Working memory constrains abstraction in schizophrenia

Evaluation sensitivity as a moderator of communication disorder in schizophrenia

BACKGROUND

Communication disturbance (thought disorder) is a central feature of schizophrenia that predicts poor functioning. We investigated the hypothesis that memory and attention deficits interact with beliefs about the gravity of being rejected (i.e. evaluation sensitivity) to produce the symptoms of communication disorder.

METHOD

Seventy-four individuals diagnosed with schizophrenia or schizo-affective disorder completed a battery of tests assessing neurocognition (attention, working and verbal memory, abstraction), symptomatology (positive, negative and affective), functioning, and dysfunctional beliefs.

RESULTS

Patients with communication deviance (n=33) performed more poorly on the neurocognitive tests and reported a greater degree of sensitivity to rejection than patients with no thought disorder (n=41). In a logistic regression analysis, evaluation sensitivity moderated the relationship between cognitive impairment and the presence of communication disorder. This finding was independent of hallucinations, delusions, negative symptoms, depression and anxiety.

CONCLUSIONS

We propose that negative appraisals about acceptance instigate communication anomalies in individuals with a pre-existing diathesis for imperfect speech production.

Defeatist beliefs as a mediator of cognitive impairment, negative symptoms, and functioning in schizophrenia

Poor social and vocational outcomes have long been observed in schizophrenia. Two of the most consistent predictors are negative symptoms and cognitive impairment. We investigate the hypothesis that cognitive content--defeatist beliefs regarding performance--provides a link between cognitive impairment, negative symptoms, and poor functioning in schizophrenia. A total of 77 individuals (55 patients diagnosed with schizophrenia or schizoaffective disorder and 22 healthy controls) participated in a cross-sectional study of psychopathology. Tests of memory, abstraction, attention, and processing speed, as well as current psychopathology, functioning, and endorsement of defeatist beliefs, were employed. Greater neurocognitive impairment was associated with elevated defeatist belief endorsement, higher negative symptom levels, and worse social and vocational functioning. Notably, statistical modeling indicated that defeatist belief endorsements were mediators in the relationship between cognitive impairment and both negative symptoms and functioning. These effects were independent of depression and positive symptom levels. The results add to the emerging biopsychosocial understanding of negative symptoms and introduce defeatist beliefs as a new psychotherapeutic target.

Working memory in schizophrenia: a meta-analysis

BACKGROUND

Memory impairment is being recognized increasingly as an important feature of the neuropsychology of schizophrenia. Dysfunction of working memory, a system for the short-term storage and manipulation of information, may relate to a number of core symptoms of schizophrenia. Many studies have examined working memory function in schizophrenia but a clear understanding of the nature and extent of any deficit has been elusive.

METHOD

A systematic review and meta-analysis of studies comparing working memory function in subjects with schizophrenia and healthy controls was performed. Following a comprehensive literature search, meta-analyses were conducted on 36 measures of phonological, visuospatial and central executive working memory functioning, encompassing 441 separate results from 187 different studies.

RESULTS

Statistically significant effect sizes were found for all working memory measures, indicating deficits in schizophrenia groups. Some of these were robust findings in the absence of evidence of significant heterogeneity or publication bias. Meta-regression analyses showed that the working memory deficit was not simply explained by discrepancies in current IQ between schizophrenia and control groups.

CONCLUSIONS

Large deficits in working memory were demonstrated in schizophrenia groups across all three working memory domains. There were, however, no clear differences across subdomains or between particular working memory tasks. There was substantial heterogeneity across results that could only be partly explained.

Endophenotypes in schizophrenia: a selective review

BACKGROUND

Given the wealth of data in the literature on schizophrenia endophenotypes, it is useful to have one source to reference their frequency data. We reviewed the literature on disease-liability associated variants in structural and functional magnetic resonance images (MRI), sensory processing measures, neuromotor abilities, neuropsychological measures, and physical characteristics in schizophrenia patients (SCZ), their first-degree relatives (REL), and healthy controls (HC). The purpose of this review was to provide a summary of the existing data on the most extensively published endophenotypes for schizophrenia.

METHODS

We searched PubMed and MedLine for all studies on schizophrenia endophenotypes comparing SCZ to HC and/or REL to HC groups. Percent abnormal values, generally defined as >2 SD from the mean (in the direction of abnormality) and/or associated effect sizes (Cohen's d) were calculated for each study.

