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

Neural dysfunction underlying working memory processing at different stages of the illness course in schizophrenia: a comparative meta-analysis

Schizophrenia, as a chronic and persistent disorder, exhibits working memory deficits across various stages of the disorder, yet the neural mechanisms underlying these deficits remain elusive with inconsistent neuroimaging findings. We aimed to compare the brain functional changes of working memory in patients at different stages: clinical high risk, first-episode psychosis, and long-term schizophrenia, using meta-analyses of functional magnetic resonance imaging studies. Following a systematic literature search, 56 whole-brain task-based functional magnetic resonance imaging studies (15 for clinical high risk, 16 for first-episode psychosis, and 25 for long-term schizophrenia) were included. The separate and pooled neurofunctional mechanisms among clinical high risk, first-episode psychosis, and long-term schizophrenia were generated by Seed-based d Mapping toolbox. The clinical high risk and first-episode psychosis groups exhibited overlapping hypoactivation in the right inferior parietal lobule, right middle frontal gyrus, and left superior parietal lobule, indicating key lesion sites in the early phase of schizophrenia. Individuals with first-episode psychosis showed lower activation in left inferior parietal lobule than those with long-term schizophrenia, reflecting a possible recovery process or more neural inefficiency. We concluded that SCZ represent as a continuum in the early stage of illness progression, while the neural bases are inversely changed with the development of illness course to long-term course.

Verbal memory impairments in mood disorders and psychotic disorders: A systematic review of comparative studies

BACKGROUND

Mood and psychotic disorders are both associated with verbal memory impairments. Verbal memory represents an important treatment target for both disorders. However, whether the neurocognitive and neurophysiological profiles of verbal memory impairments differ between specific disorders within these two diagnostic categories and healthy controls remains unclear. The current systematic review synthesized findings from comparative studies which used behavioural and neuroimaging tasks to investigate verbal memory impairments between: (1) mood disorder, psychotic disorder, and healthy control groups; and (2) mood disorder without psychotic features, mood disorder with psychotic features, and healthy control groups.

METHODS

The search strategy combined terms related to three main concepts: 'mood disorders', 'psychotic disorders', and 'verbal memory'. Searches were executed in Embase, MEDLINE, PsycInfo, and PubMed databases. A total of 38 articles met the full eligibility criteria and were included in the final narrative synthesis. Findings were stratified by memory domain (overall composite score, verbal working memory, immediate recall, delayed recall, and recognition memory) and by illness phase (acute and non-acute).

RESULTS

Mood and psychotic disorders displayed consistent verbal memory impairments compared to healthy controls during the acute and non-acute phases. Few significant differences were identified in the literature between mood and psychotic disorders, and between mood disorders with and without psychotic features. Individuals with schizophrenia were found to have decreased immediate and delayed verbal recall performance compared to bipolar disorder groups during the acute phase. Major depressive disorder groups with psychotic features were also found to have decreased delayed verbal recall performance compared to those without psychosis during the acute phase. No consistent differences were identified between mood and psychotic disorders during the non-acute phase. Finally, preliminary evidence suggests there may be functional abnormalities in important frontal and temporal brain regions related to verbal memory difficulties in both mood and psychotic disorders.

DISCUSSION

The current findings have potential implications for the diagnosis and treatment of cognitive impairments in mood and psychotic disorders. Verbal recall memory may serve as a sensitive tool in the risk stratification of cognitive impairments for certain mood and psychotic disorders. Moreover, since no widespread differences between clinical groups were identified, the evidence supports providing targeted interventions for verbal memory, such as pharmacological and non-pharmacological interventions, through a trans-diagnostic approach in mood and psychotic disorders.

Nabilone Impairs Spatial and Verbal Working Memory in Healthy Volunteers

Background: Memory impairments and psychosis-like experiences can be adverse effects of cannabis use. However, reports on the cognitive impact of cannabis use are not consistent. There are also limited studies on the psychotomimetic effects of cannabinoid compounds to reveal the association between cannabis and psychosis. Therefore, we investigated the effect of acute cannabinoid intoxication on verbal working memory (VWM) and spatial working memory (SWM) following oral doses of the synthetic cannabinoid agonist, nabilone (1-2 mg, oral). We further investigated the effect of nabilone on psychosis-like experiences (schizotypy scores) and associations of schizotypy with VWM and SWM. Methods: Healthy participants (n=28) completed spatial and digit span tasks across different delay conditions (0, 6, 12, and 18 sec) after receiving nabilone (1-2 mg, PO) or placebo in a randomized, double-blind, counterbalanced, crossover manner. A subset of participants completed a short battery of schizotypy measures (n=25). Results: Nabilone impaired VWM (p=0.03, weak effect size η2=0.02) and SWM (p=0.00016, η2=0.08). Nabilone did not significantly change overall schizotypy scores. Schizotypy scores were negatively correlated with working memory (WM) averaged across all delays and both modalities, under placebo (ρ=-0.41, p=0.04). In addition, there were significant negative correlations between occasions of cannabis use and overall WM averaged scores across drug treatments (ρ=-0.49, p=0.007) and under placebo (ρ=-0.45, p=0.004). The results showed that the drug effect in the less frequent cannabis users was more pronounced on the SWM (p<0.01) and VWM (p<0.01), whereas there appeared to be little drug effect in the frequent cannabis users. Conclusion: Low doses of synthetic cannabinoid impaired SWM and VWM, indicating that exogenous activation of the cannabinoid system influences cognitive performance. Further, the results replicated previous findings that schizotypy is correlated with deficits in WM. Clinical Trial Registry Name: Nabilone and caffeine effects on the perceptions of visually, auditory, tactile and multimodal illusions in healthy volunteers. Clinical Trial Registration Number: CT-2018-CTN-02561 (Therapeutic Goods Administration Clinical Trial Registry) and ACTRN12618001292268 (The Australian New Zealand Clinical Trials Registry).

Can neuroimaging-based biomarkers predict response to cognitive remediation in patients with psychosis? A state-of-the-art review

BACKGROUND

Cognitive Remediation (CR) is designed to halt the pathological neural systems that characterize major psychotic disorders (MPD), and its main objective is to improve cognitive functioning. The magnitude of CR-induced cognitive gains greatly varies across patients with MPD, with up to 40% of patients not showing gains in global cognitive performance. This is likely due to the high degree of heterogeneity in neural activation patterns underlying cognitive endophenotypes, and to inter-individual differences in neuroplastic potential, cortical organization and interaction between brain systems in response to learning. Here, we review studies that used neuroimaging to investigate which biomarkers could potentially serve as predictors of treatment response to CR in MPD.

METHODS

This systematic review followed the PRISMA guidelines. An electronic database search (Embase, Elsevier; Scopus, PsycINFO, APA; PubMed, APA) was conducted in March 2021. peer-reviewed, English-language studies were included if they reported data for adults aged 18+ with MPD, reported findings from randomized controlled trials or single-arm trials of CR; and presented neuroimaging data.

RESULTS

Sixteen studies were included and eight neuroimaging-based biomarkers were identified. Auditory mismatch negativity (3 studies), auditory steady-state response (1), gray matter morphology (3), white matter microstructure (1), and task-based fMRI (7) can predict response to CR. Efference copy corollary/discharge, resting state, and thalamo-cortical connectivity (1) require further research prior to being implemented.

CONCLUSIONS

Translational research on neuroimaging-based biomarkers can help elucidate the mechanisms by which CR influences the brain's functional architecture, better characterize psychotic subpopulations, and ultimately deliver CR that is optimized and personalized.

