Evidence that specific executive functions predict symptom variance among schizophrenia patients with a predominantly negative symptom profile

Associations of resilience, white matter topological organization, and cognitive functions in first-episode, drug-naïve schizophrenia patients: A moderated mediation analysis

BACKGROUND

Cognitive deficits are core symptoms of schizophrenia (SZ) and are associated with impaired resilience to stress. Different cognitive functions appeared to be interrelated, and the mechanism may involve neural alterations. The disrupted topological organization indicated abnormalities in the segregation and integration of brain networks that support various cognitive processes in SZ patients. Therefore, this study aimed to assess the direct and indirect effects of resilience on cognitive functions. We hypothesized that topological properties would moderate these associations.

METHODS

Forty-nine SZ patients and fifty-two healthy controls (HCs) were recruited in this study. The Connor-Davidson Resilience Scale and the MATRICS Consensus Cognitive Battery were used to examine resilience and cognitive functions, respectively, and a graph theory approach was used to assess white matter topological organization.

RESULTS

Compared to HCs, SZ patients showed lower levels of resilience and cognitive functions in multiple domains as well as abnormal global properties and nodal metrics. In addition, shorter characteristic path length was associated with a stronger indirect effect of resilience on working memory through processing speed in SZ patients.

CONCLUSION

Characteristic path length might moderate the mediating effects of processing speed in the relationship between resilience and working memory in schizophrenia patients.

Alexithymia in chronic schizophrenia and its mediating effect between cognitive deficits and negative symptoms

BACKGROUND

Although cognition is known to impact clinical symptoms of schizophrenia, few studies investigate the potential mediators of this relationship. This study aimed to examine the relationship between cognitive deficits and negative symptoms in schizophrenia, considering the mediating role of alexithymia as an important psychological variable. Moreover, the prevalence of alexithymia in patients with schizophrenia was investigated.

METHODS

A total of 689 patients with schizophrenia were recruited from two psychiatric hospitals. All patients completed the Positive and Negative Syndrome Scale (PANSS), 20-item Toronto Alexithymia Scale (TAS-20), and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). We used structural equation modeling to examine the hypothesized mediated model.

RESULTS

In total, 31.5 % of patients with schizophrenia were classified as alexithymia. The path analyses showed that two factors of alexithymia (i.e., the difficulty in identifying feelings and difficulty in describing feelings), played a mediating role in the pathway from cognitive deficits to negative symptoms (all p < .001).

LIMITATIONS

Self-reported measurement for alexithymia may not be sufficiently reliable due to response bias.

CONCLUSION

Our findings demonstrated a high occurrence of alexithymia in patients with schizophrenia. Moreover, the mediating role of alexithymia suggests that targeting emotion processing and cognition may be a feasible way to mitigate negative symptoms.

Mediating effect of symptom severity on the relationship between aggression, impulsivity and quality of life outcomes among patients with schizophrenia and related psychoses

Aims

Aggression and impulsivity among individuals with schizophrenia have been associated with poor clinical outcomes including worsening of symptoms and substance abuse which have been linked to a lower quality of life (QoL). The current study aimed to look at the mediating effect of symptom severity on the relationship between aggression, impulsivity and QoL among outpatients with schizophrenia and related psychoses in a multi-ethnic Asian population.

Methods

Data (n = 397) were collected from outpatients seeking treatment at the Institute of Mental Health. The World Health Organization quality of life-BREF (WHOQOL-BREF) scale, the symptoms checklist-90 revised (SCL-90-R), Buss Perry aggression questionnaire (BPAQ), and the Barratt impulsiveness scales (BIS) were used to assess subjective well-being, symptom severity, aggression, and impulsivity, respectively. Mediation analysis was performed using the PROCESS macro to understand the mediating effect of symptom severity.

Results

Motor impulsivity (MI) was indirectly associated with both the physical and psychological health domains of QoL while self-control was indirectly associated with the physical, psychological, and environmental health QoL domains through increased symptom severity.

Conclusion

The significant indirect effect of symptom severity in our study highlights one potential pathway through which impulsivity impacts the QoL of individuals with schizophrenia and related psychoses. Elucidating other factors besides symptom severity that have an indirect effect on the QoL of individuals provides alternative approaches for treatment through which better clinical outcomes can be achieved.

Executive deficits in schizophrenia: mediation by processing speed and its relationships with aging

BACKGROUND

Executive deficits are a core characteristic of schizophrenia. Yet, the origin of these impairments remains unclear as they may be caused by processing slowing. This issue is of particular interest for aging insofar as cognitive aging is also associated with a decline in executive functioning and a slowing of processing speed. As schizophrenia patients' life expectancy increases, a better understanding of the origin of older patients' cognitive deficits becomes essential so that healthcare can be adapted to suit them. This study aims to determine whether processing speed mediates how schizophrenia affects executive functions and whether these relationships are moderated by age.

METHODS

Sixty-two schizophrenia patients (27 women) and 62 healthy comparison subjects matched for age (range: 18-76 years), gender and education performed neurocognitive tests to evaluate their executive functions (shifting, updating, inhibition and access) and processing speed.

RESULTS

Processing speed mediated the effect of schizophrenia on the four specific executive functions, and age moderated this mediation for shifting, updating and access, but in different ways. Age moderated the effect of processing speed on shifting, the direct effect of schizophrenia on access, and both the effect of processing speed and the direct effect of schizophrenia on updating.

CONCLUSIONS

This research highlights the need to evaluate processing speed routinely during therapeutic follow-up, as it is easy and simple to assess and appears to be at the heart of the cognitive deficits in schizophrenia. Finally, processing speed abilities yield information about the evolution of cognition with aging in schizophrenia.

