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

Differential aberrant connectivity of precuneus and anterior insula may underpin the diagnosis of schizophrenia and mood disorders

BACKGROUND

Over the past decade, resting-state functional magnetic resonance imaging (rs-fMRI) has concentrated on brain networks such as the default mode network (DMN), the salience network (SN), and the central executive network (CEN), allowing for a better understanding of cognitive deficits observed in mental disorders, as well as other characteristic psychopathological phenomena such as thought and behavior disorganization.

AIM

To investigate differential patterns of effective connectivity across distributed brain networks involved in schizophrenia (SCH) and mood disorders.

METHODS

The sample comprised 58 patients with either paranoid syndrome in the context of SCH (n = 26) or depressive syndrome (Ds) (n = 32), in the context of major depressive disorder or bipolar disorder. The methods used include rs-fMRI and subsequent dynamic causal modeling to determine the direction and strength of connections to and from various nodes in the DMN, SN and CEN.

RESULTS

A significant excitatory connection from the dorsal anterior cingulate cortex to the anterior insula (aI) was observed in the SCH patient group, whereas inhibitory connections from the precuneus to the ventrolateral prefrontal cortex and from the aI to the precuneus were observed in the Ds group.

CONCLUSION

The results delineate specific patterns associated with SCH and Ds and offer a better explanation of the underlying mechanisms of these disorders, and inform differential diagnosis and precise treatment targeting.

Deletion of adenosine A2A receptors from astrocytes disrupts glutamate homeostasis leading to psychomotor and cognitive impairment: relevance to schizophrenia

BACKGROUND

Adenosine A2A receptors (A2AR) modulate dopamine and glutamate signaling and thereby may influence some of the psychomotor and cognitive processes associated with schizophrenia. Because astroglial A2AR regulate the availability of glutamate, we hypothesized that they might play an unprecedented role in some of the processes leading to the development of schizophrenia, which we investigated using a mouse line with a selective deletion of A2AR in astrocytes (Gfa2-A2AR knockout [KO] mice].

METHODS

We examined Gfa2-A2AR KO mice for behaviors thought to recapitulate some features of schizophrenia, namely enhanced MK-801 psychomotor response (positive symptoms) and decreased working memory (cognitive symptoms). In addition, we probed for neurochemical alterations in the glutamatergic circuitry, evaluating glutamate uptake and release and the levels of key proteins defining glutamatergic signaling (glutamate transporter-I [GLT-I], N-methyl-D-aspartate receptors [NMDA-R] and α-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors [AMPA-R]) to provide a mechanistic understanding of the phenotype encountered.

RESULTS

We show that Gfa2-A2AR KO mice exhibited enhanced MK-801 psychomotor response and decreased working memory; this was accompanied by a disruption of glutamate homeostasis characterized by aberrant GLT-I activity, increased presynaptic glutamate release, NMDA-R 2B subunit upregulation, and increased internalization of AMPA-R. Accordingly, selective GLT-I inhibition or blockade of GluR1/2 endocytosis prevented the psychomotor and cognitive phenotypes in Gfa2-A2AR KO mice, namely in the nucleus accumbens.

CONCLUSIONS

These results show that the dysfunction of astrocytic A2AR, by controlling GLT-I activity, triggers an astrocyte-to-neuron wave of communication resulting in disrupted glutamate homeostasis, thought to underlie several endophenotypes relevant to schizophrenia.

Knockdown of phospholipase C-β1 in the medial prefrontal cortex of male mice impairs working memory among multiple schizophrenia endophenotypes

BACKGROUND

Decreased expression of phospholipase C-β1 (PLC-β1) has been observed in the brains of patients with schizophrenia, but, to our knowledge, no studies have shown a possible association between this altered PLC-β1 expression and the pathogenesis of schizophrenia. Although PLC-β1-null (PLC-β1(-/-)) mice exhibit multiple endophenotypes of schizophrenia, it remains unclear how regional decreases in PLC-β1 expression in the brain contribute to specific behavioural defects.

METHODS

We selectively knocked down PLC-β1 in the medial prefrontal cortex (mPFC) using a small hairpin RNA strategy in mice.

RESULTS

Silencing PLC-β1 in the mPFC resulted in working memory deficits, as assayed using the delayed non-match-to-sample T-maze task. Notably, however, other schizophrenia-related behaviours observed in PLC-β1-/- mice, including phenotypes related to locomotor activity, sociability and sensorimotor gating, were normal in PLC-β1 knockdown mice.

