Sensory gating event-related potentials and oscillations in schizophrenia patients and their unaffected relatives

The claustrum and consciousness: An update

The seminal paper of Crick and Koch (2005) proposed that the claustrum, an enigmatic and thin grey matter structure that lies beside the insular cortex, may be involved in the processing of consciousness. As a result, this otherwise obscure structure has received ever-increasing interest in the search for neural correlates of consciousness. Here we review theories of consciousness and discuss the possible relationship between the claustrum and consciousness. We review relevant experimental evidence collected since the Crick and Koch (2005) paper and consider whether these findings support or contradict their hypothesis. We also explore how future experimental work can be designed to clarify how consciousness emerges from neural activity and to understand the role of the claustrum in consciousness.

Sensory gating, neurocognition, social cognition and real-life functioning: a 2-year follow-up of early psychosis

BACKGROUND

Diminished sensory gating (SG) is a robust finding in psychotic disorders, but studies of early psychosis (EP) are rare. It is unknown whether SG deficit leads to poor neurocognitive, social, and/or real-world functioning. This study aimed to explore the longitudinal relationships between SG and these variables.

METHODS

Seventy-nine EP patients and 88 healthy controls (HCs) were recruited at baseline. Thirty-three and 20 EP patients completed 12-month and 24-month follow-up, respectively. SG was measured using the auditory dual-click (S1 & S2) paradigm and quantified as P50 ratio (S2/S1) and difference (S1-S2). Cognition, real-life functioning, and symptoms were assessed using the MATRICS Consensus Cognitive Battery, Global Functioning: Social (GFS) and Role (GFR), Multnomah Community Ability Scale (MCAS), Awareness of Social Inference Test (TASIT), and the Positive and Negative Syndrome Scale (PANSS). Analysis of variance (ANOVA), chi-square, mixed model, correlation and regression analyses were used for group comparisons and relationships among variables controlling for potential confounding variables.

RESULTS

In EP patients, P50 ratio (p < 0.05) and difference (p < 0.001) at 24-month showed significant differences compared with that at baseline. At baseline, P50 indices (ratio, S1-S2 difference, S1) were independently associated with GFR in HCs (all p < 0.05); in EP patients, S2 amplitude was independently associated with GFS (p = 0.037). At 12-month and 24-month, P50 indices (ratio, S1, S2) was independently associated with MCAS (all p < 0.05). S1-S2 difference was a trending predictor of future function (GFS or MCAS).

CONCLUSIONS

SG showed progressive reduction in EP patients. P50 indices were related to real-life functioning.

The effect of alterations of schizophrenia-associated genes on gamma band oscillations

Abnormalities in the synchronized oscillatory activity of neurons in general and, specifically in the gamma band, might play a crucial role in the pathophysiology of schizophrenia. While these changes in oscillatory activity have traditionally been linked to alterations at the synaptic level, we demonstrate here, using computational modeling, that common genetic variants of ion channels can contribute strongly to this effect. Our model of primary auditory cortex highlights multiple schizophrenia-associated genetic variants that reduce gamma power in an auditory steady-state response task. Furthermore, we show that combinations of several of these schizophrenia-associated variants can produce similar effects as the more traditionally considered synaptic changes. Overall, our study provides a mechanistic link between schizophrenia-associated common genetic variants, as identified by genome-wide association studies, and one of the most robust neurophysiological endophenotypes of schizophrenia.

Deciphering the code: Identifying true gamma neural oscillations

Neural oscillatory activity occurring in the gamma frequency range (30-80 Hz) has been proposed to play essential roles in sensory and cognitive processing. Supporting this, abnormalities in gamma oscillations have been reported in patients with diverse neurological and neuropsychiatric disorders in which cognitive impairment is prominent. Understanding the mechanisms underpinning this relationship is the focus of extensive research. But while an increasing number of studies are investigating the intricate relationship between gamma oscillations and cognition, interpretation and generalisation of these studies is limited by the diverse, and at times questionable, methodologies used to analyse oscillatory activity. For example, a variety of different types of gamma oscillatory activity have been characterised, but all are generalised non-specifically as 'gamma oscillations'. This creates confusion, since distinct cellular and network mechanisms are likely responsible for generating these different types of rhythm. Moreover, in some instances, certain analytical measures of electrophysiological data are overinterpreted, with researchers pushing the boundaries of what would be considered rhythmic or oscillatory in nature. Here, we provide clarity on these issues, firstly presenting an overview of the different measures of gamma oscillatory activity, and describing common signal processing techniques used for analysis. Limitations of these techniques are discussed, and recommendations made on how future studies should optimise analyses, presentation and interpretation of gamma frequency oscillations. This is an essential progression in order to harmonise future studies, allowing us to gain a clearer understanding of the role of gamma oscillations in cognition, and in cognitive disorders.

Non-rapid eye movement sleep and wake neurophysiology in schizophrenia

Motivated by the potential of objective neurophysiological markers to index thalamocortical function in patients with severe psychiatric illnesses, we comprehensively characterized key non-rapid eye movement (NREM) sleep parameters across multiple domains, their interdependencies, and their relationship to waking event-related potentials and symptom severity. In 72 schizophrenia (SCZ) patients and 58 controls, we confirmed a marked reduction in sleep spindle density in SCZ and extended these findings to show that fast and slow spindle properties were largely uncorrelated. We also describe a novel measure of slow oscillation and spindle interaction that was attenuated in SCZ. The main sleep findings were replicated in a demographically distinct sample, and a joint model, based on multiple NREM components, statistically predicted disease status in the replication cohort. Although also altered in patients, auditory event-related potentials elicited during wake were unrelated to NREM metrics. Consistent with a growing literature implicating thalamocortical dysfunction in SCZ, our characterization identifies independent NREM and wake EEG biomarkers that may index distinct aspects of SCZ pathophysiology and point to multiple neural mechanisms underlying disease heterogeneity. This study lays the groundwork for evaluating these neurophysiological markers, individually or in combination, to guide efforts at treatment and prevention as well as identifying individuals most likely to benefit from specific interventions.

Neurophysiology in psychosis: The quest for disease biomarkers

Psychotic disorders affect 3% of the population at some stage in life, are a leading cause of disability, and impose a great economic burden on society. Major breakthroughs in the genetics of psychosis have not yet been matched by an understanding of its neurobiology. Biomarkers of perception and cognition obtained through non-invasive neurophysiological tools, especially EEG, offer a unique opportunity to gain mechanistic insights. Techniques for measuring neurophysiological markers are inexpensive and ubiquitous, thus having the potential as an accessible tool for patient stratification towards early treatments leading to better outcomes. In this paper, we review the literature on neurophysiological markers for psychosis and their relevant disease mechanisms, mainly covering event-related potentials including P50/N100 sensory gating, mismatch negativity, and the N100 and P300 waveforms. While several neurophysiological deficits are well established in patients with psychosis, more research is needed to study neurophysiological markers in their unaffected relatives and individuals at clinical high risk. We need to harness EEG to investigate markers of disease risk as key steps to elucidate the aetiology of psychosis and facilitate earlier detection and treatment.

Smoking as a Common Modulator of Sensory Gating and Reward Learning in Individuals with Psychotic Disorders

Motivational and perceptual disturbances co-occur in psychosis and have been linked to aberrations in reward learning and sensory gating, respectively. Although traditionally studied independently, when viewed through a predictive coding framework, these processes can both be linked to dysfunction in striatal dopaminergic prediction error signaling. This study examined whether reward learning and sensory gating are correlated in individuals with psychotic disorders, and whether nicotine—a psychostimulant that amplifies phasic striatal dopamine firing—is a common modulator of these two processes. We recruited 183 patients with psychotic disorders (79 schizophrenia, 104 psychotic bipolar disorder) and 129 controls and assessed reward learning (behavioral probabilistic reward task), sensory gating (P50 event-related potential), and smoking history. Reward learning and sensory gating were correlated across the sample. Smoking influenced reward learning and sensory gating in both patient groups; however, the effects were in opposite directions. Specifically, smoking was associated with improved performance in individuals with schizophrenia but impaired performance in individuals with psychotic bipolar disorder. These findings suggest that reward learning and sensory gating are linked and modulated by smoking. However, disorder-specific associations with smoking suggest that nicotine may expose pathophysiological differences in the architecture and function of prediction error circuitry in these overlapping yet distinct psychotic disorders.

