Progressive and interrelated functional and structural evidence of post-onset brain reduction in schizophrenia

Future clinical uses of neurophysiological biomarkers to predict and monitor treatment response for schizophrenia

Advances in psychiatric neuroscience have transformed our understanding of impaired and spared brain functions in psychotic illnesses. Despite substantial progress, few (if any) laboratory tests have graduated to clinics to inform diagnoses, guide treatments, and monitor treatment response. Providers must rely on careful behavioral observation and interview techniques to make inferences about patients' inner experiences and then secondary deductions about impacted neural systems. Development of more effective treatments has also been hindered by a lack of translational quantitative biomarkers that can span the brain-behavior treatment knowledge gap. Here, we describe an example of a simple, low-cost, and translatable electroencephalography (EEG) measure that offers promise for improving our understanding and treatment of psychotic illnesses: mismatch negativity (MMN). MMN is sensitive to and/or predicts response to some pharmacologic and nonpharmacologic interventions and accounts for substantial portions of variance in clinical, cognitive, and psychosocial functioning in schizophrenia (SZ). This measure has recently been validated for use in large-scale multisite clinical studies of SZ. Finally, MMN greatly improves our ability to forecast which individuals at high clinical risk actually develop a psychotic illness. These attributes suggest that MMN can contribute to personalized biomarker-guided treatment strategies aimed at ameliorating or even preventing the onset of psychosis.

Progressive reduction of visual P300 amplitude in patients with first-episode schizophrenia: an ERP study

OBJECTIVE

To understand the underlying dynamic neurophysiological changes over the course of schizophrenia, it is important to study subjects longitudinally from the early stage of the illness. We previously reported that visual P300 was already impaired in patients with first-episode schizophrenia (FESZ). This study demonstrates how the visual P300, as well as earlier components P1, N1, and N200, changed at the 1-year follow-up after their initial measurement.

METHODS

Visual ERPs were recorded with the same experimental paradigm and acquisition protocol at both time points in FESZ (n = 18) and healthy comparison subjects (n = 24). Participants silently counted infrequent target stimuli ("x") amid standard stimuli ("y") presented on the screen while the 64-channel electroencephalogram was recorded.

RESULTS

FESZ showed smaller visual P300, N200, P1 (trend level) amplitude and delayed P300 and N1 latency at both time points; however, only P300 showed progressive amplitude reduction over the course of the illness at 1-year follow-up. P300 latency did not change over time in either group. FESZ showed significantly reduced Spatial Span total score at both time points, and there was a significant negative correlation between P300 peak amplitude and the Brief Psychiatric Rating Scale positive symptom score at baseline.

CONCLUSION

These data show progressive P300 amplitude reduction in response to visual stimuli in the early stage of schizophrenia. These visual P300 findings support the concept of progression of schizophrenia, suggesting the usefulness of the visual P300 as a biological marker of progression.

Abnormal immune system development and function in schizophrenia helps reconcile diverse findings and suggests new treatment and prevention strategies

Extensive research implicates disturbed immune function and development in the etiology and pathology of schizophrenia. In addition to reviewing evidence for immunological factors in schizophrenia, this paper discusses how an emerging model of atypical immune function and development helps explain a wide variety of well-established - but puzzling - findings about schizophrenia. A number of theorists have presented hypotheses that early immune system programming, disrupted by pre- and perinatal adversity, often combines with abnormal brain development to produce schizophrenia. The present paper focuses on the hypothesis that disruption of early immune system development produces a latent immune vulnerability that manifests more fully after puberty, when changes in immune function and the thymus leave individuals more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Complementing neurodevelopmental models, this hypothesis integrates findings on many contributing factors to schizophrenia, including prenatal adversity, genes, climate, migration, infections, and stress, among others. It helps explain, for example, why (a) schizophrenia onset is typically delayed until years after prenatal adversity, (b) individual risk factors alone often do not lead to schizophrenia, and (c) schizophrenia prevalence rates actually tend to be higher in economically advantaged countries. Here we discuss how the hypothesis explains 10 key findings, and suggests new, potentially highly cost-effective, strategies for treatment and prevention of schizophrenia. Moreover, while most human research linking immune factors to schizophrenia has been correlational, these strategies provide ethical ways to experimentally test in humans theories about immune function and schizophrenia. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Neurophysiological models for new treatment development in schizophrenia: early sensory approaches

Schizophrenia is a major mental disorder associated with core neurocognitive impairments. The ability to recreate these deficits in animal models is limited, hampering ongoing translational drug development efforts. This paper reviews the use of electroencephalography (EEG)-based neurophysiological measures, such as event-related potentials (ERPs) or event-related spectral perturbations (ERSPs), as novel translational biomarkers for both etiological and treatment development research in neuropsychiatry. In schizophrenia, cognitive impairments manifest as deficits not only in high-level processes, such as working memory or executive processing, but also as deficits in neurophysiological responses to simple auditory and visual stimuli. Moreover, neurophysiological responses can be assessed even in untrained animals and are therefore particularly amenable to translational, cross-species investigation. To date, several sensory-level ERP measures, including auditory mismatch negativity and N1, and visual P1 and steady-state responses, have been validated in both human clinical investigations and animal models. Deficits have been tied to impaired neurotransmission at N-methyl-d-aspartate-type glutamate receptors (NMDARs). Time-frequency analysis of ERSP permits further extension of these findings from physiological to circuit/cellular levels of analysis.

Detection of cognitive impairment in patients with obstructive sleep apnea hypopnea syndrome using mismatch negativity

In this experiment, 97 patients with obstructive sleep apnea hypopnea syndrome were divided into three groups (mild, moderate, severe) according to minimum oxygen saturation, and 35 healthy subjects were examined as controls. Cognitive function was determined using the mismatch negativity paradigm and the Montreal Cognitive Assessment. The results revealed that as the disease worsened, the mismatch negativity latency was gradually extended, and the amplitude gradually declined in patients with obstructive sleep apnea hypopnea syndrome. Importantly, mismatch negativity latency in severe patients with a persistent time of minimum oxygen saturation < 60 seconds was significantly shorter than that with a persistent time of minimum oxygen saturation > 60 seconds. Correlation analysis revealed a negative correlation between minimum oxygen saturation latency and Montreal Cognitive Assessment scores. These findings indicate that intermittent night-time hypoxemia affects mismatch negativity waveforms and Montreal Cognitive Assessment scores. As indicators for detecting the cognitive functional status of obstructive sleep apnea hypopnea syndrome patients, the sensitivity of mismatch negativity is 82.93%, the specificity is 73.33%, the accuracy rate is 81.52%, the positive predictive value is 85.00%, the negative predictive value is 70.21%, the positive likelihood ratio is 3, and the negative likelihood ratio is 0.23. These results indicate that mismatch negativity can be used as an effective tool for diagnosis of cognitive dysfunction in obstructive sleep apnea hypopnea syndrome patients.

Equivalent mismatch negativity deficits across deviant types in early illness schizophrenia-spectrum patients

Neurophysiological abnormalities in auditory deviance processing, as reflected by the mismatch negativity (MMN), have been observed across the course of schizophrenia. Studies in early schizophrenia patients have typically shown varying degrees of MMN amplitude reduction for different deviant types, suggesting that different auditory deviants are uniquely processed and may be differentially affected by duration of illness. To explore this further, we examined the MMN response to 4 auditory deviants (duration, frequency, duration+frequency "double deviant", and intensity) in 24 schizophrenia-spectrum patients early in the illness (ESZ) and 21 healthy controls. ESZ showed significantly reduced MMN relative to healthy controls for all deviant types (p<0.05), with no significant interaction with deviant type. No correlations with clinical symptoms were present (all ps>0.05). These findings support the conclusion that neurophysiological mechanisms underlying processing of auditory deviants are compromised early in illness, and these deficiencies are not specific to the type of deviant presented.

