Treating working memory deficits in schizophrenia: a review of the neurobiology

Early Social Isolation Stress and Perinatal NMDA Receptor Antagonist Treatment Induce Changes in the Structure and Neurochemistry of Inhibitory Neurons of the Adult Amygdala and Prefrontal Cortex

The exposure to aversive experiences during early life influences brain development and leads to altered behavior. Moreover, the combination of these experiences with subtle alterations in neurodevelopment may contribute to the emergence of psychiatric disorders, such as schizophrenia. Recent hypotheses suggest that imbalances between excitatory and inhibitory (E/I) neurotransmission, especially in the prefrontal cortex and the amygdala, may underlie their etiopathology. In order to understand better the neurobiological bases of these alterations, we studied the impact of altered neurodevelopment and chronic early-life stress on these two brain regions. Transgenic mice displaying fluorescent excitatory and inhibitory neurons, received a single injection of MK801 (NMDAR antagonist) or vehicle solution at postnatal day 7 and/or were socially isolated from the age of weaning until adulthood (3 months old). We found that anxiety-related behavior, brain volume, neuronal structure, and the expression of molecules related to plasticity and E/I neurotransmission in adult mice were importantly affected by early-life stress. Interestingly, many of these effects were potentiated when the stress paradigm was applied to mice perinatally injected with MK801 ("double-hit" model). These results clearly show the impact of early-life stress on the adult brain, especially on the structure and plasticity of inhibitory networks, and highlight the double-hit model as a valuable tool to study the contribution of early-life stress in the emergence of neurodevelopmental psychiatric disorders, such as schizophrenia.

Cognitive functioning and employment among people with schizophrenia in vocational rehabilitation

BACKGROUND

Employment is central to recovery in schizophrenia, but little attention has been paid to its relationship with cognitive functioning.

OBJECTIVE

This cross-sectional study adds to the knowledge base of relationships between cognitive functioning and gaining competitive employment, work hours per week, and monthly income among people with schizophrenia in vocational rehabilitation. It also examines which area of cognitive function may be decisive for gaining employment.

METHODS

Thirty-nine vocational rehabilitation participants were administered a cognitive battery based on MATRICS Consensus Cognitive Battery. Socio-demographic, clinical, and vocational data were gathered and analyzed with nonparametric statistics.

RESULTS

Individuals with competitive employment differed from those without competitive employment in attention and psychomotor speed, delayed verbal recall, immediate visual recall, and planning, reasoning, and problem-solving. Higher scores in immediate and delayed verbal recall and planning, reasoning, and problem-solving correlated with more work hours per week and higher income. Immediate visual recall was related to higher income. Higher scores in planning, reasoning, and problem-solving was an indicator of competitive employment (OR = 1.48).

CONCLUSIONS

Higher order cognitive functioning of planning, reasoning, and problem-solving may have a central role in gaining employment. The findings should be considered in compensation for or improving cognitive functions for vocational rehabilitation participants.

Mice heterozygous for an inactivated allele of the schizophrenia associated Brd1 gene display selective cognitive deficits with translational relevance to schizophrenia

Schizophrenia is a debilitating brain disorder characterized by disturbances of emotion, perception and cognition. Cognitive impairments predict functional outcome in schizophrenia and are detectable even in the prodromal stage of the disorder. However, our understanding of the underlying neurobiology is limited and procognitive treatments remain elusive. We recently demonstrated that mice heterozygous for an inactivated allele of the schizophrenia-associated Brd1 gene (Brd1^+/- mice) display behaviors reminiscent of schizophrenia, including impaired social cognition and long-term memory. Here, we further characterize performance of these mice by following the preclinical guidelines recommended by the 'Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS)' and 'Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS)' initiatives to maximize translational value. Brd1^+/- mice exhibit relational encoding deficits, compromised working and long term memory, as well as impaired executive cognitive functioning with cognitive behaviors relying on medial prefrontal cortex being particularly affected. Akin to patients with schizophrenia, the cognitive deficits displayed by Brd1^+/- mice are not global, but selective. Our results underline the value of Brd1^+/- mice as a promising tool for studying the neurobiology of cognitive deficits in schizophrenia.

Cortical surface-based threshold-free cluster enhancement and cortexwise mediation

Threshold-free cluster enhancement (TFCE) is a sensitive means to incorporate spatial neighborhood information in neuroimaging studies without using arbitrary thresholds. The majority of methods have applied TFCE to voxelwise data. The need to understand the relationship among multiple variables and imaging modalities has become critical. We propose a new method of applying TFCE to vertexwise statistical images as well as cortexwise (either voxel- or vertexwise) mediation analysis. Here we present TFCE_mediation, a toolbox that can be used for cortexwise multiple regression analysis with TFCE, and additionally cortexwise mediation using TFCE. The toolbox is open source and publicly available (https://github.com/trislett/TFCE_mediation). We validated TFCE_mediation in healthy controls from two independent multimodal neuroimaging samples (N = 199 and N = 183). We found a consistent structure-function relationship between surface area and the first independent component (IC1) of the N-back task, that white matter fractional anisotropy is strongly associated with IC1 N-back, and that our voxel-based results are essentially identical to FSL randomise using TFCE (all P_FWE <0.05). Using cortexwise mediation, we showed that the relationship between white matter FA and IC1 N-back is mediated by surface area in the right superior frontal cortex (P_FWE  < 0.05). We also demonstrated that the same mediation model is present using vertexwise mediation (P_FWE  < 0.05). In conclusion, cortexwise analysis with TFCE provides an effective analysis of multimodal neuroimaging data. Furthermore, cortexwise mediation analysis may identify or explain a mechanism that underlies an observed relationship among a predictor, intermediary, and dependent variables in which one of these variables is assessed at a whole-brain scale. Hum Brain Mapp 38:2795-2807, 2017. © 2017 Wiley Periodicals, Inc.

Association of fronto-temporal function with cognitive ability in schizophrenia

Deficits in neuropsychological performance are common in schizophrenia, but their relationship with the fronto-temporal functional abnormalities associated with this condition remains unclear. We explored the relationship between neuropsychological performance as measured using the Brief Assessment of Cognition in Schizophrenia (BACS) and the Social Cognition Screening Questionnaire theory of mind (ToM) subscale and fronto-temporal function in 23 patients with schizophrenia and 23 age- and gender-matched healthy controls (HCs), using 52-channel near-infrared spectroscopy (NIRS). Regional hemodynamic changes were significantly smaller in the schizophrenia group than in the HCs group in the ventro-lateral prefrontal cortex and the anterior part of the temporal cortex (VLPFC/aTC) and dorso-lateral prefrontal cortex and frontopolar cortex (DLPFC/FPC) regions. To dissect the effect of variance in BACS cognitive domains from the relationship between ToM function and fronto-temporal function, we performed additional partial correlation analyses between ToM and NIRS data, using BACS composite score as a control variable. The correlation between ToM and NIRS data remained significant only in the DLPFC/FPC region. This finding is important to models of recovery, as it suggests that intervention programs focusing on enhancing fronto-temporal function may have a greater impact on social and occupational outcomes than traditional rehabilitation programs focusing on neuropsychological performance.

The prolyl oligopeptidase inhibitor IPR19 ameliorates cognitive deficits in mouse models of schizophrenia

Cognitive deficits are considered a key feature of schizophrenia, and they usually precede the onset of the illness and continue after psychotic symptoms appear. Current antipsychotic drugs have little or no effect on the cognitive deficits of this disorder. Prolyl oligopeptidase (POP) is an 81-kDa monomeric serine protease that is expressed in brain and other tissues. POP inhibitors have shown neuroprotective, anti-amnesic and cognition-enhancing properties. Here we studied the potential of IPR19, a new POP inhibitor, for the treatment of the cognitive symptoms related to schizophrenia. The efficacy of the inhibitor was evaluated in mouse models based on subchronic phencyclidine and acute dizocilpine administration, and in adult offspring from mothers with immune reaction induced by polyinosinic:polycytidylic acid administration during pregnancy. Acute IPR19 administration (5mg/kg, i.p.) reversed the cognitive performance deficits of the three mouse models in the novel object recognition test, T-maze, and eight-arm radial maze. The compound also ameliorates deficits of the prepulse inhibition response. The in vitro inhibitory efficacy and selectivity, brain penetration and exposure time after injection of IPR19 were also addressed. Our results indicate that the inhibition of POP using IPR19 may offer a promising strategy to develop drugs to ameliorate the cognitive deficits of schizophrenia.