Multimodal meta-analysis of structural gray matter, neurocognitive and social cognitive fMRI findings in schizophrenia patients

Neuroimaging research has shown that patients with schizophrenia (SCZ) present brain structural and functional alterations, but the results across imaging modalities and task paradigms are difficult to reconcile. Specifically, no meta-analyses have tested whether the same brain systems that are structurally different in SCZ patients are also involved in neurocognitive and social cognitive tasks. To answer this, we conducted separate meta-analyses of voxel-based morphometry, neurocognitive functional magnetic resonance imaging (fMRI), and social cognitive fMRI studies. Next, with a multimodal approach, we identified the common alterations across meta-analyses. Further exploratory meta-analyses were performed taking into account several clinical variables (illness duration, medication status, and symptom severity). A cluster covering the dorsomedial prefrontal cortex (dmPFC) and the supplementary motor area (SMA), and the right inferior frontal gyrus (IFG), presented shared structural and neurocognitive-related activation decreases, while the right angular gyrus presented shared decreases between structural and social cognitive-related activation. The exploratory meta-analyses replicated to some extent these findings, while new regions of alterations appeared in patient subgroups with specific clinical features. In conclusion, we found task-specific correlates of brain structure and function in SCZ, which help summarize and integrate a growing literature.

Atypically larger variability of resource allocation accounts for visual working memory deficits in schizophrenia

Working memory (WM) deficits have been widely documented in schizophrenia (SZ), and almost all existing studies attributed the deficits to decreased capacity as compared to healthy control (HC) subjects. Recent developments in WM research suggest that other components, such as precision, also mediate behavioral performance. It remains unclear how different WM components jointly contribute to deficits in schizophrenia. We measured the performance of 60 SZ (31 females) and 61 HC (29 females) in a classical delay-estimation visual working memory (VWM) task and evaluated several influential computational models proposed in basic science of VWM to disentangle the effect of various memory components. We show that the model assuming variable precision (VP) across items and trials is the best model to explain the performance of both groups. According to the VP model, SZ exhibited abnormally larger variability of allocating memory resources rather than resources or capacity per se. Finally, individual differences in the resource allocation variability predicted variation of symptom severity in SZ, highlighting its functional relevance to schizophrenic pathology. This finding was further verified using distinct visual features and subject cohorts. These results provide an alternative view instead of the widely accepted decreased-capacity theory and highlight the key role of elevated resource allocation variability in generating atypical VWM behavior in schizophrenia. Our findings also shed new light on the utility of Bayesian observer models to characterize mechanisms of mental deficits in clinical neuroscience.

Working memory is a core cognitive function related to a broad range of cognitive domains such as problem-solving, attention, executive control, and IQ. Although working memory deficits have been well-documented in schizophrenia, the underlying mechanisms remain unclear. Conventional working memory theories attribute working memory deficits in schizophrenia to their reduced memory capacity, overlooking the potential roles of other memory components, such as precision. In this study, we take the approach of computational psychiatry and use computational modeling to uncover the major determinants of working memory deficits. We assess working memory performance of a large cohort of participants (60 schizophrenia patients and 61 demographic matched healthy controls) and evaluate multiple mainstream computational models of visual working memory. The variable precision model turns out to be the best model for both groups. We further find that the poorer performance of schizophrenia patients arises from heterogeneous distribution of memory resources when encoding items in memory. This resource allocation variability can also predict symptom severity in schizophrenia. Our study highlights the use of computational models in psychiatric researches.

Anomalous self-experiences in cognition are negatively associated with neurocognitive functioning in schizophrenia

INTRODUCTION

Anomalous self-experiences (ASEs) are disturbances in the subjective experience of the self and are common in people with schizophrenia. Theorists have suggested that ASEs may underlie the neurocognitive deficits that are also common in people with schizophrenia; however, few studies have empirically investigated the relationship between these variables. Thus, the current study aimed to determine whether self-reported ASEs, particularly disturbances in cognitive or mental experiences, are meaningfully related to neurocognitive performance in individuals with schizophrenia.

METHODS

48 individuals with schizophrenia and 34 healthy comparison participants completed the Inventory of Psychotic-Like Anomalous Experiences (IPASE), which is composed of five subscales including disturbances in cognition, and the MATRICS Consensus Cognitive Battery (MCCB).

RESULTS

Participants with schizophrenia performed worse than controls on each MCCB domain and had higher ASE scores on the total IPASE and all five subscales. Only the IPASE-Cognition subscale was associated with cognitive performance. Specifically, IPASE-Cognition was negatively correlated with scores in attention, visual learning, reasoning, and working memory.

CONCLUSIONS

These results suggest that self-reported subjective disturbances in cognition may be meaningfully associated with several objectively-measured domains of neurocognition. Severity of ASEs may therefore be an important consideration when analysing the extent of cognitive deficits in schizophrenia.

Early-life lead exposure and neurodevelopmental disorders

Lead (Pb²⁺) exposure is a global public health problem of major proportion with an alarming number of children with blood Pb²⁺ levels > 10 >g/dL, twice the current CDC reference level for Pb²⁺ exposure. Mounting evidence from population-based studies suggests an association between chronic early life Pb²⁺ exposure (CELLE) and psychiatric disorders, specifically schizophrenia (SZ). Preclinical studies suggest a common mechanism in the pathophysiology of CELLE and SZ, NMDA receptor hypofunction. Here we describe human and experimental animal studies providing the evidence for such an association. Further, recent preclinical studies indicate that Pb²⁺-induced changes in neurotransmitter receptors that mediate the action(s) of drugs of abuse are increased in brain regions associated with addiction circuits in adolescence, a period of increased susceptibility to drug use and abuse and expression of psychiatric disease in humans. In summary, the relationship between the global burden of childhood Pb²⁺ exposure and the latent onset of psychiatric disorders and predisposition to drug use requires further investigations in human populations.

Dopamine and norepinephrine transporter inhibition for long-term fear memory enhancement

Psychostimulants are highly effective cognitive-enhancing therapeutics yet have a significant potential for abuse and addiction. While psychostimulants likely exert their rewarding and addictive properties through dopamine transporter (DAT) inhibition, the mechanisms of their procognitive effects are less certain. By one prevalent view, psychostimulants exert their procognitive effects exclusively through norepinephrine transporter (NET) inhibition, however increasing evidence suggests that DAT also plays a critical role in their cognitive-enhancing properties, including long-term memory enhancement. The present experiments test the hypothesis that combined strong NET and weak DAT inhibition will mimic the fear memory-enhancing but not the addiction-related effects of psychostimulants in mice. We examined the effects of the high affinity NET inhibitors atomoxetine or nisoxetine and the low affinity DAT inhibitor bupropion, either alone or in combination, on short- and long-term memory of Pavlovian fear conditioning. We also examined the addiction-related effects of combined strong NET and weak DAT inhibition using conditioned place preference and a locomotor activity test. While atomoxetine or nisoxetine alone enhanced short-term fear memory, the addition of bupropion was required to significantly enhance long-term fear memory. Additionally, combined atomoxetine and bupropion did not produce substantial motor stimulation or place preference. These findings suggest that combining strong NET and weak DAT inhibition could lead to the development of a highly effective cognitive enhancer that lacks the potential for addiction.