RESULTS

Combined, the articles reported an average 39.4% (SD=20.7%; range=2.2-100%) of abnormal values in SCZ, 28.1% (SD=16.6%; range=1.6-67.0%) abnormal values in REL, and 10.2% (SD=6.7%; range=0.0-34.6%) in HC groups.

CONCLUSIONS

These findings are reviewed in the context of emerging hypotheses on schizophrenia endophenotypes, as well as a discussion of clustering trends among the various intermediate phenotypes. In addition, programs for future research are discussed, as instantiated in a few recent large-scale studies on multiple endophenotypes across patients, relatives, and healthy controls.

Is executive impairment associated with schizophrenic syndromes? A meta-analysis

BACKGROUND

A key neuropsychological proposal in schizophrenia is that negative and disorganization symptoms are associated with different patterns of impairment on executive tasks.

METHOD

Studies reporting correlations between positive, negative or disorganization symptoms and any type of executive test were meta-analysed. The influence of moderating factors was also examined, including age, treatment and stage of illness and whether symptoms were relapsing or persistent. The magnitudes of the correlations were compared with those for general intellectual impairment.

RESULTS

Pooled correlations between executive impairment and both negative symptoms and disorganization were significant in the small-to-moderate range. That for positive symptoms ('reality distortion'), however, was close to zero. The pattern of correlations among different executive tests differed significantly for negative symptoms and disorganization. Patients with stable clinical pictures showed significantly higher correlations with executive impairment than those with relapsing and remitting illnesses. Both negative symptoms and disorganization also correlated significantly with general intellectual function as indexed by current IQ.

CONCLUSIONS

Meta-analysis supports the view that negative symptoms and disorganization are associated with partially dissociable patterns of executive impairment. However, co-existent general intellectual impairment has been an important confounding factor in the studies to date.

The Wisconsin Card Sorting impairment in schizophrenia is evident in the first four trials

BACKGROUND

Schizophrenia (SZ) patients' low scores on the Wisconsin Card Sorting Test (WCST) are often attributed to frequent perseverative errors, a pattern typically interpreted as a failure to shift from previously rewarded behavior in response to negative feedback. In this study we tested the hypothesis that SZ patients, due to dysregulated error-processing mechanisms, are more fundamentally impaired in their on-line, trial-to-trial use of feedback to guide behavior.

METHODS

Analysis of archival WCST data from 145 adults with schizophrenia and 80 healthy comparison subjects.

RESULTS

Schizophrenia patients' impaired use of negative feedback was evident on the first four WCST cards, where they were significantly less accurate than comparison subjects. Performance on these early cards significantly predicted overall task success as indexed by categories completed and proportion of perseverative errors.

CONCLUSIONS

Patients' poor performance on pre-shift WCST trials likely reflects a fundamental impairment in the ability to use feedback to guide behavior. Recent data from both humans and primates suggest that reward-based learning processes like those employed in the WCST are driven by phasic changes in midbrain dopamine activity. It might, therefore, be possible to interpret higher order executive dysfunction in schizophrenia as a manifestation of altered DA signaling.

Suboptimal processing strategy and working-memory impairments predict abstraction deficit in schizophrenia

We studied the relationship between abstraction and other, more basic, cognitive functions in 78 schizophrenia patients and 57 healthy controls. Patients' performance was impaired compared to that of healthy individuals. Regression analysis showed significant contributions of task latency, spatial working memory, and verbal working memory to abstraction performance. The model explained 56.9% of the variance. The latency contribution included linear and quadratic components indicating optimal strategies for normal abstraction performance. Abnormal (suboptimal) processing strategies and working-memory dysfunctions predict impaired abstraction in schizophrenia. The model presented may enable differentiation between impaired and compensating components in schizophrenia patients with an abstraction deficit.

The neurocognitive signature of psychotic bipolar disorder

BACKGROUND

Psychotic bipolar disorder may represent a neurobiologically distinct subgroup of bipolar affective illness. We sought to ascertain the profile of cognitive impairment in patients with bipolar disorder and to determine whether a distinct profile of cognitive deficits characterizes bipolar patients with a history of psychosis.

METHODS

Sixty-nine outpatients with bipolar I disorder (34 with a history of psychotic symptoms and 35 with no history of psychosis) and 35 healthy comparison subjects underwent a comprehensive neurocognitive battery. All three groups were demographically matched.

