The cognitive neuroscience of working memory: relevance to CNTRICS and schizophrenia

Medial frontal GABA is lower in older schizophrenia: a MEGA-PRESS with macromolecule suppression study

Gamma-butyric acid (GABA) dysfunction has been implicated in the pathophysiology of schizophrenia and its cognitive deficits. Proton magnetic resonance spectroscopy (MRS) was used to test the hypothesis that older participants with schizophrenia have lower anterior cingulate GABA levels compared with older control participants. One-hundred forty-five participants completed this study. For detection of GABA, spectra were acquired from the medial frontal/anterior cingulate cortex using a macromolecule-suppressed MEGA-PRESS sequence. Patients were evaluated for psychopathology and all participants completed neuropsychological tests of working memory, processing speed and functional capacity. GABA levels were significantly lower in the older participants with schizophrenia (n=31) compared with the older control (n=37) group (P=0.003) but not between the younger control (n=40) and schizophrenia (n=29) groups (P=0.994). Age strongly predicted GABA levels in the schizophrenia group accounting for 42% of the variance, but the effect of age was less in the control group accounting for 5.7% of the variance. GABA levels were specifically related to working memory but not processing speed performance, functional capacity, or positive or negative symptom severity. This is the largest MRS study of GABA in schizophrenia and the first to examine GABA without macromolecule contamination, a potentially significant issue in previous studies. GABA levels more rapidly declined with advancing age in the schizophrenia compared with the control group. Interventions targeted at halting the decline or increasing GABA levels may improve functional outcomes and quality of life as patients with schizophrenia age.

Genetics of cognitive control: Implications for Nimh's research domain criteria initiative

Cognitive control refers to a set of mental processes that modulate other cognitive and emotional systems in service of goal-directed adaptive behavior. There is growing support for the notion that cognitive control abnormalities are a central component of many of the neuropsychological deficits observed in individuals with mental illnesses, particularly those with psychotic disorders. NIMH's research domain criteria (RDoC) initiative, which is designed to develop biologically informed constructs to better understand psychopathology, designated cognitive control a construct within the cognitive systems domain. Identification of genes that influence cognitive control or its supportive brain systems will improve our understating of the RDoC construct and provide candidate genes for psychotic disorders. We examine evidence for cognitive control deficits in psychosis, determine if these measures could be useful endophenotypes, and explore work linking genetic variation to cognitive control performance. While there is a wealth of evidence to support the notion the cognitive control is a valid endophenotype for psychosis, its genetic underpinning remains ill characterized. However, existing work provides a promising foundation on which future endeavors might build. Confirming existing individual gene associations will go some way to expanding our understanding of the genetics of cognitive control, and by extension, psychotic disorders. Yet, to truly understand the molecular underpinnings of such complex traits, it may be necessary to evaluate genes in tandem, focusing not on single genes but rather on empirically derived gene sets or on functionally defined networks of genes.

Working memory genetics in schizophrenia and related disorders: An RDoC perspective

Improved classification of mental disorders through neurobiological measures will require a set of traits that map to transdiagnostic subgroups of patients and align with heritable, core psychopathological processes at the center of the disorders of interest. A promising candidate is working memory (WM) function, for which deficits have been reported across multiple diagnostic entities including schizophrenia, bipolar disorder, ADHD, autism, and major depressive disorder. Here we review genetic working memory associations and their brain functional correlates from the perspective of identifying patient subgroups across conventional diagnostic boundaries, explore the utility of multimodal investigations integrating functional information at the neural systems level and explore potential limitations as well as future directions for research.

Long-term trajectories of cognitive deficits in schizophrenia: A critical overview

BACKGROUND

Cognitive disturbances are widely pronounced in schizophrenia and schizophrenia spectrum disorders. Whilst cognitive deficits are well established in the prodromal phase and are known to deteriorate at the onset of schizophrenia, there is a certain discrepancy of findings regarding the cognitive alterations over the course of the illness.

METHODS

We bring together the results of the longitudinal studies identified through PubMed which have covered more than 3 years follow-up and to reflect on the potential factors, such as sample characteristics and stage of the illness which may contribute to the various trajectories of cognitive changes.

RESULTS

A summary of recent findings comprising the changes of the cognitive functioning in schizophrenia patients along the longitudinal course of the illness is provided. The potential approaches for addressing cognition in the course of schizophrenia are discussed.

CONCLUSIONS

Given the existing controversies on the course of cognitive changes in schizophrenia, differentiated approaches specifically focusing on the peculiarities of the clinical features and changes in specific cognitive domains could shed light on the trajectories of cognitive deficits in schizophrenia and spectrum disorders.

Neuroticism and conscientiousness respectively constrain and facilitate short-term plasticity within the working memory neural network

Individual differences in cognitive efficiency, particularly in relation to working memory (WM), have been associated both with personality dimensions that reflect enduring regularities in brain configuration, and with short‐term neural plasticity, that reflects task‐related changes in brain connectivity. To elucidate the relationship of these two divergent mechanisms, we tested the hypothesis that personality dimensions, which reflect enduring aspects of brain configuration, inform about the neurobiological framework within which short‐term, task‐related plasticity, as measured by effective connectivity, can be facilitated or constrained. As WM consistently engages the dorsolateral prefrontal (DLPFC), parietal (PAR), and anterior cingulate cortex (ACC), we specified a WM network model with bidirectional, ipsilateral, and contralateral connections between these regions from a functional magnetic resonance imaging dataset obtained from 40 healthy adults while performing the 3‐back WM task. Task‐related effective connectivity changes within this network were estimated using Dynamic Causal Modelling. Personality was evaluated along the major dimensions of Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. Only two dimensions were relevant to task‐dependent effective connectivity. Neuroticism and Conscientiousness respectively constrained and facilitated neuroplastic responses within the WM network. These results suggest individual differences in cognitive efficiency arise from the interplay between enduring and short‐term plasticity in brain configuration. Hum Brain Mapp 36:4158–4163, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Can individuals with schizophrenia be instructed to deliberately feign memory deficits?

INTRODUCTION

Neuropsychological tests are increasingly applied in research studies and clinical practice in psychiatry. In this context, the detection of poor effort is crucial to adequately interpret data. We measured schizophrenia patients' performance on a memory test designed to detect excessive malingering (the "21-Item Test"), before examining whether a second group of schizophrenia patients would excessively malinger on this test when given an incentive to feign memory impairment.

