Review of neurophysiological findings in patients with schizophrenia

Lower-level oculomotor deficits in schizophrenia during multi-line reading: Evidence from return-sweeps

Reading fluency deficits in schizophrenia (Sz) have been attributed to dysfunction in both lower-level, oculomotor processing and higher-level, lexical processing, according to the two-hit deficit model. Given that prior work examining reading deficits in individuals with Sz has primarily focused on single-line and single-word reading tasks, eye movements that are unique to passage reading, such as return-sweep saccades, have not yet been examined in Sz. Return-sweep saccades are large eye movements that are made when readers move from the end of one line to the beginning of the next line during natural passage reading. Examining return-sweeps provides an opportunity to examine lower-level, oculomotor deficits during reading under circumstances when upcoming higher-level, lexical information is not available for visual processing because visual acuity constraints do not permit detailed lexical processing of line-initial words when return-sweeps are programmed. To examine the source of reading deficits in Sz, we analysed an existing data set in which participants read multi-line passages with manipulations to line spacing. Readers with Sz made significantly more return-sweep targeting errors followed by corrective saccades compared with healthy controls. Both groups showed similar effects of line spacing on return-sweep targeting accuracy, suggesting similar sensitivities to visual crowding during reading. Furthermore, the patterns of fixation durations in readers with Sz corroborate prior work indicating reduced parafoveal processing of upcoming words. Together, these findings suggest that lower-level visual and oculomotor dysfunction contribute to reading deficits in Sz, providing support for the two-hit deficit model.

Transdiagnostic psychopathology in the light of robust single-trial event-related potentials

Recent evidence indicates that event-related potentials (ERPs) as measured on the electroencephalogram (EEG) are more closely related to transdiagnostic, dimensional measures of psychopathology (TDP) than to diagnostic categories. A comprehensive examination of correlations between well-studied ERPs and measures of TDP is called for. In this study, we recruited 50 patients with emotional disorders undergoing 14 weeks of transdiagnostic group psychotherapy as well as 37 healthy comparison subjects (HC) matched in age and sex. HCs were assessed once and patients three times throughout treatment (N = 172 data sets) with a battery of well-studied ERPs and psychopathology measures consistent with the TDP framework The Hierarchical Taxonomy of Psychopathology (HiTOP). ERPs were quantified using robust single-trial analysis (RSTA) methods and TDP correlations with linear regression models as implemented in the EEGLAB toolbox LIMO EEG. We found correlations at several levels of the HiTOP hierarchy. Among these, a reduced P3b was associated with the general p-factor. A reduced error-related negativity correlated strongly with worse symptomatology across the Internalizing spectrum. Increases in the correct-related negativity correlated with symptoms loading unto the Distress subfactor in the HiTOP. The Flanker N2 was related to specific symptoms of Intrusive Cognitions and Traumatic Re-experiencing and the mismatch negativity to maladaptive personality traits at the lowest levels of the HiTOP hierarchy. Our study highlights the advantages of RSTA methods and of using validated TDP constructs within a consistent framework. Future studies could utilize machine learning methods to predict TDP from a set of ERP features at the subject level.

Pattern glare sensitivity distinguishes subclinical autism and schizotypy

INTRODUCTION

Schizophrenia and autism spectrum disorder are distinct neurodevelopmental disorders sharing clinically relevant behaviours. However, early sensory responses show divergent responses. Individuals with schizophrenia typically exhibit cortical hypo-excitability whereas individuals with autism show cortical hyperexcitability. Identifying reliable neurobiological differences between the disorders can diminish misdiagnosis and optimise treatments.

METHODS

The pattern glare test (PGT) is a simple measure of behavioural hyperexcitability. It measures the number of illusions seen in a static horizontal grating. We collected PGT data from non-clinical adults varying in traits of autism and schizophrenia (schizotypy). 576 undergraduate students completed an online survey consisting of the Schizotypal Personality Questionnaire - Brief Revised, the Autism Spectrum Quotient, and the PGT.