RESULTS

Despite preserved general intellectual function, bipolar I patients overall showed moderate impairments on tests of episodic memory and specific executive measures (average effect size = .58), and moderate to severe deficits on attentional and processing speed tasks (average effect size = .82). Bipolar I patients with a history of psychosis were impaired on measures of executive functioning and spatial working memory compared with bipolar patients without history of psychosis.

CONCLUSIONS

Psychotic bipolar disorder was associated with differential impairment on tasks requiring frontal/executive processing, suggesting that psychotic symptoms may have neural correlates that are at least partially independent of those associated with bipolar I disorder more generally. However, deficits in attention, psychomotor speed, and memory appear to be part of the broader disease phenotype in patients with bipolar disorder.

Cognitive, neurophysiological, and functional correlates of proverb interpretation abnormalities in schizophrenia

A hallmark of schizophrenia is impaired proverb interpretation, which could be due to: (1) aberrant activation of disorganized semantic associations, or (2) working memory (WM) deficits. We assessed 18 schizophrenia patients and 18 normal control participants on proverb interpretation, and evaluated these two hypotheses by examining within patients the correlations of proverb interpretation with disorganized symptoms and auditory WM, respectively. Secondarily, we also explored the relationships between proverb interpretation and a spectrum of cognitive functions including auditory sensory-memory encoding (as indexed by the mismatch negativity (MMN) event-related brain potential (ERP)); executive function; and social/occupational function. As expected, schizophrenia patients produced less accurate and less abstract descriptions of proverbs than did controls. These proverb interpretation difficulties in patients were not significantly correlated with disorganization or other symptom factors, but were significantly correlated (p < .05) with WM impairment, as well as with impairments in sensory-memory encoding, executive function, and social/occupational function. These results offer no support for disorganized associations in abnormal proverb interpretation in schizophrenia, but implicate WM deficits, perhaps as a part of a syndrome related to generalized frontal cortical dysfunction.

Evidence for disruption in prefrontal cortical functions in juvenile bipolar disorder

OBJECTIVES

Systematic parsing of executive function processes is critical for the development of more specific models of neurobiological processes mediating disturbed cognition in youth with bipolar disorder (BPD).

METHODS

A sample of 33 children and adolescents with bipolar I disorder (BPD I) (mean age 12.1 +/- 3.0 years, 39% female) and 44 demographically matched healthy participants (mean age 12.9 +/- 2.8 years, 50% female) completed a neurocognitive battery including measures aimed at detection of disruption in prefrontal cortical circuitry (i.e., working memory, set shifting, and rule attainment).

RESULTS

Compared to healthy controls, BPD I children exhibited significant deficits in spatial working memory, visual sequencing and scanning, verbal fluency and abstract problem solving, particularly when a memory component was involved. In our spatial delayed response task, memory set size was parametrically varied; the performance pattern in BPD I children suggested deficits in short-term memory encoding and/or storage, rather than capacity limitations in spatial working memory. Earlier age at onset of illness and antipsychotic medication usage were associated with poorer performance on speeded information-processing tasks; however, severity of mood symptomatology and comorbidity with disruptive behavior disorders were not associated with task performance.

CONCLUSIONS

These results suggest impairment in measures of prefrontal cortical function in juvenile BPD I that are similar to those seen in the adult form of the illness, and implicate both the ventral and dorsolateral prefrontal cortex as loci of pathology in juvenile BPD. As these deficits were not associated with clinical state or comorbidity with other disorders, they may reflect trait-related impairments, a hypothesis that will be pursued further in longitudinal studies.

Adjudicating neurocognitive endophenotypes for schizophrenia

Although genetic influences on schizophrenia are well established, localization of the genes responsible for this illness has proven extremely difficult. Given evidence that genes predisposing to schizophrenia may be transmitted without expression of the clinical phenotype, efforts have focused on developing endophenotypes. While several neuropsychological measures have been proposed to be endophenotypes, few studies have systematically assessed batteries of neurocognitive tests to determine which tests are most sensitive to liability for the illness. Two hundred sixty-nine Latino individuals were administered a standard neuropsychological battery. Two hundred fourteen of these were members of families with at least two siblings diagnosed with schizophrenia or schizoaffective disorder. The remaining were community controls without history of major psychiatric illness. Neurocognitive measures found to be heritable were entered into analyses designed to determine which tests covary with the degree of genetic relationship to affected individuals. Although five measures were found to uniquely model genetic liability for schizophrenia, digit symbol coding was the most sensitive. To assess the specificity of these endophenotypes, performance on these measures were compared to family members with bipolar and unipolar affective disorders. These markers clearly distinguished between individuals with psychotic illnesses and those with major depression. As measures contributed uniquely to discriminate individuals at varying risk for schizophrenia, our findings imply multiple independently inherited elements to the liability for the illness. We present a practical model for adjudicating endophenotypes and determining which measures are best suited for use in linkage analyses.