Mismatch negativity (MMN) deficiency: a break-through biomarker in predicting psychosis onset

Currently, the mismatch negativity (MMN) deficit is one of the most robust and replicable findings in schizophrenia, reflecting cognitive and functional decline, psychosocial and socio-occupational impairment, and executive dysfunction in these patients. An important break-through has very recently taken place here in the prediction of conversion to psychosis when the MMN in particular to change in tone duration was recorded in clinically at risk-mental state (ARMS) individuals. Attenuations in the MMN in these patients may be very useful in helping clinicians determine who are most likely to develop a psychotic disorder, as we will review in the present article.

Sensory processing dysfunction in the personal experience and neuronal machinery of schizophrenia

Sensory processing deficits, first investigated by Kraepelin and Bleuler as possible pathophysiological mechanisms in schizophrenia, are now being recharacterized in the context of our current understanding of the molecular and neurobiological brain mechanisms involved. The National Institute of Mental Health Research Domain Criteria position these deficits as intermediaries between molecular and cellular mechanisms and clinical symptoms of schizophrenia, such as hallucinations. The prepulse inhibition of startle responses by a weaker preceding tone, the inhibitory gating of response to paired sensory stimuli characterized using the auditory P50 evoked response, and the detection of slight deviations in patterns of sensory stimulation eliciting the cortical mismatch negativity potential demonstrate deficits in early sensory processing mechanisms, whose molecular and neurobiological bases are increasingly well understood. Deficits in sensory processing underlie more complex cognitive dysfunction and are in turn affected by higher-level cognitive difficulties. These deficits are now being used to identify genes involved in familial transmission of schizophrenia and to monitor potentially therapeutic drug effects for both treatment and prevention. This research also provides a clinical reminder that patients' sensory perception of the surrounding world, even during treatment sessions, may differ considerably from others' perceptions. A person's ability to understand and interact effectively with the surrounding world ultimately depends on an underlying sensory experience of it.

Frontal lobe function and social adjustment in patients with schizophrenia: near-infrared spectroscopy

OBJECTIVE

The study evaluated relationships between frontal lobe function in patients with schizophrenia and both their social adjustment and medication, using 22-channel near-infrared spectroscopy (NIRS).

METHODS

One hundred ninety-nine stable patients with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision schizophrenia, whose medication had not been changed within the preceding 3 months and who were able to visit our clinics for NIRS, were the study subjects. As a comparator, 144 healthy volunteers who underwent a physical examination and the Mini-International Neuropsychiatric Interview also received NIRS.

RESULTS

The main outcomes evaluated were frontal lobe oxyhemoglobin concentration (OxHb) measured by NIRS, current medication, social adjustment, and scores on the Brief Psychiatric Rating Scale. The OxHb in schizophrenic patients (0.878 ± 1.1801 mM mm; n = 199) was significantly lower than that in the healthy volunteers (2.085 ± 1.7480 mM mm: n = 100) (p < 0.001). NIRS-measured OxHb values reflected disease severity and degree of social adjustment in schizophrenic patients.

CONCLUSIONS

Patients with higher OxHb values were socially better adjusted than those with lower OxHb values. Patients treated with atypical antipsychotic monotherapy showed lower treatment resistance and better social adjustment than those treated with combination therapy.

Differential Alterations of Auditory Gamma Oscillatory Responses Between Pre-Onset High-Risk Individuals and First-Episode Schizophrenia

Alterations in gamma-band auditory steady-state response (ASSR) are the most robust finding of abnormal neural oscillations in patients with first-episode (FES) and chronic schizophrenia. Gamma-band ASSRs may indicate GABAergic interneuron dysfunction. Nevertheless, it is unknown whether abnormal gamma-band ASSRs are present before the onset of psychosis. Subjects were 15 ultra-high-risk (UHR) individuals, 13 FES patients, and 21 healthy control (HC) subjects. We performed electroencephalogram recordings and measured ASSRs in each group as they were presented with click trains at 20, 30, and 40 Hz. We then conducted time-frequency analyses and calculated intertrial phase coherence and event-related spectral perturbation. The time course of gamma-band ASSRs showed significantly different features among groups. Compared with the HC group, the UHR group was characterized by intact early-latency (0-100 ms) and reduced late-latency (300-500 ms) ASSRs. In contrast, both early- and late-latency ASSRs were significantly reduced in the FES group. Gamma-band ASSRs were correlated with clinical symptoms and attentional functioning in FES (|rs| > 0.70). These results suggest differential alterations of gamma-band ASSRs between UHR and FES groups. The late-latency ASSR alteration may represent a biomarker for early detection of psychosis, while the early-latency ASSR abnormality may develop through the onset of psychosis.

Anterior cingulate abnormality as a neural correlate of mismatch negativity in schizophrenia

BACKGROUND

Limbic circuitry, especially the anterior cingulate gyrus, has been implicated in the pathophysiology and cognitive changes of schizophrenia. Previous diffusion tensor imaging studies have demonstrated that the integrity of the anterior cingulum (AC) is abnormal in schizophrenia. However, the relationship between the abnormal AC tract integrity and the pathophysiology of schizophrenia has not been fully studied.

METHODS

We performed a voxelwise group comparison of white matter fractional anisotropy (FA) by using tract-based spatial statistics in 9 patients with schizophrenia and 9 matched controls. We then measured FA specifically in the AC by using a tract-specific measurement. The latency and amplitude of the mismatch negativity (MMN) were also evaluated in all subjects.

RESULTS

In patients with schizophrenia, tract-based spatial statistics showed a reduction in FA in broad white matter areas, including the bilateral AC, compared with controls. Tract-specific measurements confirmed the specific reduction of FA in the region of the bilateral AC. The decreased FA in the AC was correlated with prolonged MMN latency in the patient group.

CONCLUSION

Our study of AC structure and electrophysiological changes in schizophrenia suggest that the disruption of limbic-cortical structural networks may be part of the neural basis underlying the changes in MMN in schizophrenia.

Biomarkers and clinical staging in psychiatry

Personalized medicine is rapidly becoming a reality in today's physical medicine. However, as yet this is largely an aspirational goal in psychiatry, despite significant advances in our understanding of the biochemical, genetic and neurobiological processes underlying major mental disorders. Preventive medicine relies on the availability of predictive tools; in psychiatry we still largely lack these. Furthermore, our current diagnostic systems, with their focus on well-established, largely chronic illness, do not support a pre-emptive, let alone a preventive, approach, since it is during the early stages of a disorder that interventions have the potential to offer the greatest benefit. Here, we present a clinical staging model for severe mental disorders and discuss examples of biological markers that have already undergone some systematic evaluation and that could be integrated into such a framework. The advantage of this model is that it explicitly considers the evolution of psychopathology during the development of a mental illness and emphasizes that progression of illness is by no means inevitable, but can be altered by providing appropriate interventions that target individual modifiable risk and protective factors. The specific goals of therapeutic intervention are therefore broadened to include the prevention of illness onset or progression, and to minimize the risk of harm associated with more complex treatment regimens. The staging model also facilitates the integration of new data on the biological, social and environmental factors that influence mental illness into our clinical and diagnostic infrastructure, which will provide a major step forward in the development of a truly pre-emptive psychiatry.

Modulation of auditory deviance detection by acute nicotine is baseline and deviant dependent in healthy nonsmokers: a mismatch negativity study

OBJECTIVE

Cognitive enhancement resulting from nicotinic acetylcholine receptor stimulation may be evidenced by increased efficiency of the auditory-frontal cortex network of auditory discrimination, which is impaired in schizophrenia, a cognitive disorder associated with excessive tobacco use. Investigating automatic (preattentive) detection of acoustic change with the mismatch negativity (MMN) brain event-related potential in response to nicotine in individuals with varying baseline levels of auditory discrimination may provide useful insight into the cholinergic regulation of this neural network and its potential amelioration with novel nicotinic agents.

METHODS

Sixty healthy, non-smoking male volunteers were presented with an 'optimal' multi-feature MMN paradigm in a randomized, placebo controlled double-blind design with 6 mg of nicotine gum.