No influence of sex on the relationship between schizotypy factors and executive control across the schizophrenia spectrum

Sex differences in symptoms and executive control across schizophrenia spectrum disorders (SSD) are consistently reported. Similarly, these findings of sex differences are also observed in schizotypy, that is, schizophrenia-like features occurring in healthy individuals in the absence of a clinical diagnosis. This study aimed to examine the relationships between performance on three major domains of executive control: performance monitoring, response inhibition, and cognitive set-shifting, and schizotypy factor scores in both SSD patients and healthy controls (HCs), and whether sex moderated any relationships observed. A total of 111 (67 males and 44 females) patients with SSD and 258 (129 males and 129 females) HCs were included in this study. Schizotypal personality traits (in both SSD and HC) was assessed using the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE). Executive control performance was assessed using seven tasks. Stepwise linear regressions revealed that performance on cognitive set-shifting tasks was significantly associated with the introvertive anhedonia, cognitive disorganisation, and unusual experiences subscales of the O-LIFE. When sex was examined as a moderator, it was not a significant moderator of any of the relationships between cognitive set-shifting tasks and schizotypy factors. The results suggest that independent of sex, cognitive set-shifting ability is associated to an increased vulnerability to schizotypal personality traits, although performance monitoring and response inhibition did not.

Executive functions in schizophrenia aging: Differential effects of age within specific executive functions

There are common cognitive and brain abnormalities in schizophrenia and healthy aging which may cumulate in schizophrenia aging. However, the course of executive deficits in late-life schizophrenia is still controversial as it remains unclear whether schizophrenia patients show accelerated aging. The use of specific models of executive functions might help to shed new lights on this issue. The aim of this study was then to determine how each of the four specific executive functions (shifting, updating, inhibition and access to long-term memory) is affected by aging in schizophrenia compared to healthy aging. 20 younger (age 18-34), 17 middle-aged (age 35-49) and 25 older (age 59-76) schizophrenia patients and 62 healthy comparison participants matched for gender, age and education performed a neurocognitive battery evaluating the four specific executive functions. Schizophrenia patients performed worse than comparison participants on shifting, updating and access, whereas inhibition appeared preserved. Age affected the four functions with increased degradation of shifting and access in schizophrenia patients, whereas updating and inhibition showed a normal decline with age. These results suggest a vulnerability of prefrontal and cingulate cortexes in schizophrenia aging. Moreover, as age affected the specific executive functions differently, remediation programs should be adapted to older patients. Models of specific executive functions are useful for understanding the complexity of cognition in schizophrenia and its course during later life so that healthcare can be adapted accordingly.

Sustaining attention to simple visual tasks: a central deficit in schizophrenia? A systematic review

Impairments in sustained attention, that is, the ability to achieve and maintain the focus of cognitive activity on a given stimulation source or task, have been described as central to schizophrenia. Today, sustained attention deficit is still considered as a hallmark of schizophrenia. Nevertheless, current findings on this topic are not consistent. To clarify these findings, we attempt to put these results into perspective according to the type of assessment (i.e., overall and over time assessment), the participants' characteristics (i.e., clinical and demographic characteristics), and the paradigms (i.e., traditionally formatted tasks, go/no-go tasks, and the sustained attention task) and measures used. Two types of assessment lead to opposite findings; they do not evaluate sustained attention the same way. Studies using overall assessments of sustained attention ability tend to reveal a deficit, whereas studies using over time assessments do not. Therefore, further research is needed to investigate the underlying cognitive control mechanisms of changes in sustained attention in schizophrenia.

Impulsive behavior and its correlates among patients with schizophrenia in a tertiary care psychiatry setting in Mansoura

BACKGROUND AND OBJECTIVES

Impulsive behavior has been repeatedly identified as a major problem in schizophrenia. Our objective was to examine the possible demographical and clinical correlates for impulsive behavior in patients with schizophrenia.

METHODS

Fifty-eight patients with schizophrenia and Seventy-seven healthy controls were recruited. Sociodemographic data were collected and they were subjected to the Barratt Impulsiveness Scale (BIS), Positive and Negative Syndrome scale (PANSS), and Trauma Assessment for Adults-Brief Revised Version (TAA).

RESULTS

Correlations between impulsive behavior and psychosocial variables were examined. A significant association between level of impulsive behavior and severity of psychopathological symptoms was observed (P=0.0001). Young age (P=0.001), male patients (P=0.0001) and those with history of childhood sexual or physical abuse (P=0.0001), were more impulsive. Linear regression (step wise) analysis model showed that male sex (P=0.001), positive symptoms (P=0.006), and childhood physical abuse (P=0.001) were significant associations.

CONCLUSION

Male gender, positive symptoms as well as history of physical and sexual abuse before 18 years of age are important predictors for high levels of impulsive behavior in schizophrenia patients.

Patients with bipolar disorder show differential executive dysfunctions: A case-control study

Executive deficits in euthymic bipolar I disorder were examined in a fractionated manner based on the "Supervisory Attentional System" (SAS) model, and the relationship between the degree of executive impairment and the demographic and clinical characteristics of bipolar I participants was explored. A battery of neurocognitive tests capturing specific components of executive function was administered on 30 patients with bipolar I disorder in euthymic state, and compared with 30 healthy controls who were matched by age, gender and IQ. A differential impairment in executive function was demonstrated in euthymic bipolar I participants by using a fractionated approach of the SAS. Euthymic bipolar I patients were found to have significantly poorer performance in immediate and delayed visual memory; and in the executive domains of "initiation", "sustained attention", and "attention allocation and planning". Those with a greater number of executive impairments had lower IQ and higher negative sub-scores on PANSS. These findings might provide a the basis for further studies on identifying the executive components that are associated with particular disease characteristics of bipolar disorder, and those with poorer functional outcome, so that rehabilitation can be focused on the selective domains concerned.

