Functional hypofrontality and working memory dysfunction in schizophrenia

Losing the sugar coating: potential impact of perineuronal net abnormalities on interneurons in schizophrenia

Perineuronal nets (PNNs) were shown to be markedly altered in subjects with schizophrenia. In particular, decreases of PNNs have been detected in the amygdala, entorhinal cortex and prefrontal cortex. The formation of these specialized extracellular matrix (ECM) aggregates during postnatal development, their functions, and association with distinct populations of GABAergic interneurons, bear great relevance to the pathophysiology of schizophrenia. PNNs gradually mature in an experience-dependent manner during late stages of postnatal development, overlapping with the prodromal period/age of onset of schizophrenia. Throughout adulthood, PNNs regulate neuronal properties, including synaptic remodeling, cell membrane compartmentalization and subsequent regulation of glutamate receptors and calcium channels, and susceptibility to oxidative stress. With the present paper, we discuss evidence for PNN abnormalities in schizophrenia, the potential functional impact of such abnormalities on inhibitory circuits and, in turn, cognitive and emotion processing. We integrate these considerations with results from recent genetic studies showing genetic susceptibility for schizophrenia associated with genes encoding for PNN components, matrix-regulating molecules and immune system factors. Notably, the composition of PNNs is regulated dynamically in response to factors such as fear, reward, stress, and immune response. This regulation occurs through families of matrix metalloproteinases that cleave ECM components, altering their functions and affecting plasticity. Several metalloproteinases have been proposed as vulnerability factors for schizophrenia. We speculate that the physiological process of PNN remodeling may be disrupted in schizophrenia as a result of interactions between matrix remodeling processes and immune system dysregulation. In turn, these mechanisms may contribute to the dysfunction of GABAergic neurons.

Association of Thalamic Dysconnectivity and Conversion to Psychosis in Youth and Young Adults at Elevated Clinical Risk

IMPORTANCE

Severe neuropsychiatric conditions, such as schizophrenia, affect distributed neural computations. One candidate system profoundly altered in chronic schizophrenia involves the thalamocortical networks. It is widely acknowledged that schizophrenia is a neurodevelopmental disorder that likely affects the brain before onset of clinical symptoms. However, no investigation has tested whether thalamocortical connectivity is altered in individuals at risk for psychosis or whether this pattern is more severe in individuals who later develop full-blown illness.

OBJECTIVES

To determine whether baseline thalamocortical connectivity differs between individuals at clinical high risk for psychosis and healthy controls, whether this pattern is more severe in those who later convert to full-blown illness, and whether magnitude of thalamocortical dysconnectivity is associated with baseline prodromal symptom severity.

DESIGN, SETTING, AND PARTICIPANTS

In this multicenter, 2-year follow-up, case-control study, we examined 397 participants aged 12-35 years of age (243 individuals at clinical high risk of psychosis, of whom 21 converted to full-blown illness, and 154 healthy controls). The baseline scan dates were January 15, 2010, to April 30, 2012.

MAIN OUTCOMES AND MEASURES

Whole-brain thalamic functional connectivity maps were generated using individuals' anatomically defined thalamic seeds, measured using resting-state functional connectivity magnetic resonance imaging.

RESULTS

Using baseline magnetic resonance images, we identified thalamocortical dysconnectivity in the 243 individuals at clinical high risk for psychosis, which was particularly pronounced in the 21 participants who converted to full-blown illness. The pattern involved widespread hypoconnectivity between the thalamus and prefrontal and cerebellar areas, which was more prominent in those who converted to full-blown illness (t(173) = 3.77, P < .001, Hedge g = 0.88). Conversely, there was marked thalamic hyperconnectivity with sensory motor areas, again most pronounced in those who converted to full-blown illness (t(173) = 2.85, P < .001, Hedge g = 0.66). Both patterns were significantly correlated with concurrent prodromal symptom severity (r = 0.27, P < 3.6 × 10(-8), Spearman ρ = 0.27, P < 4.75 × 10(-5), 2-tailed).

CONCLUSIONS AND RELEVANCE

Thalamic dysconnectivity, resembling that seen in schizophrenia, was evident in individuals at clinical high risk for psychosis and more prominently in those who later converted to psychosis. Dysconnectivity correlated with symptom severity, supporting the idea that thalamic connectivity may have prognostic implications for risk of conversion to full-blown illness.

Altered basolateral amygdala encoding in an animal model of schizophrenia

It has been proposed that schizophrenia results, in part, from the inappropriate or spurious attribution of salience to cues in the environment. We have recently reported neural correlates of salience in the basolateral amygdala (ABL) of rats during learning in an odor-guided discrimination task. Here we tested whether this dopamine-dependent salience signal is altered in rats with neonatal ventral hippocampal lesions (NVHLs), a rodent model of schizophrenia. We found that ABL signals related to violations in reward prediction were only mildly affected by NVHL; however, neurons in rats with NVHLs showed significantly stronger selectivity during odor sampling, particularly for the more salient large-reward cue. The elevated cue-evoked activity in NVHL rats was correlated with heightened orienting behavior and also with changes in firing to the shifts in reward, suggesting that it reflected abnormal signaling of the large reward-predicting cue's salience. These results are broadly consistent with the proposal that schizophrenics suffer from enhanced signaling of salience.

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.

Altered prefrontal cortical MARCKS and PPP1R9A mRNA expression in schizophrenia and bipolar disorder

BACKGROUND

We previously observed dendritic spine loss in the dorsolateral prefrontal cortex (DLPFC) from schizophrenia and bipolar disorder subjects. In the current study, we sought to determine if the mRNA expression of genes known to regulate the actin cytoskeleton and spines correlated with spine loss.

METHODS

Five candidate genes were identified using previously obtained microarray data from the DLPFC from schizophrenia and control subjects. The relative mRNA expression of the genes linked to dendritic spine growth and function, i.e. IGF1R, MARCKS, PPP1R9A, PTPRF, and ARHGEF2, was assessed using quantitative real-time PCR (qRT-PCR) in the DLPFC from a second cohort including schizophrenia, bipolar disorder, and control subjects. Functional pathway analysis was conducted to determine which actin cytoskeleton-regulatory pathways the genes of interest interact with.

RESULTS

MARCKS mRNA expression was increased in both schizophrenia and bipolar disorder subjects. PPP1R9A mRNA expression was increased in bipolar disorder subjects. For IGF1R, mRNA expression did not differ significantly among groups; however, it did show a significant, negative correlation with dendrite length. MARCKS and PPP1R9A mRNA expression did not correlate with spine loss, but they interact with NMDA receptor signaling pathways that regulate the actin cytoskeleton and spines.

CONCLUSIONS

MARCKS and PPP1R9A might contribute to spine loss in schizophrenia and bipolar disorder through their interactions, possibly indirect ones, with NMDA signaling pathways that regulate spine structure and function.