LIMITATIONS

Phenotypes of PLC-β1 knockdown mice, such as locomotion, anxiety and sensorimotor gating, have already been published in our previous studies. Further, the neural mechanisms underlying the working memory deficit in mice may be different from those in human schizophrenia.

CONCLUSION

These results indicate that PLC-β1 signalling in the mPFC is required for working memory. Importantly, these results support the notion that the decrease in PLC-β1 expression in the brains of patients with schizophrenia is a pathogenically relevant molecular marker of the disorder.

Phospholipase C-β1 Hypofunction in the Pathogenesis of Schizophrenia

Schizophrenia is a mental disorder that is characterized by various abnormal symptoms. Previous studies indicate decreased expression of phospholipase C-β1 (PLC-β1) in the brains of patients with schizophrenia. PLC-β1-null (PLC-β1(-/-)) mice exhibit multiple endophenotypes of schizophrenia. Furthermore, a study of PLC-β1 knockdown in the medial prefrontal cortex of mice has shown a specific behavioral deficit, impaired working memory. These results support the notion that disruption of PLC-β1-linked signaling in the brain is strongly involved in the pathogenesis of schizophrenia. In this review, we broadly investigate recent studies regarding schizophrenia-related behaviors as well as their various clinical and biological correlates in PLC-β1(-/-) and knockdown mouse models. This will provide a better understanding of the pathological relevance of the altered expression of PLC-β1 in the brains of patients with schizophrenia. Evidence accumulated will shed light on future in-depth studies, possibly in human subjects.

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.

Auditory false perceptions are mediated by psychosis risk factors

INTRODUCTION

Auditory hallucinations exist in psychotic disorders as well as the general population. Proneness to hallucinations, as measured by positive schizotypy, predicts false perceptions during an auditory signal detection task (Barkus, Stirling, Hopkins, McKie, & Lewis, 2007). Our aim was to replicate this result and extend it by examining effects of age and sex, both important demographic predictors of psychosis.

METHOD

A sample of 76 healthy volunteers split into 15-17 years (n=46) and 19 years plus (n=30) underwent a signal detection task designed to detect propensity towards false perceptions under ambiguous auditory conditions. Scores on the Unusual Experiences subscale (UE) of the O-LIFE schizotypy scale, IQ, and a measure of working memory were also assessed.

RESULTS

We replicated our initial finding (Barkus et al., 2007): High scores on positive schizotypy were associated with false perceptions. Younger participants who scored highly on positive schizotypy reported significantly more false perceptions compared to other groups (p=.04). Older participants who had had an imaginary friend reported more false perceptions during the signal detection task (p<.01).

CONCLUSIONS

Younger participants seem most vulnerable to the effects of positive schizotypal traits in terms of a signal detection deficit that underlies auditory hallucinations. Schizotypy may have greatest impact closer to the risk period for development of psychotic disorders.

NIH Toolbox Cognition Battery (NIHTB-CB): list sorting test to measure working memory

The List Sorting Working Memory Test was designed to assess working memory (WM) as part of the NIH Toolbox Cognition Battery. List Sorting is a sequencing task requiring children and adults to sort and sequence stimuli that are presented visually and auditorily. Validation data are presented for 268 participants ages 20 to 85 years. A subset of participants (N=89) was retested 7 to 21 days later. As expected, the List Sorting Test had moderately high correlations with other measures of working memory and executive functioning (convergent validity) but a low correlation with a test of receptive vocabulary (discriminant validity). Furthermore, List Sorting demonstrates expected changes over the age span and has excellent test-retest reliability. Collectively, these results provide initial support for the construct validity of the List Sorting Working Memory Measure as a measure of working memory. However, the relationship between the List Sorting Test and general executive function has yet to be determined.

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.

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.

A hierarchical modeling approach to data analysis and study design in a multi-site experimental fMRI study

We propose a hierarchical Bayesian model for analyzing multi-site experimental fMRI studies. Our method takes the hierarchical structure of the data (subjects are nested within sites, and there are multiple observations per subject) into account and allows for modeling between-site variation. Using posterior predictive model checking and model selection based on the deviance information criterion (DIC), we show that our model provides a good fit to the observed data by sharing information across the sites. We also propose a simple approach for evaluating the efficacy of the multi-site experiment by comparing the results to those that would be expected in hypothetical single-site experiments with the same sample size.