Developmental trajectories of executive functions in 22q11.2 deletion syndrome

Background

22q11.2 deletion syndrome (22q11.2DS) is a genetic disorder associated with a specific cognitive profile. Higher-order cognitive skills like executive functions (EF) are reported as a relative weakness in this population. The present study aimed to delineate the developmental trajectories of multiple EF domains in a longitudinal sample using a broader age range than previous studies. Given the high incidence of psychotic symptoms in 22q11.2DS, we also compared the development of EF in participants with/without comorbid psychotic symptoms. Given the importance of EF in daily life, the third aim of the study was to characterize the link between EF and adaptive functioning.

Methods

The sample consisted of 95 individuals with 22q11.2DS and 100 typically developing controls aged 6–26 years. A large proportion of the sample (55.38 %) had multiple time points available. Between-group differences in the developmental trajectories of three subdomains of EF (verbal fluency, working memory, and inhibition) were examined using mixed models regression analyses. Analyses were repeated comparing only the 22q11.2DS group based on the presence/absence of psychotic symptoms to investigate the influence of executive dysfunction on the emergence of psychotic symptoms. Hierarchical stepwise regression analyses were also conducted to investigate the predictive value of EF on adaptive functioning.

Results

We observed lower performance on EF domains, as well as atypical development of working memory and verbal fluency. Participants who presented with negative symptoms exhibited different developmental trajectories of inhibition and working memory. Adaptive functioning level was not significantly predicted by EF scores.

Conclusions

The present study highlighted domain-specific atypical trajectories of EF in individuals with 22q11.DS and explored the link with psychotic symptoms. However, no relation between EF and adaptive functioning was observed.

Clozapine improves the orienting of attention in schizophrenia

Attentional deficits are prominent in the cognitive profile of patients with schizophrenia. However, it remains unclear whether treatment with clozapine, an atypical antipsychotic and first-line intervention used to reduce positive and negative symptoms of psychosis, improves the attentional functions. We used the revised attention network test to measure alerting, orienting, and executive control of attention both pre- and post-treatment with clozapine in patients with schizophrenia (n=32) and compared performance to healthy controls (n=32). Results revealed that there were deficits in all three attentional functions pre-treatment, and while clozapine improved the orienting function in patients with schizophrenia, there was no evidence for improvement in the alerting and executive control of attention. The enhancement of the orienting function by clozapine may increase the ability of patients with schizophrenia to orient towards objects and thoughts of interest.

Perception of emotion-related conflict in human communications: what are the effects of schizophrenia?

Our ability to make sense of emotional cues is of paramount importance for understanding state of mind and communicative intent. However, emotional cues often conflict with each other; this presents a significant challenge for people with schizophrenia. We conducted a theoretical review to determine the extent and types of impaired processing of emotion-related conflict in schizophrenia; we evaluated the relationship with medication and symptoms, and considered possible mediatory mechanisms. The literature established that people with schizophrenia demonstrated impaired function: (i) when passively exposed to emotion cues whilst performing an unrelated task, (ii) when selectively attending to one source of emotion cues whilst trying to ignore interference from another source, and (iii) when trying to resolve conflicting emotion cues and judge meta-communicative intent. These deficits showed associations with both negative and positive symptoms. There was limited evidence for antipsychotic medications attenuating impaired emotion perception when there are conflicting cues, with further direct research needed. Impaired attentional control and context processing may underlie some of the observed impairments. Neuroanatomical correlates are likely to involve interhemispheric transfer via the corpus callosum, limbic regions such as the amygdala, and possibly dorsolateral prefrontal and anterior cingulate cortex through their role in conflict processing.

Deficient grip force control in schizophrenia: behavioral and modeling evidence for altered motor inhibition and motor noise

Whether upper limb sensorimotor control is affected in schizophrenia and how underlying pathological mechanisms may potentially intervene in these deficits is still being debated. We tested voluntary force control in schizophrenia patients and used a computational model in order to elucidate potential cerebral mechanisms underlying sensorimotor deficits in schizophrenia. A visuomotor grip force-tracking task was performed by 17 medicated and 6 non-medicated patients with schizophrenia (DSM-IV) and by 15 healthy controls. Target forces in the ramp-hold-and-release paradigm were set to 5N and to 10% maximal voluntary grip force. Force trajectory was analyzed by performance measures and Principal Component Analysis (PCA). A computational model incorporating neural control signals was used to replicate the empirically observed motor behavior and to explore underlying neural mechanisms. Grip task performance was significantly lower in medicated and non-medicated schizophrenia patients compared to controls. Three behavioral variables were significantly higher in both patient groups: tracking error (by 50%), coefficient of variation of force (by 57%) and duration of force release (up by 37%). Behavioral performance did not differ between patient groups. Computational simulation successfully replicated these findings and predicted that decreased motor inhibition, together with an increased signal-dependent motor noise, are sufficient to explain the observed motor deficits in patients. PCA also suggested altered motor inhibition as a key factor differentiating patients from control subjects: the principal component representing inhibition correlated with clinical severity. These findings show that schizophrenia affects voluntary sensorimotor control of the hand independent of medication, and suggest that reduced motor inhibition and increased signal-dependent motor noise likely reflect key pathological mechanisms of the sensorimotor deficit.

Category fluency in schizophrenia research: is it an executive or semantic measure?

INTRODUCTION

The semantic fluency task is described as a measure of semantic function and utilised in schizophrenia (SZ) research to demonstrate semantic deficits. Two meta-analyses support the efficacy of this task in measuring semantic function in SZ; however, a more recent meta-analysis suggests that executive dysfunction is the predominant determinant of semantic fluency performance in this group. By (1) matching the semantic and executive fluency tasks on discriminant validity, and (2) including an additional fluency task containing both semantic and executive elements (animals by size), this study aimed to determine whether semantic fluency is in fact an appropriate measure of semantic function in SZ.

