Long-term memory deficits in schizophrenia: primary or secondary dysfunction?

The Efficacy of Extended Metacognitive Training on Neurocognitive Function in Schizophrenia: A Randomized Controlled Trial

The aim of this study was to evaluate the effect of metacognitive training (MCT) on improving the neurocognitive function of Chinese patients with schizophrenia. One hundred inpatients with schizophrenia were selected by regional group randomization and divided into the control (treated as usual, TAU) group (n = 50) and the TAU + MCT group (n = 50). In this study, a 10-module MCT was used and the intervention process lasted 30 days. Cognitive function was assessed blindly using the Repeatable Battery of Neuropsychological Status (RBANS) scale at baseline, 24 h post-treatment, and 12 weeks’ post-treatment. The differences between the total RBANS score and baseline (pre-test) for the post-test and 12-week-follow-up tests were used as the primary outcome, and the difference between the RBANS dimension scores and baseline (pre-test) were used as a secondary outcome in this study. The completion rate at follow-up was high in the TAU + MCT group (94%). Intention-to-treat analysis and per-protocol analysis showed a significant increase in total neurocognitive function scores and three-dimensional scores (delayed memory, visual breadth, and attention) in the TAU + MCT group immediately after the intervention and at the 12-week follow-up compared with baseline. This study provides support for the efficacy of 10 module MCT concerning neurocognition.

Systematic Review on the Role of Lobar Cerebral Microbleeds in Cognition

BACKGROUND

Cerebral microbleeds (CMBs) are small round/oval lesions seen in MRI-specific sequences. They are divided in deep and lobar according to their location. Lobar CMBs (L-CMBs) are commonly associated with amyloid angiopathy. Although CMBs have been considered clinically silent for a long time, a growing body of evidence has shown that they could play a crucial role in cognitive functioning.

OBJECTIVE

The aim of this systematic review was to estimate the role of L-CMBs in cognitive performance.

METHODS

We selected, from the Cochrane Library, Embase, PubMed, and ScienceDirect databases, clinical studies, published from January 2000 to January 2020 and focused on the association between L-CMBs and cognitive functions. The inclusion criteria were: 1) participants grouped according to presence or absence of CMBs, 2) extensive neuropsychological examination, 3) CMBs differentiation according to topographical distribution, and 4) MRI-based CMB definition (< 10 mm and low signal in T2*/SWI). The impact of L-CMBs was separately assessed for executive functions, visuospatial skills, language, and memory.

RESULTS

Among 963 potentially eligible studies, six fulfilled the inclusion criteria. Four studies reported a greater reduction in executive performances in participants with L-CMB and two studies showed a statistically significant association between visuospatial dysfunction and L-CMBs. No association was found between hippocampal memory or language abilities and L-CMBs.

CONCLUSION

Lobar CMBs are associated with a reduction of processing speed and visuospatial performances, thus suggesting the contribution of vascular amyloid deposition to this cognitive profile. This occurrence enables us to suspect an underlying Alzheimer's disease pathology even in absence of typical hippocampal memory impairment.

Generalized neurocognitive impairment in individuals at ultra-high risk for psychosis: The possible key role of slowed processing speed

OBJECTIVE

Widespread neurocognitive impairment is well-established in individuals at ultra-high risk (UHR) for developing psychoses, but it is unknown whether slowed processing speed may underlie impairment in other neurocognitive domains, as found in schizophrenia. The study delineated domain functioning in a UHR sample and examined if neurocognitive slowing might account for deficits across domains.

METHODS

The cross-sectional study included 50 UHR individuals with no (n = 38) or minimal antipsychotic exposure (n = 12; mean lifetime dose of haloperidol equivalent = 17.56 mg; SD = 13.04) and 50 matched healthy controls. Primary analyses compared group performance across neurocognitive domains before and after covarying for processing speed. To examine the specificity of processing speed effects, post hoc analyses examined the impact of the other neurocognitive domains and intelligence as covariates.

RESULTS

UHR individuals exhibited significant impairment across all neurocognitive domains (all ps ≤ .010), with medium to large effect sizes (Cohen's ds = -0.53 to -1.12). Only processing speed used as covariate eliminated significant between-group differences in all other domains, reducing unadjusted Cohen's d values with 68% on average, whereas the other domains used as covariates averagely reduced unadjusted Cohen's d values with 20% to 48%. When covarying each of the other domains after their shared variance with speed of processing was removed, all significant between-group domain differences remained (all ps ≤ .024).

CONCLUSION

Slowed processing speed may underlie generalized neurocognitive impairment in UHR individuals and represent a potential intervention target.

The "Obsessive Paradox": The Complex Relationship Between Cognitive and Obsessive Dimensions in Schizophrenia

The objective of the study was to investigate the relationship between cognitive functions and obsessive-compulsive dimension in schizophrenia and a possible moderating effect of schizophrenia symptom dimensions on this association. Sixty-one schizophrenia patients were administered the Positive and Negative Syndrome Scale, the Yale-Brown Obsessive-Compulsive Scale (YBOCS), and the Matrics Consensus Cognitive Battery. A U-shaped curve described a gradual transition from an inverse association to a positive relationship between YBOCS and processing speed scores, along a severity gradient of obsessive dimension. This effect ("the obsessive paradox") was not moderated by other symptom dimensions. The present study suggests that severe obsessive-compulsive symptoms may participate to counterbalance processing speed impairment independently from other symptom dimensions. These results highlight the complexity of the relationship between cognitive and obsessive dimensions in schizophrenia.

Neural and neuronal discoordination in schizophrenia: From ensembles through networks to symptoms

Despite the substantial knowledge accumulated by past research, the exact mechanisms of the pathogenesis of schizophrenia and causal treatments still remain unclear. Deficits of cognition and information processing in schizophrenia are today often viewed as the primary and core symptoms of this devastating disorder. These deficits likely result from disruptions in the coordination of neuronal and neural activity. The aim of this review is to bring together convergent evidence of discoordinated brain circuits in schizophrenia at multiple levels of resolution, ranging from principal cells and interneurons, neuronal ensembles and local circuits, to large-scale brain networks. We show how these aberrations could underlie deficits in cognitive control and other higher order cognitive-behavioural functions. Converging evidence from both animal models and patients with schizophrenia is presented in an effort to gain insight into common features of deficits in the brain information processing in this disorder, marked by disruption of several neurotransmitter and signalling systems and severe behavioural outcomes.

Assessment of Cognition in Schizophrenia Using Trail Making Test: A Meta-Analysis

OBJECTIVE

The present meta-analysis aimed to analyze the cognitive performance of schizophrenia patients measured by Trail Making Tests (TMT) and the contribution of socio-demographic factors to cognitive impairments.

