Neuropsychological correlates of positive vs. negative schizophrenic symptomatology

Positive symptoms of schizophrenia and their relationship with cognitive and emotional executive functions

BACKGROUND

Positive symptoms of schizophrenia are associated with significant difficulties in daily functioning, and these difficulties have been associated with impaired executive functions (EEFF). However, specific cognitive and socio-emotional executive deficits have not been fully established.

OBJECTIVE

The present study has several objectives. First, we aimed to examine the specific deficits in cognitive and socio-emotional EEFF in a group of patients with schizophrenia with a predominance of positive symptoms, as well as to determine if these patients present clinically significant scores in any of the three fronto-subcortical behavioral syndromes: Dorsolateral, Orbitofrontal, or Anterior Cingulate.

METHOD

The sample consisted of 54 patients, 27 with a predominance of positive symptoms, and 27 healthy controls matched for gender, age, and education. The two groups completed four cognitive and three socio-emotional EEFF tasks. In the group of patients, positive symptoms were evaluated using the scale for the Evaluation of Positive Symptoms (SANS), while the behavioral alterations associated with the three fronto-subcortical syndromes were evaluated using the Frontal System Behavior Scale (FrSBe).

RESULTS

The patients, in comparison with a control group, presented specific deficits in cognitive and socio-emotional EEFF. In addition, a high percentage of patients presented clinically significant scores on the three fronto-subcortical syndromes.

CONCLUSION

The affectation that these patients present, in terms of both cognitive and emotional components, highlights the importance of developing a neuropsychological EEFF intervention that promotes the recovery of the affected cognitive capacities and improves the social and emotional functioning of the affected patients.

From Memories of Past Experiences to Present Motivation? A Meta-analysis on the Association Between Episodic Memory and Negative Symptoms in People With Psychosis

Based on findings from cognitive science, it has been theorized that the reductions in motivation and goal-directed behavior in people with psychosis could stem from impaired episodic memory. In the current meta-analysis, we investigated this putative functional link between episodic memory deficits and negative symptoms. We hypothesized that episodic memory deficits in psychosis would be related to negative symptoms in general but would be more strongly related to amotivation than to reduced expressivity. We included 103 eligible studies (13,622 participants) in the analyses. Results revealed significant, moderate negative associations of episodic memory with negative symptoms in general (k = 103; r = -.23; z = -13.40; P ≤ .001; 95% CI [-.26; -.20]), with amotivation (k = 16; r = -.18; z = -6.6; P ≤ .001; 95% CI [-.23; -.13]) and with reduced expressivity (k = 15; r = -.18; z = -3.30; P ≤.001; 95% CI[-.29; -.07]). These associations were not moderated by sociodemographic characteristics, positive symptoms, depression, antipsychotic medication or type of negative symptom scale. Although these findings provide sound evidence for the association between episodic memory deficits and amotivation, the rather small magnitude and the unspecific pattern of this relationship also indicate that episodic memory deficits are unlikely to be the only factor relevant to amotivation. This implicates that future research should investigate episodic memory in conjunction with other factors that could account for the association of episodic memory deficits and amotivation in psychosis.

Aberrant cerebellar neural activity and cerebro-cerebellar functional connectivity involving executive dysfunction in schizophrenia with primary negative symptoms

Deficit schizophrenia (DS) is a distinct subtype of schizophrenia characterized by primary and enduring negative symptoms. More severe executive dysfunctions were observed in DS patients, however, the associated neuroimaging characteristics, especially cerebellar functional anomalies in DS, remain largely unknown. We employed resting-state functional and structural MRI data of 106 male participants, including data from 29 DS patients, 39 non-deficit schizophrenia (NDS) patients and 38 healthy controls (HCs). Z-standardized fractional amplitude of low-frequency fluctuation (zfALFF) values were calculated in order to examine spontaneous regional brain activity. Cerebro-cerebellar functional connectivity and changes in the volume of gray matter in the cerebellum were also examined. Relative to the HCs, both DS and NDS patients exhibited decreased zfALFF in the bilateral cerebellar lobules VIII and IX. The zfALFF in the left Crus II was lower in DS patients compared to NDS patients. No significant difference was observed in the volume of cerebellar gray matter among the three groups. Compared with NDS patients, cerebro-cerebellar functional connectivity analysis revealed increased connectivity in the left orbital medial frontal cortex and right putamen regions in DS patients. Reduced zfALFF in the left Crus II in the DS group was significantly positively correlated with Stroop Color and Word scores, while negatively correlated with Trail-Making Test part B scores. The increased functional connectivity in the right putamen in DS patients was significantly positively correlated with Animal Naming Test and semantic Verbal Fluency Test scores. These results highlight cerebellar functional abnormality in DS patients and provide insight into the pathophysiological mechanism of executive dysfunction.