METHODS

Forty-two SZ participants and 40 healthy controls performed 3 fluency tasks: executive (F, A, S), semantic (body parts), and semantic/executive (animals by size). Performance on these tasks was analysed in two ways, (1) based on discriminant validity and (2) by matching output between the semantic and semantic/executive fluency tasks.

RESULTS

When the semantic and executive fluency tasks were matched, executive fluency performance was either (1) mildly impaired or (2) not impaired in SZ. Both semantic and semantic/executive performance was impaired in SZ regardless of calculation. Group differences on the semantic/executive task remained when executive function was controlled for, but disappeared when semantic fluency effects were controlled for.

CONCLUSIONS

The findings support earlier meta-analyses in finding that the semantic fluency task is a robust measure of semantic memory function in SZ.

Relationship between diminished expression and cognitive impairment in first-episode schizophrenia: a prospective three-year follow-up study

BACKGROUND

Diminished expression (DE) is a core sub-domain of negative symptoms construct in schizophrenia. There is limited, yet inconsistent data regarding DE and its associations with cognition, particularly in the early illness course. This study aimed to examine cross-sectional and longitudinal relationships of DE with cognitive functions in first-episode schizophrenia utilizing a prospective design.

METHOD

Ninety-three Hong Kong Chinese aged 18 to 55 years presenting with first-episode schizophrenia-spectrum disorder were studied. Severity of DE was measured as sum of individual item scores indicative of affect flattening and alogia. Symptom evaluation was conducted at intake, after clinical stabilization of first psychotic episode, at 12, 24 and 36 months. Cognitive functions were evaluated at clinical stabilization, 12, 24 and 36 months.

RESULTS

DE was significantly correlated with various cognitive functions in successive follow-up assessments. Regression analyses adjusting confounding effects of sex, pre-morbid adjustment, duration of untreated psychosis and chlorpromazine equivalents showed that DE was associated with performance on verbal fluency at 12 (p<0.01) and 24 months (p<0.05), visual reproduction at 24 (p<0.05) and 36 months (p<0.01), logical memory at 36 months (p<0.05) and Modified Wisconsin Card Sorting test at 24 (p<0.05) and 36 months (p<0.05). Neither cross-lagged associations between DE and cognition nor significant correlations between changes in these two domains over three years were observed.

CONCLUSIONS

DE and cognitive functions were correlated concurrently but no longitudinal associations between these two domains could be demonstrated. Our findings indicated that DE and cognitive impairment represented relatively independent domains of the illness with potentially distinctive therapeutic implications.

Poor savouring and low self-efficacy are predictors of anhedonia in patients with schizophrenia spectrum disorders

Previous research suggests that negative schizotypes may be impaired in their ability to savour pleasant events (Applegate et al., 2009) and that schizophrenia patients believe that everyday tasks are excessively difficult to complete so that they attempt these tasks less frequently (MacCarthy et al., 1986; Bentall et al., 2010). It is possible that these beliefs and behaviours underpin negative symptoms such as anhedonia, avolition, apathy and associality. In the present study, 50 schizophrenia patients and 100 matched controls (half employed and half unemployed) completed self-report measures of self-efficacy and savouring. Patients reported savouring past, present and future events less than employed and unemployed groups, irrespective of mood state and I.Q. Patients also rated everyday tasks as more difficult to master. Inpatients compared to outpatients rated tasks more difficult but less important although they did not differ on the savouring measure. Abnormal judgements of difficulty and the reduced propensity to mentally rehearse past or future positive experiences to up-regulate mood could explain negative symptom patients' lack of engagement in everyday activities and eventual social withdrawal. These findings suggest the need to develop cognitive-behavioural savouring and self-efficacy interventions for patients experiencing the negative symptoms of schizophrenia.

Neurocognitive phenomics: examining the genetic basis of cognitive abilities

Cognitive deficits are core to the disability associated with many psychiatric disorders. Both variation in cognition and psychiatric risk show substantial heritability, with overlapping genetic variants contributing to both. Unsurprisingly, therefore, these fields have been mutually beneficial : just as cognitive studies of psychiatric risk variants may identify genes involved in cognition, so too can genome-wide studies based on cognitive phenotypes lead to genes relevant to psychiatric aetiology. The purpose of this review is to consider the main issues involved in the phenotypic characterization of cognition, and to describe the challenges associated with the transition to genomewide approaches. We conclude by describing the approaches currently being taken by the international consortia involving many investigators in the field internationally (e.g. Cognitive Genomics Consortium; COGENT) to overcome these challenges.

Executive functioning in schizophrenia: the result of impairments in lower order cognitive skills?

Executive functioning (EF) impairments are common in schizophrenia. There are two propositions regarding the causes of these impairments: (1) executive impairments are the result of the compounding effects of deficits in lower order cognitive skills (e.g. processing speed, attention) or (2) EF impairments exist in their own right regardless of lower order skills. It is difficult to examine the separable effects of lower order cognitive skills on EF given the overlap required to complete most neuropsychological measures. One battery designed to parcel out the contributions of lower order skills from EF is the Delis-Kaplan Executive Function System (D-KEFS). Inhibition and switching specifically were examined using the D-KEFS versions of the Stroop and Trails task. No group differences in task performance after controlling for lower level skills would provide evidence for a generalised cognitive deficit. Group differences remaining after controlling for these influences would suggest a disproportionate deficit. Results supported both propositions. On both tasks, group differences reflecting slowed reaction time in the schizophrenia group disappeared when lower order skills were controlled for. Differences between groups performance in errors were only evident on the most complex versions of each task with more errors made by the schizophrenia group. These results suggest that (1) both RT and error data are needed to provide a full picture of performance and (2) the relationship between lower order and EF is too complex to provide support for one or the other proposal.

Schizophrenia and frontotemporal dementia: shared causation?

