Dysfunctional GABAergic inhibition in the prefrontal cortex leading to "psychotic" hyperactivation

Adamtsl3 mediates DCC signaling to selectively promote GABAergic synapse function

The molecular code that controls synapse formation and maintenance in vivo has remained quite sparse. Here, we identify that the secreted protein Adamtsl3 functions as critical hippocampal synapse organizer acting through the transmembrane receptor DCC (deleted in colorectal cancer). Traditionally, DCC function has been associated with glutamatergic synaptogenesis and plasticity in response to Netrin-1 signaling. We demonstrate that early post-natal deletion of Adamtsl3 in neurons impairs DCC protein expression, causing reduced density of both glutamatergic and GABAergic synapses. Adult deletion of Adamtsl3 in either GABAergic or glutamatergic neurons does not interfere with DCC-Netrin-1 function at glutamatergic synapses but controls DCC signaling at GABAergic synapses. The Adamtsl3-DCC signaling unit is further essential for activity-dependent adaptations at GABAergic synapses, involving DCC phosphorylation and Src kinase activation. These findings might be particularly relevant for schizophrenia because genetic variants in Adamtsl3 and DCC have been independently linked with schizophrenia in patients.

Analysis of networks in the dorsolateral prefrontal cortex in chronic schizophrenia: Relevance of altered immune response

The dorsolateral prefrontal cortex (DLPFC) has a crucial role in cognitive functioning and negative symptoms in schizophrenia. However, limited information of altered protein networks is available in this region in schizophrenia. We performed a proteomic analysis using single-shot liquid chromatography-tandem mass spectrometry of grey matter of postmortem DLPFC in chronic schizophrenia subjects (n = 20) and unaffected subjects (n = 20) followed by bioinformatic analysis to identify altered protein networks in schizophrenia (PXD024939 identifier in ProteomeXchange repository). Our results displayed a proteome profile in the DLPFC of 1989 proteins. 43 proteins were found significantly altered in schizophrenia. Analysis of this panel showed an enrichment of biological processes implicated in vesicle-mediated transport, processing and antigen presentation via MHC class II, intracellular transport and selenium metabolism. The enriched identified pathways were MHC class II antigen presentation, vesicle-mediated transport, Golgi ER retrograde transport, Nef mediated CD8 downregulation and the immune system. All these enriched categories were found to be downregulated. Furthermore, our network analyses showed crosstalk between proteins involved in MHC class II antigen presentation, membrane trafficking, Golgi-to-ER retrograde transport, Nef-mediated CD8 downregulation and the immune system with only one module built by 13 proteins. RAB7A showed eight interactions with proteins of all these pathways. Our results provide an altered molecular network involved in immune response in the DLPFC in schizophrenia with a central role of RAB7A. These results suggest that RAB7A or other proteins of this network could be potential targets for novel pharmacological strategies in schizophrenia for improving cognitive and negative symptoms.

Cortical control of chandelier cells in neural codes

Various cortical functions arise from the dynamic interplay of excitation and inhibition. GABAergic interneurons that mediate synaptic inhibition display significant diversity in cell morphology, electrophysiology, plasticity rule, and connectivity. These heterogeneous features are thought to underlie their functional diversity. Emerging attention on specific properties of the various interneuron types has emphasized the crucial role of cell-type specific inhibition in cortical neural processing. However, knowledge is still limited on how each interneuron type forms distinct neural circuits and regulates network activity in health and disease. To dissect interneuron heterogeneity at single cell-type precision, we focus on the chandelier cell (ChC), one of the most distinctive GABAergic interneuron types that exclusively innervate the axon initial segments (AIS) of excitatory pyramidal neurons. Here we review the current understanding of the structural and functional properties of ChCs and their implications in behavioral functions, network activity, and psychiatric disorders. These findings provide insights into the distinctive roles of various single-type interneurons in cortical neural coding and the pathophysiology of cortical dysfunction.