Male fetus susceptibility to maternal inflammation: C-reactive protein and brain development

BACKGROUND

Maternal inflammation in early pregnancy has been identified epidemiologically as a prenatal pathogenic factor for the offspring's later mental illness. Early newborn manifestations of the effects of maternal inflammation on human fetal brain development are largely unknown.

METHODS

Maternal infection, depression, obesity, and other factors associated with inflammation were assessed at 16 weeks gestation, along with maternal C-reactive protein (CRP), cytokines, and serum choline. Cerebral inhibition was assessed by inhibitory P50 sensory gating at 1 month of age, and infant behavior was assessed by maternal ratings at 3 months of age.

RESULTS

Maternal CRP diminished the development of cerebral inhibition in newborn males but paradoxically increased inhibition in females. Similar sex-dependent effects were seen in mothers' assessment of their infant's self-regulatory behaviors at 3 months of age. Higher maternal choline levels partly mitigated the effect of CRP in male offspring.

CONCLUSIONS

The male fetal-placental unit appears to be more sensitive to maternal inflammation than females. Effects are particularly marked on cerebral inhibition. Deficits in cerebral inhibition 1 month after birth, similar to those observed in several mental illnesses, including schizophrenia, indicate fetal developmental pathways that may lead to later mental illness. Deficits in early infant behavior follow. Early intervention before birth, including prenatal vitamins, folate, and choline supplements, may help prevent fetal development of pathophysiological deficits that can have life-long consequences for mental health.

Sensory hypersensitivity in Tourette syndrome: A review

Tourette syndrome (TS) is a neurodevelopmental disorder defined by tics, but most patients also experience bothersome sensory phenomena, in the form of premonitory urges and/or sensory hypersensitivity. Whereas premonitory urges are temporally paired with tics, sensory hypersensitivity is a constant, heightened awareness of external and/or internal stimuli. The intensity of sensory hypersensitivity does not strongly correlate with the severity of tics or premonitory urges, suggesting it is a dissociable clinical phenomenon. At least 80% of TS patients report subjectively enhanced perception of various sensory stimuli. These same patients demonstrate normal static detection thresholds. However, individuals with TS habituate abnormally to repetitive stimuli, indicating incapacity to appropriately filter redundant sensory input, i.e. impaired sensory gating. Physiologic support for this hypothesis is provided by abnormal pre-pulse inhibition (PPI) and event-related potential (ERP) investigations. Preclinical data implicates parvalbumin-positive (PV+) interneuron dysfunction in altered sensory gating in TS and other neurodevelopment disorders. Studies probing TS sensory hypersensitivity must methodically account for comorbid psychiatric conditions, namely obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and autism spectrum disorder (ASD), as these entities appear to involve pathophysiologic processes shared with TS. The presence of psychiatric comorbidities in TS is associated with even more profound sensory processing dysfunction. A deepened understanding of TS sensory hypersensitivity will afford novel insights into disease mechanisms, clinical phenotype, and therapeutic management.

Electroencephalography and Event-Related Potential Biomarkers in Individuals at Clinical High Risk for Psychosis

Clinical outcomes vary among youths at clinical high risk for psychosis (CHR-P), with approximately 20% progressing to full-blown psychosis over 2 to 3 years and 30% achieving remission. Recent research efforts have focused on identifying biomarkers that precede psychosis onset and enhance the accuracy of clinical outcome prediction in CHR-P individuals, with the ultimate goal of developing staged treatment approaches based on the individual's level of risk. Identifying such biomarkers may also facilitate progress toward understanding pathogenic mechanisms underlying psychosis onset, which may support the development of mechanistically informed early interventions for psychosis. In recent years, electroencephalography-based event-related potential measures with established sensitivity to schizophrenia have gained traction in the study of CHR-P and its clinical outcomes. In this review, we describe the evidence for event-related potential abnormalities in CHR-P and discuss how they inform our understanding of information processing deficits as vulnerability markers for emerging psychosis and as indicators of future outcomes. Among the measures studied, P300 and mismatch negativity are notable because deficits predict conversion to psychosis and/or CHR-P remission. However, the accuracy with which these and other measures predict outcomes in CHR-P has been obscured in the prior literature by the tendency to only report group-level differences, underscoring the need for inclusion of individual predictive accuracy metrics in future studies. Nevertheless, both P300 and mismatch negativity show promise as electrophysiological markers of risk for psychosis, as target engagement measures for clinical trials, and as potential translational bridges between human studies and animal models focused on novel drug development for early psychosis.

Abnormal beta and gamma frequency neural oscillations mediate auditory sensory gating deficit in schizophrenia

BACKGROUND

Sensory gating is a process in which the brain's response to irrelevant and repetitive stimuli is inhibited. The sensory gating deficit in schizophrenia (SZ) is typically measured by the ratio or difference score of the P50 event-related potential (ERP) amplitudes in response to a paired click paradigm. While the P50 gating effect has usually been measured in relation to the peak amplitude of the S1 and S2 P50 ERPs, there is increasing evidence that inhibitory processes may be reflected by evoked or induced oscillatory activity during the inter-click interval in the beta (20-30 Hz) and gamma (30-50 Hz) frequency bands. We therefore examined the relationship between frequency specific activity in the inter-click interval with gating effects in the time and frequency domains.

METHOD

Paired-auditory stimuli were presented to 131 participants with schizophrenia and 196 healthy controls (HC). P50 ERP amplitudes to S1 and S2as well as averaged- and single-trial beta (20-30 Hz) and gamma (30-50 Hz) frequency power during the inter-click interval were measured from the CZ electrode site.

RESULTS

In the time domain, P50 gating deficits were apparent in both ratio and difference scores. This effect was mainly due to smaller S1 amplitudes in the patient group. SZ patients exhibited less evoked beta and gamma power, particularly at the 0-100 ms time point, in response to S1. Early (0-100 ms) evoked beta and gamma responses were critical in determining the S1 amplitude and extent of P50 gating across the delay interval for both HC and SZ.

CONCLUSION

Our findings support a disruption in initial sensory registration in those with SZ, and do not support an active mechanism throughout the delay interval. The degree of response to S1 and early beta and gamma frequency oscillations in the delay interval provides information about the mechanisms supporting auditory sensory gating, and may provide a framework for studying the mechanisms that support sensory inhibition.

Polymorphisms in CRYBB2 encoding βB2-crystallin are associated with antisaccade performance and memory function

βB2-crystallin (gene symbol: Crybb2/CRYBB2) was first described as a structural protein of the ocular lens before it was detected in various brain regions of the mouse, including the hippocampus and the cerebral cortex. Mutations in the mouse Crybb2 gene lead to alterations of sensorimotor gating measured as prepulse inhibition (PPI) and reduced hippocampal size, combined with an altered number of parvalbumin-positive GABAergic interneurons. Decreased PPI and alterations of parvalbumin-positive interneurons are also endophenotypes that typically occur in schizophrenia. To verify the results found in mice, we genotyped 27 single nucleotide polymorphisms (SNPs) within the CRYBB2 gene and its flanking regions and investigated different schizophrenia typical endophenotypes in a sample of 510 schizophrenia patients and 1322 healthy controls. In the case-control study, no association with schizophrenia was found. However, 3 of the 4 investigated haplotype blocks indicated a decreased CRYBB2 mRNA expression. Two of these blocks were associated with poorer antisaccade task performance and altered working memory-linked functional magnetic resonance imaging signals. For the two haplotypes associated with antisaccade performance, suggestive evidence was found with visual memory and in addition, haplotype block 4 showed a nominally significant association with reduced sensorimotor gating, measured as P50 ratio. These results were not schizophrenia-specific, but could be detected in a combined sample of patients and healthy controls. This is the first study to demonstrate the importance of βB2-crystallin for antisaccade performance and memory function in humans and therefore provides implications for βB2-crystallin function in the human brain.