Altered spatial profile of distraction in people with schizophrenia

Attention is critical for effective processing of incoming information and has long been identified as a potential area of dysfunction in people with schizophrenia (PSZ). In the realm of visual processing, both spatial attention and feature-based attention are involved in biasing selection toward task-relevant stimuli and avoiding distraction. Evidence from multiple paradigms has suggested that PSZ may hyperfocus and have a narrower "spotlight" of spatial attention. In contrast, feature-based attention seems largely preserved, with some suggestion of increased processing of stimuli sharing the target-defining feature. In the current study, we examined the spatial profile of feature-based distraction using a task in which participants searched for a particular color target and attempted to ignore distractors that varied in distance from the target location and either matched or mismatched the target color. PSZ differed from healthy controls in terms of interference from peripheral distractors that shared the target-color presented 200 ms before a central target. Specifically, PSZ showed an amplified gradient of spatial attention, with increased distraction to near distractors and less interference to far distractors. Moreover, consistent with hyperfocusing, individual differences in this spatial profile were correlated with positive symptoms, such that those with greater positive symptoms showed less distraction by target-colored distractors near the task-relevant location. (PsycINFO Database Record

Neonatal disruption of serine racemase causes schizophrenia-like behavioral abnormalities in adulthood: clinical rescue by d-serine

BACKGROUND

D-Serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, is synthesized from L-serine by serine racemase (SRR). Given the role of D-serine in both neurodevelopment and the pathophysiology of schizophrenia, we examined whether neonatal disruption of D-serine synthesis by SRR inhibition could induce behavioral abnormalities relevant to schizophrenia, in later life.

METHODOLOGY/PRINCIPAL FINDINGS

Neonatal mice (7-9 days) were injected with vehicle or phenazine methosulfate (Met-Phen: 3 mg/kg/day), an SRR inhibitor. Behavioral evaluations, such as spontaneous locomotion, novel object recognition test (NORT), and prepulse inhibition (PPI) were performed at juvenile (5-6 weeks old) and adult (10-12 weeks old) stages. In addition, we tested the effects of D-serine on PPI deficits in adult mice after neonatal Met-Phen exposure. Finally, we assessed whether D-serine could prevent the onset of schizophrenia-like behavior in these mice. Neonatal Met-Phen treatment reduced D-serine levels in the brain, 24 hours after the final dose. Additionally, this treatment caused behavioral abnormalities relevant to prodromal symptoms in juveniles and to schizophrenia in adults. A single dose of D-serine improved PPI deficits in adult mice. Interestingly, chronic administration of D-serine (900 mg/kg/day from P35 to P70) significantly prevented the onset of PPI deficits after neonatal Met-Phen exposure.

CONCLUSIONS/SIGNIFICANCE

This study shows that disruption of D-serine synthesis during developmental stages leads to behavioral abnormalities relevant to prodromal symptoms and schizophrenia, in later life. Furthermore, early pharmacological intervention with D-serine may prevent the onset of psychosis in adult.

Cognitive function in schizophrenia and its association with socio-demographics factors

BACKGROUND

Schizophrenia is a chronic and debilitating psychiatric illness consisting primarily of positive and negative symptoms. However, cognitive deficits in various domains have been consistently replicated in patients with schizophrenia. Therefore, the present study was designed to assess cognitive impairment in schizophrenia and to correlate the same with sociodemographic factors.