The relationship between specific genes and particular diseases in neuropsychiatry is unclear, and newer studies focus on shared domains of neurobiological and cognitive pathology across different disorders. This paper reviews the evidence for an association between schizophrenia and frontotemporal dementia, including symptom similarity, familial co-morbidity, and neuroanatomical changes. Genetic as well as epigenetic findings from both schizophrenia and frontotemporal dementia are also discussed. As a result, we introduce the hypothesis of a shared susceptibility for certain subgroups of schizophrenia and frontotemporal dementia. This common causation may involve the same gene(s) at different stages of life: early in schizophrenia and late in frontotemporal dementia. Additionally, we provide a rationale for future research that should emphasize both genetic and cognitive parallels between certain forms of schizophrenia and frontotemporal dementia in a synergistic, coordinated way, placing both in the context of aberrant lateralization patterns.

Negative symptoms and executive function in schizophrenia: does their relationship change with illness duration?

BACKGROUND

Negative symptoms and cognitive dysfunction are of crucial functional and prognostic importance in schizophrenia. However, the nature of the relationship between them and the factors that may influence it have not been well established.

AIMS

To investigate whether the relationship between negative symptoms and executive function changes according to the duration of illness in schizophrenia.

METHODS

The Positive and Negative Syndrome Scale was used to assess psychopathology and the Wisconsin Card Sorting Test (WCST) to evaluate executive function in a sample of 200 schizophrenic patients who were classified in 3 groups according to their duration of illness: up to 5 years (short duration group), 6-20 years (intermediate duration group) and over 20 years of illness (long duration group).

RESULTS

Medium-sized correlations were found between negative symptoms and WCST performance as assessed by the number of completed categories in all 3 groups. However, differences were found according to the duration of schizophrenia. For patients in the short duration group, negative symptoms correlated with WCST nonperseverative errors, but for those in the long duration group the correlation was with perseverative errors.

CONCLUSION

We found a differential relationship between negative and cognitive symptoms in different stages of schizophrenia. Illness duration should be considered when studying the relationship between negative symptoms and cognition.

The cognitive atlas: toward a knowledge foundation for cognitive neuroscience

Cognitive neuroscience aims to map mental processes onto brain function, which begs the question of what “mental processes” exist and how they relate to the tasks that are used to manipulate and measure them. This topic has been addressed informally in prior work, but we propose that cumulative progress in cognitive neuroscience requires a more systematic approach to representing the mental entities that are being mapped to brain function and the tasks used to manipulate and measure mental processes. We describe a new open collaborative project that aims to provide a knowledge base for cognitive neuroscience, called the Cognitive Atlas (accessible online at http://www.cognitiveatlas.org), and outline how this project has the potential to drive novel discoveries about both mind and brain.

Heterogeneity of auditory verbal working memory in schizophrenia

The heterogeneity of schizophrenia remains an obstacle for understanding its pathophysiology. Studies using a tone discrimination screening test to classify patients have found evidence for 2 subgroups having either a specific deficit in verbal working memory (WM) or deficits in both verbal and nonverbal memory. This study aimed to (a) replicate in larger samples differences between these subgroups in auditory verbal WM; (b) evaluate their performance on tests of explicit memory and sustained attention; (c) determine the relation of verbal WM deficits to auditory hallucinations and other symptoms; and (d) examine medication effects. The verbal WM and tone discrimination performance did not differ between medicated (n = 45) and unmedicated (n = 38) patients. Patients with schizophrenia who passed the tone screening test (discriminators; n = 60) were compared with those who did not (nondiscriminators; n = 23) and healthy controls (n = 47). The discriminator subgroup showed poorer verbal WM than did controls and a deficit in verbal but not visual memory on the Wechsler Memory Scale-Revised (Wechsler, 1987), whereas the nondiscriminator subgroup showed overall poorer performance on both verbal and nonverbal tests and a marked deficit in sustained attention. Verbal WM deficits in discriminators were correlated with auditory hallucinations but not with negative symptoms. The results are consistent with a verbal memory deficit in a subgroup of schizophrenia having intact auditory perception, which may stem from dysfunction of language-related cortical regions, and a more generalized cognitive deficit in a subgroup having auditory perceptual and attentional dysfunction.

A cognitive regulatory control model of schizophrenia

A puzzling aspect of schizophrenia concerns the relationship between negative and positive symptoms. Perspectives suggesting that they arise from the same pathophysiological process are not consistent with the numerous differences such as treatment response, and the underlying neurochemistry relevant to treatment. Explanations viewing negative and positive symptoms as independent processes or diseases cannot readily account for the typical developmental course of schizophrenia, consisting of a lengthy prodromal phase of negative followed by positive symptoms. A model of schizophrenia is presented positing that negative and positive symptoms are distinct but interrelated processes, with the former bringing forth the latter due to damaged or impaired cognitive regulatory control processes. The extensive cognitive distortions, thought form variants, and sensory perceptual experiences comprising psychosis represent a natural propensity derived from the evolution of human intelligence. To facilitate reality congruency typically necessary for adaptive functioning, cognitive regulatory control processes normally prevent these extreme variants from entering the conscious and awake state. During sleep when there is no need for reality congruency the cognitive regulatory control processes are deactivated and psychotic equivalents are expressed. Psychological defensive functioning can also deactivate these processes and allow psychosis to manifest. The negative symptoms of schizophrenia are seen as arising from diverse neural deficits that impair to varying degrees the cognitive regulatory control processes, thus producing psychosis. The pattern of neural damage determines the negative symptom profile, and the impact on cognitive regulatory control processes influences whether negative or positive symptoms dominate or exist in relatively equal proportions.