Fronto-cerebellar systems are associated with infant motor and adult executive functions in healthy adults but not in schizophrenia

Delineating longitudinal relationships between early developmental markers, adult cognitive function, and adult brain structure could clarify the pathogenesis of neurodevelopmental disorders such as schizophrenia. We aimed to identify brain structural correlates of infant motor development (IMD) and adult executive function in nonpsychotic adults and to test for abnormal associations between these measures in people with schizophrenia. Representative samples of nonpsychotic adults (n = 93) and people with schizophrenia (n = 49) were drawn from the Northern Finland 1966 general population birth cohort. IMD was prospectively assessed at age 1 year; executive function testing and MRI were completed at age 33-35 years. We found that earlier motor development in infancy was correlated with superior executive function in nonpsychotic subjects. Earlier motor development was also normally associated with increased gray matter density in adult premotor cortex, striatum, and cerebellum and increased white matter density in frontal and parietal lobes. Adult executive function was normally associated with increased gray matter density in a fronto-cerebellar system that partially overlapped, but was not identical to, the gray matter regions normally associated with IMD. People with schizophrenia had relatively delayed IMD and impaired adult executive function in adulthood. Furthermore, they demonstrated no normative associations between fronto-cerebellar structure, IMD, or executive function. We conclude that frontal cortico-cerebellar systems correlated with adult executive function are anatomically related to systems associated with normal infant motor development. Disruption of this anatomical system may underlie both the early developmental and adult cognitive abnormalities in schizophrenia.

Distinguishing neurocognitive functions in schizophrenia using partially ordered classification models

Current methods for statistical analysis of neuropsychological test data in schizophrenia are inherently insufficient for revealing valid cognitive impairment profiles. While neuropsychological tests aim to selectively sample discrete cognitive domains, test performance often requires several cognitive operations or "attributes." Conventional statistical approaches assign each neuropsychological score of interest to a single attribute or "domain" (e.g., attention, executive, etc.), and scores are calculated for each. This can yield misleading information about underlying cognitive impairments. We report findings applying a new method for examining neuropsychological test data in schizophrenia, based on finite partially ordered sets (posets) as classification models. A total of 220 schizophrenia outpatients were administered the Positive and Negative Symptom Scale (PANSS) and a neuropsychological test battery. Selected tests were submitted to cognitive attribute analysis a priori by two neuropsychologists. Applying Bayesian classification methods (posets), each patient was classified with respect to proficiency on the underlying attributes, based upon his or her individual test performance pattern. Twelve cognitive "classes" are described in the sample. Resulting classification models provided detailed "diagnoses" into "attribute-based" profiles of cognitive strength/weakness, mimicking expert clinician judgment. Classification was efficient, requiring few measures to achieve accurate classification. Attributes were associated with PANSS factors in the expected manner (only the negative and cognition factors were associated with the attributes), and a double dissociation was observed in which divergent thinking was selectively associated with negative symptoms, possibly reflecting a manifestation of Kraepelin's hypothesis regarding the impact of volitional disturbances on thought. Using posets for extracting more precise cognitive information from neuropsychological data may reveal more valid cognitive endophenotypes, while dramatically reducing the amount of testing required.

Impaired working speed and executive functions as frontal lobe dysfunctions in young first-degree relatives of schizophrenic patients

The aim of the investigation was to detect neuropsychological markers, such as sustained and selective attention and executive functions, which contribute to the vulnerability to schizophrenia especially in young persons. Performance was assessed in 32 siblings and children of schizophrenic patients and 32 matched controls using Wisconsin Card Sorting Test, Colour-Word-Interference-Test, Trail Making Test, and d2-Concentration-Test. The first-degree relatives showed certain impairments on all four tests, in particular, slower times on all time-limited tests. These results suggest the need for more time when completing neuropsychological tasks involving selected and focused attention, as well as cognitive flexibility, as a possible indicator of genetic vulnerability to schizophrenia.