RESULTS

Subclinical autism and schizotypy traits were highly positively correlated. However, only schizotypy scores were significantly predictive of reporting more pattern glare (PG) illusions. When assessing the subcomponents of the schizotypy and autism scores, positive and disorganised schizotypy traits were predictive of reporting more PG illusions. Whereas, subclinical autism factors were not predictive of PG illusions.

CONCLUSIONS

High schizotypy performed the PGT in a manner consistent with behavioural hyperexcitability. The PGT distinguished subclinical autistic traits from schizotypy, suggesting potential clinical application.

A comparison of visual and acoustic mismatch negativity as potential biomarkers in schizophrenia

Mismatch negativity (MMN) is an event-related potential (ERP) component generated when an unexpected deviant stimulus occurs in a pattern of standard stimuli. Several studies showed that the MMN response to both auditory and visual stimuli is attenuated in schizophrenia. While previous studies investigated auditory and visual MMN in different cohorts, here we examined the potential clinical utility of MMN responses to auditory and visual stimuli within the same group of patients. Altogether 39 patients with schizophrenia and 39 healthy controls matched in age, gender, and education were enrolled. We recorded EEG using 64 channels in eight experimental blocks where we presented auditory and visual stimulus sequences. Mismatch responses were obtained by subtracting responses to standard from the physically identical deviant stimuli. We found a significant MMN response to the acoustic stimuli in the control group, whereas no significant mismatch response was observed in the patient group. The group difference was significant for the acoustic stimuli. The 12 vane windmill pattern evoked a significant MMN response in the early time window in the control group but not in the patient group. The 6 vane windmill pattern evoked MMN only in the patient group. However, we found no significant difference between the groups. Furthermore, we found no correlation between the clinical variables and the MMN amplitudes. Our results suggest that predictive processes underlying mismatch generation in patients with schizophrenia may be more affected in the acoustic compared to the visual domain. Acoustic MMN tends to be a more promising biomarker in schizophrenia.

Automatic identification of schizophrenia employing EEG records analyzed with deep learning algorithms

Electroencephalography is a method of detecting and analyzing electrical activity in the brain. This electrical activity can be recorded and processed to aid in the clinical diagnosis of mental disorders. In this study, a novel system for classifying schizophrenia patients from EEG recordings is presented. The developed algorithm decomposes the EEG signals into a system of radial basis functions using the method of fuzzy means. This decomposition helps to obtain the information from the various electrodes of the EEG and allows separating between healthy controls and patients with schizophrenia. The proposed method has been compared with classical machine learning algorithms, such as, K-Nearest Neighbor, Adaboost, Support Vector Machine, and Bayesian Linear Discriminant Analysis. The results show that the proposed method obtains the highest values in terms of balanced accuracy, recall, precision and F1 score, close to 93 % in all cases. The model developed in this study can be implemented in brain activity analysis systems that help in the prediction of patients with schizophrenia.

Finding normal-to-better neurocognitive indexes in individuals with schizotypal traits using a social role task

Schizophrenia patients make more errors and have longer reaction times (RTs) than healthy controls in most cognitive tasks. Deficits are also observed in subclinical participants having high scores on the schizotypal personality questionnaire (SPQ). They are accompanied by smaller amplitudes of the event-related brain potentials (ERPs) that index attention and semantic- and working-memory. These functions are thus thought to be impaired in individuals having various schizophrenia attributes (SzAs). Nevertheless, normal RTs were recently found in SzAs during a particular self-referential task where half of the stimuli were names of extraordinary social roles (e.g., genius). Each name (ordinary or extraordinary) was presented individually, and participants were asked to decide whether or not they would consider themselves performing the role at any moment of their lives. To further test an absence of cognitive deficits in this task, the ERPs elicited by names of social roles were also examined in 175 healthy participants. The absence of longer RTs in high- than in low-SPQs was replicated. Moreover, the ERPs of high SPQs had larger occipital N1s, larger P2s and larger occipital N400s than those of low SPQs while late positive potentials (LPPs) were of similar amplitudes. Such results are consistent with clinical observations of greater attention and faster processing of stimuli related to extraordinary/delusional beliefs. Further studies should test whether the cognitive deficits found in SzAs are due to the use of tasks and stimuli that are less within their focus of interest than within that of healthy controls.