Decreased chloride channel expression in the dorsolateral prefrontal cortex in schizophrenia

Alterations in GABAergic neurotransmission are implicated in several psychiatric illnesses, including schizophrenia. The Na-K-Cl and K-Cl cotransporters regulate intracellular chloride levels. Abnormalities in cotransporter expression levels could shift the chloride electrochemical gradient and impair GABAergic transmission. In this study, we performed Western blot analysis to investigate whether the Na-K-Cl and K-Cl cotransporter protein is abnormally expressed in the dorsal lateral prefrontal cortex and the anterior cingulate cortex in patients with schizophrenia versus a control group. We found decreased K-Cl cotransporter protein expression in the dorsal lateral prefrontal cortex, but not the anterior cingulate cortex, in subjects with schizophrenia, supporting the hypothesis of region level abnormal GABAergic function in the pathophysiology of schizophrenia. Subjects with schizophrenia off antipsychotic medication at the time of death had decreased K-Cl cotransporter protein expression compared to both normal controls and subjects with schizophrenia on antipsychotics. Our results provide evidence for KCC2 protein abnormalities in schizophrenia and suggest that antipsychotic medications might reverse deficits of this protein in the illness.

Early-course unmedicated schizophrenia patients exhibit elevated prefrontal connectivity associated with longitudinal change

Strong evidence implicates prefrontal cortex (PFC) as a major source of functional impairment in severe mental illness such as schizophrenia. Numerous schizophrenia studies report deficits in PFC structure, activation, and functional connectivity in patients with chronic illness, suggesting that deficient PFC functional connectivity occurs in this disorder. However, the PFC functional connectivity patterns during illness onset and its longitudinal progression remain uncharacterized. Emerging evidence suggests that early-course schizophrenia involves increased PFC glutamate, which might elevate PFC functional connectivity. To test this hypothesis, we examined 129 non-medicated, human subjects diagnosed with early-course schizophrenia and 106 matched healthy human subjects using both whole-brain data-driven and hypothesis-driven PFC analyses of resting-state fMRI. We identified increased PFC connectivity in early-course patients, predictive of symptoms and diagnostic classification, but less evidence for "hypoconnectivity." At the whole-brain level, we observed "hyperconnectivity" around areas centered on the default system, with modest overlap with PFC-specific effects. The PFC hyperconnectivity normalized for a subset of the sample followed longitudinally (n = 25), which also predicted immediate symptom improvement. Biologically informed computational modeling implicates altered overall connection strength in schizophrenia. The initial hyperconnectivity, which may decrease longitudinally, could have prognostic and therapeutic implications.

Persistent infection by HSV-1 is associated with changes in functional architecture of iPSC-derived neurons and brain activation patterns underlying working memory performance

BACKGROUND

Herpes simplex virus, type 1 (HSV-1) commonly produces lytic mucosal lesions. It invariably initiates latent infection in sensory ganglia enabling persistent, lifelong infection. Acute HSV-1 encephalitis is rare and definitive evidence of latent infection in the brain is lacking. However, exposure untraceable to encephalitis has been repeatedly associated with impaired working memory and executive functions, particularly among schizophrenia patients.

METHODS

Patterns of HSV-1 infection and gene expression changes were examined in human induced pluripotent stem cell (iPSC)-derived neurons. Separately, differences in blood oxygenation level-dependent (BOLD) responses to working memory challenges using letter n-back tests were investigated using functional magnetic resonance imaging (fMRI) among schizophrenia cases/controls.

RESULTS

HSV-1 induced lytic changes in iPSC-derived glutamatergic neurons and neuroprogenitor cells. In neurons, HSV-1 also entered a quiescent state following coincubation with antiviral drugs, with distinctive changes in gene expression related to functions such as glutamatergic signaling. In the fMRI studies, main effects of schizophrenia (P = .001) and HSV-1 exposure (1-back, P = 1.76 × 10(-4); 2-back, P = 1.39 × 10(-5)) on BOLD responses were observed. We also noted increased BOLD responses in the frontoparietal, thalamus, and midbrain regions among HSV-1 exposed schizophrenia cases and controls, compared with unexposed persons.

CONCLUSIONS

The lytic/quiescent cycles in iPSC-derived neurons indicate that persistent neuronal infection can occur, altering cellular function. The fMRI studies affirm the associations between nonencephalitic HSV-1 infection and functional brain changes linked with working memory impairment. The fMRI and iPSC studies together provide putative mechanisms for the cognitive impairments linked to HSV-1 exposure.

Prefrontal cortical dendritic spine pathology in schizophrenia and bipolar disorder

IMPORTANCE

Prior studies have demonstrated reduced dendritic spine density in the dorsolateral prefrontal cortex (DLPFC) in schizophrenia. However, it remains unclear how generalizable this finding is in schizophrenia and if it is seen in bipolar disorder, a historically distinct psychiatric condition.

OBJECTIVE

To assess whether spine loss is present in the DLPFC of individuals with schizophrenia and individuals with bipolar disorder.

DESIGN, SETTING, AND PARTICIPANTS

This study used postmortem human brain tissue from individuals with schizophrenia (n=14), individuals with bipolar disorder (n=9), and unaffected control participants (n=19). Tissue samples containing the DLPFC (Brodmann area 46) were Golgi-stained, and basilar dendrites of pyramidal cells in the deep half of layer III were reconstructed.

MAIN OUTCOMES AND MEASURES

The number of spines per dendrite, spine density, and dendrite length were compared across groups. We also assessed for the potential effects of clinical and demographic variables on dendritic parameters.

RESULTS

The mean (SD) spine density was significantly reduced (ie, by 10.5%) in individuals with bipolar disorder (0.28 [0.04] spines/μm) compared with control participants (0.31 [0.05] spines/μm) (P=.02). In individuals with schizophrenia, the mean (SD) spine density was also reduced (by 6.5%; 0.29 [0.03] spines/μm) but just missed significance when compared with control participants (P=.06). There was a significant reduction in the mean (SD) number of spines per dendrite in both individuals with schizophrenia (72.8 [24.9] spines per dendrite) and individuals with bipolar disorder (68.9 [12.9] spines per dendrite) compared with controls (92.8 [31.1] spines per dendrite) (individuals with schizophrenia vs controls: 21.6% reduction [P=.003]; individuals with bipolar disorder vs controls: 25.8% reduction [P=.005]). In addition, both individuals with schizophrenia and individuals with bipolar disorder had a reduced mean (SD) dendrite length (246.5 [67.4] and 245.6 [29.8] μm, respectively) compared with controls (301.8 [75.1] μm) (individuals with schizophrenia vs controls: 18.3% reduction [P=.005]; individuals with bipolar disorder vs controls: 18.6% reduction [P=.005]).

CONCLUSIONS AND RELEVANCE

Dendritic spine loss in the DLPFC was seen in both individuals with schizophrenia and individuals with bipolar disorder, suggesting that the 2 disorders may share some common pathophysiological features.

Dysfunctional Activation of the Cerebellum in Schizophrenia: A Functional Neuroimaging Meta-Analysis

The cognitive dysmetria framework postulates that the deficits seen in schizophrenia are due to underlying cerebello-thalamo-cortical dysfunction. The cerebellum is thought to be crucial in the formation of internal models for both motor and cognitive behaviors. In healthy individuals there is a functional topography within the cerebellum. Alterations in the functional topography and activation of the cerebellum in schizophrenia patients may be indicative of altered internal models, providing support for this framework. Using state-of-the-art neuroimaging meta-analysis, we investigated cerebellar activation across a variety of task domains affected in schizophrenia and in comparison to healthy controls. Our results indicate an altered functional topography in patients. This was especially apparent for emotion and working memory tasks, and may be related to deficits in these domains. Results suggest that an altered cerebellar functional topography in schizophrenia may be contributing to the many deficits associated with the disease, perhaps due to dysfunctional internal models.

