The neuropsychology of schizophrenia: relations with clinical and neurobiological dimensions

Verbal fluency in schizophrenia: The role of semantic clustering in category instance generation

The aim of this study was to determine whether schizophrenic patients' impairment in semantic verbal fluency tasks is due to difficulties in organizing their search or, in other words, in organizing output in terms of clusters of meaningfully related words. Consecutive association of words belonging to subcategories of the semantic task was defined as semantic clustering. A categorical verbal fluency task was first administered to 100 healthy subjects and then to 22 schizophrenic patients and 22 healthy subjects matched for sex, age and education. In the normal population, semantic clustering was found to be involved in word generation. A large number of semantic clusters indicated efficient organization of semantic knowledge and led to better word production. Schizophrenic patients showed impaired verbal fluency and generated a smaller number of semantic clusters than the control subjects. These findings point to a defect in self-initiation of semantic categorization in schizophrenia.

Computerized assessment of cognition in schizophrenia: Promises and pitfalls of CANTAB

Objective

Over the last decade, the Cambridge Neuropsychological Test Automated Battery (CANTAB), which comprises visuo-spatial tasks, has been utilized in cognitive studies of schizophrenia. A clear approach concerning the usage of CANTAB for the appraisal of neurocognitive dysfunction in schizophrenia is currently lacking.

Method

In this paper, we have first reviewed the overall applications of CANTAB and then evaluated methodological strengths and weaknesses of CANTAB as a neurocognitive battery for schizophrenia. We carried out a systematic search and assessment of studies where CANTAB was utilized to measure cognitive function in schizophrenia. We have also attempted to quantify the available data and perform a meta-analysis, but this approach turned out to be still premature.

Results

CANTAB has enabled researchers to highlight significant deficits affecting broad cognitive domains in schizophrenia, such as working memory, decision-making, attention, executive functions and visual memory. So far, the most consistent deficit observed with CANTAB testing has been attentional set-shifting, suggestive of fronto-striatal dysfunctions. In addition, preliminary evidence points towards the potential use of CANTAB to identify cognitive predictors of psychosocial functioning, to describe the relationships between symptoms and cognition, and to measure the impact of pharmacological agents on cognitive functioning.

Conclusion

CANTAB has been used successfully to highlight the range of visuo-spatial cognitive deficits in schizophrenia, producing similar results to those obtained with some traditional neuropsychological tests. Further studies validating the use of CANTAB following the standard set by Measurement And Treatment Research to Improve Cognition in Schizophrenia (MATRICS) are warranted.

Meta-Analysis of the Effects of Computerized Cognitive Training on Executive Functions: a Cross-Disciplinary Taxonomy for Classifying Outcome Cognitive Factors

The growing prevalence of neurodegenerative disorders associated with aging and cognitive decline has generated increasing cross-disciplinary interest in non-pharmacological interventions, such as computerized cognitive training (CCT), which may prevent or slow cognitive decline. However, inconsistent findings across meta-analytic reviews in the field suggest a lack of cross-disciplinary consensus and on-going debate regarding the benefits of CCT. We posit that a contributing factor is the lack of a theoretically-based taxonomy of constructs and representative tasks typically used. An integration of the Cattell-Horn-Carroll (CHC) taxonomy of broad and narrow cognitive factors and the Miyake unity-diversity theory of executive functions (EF) is proposed (CHC-M) as an attempt to clarify this issue through representing and integrating the disciplines contributing to CCT research. The present study assessed the utility of this taxonomy by reanalyzing the Lampit et al. (2014) meta-analysis of CCT in healthy older adults using the CHC-M framework. Results suggest that: 1) substantively different statistical effects are observed when CHC-M is applied to the Lampit et al. meta-analytic review, leading to importantly different interpretations of the data; 2) typically-used classification practices conflate Executive Function (EF) tasks with fluid reasoning (Gf) and retrieval fluency (Gr), and Attention with sensory perception; and 3) there is theoretical and practical advantage in differentiating attention and working-memory tasks into the narrow shifting, inhibition, and updating EF domains. Implications for clinical practice, particularly for our understanding of EF are discussed.

Validation of the cognitively normal range and below normal range subtypes in chronically hospitalized patients with schizophrenia

Background

Many studies have found a substantial minority of patients whose performance puts them within the normal range of neuropsychological functioning. Recently, a study has seen the delineation of two neurocognitive subtypes of schizophrenia –‘cognitively normal range’ (CNR) and ‘below normal range’ (BNR) – based on neurocognitive performance across multiple domains.

Methods

The participants were from two studies that collected neurocognitive, psychopathology and social function data between 2008 and 2015. In total the complete data from one hundred and thirty one patients of Han Chinese ethnicity with schizophrenia were collected on 21 neurocognitive indexes (assessing the domains of processing speed, attention, working memory, verbal memory, visual memory, reasoning and problem solving and IQ). Fifty-five patients of the one hundred and thirty one participants received additional ratings on their psychopathology and social functions. An exploratory graphic analysis was conducted on the neurocognitive measures for the entire sample. Difference analyses were also performed according to the aims of the study using the Independent t test, Chi-square test, and Cohen's d effect size.

Results

Analyses revealed the existence of two patients subtypes. The post hoc tests showed that there were significant differences on all of their neurocognitive measures and on most of the psychopathology and social functions between the two subtypes. These two subtypes could be referred to as the CNR subtype and the BNR subtype respectively.

Conclusions

There are neurocognitive subtypes of schizophrenia with differential illness characteristics comparable with the CNR and the BNR in patients of Han Chinese ethnicity with schizophrenia.

Correlation of neurological soft signs and neurocognitive performance in first episode psychosis

Neurological soft signs and neurocognitive impairments are commonly observed in first episode psychosis but the correlation of these factors remains controversial. Here, we evaluated 30 patients with remitted first episode psychosis and 30 healthy controls for the presence and severity of neurological soft signs (using the Neurological Evaluation Scale--NES) and for neurocognitive impairments (using seven subtests of the Cambridge Neuropsychological Test Automated Battery--CANTAB). NES score was higher in patients compared to controls. Neurocognitive impairment was evident in patients in the following domains: working memory, spatial recognition memory, attention set shifting, planning and inhibition. The NES revealed significant correlations with spatial working memory performance and Intra-Extra Dimensional Set Shifting (as a component of executive function). These correlations were observed both in patients and in controls. Planning and inhibition showed correlation with the total NES score and the sequencing of complex motor acts in both groups. In addition, spatial span and spatial recognition memory showed significant correlation with total NES score and the sequencing of complex motor acts in controls. The correlation between sequencing of complex motor acts and specific domains of neurocognitive tasks suggests that similar neuroanatomical substrates might be implicated in these processes.