RESULTS

Participants with low, medium, and high baseline amplitudes responded differently to nicotine (vs. placebo), and nicotine response was feature specific. Whereas MMN in individuals with high amplitudes was diminished by nicotine, MMN increased in those with low amplitudes. Nicotine effects were not shown in medium amplitude participants.

CONCLUSIONS

These findings provide preliminary support for the role of nicotinic neurotransmission in sensory memory processing of auditory change and suggest that nicotinic receptor modulation can both enhance and diminish change detection, depending on baseline MMN and its eliciting stimulus feature.

Reading deficits in schizophrenia and individuals at high clinical risk: relationship to sensory function, course of illness, and psychosocial outcome

OBJECTIVE

The ability to read passages of information fluently and with comprehension is a basic component of socioeconomic success. Reading ability depends on the integrity of underlying visual and auditory (phonological) systems. This study investigated the integrity of reading ability in schizophrenia relative to the integrity of underlying visual and auditory function.

METHOD

The participants were 45 schizophrenia patients, 19 clinical high-risk patients, and 65 comparison subjects. Reading was assessed using tests sensitive to visual or phonological reading dysfunction. Sensory, neuropsychological, and functional outcome measures were also obtained.

RESULTS

Schizophrenia patients displayed reading deficits that were far more severe (effect size >2.0) than would be predicted based on general neurocognitive impairments (effect size 1.0-1.4). The deficits correlated highly with both visual and auditory sensory measures, including impaired mismatch negativity generation (r=0.62, N=51, p=0.0002). Patients with established schizophrenia displayed both visual and phonological impairments, whereas high-risk patients showed isolated visual impairments. More than 70% of schizophrenia patients met criteria for acquired dyslexia, with 50% reading below eighth grade level despite intact premorbid reading ability. Reading deficits also correlated significantly (rp=0.4, N=30, p=0.03) with failure to match parental socioeconomic achievement, over and above contributions of more general cognitive impairment.

CONCLUSIONS

Patients with schizophrenia display severe deficits in reading ability that represent a potentially remediable cause of impaired socioeconomic function. Such deficits are not presently captured during routine clinical assessment. Deficits most likely develop during the years immediately surrounding illness onset and may contribute to the reduced educational and occupational achievement associated with schizophrenia.

Mismatch Negativity reduction in the left cortical regions in first-episode psychosis and in individuals at ultra high-risk for psychosis

Mismatch Negativity (MMN), an electrophysiological component that represents sensory memory processing, has been proposed as a potential vulnerability marker for psychosis. Some studies have reported a more evident MMN amplitude reduction in the left cortical regions in patients with schizophrenia. Little is known about this asymmetric pattern in patients in their first episode of psychosis (FEP) and individuals at ultra-high risk for psychosis (UHR). The aim of this study was to explore the scalp distribution of MMN in 20 FEP patients, 20 UHR subjects and 23 healthy controls. Both clinical groups were antipsychotic naïve. MMN was obtained during a passive auditory paradigm with duration deviant tones and analyzed from 15 frontocentral electrodes. There was a significant group effect in MMN amplitude (F=3.4, p=0.04), showing a decrement in both FEP and UHR compared to controls (FEP mean difference (MD)=-0.48, p=0.02; UHR MD=-0.44, p=0.04), and this amplitude decrement was more evident in the left middle regions for both clinical groups (p<0.01). In conclusion, we found a clear amplitude reduction of duration MMN in FEP patients and UHR individuals, especially in the left cortical regions. The observed pattern in both clinical samples supports the notion that MMN could be a vulnerability marker for psychosis. We propose to continue the study of this MMN laterality effect in future longitudinal studies.

Preattentive dysfunction in patients with bipolar disorder as revealed by the pitch-mismatch negativity: a magnetoencephalography (MEG) study

OBJECTIVES

Mismatch negativity (MMN) and its magnetic counterpart (MMNm) are thought to reflect an automatic process that detects a difference between an incoming stimulus and the sensory memory trace of preceding stimuli. In patients with schizophrenia, an attenuation of the MMN/MMNm amplitude has been repeatedly reported. Heschl's gyrus (HG) is one of the major generators of MMN and the functional alteration of HG has been reported in patients with bipolar disorder. The present study investigated the pitch-MMNm in patients with bipolar disorder using whole-head 306-ch magnetoencephalography (MEG).

METHODS

Twenty-two patients and 22 healthy controls participated in this study. Subjects were presented with two types of auditory stimulus sequences. One consisted of 1,000 Hz standards (probability = 90%) and 1,200 Hz deviants (probability = 10%), and the other consisted of 1,000 Hz standards (90%) and 1,200 Hz deviants (10%). These two tasks were each performed twice. Event-related brain responses to standard tones were subtracted from responses to deviant tones.

RESULTS

Patients with bipolar disorder showed a significant bilateral reduction in magnetic global field power (mGFP) amplitudes (p = 0.02) and dipole moments of the MMNm (p = 0.04) compared with healthy controls. Patients with admission experience showed significantly reduced mGFP amplitudes of MMNm compared with patients without admission experience (p = 0.004). Additionally, patients with more severe manic symptoms had smaller mGFP amplitudes of MMNm (ρ = -0.50, p = 0.05).

CONCLUSIONS

The results of this study suggest that patients with bipolar disorder may exhibit preattentive auditory dysfunction indexed by reduced pitch-MMNm responses. Pitch-MMNm could be a potential trait marker reflecting the global severity of bipolar disorder.

A recently-discovered NMDA receptor gene, GRIN3B, is associated with duration mismatch negativity

The study explored associations between mismatch negativity and N-methyl-d-aspartic acid receptor subunit genes, GRIN1, GRIN2B and GRIN3B in healthy subjects and schizophrenia. Nineteen single-nucleotide polymorphisms were genotyped in 138 schizophrenia patients and 103 healthy subjects. Rs2240158 of GRIN3B was significantly associated with mismatch negativity in healthy subjects.

Functional cognitive and cortical abnormalities in chronic and first-admission schizophrenia

Evoked and induced event-related neural oscillations have recently been proposed as a key mechanism supporting higher-order cognition. Cognitive decay and abnormal electromagnetic sensory gating reliably distinguish schizophrenia (SZ) patients and healthy individuals, demonstrated in chronic (CHR) and first-admission (FA) patients. Not yet determined is whether altered event-related modulation of oscillatory activity is manifested at early stages of SZ, thus reflects and perhaps embodies the development of psychopathology, and provides a mechanism for the gating deficit. The present study compared behavioral and functional brain measures in CHR and FA samples. Cognitive test performance (MATRICS Consortium Cognitive Battery, MCCB), neuromagnetic event-related fields (M50 gating ratio), and oscillatory dynamics (evoked and induced modulation of 8-12Hz alpha) during a paired-click task were assessed in 35 CHR and 31 FA patients meeting the criteria for ICD-10 diagnoses of schizophrenia as well as 28 healthy comparison subjects (HC). Both patient groups displayed poorer cognitive performance, higher M50 ratio (poorer sensory gating), and less induced modulation of alpha activity than did HC. Induced alpha power decrease in bilateral posterior regions varied with M50 ratio in HC but not SZ, whereas orbitofrontal alpha power decrease was related to M50 ratio in SZ but not HC. Results suggest disruption of oscillatory dynamics at early stages of illness, which may contribute to deficient information sampling, memory updating, and higher cognitive functioning.