Using high density EEG to assess TMS treatment in patients with schizophrenia

We present preliminary results from the ongoing study entitled “Icelandic AVH-TMS” which aim is to study the effectiveness of repetitive transcranial magnetic stimulation (rTMS) treatment for patients with schizophrenia and with persistent auditory verbal hallucinations (AVH) using symptoms and psychometric scales and high-density EEG system (256 channels). The aim of the present work was to describe cortical topography of the auditory evoked responses like P50 and N100-P300 complex in healthy participants and patients with schizophrenia and to define a robust methodology of signal quantification using dense-array EEG. Preliminary data is shown for three healthy participants and three patients in baseline conditions and for two patients we show the results recorded before and after 10 days rTMS treatment. Our results show differences in sensory gating (P50 suppresion) and a stronger N100-P300 response to rare audio stimulus after the treatment. Moreover we show the value of assessing brain electrical activity from high-density EEG (256 channels) analyzing the results in different regions of interest. However, it is premature and hazardous to assume that rTMS treatment effectiveness in patients with AVH can be assessed using P50 suppression ratio.

P50 inhibition deficit in patients with chronic schizophrenia: Relationship with cognitive impairment of MATRICS consensus cognitive battery

OBJECTIVE

Cognitive impairment is a core symptom of schizophrenia (SCZ); however, its pathophysiological mechanisms remain unclear. The sensory gating (SG) deficits reflected by P50 inhibition are recurring in SCZ, and this inhibition may be related to the cognitive deficits seen in these individuals. This study aimed to investigate the relationship between P50 inhibition and cognitive dysfunction in SCZ, which has not been fully investigated up to this point.

METHODS

A total of 270 individuals with chronic SCZ and 116 healthy controls were enrolled in the study. Psychopathology of SCZ was rated by the positive and negative syndrome scale (PANSS), while cognitive function and P50 inhibition of subjects were assessed by the MATRICS Consensus Cognitive Battery (MCCB) and the electroencephalography system.

RESULTS

The MCCB total and its 10 index scores were significantly lower in patients than those in healthy controls (all p < 0.001). SCZ patients had a lower amplitude of S1, and higher P50 ratio than healthy controls (both p < 0.01). However, there were no significant correlations between the P50 ratio and any of the PANSS total and its subscale scores in SCZ patients (all p > 0.05). Moreover, no correlation was found between the P50 components and the MCCB scores (all p > 0.05).

CONCLUSIONS

Our findings suggest that the P50 inhibition deficits occur in Chinese individuals with SCZ, which may not be associated with their clinical symptoms and cognitive impairment.

EEG-Based Brain Functional Connectivity in First-Episode Schizophrenia Patients, Ultra-High-Risk Individuals, and Healthy Controls During P50 Suppression

Dysfunctional processing of auditory sensory gating has generally been found in schizophrenic patients and ultra-high-risk (UHR) individuals. The aim of the study was to investigate the differences of functional interaction between brain regions and performance during the P50 sensory gating in UHR group compared with those in first-episode schizophrenia patients (FESZ) and healthy controls (HC) groups. The study included 128-channel scalp Electroencephalogram (EEG) recordings during the P50 auditory paradigm for 35 unmedicated FESZ, 30 drug-free UHR, and 40 HC. Cortical sources of scalp electrical activity were recomputed using exact low-resolution electromagnetic tomography (eLORETA), and functional brain networks were built at the source level and compared between the groups (FESZ, UHR, HC). A classifier using decision tree was designed for differentiating the three groups, which uses demographic characteristics, MATRICS Consensus Cognitive Battery parameters, behavioral features in P50 paradigm, and the measures of functional brain networks based on graph theory during P50 sensory gating. The results showed that very few brain connectivities were significantly different between FESZ and UHR groups during P50 sensory gating, and that a large number of brain connectivities were significantly different between FESZ and HC groups and between UHR and HC groups. Furthermore, the FESZ group had a stronger connection in the right superior frontal gyrus and right insula than the HC group. And the UHR group had an enhanced connection in the paracentral lobule and the middle temporal gyrus compared with the HC group. Moreover, comparison of classification analysis results showed that brain network metrics during P50 sensory gating can improve the accuracy of the classification for FESZ, UHR and HC groups. Our findings provide insight into the mechanisms of P50 suppression in schizophrenia and could potentially improve the performance of early identification and diagnosis of schizophrenia for the earliest intervention.

Is schizotypic maternal personality linked to sensory gating abilities during infancy?

Schizotypy is a personality dimension within the general population elevated among schizophrenia-spectrum patients and their first-degree relatives. Sensory gating is the pre-attentional habituation of responses distinguishing between important and irrelevant information. This is measured by event-related potentials, which have been found to display abnormalities in schizophrenic disorders. The current study investigated whether 6-month-old infants of mothers with schizotypic traits display sensory gating abnormalities. The paired-tone paradigm: two identical auditory tones (stimulus 1 and stimulus 2) played 500 ms apart, was used to probe the selective activation of the brain during 15-minutes of sleep. Their mothers completed the Oxford and Liverpool Inventory of Feelings and Experiences-Short Form as an index of schizotypy dimensionality, categorized into: infants of control, and infants of schizotypic, mothers. The findings revealed that although the infants' P50 components displayed significant differences between stimulus 1 and stimulus 2 in the paired-tone paradigm, there was no clear difference between infants of schizotypic and infants of control mothers. In contrast, all mothers displayed significant differences between stimulus 1 and stimulus 2, as observed in the infants, but also significant differences between their sensory gating ability correlated with schizotypy dimensionality. These findings are consistent with sensory processes, such as sensory gating, evidencing impairment in schizophrenia-spectrum disorders. The present research supports the idea that first-degree relatives of individuals who identify on this spectrum, within the sub-clinical category, do not display the same deficit at 6 postnatal months of age.

Alterations in resting-state gamma activity in patients with schizophrenia: a high-density EEG study

Alterations of EEG gamma activity in schizophrenia have been reported during sensory and cognitive tasks, but it remains unclear whether changes are present in resting state. Our aim was to examine whether changes occur in resting state, and to delineate those brain regions where gamma activity is altered. Furthermore, we wanted to identify the associations between changes in gamma activity and psychopathological characteristics. We studied gamma activity (30-48 Hz) in 60 patients with schizophrenia and 76 healthy controls. EEGs were acquired in resting state with closed eyes using a high-density, 256-channel EEG-system. The two groups were compared in absolute power measures in the gamma frequency range. Compared to controls, in patients with schizophrenia the absolute power was significantly elevated (false discovery rate corrected p < 0.05). The alterations clustered into fronto-central and posterior brain regions, and were positively associated with the severity of psychopathology, measured by the PANSS. Changes in gamma activity can lead to disturbed coordination of large-scale brain networks. Thus, the increased gamma activity in certain brain regions that we found may result in disturbances in temporal coordination of task-free/resting-state networks in schizophrenia. Positive association of increased gamma power with psychopathology suggests that altered gamma activity provides a contribution to symptom presentation.