Memory and cognition in schizophrenia

Episodic memory deficits are consistently documented as a core aspect of cognitive dysfunction in schizophrenia patients, present from the onset of the illness and strongly associated with functional disability. Over the past decade, research using approaches from experimental cognitive neuroscience revealed disproportionate episodic memory impairments in schizophrenia (Sz) under high cognitive demand relational encoding conditions and relatively unimpaired performance under item-specific encoding conditions. These specific deficits in component processes of episodic memory reflect impaired activation and connectivity within specific elements of frontal-medial temporal lobe circuits, with a central role for the dorsolateral prefrontal cortex (DLPFC), relatively intact function of ventrolateral prefrontal cortex and variable results in the hippocampus. We propose that memory deficits can be understood within the broader context of cognitive deficits in Sz, where impaired DLPFC-related cognitive control has a broad impact across multiple cognitive domains. The therapeutic implications of these findings are discussed.

Schizophrenia-related abnormalities in the triple network: a meta-analysis of working memory studies

Previous meta-analyses found abnormal brain activations in schizophrenia patients compared with normal controls when performing working memory tasks. Although most studies focused on dysfunction of the working memory activation network in schizophrenia patients, deactivation abnormalities of the working memory in the default mode network have also been reported in schizophrenia but have received less attention. Our goal was to discover whether deactivation abnormalities can also be consistently found in schizophrenia during working memory tasks and, further, to consider both activation and deactivation abnormalities. Fifty-two English language peer-reviewed studies were included in this meta-analysis. Compared with normal controls, the schizophrenia patients showed activation dysfunction of the bilateral dorsolateral prefrontal cortex and posterior parietal cortex as well as the anterior insula, anterior cingulate cortex, and supplementary motor area, which are core nodes of the central executive and salience network. In addition to dysfunction of the activation networks, the patients showed deactivation abnormalities in the ventral medial prefrontal cortex and posterior cingulate cortex, which are core nodes of the default mode network. These results suggest that both activation and deactivation abnormalities exist in schizophrenia patients and that these abnormalities should both be considered when investigating the pathophysiological mechanism of schizophrenia.

Amplitude of low-frequency fluctuations in childhood-onset schizophrenia with or without obsessive-compulsive symptoms: a resting-state functional magnetic resonance imaging study

INTRODUCTION

Childhood-onset schizophrenia with obsessive-compulsive symptoms (COSO) and without obsessive-compulsive symptoms (COS) share considerable overlap in clinical features and genetic risk factors. However, the extent of brain functional abnormalities in COSO and COS is poorly understood.

MATERIAL AND METHODS

A total of 51 first-episode childhood schizophrenic patients and 30 healthy age- and sex-matched controls were recruited. We used the Yale-Brown Obsessive Compulsive Scale to divide patients into COSO (n = 21) and COS (n = 30) groups. Resting-state functional magnetic resonance imaging images were obtained using a gradient-echo echo-planar imaging sequence. Voxel-based analysis of amplitude of low-frequency fluctuation (ALFF) maps between the two groups was performed.

RESULTS

The COS group showed significantly increased ALFF in the right caudate body, middle temporal gyrus and inferior parietal lobule (p < 0.05), while showing decreased ALFF in the left cerebellum posterior lobe (p < 0.05). The COSO group showed significantly increased ALFF in the left and right frontal lobe, cerebellum posterior lobe and precuneus (p < 0.05). When comparing the two groups, COSO showed significantly higher ALFF in the left cerebellum posterior lobe, frontal lobe, supramarginal gyrus, precuneus, right inferior frontal gyrus and medial frontal gyrus (p < 0.05). Interestingly, significantly lower ALFF was found in the right fusiform gyrus, corpus callosum and inferior parietal lobule in the group of patients with obsessive-compulsive symptoms (p < 0.05).

CONCLUSIONS

Our findings increase the understanding of the pathophysiology of schizophrenia and may provide imaging evidence for early diagnosis of COSO or COS.

Localization and Elimination of Attentional Dysfunction in Schizophrenia During Visual Search

Theories of the locus of visual selective attention dysfunction in schizophrenia propose that the deficits arise from either an inability to maintain working memory representations that guide attention, or difficulty focusing lower-level visual attention mechanisms. However, these theoretical accounts neglect the role of long-term memory representations in controlling attention. Here, we show that the control of visual attention is impaired in people with schizophrenia, and that this impairment is driven by an inability to shift top-down attentional control from working memory to long-term memory across practice. Next, we provide converging evidence for the source of attentional impairments in long-term memory by showing that noninvasive electrical stimulation of medial frontal cortex normalizes long-term memory related neural signatures and patients' behavior. Our findings suggest that long-term memory structures may be a source of impaired attentional selection in schizophrenia when visual attention is taxed during the processing of multi-object arrays.

Mechanisms Underlying Visuospatial Working Memory Impairments in Schizophrenia

Working memory deficits are observed in the vast majority of individuals diagnosed with schizophrenia and those at risk for the disorder. Working memory impairments are present during the prodromal stage and persist throughout the course of schizophrenia. Given the importance of cognition in functional outcome, working memory deficits are an important therapeutic target for schizophrenia. This chapter examines mechanisms underlying working memory deficits in schizophrenia, focusing on the roles of perception and attention in the encoding process. Lastly, we present a comprehensive discussion of neural oscillation and internal noise in the context of the etiology of working memory deficits in schizophrenia and introduce noninvasive treatment strategies that could improve encoding processes.

Neural correlates of cognitive deficits across developmental phases of schizophrenia

Schizophrenia is associated with cognitive deficits across all stages of the illness (i.e., high risk, first episode, early and chronic phases). Identifying the underlying neurobiological mechanisms of these deficits is an important area of scientific inquiry. Here, we selectively review evidence regarding the pattern of deficits across the developmental trajectory of schizophrenia using the five cognitive domains identified by the Research Domain Criteria (RDoC) initiative. We also report associated findings from neuroimaging studies. We suggest that most cognitive domains are affected across the developmental trajectory, with corresponding brain structural and/or functional differences. The idea of a common mechanism driving these deficits is discussed, along with implications for cognitive treatment in schizophrenia.

The neuropsychology of emerging psychosis and the role of working memory in episodic memory encoding

Background

Episodic memory encoding and working memory (WM) deficits are among the first cognitive signs and symptoms in the course of schizophrenia spectrum disorders. However, it is not clear whether the deficit pattern is generalized or specific in nature. We hypothesized that encoding deficits at an early stage of the disease might be due to the more fundamental WM deficits.

Methods

We examined episodic memory encoding and WM by administering the California Verbal Learning Test, a 2-back task, and the Wisconsin Card Sorting Test in 90 first-episode psychosis (FE) patients and 116 individuals with an at-risk mental state for psychosis (ARMS) compared to 57 healthy subjects.

Results

Learning progress, but not span of apprehension, was diminished to a similar extent in both the ARMS and the FE. We showed that this was due to WM impairment by applying a structural equation approach.

Conclusion

Thus, we conclude that verbal memory encoding deficits are secondary to primary WM impairment in emerging psychosis.

Evidence for a differential contribution of early perceptual and late cognitive processes during encoding to episodic memory impairment in schizophrenia

OBJECTIVES

Schizophrenia is characterised by significant episodic memory impairment that is thought to be related to problems with encoding, however the neuro-functional mechanisms underlying these deficits are not well understood. The present study used a subsequent recognition memory paradigm and event-related potentials (ERPs) to investigate temporal aspects of episodic memory encoding deficits in schizophrenia.