MATERIALS AND METHODS

Cognitive function in 100 patients with schizophrenia as per Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM IV-TR) criteria attending the psychiatry outpatient department (OPD) of Department of Psychiatry, SBKS MIRC was assessed using Addenbrooke's Cognitive Examination Revised (ACER) rating scale and Mini Mental State Examination (MMSE) and sociodemographic details was obtained using semistructured proforma. Data was analyzed by Chi-square and t-test.

RESULTS

About 70% patients of schizophrenia were found to have cognitive dysfunction for attention, concentration, memory, language, and executive function. Positive symptoms were associated with memory (P<0.001) and attention impairment (P<0.05). Patients with duration of illness >2 years and belonging to urban habitat showed more cognitive dysfunction. Male patients were associated with impairment in two domains of ACER: Language and memory.

CONCLUSION

The study findings depict that persistent cognitive deficits are seen in patients with schizophrenia. Its correlation with sociodemographic factors showed that patients with >2 years of illness and belonging to urban habitat showed more cognitive dysfunction. Male patients were associated with language and memory impairment. Our study recommends that the neurocognitive impairment should be included in the DSM-V diagnostic criteria for schizophrenia.

The relationships between schizophrenia symptom dimensions and executive functioning components

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Symptoms as mediators of the relationship between neurocognition and functional outcome in schizophrenia: a meta-analysis

BACKGROUND

Neurocognitive functioning in schizophrenia has received considerable attention because of its robust prediction of functional outcome. Psychiatric symptoms, in particular negative symptoms, have also been shown to predict functional outcome, but have garnered much less attention. The high degree of intercorrelation among all of these variables leaves unclear whether neurocognition has a direct effect on functional outcome or whether that relationship to functional outcome is partially mediated by symptoms.

METHODS

A meta-analysis of 73 published English language studies (total n=6519) was conducted to determine the magnitude of the relationship between neurocognition and symptoms, and between symptoms and functional outcome. A model was tested in which symptoms mediate the relationship between neurocognition and functional outcome. Functional outcome involved measures of social relationships, school and work functioning, and laboratory assessments of social skill.

RESULTS

Although negative symptoms were found to be significantly related to neurocognitive functioning (p<.01) positive symptoms were not (p=.97). The relationship was moderate for negative symptoms (r=-.24, n=4757, 53 studies), but positive symptoms were not at all related to neurocogniton (r=.00, n=1297, 25 studies). Negative symptoms were significantly correlated with functional outcome (r=-.42, p<.01), and again the correlation was higher than for positive symptoms (r=-.03, p=.55). Furthermore, our findings support a model in which negative symptoms significantly mediate the relationship between neurocognition and functional outcome (Sobel test p<.01).

CONCLUSIONS

Although neurocognition and negative symptoms are both predictors of functional outcome, negative symptoms might at least partially mediate the relationship between neurocognition and outcome.

Cognitive functioning and negative symptoms in first episode schizophrenia: different patterns of correlates

Negative symptoms of schizophrenia have been related to disturbances of executive functions, memory, attention and motor functioning. The executive functions dimension comprises a variety of cognitive subprocesses, including speed of processing, flexibility and working memory. We independently analysed the relationship between different cognitive tasks and clinical symptoms (negative, positive and disorganized) in a sample of 126 first-episode patients with schizophrenia spectrum disorders. Negative symptoms were significantly associated with performance on executive-functions and motor coordination tasks. Within the executive functions domain only those tests that required speeded performance showed a significant association with the negative dimension. The widely described relationship between negative symptoms and executive impairments in schizophrenia appears to be mediated by likely dysfunctions in the speed of processing instead of by working memory impairment.