Cognitive and neuroplasticity mechanisms by which congenital or early blindness may confer a protective effect against schizophrenia

Several authors have noted that there are no reported cases of people with schizophrenia who were born blind or who developed blindness shortly after birth, suggesting that congenital or early (C/E) blindness may serve as a protective factor against schizophrenia. By what mechanisms might this effect operate? Here, we hypothesize that C/E blindness offers protection by strengthening cognitive functions whose impairment characterizes schizophrenia, and by constraining cognitive processes that exhibit excessive flexibility in schizophrenia. After briefly summarizing evidence that schizophrenia is fundamentally a cognitive disorder, we review areas of perceptual and cognitive function that are both impaired in the illness and augmented in C/E blindness, as compared to healthy sighted individuals. We next discuss: (1) the role of neuroplasticity in driving these cognitive changes in C/E blindness; (2) evidence that C/E blindness does not confer protective effects against other mental disorders; and (3) evidence that other forms of C/E sensory loss (e.g., deafness) do not reduce the risk of schizophrenia. We conclude by discussing implications of these data for designing cognitive training interventions to reduce schizophrenia-related cognitive impairment, and perhaps to reduce the likelihood of the development of the disorder itself.

Association of KIBRA with episodic and working memory: a meta-analysis

WWC1 was first implicated in human cognition through a genome wide association study in 2006 that reported an association of the intronic single nucleotide polymorphism (SNP) rs17070145 with episodic memory performance. WWC1 encodes the protein KIBRA, which is almost ubiquitously expressed. Together with its binding partners, KIBRA is assumed to play a role in synaptic plasticity. T-allele carriers of SNP rs17070145 have been reported to outperform individuals that are homozygous for the C-allele in episodic memory tasks. Here we report two random effects meta-analyses testing the association of rs17070145 with episodic and working memory. All currently available population-based association studies that investigated effects of rs17070145 on episodic or working memory were included in the analyses. Where performance measures for multiple domain-specific tasks were available for a given study population, averaged effect size estimates were calculated. The performed meta-analyses relied on 17 samples that were tested for episodic memory performance (N = 8,909) and 9 samples that had performed working memory tasks (N = 4,696). We report a significant association of rs17070145 with both episodic (r = 0.068, P = 0.001) and working memory (r = 0.035, P = 0.018). In summary, our findings indicate that SNP rs17070145 located within KIBRA explains 0.5% of the variance for episodic memory tasks and 0.1% of the variance for working memory tasks in samples of primarily Caucasian background.

Effect of the interleukin-1β gene on dorsolateral prefrontal cortex function in schizophrenia: a genetic neuroimaging study

BACKGROUND

Genetic studies have found that the interleukin-1β gene (IL1B, 2q13) influences the risk for schizophrenia, but the underlying biological mechanisms of the association are still unclear. Investigation of the effects of genetic variability in this gene on brain function could provide more information about its role in the disorder.

METHODS

The present study examined the effects of a functional polymorphism at IL1B gene promoter (-511C/T; rs16944) on brain correlates of working memory performance in schizophrenia. Forty-eight schizophrenia patients and 46 control subjects underwent functional magnetic resonance imaging while performing the n-back task.

RESULTS

In the pooled sample, genetic variability at this locus was associated with differential brain activation in a bilateral frontal region including the dorsolateral prefrontal cortex. There was also a significant diagnosis × genotype interaction effect in an overlapping frontal region: the IL1B polymorphism did not affect activation in the control subjects in this area, but the schizophrenia patients who were T carriers showed significantly higher activation than the CC homozygotes.

CONCLUSIONS

The findings support a role for IL1B variability in the dorsolateral prefrontal cortex dysfunction classically associated with schizophrenia.

Cotinine: Beyond that Expected, More than a Biomarker of Tobacco Consumption

A greater incidence of tobacco consumption occurs among individuals with psychiatric conditions including post-traumatic stress disorder (PTSD), bipolar disorder, major depression, and schizophrenia, compared with the general population. Even when still controversial, it has been postulated that smoking is a form of self-medication that reduces psychiatric symptoms among individuals with these disorders. To better understand the component(s) of tobacco-inducing smoking behavior, greater attention has been directed toward nicotine. However, in recent years, new evidence has shown that cotinine, the main metabolite of nicotine, exhibits beneficial effects over psychiatric symptoms and may therefore promote smoking within this population. Some of the behavioral effects of cotinine compared to nicotine are discussed here. Cotinine, which accumulates in the body as a result of tobacco exposure, crosses the blood-brain barrier and has different pharmacological properties compared with nicotine. Cotinine has a longer plasma half-life than nicotine and showed no addictive or cardiovascular effects in humans. In addition, at the preclinical level, cotinine facilitated the extinction of fear memory and anxiety after fear conditioning, improved working memory in a mouse model of Alzheimer’s disease (AD) and in a monkey model of schizophrenia. Altogether, the new evidence suggests that the pharmacological and behavioral effects of cotinine may play a key role in promoting tobacco smoking in individuals that suffer from psychiatric conditions and represents a new potential therapeutic agent against psychiatric conditions such as AD and PTSD.