Adolescent thalamic inhibition leads to long-lasting impairments in prefrontal cortex function

Impaired cortical maturation is a postulated mechanism in the etiology of neurodevelopmental disorders, including schizophrenia. In the sensory cortex, activity relayed by the thalamus during a postnatal sensitive period is essential for proper cortical maturation. Whether thalamic activity also shapes prefrontal cortical maturation is unknown. We show that inhibiting the mediodorsal and midline thalamus in mice during adolescence leads to a long-lasting decrease in thalamo-prefrontal projection density and reduced excitatory drive to prefrontal neurons. It also caused prefrontal-dependent cognitive deficits during adulthood associated with disrupted prefrontal cross-correlations and task outcome encoding. Thalamic inhibition during adulthood had no long-lasting consequences. Exciting the thalamus in adulthood during a cognitive task rescued prefrontal cross-correlations, task outcome encoding and cognitive deficits. These data point to adolescence as a sensitive window of thalamocortical circuit maturation. Furthermore, by supporting prefrontal network activity, boosting thalamic activity provides a potential therapeutic strategy for rescuing cognitive deficits in neurodevelopmental disorders.

Parvalbumin Role in Epilepsy and Psychiatric Comorbidities: From Mechanism to Intervention

Parvalbumin is a calcium-binding protein present in inhibitory interneurons that play an essential role in regulating many physiological processes, such as intracellular signaling and synaptic transmission. Changes in parvalbumin expression are deeply related to epilepsy, which is considered one of the most disabling neuropathologies. Epilepsy is a complex multi-factor group of disorders characterized by periods of hypersynchronous activity and hyperexcitability within brain networks. In this scenario, inhibitory neurotransmission dysfunction in modulating excitatory transmission related to the loss of subsets of parvalbumin-expressing inhibitory interneuron may have a prominent role in disrupted excitability. Some studies also reported that parvalbumin-positive interneurons altered function might contribute to psychiatric comorbidities associated with epilepsy, such as depression, anxiety, and psychosis. Understanding the epileptogenic process and comorbidities associated with epilepsy have significantly advanced through preclinical and clinical investigation. In this review, evidence from parvalbumin altered function in epilepsy and associated psychiatric comorbidities were explored with a translational perspective. Some advances in potential therapeutic interventions are highlighted, from current antiepileptic and neuroprotective drugs to cutting edge modulation of parvalbumin subpopulations using optogenetics, designer receptors exclusively activated by designer drugs (DREADD) techniques, transcranial magnetic stimulation, genome engineering, and cell grafting. Creating new perspectives on mechanisms and therapeutic strategies is valuable for understanding the pathophysiology of epilepsy and its psychiatric comorbidities and improving efficiency in clinical intervention.

Calorie restriction improves aging-induced impairment of cognitive function in relation to deregulation of corticosterone status and brain regional GABA system

Aging is known to affect adversely the corticosterone status and the brain function including cognition. Calorie restricted (CR) diet has been found to improve brain aging. The objective of the present investigation is to study the effect of short-term CR diet without any food deprivation on aging-induced impairment of cognitive function in relation to the corticosterone status and the brain regional GABA system. The result showed that aging-induced deregulation of the brain regional GABA system, increase in plasma and adrenal corticosterone levels and cognitive impairment were attenuated with short-term CR diet supplementation for consecutive 1 and 2 months to the aged (18 and 24 months) rats. But in young rats (4 months) consumption of the same CR diet under similar conditions reversibly affected those above-mentioned parameters. These results, thus suggest that (a) aging down-regulates brain regional GABA system with an up-regulation of corticosterone status and impairment of cognitive function, (b) CR diet consumption improves this aging-induced deregulation of brain regional GABA system, corticosterone status, and cognitive function, (c) these attenuating effects of CR diet are greater with a longer period of consumption but (d) CR diet consumption is harmful to young rats as observed in those parameters.

Going Back to Kahlbaum's Psychomotor (and GABAergic) Origins: Is Catatonia More Than Just a Motor and Dopaminergic Syndrome?