Project among African-Americans to explore risks for schizophrenia (PAARTNERS): recruitment and assessment methods

The Project among African-Americans to Explore Risks for Schizophrenia (PAARTNERS) is a multi-site, NIMH-funded study that seeks to identify genetic polymorphisms that confer susceptibility to schizophrenia among African-Americans by linkage mapping and targeted association analyses. Because deficits in certain dimensions of cognitive ability are thought to underlie liability to schizophrenia, the project also examines cognitive abilities in individuals affected by schizophrenia and their extended family members. This article describes PAARTNERS study design, ascertainment methods and preliminary sample characteristics. We aim to recruit a sample of 1260 African-American families, all of whom have at least one proband with schizophrenia or schizoaffective disorder. The data collection protocol includes a structured Diagnostic Interview for Genetic Studies, Family Interview for Genetic Studies, focused neurocognitive assessment, medical records review, and the collection of blood or buccal cells for genetic analyses. We have currently completed study procedures for 106 affected sib-pair, 457 case-parent trio and 23 multiplex families. A total of 289 probands have completed the best estimate final diagnosis process and 1153 probands and family members have been administered the computerized neuropsychological battery. This project lays the foundation for future analysis of cognitive and behavioral endophenotypes. This novel integration of diagnostic, neurocognitive and genetic data will also generate valuable information for future phenotypic and genetic studies of schizophrenia.

Deviant Strategy on the Modified Six Elements Test in Patients with Schizophrenia

Impaired executive functioning is found in a considerable proportion of schizophrenia patients. Neuropsychological tests are originally designed to measure the behavior of neurological patients and may therefore miss psychiatry-related cognitive deficits. Qualitative information on tests for executive functioning is important in psychiatric populations. The Modified Six Elements Test (MSET) is a planning test that consists of 6 tasks, for which subjects have limited time and have to obey to switching rules. This study concerns a qualitatively different approach schizophrenia patients use on the MSET, and its relationship with cognitive measures. MSET scores and strategies of schizophrenia patients were compared to those of healthy controls, closed-head-injury patients, and peripheral injury patients. Also, schizophrenia patients and healthy controls were compared on verbal memory and vigilance. Schizophrenia patients finish fewer assignments on the MSET, receive a lower profile score compared to healthy controls, and use a different strategy on the test compared to the other groups. They also perform below healthy controls on the tests for verbal memory and vigilance. Use of the different strategy in schizophrenia patients was related to impaired cognitive functioning. An interesting strategy used by schizophrenia patients on the MSET appears to be indicative of impaired cognitive functioning. This strategy may be a compensatory strategy to spare cognitive resources. It could also be the result of a concrete interpretation of the test instructions.

Infant motor development is associated with adult cognitive categorisation in a longitudinal birth cohort study

BACKGROUND

The relationship between the age of reaching infant developmental milestones and later intellectual function within the normal population remains unresolved. We hypothesised that the age of learning to stand in infancy would be associated with adult executive function and that the association would be apparent throughout the range of abilities, rather than confined to extremes.

METHODS

The Northern Finland 1966 Birth Cohort is based upon 12,058 live-born children in a geographic and temporally defined population. Information on age at learning to stand without support was obtained at one year. At age 33-35 a random sample of 104 subjects underwent a neuropsychological test battery including tests of executive function (cognitive categorisation), visuo-spatial memory, verbal learning and visual object learning. We investigated associations between developmental data and adult neuropsychological test scores.

RESULTS

There was a significant linear relationship between age of learning to stand and adult categorisation: the earlier the attainment of the milestone, the better was the categorisation. No such relationships were observed between infant neurodevelopment and adult cognition in other neuropsychological domains.

CONCLUSION

Even within the normal range of development, early development in the gross motor domain is associated with better adult executive function (in tests of categorisation). Investigation of the determinants and sequelae of normal neural development will facilitate research into a variety of neurodevelopmental disorders.

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

INTRODUCTION

Although deficits in executive functioning in schizophrenia have been consistently reported, their precise relationship to symptomatology remains unclear. Recent approaches to executive functioning in nonschizophrenia studies have aimed to "fractionate" the individual cognitive processes involved. In this study, we hypothesised that if these processes are fractionable, then particular symptom syndromes may be selectively related to executive deficits. In particular, it was hoped that this approach could clarify whether negative and positive symptoms of schizophrenia are differentially related to particular aspects of executive/attentional functions.