NMDA Receptor Antagonist Effects on Speech-Related Mismatch Negativity and Its Underlying Oscillatory and Source Activity in Healthy Humans

Background: Previous studies in schizophrenia have consistently shown that deficits in the generation of the auditory mismatch negativity (MMN) – a pre-attentive, event-related potential (ERP) typically elicited by changes to simple sound features – are linked to N-methyl-D-aspartate (NMDA) receptor hypofunction. Concomitant with extensive language dysfunction in schizophrenia, patients also exhibit MMN deficits to changes in speech but their relationship to NMDA-mediated neurotransmission is not clear. Accordingly, our study aimed to investigate speech MMNs in healthy humans and their underlying electrophysiological mechanisms in response to NMDA antagonist treatment. We also evaluated the relationship between baseline MMN/electrocortical activity and emergent schizophrenia-like symptoms associated with NMDA receptor blockade.

Methods: In a sample of 18 healthy volunteers, a multi-feature Finnish language paradigm incorporating changes in syllables, vowels and consonant stimuli was used to assess the acute effects of the NMDA receptor antagonist ketamine and placebo on the MMN. Further, measures of underlying neural activity, including evoked theta power, theta phase locking and source-localized current density in cortical regions of interest were assessed. Subjective symptoms were assessed with the Clinician Administered Dissociative States Scale (CADSS).

Results: Participants exhibited significant ketamine-induced increases in psychosis-like symptoms and depending on temporal or frontal recording region, co-occurred with reductions in MMN generation in response to syllable frequency/intensity, vowel duration, across vowel and consonant deviants. MMN attenuation was associated with decreases in evoked theta power, theta phase locking and diminished current density in auditory and inferior frontal (language-related cortical) regions. Baseline (placebo) MMN and underlying electrophysiological features associated with the processing of changes in syllable intensity correlated with the degree of psychotomimetic response to ketamine.

Conclusion: Ketamine-induced impairments in healthy human speech MMNs and their underlying electrocortical mechanisms closely resemble those observed in schizophrenia and support a model of dysfunctional NMDA receptor-mediated neurotransmission of language processing deficits in schizophrenia.

Alterations in Schizophrenia-Associated Genes Can Lead to Increased Power in Delta Oscillations

Genome-wide association studies have implicated many ion channels in schizophrenia pathophysiology. Although the functions of these channels are relatively well characterized by single-cell studies, the contributions of common variation in these channels to neurophysiological biomarkers and symptoms of schizophrenia remain elusive. Here, using computational modeling, we show that a common biomarker of schizophrenia, namely, an increase in delta-oscillation power, may be a direct consequence of altered expression or kinetics of voltage-gated ion channels or calcium transporters. Our model of a circuit of layer V pyramidal cells highlights multiple types of schizophrenia-related variants that contribute to altered dynamics in the delta-frequency band. Moreover, our model predicts that the same membrane mechanisms that increase the layer V pyramidal cell network gain and response to delta-frequency oscillations may also cause a deficit in a single-cell correlate of the prepulse inhibition, which is a behavioral biomarker highly associated with schizophrenia.

Auditory steady state response deficits are associated with symptom severity and poor functioning in patients with psychotic disorder

OBJECTIVES

Gamma oscillation is important for cortico-cortical coordination and the integration of information across neural networks. The 40 Hz auditory steady-state response (ASSR), which reflects neural synchrony in the gamma band (30-100 Hz), is abnormal in patients with schizophrenia (SZ). The present study used the ASSR at multiple frequencies to examine (1) gamma dysfunction in patients with SZ, schizoaffective (SA), and bipolar disorder (BD) compared with controls, (2) the relationship between ASSR measures and clinical symptom severity, and (3) the relationship between ASSR measures and real-life community functioning.

METHODS

EEG was recorded from 75 controls, 52 SZ, 55 SA, and 89 BD patients during 20-30-40-Hz binaural click trains. ANCOVA was used to compare ASSR measures between groups controlling for age, sex, and education. Associations between ASSR measures, symptom severity, and community functioning were examined using linear regression and Pearson partial correlations.

RESULTS

ASSR deficits at gamma frequency were observed in all patient groups. SA patients showed additional specific deficit in the 20 Hz ASSR. Severity of manic, depressive, and anxiety symptoms mediated ASSR deficits. Severity of hallucinatory symptom and community functioning, particularly independent living/meaningful activity, were significantly and independently associated with the 40 Hz ASSR.

CONCLUSIONS

SZ, SA and BD patients are likely to share the same abnormalities in neural processes that generate gamma oscillations. 40 Hz ASSR are associated with community functioning across patients and may serve as a biomarker for predicting functional outcome.

Impact of childhood trauma on sensory gating in patients with first-episode schizophrenia

BACKGROUND

Childhood trauma (CT) has been found to contribute to the onset of schizophrenia and auditory sensory gating deficit is a leading endophenotype for schizophrenia. However, the association between the CT and sensory gating in first-episode schizophrenia remains elusive.

METHODS

Fifty-six patients and 49 age and sex-matched healthy controls were assessed using the Childhood Trauma Questionnaire-Short Form (CTQ-SF) for CT and Positive and Negative Syndrome Scale (PANSS) for symptoms severity. Sensory gating was tested using the modified paradigm, perceived spatial separation-induced prepulse inhibition (PSS-PPI), and the perceived spatial co-location PPI (PSC-PPI or classical PPI).

RESULTS

Comparing with healthy controls, the patients had significantly higher score on sexual abuse (t = 2.729, p < 0.05), lower PSS- PPI, % (ISI = 120 ms and ISI = 60 ms) (t = - 3.089, - 4.196, p < 0.05). Univariate analysis revealed the absence of a significant correlation among CT, PPI paradigms and symptoms. However, multiple linear regression analyses demonstrated the CTQ-SF total was negatively associated with PSS PPI (ISI = 120 ms) (p = 0.018).

CONCLUSION

The current study illustrates that the impact of CT on sensory gating in patients with first-episode schizophrenia, and thus we conclude that CT may be a risk factor to the occurrence of schizophrenia through its impact on sensory gating.

Gamma band oscillations in the early phase of psychosis: A systematic review

Abnormal gamma oscillations, measured by electroencephalography (EEG), have been associated with chronic psychotic disorders, but their prevalence in the early phase of psychosis is less clear. We sought to address this by systematically reviewing the relevant literature. We searched for EEG studies of gamma band oscillations in subjects at high risk for psychosis and in patients with first episode psychosis. The following measures of gamma oscillations were extracted: resting power, evoked power, induced power, connectivity and peak frequency. Forty-five studies with a total of 3099 participants were included. There were potential sources of bias in the study designs and potential artefacts. Although there were few consistent findings, several studies reported decreased evoked or induced power in both high risk subjects and first episode patients. Studies using larger samples with serial EEG measurements, and designs that minimise artefacts that occur at the gamma frequency may advance work in this area.

The coupling of low-level auditory dysfunction and oxidative stress in psychosis patients

Patients diagnosed with schizophrenia often present with low-level sensory deficits. It is an open question whether there is a functional link between these deficits and the pathophysiology of the disease, e.g. oxidative stress and glutathione (GSH) metabolism dysregulation. Auditory evoked potentials (AEPs) were recorded from 21 psychosis disorder patients and 30 healthy controls performing an active, auditory oddball task. AEPs to standard sounds were analyzed within an electrical neuroimaging framework. A peripheral measure of participants' redox balance, the ratio of glutathione peroxidase and glutathione reductase activities (GPx/GR), was correlated with the AEP data. Patients displayed significantly decreased AEPs over the time window of the P50/N100 complex resulting from significantly weaker responses in the left temporo-parietal lobe. The GPx/GR ratio significantly correlated with patients' brain activity during the time window of the P50/N100 in the medial frontal lobe. We show for the first time a direct coupling between electrophysiological indices of AEPs and peripheral redox dysregulation in psychosis patients. This coupling is limited to stages of auditory processing that are impaired relative to healthy controls and suggests a link between biochemical and sensory dysfunction. The data highlight the potential of low-level sensory processing as a trait-marker of psychosis.

