nigrostriatal dopamine system in the reinforcement of saccade-response-outcome associations. Intact performance of PDs when associations are not stochastically reinforced suggests that striatal learning systems are complemented by cognitive representations of task rules which are unaffected in the early stages of PD.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Neuroimaging of brain changes associated with cognitive impairment in Parkinson's disease

Cognitive impairment occurs frequently in Parkinson's disease (PD) and the concept of Mild Cognitive Impairment in PD (PD-MCI) has recently emerged. Patients with mild impairment are at risk of developing dementia, and thus it is a topic of growing interest. Many previous studies have investigated the neural correlates of cognitive impairment, in particular executive dysfunction, in PD patients without dementia using neuroimaging techniques including structural MRI, functional MRI and PET imaging. These studies, which have provided a foundation for understanding which brain regions and neurotransmitter systems may be involved in executive dysfunction in PD, will be reviewed. Recent neuroimaging studies that have used specific criteria to classify patients as PD-MCI, in the hopes of gaining further insight into the underlying neural mechanisms will also be discussed. In particular, this review will cover key findings involving structural MRI investigating grey and white matter changes, functional MRI to examine changes in neural activation and PET imaging to investigate metabolic and neurochemical changes that have led to an improved understanding of pathology associated with executive dysfunction in PD without dementia and PD-MCI.

Revisiting the effects of Parkinson's disease and frontal lobe lesions on task switching: the role of rule reconfiguration

This study investigated the hypothesis that rule reconfiguration in task switching can isolate aspects of intact and impaired control at different stages of Parkinson's disease (PD) by comparing switches between concrete naming rules pertaining to stimulus selection, to switches between abstract rules which allocate categorization responses to these stimuli. Based on previous findings, it was hypothesized that attentional switches, where task set competition emerges at the stimulus but not response set level, highlights striatal dopaminergic function. Conversely, increasing the degree of task set competition to encompass reconfiguration of response set when switching between abstract rules, represents a condition which engages the prefrontal cortex (PFC) and renders this manipulation sensitive to frontal damage. To this end, we investigated task switching with concrete and abstract rules in unilaterally (Hoehn & Yahr stage I) and bilaterally (Hoehn & Yahr stage II) affected PD patients, as well as striatally intact frontal lesion patients. As predicted, frontal lesion patients demonstrated switching deficits only with abstract categorization rules, where switching engendered complete task set reconfiguration and a new response, as did stage II PD patients with presumed frontal cortical pathology. Replicating previous findings, stage I PD patients with relatively circumscribed striatal pathology demonstrated no such impairment. Disease severity also impacted on attentional switching indexed by naming rules, since medicated stage II but not stage I patients demonstrated switching deficits emerging from stimulus set reconfiguration, suggesting that the ameliorative efficacy of dopaminergic medication is inversely related to the severity of the striatal deficit. These findings illustrate that the nature of the rules that are switched, and its implication in terms of reconfiguring different task set elements, highlights different neural characters of cognitive flexibility. These manipulations may help decipher the differential effects of progressive neurodegeneration on parkinsonian cognition, and provide a framework in which to conceptualize the contributions of cortical and subcortical regions to cognitive control.

Cognitive impairment in Parkinson's disease: the dual syndrome hypothesis

Research into the heterogeneous nature of cognitive impairment documented in patients with Parkinson's disease (PD) has focused on disentangling deficits that vary between individuals, evolve and respond differentially to pharmacological treatments, and relate differentially to PD dementia (PDD). We summarise studies conducted in our laboratory over the last 2 decades, outlining the incremental development of our hypotheses, the starting point for which is our early work on executive deficits mirroring fronto-striatal dysfunction. We present subsequent findings linking these deficits to a model of dopaminergic function that conforms to an inverted curvilinear function. We review studies that investigated the range of dopamine-independent attentional and visuospatial memory deficits seen in PD, demonstrating that abnormalities in these domains more accurately predict PDD. We conclude with an exposition of the dual syndrome hypothesis, which distinguishes between dopaminergically mediated fronto-striatal executive impairments and a dementia syndrome with distinctive prodromal visuospatial deficits in which cholinergic treatments offer some clinical benefits.