Cognitive task performance and symptoms contribute to personality abnormalities in first hospitalized schizophrenia

Chronic schizophrenia patients have personality abnormalities and cognitive deficits that are associated with poor clinical, social, and vocational outcomes. Very few studies have examined relationships between personality and cognitive function, and chronic illness effects may have confounded those studies. In this study personality traits in clinically stable first episode schizophrenia patients (21M, 9F) and psychiatrically healthy controls (38M, 24F) were measured with the NEO-FFI, a self-report measure of neuroticism, extraversion, openness, agreeableness, and conscientiousness. All subjects completed the Information, Digit Span, Vocabulary, and Digit Symbol subtests of the Wechsler Adult Intelligence Scale; and Trails A and B. Standard statistical techniques were used to quantify relationships between personality and symptom levels and/or task performance, and relative contributions of diagnosis and task performance to personality variance. Patients showed elevated mean neuroticism and openness, and reduced mean extraversion, agreeableness and conscientiousness. Task performance and negative symptoms contributed significantly and uniquely to most personality dimensions in patients. Task performance accounted for significant amounts of personality variance even after accounting for diagnosis, and it also contributed to personality variance in controls. These results suggest that cognitive deficits and negative symptoms contribute to consistently observed personality abnormalities in this disorder, and that the contribution of neuropsychological performance to personality variance may be independent of diagnostic classification. Personality abnormalities in schizophrenia may stem from the neurocognitive deficits associated with this disorder, and add to their adverse effects on social and vocational functioning.

Mismatch negativity in recent-onset and chronic schizophrenia: a current source density analysis

Mismatch negativity (MMN) is a component of the event-related potential elicited by deviant auditory stimuli. It is presumed to index pre-attentive monitoring of changes in the auditory environment. MMN amplitude is smaller in groups of individuals with schizophrenia compared to healthy controls. We compared duration-deviant MMN in 16 recent-onset and 19 chronic schizophrenia patients versus age- and sex-matched controls. Reduced frontal MMN was found in both patient groups, involved reduced hemispheric asymmetry, and was correlated with Global Assessment of Functioning (GAF) and negative symptom ratings. A cortically-constrained LORETA analysis, incorporating anatomical data from each individual's MRI, was performed to generate a current source density model of the MMN response over time. This model suggested MMN generation within a temporal, parietal and frontal network, which was right hemisphere dominant only in controls. An exploratory analysis revealed reduced CSD in patients in superior and middle temporal cortex, inferior and superior parietal cortex, precuneus, anterior cingulate, and superior and middle frontal cortex. A region of interest (ROI) analysis was performed. For the early phase of the MMN, patients had reduced bilateral temporal and parietal response and no lateralisation in frontal ROIs. For late MMN, patients had reduced bilateral parietal response and no lateralisation in temporal ROIs. In patients, correlations revealed a link between GAF and the MMN response in parietal cortex. In controls, the frontal response onset was 17 ms later than the temporal and parietal response. In patients, onset latency of the MMN response was delayed in secondary, but not primary, auditory cortex. However amplitude reductions were observed in both primary and secondary auditory cortex. These latency delays may indicate relatively intact information processing upstream of the primary auditory cortex, but impaired primary auditory cortex or cortico-cortical or thalamo-cortical communication with higher auditory cortices as a core deficit in schizophrenia.

Localized abnormalities in the cingulum bundle in patients with schizophrenia: a Diffusion Tensor tractography study

The cingulum bundle (CB) connects gray matter structures of the limbic system and as such has been implicated in the etiology of schizophrenia. There is growing evidence to suggest that the CB is actually comprised of a conglomeration of discrete sub-connections. The present study aimed to use Diffusion Tensor tractography to subdivide the CB into its constituent sub-connections, and to investigate the structural integrity of these sub-connections in patients with schizophrenia and matched healthy controls. Diffusion Tensor Imaging scans were acquired from 24 patients diagnosed with chronic schizophrenia and 26 matched healthy controls. Deterministic tractography was used in conjunction with FreeSurfer-based regions-of-interest to subdivide the CB into 5 sub-connections (I1 to I5). The patients with schizophrenia exhibited subnormal levels of FA in two cingulum sub-connections, specifically the fibers connecting the rostral and caudal anterior cingulate gyrus (I1) and the fibers connecting the isthmus of the cingulate with the parahippocampal cortex (I4). Furthermore, while FA in the I1 sub-connection was correlated with the severity of patients' positive symptoms (specifically hallucinations and delusions), FA in the I4 sub-connection was correlated with the severity of patients' negative symptoms (specifically affective flattening and anhedonia/asociality). These results support the notion that the CB is a conglomeration of structurally interconnected yet functionally distinct sub-connections, of which only a subset are abnormal in patients with schizophrenia. Furthermore, while acknowledging the fact that the present study only investigated the CB, these results suggest that the positive and negative symptoms of schizophrenia may have distinct neurobiological underpinnings.

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Cingulum bundle was divided into 5 sub-regions using DTI tractography.

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Fractional Anisotropy of these 5 sub-regions was assessed in schizophrenia patients.

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Schizophrenia patients exhibited FA reductions in only 2 of 5 cingulum sub-regions.

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One sub-region correlated with positive symptoms and other with negative symptoms.

Neurophysiological biomarkers informing the clinical neuroscience of schizophrenia: mismatch negativity and prepulse inhibition of startle

With the growing recognition of the heterogeneity of major brain disorders, and particularly the schizophrenias (SZ), biomarkers are being sought that parse patient groups in ways that can be used to predict treatment response, prognosis, and pathophysiology. A primary focus to date has been to identify biomarkers that predict damage or dysfunction within brain systems in SZ patients, that could then serve as targets for interventions designed to "undo" the causative pathology. After almost 50 years as the predominant strategy for developing SZ therapeutics, evidence supporting the value of this "find what's broke and fix it" approach is lacking. Here, we suggest an alternative strategy of using biomarkers to identify evidence of spared neural and cognitive function in SZ patients, and matching these residual neural assets with therapies toward which they can be applied. We describe ways to extract and interpret evidence of "spared function," using neurocognitive, and neurophysiological measures, and, suggest that further evidence of available neuroplasticity might be gleaned from studies in which the response to drug challenges and "practice effects" are measured. Finally, we discuss examples in which "better" (more normal) performance in specific neurophysiological measures predict a positive response to a neurocognitive task or therapeutic intervention. We believe that our field stands to gain tremendous therapeutic leverage by focusing less on what is "wrong" with our patients, and instead, focusing more on what is "right".

Mismatch negativity (MMN) as an index of cognitive dysfunction

Cognition is often affected in a variety of neuropsychiatric, neurological, and neurodevelopmental disorders. The neural discriminative response, reflected in mismatch negativity (MMN) and its magnetoencephalographic equivalent (MMNm), has been used as a tool to study a variety of disorders involving auditory cognition. MMN/MMNm is an involuntary brain response to auditory change or, more generally, to pattern regularity violation. For a number of disorders, MMN/MMNm amplitude to sound deviance has been shown to be attenuated or the peak-latency of the component prolonged compared to controls. This general finding suggests that while not serving as a specific marker to any particular disorder, MMN may be useful for understanding factors of cognition in various disorders, and has potential to serve as an indicator of risk. This review presents a brief history of the MMN, followed by a description of how MMN has been used to index auditory processing capability in a range of neuropsychiatric, neurological, and neurodevelopmental disorders. Finally, we suggest future directions for research to further enhance our understanding of the neural substrate of deviance detection that could lead to improvements in the use of MMN as a clinical tool.