Acute Phencyclidine Alters Neural Oscillations Evoked by Tones in the Auditory Cortex of Rats

BACKGROUND/AIMS

The onset response to a single tone as measured by electroencephalography (EEG) is diminished in power and synchrony in schizophrenia. Because neural synchrony, particularly at gamma frequencies (30-80 Hz), is hypothesized to be supported by the N-methyl-D-aspartate receptor (NMDAr) system, we tested whether phencyclidine (PCP), an NMDAr antagonist, produced similar deficits to tone stimuli in rats.

METHODS

Experiment 1 tested the effect of a PCP dose (1.0, 2.5, and 4.5 mg/kg) on response to single tones on intracranial EEG recorded over the auditory cortex in rats. Experiment 2 evaluated the effect of PCP after acute administration of saline or PCP (5 mg/kg), after continuous subchronic administration of saline or PCP (5 mg/kg/day), and after a week of drug cessation. In both experiments, a time-frequency analysis quantified mean power (MP) and phase locking factor (PLF) between 1 and 80 Hz. Event-related potentials (ERPs) were also measured to tones, and EEG spectral power in the absence of auditory stimuli.

RESULTS

Acute PCP increased PLF and MP between 10 and 30 Hz, while decreasing MP and PLF between approximately 50 and 70 Hz. Acute PCP produced a dose-dependent broad-band increase in EEG power that extended into gamma range frequencies. There were no consistent effects of subchronic administration on gamma range activity. Acute PCP increased ERP amplitudes for the P16 and N70 components.

CONCLUSIONS

Findings suggest that acute PCP-induced NMDAr hypofunction has differential effects on neural power and synchrony which vary with dose, time course of administration and EEG frequency. EEG synchrony and power appear to be sensitive translational biomarkers for disrupted NMDAr function, which may contribute to the pathophysiology of schizophrenia and other neuropsychiatric disorders.

A Meta-analytic Review of Auditory Event-Related Potential Components as Endophenotypes for Schizophrenia: Perspectives From First-Degree Relatives

INTRODUCTION

As endophenotypes bridge the gap between genetics and phenotypic disease expression, identifying reliable markers is important for fostering understanding of pathophysiology. The present aim was to conduct current meta-analyses of 3 key auditory event-related potential (ERP) components that have been held as potential endophenotypes for schizophrenia: P50, P300 amplitude and latency, and mismatch negativity (MMN), reflective of sensory gating, attention and classification speed, and perceptual discrimination ability, respectively. In order to assess endophenotype viability, these components were examined in unaffected relatives of patients with schizophrenia and healthy controls.

METHODS

Effect sizes (ES) were examined between relatives and controls for P50 suppression (10 studies, n = 360 relatives, 473 controls), P300 amplitude (20 studies, n = 868 relatives, 961 controls), P300 latency (17 studies, n = 674 relatives, 792 controls), and MMN (11 studies, n = 377 relatives, 552 controls).

RESULTS

Reliable differences in P50 suppression (ES = 0.86, P < .001), P300 amplitude (ES = -0.52, P < .001), and P300 latency (ES = 0.44, P < .05) were found between unaffected relatives and controls. A trend was found between relatives and controls for MMN (ES = 0.21, P = 0.06), and the use of extraneous channels was found to be a significant moderator (P = 0.01). When MMN was analyzed using frontocentral channel Fz, a significant difference was found (ES = 0.26, P < 0.01).

DISCUSSION

The results indicate that P50 suppression, P300 amplitude and P300 latency, and MMN may serve as viable endophenotypes for schizophrenia.

Atypical visual and somatosensory adaptation in schizophrenia-spectrum disorders

Neurophysiological investigations in patients with schizophrenia consistently show early sensory processing deficits in the visual system. Importantly, comparable sensory deficits have also been established in healthy first-degree biological relatives of patients with schizophrenia and in first-episode drug-naive patients. The clear implication is that these measures are endophenotypic, related to the underlying genetic liability for schizophrenia. However, there is significant overlap between patient response distributions and those of healthy individuals without affected first-degree relatives. Here we sought to develop more sensitive measures of sensory dysfunction in this population, with an eye to establishing endophenotypic markers with better predictive capabilities. We used a sensory adaptation paradigm in which electrophysiological responses to basic visual and somatosensory stimuli presented at different rates (ranging from 250 to 2550 ms interstimulus intervals, in blocked presentations) were compared. Our main hypothesis was that adaptation would be substantially diminished in schizophrenia, and that this would be especially prevalent in the visual system. High-density event-related potential recordings showed amplitude reductions in sensory adaptation in patients with schizophrenia (N=15 Experiment 1, N=12 Experiment 2) compared with age-matched healthy controls (N=15 Experiment 1, N=12 Experiment 2), and this was seen for both sensory modalities. At the individual participant level, reduced adaptation was more robust for visual compared with somatosensory stimulation. These results point to significant impairments in short-term sensory plasticity across sensory modalities in schizophrenia. These simple-to-execute measures may prove valuable as candidate endophenotypes and will bear follow-up in future work.

Positive and Negative Symptoms in Schizophrenia Relate to Distinct Oscillatory Signatures of Sensory Gating

Oscillatory activity in neural populations and temporal synchronization within these populations are important mechanisms contributing to perception and cognition. In schizophrenia, perception and cognition are impaired. Aberrant gating of irrelevant sensory information, which has been related to altered oscillatory neural activity, presumably contributes to these impairments. However, the link between schizophrenia symptoms and sensory gating deficits, as reflected in oscillatory activity, is not clear. In this electroencephalography study, we used a paired-stimulus paradigm to investigate frequency-resolved oscillatory activity in 22 schizophrenia patients and 22 healthy controls. We found sensory gating deficits in patients compared to controls, as reflected in reduced gamma-band power and alpha-band phase synchrony difference between the first and the second auditory stimulus. We correlated these markers of neural activity with a five-factor model of the Positive and Negative Syndrome Scale. Gamma-band power sensory gating was positively correlated with positive symptoms. Moreover, alpha-band phase synchrony sensory gating was negatively correlated with negative symptoms. A cluster analysis revealed three schizophrenia phenotypes, characterized by (i) aberrant gamma-band power and high positive symptoms, (ii) aberrant alpha-band phase synchrony, low positive, and low negative symptom scores or (iii) by intact sensory gating and high negative symptoms. Our study demonstrates that aberrant neural synchronization, as reflected in gamma-band power and alpha-band phase synchrony, relates to the schizophrenia psychopathology. Different schizophrenia phenotypes express distinct levels of positive and negative symptoms as well as varying degrees of aberrant oscillatory neural activity. Identifying the individual phenotype might improve therapeutic interventions in schizophrenia.

Startle Modification and P50 Gating in Schizophrenia Patients and Controls: Russian Population

Prepulse modification of the acoustic startle response (ASR) and P50 gating are potential neurophysiological endophenotypes of schizophrenia and may be used in the construction of valid clinical biomarkers. Such approach requires a large amount of data obtained in the representative samples from different gender, socio-typological and ethnic groups, replicating studies using the similar protocols and meta-analyses. This is a replication study of ASR and the first study of P50 suppression in Russian patients with schizophrenia (n = 28) and healthy controls (n = 25). ASR and P50 were estimated according to standard protocols. Patients exhibited increased baseline ASR latency (d = 0.35, p = .026) and reduced prepulse inhibition (PPI) at 60 ms interval (d = 0.39, p = .003) and 120 ms interval (d = 0.37, p = .005) relative to controls. In the P50 test patients displayed greater S2 response amplitude (d = 0.24, p = .036) and deficit of P50 suppression (d = 0.43, p = .001). No correlations of PPI and P50 suppression were found in both groups. Only in controls prepulse ASR facilitation (at 2500 ms interval) positively correlated with P50 suppression (r = -.514, p = .013). In patients PPI displayed significant correlations with Difficulty in abstract thinking (N5: r = -.49, p = .005) and Hallucination (P3: r = .40, p = .036) PANSS scales. Logistic regression showed that the combination of PPI and P50 suppression could serve as a diagnostic predictor. Obtained results demonstrated that both PPI and P50 could be regarded as potential schizophrenia biomarkers in Russian population.