The brain's default network: origins and implications for the study of psychosis

The brain's default network is a set of regions that is spontaneously active during passive moments. The network is also active during directed tasks that require participants to remember past events or imagine upcoming events. One hypothesis is that the network facilitates construction of mental models (simulations) that can be used adaptively in many contexts. Extensive research has considered whether disruption of the default network may contribute to disease. While an intriguing possibility, a specific challenge to this notion is the fact that it is difficult to accurately measure the default network in patients where confounds of head motion and compliance are prominent. Nonetheless, some intriguing recent findings suggest that dysfunctional interactions between front-oparietal control systems and the default network contribute to psychosis. Psychosis may be a network disturbance that manifests as disordered thought partly because it disrupts the fragile balance between the default network and competing brain systems.

Intensive cognitive training in schizophrenia enhances working memory and associated prefrontal cortical efficiency in a manner that drives long-term functional gains

We investigated whether intensive computerized cognitive training in schizophrenia could improve working memory performance and increase signal efficiency of associated middle frontal gyri (MFG) circuits in a functionally meaningful manner. Thirty schizophrenia participants and 13 healthy comparison participants underwent fMRI scanning during a letter N-back working memory task. Schizophrenia participants were then randomly assigned to either 80 h (16 weeks) of cognitive training or a computer games control condition. After this intervention, participants completed a second fMRI N-back scanning session. At baseline, during 2-back working memory trials, healthy participants showed the largest and most significant activation in bilateral MFG, which correlated with task performance. Schizophrenia participants showed impaired working memory, hypoactivation in left MFG, and no correlation between bilateral MFG signal and task performance. After training, schizophrenia participants improved their 2-back working memory performance and showed increased activation in left MFG. They also demonstrated a significant association between enhanced task performance and right MFG signal, similar to healthy participants. Both task performance and brain activity in right MFG after training predicted better generalized working memory at 6-month follow-up. Furthermore, task performance and brain activity within bilateral MFG predicted better occupational functioning at 6-month follow-up. No such findings were observed in the computer games control participants. Working memory impairments in schizophrenia and its underlying neural correlates in MFG can be improved by intensive computerized cognitive training; these improvements generalize beyond the trained task and are associated with enduring effects on cognition and functioning 6 months after the intervention.

MB-COMT promoter DNA methylation is associated with working-memory processing in schizophrenia patients and healthy controls

Many genetic studies report mixed results both for the associations between COMT polymorphisms and schizophrenia and for the effects of COMT variants on common intermediate phenotypes of the disorder. Reasons for this may include small genetic effect sizes and the modulation of environmental influences. To improve our understanding of the role of COMT in the disease etiology, we investigated the effect of DNA methylation in the MB-COMT promoter on neural activity in the dorsolateral prefrontal cortex during working memory processing as measured by fMRI - an intermediate phenotype for schizophrenia. Imaging and epigenetic data were measured in 102 healthy controls and 82 schizophrenia patients of the Mind Clinical Imaging Consortium (MCIC) study of schizophrenia. Neural activity during the Sternberg Item Recognition Paradigm was acquired with either a 3T Siemens Trio or 1.5T Siemens Sonata and analyzed using the FMRIB Software Library (FSL). DNA methylation measurements were derived from cryo-conserved blood samples. We found a positive association between MB-COMT promoter methylation and neural activity in the left dorsolateral prefrontal cortex in a model using a region-of-interest approach and could confirm this finding in a whole-brain model. This effect was independent of disease status. Analyzing the effect of MB-COMT promoter DNA methylation on a neuroimaging phenotype can provide further evidence for the importance of COMT and epigenetic risk mechanisms in schizophrenia. The latter may represent trans-regulatory or environmental risk factors that can be measured using brain-based intermediate phenotypes.

Disruption of cortical association networks in schizophrenia and psychotic bipolar disorder

IMPORTANCE

Psychotic disorders (including schizophrenia, schizoaffective disorder, and psychotic bipolar disorder) are devastating illnesses characterized by breakdown in the integration of information processing. Recent advances in neuroimaging allow for the estimation of brain networks on the basis of intrinsic functional connectivity, but the specific network abnormalities in psychotic disorders are poorly understood.

OBJECTIVE

To compare intrinsic functional connectivity across the cerebral cortex in patients with schizophrenia spectrum disorders or psychotic bipolar disorder and healthy controls.

DESIGN, SETTING, AND PARTICIPANTS

We studied 100 patients from an academic psychiatric hospital (28 patients with schizophrenia, 32 patients with schizoaffective disorder, and 40 patients with bipolar disorder with psychosis) and 100 healthy controls matched for age, sex, race, handedness, and scan quality from December 2009 to October 2011.

MAIN OUTCOMES AND MEASURES

Functional connectivity profiles across 122 regions that covered the entire cerebral cortex.

RESULTS

Relative to the healthy controls, individuals with a psychotic illness had disruption across several brain networks, with preferential reductions in functional connectivity within the frontoparietal control network (P < .05, corrected for family-wise error rate). This functionally defined network includes portions of the dorsolateral prefrontal cortex, posteromedial prefrontal cortex, lateral parietal cortex, and posterior temporal cortex. This effect was seen across diagnoses and persisted after matching patients and controls on the basis of scan quality.

CONCLUSIONS AND RELEVANCE

Our study results support the view that cortical information processing is disrupted in psychosis and provides new evidence that disruptions within the frontoparietal control network may be a shared feature across both schizophrenia and affective psychosis.

The role of pro-inflammatory cytokines in the neuroinflammation and neurogenesis of schizophrenia

Schizophrenia is a serious mental illness with chronic symptoms and significant impairment in psychosocial functioning. Although novel antipsychotics have been developed, the negative and cognitive symptoms of schizophrenia are still unresponsive to pharmacotherapy. The high level of social impairment and a chronic deteriorating course suggest that schizophrenia likely has neurodegenerative characteristics. Inflammatory markers such as pro-inflammatory cytokines are well-known etiological factors for psychiatric disorders, including schizophrenia. Inflammation in the central nervous system is closely related to neurodegeneration. In addition to pro-inflammatory cytokines, microglia also play an important role in the inflammatory process in the CNS. Uncontrolled activity of pro-inflammatory cytokines and microglia can induce schizophrenia in tandem with genetic vulnerability and glutamatergic neurotransmitters. Several studies have investigated the possible effects of antipsychotics on inflammation and neurogenesis. Additionally, anti-inflammatory adjuvant therapy has been under investigation as a treatment option for schizophrenia. Further studies should consider the confounding effects of systemic factors such as metabolic syndrome and smoking. In addition, the unique mechanisms by which pro-inflammatory cytokines are involved in the etiopathology of schizophrenia should be investigated. In this article, we aimed to review (1) major findings regarding neuroinflammation and pro-inflammatory cytokine alterations in schizophrenia, (2) interactions between neuroinflammation and neurogenesis as possible neural substrates for schizophrenia, and (3) novel pharmacological approaches.