METHODS

A total of 32 patients with schizophrenia and 16 matched controls were assessed on a series of tasks designed to tap the theoretically derived executive functions of Inhibition, Shifting set, Working memory, and Sustained attention.

RESULTS

Negative symptoms were significantly predicted by performance on an "Inhibition" task (Stroop), and not by performance on any other task. Furthermore, for a subgroup of patients with predominantly negative symptoms variance in positive symptoms was only significantly predicted by performance on a set-shifting task (Visual Elevator), and not by performance on other tasks, including inhibition.

CONCLUSIONS

Our results support the contention that negative symptoms can, at least partly, be conceived of as cognitive behaviours expressing specific executive deficits. Specifically, we discuss the possibility that negative symptoms may, in part, express a failure in response monitoring. We further suggest that the disordered metacognition resulting in positive symptoms may be mediated by cognitive flexibility in patients with a predominantly negative symptom profile.

Infant motor development and adult cognitive functions in schizophrenia

BACKGROUND

Childhood neuromotor dysfunction is a risk factor for schizophrenia, a disorder in which cognitive deficits are prominent. The relationship between early neurodevelopment and adult cognition in schizophrenia remains unclear.

METHODS

We examined the associations between infant motor development and adult cognitive functions in schizophrenia (n = 61) and the general population (n = 104) in a sample drawn from the The Northern Finland 1966 Birth Cohort. Data on ages of learning to stand and walk with or without support were obtained at age 12 months by health visitor assessment. Neurocognitive measures at age 33-35 included executive function, verbal and visual episodic memory, and visuo-spatial working memory.

RESULTS

The schizophrenia group achieved neuromotor milestones later and performed significantly worse than the control group on all measures of cognition. In pooled analyses there were associations between infant motor development and adult cognition in the domains of executive function, verbal learning and visuospatial working memory, but not in visual object learning. The pattern of associations between development and cognition was similar in schizophrenia and the general population.

CONCLUSIONS

These findings are consistent with the hypothesis that in schizophrenia mild infant motor developmental delay and adult cognitive deficits (at least in some domains) are age dependent manifestations of the same underlying neural process. Thus, they may be better considered as part of a single longitudinal syndrome.

A double-blind, cross-over comparison of the effects of amantadine or placebo on visuomotor and cognitive function in medicated schizophrenia patients

The present study aimed to test the hypothesis that dopamine agonists may enhance cognitive function. The effect of amantadine on neuropsychological function in medicated schizophrenia patients was investigated. The study comprised an add-on, double-blind, placebo-controlled, cross-over 6-week trial. Participants comprised 29 inpatients at Sha'ar Menashe Mental Health Center who were diagnosed with chronic schizophrenia or schizoaffective disorder. Amantadine 200 mg/day or identical placebo was added to ongoing antipsychotic treatment for 3 weeks. Study medications were then switched for an additional 3 weeks. Assessments were performed at baseline, and weeks 3 and 6, including cognitive and visuomotor assessments. Clinical ratings included positive, negative and depressive symptoms and extrapyramidal side-effects. Blood prolactin levels were assayed. A mixed model was used to examine differences in the data at the three assessment points. Amantadine was associated with improved visuomotor coordination compared to placebo. No significant changes in cognitive functions were noted. Clinical symptoms, extrapyramidal side-effects and blood prolactin levels were not altered. Amantadine improved visuomotor coordination independently of extrapyramidal side-effects but not cognitive function. Because prolactin concentrations were unchanged, the mechanism is more likely to involve glutaminergic NMDA than dopaminergic mechanisms. Further studies of amantadine with different doses and treatment duration, as well as more glutamate selective agents such as memantine, are indicated.

[One decade of functional imaging in schizophrenia research. From visualisation of basic information processing steps to molecular-genetic oriented imaging]

Modern neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) have contributed tremendously to our current understanding of psychiatric disorders in the context of functional, biochemical and microstructural alterations of the brain. Since the mid-nineties, functional MRI has provided major insights into the neurobiological correlates of signs and symptoms in schizophrenia. The current paper reviews important fMRI studies of the past decade in the domains of motor, visual, auditory, attentional and working memory function. Special emphasis is given to new methodological approaches, such as the visualisation of medication effects and the functional characterisation of risk genes.