Mood and cognition in healthy older European adults: the Zenith study

BACKGROUND

The study aim was to determine if state and trait intra-individual measures of everyday affect predict cognitive functioning in healthy older community dwelling European adults (n = 387), aged 55-87 years.

METHODS

Participants were recruited from centres in France, Italy and Northern Ireland. Trait level and variability in positive and negative affect (PA and NA) were assessed using self-administered PANAS scales, four times a day for four days. State mood was assessed by one PANAS scale prior to assessment of recognition memory, spatial working memory, reaction time and sustained attention using the CANTAB computerized test battery.

RESULTS

A series of hierarchical regression analyses were carried out, one for each measure of cognitive function as the dependent variable, and socio-demographic variables (age, sex and social class), state and trait mood measures as the predictors. State PA and NA were both predictive of spatial working memory prior to looking at the contribution of trait mood. Trait PA and its variability were predictive of sustained attention. In the final step of the regression analyses, trait PA variability predicted greater sustained attention, whereas state NA predicted fewer spatial working memory errors, accounting for a very small percentage of the variance (1-2%) in the respective tests.

CONCLUSION

Moods, by and large, have a small transient effect on cognition in this older sample.

Neural structures underlying set-shifting: roles of medial prefrontal cortex and anterior cingulate cortex

Impaired attentional set-shifting and inflexible decision-making are problems frequently observed during normal aging and in several psychiatric disorders. To understand the neuropathophysiology of underlying inflexible behavior, animal models of attentional set-shifting have been developed to mimic tasks such as the Wisconsin Card Sorting Task (WCST), which tap into a number of cognitive functions including stimulus-response encoding, working memory, attention, error detection, and conflict resolution. Here, we review many of these tasks in several different species and speculate on how prefrontal cortex and anterior cingulate cortex might contribute to normal performance during set-shifting.

Differential diagnosis between schizophrenia and autism in adulthood: a case report

The clinical distinction between autism spectrum disorders (ASD), also called pervasive developmental disorders (PDD), and schizophrenia is often difficult to make. Here we describe a case of an adult patient presenting with a diagnosis of schizophrenia based on a history of functional deterioration and presumed persecutory delusions. A psychiatric and psychological assessment conducted from a developmental perspective, in association with direct observation and neuropsychological evaluation for intellectual disabilities and autism, led to a diagnosis of PDD not otherwise specified, with revision of the initial diagnosis of schizophrenia.

Can genetics inform the management of cognitive deficits in schizophrenia?

There is no doubt that schizophrenia has a significant genetic component and a number of candidate genes have been identified for this debilitating disorder. Of note, several of these are implicated in cognition. Cognitive deficits constitute core symptoms of schizophrenia, and while current antipsychotic treatment strategies aim to help psychosis-related symptomatology, the cognitive symptom domain is largely inadequately treated. A number of other pharmacological approaches (e.g. using drugs that target specific neurotransmitter systems) have also been attempted for the amelioration of cognitive deficits in this population; however, these too have had limited success so far. Psychological interventions appear promising, though there has been speculation regarding whether or not these produce long-term functional improvements. Pharmacogenetic studies of the cognitive effects of currently available antipsychotics, although in relatively early stages, suggest that the treatment of cognitive deficits in schizophrenia may be advanced by focusing on genetic variants associated with specific cognitive dysfunctions in the general population and using this to match the most relevant pharmacological and/or psychological interventions with the genetic and cognitive profiles of the target population. Such a strategy would encourage bottom-up advances in drug development and provide a platform for individualised treatment of cognitive deficits in schizophrenia.

Thought disorder in Asperger syndrome and schizophrenia: issues in the differential diagnosis. A series of case reports

The relationship between Asperger syndrome (AS) and schizophrenia is still unclear. An unanswered question is, do hallucinations or delusions per se justify a diagnosis of schizophrenia when these symptoms appear in subjects with AS? The aims of the present study were: (1) to review the characteristics of thought disorder in AS and schizophrenia; (2) to describe the clinical features of six adult patients with AS who presented psychotic symptoms without mood symptoms; (3) to observe their clinical course and response to therapy in order to speculate possible relations between AS and schizophrenia. In the presence of its specific symptoms, it seems inappropriate to omit the diagnosis of AS because the DSM-IV-TR criteria for schizophrenia are also met, whether delusions and hallucinations appear early or late in the course of the disease. Recognizing and emphasizing the diagnosis of AS is not only important for clinicians to tailor the therapeutic strategy to the features of patients, but also for the patients and their relatives.

Attentional set-shifting ability in first-episode and established schizophrenia: Relationship to working memory

Patients with established schizophrenia perform poorly on attentional set-shifting tasks, due to a failure of inhibitory control and/or perseverative errors. However, attentional set-shifting is also dependent on working memory capacity, which is additionally impaired in schizophrenia. No studies in first-episode psychosis have specifically examined the contribution of working memory to set-shifting ability in schizophrenia. We investigated 48 first-episode schizophreniform psychosis/schizophrenia (FE) and 40 chronic schizophrenia (CHR) patients, compared to 67 comparable healthy subjects (CTL). All subjects were assessed using the CANTAB 'attentional set-shifting (IDED)' and 'spatial working memory (SWM)' tasks. Both FE and CHR made significantly greater errors on the SWM task (p< or =0.001). Compared with CTL, CHR was more likely to fail at intra-dimensional (p<0.05) and extra-dimensional (p<0.01) shifting and reversal stages of IDED; CHR required significantly greater trials to reach criterion, which was not explained by deficits in SWM (p<0.001). FE did not differ from CTL on IDED level reached. However, FE required significantly more trials (p=0.001); this was no longer significant after controlling for SWM deficits (p>0.05). Given that the capacity to be flexible and shift attentional set is intact only at the early stages of illness, 'neurodegenerative' processes may explain the more severe deficits in chronic schizophrenia. In contrast, deficits in SWM identified at all stages of schizophrenia may reflect incomplete maturation prior to illness onset ('neurodevelopmental arrest'). Longitudinal studies assessing these cognitive functions from illness onset or in prepsychotic individuals are required.

Memory and executive impairment in schizophrenia: comparison with frontal and temporal brain damage

BACKGROUND

Although poor neuropsychological test performance is well documented in schizophrenia, how closely it resembles that seen in patients with brain damage in terms of cognitive failures in daily life and stability over time has been little studied.