In 1874, Karl Kahlbaum described catatonia as an independent syndrome characterized by motor, affective, and behavioral anomalies. In the following years, various catatonia concepts were established with all sharing the prime focus on motor and behavioral symptoms while largely neglecting affective changes. In 21st century, catatonia is a well-characterized clinical syndrome. Yet, its neurobiological origin is still not clear because methodological shortcomings of hitherto studies had hampered this challenging effort. To fully capture the clinical picture of catatonia as emphasized by Karl Kahlbaum, 2 decades ago a new catatonia scale was developed (Northoff Catatonia Rating Scale [NCRS]). Since then, studies have used NCRS to allow for a more mechanistic insight of catatonia. Here, we undertook a systematic review searching for neuroimaging studies using motor/behavioral catatonia rating scales/criteria and NCRS published up to March 31, 2019. We included 19 neuroimaging studies. Studies using motor/behavioral catatonia rating scales/criteria depict cortical and subcortical motor regions mediated by dopamine as neuronal and biochemical substrates of catatonia. In contrast, studies relying on NCRS found rather aberrant higher-order frontoparietal networks which, biochemically, are insufficiently modulated by gamma-aminobutyric acid (GABA)-ergic and glutamatergic transmission. This is further supported by the high therapeutic efficacy of GABAergic agents in acute catatonia. In sum, this systematic review points out the difference between motor/behavioral and NCRS-based classification of catatonia on both neuronal and biochemical grounds. That highlights the importance of Kahlbaum's original truly psychomotor concept of catatonia for guiding both research and clinical diagnosis and therapy.

How obsessive-compulsive and bipolar disorders meet each other? An integrative gene-based enrichment approach

BACKGROUND

The novel approaches to psychiatric classification assume that disorders, contrary to what was previously thought, are not completely separate phenomena. In this regard, in addition to symptom-based criteria, disturbances are also considered on the basis of lower level components. With this viewpoint, identifying common biochemical markers would be beneficial in adopting a comprehensive strategy for prevention, diagnosis and treatment.

MAIN BODY

One of the problematic areas in clinical settings is the coexistence of both obsessive-compulsive disorder (OCD) and bipolar disorder (BD) that is challenging and difficult to manage. In this study, using a system biologic approach we aimed to assess the interconnectedness of OCD and BD at different levels. Gene Set Enrichment Analysis (GSEA) method was used to identify the shared biological network between the two disorders. The results of the analysis revealed 34 common genes between the two disorders, the most important of which were CACNA1C, GRIA1, DRD2, NOS1, SLC18A1, HTR2A and DRD1. Dopaminergic synapse and cAMP signaling pathway as the pathways, dopamine binding and dopamine neurotransmitter receptor activity as the molecular functions, dendrite and axon part as the cellular component and cortex and striatum as the brain regions were the most significant commonalities.

SHORT CONCLUSION

The results of this study highlight the role of multiple systems, especially the dopaminergic system in linking OCD and BD. The results can be used to estimate the disease course, prognosis, and treatment choice, particularly in the cases of comorbidity. Such perspectives, going beyond symptomatic level, help to identify common endophenotypes between the disorders and provide diagnostic and therapeutic approaches based on biological in addition to the symptomatic level.

Biophysical Psychiatry-How Computational Neuroscience Can Help to Understand the Complex Mechanisms of Mental Disorders

The brain is the most complex of human organs, and the pathophysiology underlying abnormal brain function in psychiatric disorders is largely unknown. Despite the rapid development of diagnostic tools and treatments in most areas of medicine, our understanding of mental disorders and their treatment has made limited progress during the last decades. While recent advances in genetics and neuroscience have a large potential, the complexity and multidimensionality of the brain processes hinder the discovery of disease mechanisms that would link genetic findings to clinical symptoms and behavior. This applies also to schizophrenia, for which genome-wide association studies have identified a large number of genetic risk loci, spanning hundreds of genes with diverse functionalities. Importantly, the multitude of the associated variants and their prevalence in the healthy population limit the potential of a reductionist functional genetics approach as a stand-alone solution to discover the disease pathology. In this review, we outline the key concepts of a "biophysical psychiatry," an approach that employs large-scale mechanistic, biophysics-founded computational modelling to increase transdisciplinary understanding of the pathophysiology and strive toward robust predictions. We discuss recent scientific advances that allow a synthesis of previously disparate fields of psychiatry, neurophysiology, functional genomics, and computational modelling to tackle open questions regarding the pathophysiology of heritable mental disorders. We argue that the complexity of the increasing amount of genetic data exceeds the capabilities of classical experimental assays and requires computational approaches. Biophysical psychiatry, based on modelling diseased brain networks using existing and future knowledge of basic genetic, biochemical, and functional properties on a single neuron to a microcircuit level, may allow a leap forward in deriving interpretable biomarkers and move the field toward novel treatment options.