EEG-Informed fMRI Reveals a Disturbed Gamma-Band-Specific Network in Subjects at High Risk for Psychosis

OBJECTIVES

Abnormalities of oscillatory gamma activity are supposed to reflect a core pathophysiological mechanism underlying cognitive disturbances in schizophrenia. The auditory evoked gamma-band response (aeGBR) is known to be reduced across all stages of the disease. The present study aimed to elucidate alterations of an aeGBR-specific network mediated by gamma oscillations in the high-risk state of psychosis (HRP) by means of functional magnetic resonance imaging (fMRI) informed by electroencephalography (EEG).

METHODS

EEG and fMRI were simultaneously recorded from 27 HRP individuals and 26 healthy controls (HC) during performance of a cognitively demanding auditory reaction task. We used single trial coupling of the aeGBR with the corresponding blood oxygen level depending response (EEG-informed fMRI).

RESULTS

A gamma-band-specific network was significantly lower active in HRP subjects compared with HC (random effects analysis, P < .01, Bonferroni-corrected for multiple comparisons) accompanied by a worse task performance. This network involved the bilateral auditory cortices, the thalamus and frontal brain regions including the anterior cingulate cortex, as well as the bilateral dorsolateral prefrontal cortex.

CONCLUSIONS

For the first time we report a reduced activation of an aeGBR-specific network in HRP subjects brought forward by EEG-informed fMRI. Because the HRP reflects the clinical risk for conversion to psychotic disorders including schizophrenia and the aeGBR has repeatedly been shown to be altered in patients with schizophrenia the results of our study point towards a potential applicability of aeGBR disturbances as a marker for the prediction of transition of HRP subjects to schizophrenia.

Quantitative Measures of Craniofacial Dysmorphology in a Family Study of Schizophrenia and Bipolar Illness

Several laboratories, including ours, have reported an overrepresentation of craniofacial (CF) anomalies in schizophrenia (SZ). How might this dysmorphology arise in a brain-based disorder? Because the brain and face derive from shared embryologic primordia and morphogenetic forces, maldevelopmental processes may result in both CF and brain dysmorphology.Our approach is 2-pronged. First, we have employed, for the first time in the study of psychiatric disorders, objective measures of CF morphology that utilize an extensive normative database, permitting computation of standardized scores for each subject. Second, we have rendered these findings biologically interpretable by adopting principles of embryology in the analysis of dysmorphology.Dependent measures in this investigation focused on derivatives of specific embryonic primordia and were contrasted among probands with psychotic disorders, their first-degree relatives, and normal controls (NC). Subject groups included patients with a diagnosis of SZ (N = 39) or bipolar (BP) disorder with psychotic features (N = 32), their clinically unaffected relatives (N = 82 and N = 41, respectively), and NC (N = 95) subjects.Anomalies involving derivatives of frontonasal and mandibular embryonic primordia showed a clear association with psychotic illness, as well as familial aggregation in relatives in both diagnostic groups. In contrast, one class of CF anomalies emerged only among SZ probands and their first-degree relatives: dysmorphology arising along the junction of the frontonasal and maxillary prominence derivatives, manifested as marked asymmetries. This class was not overrepresented among the BP patients nor among their relatives, indicating that this dysmorphology appears to be specific to SZ and not a generalized feature of psychosis. We discuss these findings in light of embryologic models that relate brain regions to specific CF areas.

Reduced auditory evoked gamma band response and cognitive processing deficits in first episode schizophrenia

OBJECTIVES

Gamma-band oscillations (e.g., the early auditory evoked gamma-band response, aeGBR) have been suggested to mediate cognitive and perceptual processes by driving the synchronization of local neuronal populations. Reduced aeGBR is a consistent finding in patients with schizophrenia and high-risk subjects, and has been proposed to represent an endophenotype for the illness. However, it is still unclear whether this reduction represents a deficit in sensory or cognitive processes, or a combination of the two. The present study investigated this question by manipulating the difficulty of an auditory reaction task in patients with first-episode schizophrenia and healthy controls.

METHODS

A 64-channel EEG was recorded in 23 patients with first-episode schizophrenia and 22 healthy controls during two conditions of an auditory reaction task: an easy condition that merely required low-level vigilance, and a difficult condition that placed significant demands on attention and working memory.

RESULTS

In contrast to healthy controls, patients failed to increase aeGBR power and phase-locking in the difficult condition. In patients, aeGBR power and phase-locking indices were associated with working memory deficits.

CONCLUSIONS

The observed results confirm the applicability of aeGBR disturbances as a stable endophenotype of schizophrenia, and suggest a cognitive, rather than sensory, deficit at their origin.

Prenatal choline and the development of schizophrenia

Background

The primary prevention of illness at the population level, the ultimate aim of medicine, seems out of reach for schizophrenia. Schizophrenia has a strong genetic component, and its pathogenesis begins long before the emergence of psychosis, as early as fetal brain development. Cholinergic neurotransmission at nicotinic receptors is a pathophysiological mechanism related to one aspect of this genetic risk. Choline activates these nicotinic receptors during fetal brain development. Dietary supplementation of maternal choline thus emerges as a possible intervention in pregnancy to alter the earliest developmental course of the illness.

Aim

Review available literature on the relationship of choline supplementation or choline levels during pregnancy and fetal brain development.

Methods

A Medline search was used to identify studies assessing effects of choline in human fetal development. Studies of other prenatal risk factors for schizophrenia and the role of cholinergic neurotransmission in its pathophysiology were also identified.

Results

Dietary requirements for choline are high during pregnancy because of its several uses, including membrane biosynthesis, one-carbon metabolism, and cholinergic neurotransmission. Its ability to act directly at high concentrations as a nicotinic agonist is critical for normal brain circuit development. Dietary supplementation in the second and third trimesters with phosphatidyl-choline supports these functions and is associated generally with better fetal outcome. Improvement in inhibitory neuronal functions whose deficit is associated with schizophrenia and attention deficit disorder has been observed.

Conclusion

Prenatal dietary supplementation with phosphatidyl-choline and promotion of diets rich in choline-containing foods (meats, soybeans, and eggs) are possible interventions to promote fetal brain development and thereby decrease the risk of subsequent mental illnesses. The low risk and short (sixmonth) duration of the intervention makes it especially conducive to population-wide adoption. Similar findings with folate for the prevention of cleft palate led to recommendations for prenatal pharmacological supplementation and dietary improvement. However, definitive proof of the efficacy of prenatal choline supplementation will not be available for decades (because of the 20-year lag until the onset of schizophrenia), so public health officials need to decide whether or not promoting choline supplementation is justified based on the limited information available.

Delta frequency optogenetic stimulation of the thalamic nucleus reuniens is sufficient to produce working memory deficits: relevance to schizophrenia

BACKGROUND

Low-frequency (delta/theta) oscillations in the thalamocortical system are elevated in schizophrenia during wakefulness and are also induced in the N-methyl-D-asparate receptor hypofunction rat model. To determine whether abnormal delta oscillations might produce functional deficits, we used optogenetic methods in awake rats. We illuminated channelrhodopsin-2 in the thalamic nucleus reuniens (RE) at delta frequency and measured the effect on working memory (WM) performance (the RE is involved in WM, a process affected in schizophrenia [SZ]).

METHODS

We injected RE with adeno-associated virus to transduce cells with channelrhodopsin-2. An optical fiber was implanted just dorsal to the hippocampus in order to illuminate RE axon terminals.

RESULTS

During optogenetic delta frequency stimulation, rats displayed a strong WM deficit. On the following day, performance was normal if illumination was omitted.