METHODS

Two independent studies including respectively 49 schizophrenia patients and 100 controls (study 1) and 25 schizophrenia patients and 25 controls (study 2) were conducted. In study 1, participants were asked to complete the 21-Item Test to the best of their ability. In study 2, participants were given a hypothetical scenario in which having a memory impairment would be financially advantageous for them, before completing the 21-Item Test.

RESULTS

In study 1, no participant scored at levels indicative of excessive malingering. In study 2, 84% of controls but only 36% of patients scored at excessive levels of malingering, and these patients had higher executive functioning than patients who did not excessively malinger, although it should be noted that a significantly greater proportion of patients excessively malingered in study 2 compared to study 1.

CONCLUSIONS

These results indicate that schizophrenia patients do not normally feign excessive memory impairment during psychological testing. Furthermore, they are less able and/or less inclined to excessively malinger than controls in situations where a memory impairment would be advantageous, perhaps indicating a better ability to malinger without detection. Potential clinical implications are discussed.

EEG correlates of impaired self-other integration during joint-task performance in schizophrenia

Deficits in a wide variety of social cognitive processes are well established in schizophrenia. However, research focusing on actual interacting individuals is surprisingly scarce. Problems in low-level processes such as self-other integration may importantly underlie often-reported higher-level deficits. The current study aimed at measuring possible disturbances in self-other integration in schizophrenia using both behavioral and event-related potential (ERP) measures. Sixteen healthy controls and fifteen schizophrenia patients performed a social Simon task in both a joint and an individual setting. Behaviorally, patients showed general slower reaction times, but comparable self-other integration as reflected in the social Simon effect. The ERP results for the healthy controls revealed increased no-go P3 amplitudes in the joint compared with the individual setting. Crucially, patients did not show this increase in no-go P3 amplitude. In line with previous research, the present ERP findings demonstrate that healthy volunteers needed more effort to inhibit their responses in the joint compared with the individual setting. Patients however, showed altered self-other integration when they had to withhold their responses while their co-actor had to act. These outcomes indicate that schizophrenia patients have deficits in low-level processes required for successful joint action.

Structural and functional dysconnectivity of the fronto-thalamic system in schizophrenia: a DCM-DTI study

Evidence suggests that cognitive deficits are a core feature of schizophrenia. The concept of "cognitive dysmetria" has been introduced to characterize disintegration of fronto-thalamic-cerebellar circuitry which constitutes a key network for a variety of neuropsychological symptoms in schizophrenia. The present multimodal study aimed at investigating effective and structural connectivity of the fronto-thalamic circuitry in schizophrenia. fMRI effective connectivity analysis using dynamic causal modeling (DCM) and diffusion tensor imaging (DTI) were combined to examine cognitive control processes in 38 patients with schizophrenia and 40 matched healthy controls. Significantly lower fractional anisotropy (FA) was detected in patients in the right anterior limb of the internal capsule (ALIC), the right thalamus and the right corpus callosum. During Stroop task performance patients demonstrated significantly lower activation relative to healthy controls in a predominantly right lateralized fronto-thalamo-cerebellar network. An abnormal effective connectivity was observed in the right connections between thalamus, anterior cingulate and dorsolateral prefrontal cortex. FA in the ALIC was significantly correlated with the thalamic BOLD signal, cognitive performance and fronto-thalamic effective connectivity in patients. Present data provide evidence for the notion of a structural and functional defect in the fronto-thalamo-cerebellar circuitry, which may be the basis of specific cognitive impairments in schizophrenia.

Animal paradigms to assess cognition with translation to humans

Cognition is a complex brain function that represents processes such as learning and memory, attention, working memory, and executive functions amongst others. Impairments in cognition are prevalent in many neuropsychiatric and neurological disorders with few viable treatment options. The development of new therapies is challenging, and poor efficacy in clinical development continues to be one of the most consistent reasons compounds fail to advance, suggesting that traditional animal models are not predictive of human conditions and behavior. An effort to improve the construct validity of neuropsychological testing across species with the intent of facilitating therapeutic development has been strengthening over recent years. With an emphasis on understanding the underlying biology, optimizing the use of appropriate systems (e.g., transgenic animals) to model targeted disease states, and incorporating non-rodent species (e.g., non-human primates) that may enable a closer comparison to humans, an improvement in the translatability of the results will be possible. This chapter focuses on some promising translational cognitive paradigms for use in rodents, non-human primates, and humans.

A preliminary validity study of the cambridge neuropsychological test automated battery for the assessment of executive function in schizophrenia and bipolar disorder

OBJECTIVE

Although the executive function subtests of the Cambridge Neuropsychological Test Automated Battery (CANTAB) have been used to assess cognitive function in diverse psychiatric illnesses, few studies have verified the validity of this battery for Korean psychiatric patients. Therefore, this preliminary study evaluated the construct and concurrent validity of the executive function subtests of the CANTAB for Korean psychiatric patients by comparing it with subtests of the Computerized Neuropsychological Test (CNT).

METHODS

Three subtests of the CANTAB and three subtests of the CNT were administered to 36 patients diagnosed with either schizophrenia or bipolar disorder. Subtests of the CANTAB included the Intra/Extra-Dimensional Set Shift (IED), Stockings of Cambridge (SOC), and Spatial Working Memory (SWM). Differences between groups on each subtest as well as correlations between the subtests of the CANTAB and the CNT were assessed.

RESULTS

The schizophrenia group performed significantly more poorly on the IED and the Wisconsin Card Sorting Test (WCST) compared with the bipolar disorder group. Additionally, correlation analyses revealed a significant correlation between the IED and the WCST; a positive correlation between the SOC and the Trail Making Test, Part B and the Stroop test; and a significant correlation between the SWM and the Stroop test.

CONCLUSION

This study verified the construct and concurrent validity of the executive function subtests of the CANTAB for Korean psychiatric patients and suggests that the subtests of this battery would be useful and appropriate for assessing deficits in executive function in Korean clinical settings.