Practice and Learning: Spatiotemporal Differences in Thalamo-Cortical-Cerebellar Networks Engagement across Learning Phases in Schizophrenia

BACKGROUND

Understanding how practice mediates the transition of brain-behavior networks between early and later stages of learning is constrained by the common approach to analysis of fMRI data. Prior imaging studies have mostly relied on a single scan, and parametric, task-related analyses. Our experiment incorporates a multisession fMRI lexicon-learning experiment with multivariate, whole-brain analysis to further knowledge of the distributed networks supporting practice-related learning in schizophrenia (SZ).

METHODS

Participants with SZ were compared with healthy control (HC) participants as they learned a novel lexicon during two fMRI scans over a several day period. All participants were trained to equal task proficiency prior to scanning. Behavioral-Partial Least Squares, a multivariate analytic approach, was used to analyze the imaging data. Permutation testing was used to determine statistical significance and bootstrap resampling to determine the reliability of the findings.

RESULTS

With practice, HC participants transitioned to a brain-accuracy network incorporating dorsostriatal regions in late-learning stages. The SZ participants did not transition to this pattern despite comparable behavioral results. Instead, successful learners with SZ were differentiated primarily on the basis of greater engagement of perceptual and perceptual-integration brain regions.

CONCLUSION

There is a different spatiotemporal unfolding of brain-learning relationships in SZ. In SZ, given the same amount of practice, the movement from networks suggestive of effortful learning toward subcortically driven procedural one differs from HC participants. Learning performance in SZ is driven by varying levels of engagement in perceptual regions, which suggests perception itself is impaired and may impact downstream, "higher level" cognition.

Acupuncture in the Treatment of a Female Patient Suffering from Chronic Schizophrenia and Sleep Disorders

Background. The use of acupuncture in the treatment of sleep disorders in patients with chronic schizophrenia is investigated. Case Presentation. We report the case of a 44-year-old female outpatient of German origin who had been suffering from long-term schizophrenia and sleep disorders. The patient was treated with manual acupuncture weekly for 12 weeks, and a psychological assessment was performed before, immediately after, and three months after the acupuncture treatment period. In addition, actiwatch data were collected for 14 days both before and after the acupuncture treatment period. Conclusion. Acupuncture treatment led to a decrease in general psychopathology, less severe sleep problems, and markedly improved cognitive functioning (working memory) in the patient; however, the positive and the negative symptoms remained stable. The actiwatch data revealed a beneficial effect of acupuncture, showing better sleep latency, a trend towards better sleep efficiency, and a decrease in the number of minutes that the patient was awake during the night after acupuncture treatment. In sum, this study showed that acupuncture might be beneficial in the treatment of sleep disorders in patients suffering from chronic schizophrenia, but future, large, randomized (placebo), controlled, clinical trials are needed in order to replicate the present preliminary findings.

Optimal trajectories of brain state transitions

The complexity of neural dynamics stems in part from the complexity of the underlying anatomy. Yet how white matter structure constrains how the brain transitions from one cognitive state to another remains unknown. Here we address this question by drawing on recent advances in network control theory to model the underlying mechanisms of brain state transitions as elicited by the collective control of region sets. We find that previously identified attention and executive control systems are poised to affect a broad array of state transitions that cannot easily be classified by traditional engineering-based notions of control. This theoretical versatility comes with a vulnerability to injury. In patients with mild traumatic brain injury, we observe a loss of specificity in putative control processes, suggesting greater susceptibility to neurophysiological noise. These results offer fundamental insights into the mechanisms driving brain state transitions in healthy cognition and their alteration following injury.

A method for integrating neuroimaging into genetic models of learning performance

Specific learning disorders (SLD) are an archetypal example of how clinical neuropsychological (NP) traits can differ from underlying genetic and neurobiological risk factors. Disparate environmental influences and pathologies impact learning performance assessed through cognitive examinations and clinical evaluations, the primary diagnostic tools for SLD. We propose a neurobiological risk for SLD with neuroimaging biomarkers, which is integrated into a genome-wide association study (GWAS) of learning performance in a cohort of 479 European individuals between 8 and 21 years of age. We first identified six regions of interest (ROIs) in temporal and anterior cingulate regions where the group diagnosed with learning disability has the least overall variation, relative to the other group, in thickness, area, and volume measurements. Although we used the three imaging measures, the thickness was the leading contributor. Hence, we calculated the Euclidean distances between any two individuals based on their thickness measures in the six ROIs. Then, we defined the relative similarity of one individual according to the averaged ranking of pairwise distances from the individuals to those in the SLD group. The inverse of this relative similarity is called the neurobiological risk for the individual. Single nucleotide polymorphisms in the AGBL1 gene on chromosome 15 had a significant association with learning performance at a genome-wide level. This finding was supported in an independent cohort of 2,327 individuals of the same demographic profile. Our statistical approach for integrating genetic and neuroimaging biomarkers can be extended into studying the biological basis of other NP traits.

Analysis of EEG entropy during visual evocation of emotion in schizophrenia

BACKGROUND

In this study, the international affective picture system was used to evoke emotion, and then the corresponding signals were collected. The features from different points of brainwaves, frequency, and entropy were used to identify normal, moderately, and markedly ill schizophrenic patients.

METHODS

The signals were collected and preprocessed. Then, the signals were separated according to three types of emotions and five frequency bands. Finally, the features were calculated using three different methods of entropy. For classification, the features were divided into different sections and classification using support vector machine (principal components analysis on 95%). Finally, simple regression and correlation analysis between the total scores of positive and negative syndrome scale and features were used.

RESULTS

At first, we observed that to classify normal and markedly ill schizophrenic patients, the identification result was as high as 81.5%, and therefore, we further explored moderately and markedly ill schizophrenic patients. Second, the identification rate in both moderately and markedly ill schizophrenic patient was as high as 79.5%, which at the Fz point signal in high valence low arousal fragments was calculated using the ApEn methods. Finally, the total scores of positive and negative syndrome scale were used to analyze the correlation with the features that were the five frequency bands at the Fz point signal. The results show that the p value was less than .001 at the beta wave in the 15-18 Hz frequency range.

Paliperidone reverts Toll-like receptor 3 signaling pathway activation and cognitive deficits in a maternal immune activation mouse model of schizophrenia

The pathophysiology of psychotic disorders is multifactorial, including alterations in the immune system caused by exogenous or endogenous factors. Epidemiological and experimental studies indicate that infections during the gestational period represent a risk factor to develop schizophrenia (SZ) along lifetime. Here, we tested the hypothesis that the antipsychotic paliperidone regulates immune-related brain effects in an experimental model of SZ. A well described prenatal immune activation model of SZ in mice by maternal injection of the viral mimetic poly(I:C) during pregnancy was used. Young-adult offspring animals (60PND) received paliperidone ip (0.05 mg/kg) for 21 consecutive days. One day after last injection, animals were submitted to a cognitive test and brain frontal cortex (FC) samples were obtained for biochemical determinations. The adults showed an activated innate immune receptor TLR-3 signaling pathway, oxidative/nitrosative stress and accumulation of pro-inflammatory mediators such as nuclear transcription factors (i.e., NFκB) and inducible enzymes (i.e., iNOS) in FC. Chronic paliperidone blocked this neuroinflammatory response possibly by the synergic activation and preservation of endogenous antioxidant/anti-inflammatory mechanisms such as NRF2 and PPARγ pathways, respectively. Paliperidone administration also stimulated the alternative polarization of microglia to the M2 anti-inflammatory profile. In addition, paliperidone treatment improved spatial working memory deficits of this SZ-like animal model. In conclusion, chronic administration of paliperidone to young-adult mice prenatally exposed to maternal immune (MIA) challenge elicits a general preventive anti-inflammatory/antioxidant effect at both intracellular and cellular polarization (M1/M2) level in FC, as well as ameliorates specific cognitive deficits.