Reliability and stability of oddball P300 amplitude in older adults: The role of stimulus sequence effects

The P300 may be an individual difference marker of neuro-cognitive function, which due to age-related cognitive decline may be particularly useful in older adults. Recently, we reported effects of the local stimulus sequence in an oddball task (i.e., the number of non-targets that preceded a target) on P300 amplitude in young and older adults. The same older adults completed a second session of the task 4-8 months after the first session. Here, we examined the effect of the stimulus sequence on the between- and within-session reliability and stability of P300 amplitude and RT, and their intertrial variability, in this sample of older adults. The sequence effects - an inverted U-shape effect of the number of standards preceding a target on parietal P300, and a linear effect on frontal P300 - were stable within and across sessions on the group level. Within individuals, P300 amplitude at frontal and parietal electrodes was generally very reliable and stable, mostly independently of sequence effects, encouraging its use as an individual difference marker of neuro-cognitive function in older adults. However, measures of the strength of the sequence effects themselves showed unacceptable reliability, speaking against their use as individual difference markers, at least in older adults.

Unveiling the Associations between EEG Indices and Cognitive Deficits in Schizophrenia-Spectrum Disorders: A Systematic Review

Cognitive dysfunctions represent a core feature of schizophrenia-spectrum disorders due to their presence throughout different illness stages and their impact on functioning. Abnormalities in electrophysiology (EEG) measures are highly related to these impairments, but the use of EEG indices in clinical practice is still limited. A systematic review of articles using Pubmed, Scopus and PsychINFO was undertaken in November 2021 to provide an overview of the relationships between EEG indices and cognitive impairment in schizophrenia-spectrum disorders. Out of 2433 screened records, 135 studies were included in a qualitative review. Although the results were heterogeneous, some significant correlations were identified. In particular, abnormalities in alpha, theta and gamma activity, as well as in MMN and P300, were associated with impairments in cognitive domains such as attention, working memory, visual and verbal learning and executive functioning during at-risk mental states, early and chronic stages of schizophrenia-spectrum disorders. The review suggests that machine learning approaches together with a careful selection of validated EEG and cognitive indices and characterization of clinical phenotypes might contribute to increase the use of EEG-based measures in clinical settings.

The neurophysiology of the intervention strategies of Awareness Training Program on emotion regulation

Emotion regulation is essential for healthy living. Previous studies have found that mental training such as compassion meditation could help with emotion regulation. However, the underlying neural mechanism and possible intervention strategies of group-based Mahayana Buddhist intervention involved in emotion regulation are still unclear. This event-related potential (ERP) study investigated how compassion and wisdom meditations, two key components of the Awareness Training Program (ATP), may regulate emotion during different mental processing stages, namely attention deployment, cognitive change, and response modification. Eighty-five middle-aged working adults with moderate stress were voluntarily recruited for this study, using a 128-channel electroencephalogram system. After 7 weeks of training, participants (ATP attendance, n = 42; waitlist control, n = 43) were instructed to view negative pictures while practicing compassion or wisdom meditation, with corresponding priming words. Another normal priming condition and a neutral picture condition were set as control conditions. ERP results in the ATP group showed that negative pictures induced greater prefrontal activity (N400 component) in both compassion and wisdom meditation conditions compared with the normal condition, while the control group showed little difference between the conditions. Significantly higher heart rate variability was found in the compassion but not wisdom meditation when compared with the neutral priming condition. Correspondent changes in behavioural data were also found. Converging evidence showed that compassion meditation training could modulate negative emotion processing in stages of attention deployment, cognitive change, and behavioural responses. The prefrontal lobe could play an important role in the process of emotion regulation by compassion meditation, possibly due to the emphasis of the ATP on contemplative practices.