Brain Mechanisms of Social Threat Effects on Working Memory

Social threat can have adverse effects on cognitive performance, but the brain mechanisms underlying its effects are poorly understood. We investigated the effects of social evaluative threat on working memory (WM), a core component of many important cognitive capabilities. Social threat impaired WM performance during an N-back task and produced widespread reductions in activation in lateral prefrontal cortex and intraparietal sulcus (IPS), among other regions. In addition, activity in frontal and parietal regions predicted WM performance, and mediation analyses identified regions in the bilateral IPS that mediated the performance-impairing effects of social threat. Social threat also decreased connectivity between the IPS and dorsolateral prefrontal cortex, while increasing connectivity between the IPS and the ventromedial prefrontal cortex, a region strongly implicated in the generation of autonomic and emotional responses. Finally, cortisol response to the stressor did not mediate WM impairment but was rather associated with protective effects. These results provide a basis for understanding interactions between social and cognitive processes at a neural systems level.

Assessing neurocognitive function in psychiatric disorders: a roadmap for enhancing consensus

It has been challenging to identify core neurocognitive deficits that are consistent across multiple studies in patients with Obsessive Compulsive Disorder (OCD). In turn, this leads to difficulty in translating findings from human studies into animal models to dissect pathophysiology. In this article, we use primary data from a working memory task in OCD patients to illustrate this issue. Working memory deficiencies have been proposed as an explanatory model for the evolution of checking compulsions in a subset of OCD patients. However, findings have been mixed due to variability in task design, examination of spatial vs. verbal working memory, and heterogeneity in patient populations. Two major questions therefore remain: first, do OCD patients have disturbances in working memory? Second, if there are working memory deficits in OCD, do they cause checking compulsions? In order to investigate these questions, we tested 19 unmedicated OCD patients and 23 matched healthy controls using a verbal working memory task that has increased difficulty/task-load compared to classic digit-span tasks. OCD patients did not significantly differ in their performance on this task compared to healthy controls, regardless of the outcome measure used (i.e. reaction time or accuracy). Exploratory analyses suggest that a subset of patients with predominant doubt/checking symptoms may have decreased memory confidence despite normal performance on trials with the highest working memory load. These results suggest that other etiologic factors for checking compulsions should be considered. In addition, they serve as a touchstone for discussion, and therefore help us to generate a roadmap for increasing consensus in the assessment of neurocognitive function in psychiatric disorders.

The When and Where of Working Memory Dysfunction in Early-Onset Schizophrenia-A Functional Magnetic Resonance Imaging Study

Behavioral evidence indicates that working memory (WM) in schizophrenia is already impaired at the encoding stage. However, the neurophysiological basis of this primary deficit remains poorly understood. Using event-related fMRI, we assessed differences in brain activation and functional connectivity during the encoding, maintenance and retrieval stages of a visual WM task with 3 levels of memory load in 17 adolescents with early-onset schizophrenia (EOS) and 17 matched controls. The amount of information patients could store in WM was reduced at all memory load levels. During encoding, activation in left ventrolateral prefrontal cortex (VLPFC) and extrastriate visual cortex, which in controls positively correlated with the amount of stored information, was reduced in patients. Additionally, patients showed disturbed functional connectivity between prefrontal and visual areas. During retrieval, right inferior VLPFC hyperactivation was correlated with hypoactivation of left VLPFC in patients during encoding. Visual WM encoding is disturbed by a failure to adequately engage a visual-prefrontal network critical for the transfer of perceptual information into WM. Prefrontal hyperactivation appears to be a secondary consequence of this primary deficit. Isolating the component processes of WM can lead to more specific neurophysiological markers for translational efforts seeking to improve the treatment of cognitive dysfunction in schizophrenia.

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

Cognitive deficits are a core feature of schizophrenia. Among these deficits, working memory impairment is considered a central cognitive impairment in schizophrenia. The prefrontal cortex, a region critical for working memory performance, has been demonstrated as a critical liability region in schizophrenia. As yet, there are no standardized treatment options for working memory deficits in schizophrenia. In this review, we summarize the neuronal basis for working memory impairment in schizophrenia, including dysfunction in prefrontal signaling pathways (e.g., γ-aminobutyric acid transmission) and neural network synchrony (e.g., gamma/theta oscillations). We discuss therapeutic strategies for working memory dysfunction such as pharmacological agents, cognitive remediation therapy, and repetitive transcranial magnetic stimulation. Despite the drawbacks of current approaches, the advances in neurobiological and translational treatment strategies suggest that clinical application of these methods will occur in the near future.

Assessing behavioural and cognitive domains of autism spectrum disorders in rodents: current status and future perspectives

The establishment of robust and replicable behavioural testing paradigms with translational value for psychiatric diseases is a major step forward in developing and testing etiology-directed treatment for these complex disorders. Based on the existing literature, we have generated an inventory of applied rodent behavioural testing paradigms relevant to autism spectrum disorders (ASD). This inventory focused on previously used paradigms that assess behavioural domains that are affected in ASD, such as social interaction, social communication, repetitive behaviours and behavioural inflexibility, cognition as well as anxiety behaviour. A wide range of behavioural testing paradigms for rodents were identified. However, the level of face and construct validity is highly variable. The predictive validity of these paradigms is unknown, as etiology-directed treatments for ASD are currently not on the market. To optimise these studies, future efforts should address aspects of reproducibility and take into account data about the neurodevelopmental underpinnings and trajectory of ASD. In addition, with the increasing knowledge of processes underlying ASD, such as sensory information processes and synaptic plasticity, phenotyping efforts should include multi-level automated analysis of, for example, representative task-related behavioural and electrophysiological read-outs.

The RDoC framework: facilitating transition from ICD/DSM to dimensional approaches that integrate neuroscience and psychopathology

In 2008, the National Institute of Mental Health (NIMH) included in its new Strategic Plan the following aim: "Develop, for research purposes, new ways of classifying mental disorders based on dimensions of observable behavior and neurobiological measures". The implementation of this aim was named the Research Domain Criteria project, or RDoC. RDoC is a programmatic initiative that will fund grants, contracts, early-phase trials, and similar activities for the purpose of generating studies to build a research literature that can inform future versions of psychiatric nosologies based upon neuroscience and behavioral science rather than descriptive phenomenology. RDoC departs markedly from the DSM and ICD processes, in which extensive workgroup meetings generate final and finely-honed sets of diagnoses that are modified in field tests only if problems with clinical utility arise. Rather, in keeping with its provenance as an experimental system, the RDoC provides a framework for conducting research in terms of fundamental circuit-based behavioral dimensions that cut across traditional diagnostic categories. While an important aim of the project is to validate particular dimensions as useful for eventual clinical work, an equally important goal is to provide information and experience about how to conceive and implement such an alternative approach to future diagnostic practices that can harness genetics and neuroscience in the service of more effective treatment and prevention. This paper summarizes the rationale for the RDoC project, its essential features, and potential methods of transitioning from DSM/ICD categories to dimensionally-oriented designs in research studies.