Single event-related changes in cerebral oxygenated hemoglobin using word game in schizophrenia

Neuroimaging studies have been conducted using word generation tasks and have shown greater hypofrontality in patients with schizophrenia compared with healthy subjects. In this study, we compared the characteristics of oxygenated hemoglobin changes involved in both phonological and categorical verbal fluency between 35 outpatients with schizophrenia and 35 healthy subjects during a Japanese "shiritori" task using single-event-related near-infrared spectroscopy. During this task, the schizophrenic patients showed significantly smaller activation in the prefrontal cortex area than the controls. In addition, a significant positive correlation was obtained between oxygenated hemoglobin changes (prefrontal cortex area, inferior parietal area) and the severity of positive psychiatric symptoms. It is possible that hypofrontality of patients may be a diagnostic assistance tool for schizophrenia, and that the relationship between activation and positive syndrome scores may be of help in predicting functional outcome in patients.

Computational neuropsychiatry - schizophrenia as a cognitive brain network disorder

Computational modeling of functional brain networks in fMRI data has advanced the understanding of higher cognitive function. It is hypothesized that functional networks mediating higher cognitive processes are disrupted in people with schizophrenia. In this article, we review studies that applied measures of functional and effective connectivity to fMRI data during cognitive tasks, in particular working memory fMRI studies. We provide a conceptual summary of the main findings in fMRI data and their relationship with neurotransmitter systems, which are known to be altered in individuals with schizophrenia. We consider possible developments in computational neuropsychiatry, which are likely to further our understanding of how key functional networks are altered in schizophrenia.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

Shifted neuronal balance during stimulus-response integration in schizophrenia: an fMRI study

Schizophrenia is characterized by marked deficits in executive and psychomotor functions, as demonstrated for goal-directed actions in the antisaccade task. Recent studies, however, suggest that this deficit represents only one manifestation of a general deficit in stimulus-response integration and volitional initiation of motor responses. We here used functional magnetic resonance imaging to investigate brain activation patterns during a manual stimulus-response compatibility task in 18 schizophrenic patients and 18 controls. We found that across groups incongruent vs. congruent responses recruited a bilateral network consisting of dorsal fronto-parietal circuits as well as bilateral anterior insula, dorsolateral prefrontal cortex (DLPFC) and the presupplementary motor area (preSMA). When testing for the main-effect across all conditions, patients showed significantly lower activation of the right DLPFC and, in turn, increased activation in a left hemispheric network including parietal and premotor areas as well as the preSMA. For incongruent responses patients showed significantly increased activation in a similar left hemispheric network, as well as additional activation in parietal and premotor regions in the right hemisphere. The present study reveals that hypoactivity in the right DLPFC in schizophrenic patients is accompanied by hyperactivity in several fronto-parietal regions associated with task execution. Impaired top-down control due to a dysfunctional DLPFC might thus be partly compensated by an up-regulation of task-relevant regions in schizophrenic patients.

The touchscreen operant platform for testing working memory and pattern separation in rats and mice

The automated touchscreen operant chamber for rats and mice allows for the assessment of multiple cognitive domains within the same testing environment. This protocol presents the location discrimination (LD) task and the trial-unique delayed nonmatching-to-location (TUNL) task, which both assess memory for location. During these tasks, animals are trained to a predefined criterion during ∼20-40 daily sessions. In LD sessions, touching the same location on the screen is rewarded on consecutive trials, followed by a reversal of location-reward contingencies. TUNL, a working memory task, requires animals to 'nonmatch' to a sample location after a delay. In both the LD and TUNL tasks, spatial similarity can be varied, allowing assessment of pattern separation ability, a function that is thought to be performed by the dentate gyrus (DG). These tasks are therefore particularly useful in animal models of hippocampal, and specifically DG, function, but they additionally permit discernment of changes in pattern separation from those in working memory.

Hypothetical decision making in schizophrenia: the role of expected value computation and "irrational" biases

The aim of the present study was to examine the contributions to decision making (DM) deficits in schizophrenia (SZ) patients of expected value (EV) estimation and loss aversion. Patients diagnosed with SZ (n=46) and healthy controls (n=34) completed two gambling tasks. In one task, participants chose between two options with the same EV across two conditions: Loss frames and Keep frames. A second task involved accepting or rejecting gambles, in which gain and loss amounts varied, determining the EV of each trial. SZ patients showed a reduced "framing effect" relative to controls, as they did not show an increased tendency to gamble when faced with a certain loss. SZ patients also showed a reduced tendency to modify behavior as a function of EV. The degree to which choices tracked EV correlated significantly with several cognitive measures in both patients and controls. SZ patients show distinct deviations from normal behavior under risk when their decisions are based on prospective outcomes. These deviations are two-fold: cognitive deficits prevent value-based DM in more-impaired patients, and in less-impaired patients there is a lack of influence from well-established subjective biases found in healthy people. These abnormalities likely affect everyday DM strategies in schizophrenia patients.

Distinct abnormalities of the primate prefrontal cortex caused by ionizing radiation in early or midgestation

Prenatal exposure of the brain to environmental insult causes different neurological symptoms and behavioral outcomes depending on the time of exposure. To examine the cellular bases for these differences, we exposed rhesus macaque fetuses to x-rays during early gestation (embryonic day [E]30-E42), i.e., before the onset of corticogenesis, or in midgestation (E70-E81), when superficial cortical layers are generated. Animals were delivered at term (~E165), and the size and cellular composition of prefrontal association cortex (area 46) examined in adults using magnetic resonance imaging (MRI) and stereologic analysis. Both early and midgestational radiation exposure diminished the surface area and volume of area 46. However, early exposure spared cortical thickness and did not alter laminar composition, and due to higher cell density, neuron number was within the normal range. In contrast, exposure to x-rays at midgestation reduced cortical thickness, mainly due to elimination of neurons destined for the superficial layers. A cell-sparse gap, observed within layer III, was not filled by the later-generated neurons destined for layer II, indicating that there is no subsequent replacement of the lost neurons. The distinct areal and laminar pathology consequent to temporally segregated irradiation is consistent with basic postulates of the radial unit hypothesis of cortical development. In addition, we show that an environmental disturbance inflicted in early gestation can induce subtle cytoarchitectonic alterations without loss of neurons, such as those observed in schizophrenia, whereas midgestational exposure causes selective elimination of neurons and cortical thinning as observed in some forms of mental retardation and fetal alcohol syndrome.

Characterizing thalamo-cortical disturbances in schizophrenia and bipolar illness

Schizophrenia is a devastating neuropsychiatric syndrome associated with distributed brain dysconnectivity that may involve large-scale thalamo-cortical systems. Incomplete characterization of thalamic connectivity in schizophrenia limits our understanding of its relationship to symptoms and to diagnoses with shared clinical presentation, such as bipolar illness, which may exist on a spectrum. Using resting-state functional magnetic resonance imaging, we characterized thalamic connectivity in 90 schizophrenia patients versus 90 matched controls via: (1) Subject-specific anatomically defined thalamic seeds; (2) anatomical and data-driven clustering to assay within-thalamus dysconnectivity; and (3) machine learning to classify diagnostic membership via thalamic connectivity for schizophrenia and for 47 bipolar patients and 47 matched controls. Schizophrenia analyses revealed functionally related disturbances: Thalamic over-connectivity with bilateral sensory-motor cortices, which predicted symptoms, but thalamic under-connectivity with prefrontal-striatal-cerebellar regions relative to controls, possibly reflective of sensory gating and top-down control disturbances. Clustering revealed that this dysconnectivity was prominent for thalamic nuclei densely connected with the prefrontal cortex. Classification and cross-diagnostic results suggest that thalamic dysconnectivity may be a neural marker for disturbances across diagnoses. Present findings, using one of the largest schizophrenia and bipolar neuroimaging samples to date, inform basic understanding of large-scale thalamo-cortical systems and provide vital clues about the complex nature of its disturbances in severe mental illness.