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 neuropsychology of cannabis and other substance use in schizophrenia: review of the literature and critical evaluation of methodological issues

Research on the neuropsychology of substance use in schizophrenia has been steadily growing over the past decade. However, significant gaps remain in the knowledge of individual substances and their relationship to cognition in the schizophrenia spectrum disorders. Approximately 65 studies to date have directly examined this relationship. Of these, approximately 20 have focused on nicotine, 15 on alcohol, 10 on cocaine, three on stimulants/hallucinogens, one on benzodiazepines, 10 on polydrug abuse, and seven on cannabis. Research on cannabis is especially lacking, given that worldwide it is the most commonly used illicit drug in schizophrenia, is used at higher rates in schizophrenia than in the general population, and makes its own unique contribution to the onset and prognosis of schizophrenia. In the present paper an overview of the neuropsychology literature on substance use in schizophrenia is presented, with special emphasis on cannabis. This incorporates a discussion of the methodological limitations inherent in these studies, and range of potential confounding variables that were not considered or controlled, providing directions for future research into the cognitive correlates of cannabis and other substance use in schizophrenia.

A comparison between a researcher-rated and a self-report method of insight assessment in chronic schizophrenia revisited: a replication study using the SUMD and SAIQ

Previous research in schizophrenia has not consistently found concurrent validity between researcher-rated and self-report scales of insight. Differences in the correlations between the two types of scales have been found when order of administration is varied. The current study sought to replicate this earlier study in a sample of 21 patients with chronic schizophrenia who were given the same researcher-rated scale (Scale to Assess Unawareness of Mental Disorder; SUMD) and a different self-report measure (Self-Appraisal of Illness Questionnaire; SAIQ). A counterbalanced research design was employed. Significant correlations (p < 0.05) were found between the SUMD and SAIQ subscales in the SAIQ first group but not in the SUMD first group. The present study replicated earlier findings and provides further support for the importance of order of administration effects when evaluating concurrent validity between different types of insight scales. The reliability of insight scales may be substantially improved if a self-report insight scale is administered prior to a researcher-rated scale.

Stability and validity of memory-based subtypes of schizophrenia

This study assessed whether verbal memory performance indexed by the California Verbal Learning Test (CVLT) can organize and reduce the heterogeneity of schizophrenia. The temporal stability, cognitive and clinical validity of: (a) a putatively cortical-subcortical-normative typology derived from dementia patients' scores on the CVLT and (b) a memory performance dichotomy based on a psychometric criterion and 1 CVLT summary score were evaluated. These memory subtypes were examined in 102 schizophrenia patients, 55 of whom were assessed again 3 years later. The results indicate that both methods yield potentially valuable illness distinctions on a cross-sectional basis, but fail to show truly trait-like properties. Furthermore, the evidence favors the validity of a parsimonious dichotomy over a more complex dementia-based typology.

Does self-perceived mood predict more variance in cognitive performance than clinician-rated symptoms in schizophrenia?

Symptoms are known to account for a small variance in some cognitive functions in schizophrenia, but the influence of self-perceived mood remains largely unknown. The authors examined the influence of subjective mood states, psychopathology, and depressive symptoms in cognitive performance in a single investigation in schizophrenia. A group of 40 stable medicated patients with schizophrenia (20 men, 20 women) and 30 healthy comparison subjects (15 men, 15 women) were assessed on neurocognitive measures of verbal abilities, attention, executive functioning, language, memory, motor functioning, and information processing. All subjects provided self-ratings of mood prior to cognitive testing. Patients were also rated on psychopathology and depressive symptoms. Patients performed worse than comparison subjects on most cognitive domains. Within the patient group, subjective feelings of depression-dejection, fatigue-inertia, confusion, and tension-anxiety predicted (controlling for symptoms) poor performance on measures of attention, executive function, and verbal memory. In the same group of patients, clinician-rated symptoms of psychopathology and depression predicted significantly poor performance only on tests of motor function. In comparison subjects, vigor related to better, and fatigue and inertia to worse, spatial motor performance. Self-perceived negative mood state may be a better predictor of cognitive deficits than clinician-rated symptoms in chronic schizophrenia patients.