Vagus nerve stimulation in psychiatry: a systematic review of the available evidence

Invasive and non-invasive vagus nerve stimulation (VNS) is a promising add-on treatment for treatment-refractory depression, but is also increasingly evaluated for its application in other psychiatric disorders, such as dementia, schizophrenia, somatoform disorder, and others. We performed a systematic review aiming to give a detailed overview of the available evidence of the efficacy of VNS for the treatment of psychiatric disorders. Data derived from animal models, experimental trials without health-related outcomes, case reports, single-session studies, and reviews were excluded. From 1292 publications, 33 records were included for further analyses: 25 focused on VNS as treatment of unipolar or bipolar major depressive disorder and one investigated the neurocognitive improvement after VNS in major depressive disorder. Seven focused on the improvement of cognitive function in Alzheimer´s disease, improvement of schizophrenia symptoms, treatment of obsessive compulsive disorder (OCD), panic disorder (PD) and post-traumatic stress disorder (PTSD), treatment resistant rapid-cycling bipolar disorder, treatment of fibromyalgia, and Prader-Willi syndrome. A total of 29 studies used invasive VNS, while four studies used non-invasive, transcutaneous VNS. Only 7 out of 33 studies investigated conditions other than affective disorders. The efficacy data of VNS in affective disorders is promising, whereas more in controlled and naturalistic studies are needed. In other conditions like schizophrenia, Alzheimer's disease, OCD, PD, PTSD, and fibromyalgia, either no effects or preliminary data on efficacy were reported. At this point, no final conclusion can be made regarding the efficacy of VNS to improve symptoms in psychiatric disorders other than in affective disorders.

Unraveling the genetic architecture of copy number variants associated with schizophrenia and other neuropsychiatric disorders

Recent studies show that the complex genetic architecture of schizophrenia (SZ) is driven in part by polygenic components, or the cumulative effect of variants of small effect in many genes, as well as rare single-locus variants with large effect sizes. Here we discuss genetic aberrations known as copy number variants (CNVs), which fall in the latter category and are associated with a high risk for SZ and other neuropsychiatric disorders. We briefly review recurrent CNVs associated with SZ, and then highlight one CNV in particular, a recurrent 1.6-Mb deletion on chromosome 3q29, which is estimated to confer a 40-fold increased risk for SZ. Additionally, we describe the use of genetic mouse models, behavioral tools, and patient-derived induced pluripotent stem cells as a means to study CNVs in the hope of gaining mechanistic insight into their respective disorders. Taken together, the genomic data connecting CNVs with a multitude of human neuropsychiatric disease, our current technical ability to model such chromosomal anomalies in mouse, and the existence of precise behavioral measures of endophenotypes argue that the time is ripe for systematic dissection of the genetic mechanisms underlying such disease. © 2016 Wiley Periodicals, Inc.

A heuristic model for working memory deficit in schizophrenia

BACKGROUND

The life of schizophrenia patients is severely affected by deficits in working memory. In various brain regions, the reciprocal interactions between excitatory glutamatergic neurons and inhibitory GABAergic neurons are crucial. Other neurotransmitters, in particular dopamine, serotonin, acetylcholine, and norepinephrine, modulate the local balance between glutamate and GABA and therefore regulate the function of brain regions. Persistent alterations in the balances between the neurotransmitters can result in working memory deficits.

METHODS

Here we present a heuristic computational model that accounts for interactions among neurotransmitters across various brain regions. The model is based on the concept of a neurochemical interaction matrix at the biochemical level and combines this matrix with a mobile model representing physiological dynamic balances among neurotransmitter systems associated with working memory.

RESULTS

The comparison of clinical and simulation results demonstrates that the model output is qualitatively very consistent with the available data. In addition, the model captured how perturbations migrated through different neurotransmitters and brain regions. Results showed that chronic administration of ketamine can cause a variety of imbalances, and application of an antagonist of the D2 receptor in PFC can also induce imbalances but in a very different manner.

CONCLUSIONS

The heuristic computational model permits a variety of assessments of genetic, biochemical, and pharmacological perturbations and serves as an intuitive tool for explaining clinical and biological observations.

GENERAL SIGNIFICANCE

The heuristic model is more intuitive than biophysically detailed models. It can serve as an important tool for interdisciplinary communication and even for psychiatric education of patients and relatives. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

[Non-invasive brain stimulation for treatment of schizophrenic psychoses]

Despite many different available pharmacological and psychosocial treatment options, an optimal control of symptoms is only partly possible for most schizophrenia patients. Especially, persistent auditory hallucinations, negative symptoms and cognitive impairment are difficult to treat symptoms. Several non-invasive brain stimulation techniques are increasingly being considered as new therapeutic add on options for the management of schizophrenia, targeting these symptom domains. The technique which has been available for the longest time and that is best established in clinical care is electroconvulsive therapy (ECT). New stimulation techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) allow a more pathophysiological-based approach. This review article introduces various non-invasive brain stimulation techniques and discusses recent treatment studies on schizophrenia. In total, the novel brain stimulation techniques discussed here can be considered relevant add on therapeutic approaches for schizophrenia. In this context, the best evidence is available for the application of rTMS for the treatment of negative symptoms and persistent auditory hallucinations; however, negative studies have also been published for both indications. Studies using other non-invasive brain stimulation techniques showed promising results but further research is needed to establish the clinical efficacy. Based on a growing pathophysiological knowledge, non-invasive brain stimulation techniques provide new treatment perspectives for patients with schizophrenia.

Prefrontal White Matter Structure Mediates the Influence of GAD1 on Working Memory

The glutamic acid decarboxylase 1 (GAD1) gene is a major determinant of γ-aminobutyric acid (GABA), the most abundant inhibitory neurotransmitter modulating local neuronal circuitry. GABAergic dysfunction and expression of GAD1 have been implicated in the pathophysiology of schizophrenia, and in working memory impairment. We examined the influence of the functional GAD1 rs3749034 variant on white matter fractional anisotropy (FA), cortical thickness, and working memory performance in schizophrenia patients and healthy controls (N=197). Using transcranial magnetic stimulation with electroencephalography (TMS-EEG), we subsequently examined the effect of rs3749034 on long-interval cortical inhibition (LICI) in the dorsolateral prefrontal cortex (DLPFC) in schizophrenia patients and healthy controls (N=66). We found that the rs3749034 T-allele carrier risk group had lower voxel-wise FA in the prefrontal cortex region (PFWE-corrected<0.05) but not cortical thickness. Mixed-model regression revealed a significant effect on attentional processing and working memory across four performance measures (F1,182=11.5, P=8 × 10(-4)). FA in the prefrontal cortex was associated with digit-span performance. Voxel-wise mediation analysis revealed that the effect GAD1 on poorer digit-span performance statistically predicted the lower white matter FA (PFWE-corrected<0.05). In exploratory analysis, we found a prominent GAD1 genotype-by-diagnosis interaction on DLPFC LICI (F1,56=14.3, P=4.1 × 10(-4)). Our findings converge on variation in GAD1 gene predicting a susceptibility mechanism that affects white matter FA, GABAergic inhibitory neurotransmission in the DLPFC, and working memory performance. Furthermore, via voxel mediation of FA and TMS-EEG intervention, we provide evidence for a potentially causal mechanism through which aberrant DLPFC GABA signaling may contribute to working memory dysfunction.

Language deficits in schizophrenia and autism as related oscillatory connectomopathies: An evolutionary account

Schizophrenia (SZ) and autism spectrum disorders (ASD) are characterised by marked language deficits, but it is not clear how these arise from gene mutations associated with the disorders. Our goal is to narrow the gap between SZ and ASD and, ultimately, give support to the view that they represent abnormal (but related) ontogenetic itineraries for the human faculty of language. We will focus on the distinctive oscillatory profiles of the SZ and ASD brains, in turn using these insights to refine our understanding of how the brain implements linguistic computations by exploring a novel model of linguistic feature-set composition. We will argue that brain rhythms constitute the best route to interpreting language deficits in both conditions and mapping them to neural dysfunction and risk alleles of the genes. Importantly, candidate genes for SZ and ASD are overrepresented among the gene sets believed to be important for language evolution. This translational effort may help develop an understanding of the aetiology of SZ and ASD and their high prevalence among modern populations.