METHODS

PubMed and PsycARTICLES databases were searched for the studies published between January 1985 and November 2017. Data were drawn from 19 studies encompassing 1095 patients and 324 controls. The effect size and heterogeneity were assessed with Comprehensive Meta-Analysis version 2 using random-effect model.

RESULTS

Overall, the results showed that the schizophrenia patients performed significantly (p<0.001) worse than healthy controls in both TMT-A and B. However, concurrent substance abuse, clinical status (inpatient or outpatient), duration of education and duration of illness were not associated with cognitive impairment among the schizophrenia patients.

CONCLUSION

The present meta-analysis confirmed the cognitive processing speed and flexibility of schizophrenia patients were impaired. However, their duration of education, duration of illness and clinical status (inpatient or outpatient) were not the risk factors.

Changes in Tryptophan Catabolite (TRYCAT) Pathway Patterning Are Associated with Mild Impairments in Declarative Memory in Schizophrenia and Deficits in Semantic and Episodic Memory Coupled with Increased False-Memory Creation in Deficit Schizophrenia

Evidence indicates that schizophrenia and in particular negative symptoms and deficit schizophrenia are accompanied by neurocognitive impairments and changes in the patterning of the tryptophan catabolite (TRYCAT) pathway. This cross-sectional study was carried out to examine the associations between cognitive functions (as measured with Consortium to Establish a Registry for Alzheimer's disease (CERAD)) and TRYCAT pathway patterning in patients with (n = 40) and without (n = 40) deficit schizophrenia and normal controls (n = 40). Cognitive measures were assessed with the Verbal Fluency Test (VFT), Boston Naming Test (BNT), Mini-Mental State Examination (MMSE), Word List Memory (WLM), Constructional Praxis, Word List Recall (WLRecall), and Word List Recognition (WLRecognition), while TRYCAT measurements assessed the IgA/IgM responses to noxious TRYCATs, namely quinolinic acid (QA), 3-OH-kynurenine (3HK), picolinic acid (PA), and xanthurenic (XA) acid, and more protective (PRO) TRYCATs, including kynurenic acid (KA) and anthranilic acid (AA). IgA NOX/PRO, IgM KA/3HK, and IgA/IgM NOX/PRO ratios were computed. Schizophrenia was accompanied by lower VFT and WLM, while BNT (dysnomia) and MMSE are significantly lower in multiple- than first-episode schizophrenia. Deficit schizophrenia is strongly associated with worse outcomes on VFT, MMSE, WLM, WLRecall, WLRecognition, and delayed recall savings and increased false memories. Around 40-50% of the variance in negative symptoms' scores was explained by VFT, WLM, WLRecall, and MMSE. Increases in IgA NOX/PRO, IgM KA/3HK, and/or IgA/IgM NOX/PRO ratios were associated with impairments in VFT, BNT, MMSE, WLM, WLRecall, WLRecognition, and false-memory creation. In conclusion, nondeficit schizophrenia is accompanied by mild memory impairments, while disease progression is accompanied by broader cognitive impairments. Deficit schizophrenia and negative symptoms are strongly associated with deficits in working memory, delayed recall and recognition, and increased false-memory creation. These cognitive impairments and memory deficits are in part explained by increased production and/or attenuated regulation of TRYCATs with neurotoxic, excitotoxic, immune-inflammatory, oxidative, and nitrosative potential, which may contribute to neuroprogression.

Influence of cognition, premorbid adjustment and psychotic symptoms on psycho-social functioning in first-episode psychosis

OBJECTIVE

The aim of this study is to evaluate the relationship between psycho-social functioning and symptoms, cognitive function, and premorbid adjustment, in patients with a first-episode psychosis.

METHOD

Clinical data were obtained from 90 patients, who were assessed with the Disability Assessment Scale (DAS-sv), the Positive and Negative Syndrome Scale (PANSS), the Premorbid Adjustment Scale (PAS-S) and with a battery of cognitive tests including Trail Making Tests A and B (TMTA- B), Continous Performance Test (CPT), some subscales of the Wechler Adult Intelligence Scale (WAIS), and the Verbal Learning Test España-Complutense (TAVEC).

RESULTS

The results of the study suggest that psycho-social functioning in first-episode psychosis is significantly related to: positive, negative, excitative, affective and disorganized symptoms, social premorbid adjustment, cognitive flexibility, working memory, short term and long term memory. Of these, those which best explained psycho-social functioning are the positive and excitative symptoms, premorbid adjustment, flexibility and memory.

CONCLUSIONS

These findings highlight the importance early intervention on cognitive and clinical variables to help provide a better psycho-social functioning in people with a first-episode of psychosis.

Neuropsychology, autobiographical memory, and hippocampal volume in "younger" and "older" patients with chronic schizophrenia

Despite a wide range of studies on neuropsychology in schizophrenia, autobiographical memory (AM) has been scarcely investigated in these patients. Hence, less is known about AM in older patients and hippocampal contribution to autobiographical memories of varying remoteness. Therefore, we investigated hippocampal volume and AM along with important neuropsychological domains in patients with chronic schizophrenia and the respective relationships between these parameters. We compared 25 older patients with chronic schizophrenia to 23 younger patients and an older healthy control group (N = 21) with respect to AM, additional neuropsychological parameters, and hippocampal volume. Personal episodic and semantic memory was investigated using a semi-structured interview. Additional neuropsychological parameters were assessed by using a battery of standard neuropsychological tests. Structural magnetic resonance imaging data were analyzed with an automated region-of-interest procedure. While hippocampal volume reduction and neuropsychological impairment were more pronounced in the older than in the younger patients, both groups showed equivalent reduced AM performance for recent personal episodes. In the patient group, significant correlations between left hippocampal volume and recent autobiographical episodes as well as personal semantic memories arose. Verbal memory and working memory were significantly correlated with right hippocampal volume; executive functions, however, were associated with bilateral hippocampal volumes. These findings underline the complexity of AM and its impairments in the course of schizophrenia in comparison to rather progressive neuropsychological deficits and address the importance of hippocampal contribution.