METHODS

Electroencephalographic data was recorded in 24 patients and 19 healthy controls whilst participants categorised single words as pleasant/unpleasant. ERPs were generated to subsequently recognised versus unrecognised words on the basis of a forced-choice recognition memory task. Subsequent memory effects were examined with the late positive component (LPP). Group differences in N1, P2, N400 and LPP were examined for words correctly recognised.

RESULTS

Patients performed more poorly than controls on the recognition task. During encoding patients had significantly reduced N400 and LPP amplitudes than controls. LPP amplitude correlated with task performance however amplitudes did not differ between patients and controls as a function of subsequent memory. No significant differences in N1 or P2 amplitude or latency were observed.

CONCLUSIONS

The present results indicate that early sensory processes are intact and dysfunctional higher order cognitive processes during encoding are contributing to episodic memory impairments in schizophrenia.

Speed and capacity of working memory and executive function in schizophrenia compared to unipolar depression

Schizophrenia is associated with deficits in working memory (WM) and executive functioning (EF) that are present from prodrome to chronic stages of the disease and are related to social and occupational functioning. Recent empirical findings suggest that schizophrenia patients might suffer from a specific speed deficit regarding WM operations that also affects EF. To test this hypothesis, executive functioning (EF) and working memory (WM) performance of 20 schizophrenia (SC) patients, 20 patients suffering from Major Depressive Disorder (MDD) and 40 healthy control (HC) subjects were compared. While schizophrenia patients performed worse in the measure of EF, no difference between the SC and the MDD patients was found regarding WM capacity. However, the SC group was shown to have an impaired speed in encoding, retrieval and manipulation of WM contents compared to the HC group whereas the MDD group showed no such deficit. Furthermore, while in the MDD group only WM capacity was linked to EF performance, in the SC group EF was determined by both WM capacity and WM speed. Hence, increasing the speed of WM operations might be a fruitful target for future therapeutic interventions, and assessing not only the capacity but also the speed of WM might be helpful in identifying candidates for endophenotypic cognitive markers of SC.

Murder and psychosis: Neuropsychological profiles of homicide offenders with schizophrenia

BACKGROUND

Neurocognitive dysfunction, a core feature of schizophrenia, is thought to contribute to the impulsive violent aggression manifested by some individuals with schizophrenia, but not enough is known about how homicidal individuals with schizophrenia perform on neuropsychological measures.

AIMS

The primary aim of our study was to describe the neuropsychological profiles of homicide offenders with schizophrenia. Supplementary analyses compared the criminal, psychiatric and neuropsychological features of schizophrenic homicide offenders with and without God/Satan/demon-themed psychotic symptoms.

METHODS

Twenty-five men and women diagnosed with schizophrenia who had killed another person - 21 convicted of first-degree murder and 4 found not guilty by reason of insanity - completed neuropsychological testing during forensic evaluations.

RESULTS

The sample was characterised by extensive neurocognitive impairments, involving executive dysfunction (60%), memory dysfunction (68%) and attentional dysfunction (50%), although those with God/Satan/demon-themed psychotic symptoms performed better than those with nonreligious psychotic content.

CONCLUSIONS

Our findings indicate that impaired cognition may play an important role in the commission of homicide by individuals with schizophrenia. A subgroup with God/Satan/demon delusions seem sufficiently less impaired that they might be able to engage in metacognitive treatment approaches, aimed at changing their relationship to their psychotic symptoms, thus reducing the perception of power and omnipotence of hallucinated voices and increasing their safety. Copyright © 2016 John Wiley & Sons, Ltd.

Task Performance Modulates Functional Connectivity Involving the Dorsolateral Prefrontal Cortex in Patients with Schizophrenia

Previous studies have suggested that patients with schizophrenia and healthy controls exhibit differential activation of and connectivity involving the dorsolateral prefrontal cortex (DLPFC) during working memory tasks, though their findings remain inconsistent. The functional integration perspective further suggests that working memory performance also modulates differences in functional interactions of the DLPFC between patients and controls. To explore this possibility, 45 healthy controls and 45 patients with schizophrenia were recruited to perform a 2-back task during functional magnetic resonance imaging (fMRI). Each group was further divided into two subgroups based on task performance to examine the modulatory effect of performance on functional interactions of the DLPFC, as measured via psychophysiological interaction (PPI) analyses. We observed that, in patients with schizophrenia who exhibited impaired working memory capacity and decreased brain activation/deactivation, functional interactions between the right/left DLPFC and angular cortex were decreased relative to those of healthy controls. Furthermore, we observed an interaction effect of working memory performance and diagnosis on functional connectivity between the right/left DLPFC seed region and posterior regions such as the angular cortex, fusiform gyrus, and middle occipital gyrus. This interaction effect was mainly driven by the negative correlation between functional connectivity and performance in healthy controls, and by the positive correlation in patients with schizophrenia. These results demonstrate the effects of inter-individual differences in working memory performance on functional interactions between the DLPFC and posterior regions in patients with schizophrenia as well as healthy controls, which may shed new light on the neural basis of working memory.

Functional neuroanatomical correlates of episodic memory impairment in early phase psychosis

Studies have demonstrated that episodic memory (EM) is often preferentially disrupted in schizophrenia. The neural substrates that mediate EM impairment in this illness are not fully understood. Several functional magnetic resonance imaging (fMRI) studies have employed EM probe tasks to elucidate the neural underpinnings of impairment, though results have been inconsistent. The majority of EM imaging studies have been conducted in chronic forms of schizophrenia with relatively few studies in early phase patients. Early phase schizophrenia studies are important because they may provide information regarding when EM deficits occur and address potential confounds more frequently observed in chronic populations. In this study, we assessed brain activation during the performance of visual scene encoding and recognition fMRI tasks in patients with earlyphase psychosis (n = 35) and age, sex, and race matched healthy control subjects (n = 20). Patients demonstrated significantly lower activation than controls in the right hippocampus and left fusiform gyrus during scene encoding and lower activation in the posterior cingulate, precuneus, and left middle temporal cortex during recognition of target scenes. Symptom levels were not related to the imaging findings, though better cognitive performance in patients was associated with greater right hippocampal activation during encoding. These results provide evidence of altered function in neuroanatomical circuitry subserving EM early in the course of psychotic illness, which may have implications for pathophysiological models of this illness.

Reduced model-based decision-making in schizophrenia

Individuals with schizophrenia have a diminished ability to use reward history to adaptively guide behavior. However, tasks traditionally used to assess such deficits often rely on multiple cognitive and neural processes, leaving etiology unresolved. In the current study, we adopted recent computational formalisms of reinforcement learning to distinguish between model-based and model-free decision-making in hopes of specifying mechanisms associated with reinforcement-learning dysfunction in schizophrenia. Under this framework, decision-making is model-free to the extent that it relies solely on prior reward history, and model-based if it relies on prospective information such as motivational state, future consequences, and the likelihood of obtaining various outcomes. Model-based and model-free decision-making was assessed in 33 schizophrenia patients and 30 controls using a 2-stage 2-alternative forced choice task previously demonstrated to discern individual differences in reliance on the 2 forms of reinforcement-learning. We show that, compared with controls, schizophrenia patients demonstrate decreased reliance on model-based decision-making. Further, parameter estimates of model-based behavior correlate positively with IQ and working memory measures, suggesting that model-based deficits seen in schizophrenia may be partially explained by higher-order cognitive deficits. These findings demonstrate specific reinforcement-learning and decision-making deficits and thereby provide valuable insights for understanding disordered behavior in schizophrenia. (PsycINFO Database Record

Cognition in Schizophrenia

Recent research suggests that disturbances in social and occupational functioning in individuals with schizophrenia may be more influenced by the severity of cognitive deficits than by the severity of symptoms such as hallucinations and delusions. In this article, I review evidence that one component of cognitive dysfunction in schizophrenia is a deficit in working memory, associated with disturbances in the dopamine system in dorsolateral prefrontal cortex. I suggest that although the cognitive deficits in schizophrenia include working memory dysfunction, because they arise from a disturbance in executive control processes (e.g., the representation and maintenance of context), they extend to a range of cognitive domains. Finally, I discuss the need for further research on the ways in which contextual processing deficits may influence other aspects of this illness, including emotional processing.