METHOD

Thirty patients with chronic schizophrenia, 24 patients with frontal or temporal brain damage and 30 healthy controls were given a battery of memory and executive tests. Carers of the two patient groups also completed questionnaires rating memory and executive failures in daily life. Testing was repeated 6 weeks later.

RESULTS

The schizophrenia and the brain-damaged patients were significantly impaired on most, but not all tests. The degree of carer-rated memory or executive failure was similar in the two groups, but the schizophrenia patients were rated as having significantly more executive failures than memory failures, whereas the brain-damaged patients showed the reverse pattern. Both groups of patients showed similar consistency of performance across sessions.

CONCLUSIONS

Neuropsychological impairment in schizophrenia resembles that seen in patients with brain damage, not only in terms of overall severity, but also in terms of stability and the degree to which poor test performance translates into cognitive failures in daily life.

Disorganization and cognitive impairment in schizophrenia: independent symptom dimensions?

Cognitive deficits are increasingly considered as essential in schizophrenic disorders. Positive symptoms and cognitive deficits have been found to be independent, whereas negative symptoms show only weak correlations to cognitive impairment. However, the relationship to a third symptom dimension, disorganization, is yet unclear. In a sample of n = 151 schizophrenia inpatients (DSM-IV/SCID) we assessed cognitive impairment using a comprehensive neuropsychological test battery and symptoms of schizophrenia applying the Positive and Negative Syndrome Scale (PANSS). Factor analyses resulted in three neuropsychological (attention, memory, abstraction) and five symptom factor scores (negative, impulsiveness, positive, disorganization, depression). The disorganization factor did not correlate significantly with any of the neuropsychological factor scores. Even after controlling for different demographic and clinical variables partial correlation coefficients did not reach a significant level. Thus, we could not confirm the previously reported associations between disorganization and measures of cognitive impairment. Despite a considerable conceptual overlap between interview based symptom ratings and classic neuropsychological tests the empirical association is limited. Our results suggest that disorganization and cognitive impairment represent different symptom dimensions.

Subtyping schizophrenia: implications for genetic research

Phenotypic variability and likely extensive genetic heterogeneity have been confounding the search for the causes of schizophrenia since the inception of the diagnostic category. The inconsistent results of genetic linkage and association studies using the diagnostic category as the sole schizophrenia phenotype suggest that the current broad concept of schizophrenia does not demarcate a homogeneous disease entity. Approaches involving subtyping and stratification by covariates to reduce heterogeneity have been successful in the genetic study of other complex disorders, but rarely applied in schizophrenia research. This article reviews past and present attempts at delineating schizophrenia subtypes based on clinical features, statistically derived measures, putative genetic indicators, and intermediate phenotypes, highlighting the potential utility of multidomain neurocognitive endophenotypes.

Including integrated psychological treatment as part of standard medical therapy for patients with schizophrenia: clinical outcomes

To assess the clinical outcomes associated with the inclusion of Integrated Psychological Treatment (IPT) standard medical therapy in nine regular clinical settings, nine clinical teams integrated the complete IPT program (six hierarchically arranged subprograms) with their respective standard medical therapies for outpatients with schizophrenia. A total of 90 patients, young adults to long-term mentally ill patients, participated in the program. Patients were evaluated using standardized instruments at four time points: (1) prior to including the IPT program, (2) after the first three IPT subprograms, (3) at the end of IPT, and (4) 3 to 4 months post-IPT. The IPT program was associated with positive results. Patients improved in terms of overall symptoms, subjective experiences, cognitive and social functioning, and quality of life. IPT is one of the most up-to-date programs to address the rehabilitation needs of persons suffering from schizophrenia. Our experience in nine clinical settings suggests that IPT can successfully be included as part of standard medical therapy in the rehabilitation of patients with schizophrenia.

Cognitive function in healthy older European adults: the ZENITH study

OBJECTIVE

Baseline data are reported from a study of the effects of zinc supplementation on cognitive function in older adults as assessed by the CANTAB computerised test battery.

DESIGN

This is a multicentre prospective intervention study employing a randomised double-blind design.

SETTING

European community-based study.

PARTICIPANTS

There are 387 healthy adults aged 55-87 y from centres in France, Italy and Northern Ireland.

INTERVENTIONS

Measures of visual memory, working memory and attention were obtained at baseline (prior to supplementation).

RESULTS

Younger adults (<70 y) performed significantly better than older adults (>70 y) on all tests, with minimal differences between centres. In addition, men outperformed women on tests of spatial span, pattern recognition memory and reaction times, although these gender differences varied somewhat between centres.

CONCLUSIONS

The results are generally consistent with previous age- and gender-related effects on cognitive functioning.

Cognitive functions in prepsychotic patients

OBJECTIVE

Cognitive dysfunctions are now widely understood as an essential feature of schizophrenia. A great number of cognitive disturbances have been described in drug-naive first-episode patients as well. The full-blown psychotic symptoms are usually preceded by a longer prodromal period, in which non-specific psychological disturbances are already present. The late prodromal phase is also coined as the prepsychotic state, with attenuated, isolated psychotic symptoms. The aim of the present study was to detect cognitive dysfunctions among young adults at the prepsychotic stage with the use of a standardized computer based cognitive test battery.

METHOD

Eleven (9 men, 2 women) young Hungarian adults referred to the Outpatient Clinic of the Department of Psychiatry at the University of Debrecen were studied. The patients were re-evaluated for psychotic symptoms after 12 months. The patients had no history of psychiatric disorders or psychotic episodes and were referred by general practitioners on account of non-specific emotional or behavioural abnormalities. The subjects were asked to perform a series of 13 computerized neuropsychological tests of the Cambridge Neuropsychological Test. The performance of the patients were compared to that of the standardized database of the Cambridge Neuropsychological Test.

RESULTS AND DISCUSSION

The performance of the prepsychotic patients was significantly lower compared to the healthy individuals in the paired associate learning (PAL, p<0.001), Spatial recognition memory (SRM, p<0.05), Rapid visual processing (RVP, p<0.05), and Spatial working memory (SWM, p<0.05) tests.

CONCLUSION

Cognitive deficits were found mainly in attentional, frontal and prefrontal cognitive functions. These impairments may be present at the early stages of the development of psychosis and the standardized cognitive test battery (CANTAB) might be a useful tool for the detection of early cognitive impairments and provide a rationale for early intervention in individuals at risk of developing psychosis.