The emerging role of norepinephrine in cognitive dysfunctions of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 1% of the population over age 60. In those patients cognitive dysfunction is a persistent issue that impairs quality of life and productivity. Neuropathological studies demonstrate significant damage in brain regions outside the nigral dopamine (DA) system, including early degeneration of locus coeruleus norepinephrine (LC-NE) neurons, yet discussion of PD and treatment focus has remained dopaminergic-based. Motor symptoms benefit from DA replacement for many years, but other symptoms including several cognitive deficits continue unabated. Recent interest in non-DA substrates of PD highlights early involvement of LC-NE neurons and provides evidence for a prodromal phase, with cognitive disturbance, even in sporadic PD. We outline insights from basic research in LC-NE function to clinical and pathological evidence highlighting a role for NE in PD cognitive dysfunction. We propose that loss of LC-NE regulation, particularly in higher cortical regions, critically underlies certain cognitive dysfunctions in early PD. As a major unmet need for patients, research and use of NE drugs in PD may provide significant benefits for cognitive processing.

Emotion modulates cognitive flexibility in patients with major depression

BACKGROUND

Depression is associated with alterations of emotional and cognitive processing, and executive control in particular. Previous research has shown that depressed patients are impaired in their ability to shift attention from one emotional category to another, but whether this shifting deficit is more evident on emotional relative to non-emotional cognitive control tasks remains unclear.

METHOD

The performance of patients with major depressive disorder and matched healthy control participants was compared on neutral and emotional variants of a dynamic cognitive control task that requires participants to shift attention and response from one category to another.

RESULTS

Relative to controls, depressed patients were impaired on both tasks, particularly in terms of performance accuracy. In the neutral go/no-go task, the ability of depressed patients to flexibly shift attention and response from one class of neutral stimuli to the other was unimpaired. This contrasted with findings for the emotional go/no-go task, where responding was slower specifically on blocks of trials that required participants to shift attention and response from one emotional category to the other.

CONCLUSIONS

The present data indicate that any depression-related difficulties with cognitive flexibility and control may be particularly evident on matched tasks that require processing of relevant emotional, rather than simply neutral, stimuli. The implications of these findings for our developing understanding of cognitive and emotional control processes in depression are discussed.

Attentional set-shifting deficit in Parkinson's disease is associated with prefrontal dysfunction: an FDG-PET study

The attentional set-shifting deficit that has been observed in Parkinson's disease (PD) has long been considered neuropsychological evidence of the involvement of meso-prefrontal and prefrontal-striatal circuits in cognitive flexibility. However, recent studies have suggested that non-dopaminergic, posterior cortical pathologies may also contribute to this deficit. Although several neuroimaging studies have addressed this issue, the results of these studies were confounded by the use of tasks that required other cognitive processes in addition to set-shifting, such as rule learning and working memory. In this study, we attempted to identify the neural correlates of the attentional set-shifting deficit in PD using a compound letter task and 18F-fluoro-deoxy-glucose (FDG) positron emission tomography during rest. Shift cost, which is a measure of attentional set-shifting ability, was significantly correlated with hypometabolism in the right dorsolateral prefrontal cortex, including the putative human frontal eye field. Our results provide direct evidence that dysfunction in the dorsolateral prefrontal cortex makes a primary contribution to the attentional set-shifting deficit that has been observed in PD patients.

Executive function in Parkinson's disease: contributions of the dorsal frontostriatal pathways to action and motivation

Disruption of the dorsal frontostriatal pathways in Parkinson's disease (PD) is associated with impairments in motivation, as well as in executive function. The goal of this study was to investigate whether these impairments are related and, if so, whether the disruption of frontostriatal pathways compromises the ability to process the motivational aspects of feedback in such tasks. In Experiment 1, informative feedback improved the performance of young, healthy participants in a task-switching paradigm. This task-switching paradigm was then used in Experiment 2 to test whether feedback would improve the performance of 17 PD patients and age-matched controls. The PD group benefitted from feedback to the same degree as control participants; however, depression scores on the Beck Depression Inventory were significantly related to feedback usage, especially when response selection demands were high. Regardless of feedback, PD patients were more impaired when response demands were high than in an equally difficult condition with low action demands. These results suggest that response selection is a core impairment of insufficient dopamine to the dorsal frontal striatal pathways.