Repetitive Noninvasive Brain Stimulation to Modulate Cognitive Functions in Schizophrenia: A Systematic Review of Primary and Secondary Outcomes

Despite many years of research, there is still an urgent need for new therapeutic options for the treatment of cognitive deficits in schizophrenia. Noninvasive brain stimulation (NIBS) has been proposed to be such a novel add-on treatment option. The main objective of this review was to systematically evaluate the cognitive effects of repetitive NIBS in schizophrenia. As most studies have not been specifically designed to investigate cognition as primary outcome, we have focused on both, primary and secondary outcomes. The PubMed/MEDLINE database (1985-2015) was systematically searched for interventional studies investigating the effects of repetitive NIBS on schizophrenia symptoms. All interventional clinical trials using repetitive transcranial stimulation, transcranial theta burst stimulation, and transcranial direct current stimulation for the treatment of schizophrenia were extracted and analyzed with regard to cognitive measures as primary or secondary outcomes. Seventy-six full-text articles were assessed for eligibility of which 33 studies were included in the qualitative synthesis. Of these 33 studies, only 4 studies included cognition as primary outcome, whereas 29 studies included cognitive measures as secondary outcomes. A beneficial effect of frontal NIBS could not be clearly established. No evidence for a cognitive disruptive effect of NIBS (temporal lobe) in schizophrenia could be detected. Finally, a large heterogeneity between studies in terms of inclusion criteria, stimulation parameters, applied cognitive measures, and follow-up intervals was observed. This review provides the first systematic overview regarding cognitive effects of repetitive NIBS in schizophrenia.

Working Memory in Unaffected Relatives of Patients With Schizophrenia: A Meta-Analysis of Functional Magnetic Resonance Imaging Studies

Working memory deficits, a core cognitive feature of schizophrenia may arise from dysfunction in the frontal and parietal cortices. Numerous studies have also found abnormal neural activation during working memory tasks in patients' unaffected relatives. The aim of this study was to systematically identify and anatomically localize the evidence for those activation differences across all eligible studies. Fifteen functional magnetic resonance imaging (fMRI) manuscripts, containing 16 samples of 289 unaffected relatives of patients with schizophrenia, and 358 healthy controls were identified that met our inclusion criteria: (1) used a working memory task; and (2) reported standard space coordinates. Activation likelihood estimation (ALE) identified convergence across studies. Compared to healthy controls, patients' unaffected relatives showed decreases in neural activation in the right middle frontal gyrus (BA9), as well as right inferior frontal gyrus (BA44). Increased activation was seen in relatives in the right frontopolar (BA10), left inferior parietal lobe (BA40), and thalamus bilaterally. These results suggest that the familial risk of schizophrenia is expressed in changes in neural activation in the unaffected relatives in the cortical-subcortical working memory network that includes, but is not restricted to the middle prefrontal cortex.

Cognitive Effects of High-Frequency rTMS in Schizophrenia Patients With Predominant Negative Symptoms: Results From a Multicenter Randomized Sham-Controlled Trial

Cognitive impairments are one of the main contributors to disability and poor long-term outcome in schizophrenia. Proof-of-concept trials indicate that repetitive transcranial magnetic stimulation (rTMS) applied to the left dorsolateral prefrontal cortex (DLPFC) has the potential to improve cognitive functioning. We analyzed the effects of 10-Hz rTMS to the left DLPFC on cognitive deficits in schizophrenia in a large-scale and multicenter, sham-controlled study. A total of 156 schizophrenia patients with predominant negative symptoms were randomly assigned to a 3-week intervention (10-Hz rTMS, 15 sessions, 1000 stimuli per session) with either active or sham rTMS. The Rey Auditory Verbal Learning Test, Trail Making Test A and B, Wisconsin Card Sorting Test, Digit Span Test, and the Regensburg Word Fluency Test were administered before intervention and at day 21, 45, and 105 follow-up. From the test results, a neuropsychological composite score was computed. Both groups showed no differences in any of the outcome variables before and after intervention. Both groups improved markedly over time, but effect sizes indicate a numeric, but nonsignificant superiority of active rTMS in certain cognitive tests. Active 10-Hz rTMS applied to the left DLPFC for 3 weeks was not superior to sham rTMS in the improvement of various cognitive domains in schizophrenia patients with predominant negative symptoms. This is in contrast to previous preliminary proof-of-concept trials, but highlights the need for more multicenter randomized controlled trials in the field of noninvasive brain stimulation.

Preliminary investigation of the effects of γ-tACS on working memory in schizophrenia

Working memory impairment in schizophrenia has been strongly associated with abnormalities in gamma oscillations within the dorsolateral prefrontal cortex (DLFPC). We recently published the first ever study showing that anodal transcranial direct current stimulation (tDCS) to the left DLPFC was able to significantly improve working memory in schizophrenia and did so seemingly via restoring normal gamma oscillatory function. Transcranial alternating current stimulation (tACS) is a form of electrical brain stimulation that delivers stimulation at a specific frequency and has been shown to entrain endogenous cortical oscillations. Therefore, gamma (γ) tACS may be even more effective than tDCS in improving working memory in schizophrenia. In a randomized repeated-measures study we compared the effects of γ-tACS, tDCS and sham stimulation on the performance of the two back working memory tasks in ten patients with schizophrenia. There was a significant time by stimulation interaction, with tDCS and sham showing trend-level improvements in working memory, while γ-tACS, contrary to our hypothesis, showed no change. The results are discussed in light of posited divergent effects of tACS and tDCS on the pathophysiology of working memory impairment in schizophrenia.

Alterations in High-Frequency Neuronal Oscillations in a Cynomolgus Macaque Test of Sustained Attention Following NMDA Receptor Antagonism

A growing body of evidence indicates that neuronal oscillations in the gamma frequency range (30-80 Hz) are disturbed in schizophrenic patients during cognitive processes and may represent an endophenotype of the disease. N-methyl-D-aspartate (NMDA) receptor antagonists have been used experimentally to induce schizophrenia-like symptoms including cognitive deficits in animals and humans. Here we characterized neuronal oscillations and event-related potentials (ERPs) in Cynomolgus macaques fully trained to perform a continuous performance test (CPT) in the presence and absence of the NMDA antagonist phencyclidine (PCP). Macaques (n=8) were trained to touch 'target' stimuli and ignore 'distractor' stimuli presented randomly on a touchscreen. Subsequently, all subjects were implanted with epidural EEG electrodes over frontal (FC) and parietal cortices (PC) and later tested under vehicle (saline, i.m.) or acute PCP (0.1-0.3 mg/kg, i.m.) conditions. Compared with vehicle treatment, PCP produced a significant dose-dependent decrease in CPT performance accuracy and increased reaction times. Furthermore, PCP elevated the amplitudes of 'low' (30-50 Hz) and 'high' (51-80 Hz) gamma oscillations in FC and PC around target presentations for all correct responses. The CPT accuracy was inversely correlated with the gamma band amplitude in the presence of PCP. Additionally, PCP delayed the N100 peak latency in FC, and prolonged and suppressed the cognitively relevant P300 component of mean ERPs in FC and PC, respectively. The NMDA receptor antagonist-induced alteration in neuronal oscillations and ERPs may contribute to the observed cognitive deficits in macaques, and enhance our understanding of EEG recordings as a translatable biomarker.

The association between cognitive deficits and prefrontal hemodynamic responses during performance of working memory task in patients with schizophrenia

Schizophrenia-associated cognitive deficits are resistant to treatment and thus pose a lifelong burden. The Brief Assessment of Cognition in Schizophrenia (BACS) provides reliable and valid assessments across cognitive domains. However, because the prefrontal functional abnormalities specifically associated with the level of cognitive deficits in schizophrenia have not been examined, we explored this relationship. Patients with schizophrenia (N=87) and matched healthy controls (N=50) participated in the study. Using near-infrared spectroscopy (NIRS), we measured the hemodynamic responses in the prefrontal and superior temporal cortical surface areas during a working memory task. Correlation analyses revealed a relationship between the hemodynamics and the BACS composite and domain scores. Hemodynamic responses of the left dorsolateral prefrontal cortex (DLPFC) and left frontopolar cortex (FPC) in the higher-level-of-cognitive-function schizophrenia group were weaker than the responses of the controls but similar to those of the lower-level-of-cognitive-function schizophrenia group. However, hemodynamic responses in the right DLPFC, bilateral ventrolateral PFC (VLPFC), and right temporal regions decreased with increasing cognitive deficits. In addition, the hemodynamic response correlated positively with the level of cognitive function (BACS composite scores) in the right DLPFC, bilateral VLPFC, right FPC, and bilateral temporal regions in schizophrenia. The correlation was driven by all BACS domains. Our results suggest that the linked functional deficits in the right DLPFC, bilateral VLPFC, right FPC, and bilateral temporal regions may be related to BACS-measured cognitive impairments in schizophrenia and show that linking the neurocognitive deficits and brain abnormalities can increase our understanding of schizophrenia pathophysiology.