Neuropsychological subtyping of schizophrenia

Schizophrenia tends to be associated with a general decline in cognitive functioning. However, some studies have found neuropsychologically normal schizophrenia patients. To address this contradiction, we screened first-episode schizophrenic patients according to degree of neuropsychological dysfunction. At least three different neuropsychological subtypes of schizophrenia were found. Memory, specifically delayed recall, was the most important factor that discriminated the groups. Neuropsychological assessment, covering a range of functional domains of the major dimensions of behavior, has an important role in identifying preserved and impaired capacities, in predicting outcome, and in planning treatment.

Habenula lesions cause impaired cognitive performance in rats: implications for schizophrenia

Cognitive impairment is a prominent feature of schizophrenia. Currently there is no well-accepted explanation of the aetiology of this disorder, but recent evidence indicates that dysfunction of the habenula may be involved. We therefore examined whether habenula lesions in Sprague-Dawley rats cause behavioural changes resembling those of schizophrenia. Rats received either habenula lesions, a sham operation or a small lesion of the overlying dorsal hippocampus as a check that effects observed were not due to incidental damage to this structure. As there are alterations of social behaviour, sensorimotor gating and cognition in schizophrenia, we examined comparable behaviours. Social interaction time was measured during a 5-min encounter with a novel juvenile conspecific. Prepulse inhibition of an acoustic startle response, as an index of sensorimotor gating, was measured with prepulses of various amplitudes, and spatial cognitive performance was assessed in the Morris water maze task. Histological analysis showed that habenula lesions substantially damaged both medial and lateral habenula bilaterally while largely sparing neighbouring structures. Assay of choline acetyltransferase (ChAT) in the interpeduncular nucleus terminal region of the habenulo-interpeduncular tract, showed marked reduction (by 80%) in habenula-lesioned animals. Habenula-lesioned rats, but not the control group with small dorsal hippocampus lesions, showed marked impairment of Morris maze performance compared to the sham-operated control group. Social interaction time and prepulse inhibition were not significantly altered in either lesion group. The results are consistent with a role of the habenula in cognition, and with the view that pathology of the habenula may contribute to the cognitive impairments of schizophrenia.

Using saccade tasks as a tool to analyze executive dysfunctions in schizophrenia

Executive dysfunctions can be frequently observed in schizophrenia. They are more persistent than psychotic symptoms and are assumed to contribute to a variety of clinical signs of the disease. However, the cognitive mechanisms underlying dysexecutive behaviors are not yet understood. The aim of this article is to demonstrate how saccade tasks can be used to analyze the mechanisms involved in the dysexecutive syndrome of schizophrenic patients. There are numerous reports showing that schizophrenic patients make many unwanted reflexive saccades in the antisaccade task. These errors are usually explained by an impairment of a distinct inhibitory mechanism. However, unwanted reflexive saccades may also be secondary to a more fundamental deficit in activating goal-directed behavior. Recent theoretical and empirical approaches to this issue are reviewed and discussed. An integrative view of deficits in inhibition, goal-directed behavior, and working memory in schizophrenic patients is proposed.

The cognitive neuroscience of category learning

Recently, a multidisciplinary approach has provided new insights into the mechanisms of category learning. In this article, results from theoretical modeling, experimental psychology, clinical neuropsychology, functional neuroimaging, and single-cell studies are reviewed. Although the results are not conclusive, some general principles have emerged. Areas localized in the sensory neocortex are responsible for the perceptual representation of category exemplars, whereas lateral and anterior prefrontal structures are necessary for the encoding of category boundaries and abstract rules. The prefrontal cortex may influence categorical representation in the sensory neocortex via top-down control. The neostriatum is important in stimulus-response mapping, and the orbitofrontal cortex/ventral striatum are related to stimulus-reward associations accompanying category learning. Many category learning tasks can be performed implicitly. In conclusion, category learning paradigms provide a unique opportunity to investigate cognitive processes such as perception, memory, and attention in a systematic and interactive manner. Category learning tasks are suitable for mapping damaged brain systems in clinical populations.

Impulsivity in patients with borderline personality disorder

This study investigated features of impulsivity in patients with borderline personality disorder (BPD) using the self-report Attention-Deficit Scales for Adults (ADSA) and computer-administered neurocognitive tasks. Forty-one patients with DSM-III-R BPD and 35 nonclinical control subjects were assessed by the ADSA, the National Adult Reading Test, and two computerized tasks mediated by the frontal lobes. Mean scores for seven ADSA scales (six of which relate to aspects of impulsivity) were significantly higher in the patient group compared with the control group. Also, the ADSA ratings for impaired coordination were increased in the BPD patients. The findings indicate that a range of aspects of impulsivity, as well as impaired coordination, are associated with patients selected on the basis of BPD. Also, in the patient group, but not in the control group, associations of the neurocognitive tasks indicated that, first, performance on a planning task related to dorsolateral frontal lobe functioning is correlated with aspects of impulsivity reflected by ADSA scale III ratings (involving disorganisation and lack of perseverance) and, second, performance on a decision-making task related to orbitofrontal functioning is correlated with ratings of impaired coordination. Further work is needed to establish the specificity of the findings.

Frontal lobe N-acetylaspartate correlates with psychopathology in schizophrenia: a proton magnetic resonance spectroscopy study

INTRODUCTION

Clinical, neuropsychological and functional neuroimaging studies in schizophrenia suggest impaired frontal lobe function, especially of the dorsolateral prefrontal region (DLPFR). This dysfunction has in particular been associated with negative or "deficit" symptoms. Despite these findings, morphological studies have failed to show consistent structural abnormalities in the frontal lobe. This may be because existing techniques are not sensitive enough to detect structural abnormalities or that dysfunction in the frontal lobe is caused by lesions elsewhere. We used volume-localised proton magnetic resonance spectroscopy (1H-MRS) to measure N-acetylaspartate (NAA), a neuronal marker, to evaluate the neuronal integrity of the dorsolateral prefrontal region in schizophrenic patients with persistent negative symptoms and in healthy comparison subjects.

METHOD

Twenty-five patients who fulfilled DSM-IV criteria for schizophrenia and met the criteria for the Deficit syndrome were compared to 26 healthy controls matched for age and gender. Bilateral proton MR spectra were collected from a 2-cm(3) volume in the dorsolateral prefrontal region and the absolute concentrations of N-acetylaspartate, choline (Cho) and creatine+phosphocreatine (Cr+PCr) were measured.