Decision making and executive functions in REM sleep behavior disorder

STUDY OBJECTIVES

This study was designed to assess decision making and executive functions in patients with idiopathic REM sleep behavior disorder (iRBD). IRBD is often seen as an early sign of later evolving neurodegenerative disease, most importantly Parkinson disease (PD) and Lewy body dementia (DLB). It has been proposed that iRBD patients show a cognitive profile similar to patients with PD.

DESIGN

All participants performed an extensive test battery tapping executive functions as well as the IOWA gambling task, which measures decision making under ambiguity.

SETTING

University hospital sleep disorders center.

PARTICIPANTS

16 iRBD patients and 45 age- and education-matched controls.

INTERVENTION

N.A.

MEASUREMENTS AND RESULTS

Compared with controls, iRBD patients showed disadvantageous decision making under ambiguity and did not learn by feedback over the task. IRBD patients' decision pattern was characterized by the lack of a consistent strategy, as indicated by frequent shifts between the single choices. A high proportion of iRBD patients (75%) showed random performance or worse even at the end of the task. No group differences were found in tasks assessing information sampling, flexibility and categorization, problem solving, and impulsivity.

CONCLUSIONS

As suggested by the present investigation, iRBD patients may show difficulties in decision making under ambiguity in a stage when other cognitive functions are relatively well preserved. Whether this is driven by subgroups of patients prone to develop PD or DLB has to be assessed by follow-up investigations.

Motor inhibition and cognitive flexibility in eating disorder subtypes

Anorexia Nervosa (AN) and Bulimia Nervosa (BN) are complex Eating Disorders (EDs). Even if are considered two different diagnostic categories, they share clinical relevant characteristics. The evaluation of neurocognitive functions, using standardized neuropsychological assessment, could be a interesting approach to better understand differences and similarities between diagnostic categories and clinical subtypes in EDs thus improving our knowledge of the pathophisiology of EDs spectrum. This study explored cognitive flexibility and motor inhibition in patients with AN considering both Restricter and Binge/Purge subtypes, patients with BN and healthy comparisons subjects (HC). Intra-Extra Dimentional Set shifting Test and Stop Signal Task, selected from CANTAB battery, were administered to analyzed set-shifting and motor inhibition respectively. AN patients showed a deficient motor inhibition compared to HC, while no evidence for impaired motor inhibition was found in BN patients; a significant relationship between commission errors in the Stop Signal Task and attentional impulsiveness was found. Moreover, no difference in set-shifting abilities was found comparing all clinician groups and HC. So our results indicated no cognitive impairment in these two cognitive functions in BN patients, while AN and BN showed different performances in motor inhibition. A similar cognitive profile was found in other obsessive compulsive spectrum disorders. Finally, the paper suggests a new interactive approach for the study of cognitive profile in psychiatric disorders; it might be more useful since it is more closely related to the executive functions complexity.

Flexibility in children with autism spectrum disorders (ASD): inconsistency between neuropsychological tests and parent-based rating scales

In this study, we compared neuropsychological tests and parent-based ratings of flexibility in a sample of children with autism spectrum disorders (ASD). We investigated the discriminant validity of the domain-specific flexibility measures by comparison with the domain general measures, general behavioral problems, general ASD-related traits, and general intelligence. Tests and parent-based ratings of flexibility were not significantly correlated. Parent-based ratings were strongly related with the three broadband measures, whereas the discriminant validity indices of the neuropsychological tests were satisfactory. These findings suggest that parent-based ratings do not reflect the specific executive construct of flexibility, but instead reflect a broad spectrum of general child characteristics.