Does negative symptom change relate to neurocognitive change in schizophrenia? Implications for targeted treatments

Negative symptoms and cognitive dysfunction are among the most challenging obstacles in the treatment of schizophrenia. It is unknown to what extent they are overlapping or independent disease processes. In the search for targeted treatments of negative symptoms and cognitive impairments, it is imperative to determine their longitudinal relationship. 267 stable outpatients with schizophrenia in a work and cognitive rehabilitation program were evaluated using symptom measures and a comprehensive neuropsychological test battery at baseline and at the conclusion of rehabilitation, 6 months later. Baseline negative symptom, neuropsychological variables and change scores from intake to follow-up on these variables were correlated. These analyses were repeated with a subsample (n = 161) who had clinically significant negative symptoms at baseline. ANCOVA's were performed to compare patients whose negative symptoms improved by 5 points or more (n = 69) with those whose negative symptoms got worse by 5 points or more (n = 26) on their neurocognitive performance at follow-up. Intake negative symptoms were significantly associated with theory of mind and visuomotor processing. Results failed to support a lawful relationship between change in negative symptoms and neurocognition. These findings suggest that negative symptoms and neurocognition should be viewed as relatively independent targets for intervention.

Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of clozapine, but not haloperidol

This study was undertaken to examine the effects of subsequent administration of antipsychotic drugs (clozapine and haloperidol) on cognitive deficits in mice after repeated administration of phencyclidine (PCP). In the novel object recognition test, repeated administration of PCP (10 mg/kg) significantly decreased exploratory preference in the retention test session but not in the training test session. PCP-induced deficits were significantly improved by subsequent subchronic (2 weeks) administration of clozapine (5 mg/kg), but not haloperidol (0.1 mg/kg). These findings suggest that PCP-induced cognitive deficits using the novel object recognition test may be a potential animal model of atypical antipsychotic activity.

NC-1900, an arginine–vasopressin analogue, ameliorates social behavior deficits and hyperlocomotion in MK-801-treated rats: Therapeutic implications for schizophrenia

We previously reported that chronic administration of N-methyl-D-aspartate (NMDA) antagonists reduced the density of vasopressin V1a receptors in several brain regions in rats that demonstrated social interaction deficits and increased locomotor activity. These observations indicate the ability of arginine-vasopressin (AVP), or its analogues, to modulate behavioral abnormalities associated with blockade of NMDA receptors. The present study was performed to investigate the effect of NC-1900, an AVP analogue, on social behavior and locomotor activity in rats treated with MK-801, a non-competitive NMDA receptor antagonist. Male Wistar rats were administered MK-801 (0.13 mg/kg/day ip) or saline for 14 days. Social behavior and locomotor activity were measured 45 min after the injection of NC-1900 (10 ng/kg sc) or saline together with the last MK-801 or vehicle administration. Social interaction was quantified by an automated video-tracking system, and stereotyped behavior and ataxia were manually measured. Acute administration of NC-1900 partially reversed MK-801-induced hyperlocomotion and deficits in social interaction, while NC-1900 itself did not affect these behavioral measures in animals chronically treated with vehicle saline. These results suggest that the central AVP system may interact with glutamatergic and dopaminergic transmissions, and indicate potential therapeutic effects of AVP analogues on positive and negative symptoms of schizophrenia.

Neuropsychological differentiation of late-onset schizophrenia and dementia of the Alzheimer's type

Late-onset schizophrenia and dementia of the Alzheimer's type (DAT) often present with some pathological and behavioral commonalities. Specifically, both illnesses may involve varying degrees of delusional manifestation, apathy, lateral/third-ventricular enlargement, reduced frontal lobe activity, and hippocampal atrophy. Moreover, patients with either disease have shown comparable cognitive impairment on standardized neuropsychological tests. As such, a differential diagnosis of the 2 disorders on the basis of such testing can prove to be difficult. This study evaluated the neuropsychological test results of 32 patients with late-onset schizophrenia and 32 patients with DAT to distinguish the tests that best differentiate the 2 disorders. Results indicate that the Wechsler Adult Intelligence Scale-Revised Similarities subtest and the California Verbal Learning Test (both short- and long-delay free recall) correspond to sensitive diagnostic neuropsychological measures. This investigation was preliminary in nature, and should aid in the development of a definitive differential profile.