Failure of attention focus and cognitive control in schizophrenia patients with auditory verbal hallucinations: evidence from dichotic listening

Auditory verbal hallucinations (AVHs) are speech perceptions that lack an external source, phenomenologically experienced as "hearing voices". A perceptual origin of an AVH experience in patients with schizophrenia can however not explain why the "voices" drain the attentional and cognitive capacity of the patients, making them unable to direct attention away from the "voices" and to cognitively suppress the experience. We recently reported how AVHs interfere with the perception of speech sounds, using a dichotic listening experimental paradigm. We now extend this finding by reporting on the interference caused by AVHs on attention and cognitive control, using a slight variation of the same dichotic listening paradigm. The patients (N=148) were instructed to pay attention to and report from either the right or left ear syllable of the dichotic pair. We then correlated their PANSS score for the hallucination item (P3) with the performance score on the dichotic listening task. The results showed that AVHs interfered with the ability to report the right ear syllable when instructed to pay attention to the right side, which is a marker of inability to attend to an external speech stimulus. When instructed to pay attention to the left side, AVHs interfered with the ability to report the left ear syllable, which is a marker of inability to use cognitive control to suppress attending to the "voices". The corresponding correlations for the emotional withdrawal (N2) negative symptom were all non-significant. The correlations were substantiated in an ANOVA with corresponding significant group differences between high versus low symptom score groups. The results thus extend our previous findings of a perceptual origination for AVHs by showing that AVHs interfere with the ability to attend to the outer world around the patient, and the ability to inhibit, or suppress, the "voices" once they occur. Future research should pin down the neuronal basis of both the origination and the attentional and cognitive control aspects of AVHs.

Constraints on information processing capacity in adults with ADHD

OBJECTIVE

Researchers in the cognitive sciences have demonstrated the existence of processing capacity bottlenecks in the human brain. These capacity bottlenecks restrict our ability to process and act on environmental information. The purpose of the current study was to examine whether adults with attention-deficit hyperactivity disorder (ADHD) show reduced capacity of working memory and response selection mechanisms.

METHOD

Thirty-eight young adults with ADHD and 33 comparison adults were assessed using two measures of processing capacity. A dual choice-response task (psychological refractory period [PRP] task) measured response selection capacity, and an n-back task measured working memory capacity. These tasks measured capacity by assessing the degree to which increasing processing load disrupted performance.

RESULTS

Results confirmed that performance declined as cognitive load was increased, and this was true for both groups on each task. On the PRP task, the performance decline resulting from increased cognitive load was more pronounced in the ADHD group than in the control group, indicative of reduced response selection capacity in the ADHD group. On the n-back task, however, there was no group difference in the degree to which increasing processing load disrupted performance.

CONCLUSIONS

Results indicate that adults with ADHD show a specific capacity reduction of response selection. This evidence suggests a dissociation between working memory and response selection capacities, and it may have implications for understanding cognitive dysfunction in adults with ADHD.

A quantitative system pharmacology computer model for cognitive deficits in schizophrenia

Although the positive symptoms of schizophrenia are reasonably well-controlled by current antipsychotics, cognitive impairment remains largely unaddressed. The Matrics initiative lays out a regulatory path forward and a number of targets have been tested in the clinic, so far without much success. To address this translational disconnect, we have developed a mechanism-based humanized computer model of a relevant key cortical brain network with schizophrenia pathology involved with the maintenance aspect of working memory (WM). The model is calibrated using published clinical experiments on N-back WM tests. We further simulate the opposite effect of γ-aminobutyric acid (GABA) modulators lorazepam and flumazenil and of a published augmentation trial of clozapine with risperidone, illustrating the introduction of new targets and the capacity of predicting the effects of polypharmacy. This humanized approach allows for early prospective and quantitative assessment of cognitive outcome in a central nervous system (CNS) research and development project, thereby hopefully increasing the success rate of clinical trials.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e36; doi:10.1038/psp.2013.12; advance online publication 3 April 2013.

Frequency dependent alterations in regional homogeneity of baseline brain activity in schizophrenia

Low frequency oscillations are essential in cognitive function impairment in schizophrenia. While functional connectivity can reveal the synchronization between distant brain regions, the regional abnormalities in task-independent baseline brain activity are less clear, especially in specific frequency bands. Here, we used a regional homogeneity (ReHo) method combined with resting-state functional magnetic resonance imaging to investigate low frequency spontaneous neural activity in the three different frequency bands (slow-5:0.01-0.027 Hz; slow-4:0.027-0.08 Hz; and typical band: 0.01-0.08 Hz) in 69 patients with schizophrenia and 62 healthy controls. Compared with controls, schizophrenia patients exhibited decreased ReHo in the precentral gyrus, middle occipital gyrus, and posterior insula, whereas increased ReHo in the medial prefrontal cortex and anterior insula. Significant differences in ReHo between the two bands were found in fusiform gyrus and superior frontal gyrus (slow-4> slow-5), and in basal ganglia, parahippocampus, and dorsal middle prefrontal gyrus (slow-5> slow-4). Importantly, we identified significant interaction between frequency bands and groups in the inferior occipital gyrus and caudate body. This study demonstrates that ReHo changes in schizophrenia are widespread and frequency dependent.

Brain connectivity studies in schizophrenia: unravelling the effects of antipsychotics

Impaired brain connectivity is a hallmark of schizophrenia brain dysfunction. However, the effect of drug treatment and challenges on the dysconnectivity of functional networks in schizophrenia is an understudied area. In this review, we provide an overview of functional magnetic resonance imaging studies examining dysconnectivity in schizophrenia and discuss the few studies which have also attempted to probe connectivity changes with antipsychotic drug treatment. We conclude with a discussion of possible avenues for further investigation.

The evolutionary paradox and the missing heritability of schizophrenia

Schizophrenia is one of the most detrimental common psychiatric disorders, occurring at a prevalence of approximately 1%, and characterized by increased mortality and reduced reproduction, especially in men. The heritability has been estimated around 70% and the genome-wide association meta-analyses conducted by the Psychiatric Genomics Consortium have been successful at identifying an increasing number of risk loci. Various theories have been proposed to explain why genetic variants that predispose to schizophrenia persist in the population, despite the fitness reduction in affected individuals, a question known as the evolutionary paradox. In this review, we consider evolutionary perspectives of schizophrenia and of the empirical evidence that may support these perspectives. Proposed evolutionary explanations include balancing selection, fitness trade-offs, fluctuating environments, sexual selection, mutation-selection balance and genomic conflicts. We address the expectations about the genetic architecture of schizophrenia that are predicted by different evolutionary scenarios and discuss the implications for genetic studies. Several potential sources of "missing" heritability, including gene-environment interactions, epigenetic variation, and rare genetic variation are examined from an evolutionary perspective. A better understanding of evolutionary history may provide valuable clues to the genetic architecture of schizophrenia and other psychiatric disorders, which is highly relevant to genetic studies that aim to detect genetic risk variants.