Adjunctive intranasal oxytocin improves verbal memory in people with schizophrenia

INTRODUCTION

Cognitive deficits are a prominent, disabling component of schizophrenia and current pharmacological treatments have demonstrated limited efficacy in their amelioration. Oxytocin - though it has shown promise as a novel antipsychotic in multiple clinical trials - has as-yet poorly characterized effects on cognition, with some evidence indicating an amnestic profile.

METHOD

As part of a previously reported trial of chronic adjunctive oxytocin in schizophrenia, we measured its effect on two cognitive tests: the CVLT (California Verbal Learning Test) and the LNS (Letter Number Sequence). Tests were performed at baseline and after 3 weeks of treatment.

RESULTS

We found no evidence for an amnestic effect and, in fact, significantly better performance with oxytocin on several subtests of the CVLT; namely total Recall trials 1-5 (p=0.027), short delayed free recall (p=0.032) and total recall discrimination (p=0.020). In contrast we found no difference between placebo and oxytocin on LNS performance.

CONCLUSIONS

This is the first report we are aware of documenting a beneficial effect of oxytocin on cognition in schizophrenia. Though from a small sample (n=15), these data both offset past concerns about oxytocin's amnestic effects, and may auger another potential benefit in addition to the already-demonstrated salutary effects on other components of the illness.

Abnormalities of the Duo/Ras-related C3 botulinum toxin substrate 1/p21-activated kinase 1 pathway drive myosin light chain phosphorylation in frontal cortex in schizophrenia

BACKGROUND

Recent studies on GTPases have suggested that reduced Duo and cell division cycle 42 (Cdc42) transcript expression is involved in dendritic spine loss in schizophrenia. In murine models, Duo and Cdc42 phosphorylate p21-activated kinase 1 (PAK1), which modifies the activity of regulatory myosin light chain (MLC) and cofilin by altering their phosphorylation. Therefore, we hypothesized that in schizophrenia abnormal Duo and Cdc42 expression result in changes in MLC and/or cofilin phosphorylation, which might alter actin cytoskeleton dynamics underlying dendritic spine maintenance.

METHODS

We performed Western blot protein expression analysis in postmortem brains from patients diagnosed with schizophrenia and a comparison group. We focused our studies in the anterior cingulate cortex (ACC; n = 33 comparison group; n = 36 schizophrenia) and dorsolateral prefrontal cortex (DLPFC; n = 29 comparison group; n = 35 schizophrenia).

RESULTS

In both ACC and DLPFC, we found a reduction of Duo expression and PAK1 phosphorylation in schizophrenia. Cdc42 protein expression was decreased in ACC but not in DLPFC. In ACC, we observed decreased PAK1 phosphorylation and increased MLC phosphorylation (pMLC), whereas in DLPFC pMLC remained unchanged.

CONCLUSIONS

These data suggest a novel mechanism that might underlie dendritic spine loss in schizophrenia. The increase in pMLC seen in ACC might be associated with dendritic spine shrinkage. The lack of an effect on pMLC in DLPFC suggests that in schizophrenia PAK1 downstream pathways are differentially affected in these cortical areas.

Inter-relationship of plasma markers of oxidative stress and thyroid hormones in schizophrenics

Background

The relationship of oxidative stress to thyroid hormones has not been studied in the schizophrenics. The present study determined the status and interrelationship of plasma markers of oxidative stress, nitric oxide and thyroid hormones in thirty (17 males and 13 females) newly diagnosed patients with acute schizophrenia before initiation of chemotherapy. Twenty five (13 males and 12 females) mentally healthy individuals served as controls. Patients and controls with history of hard drugs (including alcohol and cigarette), pre-diagnosis medications (e.g. antiparkinsonian/antipsychotic drugs), chronic infections, liver disease and diabetes mellitus were excluded from the study. Plasma levels of total antioxidant potential (TAP), total plasma peroxides (TPP), nitric oxide (NO), malondialdehyde (MDA), thyroxine (T4), tri-iodothyronine (T3) and thyroid stimulating hormone (TSH) were determined in all participants using spectrophotometric and enzyme linked immunosorbent assay (ELISA) methods respectively. Oxidative stress index (OSI) was calculated as the percent ratio of total plasma peroxides and total antioxidant potential.