Failed cooperative, but not competitive, interaction between large-scale brain networks impairs working memory in schizophrenia

BACKGROUND

A large-scale network named the default mode network (DMN) dynamically cooperates and competes with an external attention system (EAS) to facilitate various cognitive functioning that is prominently impaired in schizophrenia. However, it is unclear whether the cognitive deficit in schizophrenia is related to the disrupted competition and/or cooperation between these two networks.

METHOD

A total of 35 schizophrenia patients and 30 healthy controls were scanned using gradient-echo echo-planar imaging during n-back working memory (WM) processing. Brain activities of the DMN and EAS were measured using general linear modelling of the functional magnetic resonance imaging data. Dynamic interaction between the DMN and EAS was decomposed into two directions using Granger causality analysis.

RESULTS

We observed a significant failure of DMN suppression in patients with schizophrenia, which was significantly related to WM/attentional deficit. Granger causality modelling showed that in healthy controls, while the EAS inhibitorily influenced the DMN, the DMN exerted an 'excitatory' or cooperative influence back on the EAS, especially in those with lower WM accuracy. In schizophrenia, this 'excitatory' DMN→EAS influence within the reciprocal EAS-DMN loop was significantly reduced, especially in patients with WM/attentional deficit.

CONCLUSIONS

The dynamic interaction between the DMN and EAS is likely to be comprised of both competitive and cooperative influences. In healthy controls, both the 'inhibitory' EAS→DMN interaction and 'excitatory' DMN→EAS interaction are correlated with WM performance. In schizophrenia, reduced 'cooperative' influence from the DMN to dorsal nodes of the EAS occurs in the context of non-suppression of the DMN and may form a possible pathophysiological substrate of WM deficit and attention disorder.

A brief neurocognitive assessment of patients with psychosis following traumatic brain injury (PFTBI): Use of the Repeatable battery for the Assessment of Neuropsychological Status (RBANS)

Patients who develop psychosis following a traumatic brain injury (PFTBI) show impaired neurocognition; however, the degree of impairment has not been empirically investigated using a standardised battery. We administered the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) to patients with PFTBI (n=10), and to three groups of controls: traumatic brain injury (TBI) (n=10), schizophrenia (n=23), and nonclinical controls (n=23). The results confirmed that the cognitive neuropsychological profile of dually-diagnosed patients with PFTBI is significantly and substantially impaired. Seventy per cent of patients with PFTBI received a neuropsychological classification between the "extremely low" and "low average" ranges. Group-wise analyses on the RBANS indices indicated that patients with PFTBI had the lowest (Immediate Memory, Attention, Delayed Memory, Total Score), or equal lowest (visuospatial, equivalent with schizophrenia patients) scores, with the exception of the Language Index where no group differences were shown (however, the mean PFTBI score on the Language Index was two standard deviations below the RBANS normative score). These findings provide novel evidence of impaired cognitive neuropsychological processing in patients with PFTBI using a standardised and replicable battery.

Neural correlates of cognitive improvements following cognitive remediation in schizophrenia: a systematic review of randomized trials

BACKGROUND

Cognitive impairments are a core feature in schizophrenia and are linked to poor social functioning. Numerous studies have shown that cognitive remediation can enhance cognitive and functional abilities in patients with this pathology. The underlying mechanism of these behavioral improvements seems to be related to structural and functional changes in the brain. However, studies on neural correlates of such enhancement remain scarce.

OBJECTIVES

We explored the neural correlates of cognitive enhancement following cognitive remediation interventions in schizophrenia and the differential effect between cognitive training and other therapeutic interventions or patients' usual care.

METHOD

We searched MEDLINE, PsycInfo, and ScienceDirect databases for studies on cognitive remediation therapy in schizophrenia that used neuroimaging techniques and a randomized design. Search terms included randomized controlled trial, cognitive remediation, cognitive training, rehabilitation, magnetic resonance imaging, positron emission tomography, electroencephalography, magnetoencephalography, near infrared spectroscopy, and diffusion tensor imaging. We selected randomized controlled trials that proposed multiple sessions of cognitive training to adult patients with a schizophrenia spectrum disorder and assessed its efficacy with imaging techniques.

RESULTS

In total, 15 reports involving 19 studies were included in the systematic review. They involved a total of 455 adult patients, 271 of whom received cognitive remediation. Cognitive remediation therapy seems to provide a neurobiological enhancing effect in schizophrenia. After therapy, increased activations are observed in various brain regions mainly in frontal - especially prefrontal - and also in occipital and anterior cingulate regions during working memory and executive tasks. Several studies provide evidence of an improved functional connectivity after cognitive training, suggesting a neuroplastic effect of therapy through mechanisms of functional reorganization. Neurocognitive and social-cognitive training may have a cumulative effect on neural networks involved in social cognition. The variety of proposed programs, imaging tasks, and techniques may explain the heterogeneity of observed neural improvements. Future studies would need to specify the effect of cognitive training depending on those variables.

Social cognition and prefrontal hemodynamic responses during a working memory task in schizophrenia

Social cognition is an important determinant of functional impairment in schizophrenia, but its relationship with the prefrontal functional abnormalities associated with the condition is still unclear. The present study aimed to explore the relationship between social cognition and prefrontal function in patients with schizophrenia using 52-channel near-infrared spectroscopy (NIRS). Twenty-six patients with schizophrenia and 26 age-, gender-, and intelligence quotient-matched healthy controls (HCs) participated in the study. Hemodynamic responses in the prefrontal and superior temporal cortical regions were assessed during a working memory task using NIRS. Social cognition was assessed using the Social Cognition Screening Questionnaire (SCSQ). The observed hemodynamic responses were significantly reduced in the lateral prefrontal cortex (PFC), the frontopolar cortex, and temporal regions in subjects with schizophrenia compared to HCs. Additionally, lateral PFC hemodynamic responses assessed during the working memory task demonstrated a strong positive correlation with the SCSQ theory of mind (ToM) subscale score even after controlling for working memory performance. These results suggest that ToM integrity is closely related to lateral PFC functional abnormalities found in patients with schizophrenia. In addition, this study provides evidence to suggest that NIRS could be used to identify biomarkers of social cognition function in subjects with schizophrenia.

Chronic Administration of Benzo(a)pyrene Induces Memory Impairment and Anxiety-Like Behavior and Increases of NR2B DNA Methylation

Background

Recently, an increasing number of human and animal studies have reported that exposure to benzo(a)pyrene (BaP) induces neurological abnormalities and is also associated with adverse effects, such as tumor formation, immunosuppression, teratogenicity, and hormonal disorders. However, the exact mechanisms underlying BaP-induced impairment of neurological function remain unclear. The aim of this study was to examine the regulating mechanisms underlying the impact of chronic BaP exposure on neurobehavioral performance.

Methods

C57BL mice received either BaP in different doses (1.0, 2.5, 6.25 mg/kg) or olive oil twice a week for 90 days. Memory and emotional behaviors were evaluated using Y-maze and open-field tests, respectively. Furthermore, levels of mRNA expression were measured by using qPCR, and DNA methylation of NMDA receptor 2B subunit (NR2B) was examined using bisulfate pyrosequencing in the prefrontal cortex and hippocampus.

Results

Compared to controls, mice that received BaP (2.5, 6.25 mg/kg) showed deficits in short-term memory and an anxiety-like behavior. These behavioral alterations were associated with a down-regulation of the NR2B gene and a concomitant increase in the level of DNA methylation in the NR2B promoter in the two brain regions.