RESULTS

There was a significant negative correlation between severity of symptoms and NAA concentration in the schizophrenic patients. This was more marked for positive symptoms and for general psychopathology than for negative symptoms. There was also a significant correlation between NAA concentration and social functioning within the schizophrenic group. There were no significant differences between the two groups for the three metabolites.

CONCLUSIONS

The negative association between severity of symptoms and NAA in schizophrenic patients and an association of NAA with social functioning suggest that NAA may be an indicator of disease severity. The lack of significant mean difference in NAA between the two groups suggests that there is no marked neuronal loss in the dorsolateral prefrontal region in schizophrenia.

Insight and neurocognition in schizophrenia

The relationship between neurocognitive impairments in schizophrenia remains unclear. Recent literature was reviewed and the most consistent finding was an association between perseverative errors on the Wisconsin Card Sort Test (WCST) and poor insight. The aim was to confirm and extend this finding using a range of assessments relevant to perseveration, and different dimensions of insight, in a sample of 33 acutely psychotic subjects within 5 years of onset of schizophrenia and related disorders. Results showed a correlation (r=-0.59) between insight and perseverative errors, rather than more general measures of abstraction. A factor representing relabelling symptoms, derived from insight scale items, correlated even more strongly; however, other insight factors correlated more weakly, suggesting they are less dependent on neuropsychological deficits. The ability to monitor output and correct errors appears to be closely related to the core features of insight in psychosis.

Neurocognitive, behavioural and neurodevelopmental correlates of schizotypy clusters in adolescents from the general population

INTRODUCTION

Studies on the neurocognitive correlates of schizotypy dimensions have found inconsistent results. This might stem from the fact that correlational methods, in contrast to cluster analysis, do not account for the possibility that a subject presents high scores on more than one dimension simultaneously. We aimed to establish clusters of normal adolescents based on schizotypy dimensions and compare them on neurocognitive, behavioural, and neurodevelopmental markers.

METHODS

Two hundred seventy normal adolescents from the general population (mean age 13.4, SD=0.72) attending obligatory education were evaluated.

RESULTS

A K-means iterative cluster analysis was performed with the Perceptual Aberration, Revised Social Anhedonia and Physical Anhedonia Scales. A forced four-cluster model yielded the following clusters: 'negative schizotypy', 'high or mixed schizotypy', 'positive schizotypy', and 'normal scorers'. Comparisons with ANOVAs showed that 'high schizotypes' performed poorly on neurocognition (Wechsler Intelligence Scales for Children-Revised (WISC-R) and Verbal Fluency (FAS)) and obtained the highest teacher ratings (TRF) of behavioural problems. 'Negative schizotypes' had the worst WCST results and more dermatoglyphic abnormalities. Both clusters had more neurological soft signs than 'normal scorers' and 'positive schizotypes'.

CONCLUSIONS

Our results with community adolescents found the same cluster structure than the previous cluster analytic studies conducted in adult college subjects. Furthermore, we showed differences among them on neurocognitive and malneurodevelopment markers consistent with the adult literature on schizotypy.

Assessment of neuropsychological function through use of the Cambridge Neuropsychological Testing Automated Battery: performance in 4- to 12-year-old children

In this article, children's performance on subtasks from the Cambridge Neuropsychological Testing Automated Battery (CANTAB) is described. Two samples were recruited, one of which included children who spoke English as a second language. Children in this group also completed subtests from the Wechsler Intelligence Scale for Children-Third Revision (WISC-III). Despite the fact that ESL children scored over 1 SD below the norm on the WISC-III Vocabulary subtest, there were no CANTAB performance distinctions between primary versus secondary English-language speakers. In addition, several aspects of CANTAB performance were significantly correlated with verbal and nonverbal IQ. When developmental trends were examined, findings indicated that several aspects of frontal lobe function (memory span, working memory, and planning skills) are not functionally mature, by the age of 12 years. Implications for use of the CANTAB in clinical studies are discussed.

Executive functions and their disorders

The term executive function defines complex cognitive processing requiring the co-ordination of several subprocesses to achieve a particular goal. Neuropsychological evidence suggests that executive processing is intimately connected with the intact function of the frontal cortices. Executive dysfunction has been associated with a range of disorders, and is generally attributed to structural or functional frontal pathology. Neuroimaging, with PET and fMRI, has confirmed the relationship; however, attempts to link specific aspects of executive functioning to discrete prefrontal foci have been inconclusive. Instead, the emerging view suggests that executive function is mediated by dynamic and flexible networks, that can be characterised using functional integration and effective connectivity analyses. This view is compatible with the clinical presentation of executive dysfunction associated with a range of pathologies, and also with evidence that recovery of executive function can occur after traumatic brain injury, perhaps due to functional reorganisation within executive networks.

Perseveration in schizophrenia: failure to generate a plan and relationship with the psychomotor poverty subsyndrome

Although perseveration in the Wisconsin Card Sorting Test (WCST) has been studied extensively in schizophrenia, the underlying cognitive dysfunctions are not yet clear. In schizophrenia, perseveration has been found to relate to frontal and striatal abnormalities. Therefore, both a failure to generate a plan as seen in patients with frontal abnormalities, or a failure to execute a plan as observed in Parkinson patients, who suffer primarily from striatal abnormalities, could explain perseveration in schizophrenia. The aim of the present study was to distinguish between these two cognitive dysfunctions, which are described by Frith in his routes-to-action model. The main difference between these dysfunctions is the ability to use external guidance. In the present study, 39 schizophrenic patients and 36 healthy controls were assessed with the California Verbal Learning Test (CVLT) and the WCST, in which use of external guidance can be measured, and with the Positive and Negative Syndrome Scale (PANSS) to determine the relationship with symptomatology. The results showed that half of the schizophrenic patients showed perseveration, which could be explained by a failure to generate a plan and was related to the psychomotor poverty subsyndrome. No evidence was found for a failure to execute a plan. Type of antipsychotic medication used (atypical vs. typical) proved not relevant. The results are discussed in the light of evidence for involvement of the dorsolateral prefrontal cortex in perseveration in schizophrenia.