Impaired Activation in Cognitive Control Regions Predicts Reversal Learning in Schizophrenia

Reinforcement learning deficits have been associated with schizophrenia (SZ). However, the pathophysiology that gives rise to these abnormalities remains unclear. To address this question, SZ patients (N = 58) and controls (CN; N = 36) completed a probabilistic reversal-learning paradigm during functional magnetic resonance imaging scanning. During the task, participants choose between 2 stimuli. Initially, 1 stimulus was frequently rewarded (80%); the other was infrequently rewarded (20%). The reward contingencies reversed periodically because the participant learned the more rewarded stimulus. The results indicated that SZ patients achieved fewer reversals than CN, and demonstrated decreased winstay-loseshift decision-making behavior. On loseshift compared to winstay trials, SZ patients showed reduced Blood Oxygen Level Dependent activation compared to CN in a network of brain regions widely associated with cognitive control, and striatal regions. Importantly, relationships between group membership and behavior were mediated by alterations in the activity of cognitive control regions, but not striatum. These findings indicate an important role for the cognitive control network in mediating the use and updating of value representations in SZ. Such results provide biological targets for further inquiry because researchers attempt to better characterize decision-making neural circuitry in SZ as a means to discover new pathways for interventions.

Clozapine improves the orienting of attention in schizophrenia

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

Northwestern University schizophrenia data sharing for SchizConnect: A longitudinal dataset for large-scale integration

In this paper, we describe an instance of the Northwestern University Schizophrenia Data and Software Tool (NUSDAST), a schizophrenia-related dataset hosted at XNAT Central, and the SchizConnect data portal used for accessing and sharing the dataset. NUSDAST was built and extended upon existing, standard schemas available for data sharing on XNAT Central (http://central.xnat.org/). With the creation of SchizConnect, we were able to link NUSDAST to other neuroimaging data sources and create a powerful, federated neuroimaging resource.

Attention/vigilance in schizophrenia: performance results from a large multi-site study of the Consortium on the Genetics of Schizophrenia (COGS)

Attention/vigilance impairments are present in individuals with schizophrenia across psychotic and remitted states and in their first-degree relatives. An important question is whether deficits in attention/vigilance can be consistently and reliably measured across sites varying in many participant demographic, clinical, and functional characteristics, as needed for large-scale genetic studies of endophenotypes. We examined Continuous Performance Test (CPT) data from phase 2 of the Consortium on the Genetics of Schizophrenia (COGS-2), the largest-scale assessment of cognitive and psychophysiological endophenotypes relevant to schizophrenia. The CPT data from 2251 participants from five sites were examined. A perceptual-load vigilance task (the Degraded Stimulus CPT or DS-CPT) and a memory-load vigilance task (CPT-Identical Pairs or CPT-IP) were utilized. Schizophrenia patients performed more poorly than healthy comparison subjects (HCS) across sites, despite significant site differences in participant age, sex, education, and racial distribution. Patient-HCS differences in signal/noise discrimination (d') in the DS-CPT varied significantly across sites, but averaged a medium effect size. CPT-IP performance showed large patient-HCS differences across sites. Poor CPT performance was independent of or weakly correlated with symptom severity, but was significantly associated with lower educational achievement and functional capacity. Current smoking was associated with poorer CPT-IP d'. Patients taking both atypical and typical antipsychotic medication performed more poorly than those on no or atypical antipsychotic medications, likely reflecting their greater severity of illness. We conclude that CPT deficits in schizophrenia can be reliably detected across sites, are relatively independent of current symptom severity, and are related to functional capacity.

A longitudinal study on intrinsic connectivity of hippocampus associated with positive symptom in first-episode schizophrenia

Hippocampal pathology has been considered to underlie clinical, functional and cognitive impairments in schizophrenia. While longitudinal magnetic resonance imaging (MRI) studies have demonstrated progressive gray matter reduction of the hippocampus during the early phases of schizophrenia (SCZ), very little is known about whether functional connectivity (FC) between the hippocampus and other brain regions also exhibit progressive changes. In this study, resting state functional MRI (fMRI) was used to examine changes in hippocampal connectivity at baseline and follow-up scans comparing 68 patients with first episode SCZ and 62 matched controls. At baseline and follow-up, in the bilateral hippocampal network, SCZ mainly showed decreased FC with bilateral cerebellum posterior lobe, frontal gyrus temporal gyrus, precuneus, and cingulate cortex compared to controls. Furthermore, in the bilateral hippocampus, there was a significant interaction effect of group and time for FC with cerebellum posterior lobe, temporal gyrus, frontal gyrus, and posterior cingulate cortex. Interestingly, longitudinal changes of bilateral hippocampal connectivity with right middle frontal gyrus negatively correlated with positive symptom scores in SCZ. These results provide novel evidence for the progressive changes of FC between hippocampus and other brain regions in SCZ. It further suggests that longitudinal changes of bilateral hippocampal connectivity with right middle frontal gyrus can contribute to the formation and emergence of positive symptom of SCZ.

WORKING MEMORY IMPAIRMENT AS AN ENDOPHENOTYPIC MARKER OF A SCHIZOPHRENIA DIATHESIS

This chapter focuses on the viability of working memory impairment as an endophenotypic marker of a schizophrenia diathesis. It begins with an introduction of the construct of working memory. It follows with a review of the operational criteria for defining an endophenotype. Research findings regarding the working memory performance of schizophrenia and schizophrenia-spectrum patients, first-degree relatives of schizophrenia patients and healthy controls, are reviewed in terms of the criteria for being considered an endophenotypic marker. Special attention is paid to specific components of the working memory deficit (namely, encoding, maintenance, and manipulation), in terms of which aspects are likely to be the best candidates for endophenotypes. We consider the extant literature regarding working memory performance in bipolar disorder and major depression in order to address the issue of relative specificity to schizophrenia. Despite some unresolved issues, it appears that working memory impairment is a very promising candidate for an endophenotypic marker of a schizophrenia diathesis but not for mood disorders. Throughout this chapter, we identify future directions for research in this exciting and dynamic area of research and evaluate the contribution of working memory research to our understanding of schizophrenia.