Characterizing amino-acid biosignatures amongst individuals with schizophrenia: a case-control study

Amino acids and derivatives participate in the biosynthesis and downstream effects of numerous neurotransmitters. Variations in specific amino acids have been implicated in the pathophysiology of schizophrenia. Herein, we sought to compare levels of amino acids and derivatives between subjects with schizophrenia and healthy controls (HC). Two hundred and eight subjects with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria (DSM-IV)-defined schizophrenia and 175 age- and sex-matched HC were enrolled. The levels of twenty-five amino acids and seven related derivatives were measured in plasma samples using hydrophilic interaction liquid chromatography (HILIC) liquid chromatography-tandem mass spectrometry (LC-MS). After controlling for age, sex and body mass index (BMI), four amino acids and derivatives (i.e., cysteine, GABA, glutamine and sarcosine) were observed to be higher in the schizophrenia group when compared with HC; seven amino acids and derivatives were lower in the schizophrenia group (i.e., arginine, L-ornithine, threonine, taurine, tryptophan, methylcysteine, and kynurenine). Statistically significant differences in plasma amino-acid profiles between subjects with first-episode vs. recurrent schizophrenia for aspartate and glutamine were also demonstrated using generalized linear models controlling for age, sex, and BMI. The differences in amino acids and derivatives among individuals with schizophrenia when compared to HC may represent underlying pathophysiology, including but not limited to dysfunctional proteinogenic processes, alterations in excitatory and inhibitory neurotransmission, changes in ammonia metabolism and the urea cycle. Taken together, amino-acid profiling may provide a novel stratification approach among individuals with schizophrenia.

Investigating the neurobiology of schizophrenia and other major psychiatric disorders with Transcranial Magnetic Stimulation

Characterizing the neurobiology of schizophrenia and other major psychiatric disorders is one of the main challenges of the current research in psychiatry. The availability of Transcranial Magnetic Stimulation (TMS) allows to directly probe virtually any cortical areas, thus providing a unique way to assess the neurophysiological properties of cortical neurons. This article presents a review of studies employing TMS in combination with Motor Evoked Potentials (TMS/MEPs) and high density Electroencephalogram (TMS/hd-EEG) in schizophrenia and other major psychiatric disorders. Studies were identified by conducting a PubMed search using the following search item: "transcranial magnetic stimulation and (Schizophrenia or OCD or MDD or ADHD)". Studies that utilized TMS/MEP and/or TMS/hd-EEG measures to characterize cortical excitability, inhibition, oscillatory activity, and/or connectivity in psychiatric patients were selected. Across disorders, patients displayed a pattern of reduced cortical inhibition, and to a lesser extent increased excitability, in the motor cortex, which was most consistently established in Schizophrenia. Furthermore, psychiatric patients showed abnormalities in a number of TMS-evoked EEG oscillations, which was most prominent in the prefrontal cortex of Schizophrenia relative to healthy comparison subjects. Overall, results from this review point to significant impairments in cortical excitability, inhibition, and oscillatory activity, especially in frontal areas, in several major psychiatric disorders. Building on these findings, future studies employing TMS-based experimental paradigms may help elucidating the neurobiology of these psychiatric disorders, and may assess the contribution of TMS-related measures in monitoring and possibly maximizing the effectiveness of treatment interventions in psychiatric populations.

Comprehensive review: Computational modelling of schizophrenia

Computational modelling has been used to address: (1) the variety of symptoms observed in schizophrenia using abstract models of behavior (e.g. Bayesian models - top-down descriptive models of psychopathology); (2) the causes of these symptoms using biologically realistic models involving abnormal neuromodulation and/or receptor imbalance (e.g. connectionist and neural networks - bottom-up realistic models of neural processes). These different levels of analysis have been used to answer different questions (i.e. understanding behavioral vs. neurobiological anomalies) about the nature of the disorder. As such, these computational studies have mostly supported diverging hypotheses of schizophrenia's pathophysiology, resulting in a literature that is not always expanding coherently. Some of these hypotheses are however ripe for revision using novel empirical evidence. Here we present a review that first synthesizes the literature of computational modelling for schizophrenia and psychotic symptoms into categories supporting the dopamine, glutamate, GABA, dysconnection and Bayesian inference hypotheses respectively. Secondly, we compare model predictions against the accumulated empirical evidence and finally we identify specific hypotheses that have been left relatively under-investigated.