Schizophrenia, Bipolar Disorder and Pre-Attentional Inhibitory Deficits

According to recent findings schizophrenia and bipolar disorder as separate disease entities manifest similarities in neuropsychological functioning. Typical disturbances in both disorders are related to sensory gating deficits characterized by decreased inhibitory functions in responses to various insignificant perceptual signals which are experimentally tested by event related potentials (ERP) and measured P50 wave. In this context, recent findings implicate that disrupted binding and disintegration of consciousness in schizophrenia and bipolar disorder that are related to inhibitory deficits reflected in P50 response may explain similarities in psychotic disturbances in both disorders. With this aim, this review summarizes literature about P50 in both schizophrenia and bipolar disorder.

Investigating the Relationships of P3b with Negative Symptoms and Neurocognition in Subjects with Chronic Schizophrenia

Neurocognitive deficits and negative symptoms (NS) have a pivotal role in subjects with schizophrenia (SCZ) due to their impact on patients' functioning in everyday life and their influence on goal-directed behavior and decision-making. P3b is considered an optimal electrophysiological candidate biomarker of neurocognitive impairment for its association with the allocation of attentional resources to task-relevant stimuli, an important factor for efficient decision-making, as well as for motivation-related processes. Furthermore, associations between P3b deficits and NS have been reported. The current research aims to fill the lack of studies investigating, in the same subjects, the associations of P3b with multiple cognitive domains and the expressive and motivation-related domains of NS, evaluated with state-of-the-art instruments. One hundred and fourteen SCZ and 63 healthy controls (HCs) were included in the study. P3b amplitude was significantly reduced and P3b latency prolonged in SCZ as compared to HCs. In SCZ, a positive correlation was found between P3b latency and age and between P3b amplitude and the Attention-vigilance domain, while no significant correlations were found between P3b and the two NS domains. Our results indicate that the effortful allocation of attention to task-relevant stimuli, an important component of decision-making, is compromised in SCZ, independently of motivation deficits or other NS.

Rat call-evoked electrocorticographic responses and intercortical phase synchrony impaired in a cytokine-induced animal model for schizophrenia

Patients with schizophrenia exhibit impaired performance in tone-matching or voice discrimination tests. However, there is no animal model recapitulating these pathophysiological traits. Here, we tested the representation of auditory recognition deficits in an animal model of schizophrenia. We established a rat model for schizophrenia using a perinatal challenge of epidermal growth factor (EGF), exposed adult rats to 55 kHz sine tones, rat calls (50-60 kHz), or reversely played calls, analyzed electrocorticography (ECoG) of the auditory and frontal cortices. Grand averages of event-related responses (ERPs) in the auditory cortex showed between-group size differences in the P1 component, whereas the P2 component differed among sound stimulus types. In EGF model rats, gamma band amplitudes were decreased in the auditory cortex and were enhanced in the frontal cortex with sine stimulus. The model rats also exhibited a reduction in rat call-triggered intercortical phase synchrony in the beta range. Risperidone administration restored normal phase synchrony. These findings suggest that perinatal exposure to the cytokine impairs tone/call recognition processes in these neocortices. In conjunction with previous studies using this model, our findings indicate that perturbations in ErbB/EGF signaling during development exert a multiscale impact on auditory functions at the cellular, circuit, and cognitive levels.

A systematic review of the neural correlates of multisensory integration in schizophrenia

Multisensory integration (MSI), in which sensory signals from different modalities are unified, is necessary for our comprehensive perception of and effective adaptation to the objects and events around us. However, individuals with schizophrenia suffer from impairments in MSI, which could explain typical symptoms like hallucination and reality distortion. Because the neural correlates of aberrant MSI in schizophrenia help us understand the physiognomy of this psychiatric disorder, we performed a systematic review of the current research on this subject. The literature search concerned investigated MSI in diagnosed schizophrenia patients compared to healthy controls using brain imaging. Seventeen of 317 identified studies were finally included. To assess risk of bias, the Newcastle-Ottawa quality assessment was used, and the review was written according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA). The results indicated that multisensory processes in schizophrenia are associated with aberrant, mainly reduced, neural activity in several brain regions, as measured by event-related potentials, oscillations, activity and connectivity. The conclusion is that a fronto-temporal region, comprising the frontal inferior gyrus, middle temporal gyrus and superior temporal gyrus/sulcus, along with the fusiform gyrus and dorsal visual stream in the occipital-parietal lobe are possible key regions of deficient MSI in schizophrenia.