Expression of DISC1-interactome members correlates with cognitive phenotypes related to schizophrenia

Cognitive dysfunction is central to the schizophrenia phenotype. Genetic and functional studies have implicated Disrupted-in-Schizophrenia 1 (DISC1), a leading candidate gene for schizophrenia and related psychiatric conditions, in cognitive function. Altered expression of DISC1 and DISC1-interactors has been identified in schizophrenia. Dysregulated expression of DISC1-interactome genes might, therefore, contribute to schizophrenia susceptibility via disruption of molecular systems required for normal cognitive function. Here, the blood RNA expression levels of DISC1 and DISC1-interacting proteins were measured in 63 control subjects. Cognitive function was assessed using neuropsychiatric tests and functional magnetic resonance imaging was used to assess the activity of prefrontal cortical regions during the N-back working memory task, which is abnormal in schizophrenia. Pairwise correlations between gene expression levels and the relationship between gene expression levels and cognitive function and N-back-elicited brain activity were assessed. Finally, the expression levels of DISC1, AKAP9, FEZ1, NDEL1 and PCM1 were compared between 63 controls and 69 schizophrenic subjects. We found that DISC1-interactome genes showed correlated expression in the blood of healthy individuals. The expression levels of several interactome members were correlated with cognitive performance and N-back-elicited activity in the prefrontal cortex. In addition, DISC1 and NDEL1 showed decreased expression in schizophrenic subjects compared to healthy controls. Our findings highlight the importance of the coordinated expression of DISC1-interactome genes for normal cognitive function and suggest that dysregulated DISC1 and NDEL1 expression might, in part, contribute to susceptibility for schizophrenia via disruption of prefrontal cortex-dependent cognitive functions.

In vitro and ex-vivo cellular antioxidant protection and cognitive enhancing effects of an extract of Polygonum minus Huds (Lineminus™) demonstrated in a Barnes Maze animal model for memory and learning

Background

Polygonum minus Huds.is a culinary flavouring that is common in South East Asian cuisine and as a remedy for diverse maladies ranging from indigestion to poor eyesight. The leaves of this herb have been reported to be high in antioxidants. Flavonoids which have been associated with memory, cognition and protection against neurodegeneration were found in P. minus.

Method

This study examined a P. minus aqueous extract (Lineminus^™) for its antioxidant activity using the Oxygen Radical Absorbance Capacity (ORAC) assay, the ex vivo Cellular Antioxidant Protection of erythrocytes (CAP-e) assays and for potential anticholinesterase activity in vitro. Cognitive function and learning of Lineminus^™ was evaluated using scopolamine induced cognition deficits in a Barnes maze, rodent model of cognition.

Results

The extract displayed in vitro antioxidant activity with a total ORAC value of 16,964 μmole TE/gram. Cellular antioxidant protection from free radical damage using the CAP-e assay, with an IC50 of 0.58 g/L for inhibition of cellular oxidative damage, was observed. The extract inhibited cholinesterase activity with an IC50 of 0.04 mg/ml with a maximum inhibition of 68%. In a rodent model of cognition using scopolamine induced cognition deficits in the Barnes maze, the extract attenuated scopolamine induced disruptions in learning at the higher dose of 100 mg/kg.

Conclusion

These data shows that P. minus possesses antioxidant and anticholinesterase activity and demonstrated enhanced cognition in vivo. The data suggest neuroprotective properties of the extract.

Bilateral hippocampal increase following first-episode psychosis is associated with good clinical, functional and cognitive outcomes

BACKGROUND

Hippocampal pathology has been proposed to underlie clinical, functional and cognitive impairments in schizophrenia. The hippocampus is a highly plastic brain region; examining change in volume, or change bilaterally, over time, can advance understanding of the substrate of recovery in psychosis.

METHOD

Magnetic resonance imaging and outcome data were collected at baseline and 6-year follow-up in 42 first-episode psychosis subjects and 32 matched controls, to investigate whether poorer outcomes are associated with loss of global matter and hippocampal volumes. Bilateral hippocampal increase (BHI) over time, as a marker of hippocampal plasticity was hypothesized to be associated with better outcomes. Regression analyses were performed on: (i) clinical and functional outcomes with grey matter volume change and BHI as predictor variables; and (ii) cognitive outcome with BHI as predictor.

RESULTS

BHI was present in 29% of psychosis participants. There was no significant grey matter loss over time in either patient or control groups. Less severe illness course and lesser symptom severity were associated with BHI, but not with grey matter change. Employment and global function were associated with BHI and with less grey matter loss. Superior delayed verbal recall was also associated with BHI.

CONCLUSIONS

BHI occurs in a minority of patients following their first psychotic episode and is associated with good outcome across clinical, functional and cognitive domains.

Common and specific cognitive deficits in schizophrenia: relationships to function

The goals of the present study were to assess the interrelationships among tasks from the MATRICS and CNTRACS batteries, to determine the degree to which tasks from each battery capture unique variance in cognitive dysfunction in schizophrenia, and to determine the ability of tasks from each battery to predict functional outcome. Subjects were 104 schizophrenia patients and 132 healthy control subjects recruited as part of the CNTRACS initiative. All subjects completed four CNTRACS tasks and two tasks from the MATRICS battery: Brief Assessment of Cognition in Schizophrenia Symbol Coding and the Hopkins Verbal Learning Test. Functional outcome was also assessed in the schizophrenia subjects. In both the patient and control groups, we found significant intercorrelations between all higher order cognitive tasks (episodic memory, goal maintenance, processing speed, verbal learning) but minimal relationships with the visual task. For almost all tasks, scores were significantly related to measures of functional outcome, with higher associations between CNTRACS tasks and performance-based measures of function and between one of the MATRICS tasks and self-reported functioning, relative to the other functioning measures. After regressing out variance shared by other tasks, we continued to observe group differences in performance among task residuals, particularly for measures of episodic memory from both batteries, although these residuals did not correlate as robustly with functional outcome as raw test scores. These findings suggest that there exists both shared and specific variance across cognitive tasks related to cognitive and functional impairments in schizophrenia and that measures derived from cognitive neuroscience can predict functional capacity and status in schizophrenia.

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.

Northwestern University Schizophrenia Data and Software Tool (NUSDAST)

The schizophrenia research community has invested substantial resources on collecting, managing and sharing large neuroimaging datasets. As part of this effort, our group has collected high resolution magnetic resonance (MR) datasets from individuals with schizophrenia, their non-psychotic siblings, healthy controls and their siblings. This effort has resulted in a growing resource, the Northwestern University Schizophrenia Data and Software Tool (NUSDAST), an NIH-funded data sharing project to stimulate new research. This resource resides on XNAT Central, and it contains neuroimaging (MR scans, landmarks and surface maps for deep subcortical structures, and FreeSurfer cortical parcellation and measurement data), cognitive (cognitive domain scores for crystallized intelligence, working memory, episodic memory, and executive function), clinical (demographic, sibling relationship, SAPS and SANS psychopathology), and genetic (20 polymorphisms) data, collected from more than 450 subjects, most with 2-year longitudinal follow-up. A neuroimaging mapping, analysis and visualization software tool, CAWorks, is also part of this resource. Moreover, in making our existing neuroimaging data along with the associated meta-data and computational tools publically accessible, we have established a web-based information retrieval portal that allows the user to efficiently search the collection. This research-ready dataset meaningfully combines neuroimaging data with other relevant information, and it can be used to help facilitate advancing neuroimaging research. It is our hope that this effort will help to overcome some of the commonly recognized technical barriers in advancing neuroimaging research such as lack of local organization and standard descriptions.

Schizophrenia and emotional rubbernecking

Orienting toward emotionally salient information can be adaptive, as when danger needs to be avoided. Consistent with this idea, research has shown that emotionally valenced information draws attention more so than does neutral information in healthy individuals. However, at times this tendency is not adaptive, and it may distract the individual from goals. People with schizophrenia (PSZ), though they frequently show deficits in attentional control, have also been shown to exhibit diminished recognition of and attention to emotional information. In the present study, we investigated how the presentation of emotionally salient information affected performance on a working memory task for PSZ and healthy controls (HC). We found that although hit rates were equal to those of HCs for PSZ, the PSZ made fewer false alarms-resulting in overall better performance-than did the HCs. Deficits in emotional processing in PSZ appear to provide an advantage to them in situations in which salient emotional information competes with active cognitive goals.