Findings

Significantly higher plasma levels of MDA (p < 0.01), TPP (p < 0.01), OSI (p < 0.01), T3 (p < 0.01) and T4 (p < 0.05) were observed in schizophrenics when compared with the controls. The mean levels of TAP, NO and TSH were significantly lower in schizophrenics (p < 0.01) when compared with the controls. The result shows that T3 values correlate significantly with MDA (p < 0.05) and TPP (p < 0.01) in schizophrenics.

Conclusions

Higher level of TPP may enhance thyroid hormogenesis in schizophrenics. Adjuvant antioxidant therapy may be a novel approach in the treatment of schizophrenic patients.

Neocortical-hippocampal dynamics of working memory in healthy and diseased brain states based on functional connectivity

Working memory (WM) is the ability to transiently maintain and manipulate internal representations beyond its external availability to the senses. This process is thought to support high level cognitive abilities and been shown to be strongly predictive of individual intelligence and reasoning abilities. While early models of WM have relied on a modular perspective of brain functioning, more recent evidence suggests that cognitive functions emerge from the interactions of multiple brain regions to generate large-scale networks. Here we will review the current research on functional connectivity of WM processes to highlight the critical role played by neural interactions in healthy and pathological brain states. Recent findings demonstrate that WM abilities are not determined solely by local brain activity, but also rely on the functional coupling of neocortical-hippocampal regions to support WM processes. Although the hippocampus has long been held to be important for long-term declarative memory, recent evidence suggests that the hippocampus may also be necessary to coordinate disparate cortical regions supporting the periodic reactivation of internal representations in WM. Furthermore, recent brain imaging studies using connectivity measures, have shown that changes in cortico-limbic interactions can be useful to characterize WM impairments observed in different neuropathological conditions. Recent advances in electrophysiological and neuroimaging techniques to model network activity has led to important insights into how neocortical and hippocampal regions support WM processes and how disruptions along this network can lead to the memory impairments commonly reported in many neuropathological populations.

Event-related potentials and changes of brain rhythm oscillations during working memory activation in patients with first-episode psychosis

BACKGROUND

Earlier contributions have documented significant changes in sensory, attention-related endogenous event-related potential (ERP) components and θ band oscillatory responses during working memory activation in patients with schizophrenia. In patients with first-episode psychosis, such studies are still scarce and mostly focused on auditory sensory processing. The present study aimed to explore whether subtle deficits of cortical activation are present in these patients before the decline of working memory performance.

METHODS

We assessed exogenous and endogenous ERPs and frontal θ event-related synchronization (ERS) in patients with first-episode psychosis and healthy controls who successfully performed an adapted 2-back working memory task, including 2 visual n-backworking memory tasks as well as oddball detection and passive fixation tasks.

RESULTS

We included 15 patients with first-episode psychosis and 18 controls in this study. Compared with controls, patients with first-episode psychosis displayed increased latencies of early visual ERPs and phasic θ ERS culmination peak in all conditions. However, they also showed a rapid recruitment of working memory-related neural generators, even in pure attention tasks, as indicated by the decreased N200 latency and increased amplitude of sustained θ ERS in detection compared with controls.

LIMITATIONS

Owing to the limited sample size, no distinction was made between patients with first-episode psychosis with positive and negative symptoms. Although we controlled for the global load of neuroleptics, medication effect cannot be totally ruled out.

CONCLUSION

The present findings support the concept of a blunted electroencephalographic response in patients with first-episode psychosis who recruit the maximum neural generators in simple attention conditions without being able to modulate their brain activation with increased complexity of working memory tasks.

Altered topological properties of functional network connectivity in schizophrenia during resting state: a small-world brain network study

Aberrant topological properties of small-world human brain networks in patients with schizophrenia (SZ) have been documented in previous neuroimaging studies. Aberrant functional network connectivity (FNC, temporal relationships among independent component time courses) has also been found in SZ by a previous resting state functional magnetic resonance imaging (fMRI) study. However, no study has yet determined if topological properties of FNC are also altered in SZ. In this study, small-world network metrics of FNC during the resting state were examined in both healthy controls (HCs) and SZ subjects. FMRI data were obtained from 19 HCs and 19 SZ. Brain images were decomposed into independent components (ICs) by group independent component analysis (ICA). FNC maps were constructed via a partial correlation analysis of ICA time courses. A set of undirected graphs were built by thresholding the FNC maps and the small-world network metrics of these maps were evaluated. Our results demonstrated significantly altered topological properties of FNC in SZ relative to controls. In addition, topological measures of many ICs involving frontal, parietal, occipital and cerebellar areas were altered in SZ relative to controls. Specifically, topological measures of whole network and specific components in SZ were correlated with scores on the negative symptom scale of the Positive and Negative Symptom Scale (PANSS). These findings suggest that aberrant architecture of small-world brain topology in SZ consists of ICA temporally coherent brain networks.