Sensory gating is related to positive and disorganised schizotypy in contrast to smooth pursuit eye movements and latent inhibition

Since the characteristics and symptoms of both schizophrenia and schizotypy are manifested heterogeneously, it is possible that different endophenotypes and neurophysiological measures (sensory gating and smooth pursuit eye movement errors) represent different clusters of symptoms. Participants (N = 205) underwent a standard conditioned-pairing paradigm to establish their sensory gating ratio, a smooth-pursuit eye-movement task, a latent inhibition task, and completed the Schizotypal Personality Questionnaire. A Multidimensional Scaling analysis revealed that sensory gating was related to positive and disorganised dimensions of schizotypy. Latent inhibition and prepulse inhibition were not related to any dimension of schizotypy. Smooth pursuit eye movement error was unrelated to sensory gating and latent inhibition, but was related to negative dimensions of schizotypy. Our findings suggest that the symptom clusters associated with two main endophenotypes are largely independent. To fully understand symptomology and outcomes of schizotypal traits, the different subtypes of schizotypy (and potentially, schizophrenia) ought to be considered separately rather than together.

Early and middle latency auditory event-related potentials do not explain differences in neuropsychological performance between schizophrenia spectrum patients and matched healthy controls

Abnormalities of early and middle latency auditory event-related potentials (ERPs) are widespread in schizophrenia and have been suggested to be associated with cognitive deficits in schizophrenia patients. In this cross-sectional study with schizophrenia patients (n=30) and psychiatrically healthy counterparts (n=31) (matched for age, sex, education), we investigated whether auditory information processing (measured via amplitudes and gating of the auditory ERPs P50, N100 and P200) correlates with neuropsychological performance across cognitive domains. The groups differed significantly in amplitudes and gating of N100 and P200 potentials as well as in neuropsychological performance, but not in P50 amplitude and gating. Neither amplitudes nor gating of auditory ERPs correlated with neuropsychological performance. Neuropsychological intergroup differences could not be explained by abnormalities in auditory information processing. Although pronounced impairments exist on the levels of both auditory information processing and cognitive performance in schizophrenia, these abnormalities are not directly associated with each other.

Predicting Long-Term Outcomes in First-Admission Psychosis: Does the Hierarchical Taxonomy of Psychopathology Aid DSM in Prognostication?

The Hierarchical Taxonomy of Psychopathology (HiTOP) is an empirical, dimensional model of psychological symptoms and functioning. Its goals are to augment the use and address the limitations of traditional diagnoses, such as arbitrary thresholds of severity, within-disorder heterogeneity, and low reliability. HiTOP has made inroads to addressing these problems, but its prognostic validity is uncertain. The present study sought to test the prediction of long-term outcomes in psychotic disorders was improved when the HiTOP dimensional approach was considered along with traditional (ie, DSM) diagnoses. We analyzed data from the Suffolk County Mental Health Project (N = 316), an epidemiologic study of a first-admission psychosis cohort followed for 20 years. We compared 5 diagnostic groups (schizophrenia/schizoaffective, bipolar disorder with psychosis, major depressive disorder with psychosis, substance-induced psychosis, and other psychoses) and 5 dimensions derived from the HiTOP thought disorder spectrum (reality distortion, disorganization, inexpressivity, avolition, and functional impairment). Both nosologies predicted a significant amount of variance in most outcomes. However, except for cognitive functioning, HiTOP showed consistently greater predictive power across outcomes-it explained 1.7-fold more variance than diagnoses in psychiatric and physical health outcomes, 2.1-fold more variance in community functioning, and 3.4-fold more variance in neural responses. Even when controlling for diagnosis, HiTOP dimensions incrementally predicted almost all outcomes. These findings support a shift away from the exclusive use of categorical diagnoses and toward the incorporation of HiTOP dimensions for better prognostication and linkage with neurobiology.