Conclusions

Chronic BaP exposure induces an increase in DNA methylation in the NR2B gene promoter and down-regulates NR2B expression, which may contribute to its neurotoxic effects on behavioral performance. The results suggest that NR2B vulnerability represents a target for environmental toxicants in the brain.

Developmental Inhibition of Gsk3 Rescues Behavioral and Neurophysiological Deficits in a Mouse Model of Schizophrenia Predisposition

While the genetic basis of schizophrenia is increasingly well characterized, novel treatments will require establishing mechanistic relationships between specific risk genes and core phenotypes. Rare, highly penetrant risk genes such as the 22q11.2 microdeletion are promising in this regard. Df(16)A(+/-) mice, which carry a homologous microdeletion, have deficits in hippocampal-prefrontal connectivity that correlate with deficits in spatial working memory. These mice also have deficits in axonal development that are accompanied by dysregulated Gsk3β signaling and can be rescued by Gsk3 antagonists. Here we show that developmental inhibition of Gsk3 rescues deficits in hippocampal-prefrontal connectivity, task-related neural activity, and spatial working memory behavior in Df(16)A(+/-) mice. Taken together, these results provide mechanistic insight into how the microdeletion results in cognitive deficits, and they suggest possible targets for novel therapies.

Postnatal Phencyclidine (PCP) as a Neurodevelopmental Animal Model of Schizophrenia Pathophysiology and Symptomatology: A Review

Cognitive dysfunction and negative symptoms of schizophrenia remain an unmet clinical need. Therefore, it is essential that new treatments and approaches are developed to recover the cognitive and social impairments that are seen in patients with schizophrenia. These may only be discovered through the use of carefully validated, aetiologically relevant and translational animal models. With recent renewed interest in the neurodevelopmental hypothesis of schizophrenia, postnatal administration of N-methyl-D-aspartate receptor (NMDAR) antagonists such as phencyclidine (PCP) has been proposed as a model that can mimic aspects of schizophrenia pathophysiology. The purpose of the current review is to examine the validity of this model and compare it with the adult subchronic PCP model. We review the ability of postnatal PCP administration to produce behaviours (specifically cognitive deficits) and neuropathology of relevance to schizophrenia and their subsequent reversal by pharmacological treatments. We review studies investigating effects of postnatal PCP on cognitive domains in schizophrenia in rats. Morris water maze and delayed spontaneous alternation tasks have been used for working memory, attentional set-shifting for executive function, social novelty discrimination for selective attention and prepulse inhibition of acoustic startle for sensorimotor gating. In addition, we review studies on locomotor activity and neuropathology. We also include two studies using dual hit models incorporating postnatal PCP and two studies on social behaviour deficits following postnatal PCP. Overall, the evidence we provide supports the use of postnatal PCP to model cognitive and neuropathological disturbances of relevance to schizophrenia. To date, there is a lack of evidence to support a significant advantage of postnatal PCP over the adult subchronic PCP model and full advantage has not been taken of its neurodevelopmental component. When thoroughly characterised, it is likely that it will provide a useful neurodevelopmental model to complement other models such as maternal immune activation, particularly when combined with other manipulations to produce dual or triple hit models. However, the developmental trajectory of behavioural and neuropathological changes induced by postnatal PCP and their relevance to schizophrenia must be carefully mapped out. Overall, we support further development of dual (or triple) hit models incorporating genetic, neurodevelopmental and appropriate environmental elements in the search for more aetiologically valid animal models of schizophrenia and neurodevelopmental disorders (NDDs).

Prefrontal-Hippocampal Interactions in Memory and Emotion

The hippocampal formation (HPC) and medial prefrontal cortex (mPFC) have well-established roles in memory encoding and retrieval. However, the mechanisms underlying interactions between the HPC and mPFC in achieving these functions is not fully understood. Considerable research supports the idea that a direct pathway from the HPC and subiculum to the mPFC is critically involved in cognitive and emotional regulation of mnemonic processes. More recently, evidence has emerged that an indirect pathway from the HPC to the mPFC via midline thalamic nucleus reuniens (RE) may plays a role in spatial and emotional memory processing. Here we will consider how bidirectional interactions between the HPC and mPFC are involved in working memory, episodic memory and emotional memory in animals and humans. We will also consider how dysfunction in bidirectional HPC-mPFC pathways contributes to psychiatric disorders.

Ketamine-Induced Changes in the Signal and Noise of Rule Representation in Working Memory by Lateral Prefrontal Neurons

Working memory dysfunction is an especially debilitating symptom in schizophrenia. The NMDA antagonist ketamine has been successfully used to model working memory deficits in both rodents and nonhuman primates, but how it affects the strength and the consistency of working memory representations remains unclear. Here we recorded single-neuron activity in the lateral prefrontal cortex of macaque monkeys before and after the administration of subanesthetic doses of ketamine in a rule-based working memory task. The rule was instructed with a color cue before each delay period and dictated the correct prosaccadic or antisaccadic response to a peripheral stimulus appearing after the delay. We found that acute ketamine injections both weakened the rule signal across all delay periods and amplified the trial-to-trial variance in neural activities (i.e., noise), both within individual neurons and at the ensemble level, resulting in impaired performance. In the minority of postinjection trials when the animals responded correctly, the preservation of the signal strength during the delay periods was predictive of their subsequent success. Our findings suggest that NMDA receptor function may be critical for establishing the optimal signal-to-noise ratio in information representation by ensembles of prefrontal cortex neurons.

SIGNIFICANCE STATEMENT

In schizophrenia patients, working memory deficit is highly debilitating and currently without any efficacious treatment. An improved understanding of the pathophysiology of this symptom may provide critical information to treatment development. The NMDA antagonist ketamine, when injected at a subanesthetic dose, produces working memory deficit and other schizophrenia-like symptoms in humans and other animals. Here we investigated the effects of ketamine on the representation of abstract rules by prefrontal neurons, while macaque monkeys held the rules in working memory before responding accordingly. We found that ketamine weakened the signal-to-noise ratio in rule representation by simultaneously weakening the signal and augmenting noise. Both processes may be relevant in an effective therapy for working memory impairment in schizophrenia.

Load-related brain activation predicts spatial working memory performance in youth aged 9-12 and is associated with executive function at earlier ages

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Spatial working memory load modulates activation in fronto-parietal regions in youth.

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Performance correlates with load-dependent deactivation in default network regions.

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Performance correlates with functional coupling between fronto-parietal regions.

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Executive function scores at age 3, 6 and 9 predict performance and brain activity.

Spatial working memory is a central cognitive process that matures through adolescence in conjunction with major changes in brain function and anatomy. Here we focused on late childhood and early adolescence to more closely examine the neural correlates of performance variability during this important transition period. Using a modified spatial 1-back task with two memory load conditions in an fMRI study, we examined the relationship between load-dependent neural responses and task performance in a sample of 39 youth aged 9–12 years. Our data revealed that between-subject differences in task performance was predicted by load-dependent deactivation in default network regions, including the ventral anterior cingulate cortex (vACC) and posterior cingulate cortex (PCC). Although load-dependent increases in activation in prefrontal and posterior parietal regions were only weakly correlated with performance, increased prefrontal–parietal coupling was associated with better performance. Furthermore, behavioral measures of executive function from as early as age 3 predicted current load-dependent deactivation in vACC and PCC. These findings suggest that both task positive and task negative brain activation during spatial working memory contributed to successful task performance in late childhood/early adolescence. This may serve as a good model for studying executive control deficits in developmental disorders.

Cluster analysis differentiates high and low community functioning in schizophrenia: Subgroups differ on working memory but not other neurocognitive domains

BACKGROUND

Schizophrenia is characterized by impairment in multiple aspects of community functioning. Available literature suggests that community functioning may be enhanced through cognitive remediation, however, evidence is limited regarding whether specific neurocognitive domains may be treatment targets. We characterized schizophrenia subjects based on their level of community functioning through cluster analysis in an effort to identify whether specific neurocognitive domains were associated with variation in functioning.

METHODS

Schizophrenia (SCZ, n=60) and control (CON, n=45) subjects completed a functional capacity task, social competence role-play, functional attainment interview, and a neuropsychological battery. Multiple cluster analytic techniques were used on the measures of functioning in the schizophrenia subjects to generate functionally-defined subgroups. MANOVA evaluated between-group differences in neurocognition.