Altered cognitive development in the siblings of individuals with schizophrenia

The goal of the current study was to further investigate the late neurodevelopmental hypothesis of schizophrenia by examining cross-sectional, age-related changes in cognitive function among young adult: 1) siblings of individuals with schizophrenia (N = 66); (2) healthy control participants (N = 77); and (3) the siblings of healthy controls (N = 77). All subjects participated in a battery of tasks in four domains: 1) IQ; 2) working memory; 3) episodic memory; and 4) executive function. We found significant group differences in the relationships between age and performance in working memory and episodic memory, with similar patterns for executive function and verbal IQ. The siblings of individuals with schizophrenia showed impaired performance in working memory, episodic memory, and executive function. In addition, healthy controls and/or their siblings showed age-related improvements in all four cognitive domains, while the siblings of individuals with schizophrenia only showed this for verbal IQ.

The nature and extent of working memory dysfunction in schizophrenia

This study aimed to examine verbal and visual-spatial working memory (WM) dysfunction in patients with schizophrenia. We compared 60 patients with schizophrenia with 57 healthy controls (matched for age, educational level, and IQ) on three WM tasks. Patients with schizophrenia performed significantly more poorly than healthy controls on verbal, visual, and spatial WM tests. Moreover, WM deficits were inversely associated with both the positive and negative symptoms of the patients. Taken together, these findings suggest that there are pervasive WM impairments in patients with schizophrenia. In addition, clinical features may play a significant role in the expression of WM deficits.

Memory deficits in schizophrenia: a selective review of functional magnetic resonance imaging (FMRI) studies

Schizophrenia is a complex chronic mental illness that is characterized by positive, negative and cognitive symptoms. Cognitive deficits are most predictive of long-term outcomes, with abnormalities in memory being the most robust finding. The advent of functional magnetic resonance imaging (fMRI) has allowed exploring neural correlates of memory deficits in vivo. In this article, we will give a selective review of fMRI studies probing brain regions and functional networks that are thought to be related to abnormal memory performance in two memory systems prominently affected in schizophrenia; working memory and episodic memory. We revisit the classic "hypofrontality" hypothesis of working memory deficits and explore evidence for frontotemporal dysconnectivity underlying episodic memory abnormalities. We conclude that fMRI studies of memory deficits in schizophrenia are far from universal. However, the current literature does suggest that alterations are not isolated to a few brain regions, but are characterized by abnormalities within large-scale brain networks.

Discrimination within Recognition Memory in Schizophrenia

Episodic memory is one of the most affected cognitive domains in schizophrenia. First-degree biological relatives of individuals with schizophrenia also have been found to exhibit a similar, but milder, episodic memory deficit. Unlike most studies that focus on the percent of previously presented items recognized, the current investigation sought to further elucidate the nature of memory dysfunction associated with schizophrenia by examining the discrimination of old and new material during recognition (measured by d') to consider false recognition of new items. Using the Recurring Figures Test and the California Verbal Learning Test (CVLT), we studied a sample of schizophrenia probands and the first-degree biological relatives of patients with schizophrenia, as well as probands with bipolar disorder and first-degree biological relatives to assess the specificity of recognition memory dysfunction to schizophrenia. The schizophrenia sample had poorer recognition discrimination in both nonverbal and verbal modalities; no such deficits were identified in first-degree biological relatives or bipolar disorder probands. Discrimination in schizophrenia and bipolar probands failed to benefit from the geometric structure in the designs in the manner that controls did on the nonverbal test. Females performed better than males in recognition of geometric designs. Episodic memory dysfunction in schizophrenia is present for a variety of stimulus domains and reflects poor use of item content to increase discrimination of old and new items.

fMRI assessment of thalamocortical connectivity during attentional performance

Functional magnetic resonance imaging (fMRI) studies have shown dysfunction in key areas associated with the thalamocortical circuit in patients with schizophrenia. This study examined the functional connectivity involving the frontal-thalamic circuitry during a spatial focusing-of-attention task in 18 unmedicated patients with schizophrenia and 38 healthy controls. Functional connectivity was analyzed by assigning seed regions (in the thalamic nuclei (mediodorsal nucleus (MDN), pulvinar, anterior nucleus (AN)), the dorsolateral prefrontal cortex (Brodmann areas 9 and 46), and the caudate), and correlating their respective activity with that in the non-seed regions voxel-wise. Functional connectivity analysis demonstrated that functional connectivity was significantly impaired in patients, e.g., between the right pulvinar and regions such as the prefrontal and temporal cortices and the cerebellum. On the other hand, enhanced functional connectivity was found in patients, e.g., between the AN and regions such as the prefrontal and temporal cortices. In addition, the patients had significantly lower task performance and less (but non-significant) brain activation than those of controls. These results revealed disturbed functional integration in schizophrenia, and suggested that the functional connectivity abnormalities in the thalamocortical circuitry, especially the frontal-thalamic circuitry, may underlie the attention deficits in schizophrenia patients. Further, this study suggested that functional connectivity analysis might be more sensitive than brain activation analysis in detecting the functional abnormalities in schizophrenia.

Visuospatial imagery and working memory in schizophrenia

INTRODUCTION

The ability to form mental images that reconstruct former perceptual experiences is closely related to working memory (WM) ability. However, whereas WM deficits are established as a core feature of schizophrenia, an independent body of work suggests that mental imagery ability is enhanced in the disorder. Across two experiments we investigated mental imagery in schizophrenia and its relationship with WM.

METHODS

In Experiment 1, individuals with schizophrenia (SZ: n=15) and matched controls (CO: n=14) completed a mental imagery generation and inspection task and a spatial delayed-response WM task. In Experiment 2, SZ (n=16) and CO (n=16) completed a novel version of the mental imagery task modified to increase WM maintenance demand.

RESULTS

In Experiment 1, SZ demonstrated enhanced mental imagery performance, as evidenced by faster response times relative to CO, with preserved accuracy. However, enhanced mental imagery in SZ was accompanied by impaired WM as assessed by the delayed-response task. In Experiment 2, when WM maintenance load was increased, SZ no longer showed superior imagery performance.

CONCLUSIONS

We found evidence for enhanced imagery manipulation in SZ despite their WM maintenance deficit. However, this imagery enhancement was abolished when WM maintenance demands were increased. This profile of enhanced imagery manipulation but impaired maintenance could be used to implement novel remediation strategies in the disorder.

Social isolation rearing induces mitochondrial, immunological, neurochemical and behavioural deficits in rats, and is reversed by clozapine or N-acetyl cysteine

Apart from altered dopamine (DA) function, schizophrenia displays mitochondrial and immune-inflammatory abnormalities, evidenced by oxidative stress, altered kynurenine metabolism and cytokine release. N-acetyl cysteine (NAC), an antioxidant and glutamate modulator, is effective in the adjunctive treatment of schizophrenia. Social isolation rearing (SIR) in rats is a valid neurodevelopmental animal model of schizophrenia. This study evaluated whether SIR-induced behavioural deficits may be explained by altered plasma pro- and anti-inflammatory cytokines, kynurenine metabolism, and cortico-striatal DA and mitochondrial function (via adenosine triphosphate (ATP) release), and if clozapine or NAC (alone and in combination) reverses these changes. SIR induced pronounced deficits in social interactive behaviours, object recognition memory, and prepulse inhibition (PPI), while simultaneously increasing striatal but reducing frontal cortical accumulation of ATP as well as DA. SIR increased pro- vs. anti-inflammatory cytokine balance and altered kynurenine metabolism with a decrease in neuroprotective ratio. Clozapine (5mg/kg/day×14days) as well as clozapine+NAC (5mg/kg/day and 150mg/kg/day×14days) reversed these changes, with NAC (150mg/kg/day) alone significantly but partially effective in some parameters. Clozapine+NAC was more effective than clozapine alone in reversing SIR-induced PPI, mitochondrial, immune and DA changes. In conclusion, SIR induces mitochondrial and immune-inflammatory changes that underlie cortico-striatal DA perturbations and subsequent behavioural deficits, and responds to treatment with clozapine or NAC, with an additive effect following combination treatment. The data provides insight into the mechanisms that might underlie the utility of NAC as an adjunctive treatment in schizophrenia.