Synaptic plasticity, neural circuits, and the emerging role of altered short-term information processing in schizophrenia

Synaptic plasticity alters the strength of information flow between presynaptic and postsynaptic neurons and thus modifies the likelihood that action potentials in a presynaptic neuron will lead to an action potential in a postsynaptic neuron. As such, synaptic plasticity and pathological changes in synaptic plasticity impact the synaptic computation which controls the information flow through the neural microcircuits responsible for the complex information processing necessary to drive adaptive behaviors. As current theories of neuropsychiatric disease suggest that distinct dysfunctions in neural circuit performance may critically underlie the unique symptoms of these diseases, pathological alterations in synaptic plasticity mechanisms may be fundamental to the disease process. Here we consider mechanisms of both short-term and long-term plasticity of synaptic transmission and their possible roles in information processing by neural microcircuits in both health and disease. As paradigms of neuropsychiatric diseases with strongly implicated risk genes, we discuss the findings in schizophrenia and autism and consider the alterations in synaptic plasticity and network function observed in both human studies and genetic mouse models of these diseases. Together these studies have begun to point toward a likely dominant role of short-term synaptic plasticity alterations in schizophrenia while dysfunction in autism spectrum disorders (ASDs) may be due to a combination of both short-term and long-term synaptic plasticity alterations.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Improving Outcome of Psychosocial Treatments by Enhancing Memory and Learning

Mental disorders are prevalent and can lead to significant impairment. Some progress has been made toward establishing treatments; however, effect sizes are small to moderate, gains may not persist, and many patients derive no benefit. Our goal is to highlight the potential for empirically supported psychosocial treatments to be improved by incorporating insights from cognitive psychology and research on education. Our central question is: If it were possible to improve memory for the content of sessions of psychosocial treatments, would outcome substantially improve? We leverage insights from scientific knowledge on learning and memory to derive strategies for transdiagnostic and transtreatment cognitive support interventions. These strategies can be applied within and between sessions and to interventions delivered via computer, the Internet, and text message. Additional novel pathways to improving memory include improving sleep, engaging in exercise, and using imagery. Given that memory processes change across the lifespan, services to children and older adults may benefit from different types and amounts of cognitive support.

Memory deficits in aging and neurological diseases

Memory is central to our ability to perform daily life activities and correctly function in society. Improvements in public health and medical treatment for a variety of diseases have resulted in longer life spans; however, age-related memory impairments have been significant sources of morbidity. Loss in memory function is not only associated with aging population but is also a feature of neurodegenerative diseases such as Alzheimer's disease and other psychiatric and neurological disorders. Here, we focus on current understanding of the impact of normal aging on memory and what is known about its mechanisms, and further review pathological mechanisms behind the cause of dementia in Alzheimer's disease. Finally, we discuss schizophrenia and look into abnormalities in circuit function and neurotransmitter systems that contribute to memory impairment in this illness.

A model of memory impairment in schizophrenia: cognitive and clinical factors associated with memory efficiency and memory errors

BACKGROUND

Memory impairments in patients with schizophrenia have been associated with various cognitive and clinical factors. Hallucinations have been more specifically associated with errors stemming from source monitoring failure.

METHODS

We conducted a broad investigation of verbal memory and visual memory as well as source memory functioning in a sample of patients with schizophrenia. Various memory measures were tallied, and we studied their associations with processing speed, working memory span, and positive, negative, and depressive symptoms.

RESULTS

Superficial and deep memory processes were differentially associated with processing speed, working memory span, avolition, depression, and attention disorders. Auditory/verbal and visual hallucinations were differentially associated with specific types of source memory error.

CONCLUSIONS

We integrated all the results into a revised version of a previously published model of memory functioning in schizophrenia. The model describes the factors that affect memory efficiency, as well as the cognitive underpinnings of hallucinations within the source monitoring framework.

Cognitive correlates of verbal memory and verbal fluency in schizophrenia, and differential effects of various clinical symptoms between male and female patients

BACKGROUND

Impairment of higher cognitive functions in patients with schizophrenia might stem from perturbation of more basic functions, such as processing speed. Various clinical symptoms might affect cognitive efficiency as well. Notably, previous research has revealed the role of affective symptoms on memory performance in this population, and suggested sex-specific effects.

METHOD

We conducted a post-hoc analysis of an extensive neuropsychological study of 88 patients with schizophrenia. Regression analyses were conducted on verbal memory and verbal fluency data to investigate the contribution of semantic organisation and processing speed to performance. The role of negative and affective symptoms and of attention disorders in verbal memory and verbal fluency was investigated separately in male and female patients.

RESULTS

Semantic clustering contributed to verbal recall, and a measure of reading speed contributed to verbal recall as well as to phonological and semantic fluency. Negative symptoms affected verbal recall and verbal fluency in the male patients, whereas attention disorders affected these abilities in the female patients. Furthermore, depression affected verbal recall in women, whereas anxiety affected it in men.

CONCLUSIONS

These results confirm the association of processing speed with cognitive efficiency in patients with schizophrenia. They also confirm the previously observed sex-specific associations of depression and anxiety with memory performance in these patients, and suggest that negative symptoms and attention disorders likewise are related to cognitive efficiency differently in men and women.

Emotional memory modulation in schizophrenia: an overview

OBJECTIVE

In healthy controls, the emotional charge of stimuli influences how well stimuli are remembered. Although patients with schizophrenia (SCZ) have deficits in memory and in emotional processing, studies on emotional memory modulation (EMM) in SCZ report contradictory results. The aim of this review was to investigate whether methodological differences could explain these contradictory results.

METHOD

We reviewed the literature to investigate whether task differences could explain these differences. Due to the methodological differences, a meta-analysis was not possible.

RESULTS

Fourteen studies were identified that used a total of 22 tasks to study EMM in patients with SCZ. Two-thirds of the tasks showed no differences in EMM between patients with SCZ and healthy controls. Differences in EMM were found more often when long-term compared to short-term memory was measured, when memory instructions were implicit instead of explicit and when stronger emotional stimuli were used. An overall memory deficit or the mode of retrieval was not related to EMM.

CONCLUSION

Deficits in EMM in long-term compared to short-term memory point toward impaired emotional modulation of memory consolidation. Reduced EMM on implicit, but not explicit, tasks suggests a deficit in unconsciously using emotional content to modulate memory.

Processing speed and executive functions predict real-world everyday living skills in adolescents with early-onset schizophrenia

Cognition and clinical variables are known to be among the most predictive factors of real-world social functioning and daily living skills in adult-onset schizophrenia. Fewer studies have focused on their impact in adolescents with early-onset schizophrenia (EOS). The aim of this study is to examine the relationships and the predictive value of cognition and clinical variables on real-world daily living skills in a sample of adolescents with EOS. Cognitive, clinical and real-world everyday living skills measures were administered to 45 clinically and pharmacologically stabilized adolescent outpatients with EOS and 45 healthy control subjects matched by age and sex. Multi-variant analyses to compare cognitive and real-world functioning profiles between patients and controls and regression analysis to identify predictors of real-world functioning scores in patients were used. Adolescents with EOS showed a generalized cognitive and real-world daily living skills dysfunction. Several cognitive and clinical variables significantly correlated with real-world daily living skills functioning but only the processing speed and executive functions emerged as independent predictors of everyday living skills scores, explaining 25.1% of the variance. Slowness in processing information and executive dysfunction showed a significant impact on real-world daily living skills in EOS, independently from clinical symptoms and other cognitive variables. Nevertheless, much of the variance in the daily living skills measure remained unaccounted for, suggesting that other factors were involved as well in this young population.