Neural correlates of relational and item-specific encoding during working and long-term memory in schizophrenia

Successful long-term memory (LTM) depends upon effective control of information in working memory (WM), and there is evidence that both WM and LTM are impaired by schizophrenia. This study tests the hypothesis that LTM deficits in schizophrenia may result from impaired control of relational processing in WM due to dorsolateral prefrontal cortex (DLPFC) dysfunction. fMRI was performed on 19 healthy controls and 20 patients with schizophrenia during WM tasks emphasizing relational (reorder trials) versus item-specific (rehearse trials) processing. WM activity was also examined with respect to LTM recognition on a task administered outside the scanner. Receiver operator characteristic analysis assessed familiarity and recollection components of LTM. Patients showed a disproportionate familiarity deficit for reorder versus rehearse trials against a background of generalized LTM impairments. Relational processing during WM led to DLPFC activation in both groups. However, this activation was less focal in patients than in controls, and patients with more severe negative symptoms showed less of a DLPFC increase. fMRI analysis of subsequent recognition performance revealed a group by condition interaction. High LTM for reorder versus rehearse trials was associated with bilateral DLPFC activation in controls, but not in patients who activated the left middle temporal and inferior occipital gyrus. Results indicate that although patients can activate the DLPFC on a structured relational WM task, this activation is less focal and does not translate to high retrieval success, suggesting a disruption in the interaction between WM and LTM processes in schizophrenia.

Glycine transporter 1 as a potential therapeutic target for schizophrenia-related symptoms: evidence from genetically modified mouse models and pharmacological inhibition

Schizophrenia is characterized by positive symptoms such as hallucinations, negative symptoms such as blunted affect, and symptoms of cognitive deficiency such as deficits in working memory and selective attention. N-methyl-d-aspartate receptor (NMDAR) hypofunction has been implicated in all three pathophysiological aspects of the disease. Due to the severe side effects of direct NMDAR agonists, targeting the modulatory co-agonist glycine-B site of the NMDAR is considered to be a promising strategy to ameliorate NMDAR hypofunction. To assess the antipsychotic and pro-cognitive potential of this approach, we examine the strategies designed to enhance glycine-B site occupancy through glycine transporter 1 (GlyT1) blockade. Among the existing transgenic mouse models with GlyT1 deficits, the one specifically targeting forebrain neuronal GlyT1 has yielded the most promising data on cognitive enhancement. Parallel advances in the pharmacology of GlyT1 inhibition point not only to an enhancement of attention, learning and memory but also include suggestions of mood enhancing effects that might be valuable for treating negative symptoms. Thus, interventions at GlyT1 are highly effective in modifying multiple brain functions, and dissection of their respective mechanisms is expected to further maximize their therapeutic potential for human mental diseases.

Qualifying brain functional MRI parameters as endophenotypes in schizophrenia

Although the genetic contribution to schizophrenia pathogenesis has been well established, with an approximate heritability of 81%, the endeavor to elucidate the complex genetic architecture of schizophrenia has met limited success. ‘Endophenotypes’, or ‘intermediate phenotypes’, are more restricted constructs of genetic risk than the clinical manifestations hitherto employed by molecular geneticists. They are, putatively, intermediate in the pathophysiological pathway between genetic variation and clinical phenomenology and can possibly be used to assist in the elucidation of genetic diathesis for schizophrenia. In this article, we present the current evidence that supports functional MRI parameters as promising candidate endophenotypes in schizophrenia.

Substance use in adolescence and psychosis: clarifying the relationship

Adolescence is a time of exploration of the self, and this exploration may involve the use of alcohol and drugs. Sadly, for some, adolescence also marks the first signs of a psychosis. The temporal proximity between the onset of substance use and of psychosis has been the cause of much debate. Here we review the association of alcohol, cannabis, stimulants, and other drugs with psychosis, and we conclude that the use of cannabis and the amphetamines significantly contributes to the risk of psychosis.