Dissecting the brain's internal clock: how frontal-striatal circuitry keeps time and shifts attention

The ability of organisms to time and coordinate temporal sequences of events and to select particular aspects of their internal and external environments to which they will attend is vital to the organism's ability to adapt to the world around them. Numerous psychological theories have been proposed that describe how organisms might accomplish such stimulus selection and represent discrete temporal events as well as rhythm production. In addition, a large number of studies have demonstrated that damage to the frontostriatal circuitry appears to compromise the ability of organisms to successfully shift attention and behavior to adapt to changing temporal contexts. This suggests that frontostriatal circuitry is involved in the ability to make such shifts and to process temporal intervals. A selective review is accomplished in this article which focuses upon the specific neural mechanisms that may be involved in interval timing and set shifting. It is concluded that prefrontal cortex, substantia nigra pars compacta, pedunculopontine nucleus, and the direct and indirect pathways from the caudate to the thalamus may provide the neuroanatomical and neurophysiological substrates that underlie the organism's ability to shift its attention from one temporal context to another.

Spatio-temporal disintegration of visual perception in schizophrenia as revealed by a novel cognitive task, the Searchlight Test

We developed a novel computer-assisted psychological test (the Searchlight Test) in order to explore 'cognitive fragmentation' and its relation to thought disorder in schizophrenic patients. Participants were instructed to search geometric figures through a small hole (3 cm in diameter) on a display monitor by moving a mouse device and to reconstruct an image of the whole from the temporally and spatially fragmented visual stimuli.The cognitive function measures in 24 schizophrenic patients and 14 normal controls showed that the error rates of the recall task (drawing the figure from memory) and the recognition task (selecting the correct figure from several similar figures) were significantly higher in schizophrenic patients than in normal controls. The error rates of both tasks significantly correlated with disorganization syndrome in schizophrenia, but not with reality distortion or with psychomotor poverty syndrome.The present data obtained with the Searchlight Test suggest the spatio-temporal disintegration of visual perception in schizophrenia and its correlation with disorganization. This test appears to provide a useful tool for studying the pathophysiology of disorganization syndrome, thought disorder and the related cognitive dysfunction of schizophrenia.

Velo-cardio-facial syndrome: a model for understanding the genetics and pathogenesis of schizophrenia

BACKGROUND

Individuals with velocardio-facial syndrome (VCFS), a genetic disorder associated with microdeletions of chromosome 22q11, are reported to have high rates of psychiatric disorder, particularly schizophrenia.

AIMS

To review the evidence for an association between VCFS and schizophrenia: to outline recent neuropsychological, neuroanatomical and genetic studies of individuals with VCFS; and to make recommendations for future work.

METHOD

A selective literature review was undertaken.

RESULTS

Individuals with VCFS have high rates of psychotic disorders, particularly schizophrenia. In addition, specific neuropsychological and neuroanatomical abnormalities have been reported although it is unclear whether such abnormalities relate to the presence of psychiatric disorder in affected individuals.

CONCLUSIONS

Deletion of chromosome 22q11 represents one of the highest known risk factors for the development of schizophrenia. It is likely that haploinsufficiency (reduced gene dosage) of a neurodevelopmental gene or genes mapping to chromosome 22q11, leading to disturbed neuronal migration, underlies susceptibility to psychosis in VCFS.

Dementia as a complication of schizophrenia

OBJECTIVES

Cognitive impairment is known to occur in schizophrenia, and may be marked in institutionalised patients. The aim of this study was to determine whether it ever warrants an additional diagnosis of dementia.

METHODS

A population of chronic schizophrenic patients who were aged 65 or younger and showed no organic risk factors for dementia were screened for presence of disorientation. Any showing this underwent neuropsychological testing, physical investigations, and structural and functional neuroimaging. Information about day to day cognitive function was also obtained from carers.

RESULTS

Eight patients aged 28 to 64 were identified who showed disorientation; in all cases this was accompanied by general intellectual impairment and objective evidence of a dementia syndrome. The patients' schizophrenic symptoms were unexceptional and did not seem sufficient to account for their cognitive impairment. Neuropsychological testing disclosed relative sparing of visual and visuospatial function and language syntax, but pervasive deficits in memory and executive function. Brain CT demonstrated only minor abnormalities but most of the patients showed frontal or temporal hypoperfusion on SPECT.

CONCLUSIONS

Dementia in schizophrenia seems to be a real entity with a neuropsychological signature similar to that of frontotemporal dementia. Functional but not structural imaging abnormalities may also be characteristic.

The contribution of early traumatic events to schizophrenia in some patients: a traumagenic neurodevelopmental model

The current diathesis-stress model of schizophrenia proposes that a genetic deficit creates a predisposing vulnerability in the form of oversenstivity to stress. This model positions all psychosocial events on the stress side of the diathesis-stress equation. As an example of hypotheses that emerge when consideration is given to repositioning adverse life events as potential contributors to the diathesis, this article examines one possible explanation for the high prevalence of child abuse found in adults diagnosed schizophrenic. A traumagenic neurodevelopmental (TN) model of schizophrenia is presented, documenting the similarities between the effects of traumatic events on the developing brain and the biological abnormalities found in persons diagnosed with schizophrenia, including overreactivity of the hypothalamic-pituitary-adrenal (HPA) axis; dopamine, norepinephrine, and serotonin abnormalities; and structural changes to the brain such as hippocampal damage, cerebral atrophy, ventricular enlargement, and reversed cerebral asymmetry. The TN model offers potential explanations for other findings in schizophrenia research beyond oversensitivity to stress, including cognitive impairment, pathways to positive and negative symptoms, and the relationship between psychotic and dissociative symptomatology. It is recommended that clinicians and researchers explore the presence of early adverse life events in adults with psychotic symptoms in order to ensure comprehensive formulations and appropriate treatment plans, and to further investigate the hypotheses generated by the TN model.

'Obsessions' in children with autism or Asperger syndrome. Content analysis in terms of core domains of cognition

BACKGROUND

We report a survey of the content of obsessions in children with autism spectrum conditions. We use the term 'obsessions' narrowly, to indicate strong, repetitive interests. We predicted that obsessions would not cluster randomly, but rather would occur significantly more often in the domain of 'folk physics' (an interest in how things work), and significantly less often in the domain of 'folk psychology' (an interest in how people work). These predictions were tested relative to a control group of 33 children with Tourette syndrome.

AIMS

To examine the content of autistic obsessions, and to test the theory that these reflect an evolved cognitive style of good folk physics alongside impaired folk psychology.

METHOD

Ninety-two parents returned a questionnaire designed to determine the subject of their child's obsessional interests. The results were analysed in terms of core domains of cognition.

RESULTS

Both predictions were confirmed.

CONCLUSIONS

These results suggest that impaired folk psychology and superior folk physics are part of the cognitive phenotype of autism. A content-free theory of obsessions is inadequate.