Hierarchical structure of the cognitive processes in schizophrenia: the fundamental role of processing speed

OBJECTIVE

Decreased processing speed (PS) is a key feature of schizophrenia with respect to cognition, functional outcome and clinical symptoms. Our objective was to test whether PS slowing mediates other neuropsychological deficits among patients with chronic schizophrenia.

METHOD

One hundred patients with schizophrenia and 53 healthy adults completed a series of neuropsychological measures that assess six cognitive domains. In addition to PS these included attention, verbal memory, visual memory, working memory, and executive functioning. Confirmatory factor analysis (CFA) was used to evaluate the fit of the 6-factor model. The cognitive performances of both groups were compared before and after controlling for the effect of PS, but also after controlling for the effect of each cognitive factor at a time. Finally, the PS-related variance was removed and the effect of the other cognitive factors was tested again.

RESULTS

CFA supported the hypothesized 6-factor cognitive structure. As expected, the patients and controls differed on all cognitive measures. However, after controlling for the effects of PS, group differences on the other five cognitive factors decreased substantially. Controlling for other factors produced smaller attenuation of group differences, and these effects were also partially accounted for by decreased PS.

CONCLUSIONS

PS deficits account for most of the differences in cognition between patients with schizophrenia and healthy controls. PS slowing appears to be a core feature of schizophrenia, one that underlies impairments of working memory, executive functioning, and other abilities.

Ketamine disrupts θ modulation of γ in a computer model of hippocampus

Abnormalities in oscillations have been suggested to play a role in schizophrenia. We studied theta-modulated gamma oscillations in a computer model of hippocampal CA3 in vivo with and without simulated application of ketamine, an NMDA receptor antagonist and psychotomimetic. Networks of 1200 multicompartment neurons [pyramidal, basket, and oriens-lacunosum moleculare (OLM) cells] generated theta and gamma oscillations from intrinsic network dynamics: basket cells primarily generated gamma and amplified theta, while OLM cells strongly contributed to theta. Extrinsic medial septal inputs paced theta and amplified both theta and gamma oscillations. Exploration of NMDA receptor reduction across all location combinations demonstrated that the experimentally observed ketamine effect occurred only with isolated reduction of NMDA receptors on OLMs. In the ketamine simulations, lower OLM activity reduced theta power and disinhibited pyramidal cells, resulting in increased basket cell activation and gamma power. Our simulations predict the following: (1) ketamine increases firing rates; (2) oscillations can be generated by intrinsic hippocampal circuits; (3) medial-septum inputs pace and augment oscillations; (4) pyramidal cells lead basket cells at the gamma peak but lag at trough; (5) basket cells amplify theta rhythms; (6) ketamine alters oscillations due to primary blockade at OLM NMDA receptors; (7) ketamine alters phase relationships of cell firing; (8) ketamine reduces network responsivity to the environment; (9) ketamine effect could be reversed by providing a continuous inward current to OLM cells. We suggest that this last prediction has implications for a possible novel treatment for cognitive deficits of schizophrenia by targeting OLM cells.

Processing speed and working memory span: their differential role in superficial and deep memory processes in schizophrenia

Previous work has suggested that decrement in both processing speed and working memory span plays a role in the memory impairment observed in patients with schizophrenia. We undertook a study to examine simultaneously the effect of these two factors. A sample of 49 patients with schizophrenia and 43 healthy controls underwent a battery of verbal and visual memory tasks. Superficial and deep encoding memory measures were tallied. We conducted regression analyses on the various memory measures, using processing speed and working memory span as independent variables. In the patient group, processing speed was a significant predictor of superficial and deep memory measures in verbal and visual memory. Working memory span was an additional significant predictor of the deep memory measures only. Regression analyses involving all participants revealed that the effect of diagnosis on all the deep encoding memory measures was reduced to non-significance when processing speed was entered in the regression. Decreased processing speed is involved in verbal and visual memory deficit in patients, whether the task require superficial or deep encoding. Working memory is involved only insofar as the task requires a certain amount of effort.

Developmental differences in explicit and implicit conceptual memory tests: a processing view account

The present study addressed contradictory results in childhood literature about conceptual priming. Based on the processing view, two forms of conceptual priming were investigated across two experiments in children aged from 7 to 16: associative priming (using the free-association test) and relational (categorical) priming (using the categorical exemplar generation test) as well as their explicit memory measure counterparts (the associative-cued recall and the category-cued recall). Experiment 1 compared age differences in associative and relational (categorical) priming. Experiment 2 focused on relational (categorical) priming with manipulations of blocked/unblocked words per category. The results showed that (a) associative priming was unchanged in children aged from 7 to 16, whereas relational (categorical) priming improved from 7-9 to 13-16 years old, and (b) age differences in relational (categorical) priming still occurred under unblocked conditions and blocked condition, while age differences in explicit measures were reduced under blocked conditions. These findings were discussed in line with the debate between the system and processing view and in terms of knowledge and automaticity development.

Reinforcement ambiguity and novelty do not account for transitive inference deficits in schizophrenia

The capacity for transitive inference (TI), a form of relational memory organization, is impaired in schizophrenia patients. In order to disambiguate deficits in TI from the effects of ambiguous reinforcement history and novelty, 28 schizophrenia and 20 nonpsychiatric control subjects were tested on newly developed TI and non-TI tasks that were matched on these 2 variables. Schizophrenia patients performed significantly worse than controls on the TI task but were able to make equivalently difficult nontransitive judgments as well as controls. Neither novelty nor reinforcement ambiguity accounted for the selective deficit of the patients on the TI task. These findings implicate a disturbance in relational memory organization, likely subserved by hippocampal dysfunction, in the pathophysiology of schizophrenia.