Reduced prefrontal cortex activation using the Trail Making Test in schizophrenia

Schizophrenia has been associated with a deficit of the prefrontal cortex, which is involved in attention, executive processes, and working memory. The Trail Making Test (TMT) is administered in two parts, TMT-A and TMT-B. It is suggested that the difference in performance between part A and part B reflects executive processes. In this study, we compared the characteristics of hemodynamic changes during TMT tasks between 14 outpatients with schizophrenia and 14 age- and gender-matched healthy control subjects. Using multichannel near-infrared spectroscopy, we measured relative changes in oxygenated hemoglobin concentration, which reflects brain activity of the prefrontal cortex during this task. In both tasks, patients showed significantly smaller activation than controls and, in an assessment of executive functions, a subtraction of oxygenated hemoglobin (oxy-Hb) changes during TMT-A from those of TMT-B showed a decrease in cerebral lateralization and hypoactivity in patients. There was a significant negative correlation between oxy-Hb changes and the severity of psychiatric symptoms. These findings may characterize disease-related features, suggesting the usefulness of oxy-Hb change measurement during TMT tasks for assessing functional outcomes in schizophrenic patients.

Estudos transcriptômicos no contexto da conectividade perturbada em esquizofrenia

Esquizofrenia é uma severa doença neurobiológica com fatores genéticos e ambientais desempenhando um papel na fisiopatologia. Diversas regiões cerebrais têm sido implicadas no processo da doença e estão conectadas em complexos circuitos neuronais. Nos níveis molecular e celular, a conectividade afetada entre essas regiões, envolvendo mielinização disfuncional dos axônios neuronais, bem como as alterações no nível sináptico e metabolismo energético levando a distúrbios na plasticidade sináptica, são os maiores achados em estudos post-mortem. Estudos de microarranjos investigando a expressão gênica contribuíram para os achados de alterações em vias complexas em regiões cerebrais relevantes na esquizofrenia. Além disso, estudos utilizando microdissecção e captura a laser permitiram a investigação da expressão gênica em grupos específicos de neurônios. Entretanto, deve ser mantido em mente que em estudos post-mortem, confusos efeitos de medicação, qualidade de RNAm, bem como capacidade de mecanismos regenerativos neuroplásticos do cérebro em indivíduos com história de vida de esquizofrenia, podem influenciar o complexo padrão de alterações no nível molecular. Apesar dessas limitações, estudos transcriptômicos livres de hipóteses em tecido cerebral de pacientes esquizofrênicos oferecem uma possibilidade única para aprender mais sobre os mecanismos subjacentes, levando a novas ópticas da fisiopatologia da doença.

Excessive attractor instability accounts for semantic priming in schizophrenia

One of the most pervasive findings in studies of schizophrenics with thought disorders is their peculiar pattern of semantic priming, which presumably reflects abnormal associative processes in the semantic system of these patients. Semantic priming is manifested by faster and more accurate recognition of a word-target when preceded by a semantically related prime, relative to an unrelated prime condition. Compared to control, semantic priming in schizophrenics is characterized by reduced priming effects at long prime-target Stimulus Onset Asynchrony (SOA) and, sometimes, augmented priming at short SOA. In addition, unlike controls, schizophrenics consistently show indirect (mediated) priming (such as from the prime ‘wedding’ to the target ‘finger’, mediated by ‘ring’). In a previous study, we developed a novel attractor neural network model with synaptic adaptation mechanisms that could account for semantic priming patterns in healthy individuals. Here, we examine the consequences of introducing attractor instability to this network, which is hypothesized to arise from dysfunctional synaptic transmission known to occur in schizophrenia. In two simulated experiments, we demonstrate how such instability speeds up the network’s dynamics and, consequently, produces the full spectrum of priming effects previously reported in patients. The model also explains the inconsistency of augmented priming results at short SOAs using directly related pairs relative to the consistency of indirect priming. Further, we discuss how the same mechanism could account for other symptoms of the disease, such as derailment (‘loose associations’) or the commonly seen difficulty of patients in utilizing context. Finally, we show how the model can statistically implement the overly-broad wave of spreading activation previously presumed to characterize thought-disorders in schizophrenia.

Impaired passive maintenance and spared manipulation of internal representations in patients with schizophrenia

Working memory (WM) impairment is a core feature of schizophrenia (SZ), but the integrity of the various components of WM is unclear. After encoding, mental representations must be maintained in WM during the delay period. In addition to maintenance, manipulation of internal representation can occur in WM. It has been argued that manipulation of items in WM is more impaired than simple maintenance in SZ, but direct empirical data to support this claim have been mixed. Discrepant findings among studies might be explained by task parameters, specifically the degree to which the manipulation task places demands on encoding and maintenance processes. The present study set out to examine these components of WM in patients with SZ (n = 20) and demographically matched healthy controls (n = 19) using a spatial delayed response task (DRT) to measure maintenance processes and 2 mental rotation tasks (allocentric and egocentric) with no delay period or restriction on encoding time to measure manipulation processes. Consistent with previous findings, patients were impaired on the spatial DRT. However, patients performed equally well on the egocentric mental rotation task and were more accurate than controls on the allocentric mental rotation task as the required degree of rotation increased. These results indicated impaired maintenance and spared manipulation of representations in WM and suggest a pocket of cognitive function that might be enhanced in SZ.

Cognitive and prepulse inhibition deficits in psychometrically high schizotypal subjects in the general population: relevance to schizophrenia research

Schizophrenia and schizotypal personality disorder share common clinical profiles, neurobiological and genetic substrates along with Prepulse Inhibition and cognitive deficits; among those, executive, attention, and memory dysfunctions are more consistent. Schizotypy is considered to be a non-specific "psychosis-proneness," and understanding the relationship between schizotypal traits and cognitive function in the general population is a promising approach for endophenotypic research in schizophrenia spectrum disorders. In this review, findings for executive function, attention, memory, and Prepulse Inhibition impairments in psychometrically defined schizotypal subjects have been summarized and compared to schizophrenia patients and their unaffected first-degree relatives. Cognitive flexibility, sustained attention, working memory, and Prepulse Inhibition impairments were consistently reported in high schizotypal subjects in accordance to schizophrenia patients. Genetic studies assessing the effects of various candidate gene polymorphisms in schizotypal traits and cognitive function are promising, further supporting a polygenic mode of inheritance. The implications of the findings, methodological issues, and suggestions for future research are discussed.

Long-term and within-day variability of working memory performance and EEG in individuals

OBJECTIVE

Assess individual-subject long-term and within-day variability of a combined behavioral and EEG test of working memory.

METHODS

EEGs were recorded from 16 adults performing n-back working memory tasks, with 10 tested in morning and afternoon sessions over several years. Participants were also tested after ingesting non-prescription medications or recreational substances. Performance and EEG measures were analyzed to derive an Overall score and three constituent sub-scores characterizing changes in performance, cortical activation, and alertness from each individual's baseline. Long-term and within-day variability were determined for each score; medication effects were assessed by reference to each individual's normal day-to-day variability.

RESULTS

Over the several year period, the mean Overall score and sub-scores were approximately zero with standard deviations less than one. Overall scores were lower and their variability higher in afternoon relative to morning sessions. At the group level, alcohol, diphenhydramine and marijuana produced significant effects, but there were large individual differences.

CONCLUSIONS

Objective working memory measures incorporating performance and EEG are stable over time and sensitive at the level of individual subjects to interventions that affect neurocognitive function.