A simple spatial working memory and attention test on paired symbols shows developmental deficits in schizophrenia patients

People with neuropsychiatric disorders such as schizophrenia often display deficits in spatial working memory and attention. Evaluating working memory and attention in schizophrenia patients is usually based on traditional tasks and the interviewer's judgment. We developed a simple Spatial Working Memory and Attention Test on Paired Symbols (SWAPS). It takes only several minutes to complete, comprising 101 trials for each subject. In this study, we tested 72 schizophrenia patients and 188 healthy volunteers in China. In a healthy control group with ages ranging from 12 to 60, the efficiency score (accuracy divided by reaction time) reached a peak in the 20-27 age range and then declined with increasing age. Importantly, schizophrenia patients failed to display this developmental trend in the same age range and adults had significant deficits compared to the control group. Our data suggests that this simple Spatial Working Memory and Attention Test on Paired Symbols can be a useful tool for studies of spatial working memory and attention in neuropsychiatric disorders.

Auditory event-related potentials and α oscillations in the psychosis prodrome: neuronal generator patterns during a novelty oddball task

Prior research suggests that event-related potentials (ERP) obtained during active and passive auditory paradigms, which have demonstrated abnormal neurocognitive function in schizophrenia, may provide helpful tools in predicting transition to psychosis. In addition to ERP measures, reduced modulations of EEG alpha, reflecting top-down control required to inhibit irrelevant information, have revealed attentional deficits in schizophrenia and its prodromal stage. Employing a three-stimulus novelty oddball task, nose-referenced 48-channel ERPs were recorded from 22 clinical high-risk (CHR) patients and 20 healthy controls detecting target tones (12% probability, 500Hz; button press) among nontargets (76%, 350Hz) and novel sounds (12%). After current source density (CSD) transformation of EEG epochs (-200 to 1000ms), event-related spectral perturbations were obtained for each site up to 30Hz and 800ms after stimulus onset, and simplified by unrestricted time-frequency (TF) principal components analysis (PCA). Alpha event-related desynchronization (ERD) as measured by TF factor 610-9 (spectral peak latency at 610ms and 9Hz; 31.9% variance) was prominent over right posterior regions for targets, and markedly reduced in CHR patients compared to controls, particularly in three patients who later developed psychosis. In contrast, low-frequency event-related synchronization (ERS) distinctly linked to novels (260-1; 16.0%; mid-frontal) and N1 sink across conditions (130-1; 3.4%; centro-temporoparietal) did not differ between groups. Analogous time-domain CSD-ERP measures (temporal PCA), consisting of N1 sink, novelty mismatch negativity (MMN), novelty vertex source, novelty P3, P3b, and frontal response negativity, were robust and closely comparable between groups. Novelty MMN at FCz was, however, absent in the three converters. In agreement with prior findings, alpha ERD and MMN may hold particular promise for predicting transition to psychosis among CHR patients.

GluN2B-containing NMDA receptors and AMPA receptors in medial prefrontal cortex are necessary for odor span in rats

Working memory is a type of short-term memory involved in the maintenance and manipulation of information essential for complex cognition. While memory span capacity has been extensively studied in humans as a measure of working memory, it has received considerably less attention in rodents. Our aim was to examine the role of the N-methyl-D-aspartate (NMDA) and α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors in odor span capacity using systemic injections or infusions of receptor antagonists into the medial prefrontal cortex (mPFC). Long Evans rats were trained on a well-characterized odor span task (OST). Initially, rats were trained to dig for a food reward in sand followed by training on a non-match to sample discrimination using sand scented with household spices. The rats were then required to perform a serial delayed non-match to sample procedure which was their odor span. Systemic injection of the broad spectrum NMDA receptor antagonist 3-(2-Carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) (10 mg/kg) or the GluN2B-selective antagonist Ro 25-6981 (10 mg/kg but not 6 mg/kg) significantly reduced odor span capacity. Infusions of the GluN2B- selective antagonist Ro 25-6981 (2.5 μg/hemisphere) into mPFC reduced span capacity, an effect that was nearly significant (p = 0.069). Infusions of the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (1.25 μg/hemisphere) into mPFC reduced span capacity and latency for the rats to make a choice in the task. These results demonstrate span capacity in rats depends on ionotropic glutamate receptor activation in the mPFC. Further understanding of the circuitry underlying span capacity may aid in the novel therapeutic drug development for persons with working memory impairments as a result of disorders such as schizophrenia and Alzheimer's disease.

Inactivation of medial prefrontal cortex or acute stress impairs odor span in rats

The capacity of working memory is limited and is altered in brain disorders including schizophrenia. In rodent working memory tasks, capacity is typically not measured (at least not explicitly). One task that does measure working memory capacity is the odor span task (OST) developed by Dudchenko and colleagues. In separate experiments, the effects of medial prefrontal cortex (mPFC) inactivation or acute stress on the OST were assessed in rats. Inactivation of the mPFC profoundly impaired odor span without affecting olfactory sensitivity. Acute stress also significantly reduced odor span. These findings support a potential role of the OST in developing novel therapeutics for disorders characterized by impaired working memory capacity.

The relationship between antipsychotic D2 occupancy and change in frontal metabolism and working memory : A dual [(11)C]raclopride and [(18) F]FDG imaging study with aripiprazole

RATIONALE

The effects of aripiprazole on cognitive function are obscure, possibly due to the difficulty in disentangling the specific effects on cognitive function from effects secondary to the improvement of other schizophrenic symptoms. This prompts the necessity of using an intermediate biomarker relating the drug effect on the brain to change in cognitive function.

OBJECTIVES

To explore the effect of aripiprazole on cognitive function, we measured changes in frontal metabolism as an intermediate biomarker and sought to determine its relationship with D2 receptor occupancy and changes in working memory.