The relationship between IQ, memory, executive function, and processing speed in recent-onset psychosis: 1-year stability and clinical outcome

Studies commonly report poor performance in psychotic patients compared with controls on tasks testing a range of cognitive functions, but, because current IQ is often not matched between these groups, it is difficult to determine whether this represents a generalized deficit or specific abnormalities. Fifty-three first-episode psychosis patients and 53 healthy controls, one-to-one matched for sex, age, and full-scale current IQ, were compared on Wechsler Adult Intelligence Scale (WAIS) subtests representing indices of perceptual organization, verbal comprehension, processing speed, and working memory as well as other tests of executive function and episodic memory. The groups showed an equivalent pattern of performance on all WAIS subtests except digit symbol processing speed, on which the patients were significantly worse. Patients were also worse on measures where performance correlated with digit symbol score, namely working and verbal memory tasks. Standardized residual scores for each subtest were calculated for each patient using the difference between their actual subtest score and a predicted subtest score based on their full-scale IQ and the performance of controls. Scaled scores and residual scores were examined for relationships with clinical measures. Digit symbol-scaled score was significantly correlated with concurrent negative syndrome score at baseline, and digit symbol residual score significantly predicted residual negative symptoms at 1-year follow-up. In summary, our comparison of patients and controls precisely matched for IQ revealed that processing speed was attenuated in recent-onset schizophrenia, contributed significantly to working and episodic memory deficits, and was a prognostic factor for poor outcome at 1 year.

Working memory and long-term memory deficits in schizophrenia: is there a common substrate?

Patients with schizophrenia exhibit substantial deficits in both working memory (WM) and long-term memory (LTM) tasks. While these two forms of memory are generally viewed as distinct, recent evidence from healthy subjects has challenged the robustness of the double-dissociation between these two types of memory. In light of an emerging view of WM and LTM as being subserved by a largely overlapping network of brain regions, it is possible that WM and LTM deficits in patients with schizophrenia share a common neurobiological substrate. This review revisits the functional neuroimaging literature on both WM and LTM in patients with schizophrenia with these considerations in mind, and reveals a number of commonalities in research findings in both literatures. While there is a paucity of direct evidence bearing on whether patient deficits in these tasks arise from a common functional abnormality, the available literature is consistent with the hypothesis that these deficits have the same origin.

Is semantic memory impaired in schizophrenia? A systematic review and meta-analysis of 91 studies

INTRODUCTION

Semantic memory impairments in schizophrenia have been reported across a wide range of neuropsychological tests. Set against a backdrop of fairly widespread cognitive impairments, it is difficult to know whether there is a primary, or secondary, impairment of semantic memory in schizophrenia. Also, whether there is a profile of differential impairment across the range of neuropsychological tests.

METHODS

Employing a systematic search strategy, 91 papers were identified which have assessed participants with schizophrenia on a measure of semantic memory. A series of meta-analyses were then conducted which provided combined weighted means for performance on tasks of naming, word-picture matching, verbal fluency, priming, and categorisation.

RESULTS

An uneven profile of impairment is reported with large effect sizes for tests of naming and verbal fluency, medium effect sizes for word-picture matching and association and small effect sizes for categorisation and priming tests.

CONCLUSIONS

This uneven profile supports the claim that a degradation of semantic knowledge may not be adequate in explaining the semantic memory impairment in schizophrenia. This conclusion is supported by the data which report a relationship between an executive dysfunction and poor priming and fluency performance particularly. The data support a link between Formal Thought Disorder and semantic memory impairments on tests of naming and verbal fluency but on other tests evidence is equivocal.

Dissociation of long-term verbal memory and fronto-executive impairment in first-episode psychosis

BACKGROUND

Verbal memory is frequently and severely affected in schizophrenia and has been implicated as a mediator of poor clinical outcome. Whereas encoding deficits are well demonstrated, it is unclear whether retention is impaired. This distinction is important because accelerated forgetting implies impaired consolidation attributable to medial temporal lobe (MTL) dysfunction whereas impaired encoding and retrieval implicates involvement of prefrontal cortex.

METHOD

We assessed a group of healthy volunteers (n=97) and pre-morbid IQ- and sex-matched first-episode psychosis patients (n=97), the majority of whom developed schizophrenia. We compared performance of verbal learning and recall with measures of visuospatial working memory, planning and attentional set-shifting, and also current IQ.

RESULTS

All measures of performance, including verbal memory retention, a memory savings score that accounted for learning impairments, were significantly impaired in the schizophrenia group. The difference between groups for delayed recall remained even after the influence of learning and recall was accounted for. Factor analyses showed that, in patients, all variables except verbal memory retention loaded on a single factor, whereas in controls verbal memory and fronto-executive measures were separable.

CONCLUSIONS

The results suggest that IQ, executive function and verbal learning deficits in schizophrenia may reflect a common abnormality of information processing in prefrontal cortex rather than specific impairments in different cognitive domains. Verbal memory retention impairments, however, may have a different aetiology.

Contribution of K+-Cl- cotransporter 2 in MK-801-induced impairment of long term potentiation

Previous studies have indicated that GABAergic disinhibition contributes to cognitive deficits mediated by NMDA receptor hypofunction in schizophrenia model of rats. However, the underlying mechanism of GABAergic disinhibition in schizophrenia remains elusive. In this study, we found that the maintenance of long term potentiation (LTP) was impaired in the hippocampus of rats with MK-801-induced cognitive impairments. The impairment of LTP maintenance was significantly reversed by picrotoxinin, a specific GABA(A) receptor-chloride channel blocker and furosemide, a K+-Cl- cotransporter 2 (KCC2) blocker, respectively. Furthermore, immunoblotting results indicated KCC2 expression in hippocampal CA1 of MK-801-treated rats was lower than that of normal rats before LTP induction. Additionally, LTP-accompanied downregulation of KCC2 was prevented in MK-801-treated rats during LTP induction. Our results suggested that KCC2 expression in hippocampal CA1 of MK-801-treated rats was not further decreased by LTP induction because of its low expression caused by MK-801 treatment. Accordingly, GABAergic inhibition was not further decreased during LTP induction due to the depressed basal GABAergic tone in MK-801-treated rats, Therefore, GABAergic disinhibition in MK-801-treated rats restricts the further downregulation of KCC2 during LTP induction and contributes to the stable GABAergic inhibition and the impaired LTP expression. Our results thus reveal the mechanism that GABAergic disinhibition contributes to cognitive deficits.

Exploring predictors of outcome in the psychosis prodrome: implications for early identification and intervention

Functional disability is a key component of many psychiatric illnesses, particularly schizophrenia. Impairments in social and role functioning are linked to cognitive deficits, a core feature of psychosis. Retrospective analyses demonstrate that substantial functional decline precedes the onset of psychosis. Recent investigations reveal that individuals at clinical-high-risk (CHR) for psychosis show impairments in social relationships, work/school functioning and daily living skills. CHR youth also demonstrate a pattern of impairment across a range of cognitive domains, including social cognition, which is qualitatively similar to that of individuals with schizophrenia. While many studies have sought to elucidate predictors of clinical deterioration, specifically the development of schizophrenia, in such CHR samples, few have investigated factors relevant to psychosocial outcome. This review integrates recent findings regarding cognitive and social-cognitive predictors of outcome in CHR individuals, and proposes potential directions for future research that will contribute to targeted interventions and improved outcome for at-risk youth.