Mismatch negativity indexes illness-specific impairments of cortical plasticity in schizophrenia: a comparison with bipolar disorder and Alzheimer's disease

Cognitive impairment is an important predictor of functional outcome in patients with schizophrenia, yet its neurobiology is still incompletely understood. Neuropathological evidence of impaired synaptic connectivity and NMDA receptor-dependent transmission in superior temporal cortex motivated us to explore the correlation of in vivo mismatch negativity (MMN) with cognitive status in patients with schizophrenia. MMN elicited in a roving stimulus paradigm displayed a response proportional to the number of stimulus repetitions (memory trace effect). Preliminary evidence in patients with chronic schizophrenia suggests that attenuation of this MMN memory trace effect was correlated with the degree of neuropsychological memory dysfunction. Here we present data from a larger confirmatory study in patients with schizophrenia, bipolar disorder, probable Alzheimer's disease and healthy controls. We observed that the diminution of the MMN memory trace effect and its correlation with memory impairment was only found in the schizophrenia group. Recent pharmacological studies using the roving paradigm suggest that attenuation of the MMN trace effect can be understood as abnormal modulation of NMDA receptor-dependent plasticity. We suggest that the convergence of the previously identified synaptic pathology in supragranular cortical layers with the intracortical locus of MMN generation accounts for the remarkable robustness of MMN impairments in schizophrenia. We further speculate that this layer-specific synaptic pathology identified in supragranular neurons plays a pivotal computational role, by weakening the encoding and propagation of prediction errors to higher cortical modules. According to predictive coding theory such breakdown will have grave implications not only for perception, but also for higher-order cognition and may thus account for the MMN-cognition correlations observed here. Finally, MMN is a sensitive and specific biomarker for detecting the early prodromal phase of schizophrenia and is well suited for the exploration of novel cognition-enhancing agents in humans.

Chronic effects of cannabis use on the auditory mismatch negativity

BACKGROUND

Cannabis use is associated with the development of psychotic symptoms and increased risk for schizophrenia. The mismatch negativity (MMN) is a brain event-related potential marker of change detection thought to index glutamatergic N-methyl-D-aspartate receptor-mediated neurotransmission, which is known to be deficient in schizophrenia. This study examined auditory MMN in otherwise healthy chronic cannabis users compared with nonuser control subjects.

METHODS

Forty-two chronic cannabis users and 44 nonuser healthy control subjects completed a multi-feature MMN paradigm, which included duration, frequency, and intensity deviants (deviants 6%; standards 82%). The MMN was compared between users and control subjects as well as between long- and short-term users and age- and gender-matched control subjects. Associations between MMN, cannabis use measures, and symptoms were examined.

RESULTS

The MMN amplitude was significantly reduced to frequency but not duration or intensity deviants in overall cannabis users relative to control subjects. Frequency MMN was similarly attenuated in short- and long-term users relative to control subjects. Long-term users also exhibited reduced duration MMN relative to control subjects and short-term users and this was correlated with increased duration of exposure to cannabis and increased psychotic-like experiences during intoxication. In short-term users, a younger age of onset of regular cannabis use and greater frequency of use were associated with greater psychotic-like experiences and symptomatic distress.

CONCLUSIONS

These results suggest impaired sensory memory that might reflect N-methyl-D-aspartate receptor dysfunction in chronic cannabis users. The pattern of MMN alterations in cannabis users differed from that typically observed in patients with schizophrenia, indicating overlapping but distinct underlying pathology.

Automatic auditory processing deficits in schizophrenia and clinical high-risk patients: forecasting psychosis risk with mismatch negativity

BACKGROUND

Only about one third of patients at high risk for psychosis based on current clinical criteria convert to a psychotic disorder within a 2.5-year follow-up period. Targeting clinical high-risk (CHR) individuals for preventive interventions could expose many to unnecessary treatments, underscoring the need to enhance predictive accuracy with nonclinical measures. Candidate measures include event-related potential components with established sensitivity to schizophrenia. Here, we examined the mismatch negativity (MMN) component of the event-related potential elicited automatically by auditory deviance in CHR and early illness schizophrenia (ESZ) patients. We also examined whether MMN predicted subsequent conversion to psychosis in CHR patients.

METHODS

Mismatch negativity to auditory deviants (duration, frequency, and duration + frequency double deviant) was assessed in 44 healthy control subjects, 19 ESZ, and 38 CHR patients. Within CHR patients, 15 converters to psychosis were compared with 16 nonconverters with at least 12 months of clinical follow-up. Hierarchical Cox regression examined the ability of MMN to predict time to psychosis onset in CHR patients.

RESULTS

Irrespective of deviant type, MMN was significantly reduced in ESZ and CHR patients relative to healthy control subjects and in CHR converters relative to nonconverters. Mismatch negativity did not significantly differentiate ESZ and CHR patients. The duration + frequency double deviant MMN, but not the single deviant MMNs, significantly predicted the time to psychosis onset in CHR patients.

CONCLUSIONS

Neurophysiological mechanisms underlying automatic processing of auditory deviance, as reflected by the duration + frequency double deviant MMN, are compromised before psychosis onset and can enhance the prediction of psychosis risk among CHR patients.

What's intact and what's not within the mismatch negativity system in schizophrenia

Repetitive patterning facilitates inferences about likely properties of sound to follow. Mismatch negativity (MMN) occurs when sound fails to match an inference. Smaller MMN in schizophrenia indexes deficient gain control (difference in utilizing a limited dynamic range). Although it is clear that this group has a lower limit to MMN size, this study addressed whether smaller MMN indicates impaired perceptual inference. MMN was elicited to four deviants in two sequences: one in which occurrence was random and one in which it was paired. Despite smaller MMN, persons with schizophrenia are equally able to reduce MMN size evoked by a deviant when its occurrence is cued. Results also expose alterations in the evoked response to repeated sounds that appear to be exacerbations of age-related amplitude decline. Since these anomalies impact the computed MMN, they highlight the need to identify all contributions to limits in gain control in schizophrenia.

Changes in the duration and frequency of deviant stimuli engender different mismatch negativity patterns in temporal lobe epilepsy

Mismatch negativity (MMN) is an event-related potential (ERP) component that reflects preattentive sensory memory functions. Previous research revealed that MMN is generated by distinct sources in the frontal and temporal lobes. Event-related potential abnormalities have been shown in the vicinity of seizure foci in epilepsy. Additionally, no published study has investigated the MMN in response to variations in both frequency and duration deviants in patients with temporal lobe epilepsy (TLE). The aims of this study were to compare MMN changes between the frontocentral sites and the mastoid sites and to compare MMNs related to deviant stimuli with different durations and frequencies in patients with TLE. We recorded MMNs elicited by duration and frequency changes of deviant stimuli from 15 patients with TLE and 15 healthy control subjects. We found that mean MMN amplitudes related to duration deviants were lower in patients with TLE at the mastoid sites relative to controls, whereas the MMN amplitudes at the frontocentral sites did not differ between the two groups. There were no MMN differences related to frequency deviants between TLE subjects and controls at the frontocentral sites or the mastoid sites. Mismatch negativity parameters related to duration deviants did not correlate with those related to deviant frequencies in the group with TLE. The present findings suggest selective impairments among multiple mismatch generators in TLE and suggest that processing of temporal information of auditory stimuli is selectively disturbed in TLE. Changes in MMN amplitudes related to duration deviants at the mastoid sites may represent deficits in time-dependent processing in TLE.

Profile of minocycline and its potential in the treatment of schizophrenia

Accumulating evidence suggests that neuroinflammation affecting microglia plays an important role in the etiology of schizophrenia, and appropriate control of microglial activation may be a promising therapeutic strategy for schizophrenia. Minocycline, a second-generation tetracycline that inhibits microglial activation, has been shown to have a neuroprotective effect in various models of neurodegenerative disease, including anti-inflammatory, antioxidant, and antiapoptotic properties, and an ability to modulate glutamate-induced excitotoxicity. Given that these mechanisms overlap with neuropathologic pathways, minocycline may have a potential role in the adjuvant treatment of schizophrenia, and improve its negative symptoms. Here, we review the relevant studies of minocycline, ranging from preclinical research to human clinical trials.