METHODS

Fifteen healthy male volunteers participated in the study. Serial positron emission tomography (PET) scans with [(11)C]raclopride and [(18) F]FDG were conducted 1 day before and 2 days after the administration of aripiprazole. The subjects performed the N-back task just after finishing the [(18) F]FDG scan.

RESULTS

The mean (±SD) D2 receptor occupancies were 22.2 ± 16.0 % in the 2 mg group, 35.5 ± 3.6 % in the 5 mg group, 63.2 ± 9.9 % in the 10 mg group and 72.8 ± 2.1 % in the 30 mg group. The frontal metabolism was significantly decreased after the administration of aripiprazole (t = 2.705, df = 14, p = 0.017). Greater striatal D2 receptor occupancy was related to greater decrease in frontal metabolism (r = -0.659, p = 0.010), and greater reduction in frontal metabolism was associated with longer reaction times (r = -0.597, p = 0.019) under the greatest task load.

CONCLUSIONS

Aripiprazole can affect cognitive function and alter frontal metabolic function. The changes in these functions are linked to greater D2 receptor occupancy. This suggests that it may be important to find the lowest effective dose of aripiprazole in order to prevent adverse cognitive effects.

Association study of neuregulin-1 gene polymorphisms in a North Indian schizophrenia sample

BACKGROUND

Neuregulin-1 (NRG1) gene polymorphisms have been proposed as risk factors for several common disorders. Associations with cognitive variation have also been tested. With regard to schizophrenia (SZ) risk, studies of Caucasian ancestry samples indicate associations more consistently than East Asian samples, suggesting heterogeneity. To exploit the differences in linkage disequilibrium (LD) structure across ethnic groups, we conducted a SZ case-control study (that included cognitive evaluations) in a sample from the north Indian population.

METHODS

NRG1 variants (n=35 SNPs, three microsatellite markers) were initially analyzed among cases (DSM IV criteria, n=1007) and controls (n=1019, drawn from two groups) who were drawn from the same geographical region in North India. Nominally significant associations with SZ were next analyzed in relation to neurocognitive measures estimated with a computerized neurocognitive battery in a subset of the sample (n=116 cases, n=170 controls).

RESULTS

Three variants and one microsatellite showed allelic association with SZ (rs35753505, rs4733263, rs6994992, and microsatellite 420M9-1395, p≤0.05 uncorrected for multiple comparisons). A six marker haplotype 221121 (rs35753505-rs6994992-rs1354336-rs10093107-rs3924999-rs11780123) showed (p=0.0004) association after Bonferroni corrections. Regression analyses with the neurocognitive measures showed nominal (uncorrected) associations with emotion processing and attention at rs35753505 and rs6994992, respectively.

CONCLUSIONS

Suggestive associations with SZ and SZ-related neurocognitive measures were detected with two SNPs from the NRG1 promoter region in a north Indian cohort. The functional role of the alleles merits further investigation.

Disruption of component processes of spatial working memory by electroconvulsive shock but not magnetic seizure therapy

Self-ordered spatial working memory measures provide important information regarding underlying cognitive strategies, such as stereotypy. This strategy is based on repetitive sequential selection of a spatial pattern once a correct sequence has been identified. We previously reported that electroconvulsive shock (ECS) but not magnetic seizure therapy (MST) impaired performance on a spatial working memory task in a preclinical model. Here we tested the hypothesis that ECS disrupted stereotyped patterns in the selection of spatial stimuli. In a within-subject study design, we assessed the effects of ECS, MST, and sham on stereotypy and reaction time in a preclinical model. Stereotypy was assessed by the correlation of actual and predicted response patterns of spatial stimuli. Predicted patterns were based on performance during baseline sessions. ECS resulted in lower correlations between predicted and actual responses to spatial stimuli in two of the three subjects, and it also disrupted stereotypy. For one subject, there was change in the predictability of the spatial locus of responses between experimental conditions. For all three subjects, reaction time was significantly longer in ECS, relative to MST and sham. This is the first study to examine the effect of ECS, and to contrast the effects of ECS and MST, on spatial working memory component processes. Our preliminary findings show that ECS, but not MST decreased stereotypy and increased reaction time. This line of investigation may have significant implications in our understanding cognitive component processes of memory function and impairment.

Cortical circuit dysfunction and cognitive deficits in schizophrenia--implications for preemptive interventions

Schizophrenia is a devastating disorder that is common, usually chronic, frequently associated with substantial co-morbidity for addictive and medical disorders and, as a consequence, very costly in both personal and economic terms. At present, no proven means for preventing or modifying the course of the illness exist. This review discusses evidence supporting the ideas that: (i) impairments in certain cognitive processes are the core feature of schizophrenia; (ii) these cognitive impairments reflect abnormalities in specific cortical circuits; and (iii) these circuitry abnormalities arise during childhood-adolescence. The implications of these findings for the development and implementation of safe, preemptive, disease-modifying interventions in individuals at high risk for a clinical diagnosis of schizophrenia are considered.

Medial prefrontal lesions in mice impair sustained attention but spare maintenance of information in working memory

Working memory and attention are complex cognitive functions that are disrupted in several neuropsychiatric disorders. Mouse models of such human diseases are commonly subjected to maze-based tests that can neither distinguish between these cognitive functions nor isolate specific aspects of either function. Here, we have adapted a simple visual discrimination task, and by varying only the timing of events within the same task construct, we are able to measure independently the behavioral response to increasing attentional demand and increasing length of time that information must be maintained in working memory. We determined that mPFC lesions in mice impair attention but not working memory maintenance.

Empirically defined patterns of executive function deficits in schizophrenia and their relation to everyday functioning: a person-centered approach

Executive function (EF) deficits in schizophrenia (SZ) are well documented, although much less is known about patterns of EF deficits and their association to differential impairments in everyday functioning. The present study empirically defined SZ groups based on measures of various EF abilities and then compared these EF groups on everyday action errors. Participants (n = 45) completed various subtests from the Delis-Kaplan Executive Function System (D-KEFS) and the Naturalistic Action Test (NAT), a performance-based measure of everyday action that yields scores reflecting total errors and a range of different error types (e.g., omission, perseveration). Results of a latent class analysis revealed three distinct EF groups, characterized by (a) multiple EF deficits, (b) relatively spared EF, and (c) perseverative responding. Follow-up analyses revealed that the classes differed significantly on NAT total errors, total commission errors, and total perseveration errors; the two classes with EF impairment performed comparably on the NAT but performed worse than the class with relatively spared EF. In sum, people with SZ demonstrate variable patterns of EF deficits, and distinct aspects of these EF deficit patterns (i.e., poor mental control abilities) may be associated with everyday functioning capabilities.