The ventral portion of the CA1 region of the hippocampus and the prefrontal cortex as candidate regions for neuromodulation in schizophrenia

Existing antipsychotic drugs are most effective in the treatment of the positive symptoms of schizophrenia. However, they are associated with considerable side effects and have relatively low efficacy. Diminished inhibitory control in the hippocampus has been suggested to lead to hyperactivation of the dopamine system thus underpinning the dopamine-dependent psychosis associated with schizophrenia. Similarly, diminished inhibitory control is thought to underpin the cortical disruption associated with the cognitive dysfunctions. Impairment of a specific class of parvalbumin-positive inhibitory interneuron has been consistently identified in the prefrontal cortex and hippocampus of schizophrenics. Thus, this impairment common to both regions, may subserve these distinct symptom domains. Deep brain stimulation has been suggested to act, at least in part, through the modulation of interneuron function and here we propose the prefrontal cortex and hippocampus as potential targets for neuromodulatory intervention in the treatment of schizophrenia. Further, we specifically consider whether multiple targets and multiple neuromodulatory approaches may be necessary in the treatment of this multi-faceted disease. Finally we propose that deep brain stimulation of the ventral protion of the CA1 region of the hippocampus may be the most promising single target for neuromodulation in schizophrenia.

Can repetitive magnetic stimulation improve cognition in schizophrenia? Pilot data from a randomized controlled trial

BACKGROUND

Working memory represents a core cognitive domain that is impaired in schizophrenia for which there are currently no satisfactory treatments. Repetitive transcranial magnetic stimulation (rTMS) targeted over the dorsolateral prefrontal cortex has been shown to modulate neurophysiological mechanisms linked to working memory in schizophrenia and improves working memory performance in healthy subjects and might therefore represent a treatment modality for schizophrenia patients. The objectives were to evaluate the effects of rTMS on working memory performance in schizophrenia patients and evaluate whether rTMS normalizes performance to healthy subject levels.

METHODS

In a 4-week randomized double-blind sham-controlled pilot study design, 27 medicated schizophrenia patients were tested at the Centre for Addiction and Mental Health (a university teaching hospital that provides psychiatric care to a large urban catchment area and serves as a tertiary referral center for the province of Ontario). Patients performed the verbal working memory n-back task before and after rTMS magnetic resonance image targeted bilaterally sequentially to left and right dorsolateral prefrontal cortex 750 pulses/side at 20 Hz for 20 treatments. The main outcome measure was mean magnitude of change in the n-back accuracy for target responses with active (n = 13) or sham (n = 12) rTMS treatment course.

RESULTS

The rTMS significantly improved 3-back accuracy for targets compared with placebo sham (Cohen's d = .92). The improvement in 3-back accuracy was also found to be at a level comparable to healthy subjects.

CONCLUSIONS

These pilot data suggest that bilateral rTMS might be a novel, efficacious, and safe treatment for working memory deficits in patients with schizophrenia.

Toxoplasma gondii infection, from predation to schizophrenia: can animal behaviour help us understand human behaviour?

We examine the role of the protozoan Toxoplasma gondii as a manipulatory parasite and question what role study of infections in its natural intermediate rodent hosts and other secondary hosts, including humans, may elucidate in terms of the epidemiology, evolution and clinical applications of infection. In particular, we focus on the potential association between T. gondii and schizophrenia. We introduce the novel term 'T. gondii-rat manipulation-schizophrenia model' and propose how future behavioural research on this model should be performed from a biological, clinical and ethically appropriate perspective.

The effects of perceptual encoding on the magnitude of object working memory impairment in schizophrenia

Deficits in the visual working memory (WM) system have been consistently reported in schizophrenia patients, but the relative contribution of initial perceptual encoding to these deficits remains unsettled. We assessed the role of visual perceptual encoding on performance on an object WM task. Schizophrenia patients (N=37) and nonpsychiatric control subjects (N=33) were tested on an object WM task involving three delay periods: 200 ms, 3s, and 10s. Schizophrenia patients performed significantly less accurately than controls on all three conditions. However, after controlling for the effect of perceptual encoding (accuracy on the 200 ms delay condition) on performance in the two memory load conditions, schizophrenia patients demonstrated intact WM in the 3s delay condition, and showed a weak trend for decreased accuracy on the 10s delay compared with controls. Analysis of individual differences in pattern of performance revealed that a distinct subgroup of poor encoder patients had a significantly greater reduction in accuracy at 3s than the other patient subgroups and controls. In contrast, among schizophrenia patients who performed poorly on the 10s delay, accuracy was equivalently reduced independent of encoding ability. WM deficits in controls were independent of encoding ability at both delay intervals. These results indicate that encoding ability titrates the magnitude of WM impairment in schizophrenia patients but not in controls, and that heterogeneity has to be taken into account to correctly estimate the effects of perceptual encoding on visual object WM deficits in schizophrenia.

Pavlovian reward prediction and receipt in schizophrenia: relationship to anhedonia

Reward processing abnormalities have been implicated in the pathophysiology of negative symptoms such as anhedonia and avolition in schizophrenia. However, studies examining neural responses to reward anticipation and receipt have largely relied on instrumental tasks, which may confound reward processing abnormalities with deficits in response selection and execution. 25 chronic, medicated outpatients with schizophrenia and 20 healthy controls underwent functional magnetic resonance imaging using a pavlovian reward prediction paradigm with no response requirements. Subjects passively viewed cues that predicted subsequent receipt of monetary reward or non-reward, and blood-oxygen-level-dependent signal was measured at the time of cue presentation and receipt. At the group level, neural responses to both reward anticipation and receipt were largely similar between groups. At the time of cue presentation, striatal anticipatory responses did not differ between patients and controls. Right anterior insula demonstrated greater activation for nonreward than reward cues in controls, and for reward than nonreward cues in patients. At the time of receipt, robust responses to receipt of reward vs. nonreward were seen in striatum, midbrain, and frontal cortex in both groups. Furthermore, both groups demonstrated responses to unexpected versus expected outcomes in cortical areas including bilateral dorsolateral prefrontal cortex. Individual difference analyses in patients revealed an association between physical anhedonia and activity in ventral striatum and ventromedial prefrontal cortex during anticipation of reward, in which greater anhedonia severity was associated with reduced activation to money versus no-money cues. In ventromedial prefrontal cortex, this relationship held among both controls and patients, suggesting a relationship between anticipatory activity and anhedonia irrespective of diagnosis. These findings suggest that in the absence of response requirements, brain responses to reward receipt are largely intact in medicated individuals with chronic schizophrenia, while reward anticipation responses in left ventral striatum are reduced in those patients with greater anhedonia severity.