Working memory in schizophrenia: a meta-analysis

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

IQ as a predictor of functional outcome in schizophrenia: a longitudinal, four-year study of first-episode psychosis

Studies of established schizophrenia have consistently found that cognitive function predicts social and clinical outcomes. The findings from first-episode studies have been more variable, with only some studies reporting predictive relationships. We tested the possibility that an index of general cognitive ability, IQ, may be a more sensitive and reliable predictor of outcome in first-episode schizophrenia than specific measures of memory and executive function. Fifty-four patients with first-episode schizophrenia or schizoaffective disorder were assessed for cognitive and social function as well as symptoms at three time points over the four years following first presentation of their psychotic illness. Regression analyses were performed to determine whether IQ and specific neuropsychological measures at first episode and one-year follow-up predicted four-year social function and residual symptoms. The effects of premorbid and concurrent IQ on outcome were also assessed. Premorbid IQ and IQ at each assessment significantly predicted social function at four-year follow-up. This relationship remained significant after the social function or symptom scores at first presentation were accounted for in the regression. Specific measures predicted certain domains of social function, but these were weaker and less consistent than IQ. The predictive values of cognition on residual symptoms were less strong; the most consistent finding was a relationship between IQ and the negative syndrome. This study suggests that early in the course of schizophrenia, general cognitive ability, as measured by IQ, is a more sensitive and reliable predictor of functional outcome than measures of specific ability.

Role of processing speed and premorbid IQ on visual recognition in patients with schizophrenia

Previous research had shown that processing speed and premorbid IQ are predictors of verbal-memory efficiency in patients with schizophrenia. We investigated whether the same factors are involved in visual memory. A total of 49 patients with schizophrenia and 43 healthy controls were administered a picture recognition task. Half of the pictures were black and white, and half were in color, in order to vary the depth of encoding. Processing speed was measured by three standard tasks, and premorbid IQ was measured by the National Adult Reading Test (NART). Patients were significantly impaired in picture recognition. Regression analyses revealed that NART score was a significant predictor of the recognition of both types of picture in patients. Processing speed was a significant predictor of the recognition of the colored pictures. The effect of diagnosis on the recognition of colored pictures was reduced to nonsignificance when processing speed was entered in the regression. These data suggest that premorbid IQ is involved in visual-recognition efficiency. However, the deficit observed in patients is accounted for by decreased processing speed.

Less unique variance than meets the eye: overlap among traditional neuropsychological dimensions in schizophrenia

The magnitude of the overlap among dimensions of neuropsychological test performance in schizophrenia has been the subject of perennial controversy. This issue has taken on renewed importance with the recent focus on cognition as a treatment target in schizophrenia. A substantial body of factor analytic literature indicates that dimensions are separable in schizophrenia. However, this literature is generally uninformative as to whether the separable dimensions are independent, weakly correlated, or strongly correlated. Factor analyses have often used methods (ie, principal components analysis with orthogonal rotation) that preclude this determination, and correlations among factor-based domain composites and underlying measures have been reported infrequently in these studies. Current meta-analyses of reported "between-dimension" correlations for individual neuropsychological measures and for cognitive domain composite variables indicate that cognition variables in schizophrenia are correlated, on average, at a "medium" level of r = 0.37 for individual measures from different cognitive dimensions and r = 0.45 for domain composites. Because these are mean bivariate correlations, the multiple correlation of an individual measure with all the other measures in a cognitive battery is likely to be higher. Measure reliabilities of 0.80 or less also imply greater commonality among traditional neuropsychological measures. In short, there are underappreciated constraints on the amount of reliable cognitive performance variance in traditional neuropsychological test batteries that is free to vary independently. The ability of such batteries to reveal cognitive domain-specific treatment effects in schizophrenia may be much more limited than is generally assumed.

Cognitive dysfunction in first-episode psychosis: the processing speed hypothesis

BACKGROUND

Speed of processing is a cognitive process underlying cognitive dysfunction in people with chronic schizophrenia.

AIMS

To investigate the contribution of speed of processing to the cognitive deficits observed in a representative large sample with first-episode schizophrenia.

METHOD

People with a diagnosis of first-episode schizophrenia-spectrum disorders (n=26) and healthy controls (n=28) were compared on several cognitive measures before and after controlling for speed of processing.

RESULTS

Before controlling for speed of processing, patients and controls differed significantly on all cognitive measures. All significant differences in cognitive functioning disappeared when the result of the Digital Symbol Substitution Test was included as an additional covariate.

CONCLUSIONS

Speed of information processing may be considered a core cognitive deficit in schizophrenia and might be mediating a broader diversity of cognitive disturbances.

Abnormal EEG complexity in patients with schizophrenia and depression

OBJECTIVE

Schizophrenics are usually unable to perform well on cognitive tasks due to disturbances in cortical information processing that are observable as abnormalities in electroencephalogram (EEG) signals. However, whether such cortical disturbances can be assessed by quantitative EEG analysis remains unclear. The purpose of this study was to characterize EEG disturbances, using the Lempel-Ziv complexity (LZC), in the subjects with schizophrenia at rest or while performing mental arithmetic tasks. The results were compared to those from the subjects with depression and with healthy controls.

METHODS

The subjects included 62 schizophrenia patients, 48 depression patients and 26 age-matched healthy controls. EEG was recorded under two conditions: (i) resting with eyes closed, and (ii) a mentally active condition wherein the subjects were asked to subtract 7 from 100 iteratively with their eyes closed. EEG signals were analyzed by LZC and conventional spectral methods.

RESULTS

In all the groups, LZC of EEG decreased during the mental arithmetic compared with those under the resting conditions. Both the schizophrenia and the depression groups had a higher LZC (p<0.05) than the controls. Also, the schizophrenia group had a lower LZC (p<0.05) than the depression group during the mental arithmetic task as well as during the resting state. Significant differences in LZC, at some symmetrically located loci (FP1/FP2, F7/F8), between the two hemispheres were found in all the patient groups only during the arithmetic task.

CONCLUSIONS

Compared with conventional spectral analysis, LZC was more sensitive to both the power spectrum and the temporal amplitude distribution. LZC was associated with the ability to attend to the task and adapt the information processing system to the cognitive challenge. Thus, it would be useful in studying the disturbances in the cortical information processing patients with depression or schizophrenia.