Hemispheric asymmetry of primary auditory cortex and Heschl's gyrus in schizophrenia and nonpsychiatric brains

Heschl's gyrus (HG) is reported to have a normal left>right hemispheric volume asymmetry, and reduced asymmetry in schizophrenia. Primary auditory cortex (A1) occupies the caudal-medial surface of HG, but it is unclear if A1 has normal asymmetry, or whether its asymmetry is altered in schizophrenia. To address these issues, we compared bilateral gray matter volumes of HG and A1, and neuron density and number in A1, in autopsy brains from male subjects with or without schizophrenia. Comparison of diagnostic groups did not reveal altered gray matter volumes, neuron density, neuron number or hemispheric asymmetries in schizophrenia. With respect to hemispheric differences, HG displayed a clear left>right asymmetry of gray matter volume. Area A1 occupied nearly half of HG, but had less consistent volume asymmetry, that was clearly present only in a subgroup of archival brains from elderly subjects. Neuron counts, in layers IIIb-c and V-VI, showed that the A1 volume asymmetry reflected differences in neuron number, and was not caused simply by changes in neuron density. Our findings confirm previous reports of striking hemispheric asymmetry of HG, and additionally show evidence that A1 has a corresponding asymmetry, although less consistent than that of HG.

Mismatch negativity: translating the potential

The mismatch negativity (MMN) component of the auditory event-related potential has become a valuable tool in cognitive neuroscience. Its reduced size in persons with schizophrenia is of unknown origin but theories proposed include links to problems in experience-dependent plasticity reliant on N-methyl-d-aspartate glutamate receptors. In this review we address the utility of this tool in revealing the nature and time course of problems in perceptual inference in this illness together with its potential for use in translational research testing animal models of schizophrenia-related phenotypes. Specifically, we review the reasons for interest in MMN in schizophrenia, issues pertaining to the measurement of MMN, its use as a vulnerability index for the development of schizophrenia, the pharmacological sensitivity of MMN and the progress in developing animal models of MMN. Within this process we highlight the challenges posed by knowledge gaps pertaining to the tool and the pharmacology of the underlying system.

Contributions of experimental psychiatry to research on the psychosis prodrome

In the recent decades, a paradigmatic change in psychosis research and treatment shifted attention toward the early and particularly the prodromal stages of illness. Despite substantial progress with regard to the neuronal underpinnings of psychosis development, the crucial biological mechanisms leading to manifest illness are yet insufficiently understood. Until today, one significant approach to elucidate the neurobiology of psychosis has been the modeling of psychotic symptoms by psychedelic substances in healthy individuals. These models bear the opportunity to evoke particular neuronal aberrations and the respective psychotic symptoms in a controlled experimental setting. In the present paper, we hypothesize that experimental psychiatry bears unique opportunities in elucidating the biological mechanisms of the prodromal stages of psychosis. Psychosis risk symptoms are attenuated, transient, and often only retrospectively reported. The respective neuronal aberrations are thought being dynamic. The correlation of unstable psychopathology with observed neurofunctional disturbances is thus yet largely unclear. In modeling psychosis, the experimental setting allows not only for evoking particular symptoms, but for the concomitant assessment of psychopathology, neurophysiology, and neuropsychology. Herein, the glutamatergic model will be highlighted exemplarily, with special emphasis on its potential contribution to the elucidation of psychosis development. This model of psychosis appears as candidate for modeling the prodrome by inducing psychotic-like symptoms in healthy individuals. Furthermore, it alters pre-attentive processing like the Mismatch Negativity, an electrophysiological component which has recently been identified as a potential predictive marker of psychosis development. In summary, experimental psychiatry bears the potential to further elucidate the biological mechanisms of the psychosis prodrome. A better understanding of the respective pathophysiology might assist in the identification of predictive markers, and the development of preventive treatments.

Cortical thickness as a contributor to abnormal oscillations in schizophrenia?

Introduction

Although brain rhythms depend on brain structure (e.g., gray and white matter), to our knowledge associations between brain oscillations and structure have not been investigated in healthy controls (HC) or in individuals with schizophrenia (SZ). Observing function–structure relationships, for example establishing an association between brain oscillations (defined in terms of amplitude or phase) and cortical gray matter, might inform models on the origins of psychosis. Given evidence of functional and structural abnormalities in primary/secondary auditory regions in SZ, the present study examined how superior temporal gyrus (STG) structure relates to auditory STG low-frequency and 40 Hz steady-state activity. Given changes in brain activity as a function of age, age-related associations in STG oscillatory activity were also examined.

Methods

Thirty-nine individuals with SZ and 29 HC were recruited. 40 Hz amplitude-modulated tones of 1 s duration were presented. MEG and T1-weighted sMRI data were obtained. Using the sources localizing 40 Hz evoked steady-state activity (300 to 950 ms), left and right STG total power and inter-trial coherence were computed. Time–frequency group differences and associations with STG structure and age were also examined.

Results

Decreased total power and inter-trial coherence in SZ were observed in the left STG for initial post-stimulus low-frequency activity (~ 50 to 200 ms, ~ 4 to 16 Hz) as well as 40 Hz steady-state activity (~ 400 to 1000 ms). Left STG 40 Hz total power and inter-trial coherence were positively associated with left STG cortical thickness in HC, not in SZ. Left STG post-stimulus low-frequency and 40 Hz total power were positively associated with age, again only in controls.

Discussion

Left STG low-frequency and steady-state gamma abnormalities distinguish SZ and HC. Disease-associated damage to STG gray matter in schizophrenia may disrupt the age-related left STG gamma-band function–structure relationships observed in controls.

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Associations between brain oscillations and structure were investigated in SZ

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The present study examined how superior temporal gyrus (STG) structure and agerelate to auditory STG low-frequency and 40 Hz steady-state activity

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Decreased total power and inter-trial coherence in SZ were observed in the left STG for early low-frequency activity (~ 50 to 200 ms, ~ 4 to 16 Hz) as well as 40 Hz steady-state activity (~ 400 to 1000 ms)

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Left STG 40 Hz total power and inter-trial coherence were positively associated with left STG cortical thickness in HC, not in SZ

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Disease-associated damage to STG gray matter in schizophrenia may disrupt the age-related left STG function-structure relationships observed in controls.

Review of neurophysiological findings in patients with schizophrenia

Schizophrenia has been conceptualized as a failure of cognitive integration, and abnormalities in neural circuitry have been proposed as a basis for this disorder. In this article, we focus on electroencephalography and magnetoencephalography findings in patients with schizophrenia. Auditory-P50, -N100, and -P300 findings, visual-P100, -N170, and -N400 findings, and neural oscillations in patients with schizophrenia are overviewed. Published results suggest that patients with schizophrenia have neurophysiological deficits from the very early phase of sensory processing (i.e., P50, P100, N100) to the relatively late phase (i.e., P300, N400) in both auditory and visual perception. Exploring the associations between neural substrates, including neurotransmitter systems, and neurophysiological findings, will lead to a more comprehensive understanding of the pathophysiology of schizophrenia.

Auditory mismatch negativity and P3a in response to duration and frequency changes in the early stages of psychosis

BACKGROUND

A shorter duration of untreated psychosis in patients with schizophrenia results in better symptomatic and functional outcomes. Therefore, identifying biological markers in the early stages of psychosis is an important step toward early detection and intervention. Mismatch negativity (MMN) and P3a are leading candidate biomarkers. MMN measures differ in their sensitivity to varying deviants. However, this has not been fully addressed in assessing the early stages of psychosis. In the current study, we examined MMN/P3a to duration deviant (dMMN/dP3a) and frequency deviant (fMMN/fP3a) in the early stages of psychosis. To our knowledge, this is the first study that examined both MMN/P3a to duration deviant (dMMN/dP3a) and frequency deviant (fMMN/fP3a) in the early stages of psychosis.

METHODS

Participants consisted of 20 patients with first episode schizophrenia (FES), 21 ultra-high risk (UHR) individuals, and 22 healthy controls (HC). We measured dMMN/dP3a and fMMN/fP3a ERP components by means of a 64 electrodes-cap for EEG recording, and we used two-tone auditory oddball paradigms with 2000 stimuli.

RESULTS

The amplitude of dMMN was significantly reduced in FES and UHR compared to HC. The amplitude of fMMN showed no significant difference among the three groups. The amplitudes of dP3a and fP3a were significantly reduced in FES and UHR compared to HC.

CONCLUSION

These findings suggest that dMMN may have higher sensitivity than fMMN whereas dP3a and fP3a may have similar sensitivity in the early stages of psychosis.