Insight into illness in schizophrenia

Lack of insight of patients with schizophrenia into various aspects of their illness and treatment is an important clinical issue. Poor insight has been reported to be associated with neurocognitive deficits, particularly in the frontal and parietal functions. The aim of this study was to examine relationships between insight and cognitive and emotional function in patients with schizophrenia. Thirty-five male forensic patients suffering from chronic schizophrenia participated. The Scale for the Assessment of Unawareness of Mental Disorder was used to assess insight. Neuropsychological function was assessed with a comprehensive battery of tests. Clinical state was also assessed. Of 35 patients, 18 (51%) believed that they had a mental disorder. A similar proportion reported awareness of a need for medication and correctly attributed symptoms to illness. Measures of insight showed significant associations with visual object learning, verbal working memory, and identification of facial emotions but not with measures of frontal lobe function. Poorer insight was associated with a higher occurrence of violent events. Our findings support an association between poor insight and cognitive impairment in patients with chronic schizophrenia but suggest that the relationship may not specifically involve frontal lobe dysfunction.

A Meta-Analysis of Cognitive Deficits in Adults with a Diagnosis of Schizophrenia

This review identified 1275 studies examining cognitive deficits in people with schizophrenia, published between 1990 and 2003. Data from 113 studies (4365 patients and 3429 controls) were combined in a meta-analysis carried out on the five cognitive domains of IQ, memory, language, executive function, and attention. Studies were excluded where they lacked a suitable control group or failed to present complete information. In all five cognitive domains, analysis indicated a consistent trend for patients to perform more poorly than healthy controls, with significant heterogeneity across studies. Sources of heterogeneity were analyzed and a need to ensure more appropriate composition of patient and control groups and to adopt a more refined and methodologically correct, hypothesis-driven approach was identified.

Negative attitude towards medication is associated with working memory impairment in schizophrenia patients

A lack of insight into illness and negative attitudes towards medication are common among individuals with schizophrenia and impact clinical outcomes. This study aimed to examine the relationships between attitudes towards medication and cognitive function in schizophrenia patients. Thirty-five male forensic inpatients who were suffering from chronic schizophrenia participated in the study. A drug attitude inventory was used to evaluate the attitudes of the patients towards medication. Neuropsychological function was assessed with a comprehensive battery of tests. Patients with positive attitudes towards medication performed significantly better than those with negative attitudes on tests of verbal working memory (digit span forwards and backwards), inhibition and set shifting (Penn Inhibition test), delayed object memory and overall mental status (Mini Mental State Examination). There were no differences in age, education, hospitalizations or clinical symptoms between the groups. Our findings support an association between negative attitudes towards medication and poor cognitive performance, particularly of working memory.

Targeting synapses and myelin in the prevention of schizophrenia

Many of the functions that are mediated by the prefrontal cortex (PFC) are severely impaired in schizophrenia. The maturation of these functions takes place during late adolescence and early adulthood, which coincides with the period of time when overt symptomatology of schizophrenia most commonly emerges. Two developmental processes occurring during the periadolescence period appear to mediate the functional maturation of the PFC: pruning of exuberant synapses and myelination of axons. It has long been speculated in the literature that disturbances of these processes may result in dysfunction of the PFC and thereby trigger the emergence of symptoms and deficits of schizophrenia. Alternatively, but not mutually exclusively, it has also been suggested that these late developmental processes may not be aberrant but they "unmask" preexisting deficits in the PFC, resulting in the onset of symptoms. The important implication of both of these scenarios is that in either case the emergence of PFC functional disturbances and the onset of symptoms and deficits of schizophrenia would in theory be preventable by pharmacologic manipulation of the synaptic pruning and/or axonal myelination processes. Thus, better understanding of the cellular and molecular mechanisms that mediate these processes will provide truly novel insight into the therapeutics and prevention of schizophrenia.

Working memory functioning in schizophrenia patients and their first-degree relatives: cognitive functioning shedding light on etiology

There is accumulating evidence for involvement of the prefrontal cortex (PFC) in the pathophysiology of schizophrenia. A primary function supported by the PFC is working memory (WM). Findings from WM studies in schizophrenia can provide insight into the nature of clinical symptoms and cognitive deficits associated with this disorder, as well as begin to suggest areas of underlying neuropathology. To date, studies have not adequately investigated different WM domains (e.g., verbal, spatial, or object) or processing requirements (e.g., maintenance, monitoring, or manipulation), shown to be associated with distinct patterns of neural activation, in schizophrenia patients and their well relatives. Accordingly, this study evaluated the performance of schizophrenia patients, their first-degree biological relatives, and nonpsychiatric controls on a comprehensive battery of WM tasks and investigated the association among WM deficits and schizophrenia-spectrum psychopathology. The findings indicate that schizophrenia patients are consistently impaired on WM tasks, irrespective of WM domain or processing requirements. In contrast, their unaffected relatives are only impaired on WM tasks with higher central executive processing requirements. This pattern of WM performance may further implicate DLPFC dysfunction in the liability for schizophrenia and has implications for future cognitive, genetic, and neurodevelopmental research.