The dopamine D2 agonist quinpirole impairs frontal mismatch responses to sound frequency deviations in freely moving rats

Aim

A reduced mismatch negativity (MMN) response is a promising electrophysiological endophenotype of schizophrenia that reflects neurocognitive impairment. Dopamine dysfunction is associated with symptoms of schizophrenia. However, whether the dopamine system is involved in MMN impairment remains controversial. In this study, we investigated the effects of the dopamine D2‐like receptor agonist quinpirole on mismatch responses to sound frequency changes in an animal model.

Methods

Event‐related potentials were recorded from electrocorticogram electrodes placed on the auditory and frontal cortices of freely moving rats using a frequency oddball paradigm consisting of ascending and equiprobable (ie, many standards) control sequences before and after the subcutaneous administration of quinpirole. To detect mismatch responses, difference waveforms were obtained by subtracting nondeviant control waveforms from deviant waveforms.

Results

Here, we show the significant effects of quinpirole on frontal mismatch responses to sound frequency deviations in rats. Quinpirole delayed the frontal N18 and P30 mismatch responses and reduced the frontal N55 MMN‐like response, which resulted from the reduction in the N55 amplitude to deviant stimuli. Importantly, the magnitude of the N55 amplitude was negatively correlated with the time of the P30 latency in the difference waveforms. In contrast, quinpirole administration did not clearly affect the temporal mismatch responses recorded from the auditory cortex.

Conclusion

These results suggest that the disruption of dopamine D2‐like receptor signaling by quinpirole reduces frontal MMN to sound frequency deviations and that delays in early mismatch responses are involved in this MMN impairment.

The subcutaneous administration of quinpirole delayed early mismatch response latencies and reduced a late MMN‐like response amplitude recorded from the frontal cortex but had no effect on those recorded from the auditory cortex. These observations suggest that increased dopamine D2‐like receptor signaling impairs MMN generation to sound frequency changes in the frontal cortex and that the neurochemical mechanisms of MMN vary according to the cortical area. As MMN is associated with cognitive function, these new findings may help develop treatment modalities for cognitive dysfunctions in schizophrenia.

Differential auditory brain response abnormalities in two intellectual disability conditions: SYNGAP1 mutations and Down syndrome

OBJECTIVE

Altered sensory processing is common in intellectual disability (ID). Here, we study electroencephalographic responses to auditory stimulation in human subjects presenting a rare condition (mutations in SYNGAP1) which causes ID, epilepsy and autism.

METHODS

Auditory evoked potentials, time-frequency and inter-trial coherence analyses were used to compare subjects with SYNGAP1 mutations with Down syndrome (DS) and neurotypical (NT) participants (N = 61 ranging from three to 19 years of age).

RESULTS

Altered synchronization in the brain responses to sound were found in both ID groups. The SYNGAP1 mutations group showed less phase-locking in early time windows and lower frequency bands compared to NT, and in later time windows compared to NT and DS. Time-frequency analysis showed more power in beta-gamma in the SYNGAP1 group compared to NT participants.

CONCLUSIONS

This study indicated reduced synchronization as well as more high frequencies power in SYNGAP1 mutations, while maintained synchronization was found in the DS group. These results might reflect dysfunctional sensory information processing caused by excitation/inhibition imbalance, or an imperfect compensatory mechanism in SYNGAP1 mutations individuals.

SIGNIFICANCE

Our study is the first to reveal brain response abnormalities in auditory sensory processing in SYNGAP1 mutations individuals, that are distinct from DS, another ID condition.