SIGNIFICANCE

With further research these measures may be suitable for use in individualized medical care by providing a sensitive assessment of incipient illness and response to treatment.

Antipsychotic medication and prefrontal cortex activation: a review of neuroimaging findings

Decreased prefrontal activation (hypofrontality) in schizophrenia is thought to underlie negative symptoms and cognitive impairments, and may contribute to poor social outcome. Hypofrontality does not always improve during treatment with antipsychotics. We hypothesized that antipsychotics, which share antagonism at dopamine receptors, with a relatively low dopamine receptor affinity and high serotonin receptor affinity may have a sparing effect on prefrontal function compared to strong dopamine receptor antagonists. We systematically investigated the relation between serotonin and dopamine antagonism of antipsychotics and prefrontal functioning by reviewing neuroimaging studies. The weight of the evidence was consistent with our hypothesis that antipsychotics with low dopaminergic receptor affinity and moderate to high serotonergic affinity were associated with higher activation of the prefrontal cortex. However, clozapine, a weak dopamine and strong serotonin antagonist, was associated with decrease in prefrontal activation. Future studies should further elucidate the link between prefrontal activation and negative symptoms using prospective designs and advanced neuroimaging techniques, which may ultimately benefit the development of treatments for disabling negative symptoms.

Modafinil reverses phencyclidine-induced deficits in cognitive flexibility, cerebral metabolism, and functional brain connectivity

OBJECTIVE

In the present study, we employ mathematical modeling (partial least squares regression, PLSR) to elucidate the functional connectivity signatures of discrete brain regions in order to identify the functional networks subserving PCP-induced disruption of distinct cognitive functions and their restoration by the procognitive drug modafinil.

METHODS

We examine the functional connectivity signatures of discrete brain regions that show overt alterations in metabolism, as measured by semiquantitative 2-deoxyglucose autoradiography, in an animal model (subchronic phencyclidine [PCP] treatment), which shows cognitive inflexibility with relevance to the cognitive deficits seen in schizophrenia.

RESULTS

We identify the specific components of functional connectivity that contribute to the rescue of this cognitive inflexibility and to the restoration of overt cerebral metabolism by modafinil. We demonstrate that modafinil reversed both the PCP-induced deficit in the ability to switch attentional set and the PCP-induced hypometabolism in the prefrontal (anterior prelimbic) and retrosplenial cortices. Furthermore, modafinil selectively enhanced metabolism in the medial prelimbic cortex. The functional connectivity signatures of these regions identified a unifying functional subsystem underlying the influence of modafinil on cerebral metabolism and cognitive flexibility that included the nucleus accumbens core and locus coeruleus. In addition, these functional connectivity signatures identified coupling events specific to each brain region, which relate to known anatomical connectivity.

CONCLUSIONS

These data support clinical evidence that modafinil may alleviate cognitive deficits in schizophrenia and also demonstrate the benefit of applying PLSR modeling to characterize functional brain networks in translational models relevant to central nervous system dysfunction.

Increased ratio of calcineurin immunoreactive neurons in the caudate nucleus of patients with schizophrenia

Calcineurin (CaN) has been investigated extensively in numerous biochemical, behavioral, and genetic studies in schizophrenia because its function is closely related to dopamine-glutamate signal transduction, which is thought to be associated with pathophysiological changes in schizophrenia. Although evidence has suggested that dysfunction of CaN may be a risk factor for schizophrenia, there have been few reports focusing on the expression of CaN mRNA and CaN protein levels in the brains of schizophrenic patients. In addition, findings on CaN expression in postmortem brains from patients with schizophrenia have been inconsistent. Here, we conducted immunohistochemical examinations of several regions in postmortem brains, including the dorsolateral prefrontal cortex (DLPFC), hippocampus, caudate nucleus, and putamen, using specific antibodies, and compared the results from the brains of nine schizophrenic subjects to nine age- and sex-matched control subjects. There was no significant difference in the ratio of CaN immunoreactive (IR) neurons between schizophrenia and control groups in the DLPFC or hippocampus, and a significantly increased ratio of CaN-IR neurons was seen in the caudate nucleus in the brains from schizophrenia patients. As the striatum contains most of the brain dopamine, the results of the present study have critical implications and suggest that alterations in CaN signaling in the caudate contribute to the pathogenesis of schizophrenia. This is the first report of caudate CaN abnormalities in schizophrenia.

New translational assays for preclinical modelling of cognition in schizophrenia: the touchscreen testing method for mice and rats

We describe a touchscreen method that satisfies a proposed 'wish-list' of desirables for a cognitive testing method for assessing rodent models of schizophrenia. A number of tests relevant to schizophrenia research are described which are currently being developed and validated using this method. These tests can be used to study reward learning, memory, perceptual discrimination, object-place associative learning, attention, impulsivity, compulsivity, extinction, simple Pavlovian conditioning, and other constructs. The tests can be deployed using a 'flexible battery' approach to establish a cognitive profile for a particular mouse or rat model. We have found these tests to be capable of detecting not just impairments in function, but enhancements as well, which is essential for testing putative cognitive therapies. New tests are being continuously developed, many of which may prove particularly valuable for schizophrenia research.

Neuroimaging of frontal-limbic dysfunction in schizophrenia and epilepsy-related psychosis: toward a convergent neurobiology

Psychosis is a devastating, prevalent condition considered to involve dysfunction of frontal and medial temporal limbic brain regions as key nodes in distributed brain networks involved in emotional regulation. The psychoses of epilepsy represent an important, though understudied, model relevant to understanding the pathophysiology of psychosis in general. In this review, we (1) discuss the classification of epilepsy-related psychoses and relevant neuroimaging and other studies; (2) review structural and functional neuroimaging studies of schizophrenia focusing on evidence of frontal-limbic dysfunction; (3) report our laboratory's PET, fMRI, and electrophysiological findings; (4) describe a theoretical framework in which frontal hypoactivity and intermittent medial temporal hyperactivity play a critical role in the etiopathology of psychosis both associated and unassociated with epilepsy; and (5) suggest avenues for future research.

Control of working memory content in schizophrenia

People with schizophrenia (PSZ) exhibit signs of reduced working memory (WM) capacity. However, this may reflect an impairment in managing its content, e.g. preventing irrelevant information from taking up available storage space, rather than a true capacity reduction. We tested the ability to eliminate and update WM content in 38 PSZ and 30 healthy control subjects (HCS). Images of real-world objects were presented consecutively, and a tone cued the item most likely to be tested for memory. On half the trials, randomly intermixed, a second tone occurred. Participants were informed that the item cued by the second tone was now the most likely to be tested, and the item cued by the first tone now the least likely, providing incentive to eliminate the first cued item from WM. Both HCS and PSZ displayed a robust performance advantage for cued items. Unexpectedly, PSZ more efficiently removed the no-longer-essential item from WM than HCS. The magnitude of the WM clearance of this first cued item correlated with memory performance for the newly prioritized second cued item in PSZ, indicating that it was adaptive. However, WM clearance was not associated with WM capacity, ruling out the need to budget limited resources as an explanation for greater clearance in PSZ. A robust correlation between WM clearance and poverty of speech in PSZ instead suggests that the propensity to rapidly clear non-essential information and minimize the number of items in WM may be the reflection of a negative symptom trait. This finding may reflect a more general tendency of PSZ to focus processing more narrowly than HCS.