Working Memory Impairments in Schizophrenia: A Meta-Analysis

Working memory (WM) deficit is a cardinal cognitive symptom of schizophrenia, but the differences among the tasks and measures used to assess WM make it difficult to compare across studies. The authors conducted a meta-analytic review to address 3 major questions: (a) Do patients with schizophrenia show WM deficits across diverse methodology; (b) Is WM deficit supramodal; and (c) Does the WM deficit worsen with longer delays? The results indicate that significant WM deficit was present in schizophrenia patients in all modalities examined. Increasing delay beyond 1 s did not influence the performance difference between schizophrenia patients and healthy control participants in WM. These results suggest that WM deficit in schizophrenia is modality independent and that encoding and/or early part of maintenance may be problematic.

Do schizophrenia patients make more perseverative than non-perseverative errors on the Wisconsin Card Sorting Test? A meta-analytic study

The Wisconsin Card Sorting Test (WCST) is widely used to explore executive functions in patients with schizophrenia. Among other findings, a higher number of perseverative errors has been suggested to implicate a deficit in task switching and inhibitory functions in schizophrenia. Many studies of patients with schizophrenia have focused on perseverative errors as the primary performance index in the WCST. However, do schizophrenia patients characteristically make more perseverative than non-perseverative errors compared with healthy controls? We reviewed the literature where schizophrenia patients were engaged in the WCST irrespective of the primary goal of the study. The results showed that while both schizophrenia patients and healthy participants made more perseverative than non-perseverative errors, the contrast between perseverative and non-perseverative errors is higher in schizophrenia patients only at a marginal level of significance. This result suggests that schizophrenia patients do make a comparable number of non-perseverative errors and cautions against simplistic interpretation of poor performance of schizophrenia patients in WCST as entirely resulting from impairment in set-shifting or inhibitory functions.

Wisconsin Card Sorting Test performance in schizophrenia: the role of working memory

Schizophrenia typically results in reduced performance on the Wisconsin Card Sorting Test (WCST). In the current study, we used a variety of approaches to examine the role of working memory (WM) in this deficit. One approach was to examine patterns of perseverative and non-perseverative errors. A second approach involved the comparison of the standard WCST to a modified version that used visual cues to reduce demands on WM. A third approach was to quantify the impact of WM demands on performance on a trial by trial basis. Consistent with theories of WM, the schizophrenia group showed increases in both perseverative and non-perseverative errors and differences between individuals with schizophrenia and controls were largest when WM demands were high. The visual cues helped the schizophrenia group overcome the high WM demands of the test, although they did not reduce the impairment in terms of standard scoring procedures. All impairments disappeared, however, after controlling for group differences on a measure of the speed of encoding information in WM. The pattern of results supports the conclusion that WM impairment contributes to poor performance on the WCST in individuals with schizophrenia, with additional evidence that this impairment results from generalized slowing of information processing.

Spatial working memory performance in patients with schizoaffective psychosis versus schizophrenia: a tale of two disorders?

We explored the relationship between schizophrenia and schizoaffective disorder by comparing the two patient groups in terms of their performance on measures of executive functioning (spatial working memory and Wisconsin Card Sorting Test). Patients with schizophrenia (N=34) and those with schizoaffective disorder (N=23) performed significantly poorer than community controls (N=30). However, the schizoaffective and schizophrenia groups did not differ from each other in terms of working memory accuracy or mean response latencies. Similarly, the two patient groups did not differ in terms of the number of categories achieved or number of perseverative errors on the Wisconsin Card Sorting Test. Among the patients, working memory accuracy was associated with number of WCST perseverative errors and number of categories achieved, though working memory performance was not associated with number of WCST nonperseverative errors. These findings indicate that both schizophrenia and schizoaffective disorder are associated with executive functioning deficits. The findings are discussed in the context of the ongoing debate regarding the conceptualization of schizoaffective disorder.