Cognitive deficits in schizophrenia on the WAIS-R NI Sentence Arrangement Subtest. Wechsler Adult Intelligence Scale-Revised Neuropsychological Inventory

Performance of participants diagnosed with schizophrenia on the Sentence Arrangement subtest of the WAIS-R NI and several tests sensitive to frontal lobe dysfunction was significantly poorer than that of manic depressive or control participants. Several measures of performance of patients diagnosed with schizophrenia on the WAIS-R NI Sentence Arrangement subtest appeared to support recent interpretations of the cognitive deficit seen in schizophrenia. These data represent the first demonstration of deficit performance by patients with schizophrenia on the Sentence Arrangement subtest. This is also supportive of the prediction that one of the areas whose activity may influence scores on this subtest is the prefrontal cortex. In addition, neither positive nor negative symptoms systematically correlated with the cognitive deficits reported despite specific predictions from the current literature.

Cognitive deficits and cognitive training in schizophrenic patients: a review

OBJECTIVE

The aim of this paper is to review the current status of knowledge of cognitive deficits and remediation in patients with schizophrenia.

METHOD

Relevant reports were identified by a literature survey. In addition, some outstanding researchers in these areas were asked to add to the identified list relevant literature that was not included.

RESULTS

Our review focuses on the cognitive deficits observed in the areas of attention, memory and executive functions. We attempt to classify dysfunctions as vulnerability- or symptom-linked factors, and we discuss the methodological question of a general performance deficit vs. a differential deficit. Furthermore, we briefly delineate how antipsychotics affect cognitive functions. Finally, controlled studies of cognitive training are discussed in more detail.

CONCLUSION

The most outstanding cognitive dysfunctions in patients with schizophrenia can be related to the areas of attention, memory and executive functions. Interest in cognitive remediation has to some extent been rekindled in the 1990s. However, few studies on the effects of cognitive training programs have been conducted.

Comparison of set-shifting ability in patients with chronic schizophrenia and frontal lobe damage

Neuropsychological studies of patients with schizophrenia have consistently identified deficits on tests sensitive to frontal lobe function. One paradigm that has been widely used is that of attentional set-shifting using the Wisconsin Card Sorting Test (WCST). In the present study, patients with chronic schizophrenia and with frontal lobe lesions were assessed on a computerised set-shifting task that provides a componential analysis of the WCST by distinguishing between intra-dimensional and extra-dimensional set-shifting. Out of 51 patients with schizophrenia, those with high IQ (n =24) were compared with patients with lesions in prefrontal cortex (n = 22) and with normal control subjects (n= 18). These three groups were well matched for age, sex and National Adult Reading Test (NART) IQ. The schizophrenic group showed a significantly higher rate of attrition at the intra-dimensional shift stage of learning compared with the other two groups. At the extra-dimensional shift stage, both the schizophrenic and frontal lesioned groups showed greater attrition than controls. Further, patients with schizophrenia who were able to learn the intradimensional reversal stage required more trials and made significantly more errors at that stage than the other two groups. In comparison with high IQ patients with schizophrenia, those with low IQ performed at a lower level but showed a qualitatively similar pattern of performance, providing further evidence that the set-shifting deficits were not simply explained by any global intellectual decline. Patients with schizophrenia who dropped out at the extradimensional shift stage had higher negative symptom scores compared with patients dropping out at previous learning stages, while patients failing at the intra-dimensional shift stage had lower scores for bradyphrenia (slowness of thought). The results suggest that patients with chronic schizophrenia fail to 'learn set' and are impaired at both set-shifting and concept formation. The relevance of these findings to understanding the nature of prefrontal cortical deficits in chronic schizophrenia is discussed. The implication of these findings to the rehabilitation of these patients is considered.

The neuropathology of schizophrenia. A critical review of the data and their interpretation

Despite a hundred years' research, the neuropathology of schizophrenia remains obscure. However, neither can the null hypothesis be sustained--that it is a 'functional' psychosis, a disorder with no structural basis. A number of abnormalities have been identified and confirmed by meta-analysis, including ventricular enlargement and decreased cerebral (cortical and hippocampal) volume. These are characteristic of schizophrenia as a whole, rather than being restricted to a subtype, and are present in first-episode, unmedicated patients. There is considerable evidence for preferential involvement of the temporal lobe and moderate evidence for an alteration in normal cerebral asymmetries. There are several candidates for the histological and molecular correlates of the macroscopic features. The probable proximal explanation for decreased cortical volume is reduced neuropil and neuronal size, rather than a loss of neurons. These morphometric changes are in turn suggestive of alterations in synaptic, dendritic and axonal organization, a view supported by immunocytochemical and ultrastructural findings. Pathology in subcortical structures is not well established, apart from dorsal thalamic nuclei, which are smaller and contain fewer neurons. Other cytoarchitectural features of schizophrenia which are often discussed, notably entorhinal cortex heterotopias and hippocampal neuronal disarray, remain to be confirmed. The phenotype of the affected neuronal and synaptic populations is uncertain. A case can be made for impairment of hippocampal and corticocortical excitatory pathways, but in general the relationship between neurochemical findings (which centre upon dopamine, 5-hydroxytryptamine, glutamate and GABA systems) and the neuropathology of schizophrenia is unclear. Gliosis is not an intrinsic feature; its absence supports, but does not prove, the prevailing hypothesis that schizophrenia is a disorder of prenatal neurodevelopment. The cognitive impairment which frequently accompanies schizophrenia is not due to Alzheimer's disease or any other recognized neurodegenerative disorder. Its basis is unknown. Functional imaging data indicate that the pathophysiology of schizophrenia reflects aberrant activity in, and integration of, the components of distributed circuits involving the prefrontal cortex, hippocampus and certain subcortical structures. It is hypothesized that the neuropathological features represent the anatomical substrate of these functional abnormalities in neural connectivity. Investigation of this proposal is a goal of current neuropathological studies, which must also seek (i) to establish which of the recent histological findings are robust and cardinal, and (ii) to define the relationship of the pathological phenotype with the clinical syndrome, its neurochemistry and its pathogenesis.

A meta-analytic review of Wisconsin Card Sort studies in schizophrenia: general intellectual deficit in disguise?