Reduced natural oscillatory frequency of frontal thalamocortical circuits in schizophrenia

CONTEXT

Converging evidence from electrophysiological studies suggests that in individuals with schizophrenia, electroencephalographic frontal fast oscillations are reduced. It is still unclear whether this reduction reflects an intrinsic deficit of underlying cortical/thalamocortical circuits and whether this deficit is specific for frontal regions. Recent electrophysiological studies in healthy individuals have established that, when perturbed, different brain regions oscillate at a specific, intrinsically generated dominant frequency, the natural frequency.

OBJECTIVE

To assess the natural frequency of the posterior parietal, motor, premotor, and prefrontal cortices in patients with schizophrenia and healthy control subjects.

DESIGN

High-density electroencephalographic recordings during transcranial magnetic stimulation of 4 cortical areas were performed. Several transcranial magnetic stimulation–evoked electroencephalographic oscillation parameters, including synchronization, amplitude, and natural frequency, were compared across the schizophrenia and healthy control groups.

SETTING

Wisconsin Psychiatric Institute and Clinic, University of Wisconsin–Madison.

PARTICIPANTS

Twenty patients with schizophrenia and 20 age-matched healthy control subjects.

MAIN OUTCOME MEASURES

High-density electroencephalographic measurements of transcranial magnetic stimulation–evoked activity in 4 cortical areas, scores on the Positive and Negative Syndrome Scale, and performance scores (reaction time, accuracy) on 2 computerized tasks (word memory [Penn Word Recognition Test] and facial memory [Penn Facial Memory Test]).

RESULTS

Patients with schizophrenia showed a slowing in the natural frequency of the frontal/prefrontal regions compared with healthy control subjects (from an average of a 2-Hz decrease for the motor area to an almost 10-Hz decrease for the prefrontal cortex). The prefrontal natural frequency of individuals with schizophrenia was slower than in any healthy comparison subject and correlated with both positive Positive and Negative Syndrome Scale scores and reaction time on the Penn Word Recognition Test.

CONCLUSIONS

These findings suggest that patients with schizophrenia have an intrinsic slowing in the natural frequency of frontal cortical/thalamocortical circuits, that this slowing is not present in parietal areas, and that the prefrontal natural frequency can predict some of the symptoms as well as the cognitive dysfunctions of schizophrenia.

Sustained versus transient brain responses in schizophrenia: the role of intrinsic neural activity

Schizophrenia patients (SZ) show early visual processing deficits in many, but not all, tasks. These deficits may be associated with dysregulation of intrinsic oscillatory activity that compromises signal-to-noise in the SZ brain. This question was studied using visual steady-state stimulation and post-steady-state presentation of transient visual stimuli. SZ had higher intrinsic oscillatory activity at the steady-state stimulation frequency (12.5 Hz) and at the 6.25 Hz subharmonic, showed a significant decrease in visual steady-state magnitude over 2s of stimulation, and were unable to promptly terminate the steady-state response following stimulation offset. If adjustment for levels of intrinsic brain activity were made, however, it would have appeared that SZ had activity of similar magnitude as healthy subjects following steady-state stimulus termination, indicating that such adjustments could substantially alter theoretical interpretations. Visual evoked potential abnormalities (N1/P2 amplitudes) present among SZ at the initiation of steady-state stimulation were less apparent in the 750 ms immediately following steady-state stimulation offset. Higher intrinsic oscillatory brain activity may be a fundamental characteristic of SZ that merits further evaluation for understanding this disorder's neuropathological correlates and associated symptomatology.

Neurocognitive performance, alcohol withdrawal, and effects of a combination of flumazenil and gabapentin in alcohol dependence

BACKGROUND

Among some alcohol-dependent individuals, early alcohol abstinence is marked by alcohol withdrawal (AW), a phenomenon mediated by GABA and glutamate signaling. We previously reported that a combination of 2 medications that affect GABA and glutamate tone, gabapentin and flumazenil, more effectively reduced drinking among individuals with higher pretreatment AW (Anton et al., 2009). This study evaluated whether this finding is related to changes in neurocognitive performance, which is also affected by cortical GABA and glutamate tone.

METHODS

Neurocognitive performance was assessed at baseline and twice during the first week of treatment among 60 alcohol-dependent participants in the previously published clinical trial.