Neuroticism and visual memory impairments as predictors of the severity of delusions in schizophrenia

This study examined whether levels of emotional distress and impairments in visual memory were uniquely associated with severity of delusions in schizophrenia. Severity of delusions was assessed using select items from the positive component of the Positive and Negative Syndrome Scale among 44 persons with schizophrenia or schizoaffective disorder in a post-acute phase of illness. Emotional distress was assessed using the neuroticism subscale of the NEO Five Factor Inventory, and visual memory was assessed using the Rey Complex Figure Test. Controlling for executive function, visual attention, and verbal memory, a multiple regression analysis revealed that visual memory and neuroticism were each significantly related to severity of delusions, with the two combined accounting for one quarter of the variance. These same variables were unrelated to negative and excitement symptoms. Severity of delusions is linked to both higher levels of neuroticism and greater impairment in visual memory.

Verbal declarative memory dysfunction in schizophrenia: from clinical assessment to genetics and brain mechanisms

The recent literature on the neuropsychology of schizophrenia has emphasized memory deficits as a key area of impairment. Abnormalities in the medial temporal lobe, a brain region crucial for long-term memory formation, have also consistently been reported. We conducted a comprehensive review of verbal declarative memory (VDM) in schizophrenia with the aim of systematically addressing the nature of this impairment. We conclude that verbal declarative memory is significantly impaired in schizophrenia and is largely accounted for by deficits in the encoding stage. Subtle impairments in increased rates of forgetting are present, but are mild compared with those in amnestic disorders. Impairment in other cognitive domains studied thus far (e.g., attention), medication effects, or fluctuations in symptoms do not completely account for the deficit. VDM is among the most impaired neurocognitive domains in schizophrenia (along with attention and executive functions). Milder encoding deficits are present in high-risk subjects and non-psychotic relatives of individuals with schizophrenia suggesting that components of the deficit are associated with a genetic vulnerability to the illness, and are independent of the frank psychotic illness. Furthermore, VDM is observed in individuals experiencing their first-psychotic episode and it remains fairly consistent over time. Preliminary imaging studies and other work suggest abnormalities in prefrontal-hippocampal processing networks. Future work should emphasize delineating specific information processing components contributing to the deficit. This would allow imaging studies to determine which brain regions contribute to specific information processing deficits in schizophrenia.

Schizophrenia and memory impairment: evidence for a neurocognitive subtype

Evidence is presented that verbal memory impairment distinguishes a subgroup of patients with schizophrenia who also differ in symptom profile and illness adjustment. On the basis of the California Verbal Learning Test (CVLT), a sample of patients was partitioned into memory-impaired (n=16) and memory-unimpaired groups (n=16). Groups were matched for age, sex, IQ, and anti-psychotic medication. These groups were then compared using the Brief Psychiatric Rating Scale (BPRS) and the Sickness Impact Profile (SIP). Results indicate that memory-impaired schizophrenia patients experience significantly more positive symptoms and a poorer quality of life than their memory-unimpaired counterparts. This finding supports the idea that neurocognitive measures are a valuable way of organizing the heterogeneous disease states of schizophrenia.

Correlation between clinical syndromes and neuropsychological tasks in unmedicated patients with recent onset schizophrenia

The aim of this study is to circumscribe the cognitive deficits according to schizophrenic syndromes in a population of sub-acute untreated patients. We have studied the cross-sectional correlation between cognitive deficits and schizophrenic symptoms, in a group of 24 untreated patients (including 17 neuroleptic-naive patients) with recent onset of the disease. A task of alertness, a working memory (WM) test (including two levels of difficulty) and an abbreviated version of the Wisconsin Card Sorting Test (WCST) were selected. WM deficits and poor performance on the WCST were highly correlated with disorganized symptoms, modestly with the positive syndrome and not with the negative syndrome. Thus, disorganized symptoms, more than any other, appear to be related to the impairment of executive function and WM in recent onset unmedicated patients with schizophrenia.