The relationships between schizophrenia symptom dimensions and executive functioning components

Research investigating the relationships between executive functioning impairments and the positive, negative, and cognitive schizophrenia symptoms has produced inconsistent results. This inconsistency may be due to the tendency to view executive functioning as a unified process as opposed to multiple fractionated processes. A fractionated model of executive functioning has been supported in several studies of various populations, but few schizophrenia studies have used the factor analytic methods of these studies to empirically determine separate executive functioning components, causing conclusions regarding the relationships between these components and schizophrenia symptoms to be unreliable. The purposes of the present study were to (1) identify separate components of executive functioning by conducting a factor analysis of the performance of individuals with schizophrenia on the Delis Kaplan Executive Function System (D-KEFS) and (2) investigate the relationships between executive functioning components and the three schizophrenia symptom dimensions by correlating the derived factor scores with the scale scores of the Positive and Negative Symptom Scale (PANSS). An exploratory factor analysis revealed two separate components: inhibition/set shifting and mental flexibility. The results showed that the symptom dimensions were differentially related to impairments in executive functioning, with both negative and cognitive symptoms associated with the inhibition/set shifting component, cognitive symptoms alone associated with the mental flexibility component, and positive symptoms unrelated to either component.

Disorganization and reality distortion in schizophrenia: a meta-analysis of the relationship between positive symptoms and neurocognitive deficits

BACKGROUND

Factor analytic studies have shown that in schizophrenia patients, disorganization (e.g., conceptual disorganization and bizarre behavior) is a separate dimension from other types of positive symptoms such as reality distortion (delusions and hallucinations). Although some studies have found that disorganization is more strongly linked to neurocognitive deficits and poor functional outcomes than reality distortion, the findings are not always consistent.

METHODS

A meta-analysis of 104 studies (combined n=8015) was conducted to determine the magnitude of the relationship between neurocognition and disorganization as compared to reality distortion. Additional analyses were conducted to determine whether the strength of these relationships differed depending on the neurocognitive domain under investigation.

RESULTS

The relationship between reality distortion and neurocognition was weak (r=-.04; p=.03) as compared to the moderate association between disorganization and neurocognition (r=-.23; p<.01). In each of the six neurocognitive domains that were examined, disorganization was more strongly related to neurocognition (r's range from -.20 to -.26) than to reality distortion (r's range from .01 to -.12).

CONCLUSIONS

The effect size of the relationship between neurocognition and disorganization was significantly larger than the effect size of the relationship between neurocognition and reality distortion. These results hold across several neurocognitive domains. These findings support a dimensional view of positive symptoms distinguishing disorganization from reality distortion.

Impaired modulation of attention and emotion in schizophrenia

OBJECTIVE

Fronto-limbic interactions facilitate the generation of task-relevant responses while inhibiting interference from emotionally distracting information. Schizophrenia is associated with deficits in both executive attention and affective regulation. This study aims to elucidate the neural correlates of emotion-attention regulation and shifting in schizophrenia.

METHOD

We employed functional magnetic resonance imaging to probe the fronto-limbic regions in 16 adults with schizophrenia and 13 matched adults with no history of psychiatric illness. Subjects performed a forced-choice visual oddball task where they detected infrequent target circles embedded in a series of infrequent nontarget aversive and neutral pictures and frequent squares.

RESULTS

In control participants, target events activated a dorsal frontoparietal network, whereas these regions were deactivated by aversive stimuli. Conversely, ventral frontolimbic brain regions were activated by aversive stimuli and deactivated by target events. In the patient group, regional hemodynamic timecourses revealed not only reduced activation to target and aversive events in dorsal executive and ventral limbic regions, respectively, but also reduced deactivation to target and aversive stimuli in ventral and dorsal regions, respectively, relative to the control group. Patients further showed reduced spatial extent of activation in the right inferior frontal gyrus during the target and aversive conditions. Activation of the anterior cingulate to aversive images was inversely related to severity of avolition and anhedonia symptoms in the schizophrenia group.

CONCLUSIONS

These results suggest both frontal and limbic dysfunction in schizophrenia as well as aberrant reciprocal inhibitions between these regions during attention-emotion modulation in this disorder.

Cognitive impairment of executive function as a core symptom of schizophrenia

Cognitive dysfunction is a common finding in schizophrenia. Nevertheless the specific pattern of neuropsychological impairment in schizophrenia compared to other severe mental illnesses has not been intensively studied. Twenty-four patients with schizophrenia belonging to different stages of the disease (11 first-episode patients, 13 patients with multiple episodes), 18 patients with bipolar disorder and 23 healthy control subjects underwent standardized neuropsychological assessment. Statistical analysis of covariance (ANCOVA) demonstrated that, compared to control subjects, patients with schizophrenia performed significantly worse in the trail-making test (P = 0.012), verbal fluency (category letter, P = 0.004), verbal learning/memory (P = 0.005), and the Wisconsin Card Sorting Test (WCST) (P = 0.004 for administered trials; P = 0.025 for perseverative responses, T value) indicating significant deficits in attention and psychomotor performance, and in particular in verbal working memory and cognitive flexibility for schizophrenic patients. A significant difference between schizophrenic and bipolar patients was found only in the WCST. Schizophrenic patients made significantly more perseverative responses (P = 0.002, ANCOVA), indicating a more pronounced and specific deficit in cognitive flexibility and frontally based executive function. In conclusion, these results may suggest a cognitive endophenotype in schizophrenia and underline the role of the prefrontal cortex in schizophrenic pathophysiology.

The comprehension of idiomatic expressions in schizophrenic patients

Recent fMRI and TMS studies on idiom comprehension have shown that the prefrontal cortex is involved in idiom processing. Since schizophrenic patients exhibit prefrontal structural changes and dysexecutive behavioural deficits, we hypothesised an impairment in idiom comprehension, correlating with performance on executive tasks. In this study, idiom comprehension was evaluated by means of a sentence-to-picture-matching task in 45 schizophrenic patients and 45 control subjects, matched for age and educational level. The task included 62 idiomatic and 62 literal sentences. Participants were presented with a written sentence, either literal or idiomatic, followed by a picture, which appeared below the sentence. They were instructed to judge whether the picture represented the meaning of the sentence or not, and responded by pressing one of two response keys. Half of the items correctly represented the meaning, half did not. Reaction times and accuracy were measured. Schizophrenics were impaired in both types of idiomatic sentence. However, their performance was particularly poor in the case of ambiguous idioms. Wisconsin Card Sorting Test and Digit Sequencing were the unique predictors of performance for idiom comprehension in general, while thought disorganization was not. Cognitive decline either did not appear to predict performance.