A majority of studies show that schizophrenics perform poorly on so-called tests of executive or frontal lobe function--the paradigmatic case being the Wisconsin Card Sort Test (WCST). Nevertheless, the specific character of this deficit in schizophrenia remains underspecified. In particular, it seems premature to assume that schizophrenia is characterised by an executive dysfunction and/or a disorder of frontal lobe function before determining whether any deficit is: selective; disproportionate to the general level of intellectual functioning; or qualitatively comparable with that of frontal lobe patients. A meta-analysis was conducted on 29 studies comparing the performance of schizophrenics and normal controls on the WCST. This showed that the mean weighted effect size was large for categories achieved (d = 0.91), medium for absolute level of perseveration (d = 0.53), but only small for the proportion of perseverative errors (d = 0.18). By contrast, the effect size for Wechsler Adult Intelligence Scale Intelligence Quotient (WAIS IQ) in a subset of these studies (d = 1.23) was significantly larger than for any WCST measures. This pattern of findings challenges notions that schizophrenia is characterised by an executive dysfunction that is: selective; disproportionate to IQ level; and analogous to that found in frontal lobe patients. Rather, the poor WCST performance of schizophrenics appears to reflect a generalised intellectual deficit.

Late paraphrenia: a variant of schizophrenia manifest in late life or an organic clinical syndrome? A review of recent evidence

A large amount of research has been devoted during the past 15 years to the clinical and neurobiological aspects of the disorder named as 'late paraphrenia' (LP) in 1955. The symptomatology and diagnosis of the disorder, its prognosis, the cognitive functioning of those affected, the structural changes in the brain as revealed by modern techniques of brain imaging and its postmortem neuropathology have all been submitted to investigation. The results have been widely regarded as consistent with the concept of LP as an organic disease of the brain, but increased knowledge of the neurobiology of schizophrenia and of the age-related changes that occur in the brains of elderly people casts doubt on the validity of this interpretation. The findings are consistent with the view that LP is the form in which schizophrenia is manifest in old age. The proposal that LP has a closer kinship with affective disorder than with schizophrenia is part of a general theory of the sex differences in schizophrenia. In LP it becomes entangled with the organicity hypothesis, suggesting that neither of these explanations is adequate, and most of the evidence points to a unitary concept which views LP as a variant of a single disorder, namely schizophrenia, which, however, requires a broad definition. This concept has implications for fresh paths of enquiry.

Test/re-test reliability of the CANTAB and ISPOCD neuropsychological batteries: theoretical and practical issues. Cambridge Neuropsychological Test Automated Battery. International Study of Post-Operative Cognitive Dysfunction

Neuropsychological test batteries are repeatedly administered to evaluate changes over time or the effects of clinical interventions. Relationships between scores on different tests within batteries are also examined to test models for associations between functional deficits. These comparisons may be misleading unless Test/Re-test reliability for individual tests is satisfactory. Interpretations of repeated measurements also depend on the extent to which improvement with practice varies between tasks and between more and less able individuals. Test/Re-test correlations and practice effects for two neuropsychological test batteries (CANTAB, ISPOCD) and from laboratory tasks commonly used in cognitive assessments of older people were obtained from large groups of healthy elderly. Tests in neuropsychological batteries varied markedly in test/re-test reliability which, in some cases, fell below levels considered methodologically acceptable. Putative measures of 'frontal' or 'executive' function, in which performance may be markedly improved by abrupt discovery of an appropriate strategy, were especially likely to show low reliability. Most tests showed significant practice effects, and on some these are substantial enough to compromise comparisons on repeated testing. On a minority of tests practice effects were counter-intuitive, in that less able showed significantly more gains than more able individuals.

Defective inhibition of dream event memory formation: a hypothesized mechanism in the onset and progression of symptoms of schizophrenia

An average person normally spends at least 90 min to 2 h per night dreaming. Nevertheless, memories of dream events are not retrieved while awake unless the person awoke shortly after a dream. It is hypothesized here that schizophrenic delusions initially arise because a system that normally inhibits the formation of memories of dream events is defective. Therefore, memories of dream events or fragments would be occasionally made and placed in the normal memory store. The only reason that we really know anything happened to us in the past is that we have a memory of it, and having a memory of an event is sufficient to really believe it. Therefore, the schizophrenic would believe that the dream events actually happened. It is proposed that this is the basis of primary delusions. Because memories are represented by strengthened neural connections there will be an accumulation of connections that do not correspond to reality. This accumulation may account for other symptoms of schizophrenia such as thought disorder, loosening of associations, and hallucinations. The brain trying to draw conclusions from several memories may be the basis of secondary delusions. Evidence is presented for the ideas that primary delusions are due to memories of dream events, that a substance, with vasotocin-like bioactivity, is released in the brain during dreaming and inhibits memory formation, that the lateral habenula is a brain area involved in vasotocin actions and is affected by neuroleptics, and that brain mechanisms involved in vasotocin actions show pathological alterations in schizophrenia.

Stability in cognitive dysfunctions in schizophrenic patients

The purpose of the present study was to classify cognitive dysfunctions in schizophrenic subjects according to a trait/state model. A sample of 15 patients was examined on 10 different cognitive measures in two distinctly different phases: an acute psychotic state and partial remission. To determine the degree of dysfunction at the two stages of illness, the schizophrenic patients were also compared to 14 non-psychiatric controls. Six of the 10 measures examined can be classified as cognitive deficits in schizophrenics. Four measures are possibly trait-dependent components: two backward masking scores and two long-term memory measures. A short-term memory measure is the only one that can be classified as an episode-linked factor. The other cognitive deficits found can be characterized as mediating vulnerability factors, i.e. they are more prominent in the acute psychotic state, but do not completely disappear during remission states.

Effects of ibotenic acid-induced loss of neurons in the medial prefrontal cortex of rats on behavioral vigilance: evidence for executive dysfunction

Rats were trained in a previously validated task for the assessment of sustained attention, or vigilance. This task required the animals to discriminate between signals of variable lengths and non-signal events by making an appropriate lever press. The performance of sham-lesioned animals in this task was characterized by a signal-length dependent number of hits. Also, approximately 70 percent of the non-signals were correctly rejected. Ibotenic acid-induced lesions of the medial prefrontal cortex decreased the relative number of hits and correct rejections and, in essence, resulted in random lever selection. The lesion did not affect the number of omissions or side bias. Furthermore, the performance of lesioned animals was insensitive to the detrimental effects of distractors. The effects of the lesions do not support an interpretation in terms of sustained attention. Rather, the pattern of the lesioned animals' performance is speculated to reveal a fundamental disruption of decisional processes, reminiscent of the executive dysfunctions observed in patients with damage to ventromedial prefrontal areas or with schizophrenia.