The histone deacetylase inhibitor, sodium butyrate, alleviates cognitive deficits in pre-motor stage PD

Parkinson's disease (PD) patients often times experience impairment in their cognitive abilities early on in the progression of the disease. The reported deficits appear to mainly involve functions that are associated with frontal lobe and frontal-striatal pathways subserving attentional set-shifting, working memory and executive function. The current study explored executive function deficits in a rat model of PD in the pre-motor deficit stage. The rats were lesioned with 12 μg of 6-hydroxydonpamine (6-OHDA) in the striatum in a two step process (10 μg/μl followed by 2 μg/μl) 48 hours apart. Executive function was tested at 3 weeks post-surgery using a rat analogue of Wisconsin card sorting test called the Extra Dimensional/Intra Dimensional (ED/ID) set-shifting task. The results demonstrated that performance by the pre-motor rat model of PD was equivalent to that of the control groups in the simple and the compound discriminations as well as the intra-dimensional set-shifting. However the PD group exhibited attentional set-shifting deficits similar to those observed in PD patients. Additionally, sodium butyrate, a short chain fatty acid derivative and inhibitor of class I and II histone deacetylase (HDACi), was tested as a potential therapeutic agent to mitigate the pre-motor cognitive deficits in PD. The results indicated that the sodium butyrate treatment not only effectively alleviated the set-shifting deficits, but also improved the attentional set formation in the treated rats.

Behavioral toxicology of cognition: extrapolation from experimental animal models to humans: behavioral toxicology symposium overview

A variety of behavioral instruments are available for assessing important aspects of cognition in both animals and humans and, in many cases, the same instruments can be used in both. While nonhuman primates are phylogenetically closest to humans, rodents, pigeons and other animals also offer behaviors worthy of note. Delay Discounting procedures are as useful as any in studies of impulsivity and may have utility in shedding light on processes associated with drug abuse. Specific memory tests such as Visual Paired Comparisons tasks (similar to the Fagan test of infant intelligence) can be modified to allow for assessment of different aspects of memory such as spatial memory. Use of these and other specific memory tasks can be used to directly monitor aspects of cognitive development in infant animals, particularly in nonhuman primates such as monkeys, and children and to draw inferences with respect to possible neuroanatomical substrates sub-serving their functions. Tasks for assessing working memory such as Variable Delayed Response (VDR), modified VDR and Spatial Working Memory tasks are now known to be affected in Parkinson's disease (PD). These and other cognitive function tasks are being used in a monkey model of PD to assess the ability of anti-Parkinson's disease therapies to ameliorate these cognitive deficits without diminishing their therapeutic effects on motor dysfunction. Similarly, in a rat model of the cognitive deficits associated with perinatal exposure to polychlorinated biphenyls (PCBs), clear parallels with children can be seen in at least two areas of executive function: cognitive flexibility and response inhibition. In the rat model, discrimination reversal tasks were utilized to assess cognitive flexibility, a function often assessed in humans using the Wisconsin Card Sorting Task. Response inhibition was assessed using performance in a Differential Reinforcement of Low Response Rates (DRL) task. As the data continue to accumulate, it becomes more clear that our attempts to adapt animal-appropriate tasks for the study of important aspects of human cognition have proven to be very fruitful.

Attentional set-shifting in fragile X syndrome

The ability to flexibly adapt to the changing demands of the environment is often reported as a core deficit in fragile X syndrome (FXS). However, the cognitive processes that determine this attentional set-shifting deficit remain elusive. The present study investigated attentional set-shifting ability in fragile X syndrome males with the well-validated intra/extra dimensional set-shifting paradigm (IED) which offers detailed assessment of rule learning, reversal learning, and attentional set-shifting ability within and between stimulus dimensions. A novel scoring method for IED stage errors was employed to interpret set-shifting failure in terms of repetitive decision-making, distraction to irrelevance, and set-maintenance failure. Performance of FXS males was compared to typically developing children matched on mental age, adults matched on chronological age, and individuals with Down syndrome matched on both mental and chronological age. Results revealed that a significant proportion of FXS males already failed prior to the intra-dimensional set-shift stage, whereas all control participants successfully completed the stages up to the crucial extra-dimensional set-shift. FXS males showed a specific weakness in reversal learning, which was characterized by repetitive decision-making during the reversal of newly acquired stimulus-response associations in the face of simple stimulus configurations. In contrast, when stimulus configurations became more complex, FXS males displayed increased distraction to irrelevant stimuli. These findings are interpreted in terms of the cognitive demands imposed by the stages of the IED in relation to the alleged neural deficits in FXS.