A systematic review and meta-analysis of proton magnetic resonance spectroscopy and mismatch negativity in bipolar disorder

Aberrant glutamate neurotransmission has been implicated in the pathophysiology of bipolar disorder with accumulating evidence from imaging, post-mortem and pathology studies. Studies investigating in vivo changes to the glutamatergic system have not been as consistent and warrant clarification. Studies utilizing proton-magnetic resonance spectroscopy ((1)H-MRS) have reported increased levels of combined glutamate and glutamine ("Glx"), which have been linked to impairments in N-methyl-d-aspartate (NMDA) receptor function. Similarly, neurophysiological studies utilising mismatch negativity (MMN) as an index of NMDA receptor function, have reported impairments in bipolar disorder. Here, we provide a systematic review of the literature in regards to the concentration of Glx and the magnitude of MMN in bipolar disorder. Separate meta-analyses revealed that bipolar disorder was associated with increased Glx concentration and decreased MMN-both measured frontally. The current findings corroborate previous evidence indicating that bipolar disorder is characterized by a perturbed frontal glutamate system. These observed changes in bipolar disorder might manifest as impairments in neuronal-glial interactions that lead to disrupted neuronal output and ultimately result in the characteristic neurocognitive sequelae associated with this disorder.

Longitudinal associations between mismatch negativity and disability in early schizophrenia- and affective-spectrum disorders

BACKGROUND

Impaired mismatch negativity (MMN) is a robust finding in schizophrenia and, more recently, similar impairments have been reported in other psychotic- and affective-disorders (including at early stages of illness). Although cross-sectional studies have been numerous, there are few longitudinal studies that have explored the predictive value of this event-related potential in relation to clinical/functional outcomes. This study assessed changes in MMN (and the concomitant P3a) amplitude over time and aimed to determine the longitudinal relationship between MMN/P3a and functional outcomes in patients recruited during the early stage of a schizophrenia- or affective-spectrum disorder.

METHODS

Sixty young patients with schizophrenia- and affective-spectrum disorders and 30 healthy controls underwent clinical, neuropsychological and neurophysiological assessment at baseline. Thirty-one patients returned for clinical and neuropsychological follow-up 12-30months later, with 28 of these patients also repeating neurophysiological assessment. On both occasions, MMN/P3a was elicited using a two-tone passive auditory paradigm with duration deviants.

RESULTS

Compared with controls, patients showed significantly impaired temporal MMN amplitudes and trend-level deficits in central MMN/P3a amplitudes at baseline. There were no significant differences for MMN measures between the diagnostic groups, whilst the schizophrenia-spectrum group showed reduced P3a amplitudes compared to those with affective-spectrum disorders. For those patients who returned for follow-up, reduced temporal MMN amplitude at baseline was significantly associated with greater levels of occupational disability, and showed trend-level associations with general and social disability at follow-up. Paired t-tests revealed that MMN amplitudes recorded at the central-midline site were significantly reduced in patients over time. Interestingly, those patients who did not return for follow-up showed reduced frontal MMN and fronto-central P3a amplitudes compared to their peers who did return for repeat assessment.

CONCLUSIONS

This study provides some evidence of the predictive utility of MMN at the early stages of schizophrenia- and affective-spectrum disorders and demonstrated that MMN impairments in such patients may worsen over time. Specifically, we found that young patients with the most impaired MMN amplitudes at baseline showed the most severe levels of disability at follow-up. Furthermore, in the subset of patients with repeat neurophysiological testing, central MMN was further impaired suggestive of neurodegenerative effects. MMN may serve as a neurophysiological biomarker to more accurately predict functional outcomes and prognosis, particularly at the early stages of illness.

Mismatch negativity as a "translatable" brain marker toward early intervention for psychosis: a review

Recent reviews and meta-analyses suggest that reducing the duration of untreated psychosis leads to better symptomatic and functional outcome in patients with psychotic disorder. Early intervention attenuates the symptoms of individuals at clinical high-risk (HR) for psychosis and may delay or prevent their transition to psychosis. Identifying biological markers in the early stages of psychotic disorder is an important step toward elucidating the pathophysiology, improving prediction of the transition to psychosis, and introducing targeted early intervention for help-seeking individuals aiming for better outcome. Mismatch negativity (MMN) is a component of event-related potentials that reflects preattentive auditory sensory memory and is a promising biomarker candidate for schizophrenia. Reduced MMN amplitude is a robust finding in patients with chronic schizophrenia. Recent reports have shown that people in the early stages of psychotic disorder exhibit attenuation of MMN amplitude. MMN in response to duration deviants and in response to frequency deviants reveals different patterns of deficits. These findings suggest that MMN may be useful for identifying clinical stages of psychosis and for predicting the risk of development. MMN may also be a "translatable" biomarker since it reflects N-methyl-d-aspartte receptor function, which plays a fundamental role in schizophrenia pathophysiology. Furthermore, MMN-like responses can be recorded in animals such as mice and rats. This article reviews MMN studies conducted on individuals with HR for psychosis, first-episode psychosis, recent-onset psychosis, and on animals. Based on the findings, the authors discuss the potential of MMN as a clinical biomarker for early intervention for help-seeking individuals in the early stages of psychotic disorder, and as a translatable neurophysiological marker for the preclinical assessment of pharmacological agents used in animal models that mimic early stages of the disorder.

Intracortical excitatory and thalamocortical boutons are intact in primary auditory cortex in schizophrenia

Schizophrenia is associated with auditory processing impairments that could arise as a result of primary auditory cortex excitatory circuit pathology. We have previously reported a deficit in dendritic spine density in deep layer 3 of primary auditory cortex in subjects with schizophrenia. As boutons and spines can be structurally and functionally co-regulated, we asked whether the densities of intracortical excitatory or thalamocortical presynaptic boutons are also reduced. We studied 2 cohorts of subjects with schizophrenia and matched controls, comprising 27 subject pairs, and assessed the density, number, and within-bouton vesicular glutamate transporter (VGluT) protein level of intracortical excitatory (VGluT1-immunoreactive) and thalamocortical (VGluT2-immunoreactive) boutons in deep layer 3 of primary auditory cortex using quantitative confocal microscopy and stereologic sampling methods. We found that VGluT1- and VGluT2-immunoreactive puncta densities and numbers were not altered in deep layer 3 of primary auditory cortex of subjects with schizophrenia. Our results indicate that reduced dendritic spine density in primary auditory cortex of subjects with schizophrenia is not matched by a corresponding reduction in excitatory bouton density. This suggests excitatory boutons in primary auditory cortex in schizophrenia may synapse with structures other than spines, such as dendritic shafts, with greater frequency. The discrepancy between dendritic spine reduction and excitatory bouton preservation may contribute to functional impairments of the primary auditory cortex in subjects with schizophrenia.

Altered visual information processing systems in bipolar disorder: evidence from visual MMN and P3

Objective: Mismatch negativity (MMN) and P3 are unique ERP components that provide objective indices of human cognitive functions such as short-term memory and prediction. Bipolar disorder (BD) is an endogenous psychiatric disorder characterized by extreme shifts in mood, energy, and ability to function socially. BD patients usually show cognitive dysfunction, and the goal of this study was to access their altered visual information processing via visual MMN (vMMN) and P3 using windmill pattern stimuli.

Methods: Twenty patients with BD and 20 healthy controls matched for age, gender, and handedness participated in this study. Subjects were seated in front of a monitor and listened to a story via earphones. Two types of windmill patterns (standard and deviant) and white circle (target) stimuli were randomly presented on the monitor. All stimuli were presented in random order at 200-ms durations with an 800-ms inter-stimulus interval. Stimuli were presented at 80% (standard), 10% (deviant), and 10% (target) probabilities. The participants were instructed to attend to the story and press a button as soon as possible when the target stimuli were presented. Event-related potentials (ERPs) were recorded throughout the experiment using 128-channel EEG equipment. vMMN was obtained by subtracting standard from deviant stimuli responses, and P3 was evoked from the target stimulus.