RESULTS

AW was associated with poorer baseline performance on 4 of 8 measures, and individuals with higher baseline AW who received the gabapentin and flumazenil combination demonstrated greater improvement on a measure of response inhibition than those with lower AW or those who received a combination of placebos. Improvement in response inhibition during the first week and medication group interacted in their effect on subsequent drinking, such that improvement predicted greater abstinence only among individuals who received gabapentin and flumazenil. Improvement on other neurocognitive measures was neither differentially impacted by medication or baseline AW nor related to subsequent drinking.

CONCLUSIONS

Taken together, these data suggest that acute AW accounts for a small proportion of variance in neurocognitive performance, that gabapentin and flumazenil slightly improve response inhibition during early abstinence, and that such improvement may somewhat reduce later drinking. However, these medications may not affect other neurocognitive domains.

Critical examination of a correlation between brain gamma-aminobutyric acid (GABA) concentrations and a personality trait of extroversion in healthy volunteers as measured by a 3 Tesla proton magnetic resonance spectroscopy study

We hypothesized that brain gamma-aminobutyric acid (GABA) levels are associated with neuroticism, a trait associated with depression and anxiety disorders. We examined the correlation between brain GABA concentrations and the five factors included in the NEO Five-Factor Inventory (NEO-FFI) in healthy volunteers using magnetic resonance spectroscopy (MRS) at 3 T. Forty-one healthy subjects (21 males, 20 females; age: 35+/-7 years) were enrolled in this study. Each subject underwent a 3T 1H-MRS study with a MEGA-PRESS sequence. Spectroscopy voxels (3 cm x 3 cm x 3 cm) were placed in the frontal lobe and the parieto-occipital lobe. A negative correlation was found between the GABA/creatine ratios in the frontal lobe and scores of extroversion on the NEO-FFI. These results suggest that GABAergic neurons are related to personality traits of healthy subjects.

Association study of the gamma-aminobutyric acid type a receptor gamma2 subunit gene with schizophrenia

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with a strong genetic basis. We analyzed eight GABRG2 and one DRD5 tag single-nucleotide polymorphisms for association with SCZ in 109 small nuclear families and 229 independent SCZ case-control pairs. The marker rs183294 in the 5' region of GABRG2 was found to be associated with SCZ in both samples with the C allele over-represented in SCZ cases and over-transmitted in SCZ families (combined z=9.18; p<1 x 10(-3)). Taken together, the results of the present study suggest that GABRG2 may be involved in SCZ susceptibility, but further studies are required.

Prefrontal GABA(B) receptor activation attenuates phencyclidine-induced impairments of prepulse inhibition: involvement of nitric oxide

Recent theories propose that both GABA and glutamate signaling are compromised in patients with schizophrenia. These deficits can be observed in several brain regions including the prefrontal cortex (PFC), an area extensively linked to the cognitive dysfunction in this disease and notably affected by NMDA receptor antagonists such as phencyclidine (PCP). We have previously demonstrated that inhibition of the nitric oxide (NO) pathways in the brain, particularly in the PFC, prevents a wide range of PCP-induced behavioral deficits including disruption of prepulse inhibition (PPI). This study investigated the role of GABA(B) receptor signaling and NO in the effects of PCP on PPI. Mice received systemic or prefrontal injections of the GABA(B) receptor agonist baclofen (2.5-5 mg/kg and 1 mM) before PCP treatment (5 mg/kg) and were thereafter tested for PPI. GABA/NO interactions were studied by combining baclofen and the NO synthase inhibitor L-NAME (20 mg/kg) in subthreshold doses. The role of GABA(B) receptors for NO production in vivo was assessed using NO-sensors implanted into the rat PFC. PCP-induced PPI deficits were attenuated in an additive manner by systemic baclofen treatment, whereas prefrontal microinjections of baclofen completely blocked the effects of PCP, without affecting PPI per se. The combination of baclofen and L-NAME was more effective in preventing the effects of PCP than any compound by itself. Additionally, baclofen decreased NO release in the PFC in a dose-related manner. This study proposes a role for GABA(B) receptor signaling in the effects of PCP, with altered NO levels as a downstream consequence. Thus, prefrontal NO signaling mirrors an altered level of cortical inhibition that may be of importance for information processing deficits in schizophrenia.