Using virtual reality to evaluate executive functioning among persons with schizophrenia: a validity study

Persons with Schizophrenia experience difficulties with Executive Functioning (EF) that affect independence and participation in activities. Specifically, EF impacts performance in Instrumental Activities of Daily Living (IADL) that require flexible thinking and accommodation to complex environments. However, less is known how schizophrenia affects EF and individuals' performance in activities. IADL performance can be tested using a virtual reality (VR) environment that simulates real life activities. The purpose of this study was: 1) to examine the feasibility and validity of the Virtual Action Planning-Supermarket (VAP-S) to assess EF in persons with schizophrenia as compared to a standardized EF measure (the Behavioral Assessment of Dysexecutive Syndrome, BADS); 2) to compare performance of persons with schizophrenia and healthy controls in the VAP-S; 3) to assess the ability of the VAP-S to differentiate between different levels of EF within schizophrenia; 4) to explore the relationships between negative and positive symptoms and performance on the tests. Thirty persons with schizophrenia were matched with 30 healthy controls. Significant differences in performance between research and control groups were detected on the VAP-S and BADS, with the research group performing worse. Large variations in number of purchases within the VAP-S by the research group point to level of task completion thus secondary analysis was conducted. There was a significant negative correlation between level of the negative signs and overall performance on the BADS and on most measures of the VAP-S. Results of this study support the use the VAP-S to assess EF among persons with Schizophrenia.

Behavioral disinhibition: liability for externalizing spectrum disorders and its genetic and environmental relation to response inhibition across adolescence

Behavioral disinhibition has been characterized as a generalized vulnerability to externalizing disorders. Despite increasing evidence for its validity and heritability, the structural stability of behavioral disinhibition across adolescence and the strength and etiology of its relation to executive functions have not been studied. In this multivariate twin study, the authors assessed behavioral disinhibition using measures tapping substance use, conduct disorder, attention-deficit/hyperactivity disorder (ADHD), and novelty seeking at ages 12 and 17. Executive functions were assessed with laboratory-based cognitive tasks at age 17. Results indicated that, at age 12, behavioral disinhibition was dominated by ADHD and conduct problems and was highly heritable. At age 17, the contributions of the 4 components were more balanced, and the proportion of variance attributable to genetic factors was somewhat smaller, with additional variance due to shared environmental influences. At both ages, behavioral disinhibition was more closely related to response inhibition than other executive functions (working memory updating and task-set shifting), and this relationship was primarily genetic in origin. These results highlight the dynamic nature of behavioral disinhibition across adolescence and suggest that response inhibition may be an important mechanism underlying vulnerability to disinhibitory psychopathology.

Schizophrenia: genetics, prevention and rehabilitation

OBJECTIVE

Genetic factors are largely implicated in predisposing to schizophrenia. Environmental factors contribute to the onset of the disorder in individuals at increased genetic risk. Cognitive deficits have emerged as endophenotypes and potential therapeutic targets for schizophrenia because of their association with functional outcome. The aims of this review were to analyse the joint effect of genetic and environmental (G×E) factors on liability to schizophrenia and to investigate relationships between genes and cognitive endophenotypes focusing on practical applications for prevention and rehabilitation.

METHODS

Medline search of relevant studies published between 1990 and 2008.

RESULTS

In schizophrenia, examples of G×E interaction include the catechol-O-methyl transferase (COMT) (Val158Met) polymorphism, which was found to moderate the onset of psychotic manifestations in response to stress and to increase the risk for psychosis related to cannabis use, and neurodevelopmental genes such as AKT1 (serine-threonine kinase), brain-derived neurotrophic factor (BDNF), DTNBP1 (dysbindin) and GRM3 (metabotropic glutamate receptor 3), which were associated with development of schizophrenia in adulthood after exposure to perinatal obstetric complications. Neurocognitive deficits are recognised as core features of schizophrenia that facilitate the onset of the disorder and have a great impact on functional outcome. Neurocognitive deficits are also endophenotypes that have been linked to a variety of genes [COMT, neuregulin (NRG1), BDNF, Disrupted-In-Schizophrenia 1 (DISC1) and dysbindin] conferring susceptibility to schizophrenia. Recently, it has emerged that cognitive improvement during rehabilitation therapy was under control of COMT (Val158Met) polymorphism.

CONCLUSION

This review could indicate a pivotal role of psychiatric genetics in prevention and rehabilitation of schizophrenic psychoses.

Insight and executive functioning in schizophrenia: a multidimensional approach

Past research suggests that unawareness of illness in schizophrenia is associated with deficits in executive functions; however, the relationships between executive processes and the various dimensions of insight are still unclear. Recent models of executive functioning have proposed that four executive processes - inhibition, updating, shifting and dual task coordination - are moderately related yet separable. In this study, we proposed to investigate and clarify the relationships between insight dimensions and the aforementioned four executive components. A total of 60 patients were administered the Test for Attentional Performance and the Scale to Assess Unawareness of Mental Disorder. The effect of potential confounding variables such as medication, symptomatology, demography, psycho-affective state, and general processing speed were also examined in a preliminary statistical analysis. We found that both awareness of disorder and awareness of response to medication were significantly related to Updating. Awareness of the social consequences of the disease was significantly related to Updating, Divided Attention and Inhibition Processes. The analysis indicates that poor insight in schizophrenia may be partially related to executive dysfunction. Finally, our study emphasizes the possible role of neuropsychological intervention in improving patients' insight into illness.