SIGNIFICANCE

LZC of EEG is associated with mental activity. Thus, LZC analysis can be an important tool in understanding the pathophysiology of schizophrenia and depression in future studies.

Processing speed mediates the relationship between verbal memory, verbal fluency, and functional outcome in chronic schizophrenia

Verbal fluency and verbal memory have been reported to be diminished in patients with schizophrenia. These deficits could partially predict functional disability in this pathology. However, processing speed often mediates the relationship among cognitive processes in the disorder. Our goal was to analyse the influence of processing speed as mediator of the relation between verbal fluency-verbal memory and functional disability in chronic schizophrenia. We examined 90 hospitalized patients and 30 healthy controls (matched for gender, age and years of education). The neuropsychological battery included tests for verbal fluency, verbal memory, motor speed and processing speed. Outcome measures included Disability Assessment Schedule (DAS-WHO) and number of hospitalizations (NH). Results confirmed chronicity on clinical symptoms (PANSS total X=48.94+14.97 PANSS negative X=27.81+10.18, PANSS positive X=23.51+10.81) and impairment on functional disability (DAS-WHO X=13.62+4.28). As expected, verbal fluency was severely impaired in patients and significantly predicted functional outcome. Immediate and Delayed Verbal Memory were also severely impaired and predicted functional outcome. However, when processing speed was entered in the regression analyses the significance of verbal fluency and verbal memory decreased significantly. Sobel's equation was significant, suggesting full mediation. Our findings suggest that processing speed may be a central factor in the relation between cognitive symptoms and functional outcome in chronic schizophrenia.

Long-term effects of risperidone versus haloperidol on verbal memory, attention, and symptomatology in schizophrenia

There is evidence in the literature that cognitive functions in schizophrenia (SC) may be improved by atypical neuroleptics (NLPs) in contrast to typical medication, but there is still controversy regarding this apparent superiority of atypical drugs. In this study, we assessed the differential effects of risperidone and haloperidol on verbal memory, attention, and psychiatric symptoms in SC. The performance of 28 SC participants, randomly assigned to risperidone (2-6 mg/day) or haloperidol (2-40 mg/day), was compared with that of healthy controls. The California Verbal Learning Test (CVLT), the d2 Cancellation Test, and the Positive and Negative Symptoms Scale were administered at baseline and 3, 6, and 12 months. Relative to controls, all SC participants showed markedly impaired verbal memory and processing speed at each assessment period. There was no differential effect between the two NLPs on CVLT and d2 performance. However, risperidone was more effective than haloperidol in reducing psychiatric symptoms. Improvement in symptom severity was not associated with improvement in neurocognitive performance on these specific tests. Neither conventional nor atypical neuroleptic medications improved neurocognitive functioning over a 12-month follow-up, suggesting that psychopathological improvement under risperidone is independent of cognitive function.

Neuropsychological and activity of daily living script performance in patients with positive or negative schizophrenia

Cognitive and psychiatric determinants of impairment of complex activities of daily living (ADLs) were investigated in 33 schizophrenic patients and 16 normal comparison subjects. The schizophrenic patients were cognitively impaired and were deficient in the ADL. However, the impairment of ADL could not be explained specifically by impairment of higher-order executive function or by negative symptoms: memory functions were more related to impairment of ADL and positive symptoms as much as the negative ones. Positive symptoms were significantly related to commissive errors in the ADL, whereas negative symptoms were nonsignificantly related to omissive errors. Negative symptoms were significantly more related to memory impairment than to impairment on measures of higher-order executive function (working memory). This investigation demonstrates that an ecologically oriented approach to test development and measurement of ADL is fruitful in understanding schizophrenia-especially if it is constrained by cognitive constructs compatible with the phenomenology of the disease.

The relationship between neuropsychological measures and the Timed Instrumental Activities of Daily Living task in multiple sclerosis

Multiple sclerosis (MS) can result in cognitive deficits and a loss of functional independence. To date, little research has linked the observed cognitive and behavioral deficits in MS, especially those in the processing speed domain, to performance on tasks of everyday functioning. The present study examined the relationship between neuropsychological test performance and performance on the Timed Instrumental Activities of Daily Living task (TIADL) in individuals with MS, and in healthy controls (HCs). The TIADL is a functional measure, which assesses both accuracy and speed in one's performance of everyday activities. The MS group performed significantly worse on the TIADL relative to the HC group. Additionally, TIADL scores of individuals with MS were significantly correlated with neuropsychological measures of processing speed. TIADL scores were not, however, correlated with neuropsychological measures of verbal episodic memory or working memory. These results indicate that the impairments in processing speed may contribute to impairments in activities of everyday living in persons with MS. Multiple Sclerosis 2007; 13: 636-644. http://msj.sagepub.com

Hippocampal abnormalities and memory deficits: new evidence of a strong pathophysiological link in schizophrenia

The central goals of this manuscript are (1) to better characterize what appears to be the most parsimonious account of schizophrenic long-term memory impairment in the neuropsychological literature: a contextual binding deficit rooted in the medial temporal lobes; (2) to link this deficit to concrete abnormalities at the level of the hippocampus; and (3) to suggest that this deficit could lead to the functional impairment experienced by schizophrenia patients in their daily lives. As far as long-term memory is concerned in schizophrenia, there seems to be a general agreement to conclude that explicit mechanisms are disturbed compared to relatively spared implicit mechanisms. More precisely, both subsystems of explicit memory (i.e., episodic and semantic) appear to be dysfunctional in this patient population. Errors during the encoding processes could be responsible for this dysfunction even if retrieval per se is not totally spared. Recently, a number of studies have suggested that impairments in conscious recollection and contextual binding are closely linked to episodic memory deficit. Since the hippocampal formation is considered to be the central element in the neural support for contextual binding and episodic memory, we have conducted an extensive review of the literature concerning the hippocampal formation in schizophrenia. Emerging evidence from varying disciplines confirm the coherence of the different anomalies reported concurrently at the neuroanatomical, neurodevelopmental, biochemical, and genetic levels. It seems highly probable that the synaptic disorganization in the hippocampus concerns the regions crucial for encoding and contextual binding memory processes. The consequences of these deficits could result in schizophrenia patients experiencing major difficulties when facing usual events which have not been encoded with their proper context.