Psychopathology and the human connectome: toward a transdiagnostic model of risk for mental illness

The panoply of cognitive, affective, motivational, and social functions that underpin everyday human experience requires precisely choreographed patterns of interaction between networked brain regions. Perhaps not surprisingly, diverse forms of psychopathology are characterized by breakdowns in these interregional relationships. Here, we discuss how functional brain imaging has provided insights into the nature of brain dysconnectivity in mental illness. Synthesizing work to date, we propose that genetic and environmental risk factors impinge upon systems-level circuits for several core dimensions of cognition, producing transdiagnostic symptoms. We argue that risk-associated disruption of these circuits mediates susceptibility to broad domains of psychopathology rather than discrete disorders.

Auditory working memory impairments in individuals at familial high risk for schizophrenia

OBJECTIVES

The search for predictors of schizophrenia has accelerated with a growing focus on early intervention and prevention of psychotic illness. Studying nonpsychotic relatives of individuals with schizophrenia enables identification of markers of vulnerability for the illness independent of confounds associated with psychosis. The goal of these studies was to develop new auditory continuous performance tests (ACPTs) and evaluate their effects in individuals with schizophrenia and their relatives.

METHODS

We carried out two studies of auditory vigilance with tasks involving working memory (WM) and interference control with increasing levels of cognitive load to discern the information-processing vulnerabilities in a sample of schizophrenia patients, and two samples of nonpsychotic relatives of individuals with schizophrenia and controls. Study 1 assessed adults (mean age = 41), and Study 2 assessed teenagers and young adults age 13-25 (M = 19).

RESULTS

Patients with schizophrenia were impaired on all five versions of the ACPTs, whereas relatives were impaired only on WM tasks, particularly the two interference tasks that maximize cognitive load. Across all groups, the interference tasks were more difficult to perform than the other tasks. Schizophrenia patients performed worse than relatives, who performed worse than controls. For patients, the effect sizes were large (Cohen's d = 1.5), whereas for relatives they were moderate (d = ~0.40-0.50). There was no age by group interaction in the relatives-control comparison except for participants <31 years of age.

CONCLUSIONS

Novel WM tasks that manipulate cognitive load and interference control index an important component of the vulnerability to schizophrenia.

Estrogens and memory in physiological and neuropathological conditions

Ovarian hormones can influence brain regions crucial to higher cognitive functions, such as learning and memory, acting at structural, cellular and functional levels, and modulating neurotransmitter systems. Among the main effects of estrogens, the protective role that they may play against the deterioration of cognitive functions occurring with normal aging is of essential importance. In fact, during the last century, there has been a 30 years increase in female life expectancy, from 50 to 83 years; however, the mean age of spontaneous menopause remains stable, 50-51 years, with variability related to race and ethnicity. Therefore, women are now spending a greater fraction of their lives in a hypoestrogenic state. Although many cognitive functions seem to be unaffected by normal aging, age-related impairments are particularly evident in tasks involving working memory (WM), whose deficits are a recognized feature of Alzheimer's disease (AD). Many studies conducted over the past two decades showed that the female gonadal hormone estradiol can influence performance of learning and memory tasks, both in animal and humans. There is a great deal of evidence, mostly from animal models, that estrogens can facilitate or enhance performance on WM tasks; therefore, it is very important to clarify their role on this type of memory. To this aim, in this review we briefly describe the most relevant neurobiological bases of estrogens, that can explain their effects on cognitive functioning, and then we summarize the results of works conducted in our laboratory, both on animals and humans, utilizing the menstrual/estrous cycle as a useful noninvasive model. Finally, we review the possible role of estrogens in neuropathological conditions, such as AD and schizophrenia.

Self-reported empathy deficits are uniquely associated with poor functioning in schizophrenia

BACKGROUND

Social cognitive deficits have been proposed to be among the causes of poor functional outcome in schizophrenia. Empathy, or sharing and understanding the unique emotions and experiences of other people, is one of the key elements of social cognition, and prior studies suggest that empathic processes are impaired in schizophrenia. The current study examined whether impairments in self-reported empathy were associated with poor functioning, above and beyond the influences of neurocognitive deficits and psychopathology.

METHODS

Individuals with schizophrenia (n=46) and healthy controls (n=37) completed the Interpersonal Reactivity Index (IRI), a measure of emotional and cognitive empathy. Participants also completed a neuropsychological test battery, clinical ratings of psychopathology, and functional outcome measures assessing both functional capacity and community functioning. After testing for between-group differences, we assessed the relationships between self-reported empathy and the measures of functioning, neurocognition, and psychopathology. Regression analyses examined whether empathic variables predicted functional outcomes.

RESULTS

Individuals with schizophrenia reported lower IRI scores for perspective-taking and empathic concern, and higher IRI scores for personal distress than controls. Among individuals with schizophrenia, lower perspective-taking, greater disorganized symptoms, and deficits in working memory and episodic memory were correlated with poorer functional capacity and community functioning. Lower scores for perspective-taking explained significant incremental variance in both functional capacity (ΔR(2)=.09, p<.05) and community functioning (ΔR(2)=.152, p<.01) after accounting for relevant neurocognitive and psychopathological variables.

CONCLUSIONS

Impaired perspective-taking, a component of cognitive empathy, is associated with poor functioning even after taking into account the influences of neurocognitive deficits and psychopathology. These findings support further efforts to clarify the underlying causes of empathic disturbances and suggest that treatments for these disturbances may help functional recovery in schizophrenia.