The complex relationships between executive functions and positive symptoms in schizophrenia

BACKGROUND

Relationships between performance on various tests of executive functions and positive symptoms, especially delusions and hallucinations, have not been found consistently. This may be related to method of rating symptoms, to possible interactions between them, as well as to the low specificity of the cognitive test measures used. In this study, we have investigated the relationships between different aspects of positive symptomatology and several executive subprocesses.

METHOD

Stable schizophrenia patients (n=96) were assessed for disorganization, delusion and hallucination symptoms rated from the Scale for Assessment of Positive Symptoms and the Scale for Assessment of Negative Symptoms. Interference sensitivity, inhibition and flexibility were assessed using the Wickens paradigm. The relationships between symptom dimensions as well as with cognitive and other potentially confounding variables were assessed using Pearson correlations and (simple and partial) stepwise regressions.

RESULTS

Generally consistent with the cognitive constructs used to account for positive symptoms, the results indicated relationships between delusions, disorganization and inhibition, and between hallucinations and interference sensitivity. However, these relationships appeared more complex than expected, with some being dependent on interactions between symptoms.

CONCLUSIONS

These results suggest: (i) that the global measures usually employed may not be appropriate for demonstrating specific relationships between symptoms and executive functions and (ii) that it is necessary to take into account the interactions between positive symptoms as well as with other factors to reveal these relationships.

Neuropsychological and symptom predictors of aggression on the psychiatric inpatient service

Neuropsychological assessment of executive dysfunction may identify psychiatric patients who may be at high risk for aggressive behavior because impairment of the prefrontal cortex has been indicated as a possible anatomical correlate of aggression. No consensus, however, has been reached on the extent that executive dysfunction contributes to the formation of psychopathology and to aggressive behavior in psychiatric inpatients. We hypothesized a mediating model wherein patients' executive-functioning deficits contribute to the formation of psychopathological symptoms, which then underlies aggressive behavior. To test this model, we examined the relationship between executive functioning, psychiatric symptomatology, and aggressive behavior in 85 psychiatric inpatients presenting over an acute hospital admission using structure equation modeling techniques. The results revealed that psychiatric inpatients' executive function impairment significantly predicted the formation of psychiatric symptomatology, which in turn significantly contributed to the manifestation of aggressive behavior. Executive dysfunction also directly predicted inpatient aggressive behavior. Combining the indirect and direct effects, 59% of our inpatient aggression measure factor variance was accounted for by our measures of executive dysfunction and clinical symptom severity. These findings suggest that neurocognitive deficits underlie both psychiatric symptom formation and aggression. Patients with executive dysfunction may not possess the behavioral inhibition skills needed to cope with the presence of symptoms and other stressful events that accompany acute psychosis and hospitalization that may result, consequently, in increased manifestations of aggressive behavior.

Executive function in schizophrenia: what impact do antipsychotics have?

Cognitive dysfunction is a major component of schizophrenia, with deficits in executive function particularly pertinent to successful daily living and outcome. Executive deficits and negative/disorganised symptoms remain relatively resistant to amelioration by antipsychotic medication in comparison to positive symptoms. While there is a relative paucity of data on the effects of antipsychotics on specific executive deficits, atypical antipsychotics would appear to be more beneficial than typical antipsychotics at improving these functions, with muscarinic, glutamatergic and cholinergic systems variously implicated. Recent research focusing on the relationships between specific symptoms and specific executive deficits holds important implications for future psychopharmacological interventions in the area by elucidating the neural substrates and pathways which underpin schizophrenic symptomatology. This review attempts to evaluate the research thus far for the specific executive components of spatial working memory (SWM), inhibition, sustained attention and set shifting. Issues significant to future psychopharmacology in the area are discussed, with particular emphasis on the need for a greater consensus in methodology and definition executive function research in schizophrenia.

Variance in neurocognitive performance is associated with dysbindin-1 in schizophrenia: A preliminary study

Susceptibility genes for schizophrenia have been hypothesised to mediate liability for the disorder at least partly by influencing cognitive performance. We investigated the association between genotype and cognitive performance for a Dysbindin risk haplotype which is associated with schizophrenia in our sample. Fifty-two patients with schizophrenia or schizoaffective disorder (24 risk haplotypes carriers versus 28 non-risk haplotype carriers) were assessed in areas of cognition showing evidence of familial deficits in schizophrenia. Verbal and spatial memory, working memory, and attentional control was assessed using selected measures from the Weschler memory scale (WMS), Cambridge automated test battery (CANTAB), continuous performance test (CPT), and a simple go/no-go task. Pre-morbid IQ was also assessed using the Weschler Test of Adult Reading (WTAR). Patients carrying the Dysbindin risk haplotype showed significantly lower spatial working memory performance than patients who were non-risk carriers, with genotype explaining 12% of variance in performance. Our study suggests that the increased risk for schizophrenia associated with dysbindin may be partly mediated by its influence on pre-frontal function.

Do antisaccade deficits in schizophrenia provide evidence of a specific inhibitory function?

BACKGROUND

Despite its inhibitory control requirements, antisaccade deficits have been consistently associated with working memory impairments in schizophrenia. We investigated whether variance in antisaccade performance could be better accounted for in terms of a specific inhibitory function.

METHOD

We assessed 48 clinically stable out-patients with schizophrenia on an antisaccade task, as well as on measures of spatial and verbal working memory, sustained selective attention, and a simple motoric go/no-go measure of response inhibition.

RESULTS

In a stepwise multiple regression analysis, go/no-go task performance accounted for a considerably greater percentage of variance in antisaccade performance (25.3%) than either working memory (8.4%) or sustained selective attention task (9.1%).

DISCUSSION

We conclude that antisaccade deficits in schizophrenia appear to be better understood in terms of a specific deficit of inhibitory control than in terms of more general difficulties with context maintenance or goal neglect.