Muscarinic agonists and antagonists in schizophrenia: recent therapeutic advances and future directions

Existing therapies for schizophrenia have limited efficacy, and significant residual positive, negative, and cognitive symptoms remain in many individuals with the disorder even after treatment with the current arsenal of antipsychotic drugs. Preclinical and clinical data suggest that selective activation of the muscarinic cholinergic system may represent novel therapeutic mechanisms for the treatment of schizophrenia. The therapeutic relevance of earlier muscarinic agonists was limited by their lack of receptor selectivity and adverse event profile arising from activation of nontarget muscarinic receptors. Recent advances in developing compounds that are selective to muscarinic receptor subtypes or activate allosteric receptor sites offer tremendous promise for therapeutic targeting of specific muscarinic receptor subtypes in schizophrenia.

Working memory and multidimensional schizotypy: dissociable influences of the different dimensions

Compromised working memory is considered a core deficit of schizophrenia and a potential endophenotype for the liability to develop schizophrenia. In keeping with this suggestion, working memory has also been found to be disrupted in people with high levels of schizotypy. However, it is unclear whether this disruption is linked to positive, negative, or disorganized symptoms/characteristics. This issue is the focus of the present investigation. The relationship between multidimensional schizotypy and working memory performance was investigated in 289 participants. Working memory was measured using an n-back task with three conditions; 0-back, 1-back, and 2-back. Covarying for the effect of shared variance between the schizotypy dimensions, we found reduced working memory performance in participants who displayed high levels of positive schizotypy and, to some extent, in participants with low levels of negative schizotypy. The results are discussed in terms of Baddeley's (1986) model of working memory and potential underlying neurological mechanisms.

BSMac: a MATLAB toolbox implementing a Bayesian spatial model for brain activation and connectivity

We present a statistical and graphical visualization MATLAB toolbox for the analysis of functional magnetic resonance imaging (fMRI) data, called the Bayesian Spatial Model for activation and connectivity (BSMac). BSMac simultaneously performs whole-brain activation analyses at the voxel and region of interest (ROI) levels as well as task-related functional connectivity (FC) analyses using a flexible Bayesian modeling framework (Bowman et al., 2008). BSMac allows for inputting data in either Analyze or Nifti file formats. The user provides information pertaining to subgroup memberships, scanning sessions, and experimental tasks (stimuli), from which the design matrix is constructed. BSMac then performs parameter estimation based on Markov Chain Monte Carlo (MCMC) methods and generates plots for activation and FC, such as interactive 2D maps of voxel and region-level task-related changes in neural activity and animated 3D graphics of the FC results. The toolbox can be downloaded from http://www.sph.emory.edu/bios/CBIS/. We illustrate the BSMac toolbox through an application to an fMRI study of working memory in patients with schizophrenia.

Genetic influence on the working memory circuitry: behavior, structure, function and extensions to illness

Working memory is a highly heritable complex cognitive trait that is critical for a number of higher-level functions. However, the neural substrates of this behavioral phenotype are intricate and it is unknown through what precise biological mechanism variation in working memory is transmitted. In this review we explore different functional and structural components of the working memory circuitry, and the degree to which each of them is contributed to by genetic factors. Specifically, we consider dopaminergic function, glutamatergic function, white matter integrity and gray matter structure all of which provide potential mechanisms for the inheritance of working memory deficits. In addition to discussing the overall heritability of these measures we also address specific genes that may play a role. Each of these heritable components has the potential to uniquely contribute to the working memory deficits observed in genetic disorders, including 22q deletion syndrome, fragile X syndrome, phenylketonuria (PKU), and schizophrenia. By observing the individual contributions of disruptions in different components of the working memory circuitry to behavioral performance, we highlight the concept that there may be many routes to a working memory deficit; even though the same cognitive measure may be a valid endophenotype across different disorders, the underlying cause of, and treatment for, the deficit may differ. This has implications for our understanding of the transmission of working memory deficits in both healthy and disordered populations.

Investigating the neural correlates of psychopathy: a critical review

In recent years, an increasing number of neuroimaging studies have sought to identify the brain anomalies associated with psychopathy. The results of such studies could have significant implications for the clinical and legal management of psychopaths, as well as for neurobiological models of human social behavior. In this article, we provide a critical review of structural and functional neuroimaging studies of psychopathy. In particular, we emphasize the considerable variability in results across studies, and focus our discussion on three methodological issues that could contribute to the observed heterogeneity in study data: (1) the use of between-group analyses (psychopaths vs non-psychopaths) as well as correlational analyses (normal variation in 'psychopathic' traits), (2) discrepancies in the criteria used to classify subjects as psychopaths and (3) consideration of psychopathic subtypes. The available evidence suggests that each of these issues could have a substantial effect on the reliability of imaging data. We propose several strategies for resolving these methodological issues in future studies, with the goal of fostering further progress in the identification of the neural correlates of psychopathy.

Mice lacking urea transporter UT-B display depression-like behavior

Urea transporter B is one of urea transporters that selectively transport urea driven by urea gradient across membrane and expressed abundantly in brain. To determine the physiological role of UT-B in brain, UT-B localization, urea concentration, tissue morphology of brain, and behavioral phenotypes were studied in UT-B heterozygous mice via UT-B null mice. UT-B mRNA was expressed in olfactory bulb, cortex, caudate nucleus, hippocampus and hypothalamus of UT-B heterozygous mice. UT-B null mice exhibited depression-like behavior, with urea accumulation, nitric oxide reduction, and selective neuronal nitric oxide synthase level increase in hippocampus. After acute urea loading, the urea level increased, NO production decreased in hippocampus from both types of mice. Moreover, urea level was higher, and NO concentration was lower consistently in UT-B null hippocampus than that in heterozygous hippocampus. In vitro, 25 mM urea inhibited NO production too. Furthermore, UT-B knockout induced a long-lasting notable decrease in regional cerebral blood flow and altered morphology, such as loss of neurons in CA3 region, swelling, and membranous myelin-like structure formation within myelinated and unmyelinated fibers in hippocampus. These results suggest that urea accumulation in the hippocampus induced by UT-B deletion can cause depression-like behavior, which possibly attribute to disturbance in NOS/NO system.

Sensory and motor encoding strategies in n-back tasks: a simulation of schizophrenic working memory deficits in healthy subjects

AIMS

Different patterns of intact and disturbed working memory function can be observed in schizophrenic patients depending on the type of n-back task. We investigated whether these patterns can be induced in healthy subjects by experimentally preventing a motor encoding strategy.

METHODS

Thirty-two healthy subjects were asked to solve 2 types of n-back task. In the continuous matching task, the subjects had to compare the present stimulus with the one occurring n stimuli back. In the continuous delayed response task (CDRT), the subjects had to select a response depending on the stimulus n stimuli back. Both types of n-back task are assumed to differ with respect to the encoding strategies that can be used to solve the tasks. The use of a motor strategy was prevented by a random arrangement of the target buttons.

RESULTS

When the position of the target buttons was predictable, CDRT was solved faster and with higher accuracy than the continuous matching task. However, CDRT was solved more slowly and less accurately when the arrangement of the target buttons varied between the trials. This resulted in a comparable performance in both types of the n-back task.

CONCLUSIONS

The behavioural alteration in schizophrenic patients in n-back tasks can be induced in healthy subjects by experimentally preventing the use of a motor encoding strategy.