Electrical field distribution of Change-N1 and its prepulse inhibition

An abrupt change in a sound feature (Test) in a continuous sound elicits an auditory evoked potential, peaking at approx. 100-180 ms (Change-N1) after the change onset. Change-N1 is attenuated by a preceding weak change stimulus (Prepulse), in the phenomenon known as prepulse inhibition (PPI). In this electroencephalographic study, we compared these two indexes among scalp electrodes. Change-N1 was elicited by an abrupt 10-dB increase in sound pressure in repeats of a 70-dB click sound at 100 Hz and was recorded using 22 electrodes in 31 healthy subjects. The prepulse was a 10-dB decrease in three consecutive clicks at 30, 40, and 50 ms before the Test onset. Four stimuli (Test alone, Test with Prepulse, Prepulse alone, and background alone) were presented randomly through headphones at an even probability. The results demonstrated that: (1) Electrodes at the frontal/central midline were reconfirmed to be suitable to record Change-N1; (2) Change-N1 showed right-hemisphere predominance; (3) There was no difference in the %PPI among regions (prefrontal/frontal/central) and hemispheres (midline/left/right); and (4) the Change-N1 amplitude and its PPI at prefrontal electrodes were positively correlated with those at the frontal electrodes. These results support the use of Change-N1 and its PPI as a tool to evaluate the change detection sensitivity and inhibitory function in individuals. The use of prefrontal electrodes can be an option for a screening test.

Advanced EEG-based learning approaches to predict schizophrenia: Promises and pitfalls

The complexity and heterogeneity of schizophrenia symptoms challenge an objective diagnosis, which is typically based on behavioral and clinical manifestations. Moreover, the boundaries of schizophrenia are not precisely demarcated from other nosologic categories, such as bipolar disorder. The early detection of schizophrenia can lead to a more effective treatment, improving patients' quality of life. Over the last decades, hundreds of studies aimed at specifying the neurobiological mechanisms that underpin clinical manifestations of schizophrenia, using techniques such as electroencephalography (EEG). Changes in event-related potentials of the EEG have been associated with sensory and cognitive deficits and proposed as biomarkers of schizophrenia. Besides contributing to a more effective diagnosis, biomarkers can be crucial to schizophrenia onset prediction and prognosis. However, any proposed biomarker requires substantial clinical research to prove its validity and cost-effectiveness. Fueled by developments in computational neuroscience, automatic classification of schizophrenia at different stages (prodromal, first episode, chronic) has been attempted, using brain imaging pattern recognition methods to capture differences in functional brain activity. Advanced learning techniques have been studied for this purpose, with promising results. This review provides an overview of recent machine learning-based methods for schizophrenia classification using EEG data, discussing their potentialities and limitations. This review is intended to serve as a starting point for future developments of effective EEG-based models that might predict the onset of schizophrenia, identify subjects at high-risk of psychosis conversion or differentiate schizophrenia from other disorders, promoting more effective early interventions.

40-Hz Auditory Steady-State Response (ASSR) as a Biomarker of Genetic Defects in the SHANK3 Gene: A Case Report of 15-Year-Old Girl with a Rare Partial SHANK3 Duplication

SHANK3 encodes a scaffold protein involved in postsynaptic receptor density in glutamatergic synapses, including those in the parvalbumin (PV)+ inhibitory neurons—the key players in the generation of sensory gamma oscillations, such as 40-Hz auditory steady-state response (ASSR). However, 40-Hz ASSR was not studied in relation to SHANK3 functioning. Here, we present a 15-year-old girl (SH01) with previously unreported duplication of the first seven exons of the SHANK3 gene (22q13.33). SH01’s electroencephalogram (EEG) during 40-Hz click trains of 500 ms duration binaurally presented with inter-trial intervals of 500–800 ms were compared with those from typically developing children (n = 32). SH01 was diagnosed with mild mental retardation and learning disabilities (F70.88), dysgraphia, dyslexia, and smaller vocabulary than typically developing (TD) peers. Her clinical phenotype resembled the phenotype of previously described patients with 22q13.33 microduplications (≈30 reported so far). SH01 had mild autistic symptoms but below the threshold for ASD diagnosis and microcephaly. No seizures or MRI abnormalities were reported. While SH01 had relatively preserved auditory event-related potential (ERP) with slightly attenuated P1, her 40-Hz ASSR was totally absent significantly deviating from TD’s ASSR. The absence of 40-Hz ASSR in patients with microduplication, which affected the SHANK3 gene, indicates deficient temporal resolution of the auditory system, which might underlie language problems and represent a neurophysiological biomarker of SHANK3 abnormalities.