RESULTS

The cluster analysis revealed two distinct groups, consisting of 36 SCZ characterized by high levels of community functioning (HF-SCZ) and 24 SCZ with low levels of community functioning (LF-SCZ). There was a main group effect for neurocognitive performance (p<0.001) with CON outperforming both SCZ groups in all neurocognitive domains. Post-hoc tests revealed that HF-SCZ had higher verbal working memory compared to LF-SCZ (p≤0.05, Cohen's d=0.78) but the two groups did not differ in remaining domains.

CONCLUSION

The cluster analysis classified schizophrenia subjects in HF-SCZ and LF-SCZ using a multidimensional assessment of community functioning. Moreover, HF-SCZ demonstrated rather preserved verbal working memory relative to LF-SCZ. The results suggest that verbal working memory may play a critical role in community functioning, and is a potential cognitive treatment target for schizophrenia subjects.

Transcriptional regulation of GAD1 GABA synthesis gene in the prefrontal cortex of subjects with schizophrenia

Expression of GAD1 GABA synthesis enzyme is highly regulated by neuronal activity and reaches mature levels in the prefrontal cortex not before adolescence. A significant portion of cases diagnosed with schizophrenia show deficits in GAD1 RNA and protein levels in multiple areas of adult cerebral cortex, possibly reflecting molecular or cellular defects in subtypes of GABAergic interneurons essential for network synchronization and cognition. Here, we review 20years of progress towards a better understanding of disease-related regulation of GAD1 gene expression. For example, deficits in cortical GAD1 RNA in some cases of schizophrenia are associated with changes in the epigenetic architecture of the promoter, affecting DNA methylation patterns and nucleosomal histone modifications. These localized chromatin defects at the 5' end of GAD1 are superimposed by disordered locus-specific chromosomal conformations, including weakening of long-range promoter-enhancer loopings and physical disconnection of GAD1 core promoter sequences from cis-regulatory elements positioned 50 kilobases further upstream. Studies on the 3-dimensional architecture of the GAD1 locus in neurons, including developmentally regulated higher order chromatin compromised by the disease process, together with exploration of locus-specific epigenetic interventions in animal models, could pave the way for future treatments of psychosis and schizophrenia.

Altered prefrontal activity and connectivity predict different cognitive deficits in schizophrenia

BACKGROUND

Cognitive dysfunction is considered a core feature of schizophrenia, and impaired performances in episodic memory (EM) and executive function (EF) tasks are consistently reported in schizophrenia patients. Traditional fMRI and EEG studies have helped identifying brain areas, including the prefrontal cortex (PFC), involved in these tasks. However, it is unclear whether intrinsic defects in prefrontal function per se contribute to poor performance in schizophrenia, given the presence of confounds like reduced motivation and psychotic symptoms. TMS/hd-EEG measurements are obtained without cognitive effort, and can be calculated in any cortical area.

METHODS

We performed TMS/hd-EEG recordings in parietal, motor, premotor, and PFC in healthy individuals (N=20) and schizophrenia patients (N=20). Source modeling of TMS-evoked responses was performed, and measures of cortical activity (significant current density, SCD) and connectivity (significant current scattering, SCS) were computed. Patients with schizophrenia also performed Penn Word memory delayed (CPWd) and Penn Conditional Exclusion Test (PCET). CPWd evaluates EM and involves primarily PFC, whereas PCET reflects EF and implicates PFC with other brain regions.

FINDINGS

We found no difference in SCD and SCS after TMS of parietal/motor cortices, whereas those parameters were reduced in premotor/prefrontal areas in schizophrenia patients. In PFC, where these measures were most defective, SCD was negatively correlated with performance in CPWd whereas higher SCS values were associated with more errors in PCET.

CONCLUSION

These findings indicate that schizophrenia patients have intrinsic defects in both activity and connectivity of PFC, and that these defects are specifically associated with impairments in cognitive abilities.

The effect of transcranial Direct Current Stimulation on gamma activity and working memory in schizophrenia

Working memory impairments in schizophrenia have been strongly associated with abnormalities in gamma oscillations within the dorsolateral prefrontal cortex (DLFPC). We recently published the first ever study showing that anodal transcranial Direct Current Stimulation (tDCS) to the left DLPFC was able to significantly improve working memory performance in schizophrenia. In the current paper we present a secondary analysis from this study, specifically looking at the effect of tDCS on gamma activity and its relationship to working memory. In a repeated measures design we assessed the impact of anodal tDCS (1mA, 2mA, sham) on gamma activity in the left DLPFC at three time-points post-stimulation (0min, 20min, 40min). EEG data was available for 16 participants in the 2mA condition, 13 in the 1mA condition and 12 in the sham condition. Following 2mA stimulation we found a significant increase in gamma event-related synchronisation in the left DLPFC, this was in the context of a significantly improved working memory performance. There was also a significant decrease in gamma event-related synchronisation, with no changes in working memory, following sham stimulation. The current study provides preliminary evidence that tDCS may enhance working memory in schizophrenia by restoring normal gamma oscillatory function.

Functional and clinical insights from neuroimaging studies in childhood-onset schizophrenia

Childhood-onset schizophrenia is a rare pediatric onset psychiatric disorder continuous with and typically more severe than its adult counterpart. Neuroimaging research conducted on this population has revealed similarly severe neural abnormalities. When taken as a whole, neuroimaging research in this population shows generally decreased cortical gray matter coupled with white matter connectivity abnormalities, suggesting an anatomical basis for deficits in executive function. Subcortical abnormalities are pronounced in limbic structures, where volumetric deficits are likely related to social skill deficits, and cerebellar deficits that have been correlated to cognitive abnormalities. Structures relevant to motor processing also show a significant alteration, with volumetric increase in basal ganglia structures likely due to antipsychotic administration. Neuroimaging of this disorder shows an important clinical image of exaggerated cortical loss, altered white matter connectivity, and differences in structural development of subcortical areas during the course of development and provides important background to the disease state.

NR2B subunit in the prefrontal cortex: A double-edged sword for working memory function and psychiatric disorders

The prefrontal cortex (PFC) is a brain region featured with working memory function. The exact mechanism of how working memory operates within the PFC circuitry is unknown, but persistent neuronal firing recorded from prefrontal neurons during a working memory task is proposed to be the neural correlate of this mnemonic encoding. The PFC appears to be specialized for sustaining persistent firing, with N-methyl-D-aspartate (NMDA) receptors, especially slow-decay NR2B subunits, playing an essential role in the maintenance of sustained activity and normal working memory function. However, the NR2B subunit serves as a double-edged sword for PFC function. Because of its slow kinetics, NR2B endows the PFC with not only "neural psychic" properties, but also susceptibilities for neuroexcitotoxicity and psychiatric disorders. This review aims to clarify the interplay among working memory, the PFC, and NMDA receptors; demonstrate the importance of NR2B in the maintenance of persistent activity; understand the risks and vulnerabilities of how NR2B is related to the development of neuropsychiatric disorders; identify gaps that currently exist in our understanding of these processes; and provide insights regarding future directions that may clarify these issues. We conclude that the PFC is a specialized brain region with distinct delayed maturation, unique neuronal circuitry, and characteristic NMDA receptor function. The unique properties and development of NMDA receptors, especially enrichment of NR2B subunits, endow the PFC with not only the capability to generate sustained activity for working memory, but also serves as a major vulnerability to environmental insults and risk factors for psychiatric disorders.

Dysfunctional prefrontal gamma-band oscillations reflect working memory and other cognitive deficits in schizophrenia

Impairments in working memory (WM) and other cognitive functions are cardinal neuropsychological symptoms in schizophrenia (ScZ). The prefrontal cortex (PFC) is important for mediating and executing these functions. Functional neuroimaging and molecular studies have consistently shown PFC abnormalities in ScZ. In addition, recent studies have suggested that impairments in oscillatory activity, especially in the gamma band (approximately 30-80 Hz), reflect disturbed cortical information processing in this patient group. Here we review evidence that dysfunctional gamma-band responses (GBR) in the PFC could be a factor contributing to WM and other cognitive deficits in ScZ. We provide an overview of noninvasive electrophysiological studies reporting frontal GBR abnormalities in ScZ patients during WM and other cognitive tasks. In agreement with the often-reported hypofrontality in functional neuroimaging studies, the majority of reviewed studies revealed reduced amplitudes or reduced phase locking of GBR over frontal areas in this patient group. Clinical implications derived from these findings and possibilities to foster future studies on GBR abnormalities in ScZ patients, are discussed. Since oscillatory activity in the gamma band has previously been linked to a variety of neurotransmitters, such as the gamma-aminobutyric acid-ergic system, the study of prefrontal GBR could also have implications for pharmacologic approaches in the treatment of WM and other cognitive deficits in ScZ.