Similarities and differences between pathological gambling and substance use disorders: a focus on impulsivity and compulsivity

RATIONALE

Pathological gambling (PG) has recently been considered as a "behavioral" or nonsubstance addiction. A comparison of the characteristics of PG and substance use disorders (SUDs) has clinical ramifications and could help advance future research on these conditions. Specific relationships with impulsivity and compulsivity may be central to understanding PG and SUDs.

OBJECTIVES

This review was conducted to compare and contrast research findings in PG and SUDs pertaining to neurocognitive tasks, brain function, and neurochemistry, with a focus on impulsivity and compulsivity.

RESULTS

Multiple similarities were found between PG and SUDs, including poor performance on neurocognitive tasks, specifically with respect to impulsive choice and response tendencies and compulsive features (e.g., response perseveration and action with diminished relationship to goals or reward). Findings suggest dysfunction involving similar brain regions, including the ventromedial prefrontal cortex and striatum and similar neurotransmitter systems, including dopaminergic and serotonergic. Unique features exist which may in part reflect influences of acute or chronic exposures to specific substances.

CONCLUSIONS

Both similarities and differences exist between PG and SUDs. Understanding these similarities more precisely may facilitate treatment development across addictions, whereas understanding differences may provide insight into treatment development for specific disorders. Individual differences in features of impulsivity and compulsivity may represent important endophenotypic targets for prevention and treatment strategies.

Visual misperceptions and hallucinations in Parkinson's disease: dysfunction of attentional control networks?

Visual misperceptions and hallucinations are a major cause of distress in patients with Parkinson's disease (PD), particularly in the advanced stages of the condition. Recent work has provided a framework for understanding the pathogenesis of these symptoms, implicating impairments from the retina to the integration of external information with preformed internal images. In this article, we propose a novel hypothesis that attempts to explain the presence of visual misperceptions and hallucinations in PD through the aberrant coordination of complimentary yet competing neural networks. We propose that hallucinations in PD reflect the relative inability to recruit activation in the dorsal attention network in the presence of an ambiguous percept, leading to overreliance on default mode network processing and salience arising from the ventral attention network. This inability is proposed to stem from improper function across cortical and subcortical structures secondary to the presence of Lewy body pathology. This hypothesis may be empirically tested by the use of targeted cognitive paradigms. In turn, this may assist our understanding of the pathophysiological mechanisms and cognitive processes contributing to visual misperceptions and hallucinations and ultimately may inform more effective treatment strategies for this troubling symptom.

Factor analysis of attentional set-shifting performance in young and aged mice

Background

Executive dysfunction may play a major role in cognitive decline with aging because frontal lobe structures are particularly vulnerable to advancing age. Lesion studies in rats and mice have suggested that intradimensional shifts (IDSs), extradimensional shifts (EDSs), and reversal learning are mediated by the anterior cingulate cortex, the medial prefrontal cortex, and the orbitofrontal cortex, respectively. We hypothesized that the latent structure of cognitive performance would reflect functional localization in the brain and would be altered by aging.

Methods

Young (4 months, n = 16) and aged (23 months, n = 18) C57BL/6N mice performed an attentional set-shifting task (ASST) that evaluates simple discrimination (SD), compound discrimination (CD), IDS, EDS, and reversal learning. The performance data were subjected to an exploratory factor analysis to extract the latent structures of ASST performance in young and aged mice.

Results

The factor analysis extracted two- and three-factor models. In the two-factor model, the factor associated with SD and CD was clearly separated from the factor associated with the rest of the ASST stages in the young mice only. In the three-factor model, the SD and CD loaded on distinct factors. The three-factor model also showed a separation of factors associated with IDS, EDS, and CD reversal. However, the other reversal learning variables, ID reversal and ED reversal, had somewhat inconsistent factor loadings.

Conclusions

The separation of performance factors in aged mice was less clear than in young mice, which suggests that aged mice utilize neuronal networks more broadly for specific cognitive functions. The result that the factors associated with SD and CD were separated in the three-factor model may suggest that the introduction of an irrelevant or distracting dimension results in the use of a new/orthogonal strategy for better discrimination.