Cognitive performance in schizophrenia: relationship to regional brain volumes and psychiatric symptoms

In an all-male sample of schizophrenic patients stabilized by medication (n=62) and normal controls (n=27), we obtained neuropsychological test data and high-resolution whole brain magnetic resonance scans, as well as detailed psychiatric rating scales on a subset of the patients (n=47). Schizophrenic patients had significantly worse overall age-adjusted cognitive performance than normal controls (average z-score=-0.90, range=-0.60 to -1.81), which included relatively more severe deficits with different types of memory, psychomotor speed, verbal fluency and verbal abstraction. Schizophrenic patients also had significantly smaller bilateral volumes in gray but not white matter in the prefrontal region, superior temporal gyrus and whole temporal lobe, but no group differences were observed in the hippocampus and parahippocampus. Correlations between the brain regions and cognitive performance revealed different sets of significant relationships for the two groups, particularly in the prefrontal and hippocampal regions. In addition, inverse correlations were observed between certain cognitive abilities (psychomotor speed, cognitive flexibility and verbal fluency) and patients' psychiatric ratings, especially with measures of negative symptoms. The convergence of findings for schizophrenic patients regarding the prefrontal region, negative symptoms, psychomotor speed and cognitive flexibility suggests that schizophrenic negative symptoms may involve disruption of frontal-subcortical connections.

Visual processing and neuropsychological function in schizophrenia and schizoaffective disorder

Persons with schizophrenia and schizoaffective disorder exhibit deficits in both visual processing and neuropsychological tasks. Little is known, however, about whether these deficits are related to one another. We administered psychophysical tests of visual discrimination and recognition, and neuropsychological tests of abstract flexibility, verbal learning, visual memory, working memory and attention to 42 outpatients with stable but chronic schizophrenia or schizoaffective disorder. Multiple regression analyses were performed to determine the relationship between these measures of neuropsychological function and visual psychophysical performance. Results indicated that motion perception was associated with working memory, and that the addition of a memory component to motion perception (motion recognition) was associated with both working memory and visual memory. Visual performance was not associated with symptom severity as measured by the PANSS. These results suggest that psychophysical tests of visual processing may contribute to deficits on neuropsychological tests of visual cognition, and may also reflect cross-modal disturbances of working memory function.

Relationship between subjective cognitive symptoms and frontal executive abilities in chronic schizophrenic outpatients

The aim of this study was to investigate the relationship between executive abilities and subjective basic symptoms in a group of outpatients with schizophrenia. Fifty patients underwent a neuropsychological testing battery. Basic symptoms were assessed using the Frankfurt Complaint Questionnaire. Using Pearson's product-moment correlations or partial correlations calculated by regression procedure, cognitive performance was not related to subjective experience. When patients were divided into two groups, with and without 'hypofrontality', as assessed by the neuropsychological testing, we did not find any significant difference in basic symptoms rating. Thus, it is likely that basic symptoms and neurocognitive functioning are unrelated in schizophrenic outpatients, probably because the expression of subjective experience and cognitive impairment is less pronounced than in inpatients. Also, subjective self-perceived basic symptoms and neurocognitive functioning may be unrelated, because these concepts are based on different theoretical backgrounds.

Functional neuroanatomy of auditory working memory in schizophrenia: relation to positive and negative symptoms

Functional brain imaging studies of working memory (WM) in schizophrenia have yielded inconsistent results regarding deficits in the dorsolateral prefrontal (DLPFC) and parietal cortices. In spite of its potential importance in schizophrenia, there have been few investigations of WM deficits using auditory stimuli and no functional imaging studies have attempted to relate brain activation during auditory WM to positive and negative symptoms of schizophrenia. We used a two-back auditory WM paradigm in a functional MRI study of men with schizophrenia (N = 11) and controls (N = 13). Region of interest analysis was used to investigate group differences in activation as well as correlations with symptom scores from the Brief Psychiatric Rating Scale. Patients with schizophrenia performed significantly worse and were slower than control subjects in the WM task. Patients also showed decreased lateralization of activation and significant WM related activation deficits in the left and right DLPFC, frontal operculum, inferior parietal, and superior parietal cortex but not in the anterior cingulate or superior temporal gyrus. These results indicate that in addition to the prefrontal cortex, parietal cortex function is also disrupted during WM in schizophrenia. Withdrawal-retardation symptom scores were inversely correlated with frontal operculum activation. Thinking disturbance symptom scores were inversely correlated with right DLPFC activation. Our findings suggest an association between thinking disturbance symptoms, particularly unusual thought content, and disrupted WM processing in schizophrenia.