Results: Mean reaction times for target stimuli in the BD group were significantly higher than those in the control group. Additionally, mean vMMN-amplitudes and peak P3-amplitudes were significantly lower in the BD group than in controls.

Conclusions: Abnormal vMMN and P3 in patients indicate a deficit of visual information processing in BD, which is consistent with their increased reaction time to visual target stimuli.

Significance: Both bottom-up and top-down visual information processing are likely altered in BD.

The loudness dependence of auditory evoked potentials (LDAEP) as an indicator of serotonergic dysfunction in patients with predominant schizophrenic negative symptoms

Besides the influence of dopaminergic neurotransmission on negative symptoms in schizophrenia, there is evidence that alterations of serotonin (5-HT) system functioning also play a crucial role in the pathophysiology of these disabling symptoms. From post mortem and genetic studies on patients with negative symptoms a 5-HT dysfunction is documented. In addition atypical neuroleptics and some antidepressants improve negative symptoms via serotonergic action. So far no research has been done to directly clarify the association between the serotonergic functioning and the extent of negative symptoms. Therefore, we examined the status of brain 5-HT level in negative symptoms in schizophrenia by means of the loudness dependence of auditory evoked potentials (LDAEP). The LDAEP provides a well established and non-invasive in vivo marker of the central 5-HT activity. We investigated 13 patients with schizophrenia with predominant negative symptoms treated with atypical neuroleptics and 13 healthy age and gender matched controls with a 32-channel EEG. The LDAEP of the N1/P2 component was evaluated by dipole source analysis and single electrode estimation at Cz. Psychopathological parameters, nicotine use and medication were assessed to control for additional influencing factors. Schizophrenic patients showed significantly higher LDAEP in both hemispheres than controls. Furthermore, the LDAEP in the right hemisphere in patients was related to higher scores in scales assessing negative symptoms. A relationship with positive symptoms was not found. These data might suggest a diminished central serotonergic neurotransmission in patients with predominant negative symptoms.

Evidence for impaired visual prediction error in schizophrenia

BACKGROUND

Mismatch negativity (MMN) is regarded a prediction error signal that is deficient in schizophrenia in the auditory modality. If, however, MMN reflects a general computational signal of the cortex, then MMN should be also deficient in the visual modality in schizophrenia patients.

METHODS

Twenty-two schizophrenia patients and 24 matched healthy controls finished a visual oddball task while high-density electroencephalogram was recorded. Visual mismatch negativity was computed as a surrogate marker of prediction error.

RESULTS

Visual MMN, as measured over posterior extra-striate cortical areas, was significantly reduced in schizophrenia at about 300 ms post stimulus. Standardized mean difference was -.98, corresponding to a large effect size.

CONCLUSIONS

A posterior visual MMN deficit in schizophrenia is demonstrated for the first time. Our results tentatively suggest a supra-modal MMN deficit in schizophrenia and thus argue in favor of reduced prediction error estimation in schizophrenia.

MK-801 disrupts and nicotine augments 40 Hz auditory steady state responses in the auditory cortex of the urethane-anesthetized rat

Patients with schizophrenia show marked deficits in processing sensory inputs including a reduction in the generation and synchronization of 40 Hz gamma oscillations in response to steady-state auditory stimulation. Such deficits are not readily demonstrable at other input frequencies. Acute administration of NMDA antagonists to healthy human subjects or laboratory animals is known to reproduce many sensory and cognitive deficits seen in schizophrenia patients. In the following study, we tested the hypothesis that the NMDA antagonist MK-801 would selectively disrupt steady-state gamma entrainment in the auditory cortex of urethane-anesthetized rat. Moreover, we further hypothesized that nicotinic receptor activation would alleviate this disruption. Auditory steady state responses were recorded in response to auditory stimuli delivered over a range of frequencies (10-80 Hz) and averaged over 50 trials. Evoked power was computed under baseline condition and after vehicle or MK-801 (0.03 mg/kg, iv). MK-801 produced a significant attenuation in response to 40 Hz auditory stimuli while entrainment to other frequencies was not affected. Time-frequency analysis revealed deficits in both power and phase-locking to 40 Hz. Nicotine (0.1 mg/kg, iv) administered after MK-801 reversed the attenuation of the 40 Hz response. Administered alone, nicotine augmented 40 Hz steady state power and phase-locking. Nicotine's effects were blocked by simultaneous administration of the α4β2 antagonist DHßE. Thus we report for the first time, a rodent model that mimics a core neurophysiological deficit seen in patients with schizophrenia and a pharmacological approach to alleviate it.

The role of the primary auditory cortex in the neural mechanism of auditory verbal hallucinations

Auditory verbal hallucinations (AVHs) are a subjective experience of "hearing voices" in the absence of corresponding physical stimulation in the environment. The most remarkable feature of AVHs is their perceptual quality, that is, the experience is subjectively often as vivid as hearing an actual voice, as opposed to mental imagery or auditory memories. This has lead to propositions that dysregulation of the primary auditory cortex (PAC) is a crucial component of the neural mechanism of AVHs. One possible mechanism by which the PAC could give rise to the experience of hallucinations is aberrant patterns of neuronal activity whereby the PAC is overly sensitive to activation arising from internal processing, while being less responsive to external stimulation. In this paper, we review recent research relevant to the role of the PAC in the generation of AVHs. We present new data from a functional magnetic resonance imaging (fMRI) study, examining the responsivity of the left and right PAC to parametrical modulation of the intensity of auditory verbal stimulation, and corresponding attentional top-down control in non-clinical participants with AVHs, and non-clinical participants with no AVHs. Non-clinical hallucinators showed reduced activation to speech sounds but intact attentional modulation in the right PAC. Additionally, we present data from a group of schizophrenia patients with AVHs, who do not show attentional modulation of left or right PAC. The context-appropriate modulation of the PAC may be a protective factor in non-clinical hallucinations.

The role of the primary auditory cortex in the neural mechanism of auditory verbal hallucinations

Auditory verbal hallucinations (AVHs) are a subjective experience of “hearing voices” in the absence of corresponding physical stimulation in the environment. The most remarkable feature of AVHs is their perceptual quality, that is, the experience is subjectively often as vivid as hearing an actual voice, as opposed to mental imagery or auditory memories. This has lead to propositions that dysregulation of the primary auditory cortex (PAC) is a crucial component of the neural mechanism of AVHs. One possible mechanism by which the PAC could give rise to the experience of hallucinations is aberrant patterns of neuronal activity whereby the PAC is overly sensitive to activation arising from internal processing, while being less responsive to external stimulation. In this paper, we review recent research relevant to the role of the PAC in the generation of AVHs. We present new data from a functional magnetic resonance imaging (fMRI) study, examining the responsivity of the left and right PAC to parametrical modulation of the intensity of auditory verbal stimulation, and corresponding attentional top-down control in non-clinical participants with AVHs, and non-clinical participants with no AVHs. Non-clinical hallucinators showed reduced activation to speech sounds but intact attentional modulation in the right PAC. Additionally, we present data from a group of schizophrenia patients with AVHs, who do not show attentional modulation of left or right PAC. The context-appropriate modulation of the PAC may be a protective factor in non-clinical hallucinations.

Neuroinflammation in schizophrenia especially focused on the role of microglia

An accumulating body of evidence point to the significance of neuroinflammation and immunogenetics also in schizophrenia. Recent genome-wide studies in schizophrenia suggest immune involvement in schizophrenia. Microglia are the resident macrophage of the brain and major players in innate immunity in the CNS. They respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia is closely associated with microglial activation. We and other researchers have shown the inhibitory effects of some typical or atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which are not only directly toxic to neurons but also cause a decrease in neurogenesis as well as white matter abnormalities in the brains of the patients with schizophrenia. The treatment through the inhibition of microglial activation may shed new light on the therapeutic strategy of schizophrenia.