CONCLUSIONS

The optogenetic experiments show that delta frequency stimulation of a thalamic nucleus is sufficient to produce deficits in WM. This result supports the hypothesis that delta frequency bursting in particular thalamic nuclei has a causal role in producing WM deficits in SZ. The action potentials in these bursts may "jam" communication through the thalamus, thereby interfering with behaviors dependent on WM. Studies in thalamic slices using the N-methyl-D-asparate receptor hypofunction model show that delta frequency bursting is dependent on T-type Ca(2+) channels, a result that we confirmed here in vivo. These channels, which are strongly implicated in SZ by genome-wide association studies, may thus be a therapeutic target for treatment of SZ.

Stimulus train duration but not attention moderates γ-band entrainment abnormalities in schizophrenia

Electroencephalographic (EEG) studies of auditory steady-state responses (aSSRs) non-invasively probe gamma-band (40-Hz) oscillatory capacity in sensory cortex with high signal-to-noise ratio. Consistent reports of reduced 40-Hz aSSRs in persons with schizophrenia (SZ) indicate its potential as an efficient biomarker for the disease, but studies have been limited to passive or indirect listening contexts with stereotypically short (500ms) stimulus trains. An inability to modulate sensorineural processing in accord with behavioral goals or within the sensory environmental context may represent a fundamental deficit in SZ, but whether and how this deficit relates to reduced aSSRs is unknown. We systematically varied stimulus duration and attentional contexts to further mature the 40-Hz aSSR as biomarker for future translational or mechanistic studies. Eighteen SZ and 18 healthy subjects (H) were presented binaural pure-tones with or without sinusoidal amplitude modulation at 40-Hz. Stimulus duration (500-ms or 1500-ms) and attention (via a button press task) were varied across 4 separate blocks. Evoked potentials recorded with dense-array EEGs were analyzed in the time-frequency domain. SZ displayed reduced 40-Hz aSSRs to typical stimulation parameters, replicating previous findings. In H, aSSRs were reduced when stimuli were presented in longer trains and were slightly enhanced by attention. Only the former modulation was impaired in SZ and correlated with sensory discrimination performance. Thus, gamma-band aSSRs are modulated by both attentional and stimulus duration contexts, but only modulations related to physical stimulus properties are abnormal in SZ, supporting its status as a biomarker of psychotic perceptual disturbance involving non-attentional sensori-cortical circuits.

Clarifying the functional process represented by P50 suppression

P50 suppression refers to the amplitude-reduction of the P50 event related potential to the second (S2) relative to the first (S1) of identical auditory stimuli presented 500ms apart. Theory suggests that refractory periods (RPs) and/or inhibitory inputs (II) underlie P50 suppression. The present study manipulated interval between stimulus pairs (IPI: 2, 8s) and direction of participants' attention (Attention, Non-Attention) in order to determine which theory best explains P50 suppression. The rationale is that: 1/ RP and II predict opposite effects of manipulating the functionality of the mechanism responsible for S2P50 suppression (e.g. reducing function would increase S2P50 according to the II and decrease S2P50 according to the RP hypothesis); 2/ IPI2 (relative to IPI8) will reduce functionality of the mechanism responsible for S2P50 suppression, as it results in less recovery of (and a greater challenge to) that mechanism - RP would thus predict reduced S2P50, whereas II would predict enhanced S2P50 amplitude; and 3/ where the mechanism responsible for S2P50 suppression is challenged (i.e. at IPI2, due to insufficient recovery), Attention (relative to Non-Attention) will enhance functionality of this mechanism - RP would thus predict increased S2P50, whereas II would predict reduced S2P50 amplitude. In the Non-Attention paradigm, reducing IPI from 8 to 2s tended to increase S2P50 amplitude (and consequently impaired P50 suppression), and in the 2s IPI paradigm, directing attention towards the stimuli reduced S2P50 amplitude (and improved P50 suppression), with both effects supporting the II hypothesis only.

Genomewide association analyses of electrophysiological endophenotypes for schizophrenia and psychotic bipolar disorders: a preliminary report

Several event-related potentials (ERP), including P3, sensory gating (P50), and gamma oscillation, are robustly impaired in patients with schizophrenia (SCZ) and bipolar disorder (BIP). Although these ERPs are known to be heritable, little is known about the specific genetic loci involved and the degree to which they overlap with loci influencing mood and psychotic disorders. In the present study, we conducted GWAS to a) identify common variants associated with ERP endophenotypes, and b) construct polygenic risk scores (PRS) to examine overlap between genetic components of ERPs and mood and psychotic disorders. The sample consisted of 271 patients with SCZ or psychotic BIP diagnosis and 128 controls for whom ERP and genomewide data were available. GWAS were conducted using the full sample. PRS, derived from the Psychiatric Genomics Consortium (PGC) analyses of SCZ, BIP, and major depressive disorder were applied to each ERP phenotype. We identified a region on chromosome 14 that was significantly associated with sensory gating (peak SNP rs10132223, P = 1.27 × 10(-9) ). This locus has not been previously associated with psychotic illness in PGC-GWAS. In the PRS analyses, patients with a higher load of SCZ risk alleles had reduced gamma response whereas patients with a higher load of BIP risk alleles had smaller P3 amplitude. We observed a genomewide significant locus on chromosome 14 for P50. This locus may influence P50 but not psychotic illness. Among patients with psychotic illness, PRS results indicated genetic overlap between SCZ loci and gamma oscillation and between BIP loci and P3 amplitude.

Pyramidal cell selective ablation of N-methyl-D-aspartate receptor 1 causes increase in cellular and network excitability

BACKGROUND

Neuronal activity at gamma frequency is impaired in schizophrenia (SZ) and is considered critical for cognitive performance. Such impairments are thought to be due to reduced N-methyl-D-aspartate receptor (NMDAR)-mediated inhibition from parvalbumin interneurons, rather than a direct role of impaired NMDAR signaling on pyramidal neurons. However, recent studies suggest a direct role of pyramidal neurons in regulating gamma oscillations. In particular, a computational model has been proposed in which phasic currents from pyramidal cells could drive synchronized feedback inhibition from interneurons. As such, impairments in pyramidal neuron activity could lead to abnormal gamma oscillations. However, this computational model has not been tested experimentally and the molecular mechanisms underlying pyramidal neuron dysfunction in SZ remain unclear.

METHODS

In the present study, we tested the hypothesis that SZ-related phenotypes could arise from reduced NMDAR signaling in pyramidal neurons using forebrain pyramidal neuron specific NMDA receptor 1 knockout mice.

RESULTS

The mice displayed increased baseline gamma power, as well as sociocognitive impairments. These phenotypes were associated with increased pyramidal cell excitability due to changes in inherent membrane properties. Interestingly, mutant mice showed decreased expression of GIRK2 channels, which has been linked to increased neuronal excitability.

CONCLUSIONS

Our data demonstrate for the first time that NMDAR hypofunction in pyramidal cells is sufficient to cause electrophysiological, molecular, neuropathological, and behavioral changes related to SZ.

Preliminary evidence for reduced auditory lateral suppression in schizophrenia

BACKGROUND

Well-documented auditory processing deficits such as impaired frequency discrimination and reduced suppression of auditory brain responses in schizophrenia (SZ) may contribute to abnormal auditory functioning in everyday life. Lateral suppression of non-stimulated neurons by stimulated neurons has not been extensively assessed in SZ and likely plays an important role in precise encoding of sounds. Therefore, this study evaluated whether lateral suppression of activity in auditory cortex is impaired in SZ.

METHODS

SZ participants and control participants watched a silent movie with subtitles while listening to trials composed of a 0.5s control stimulus (CS), a 3s filtered masking noise (FN), and a 0.5s test stimulus (TS). The CS and TS were identical on each trial and had energy corresponding to the high energy (recurrent suppression) or low energy (lateral suppression) portions of the FN. Event-related potentials were recorded and suppression was measured as the amplitude change between CS and TS.