Role of processing speed and depressed mood on encoding, storage, and retrieval memory functions in patients diagnosed with schizophrenia

The role of various types of slowing of processing speed, as well as the role of depressed mood, on each stage of verbal memory functioning in patients diagnosed with schizophrenia was investigated. Mixed lists of high- and low-frequency words were presented, and immediate and delayed free recall and recognition were required. Two levels of encoding were studied by contrasting the relatively automatic encoding of the high-frequency words and the more effortful encoding of the low-frequency words. Storage was studied by contrasting immediate and delayed recall. Retrieval was studied by contrasting free recall and recognition. Three tests of motor and cognitive processing speed were administered as well. Regression analyses involving the three processing speed measures revealed that cognitive speed was the only predictor of the recall and recognition of the low-frequency words. Furthermore, slowing in cognitive speed accounted for the deficit in recall and recognition of the low-frequency words relative to a healthy control group. Depressed mood was significantly associated with recognition of the low-frequency words. Neither processing speed nor depressed mood was associated with storage efficiency. It is concluded that both cognitive speed slowing and depressed mood impact on effortful encoding processes.

A neuropsychological study of patients with temporal lobe epilepsy and chronic interictal psychosis

PURPOSE

To characterize the pattern of cognitive deficits in patients with temporal lobe epilepsy (TLE) and interictal (schizophrenia-like) psychosis and to examine the relationship between neuropsychological deficits and Magnetization transfer imaging.

METHODS

Twenty patients with TLE and interictal psychosis were compared to 20 non-psychotic TLE patients. Patients were matched with respect to premorbid IQ, age and conventional MRI findings. A battery of neuropsychological tests was administered. The neuropsychological tests which showed significant group differences were used for correlational analysis with magnetization transfer ratio (MTR) which provides a quantitative measure of macromolecular structural integrity.

RESULTS

Patients with interictal psychosis were significantly more impaired on executive and semantic memory tasks than the non-psychotic TLE group. Vocabulary test scores correlated significantly with MTR reduction in the left fusiform gyrus in the psychotic but not the non-psychotic group.

DISCUSSION

In this study, patients with TLE and interictal psychosis were more cognitively impaired than non-psychotic TLE patients. Our findings suggest that the cognitive deterioration in these patients may occur as the illness progresses and the causes for this are probably multifactorial. Our study also provides further evidence that MTR may be useful in investigating structural correlates of cognitive impairment.

Processing speed: a strong predictor of verbal memory performance in schizophrenia

The role of slowing of processing speed in verbal memory impairment in patients with schizophrenia was investigated. Forty-one patients with schizophrenia and 41 healthy control subjects were administered a verbal memory task involving free recall of three lists of words, which varied in their degree of semantic organization. Standard processing speed tests were administered as well. Regression analyses were conducted on the number of words recalled in each list. A global processing speed measure was a significant predictor of the recall of each list in patients. Patients were very significantly impaired in the recall of the three lists relative to healthy controls. However, when the processing speed measure was entered in the regression, the significance of diagnosis was considerably reduced for one of the lists, with no semantic organization, and eliminated for the other two lists which contained semantic organization. These findings suggest that slowing in processing speed is an important contributor to verbal memory impairment in patients with schizophrenia. The possible role of various specific slowing functions is discussed.

Neuropsychological performance over time in people at high risk of developing schizophrenia and controls

BACKGROUND

Neuropsychological assessments of relatives of schizophrenics have shown subtle impairments in verbal memory, executive and intellectual function, which are stable in those beyond the age of maximum risk for the disorder. We sought to: (1) determine baseline neurocognitive predictors of psychosis, and (2) compare performance over time between relatives within the age of maximum risk, and controls.

METHODS

(1) and (2) were examined in 118 individuals at familial high risk of schizophrenia (HR) and 30 controls (C), using one-way analyses of variance (ANOVAs) and repeated measures analyses of covariance (ANCOVAs), controlling for intelligence quotient, time between and number of assessments, and correcting for multiple comparisons.

RESULTS

HR who became ill (n = 13) performed nonsignificantly less well at baseline than HR who did not (n = 105) on a test of verbal learning (t(109) = 2.1, p = .03). Across assessments, C performed significantly better than the entire HR group on immediate (F(3,133) = 5.11, p = .002) and delayed (F(3,133) = 5.02, p = .002) story recall. There were no significant interactions of time by group.

CONCLUSIONS

Results suggest greater verbal memory impairment in HR who go on to develop schizophrenia. Stable differences between groups over time suggest a trait deficit, which is relatively unaffected by the presence of psychotic symptoms and psychosis onset. Alternatively, small numbers may have precluded detection of group by time interactions.

Effort and cognition in schizophrenia patients

OBJECTIVE

The aim of this study was to determine whether low cognitive test scores in schizophrenia patients are due to insufficient effort and, if so, to what extent.

METHOD

Mental effort was measured with the Word Memory Test (WMT), an effort test that has been extensively validated. Schizophrenic patients (n=64), non-psychotic psychiatric patients (n=63), neurological controls (n=20), and normal controls (n=44) were tested with a neuropsychological test battery measuring memory, attention and executive functioning.

RESULTS

The majority of the schizophrenia patients and a quarter of the psychiatric patients scored below the cut-offs for normal effort on the WMT. Scores on the effort test explained a significant amount of variance in the neuropsychological test performance of schizophrenic patients. This lends support to the notion that cognitive functioning in schizophrenia is compromised by insufficient effort. Furthermore, poor mental effort was related to negative symptoms.

CONCLUSIONS

Poor mental effort might be considered a core symptom of schizophrenia, representing an executive, monitoring or motivational problem. Mental effort should be taken into consideration in the neuropsychological assessment of schizophrenic patients and of psychiatric patients in general. Controlling for this variable may have a considerable impact on research, assessment and treatment of cognitive disorders in schizophrenic patients.

Word frequency effects on free recall and recognition in patients with schizophrenia

BACKGROUND

Word frequency paradigms have been used repeatedly in healthy populations to help understand the functioning of verbal memory. We investigated the word frequency effects in a sample of patients with schizophrenia, assuming these data may shed light on certain encoding processes.

METHODS

Two mixed lists of high- and low-frequency words were presented to 46 patients with schizophrenia and 43 healthy control subjects. List learning was followed by free recall and recognition in immediate and delayed conditions.

RESULTS

Overall the high-frequency words were better recalled, whereas the low-frequency words were better recognised. The lack of interaction with diagnosis indicates that these effects were equivalent in both groups. In immediate recognition, the discrimination deficit for the high-frequency words in patients tended to be increased relative to that for the low-frequency words, suggesting greater impairment in the encoding of those words.

CONCLUSION

It is argued that the encoding of the distinct low-frequency words is less efficient in patients, but qualitatively unimpaired. By contrast, the familiar words might be more difficult for patients to encode, as they are more easily confused with other common words stored in long-term memory.