Working memory and the homeostatic control of brain adenosine by adenosine kinase

The neuromodulator adenosine maintains brain homeostasis and regulates complex behaviour via activation of inhibitory and excitatory adenosine receptors (ARs) in a brain region-specific manner. AR antagonists such as caffeine have been shown to ameliorate cognitive impairments in animal disease models but their effects on learning and memory in normal animals are equivocal. An alternative approach to reduce AR activation is to lower the extracellular tone of adenosine, which can be achieved by up-regulating adenosine kinase (ADK), the key enzyme of metabolic adenosine clearance. However, mice that globally over-express an Adk transgene ('Adk-tg' mice) were devoid of a caffeine-like pro-cognitive profile; they instead exhibited severe spatial memory deficits. This may be mechanistically linked to cortical/hippocampal N-methyl-d-aspartate receptor (NMDAR) hypofunction because the motor response to acute MK-801 was also potentiated in Adk-tg mice. Here, we evaluated the extent to which the behavioural phenotypes of Adk-tg mice might be modifiable by up-regulating adenosine levels in the cortex/hippocampus. To this end, we investigated mutant 'fb-Adk-def' mice in which ADK expression was specifically reduced in the telencephalon leading to a selective increase in cortical/hippocampal adenosine, while the rest of the brain remained as adenosine-deficient as in Adk-tg mice. The fb-Adk-def mice showed an even greater impairment in spatial working memory and a more pronounced motor response to NMDAR blockade than Adk-tg mice. These outcomes suggest that maintenance of cortical/hippocampal adenosine homeostasis is essential for effective spatial memory and deviation in either direction is detrimental with increased expression seemingly more disruptive than decreased expression.

Cognitive control components and speech symptoms in people with schizophrenia

Previous schizophrenia research suggests poor cognitive control is associated with schizophrenia speech symptoms. However, cognitive control is a broad construct. Two important cognitive control components are poor goal maintenance and poor verbal working memory storage. In the current research, people with schizophrenia (n=45) performed three cognitive tasks that varied in their goal maintenance and verbal working memory storage demands. Speech symptoms were assessed using clinical rating scales, ratings of disorganized speech from typed transcripts, and self-reported disorganization. Overall, alogia was associated with both goal maintenance and verbal working memory tasks. Objectively rated disorganized speech was associated with poor goal maintenance and with a task that included both goal maintenance and verbal working memory storage demands. In contrast, self-reported disorganization was unrelated to either amount of objectively rated disorganized speech or to cognitive control task performance, instead being associated with negative mood symptoms. Overall, our results suggest that alogia is associated with both poor goal maintenance and poor verbal working memory storage and that disorganized speech is associated with poor goal maintenance. In addition, patients' own assessment of their disorganization is related to negative mood, but perhaps not to objective disorganized speech or to cognitive control task performance.

A promoter variant of SHANK1 affects auditory working memory in schizophrenia patients and in subjects clinically at risk for psychosis

Mutations in postsynaptic scaffolding genes contribute to autism, thus suggesting a role in pathological processes in neurodevelopment. Recently, two de novo mutations in SHANK3 were described in schizophrenia patients. In most cases, abnormal SHANK3 genotype was also accompanied by cognitive disruptions. The present study queries whether common SHANK variants may also contribute to neuropsychological dysfunctions in schizophrenia. We genotyped five common coding or promoter variants located in SHANK1, SHANK2 and SHANK3. A comprehensive test battery was used to assess neuropsychological functions in 199 schizophrenia patients and 206 healthy control subjects. In addition, an independent sample of 77 subjects at risk for psychosis was analyzed for replication of significant findings. We found the T allele of the SHANK1 promoter variant rs3810280 to lead to significantly impaired auditory working memory as assessed with digit span (12.5 ± 3.6 vs. 14.8 ± 4.1, P < .001) in schizophrenia cases, applying strict Bonferroni correction for multiple testing. This finding was replicated for forward digit span in the at-risk sample (7.1 ± 2.0 vs. 8.3 ± 2.0, P = .044). Previously, altered memory functions and reduced dendritic spines and postsynaptic density of excitatory synapses were reported in SHANK1 knock-out mice. Moreover, the atypical neuroleptic clozapine was found to increase SHANK1 density in rats. Our findings suggest a role of SHANK1 in working memory deficits in schizophrenia, which may arise from neurodevelopmental changes to prefrontal cortical areas.

Face and body perception in schizophrenia: a configural processing deficit?

Face and body perception rely on common processing mechanisms and activate similar but not identical brain networks. Patients with schizophrenia show impaired face perception, and the present study addressed for the first time body perception in this group. Seventeen patients diagnosed with schizophrenia or schizoaffective disorder were compared to 17 healthy controls on standardized tests assessing basic face perception skills (identity discrimination, memory for faces, recognition of facial affect). A matching-to-sample task including emotional and neutral faces, bodies and cars either in an upright or in an inverted position was administered to assess potential category-specific performance deficits and impairments of configural processing. Relative to healthy controls, schizophrenia patients showed poorer performance on the tasks assessing face perception skills. In the matching-to-sample task, they also responded more slowly and less accurately than controls, regardless of the stimulus category. Accuracy analysis showed significant inversion effects for faces and bodies across groups, reflecting configural processing mechanisms; however reaction time analysis indicated evidence of reduced inversion effects regardless of category in schizophrenia patients. The magnitude of the inversion effects was not related to clinical symptoms. Overall, the data point towards reduced configural processing, not only for faces but also for bodies and cars in individuals with schizophrenia.

Evidence of some strategic preservation of episodic learning in patients with schizophrenia

The aim of this study was to gain a better understanding of schizophrenia patients' strategic use of learning time allocation during encoding, and determine whether they are able to use their monitoring and previous performances to adapt their learning behavior efficiently. Schizophrenia is considered to be a pathology of consciousness as well as being associated with impaired awareness of cognitive processes. In this study, after a learning session, individuals may express a Judgment of Learning (JOL), which reflects their sense of being able to retrieve the information later and which forms the basis for their decision whether or not to carry on learning. The introspective abilities of schizophrenia patients and subsequent strategic control of study time during the encoding of easy or difficult word pairs were investigated in 23 patients and 23 healthy comparison subjects. In spite of their memory impairment, patients were able to judge the difficulty of the word pairs with accuracy and adapt their learning time accordingly. Schizophrenia patients are sensitive to difficulty when rating JOLs and afterwards controlling study time. Monitoring their knowledge at the start helped patients to adapt their learning efficiently. These findings may be of value for cognitive remediation.