RESULTS

Peak amplitudes of the auditory P2 component (160-260ms) showed reduced lateral but not recurrent suppression in SZ participants.

CONCLUSIONS

Reduced lateral suppression in SZ participants may lead to overlap of neuronal populations representing different auditory stimuli. Such imprecise neural representations may contribute to the difficulties SZ participants have in discriminating complex stimuli in everyday life.

Neural oscillations as a translational tool in schizophrenia research: rationale, paradigms and challenges

Neural oscillations have received recently a great deal of interest in schizophrenia research because of the possibility to integrate findings from non-invasive electro/magnetoencephalographical recordings with pre-clinical research, which could potentially lead to the identification of pathophysiological mechanisms and novel treatment targets. In the current paper, we review the potential as well as the challenges of this approach by summarizing findings on alterations in rhythmic activity from both animal models and human data which have implicated dysfunctional neural oscillations in the explanation of cognitive deficits and certain clinical symptoms of schizophrenia. Specifically, we will focus on findings that have examined neural oscillations during 1) perceptual processing, 2) working memory and executive processes and 3) spontaneous activity. The importance of the development of paradigms suitable for human and animal models is discussed as well as the search for mechanistic explanation for oscillatory dysfunctions.

Neuronal activity of the prefrontal cortex is reduced in rats selectively bred for deficient sensorimotor gating

Rats selectively bred for deficient prepulse inhibition (PPI), an operant measure of sensorimotor gating in which a weak prepulse stimulus attenuates the response to a subsequent startling stimulus, may be used to study certain pathophysiological mechanisms and therapeutic strategies for neuropsychiatric disorders with abnormalities in information processing, such as schizophrenia and Tourette's syndrome (TS). Little is known about neuronal activity in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAC), which are involved in the modulation of PPI. Here, we examined neuronal activity in these structures, and also in the entopeduncular nucleus (EPN), since lesions of this region alleviate the PPI deficit. Male rats with breeding-induced high and low expression of PPI (n=7, each) were anesthetized with urethane (1.4 mg/kg). Single-unit activity and local field potentials were recorded in the mPFC, the NAC and in the EPN. In the mPFC discharge rate, measures of irregularity and burst activity were significantly reduced in PPI low compared to PPI high rats (P<0.05), while analysis in the NAC showed approximately inverse behavior. In the EPN no difference between groups was found. Additionally, the oscillatory theta band activity (4-8 Hz) was enhanced and the beta band (13-30 Hz) and gamma band (30-100 Hz) activity was reduced in the NAC in PPI low rats. Reduced neuronal activity in the mPFC and enhanced activity in the NAC of PPI low rats, together with altered oscillatory behavior are clearly associated with reduced PPI. PPI low rats may thus be used to study the pathophysiology and therapeutic strategies for neuropsychiatric disorders accompanied by deficient sensorimotor gating.

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.

Resting EEG in psychosis and at-risk populations--a possible endophenotype?

BACKGROUND

Finding reliable endophenotypes for psychosis could lead to an improved understanding of aetiology, and provide useful alternative phenotypes for genetic association studies. Resting quantitative electroencephalography (QEEG) activity has been shown to be heritable and reliable over time. However, QEEG research in patients with psychosis has shown inconsistent and even contradictory findings, and studies of at-risk populations are scarce. Hence, this study aimed to investigate whether resting QEEG activity represents a candidate endophenotype for psychosis.

METHOD

QEEG activity at rest was compared in four frequency bands (delta, theta, alpha, and beta), between chronic patients with psychosis (N=48), first episode patients (N=46), at-risk populations ("at risk mental state", N=33; healthy relatives of patients, N=45), and healthy controls (N=107).

RESULTS

Results showed that chronic patients had significantly increased resting QEEG amplitudes in delta and theta frequencies compared to healthy controls. However, first episode patients and at-risk populations did not differ from controls in these frequency bands. There were no group differences in alpha or beta frequency bands.

CONCLUSION

Since no abnormalities were found in first episode patients, ARMS, or healthy relatives, resting QEEG activity in the frequency bands examined is unlikely to be related to genetic predisposition to psychosis. Rather than endophenotypes, the low frequency abnormalities observed in chronic patients are probably related to illness progression and/or to the long-term effects of treatments.

Diagnostic specificity and familiality of early versus late evoked potentials to auditory paired stimuli across the schizophrenia-bipolar psychosis spectrum

Disrupted sensory processing is a core feature of psychotic disorders. Auditory paired stimuli (PS) evoke a complex neural response, but it is uncertain which aspects reflect shared and/or distinct liability for the most common severe psychoses, schizophrenia (SZ) and psychotic bipolar disorder (BDP). Evoked time-voltage/time-frequency domain responses quantified with EEG during a typical PS paradigm (S1-S2) were compared among proband groups (SZ [n = 232], BDP [181]), their relatives (SZrel [259], BDPrel [220]), and healthy participants (H [228]). Early S1-evoked responses were reduced in SZ and BDP, while later/S2 abnormalities showed SZ/SZrel and BDP/BDPrel specificity. Relatives' effects were absent/small despite significant familiality of the entire auditorineural response. This pattern suggests general and divergent biological pathways associated with psychosis, yet may reflect complications with conditioning solely on clinical phenomenology.

Neurophysiologic effect of GWAS derived schizophrenia and bipolar risk variants

Genome-wide association studies (GWAS) have identified multiple single nucleotide polymorphisms (SNPs) as disease associated variants for schizophrenia (SCZ), bipolar disorder (BPD), or both. Although these results are statistically robust, the functional effects of these variants and their role in the pathophysiology of SCZ or BPD remain unclear. Dissecting the effects of risk genes on distinct domains of brain function can provide important biological insights into the mechanisms by which these genes may confer illness risk. This study used quantitative event related potentials to characterize the neurophysiological effects of well-documented GWAS-derived SCZ/BPD susceptibility variants in order to map gene effects onto important domains of brain function. We genotyped 199 patients with DSM-IV diagnoses of SCZ or BPD and 74 healthy control subjects for 19 risk SNPs derived from previous GWAS findings and tested their association with five neurophysiologic traits (P3 amplitude, P3 latency, N1 amplitude, P2 amplitude, and P50 sensory gating responses) known to be abnormal in psychosis. The TCF4 SNP rs17512836 risk allele showed a significant association with reduced auditory P3 amplitude (P = 0.00016) after correction for multiple testing. The same allele was also associated with delayed P3 latency (P = 0.005). Our results suggest that a SCZ risk variant in TCF4 is associated with neurophysiologic traits thought to index attention and working memory abnormalities in psychotic disorders. These findings suggest a mechanism by which TCF4 may contribute to the neurobiological basis of psychotic illness.

Evidence for gamma and beta sensory gating deficits as translational endophenotypes for schizophrenia

Thorough analysis of translational endophenotypes is needed to improve therapeutic development in schizophrenia. Abnormal sensory gating, one such endophenotype, is associated with reduced expression of the α7 nicotinic receptor. However, typical gating measures such as the P50 evoked response are often low-pass filtered, and it is unclear how α7 expression affects gating at higher frequencies. Therefore, this study used time-frequency analysis to compare sensory gating at the beta and gamma frequencies between human patients and healthy controls as well as between α7 heterozygote mutant mice and wild-type. Gating of total beta (15-26Hz) and gamma (30-50Hz) power during paired clicks was assessed from mouse in vivo hippocampal CA3 recordings. Gating was also assessed in schizophrenia patients and healthy controls using electroencephalography. Relative to wild-type, α7 heterozygote mice showed impaired gating of total beta and gamma power. Similarly, relative to controls, patients showed impaired gating of total beta and gamma power. Poor beta gating was associated with negative symptoms. These results demonstrate that schizophrenia patients and α7 heterozygote mice show similar deficits in gating high frequency power. Time-frequency analysis of beta and gamma gating may thus be a translational method of assessing the genetic basis of gating deficits in schizophrenia.

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.