A Neurophysiological and Neuropsychological Consideration of Mindful Movement: Clinical and Research Implications

In this article, we present ideas related to three key aspects of mindfulness training: the regulation of attention via noradrenaline, the importance of working memory and its various components (particularly the central executive and episodic buffer), and the relationship of both of these to mind-wandering. These same aspects of mindfulness training are also involved in the preparation and execution of movement and implicated in the pathophysiology of psychosis. We argue that by moving in a mindful way, there may be an additive effect of training as the two elements of the practice (mindfulness and movement) independently, and perhaps synergistically, engage common underlying systems (the default mode network). We discuss how working with mindful movement may be one route to mindfulness training for individuals who would struggle to sit still to complete the more commonly taught mindfulness practices. Drawing on our clinical experience working with individuals with severe and enduring mental health conditions, we show the real world application of these ideas and how they can be used to help those who are suffering and for whom current treatments are still far from adequate.

Effects of environmental and pharmacological manipulations on a novel delayed nonmatching-to-sample 'working memory' procedure in unrestrained rhesus monkeys

BACKGROUND

Working memory is a domain of 'executive function.' Delayed nonmatching-to-sample (DNMTS) procedures are commonly used to examine working memory in both human laboratory and preclinical studies.

NEW METHOD

The aim was to develop an automated DNMTS procedure maintained by food pellets in rhesus monkeys using a touch-sensitive screen attached to the housing chamber. Specifically, the DNMTS procedure was a 2-stimulus, 2-choice recognition memory task employing unidimensional discriminative stimuli and randomized delay interval presentations.

RESULTS

DNMTS maintained a delay-dependent decrease in discriminability that was independent of the retention interval distribution. Eliminating reinforcer availability during a single delay session or providing food pellets before the session did not systematically alter accuracy, but did reduce total choices. Increasing the intertrial interval enhanced accuracy at short delays. Acute Δ(9)-THC pretreatment produced delay interval-dependent changes in the forgetting function at doses that did not alter total choices. Acute methylphenidate pretreatment only decreased total choices.

COMPARISON WITH EXISTING METHODS

All monkeys were trained to perform NMTS at the 1s training delay within 60 days of initiating operant touch training. Furthermore, forgetting functions were reliably delay interval-dependent and stable over the experimental period (∼6 months).

CONCLUSIONS

Consistent with previous studies, increasing the intertrial interval improved DNMTS performance, whereas Δ(9)-THC disrupted DNMTS performance independent of changes in total choices. Overall, the touchscreen-based DNMTS procedure described provides an efficient method for training and testing experimental manipulations on working memory in unrestrained rhesus monkeys.

Improvement in verbal memory following SSRI augmentation of antipsychotic treatment is associated with changes in the expression of mRNA encoding for the GABA-A receptor and BDNF in PMC of schizophrenic patients

Verbal memory impairment in schizophrenia is associated with abnormalities in gamma-aminobutyric acid (GABA)-ergic and brain-derived neurotrophic factor (BDNF) systems. Recent evidence from animal and clinical studies that adding fluvoxamine to antipsychotics alters the expression of transcripts encoding for the GABA-A receptor and BDNF led us to postulate that fluvoxamine augmentation may improve memory in schizophrenia. To test this, we examined the effect of add-on fluvoxamine on verbal memory and other cognitive functions and related it to the expression of mRNA coding for the GABA-A receptor and BDNF in peripheral mononuclear cells (PMC) of schizophrenic patients. Twenty-nine patients completed a 6-week study in which fluvoxamine (100 mg/day) was added to ongoing antipsychotic treatment. Verbal memory, abstraction working memory, object and face recognition, and psychomotor speed and clinical symptoms were assessed at baseline and after 3 and 6 weeks of treatment. Blood samples were taken at baseline and weeks 1, 3, and 6 and PMC was assayed for the GABA-A beta3 receptor and BDNF mRNA by quantitative real-time reverse transcription-PCR. Associative and logical verbal memory improved significantly and showed a significant correlation with changes in PMC BDNF and GABA-A beta3 receptor mRNA, which increased during treatment. Abstraction and object recognition improved, but this did not correlate with PMC measures. Negative and positive symptoms improved significantly; the latter showed significant correlations with changes in PMC measures. Addition of fluvoxamine to antipsychotics improves verbal memory. It is postulated that the mechanism involves enhanced GABA-A receptor/BDNF-dependent synaptic plasticity in the hippocampus.

Dopaminergic modulation of synaptic plasticity in rat prefrontal neurons

The prefrontal cortex (PFC) is thought to store the traces for a type of long-term memory - the abstract memory that determines the temporal structure of behavior often termed a "rule" or "strategy". Long-term synaptic plasticity might serve as an underlying cellular mechanism for this type of memory. We therefore studied the induction of synaptic plasticity in rat PFC neurons, maintained in vitro, with special emphasis on the functionally important neuromodulator dopamine. First, the induction of long-term potentiation (LTP) was facilitated in the presence of tonic/background dopamine in the bath, and the dose-dependency of this background dopamine followed an "inverted-U" function, where too high or too low dopamine levels could not facilitate LTP. Second, the induction of long-term depression (LTD) by low-frequency stimuli appeared to be independent of background dopamine, but required endogenous, phasically-released dopamine during the stimuli. Blockade of dopamine receptors during the stimuli and exaggeration of the effect of this endogenously-released dopamine by inhibition of dopamine transporter activity both blocked LTD. Thus, LTD induction also followed an inverted-U function in its dopamine-dependency. We conclude that PFC synaptic plasticity is powerfully modulated by dopamine through inverted-U-shaped dose-dependency.

Exploring prefrontal cortex functions in healthy humans by transcranial electrical stimulation

The prefrontal cortex is involved in a multitude of cognitive, emotional, motivational, and social processes, so exploring its specific functions is crucial for understanding human experience and behavior. Functional imaging approaches have largely contributed to the enhancement of our understanding, but might have limitations in establishing causal relationships between physiology and the related psychological and behavioral processes. Non-invasive electrical stimulation with direct or alternating currents can help to enhance our understanding with regard to specific processes, and might provide future protocols able to improve them in case of malfunctions. We review the current state of the field, and provide an outlook for future developments.

Developing treatments for cognitive deficits in schizophrenia: the challenge of translation

Schizophrenia is a life-long debilitating mental disorder affecting tens of millions of people worldwide. The serendipitous discovery of antipsychotics focused pharmaceutical research on developing a better antipsychotic. Our understanding of the disorder has advanced however, with the knowledge that cognitive enhancers are required for patients in order to improve their everyday lives. While antipsychotics treat psychosis, they do not enhance cognition and hence are not antischizophrenics. Developing pro-cognitive therapeutics has been extremely difficult, however, especially when no approved treatment exists. In lieu of stumbling on an efficacious treatment, developing targeted compounds can be facilitated by understanding the neural mechanisms underlying altered cognitive functioning in patients. Equally importantly, these cognitive domains will need to be measured similarly in animals and humans so that novel targets can be tested prior to conducting expensive clinical trials. To date, the limited similarity of testing across species has resulted in a translational bottleneck. In this review, we emphasize that schizophrenia is a disorder characterized by abnormal cognitive behavior. Quantifying these abnormalities using tasks having cross-species validity would enable the quantification of comparable processes in rodents. This approach would increase the likelihood that the neural substrates underlying relevant behaviors will be conserved across species. Hence, we detail cross-species tasks which can be used to test the effects of manipulations relevant to schizophrenia and putative therapeutics. Such tasks offer the hope of providing a bridge between non-clinical and clinical testing that will eventually lead to treatments developed specifically for patients with deficient cognition.