CNTRICS imaging biomarkers selection: Working memory

The sixth meeting of the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) consortium was focused on selecting promising imaging biomarker measures for each of the cognitive constructs selected in the first CNTRICS meeting. In the domain of working memory (WM), the 2 constructs of interest were "goal maintenance" and "interference control." CNTRICS received 7 task nominations for goal maintenance and 3 task nominations for interference control. For goal maintenance, the breakout group for WM recommended the AX Continuous Performance Test/Dot Pattern Expectancy (DPX) and the Switching Stroop task for translation and further development for use in clinical trial contexts in schizophrenia research. Notably, these same 2 paradigms were recommended for "rule generation and selection" in executive control, a highly related construct. For interference control, the breakout group recommended the Suppress Task and the Sternberg Item Recognition Paradigm for translation for use in clinical trials. This manuscript describes the ways in which each of these tasks met the criteria used by the breakout group to recommend tasks for further development. In addition, the group revisited the construct of WM capacity. Since the initial CNTRICS meeting, a growing body of work has emerged on the neurobiological substrates of WM capacity, making measure of this construct ready for translation. The group suggested a promising imaging biomarker measure for capacity, a version of the change detection task that measures delay activity over posterior parietal and occipital cortex.

Mutation of Semaphorin-6A disrupts limbic and cortical connectivity and models neurodevelopmental psychopathology

Psychiatric disorders such as schizophrenia and autism are characterised by cellular disorganisation and dysconnectivity across the brain and can be caused by mutations in genes that control neurodevelopmental processes. To examine how neurodevelopmental defects can affect brain function and behaviour, we have comprehensively investigated the consequences of mutation of one such gene, Semaphorin-6A, on cellular organisation, axonal projection patterns, behaviour and physiology in mice. These analyses reveal a spectrum of widespread but subtle anatomical defects in Sema6A mutants, notably in limbic and cortical cellular organisation, lamination and connectivity. These mutants display concomitant alterations in the electroencephalogram and hyper-exploratory behaviour, which are characteristic of models of psychosis and reversible by the antipsychotic clozapine. They also show altered social interaction and deficits in object recognition and working memory. Mice with mutations in Sema6A or the interacting genes may thus represent a highly informative model for how neurodevelopmental defects can lead to anatomical dysconnectivity, resulting, either directly or through reactive mechanisms, in dysfunction at the level of neuronal networks with associated behavioural phenotypes of relevance to psychiatric disorders. The biological data presented here also make these genes plausible candidates to explain human linkage findings for schizophrenia and autism.

Aberrant visual circuitry associated with normal spatial match-to-sample accuracy in schizophrenia

A goal of this study was to evaluate the function of the anterior cingulate cortex (ACC) and of the dorsolateral prefrontal cortex (DLPFC) in medicated patients with schizophrenia (SZ), a small group of first-degree relatives, and healthy controls using a visual delayed match-to-sample task in conjunction with functional magnetic resonance imaging (fMRI). To mitigate performance differences between SZ and healthy controls, we used a novel task that allows for individualized adjustment of task difficulty to match ability level. We also trained participants on the task prior to scanning. Using an event-related design, we modeled three components of the match-to-sample trial: visual encoding, delay, and discrimination. We did not find significant differences in ACC/medial frontal cortex activation between the groups. However, compared to healthy controls, SZ showed decreased activation in visual processing areas during the encoding and discrimination phases of the task and in the ventrolateral prefrontal cortex during the delay. These findings emphasize the tendency of schizophrenia subjects to solve perceptual memory problems by engaging diverse regions.

Epigenetic regulation of gene expression in physiological and pathological brain processes

Over the past decade, it has become increasingly obvious that epigenetic mechanisms are an integral part of a multitude of brain functions that range from the development of the nervous system over basic neuronal functions to higher order cognitive processes. At the same time, a substantial body of evidence has surfaced indicating that several neurodevelopmental, neurodegenerative, and neuropsychiatric disorders are in part caused by aberrant epigenetic modifications. Because of their inherent plasticity, such pathological epigenetic modifications are readily amenable to pharmacological interventions and have thus raised justified hopes that the epigenetic machinery provides a powerful new platform for therapeutic approaches against these diseases. In this review, we give a detailed overview of the implication of epigenetic mechanisms in both physiological and pathological brain processes and summarize the state-of-the-art of "epigenetic medicine" where applicable. Despite, or because of, these new and exciting findings, it is becoming apparent that the epigenetic machinery in the brain is highly complex and intertwined, which underscores the need for more refined studies to disentangle brain-region and cell-type specific epigenetic codes in a given environmental condition. Clearly, the brain contains an epigenetic "hotspot" with a unique potential to not only better understand its most complex functions, but also to treat its most vicious diseases.

Slow and steady: sustained effects of lexico-semantic associations can mediate referential impairments in schizophrenia

The present study investigated the contribution of lexico-semantic associations to impairments in establishing reference in schizophrenia. We examined event-related potentials as schizophrenia patients and healthy, demographically matched controls read five-sentence scenarios. Sentence 4 introduced a noun that referred back to three possible referents introduced in Sentences 1-3. These referents were contextually appropriate, contextually inappropriate but lexico-semantically associated, and contextually inappropriate and lexico-semantically nonassociated. In order to determine whether participants had correctly linked the anaphor to its referent, the final sentence reintroduced each referent, and participants indicated whether the last two sentences referred to the same entity. Results indicated that between 300 and 400 ms, patients, like healthy controls, used discourse context to link the noun with its preceding referent. However, between 400 and 500 ms, neural activity in patients was modulated only by lexico-semantic associations, rather than by discourse context. Moreover, patients were also more likely than controls to incorrectly link the noun with contextually inappropriate but lexico-semantically associated referents. These results suggest that at least some types of referential impairments may be driven by sustained activation of contextually inappropriate lexico-semantic associations.

Postnatal developmental trajectories of neural circuits in the primate prefrontal cortex: identifying sensitive periods for vulnerability to schizophrenia

Schizophrenia is a disorder of cognitive neurodevelopment with characteristic abnormalities in working memory attributed, at least in part, to alterations in the circuitry of the dorsolateral prefrontal cortex. Various environmental exposures from conception through adolescence increase risk for the illness, possibly by altering the developmental trajectories of prefrontal cortical circuits. Macaque monkeys provide an excellent model system for studying the maturation of prefrontal cortical circuits. Here, we review the development of glutamatergic and γ-aminobutyric acid (GABA)-ergic circuits in macaque monkey prefrontal cortex and discuss how these trajectories may help to identify sensitive periods during which environmental exposures, such as those associated with increased risk for schizophrenia, might lead to the types of abnormalities in prefrontal cortical function present in schizophrenia.