Abnormal Contingent Negative Variation Drifts During Facial Expression Judgment in Schizophrenia Patients

Schizophrenia patients often show impaired facial expression recognition, which leads to difficulties in adaptation to daily life. However, it remains unclear whether the deficit is at the perceptual or higher cognitive level of facial emotion processing. Recent studies have shown that earlier face-evoked event-related potential (ERP) components such as N170 and P100 can effectively distinguish schizophrenia patients from healthy controls; however, findings for later waveforms are ambiguous. To clarify this point, in this study we compared electroencephalographic signals in schizophrenia patients and control subjects during a facial expression judgment task. We found that group effects of the occipital N170 and frontal lobe contingent negative variation (CNV) were both significant. The effect sizes (ESs) of N170 and CNV amplitudes were generally medium or small, whereas that of CNV slope for an upright face was large (>0.8). Moreover, N170 amplitude and CNV slope but not CNV amplitude was correlated with Personal and Social Performance (PSP) Scale score. These results suggest that the slope of CNV drift during facial expression processing has a potential clinical value for schizophrenia.

Weaker prepulse exerts stronger suppression of a change-detecting neural circuit

Change-N1 peaking 90-180 ms after changes in a sound feature of a continuous sound is clearly attenuated by a preceding change stimulus (called a "prepulse"). Here, we investigated the effects of a preceding decrease in sound pressure on the degree of inhibition of the subsequent Change-N1 amplitude. Using 100-Hz click train sounds, we obtained Change-N1s from 11 healthy volunteers. The two types of test stimuli were an abrupt 10-dB increase from the baseline (70 dB) and the insertion of a 0.45-ms inter-aural time difference in the middle of the sound. Three consecutive clicks at 30, 40, and 50 ms before the change onset that was used as a prepulse were weaker than the background by 5 or 10 dB. The Change-N1 elicited by the two test stimuli was attenuated more strongly by the weaker prepulse, which was not congruent with the theory that the inhibition of the subsequent sensory/sensory-motor processing depends on the sound pressure level of a prepulse. These results suggest that a change in any type of sound feature elicits a change-related response that is inhibited by any type of preceding change stimulus, which reflects auto-inhibition of the change-responding circuit.

The P300 event-related potential in bipolar disorder: A systematic review and meta-analysis

BACKGROUND

Neurophysiology including P300, that is a typical index of event-related potential, may be potential biomarkers for bipolar disorder (BD) and it can be useful towards elucidating the pathophysiology of BD. However, previous findings from P300 studies were inconsistent due to the heterogeneity of research methods, which make it difficult to understand the neurobiological significance of them. The aim of this study is to conduct a meta-analysis on P300 in patients with BD.

METHOD

A literature search was conducted using PubMed to identify studies that compared P300 event-related potential between patients with BD and healthy controls (HCs). We analyzed P300 indices such as amplitude and latency of P3a and P3b in auditory or visual paradigms. Further, moderator analyses were conducted to investigate the influence of patient characteristics (i.e. history of psychosis, diagnostic subcategories [BD-I/BD-II], and phase of illness [euthymic, manic, or depressive]) on P300 indices.

RESULT

Out of 124 initial records, we included 30 articles (BD: N = 1331; HCs: N = 1818). Patients with BD showed reduced P3a and P3b amplitude in both paradigms and delayed P3b latency in auditory paradigms compared to HCs. There was no influence on the history of psychosis, diagnostic subcategories, or phase of illness on P300 indices.

LIMITATION

The difference in medication use was difficult to control and it may affect the results.

CONCLUSION

This meta-analysis provides evidence for P300 abnormalities in patients with BD compared to HCs. Our results suggest that P300 may be trait markers rather than state markers in this illness.

Effects of Sound-Pressure Change on the 40 Hz Auditory Steady-State Response and Change-Related Cerebral Response

The auditory steady-state response (ASSR) elicited by a periodic sound stimulus is a neural oscillation recorded by magnetoencephalography (MEG), which is phase-locked to the repeated sound stimuli. This ASSR phase alternates after an abrupt change in the feature of a periodic sound stimulus and returns to its steady-state value. An abrupt change also elicits a MEG component peaking at approximately 100-180 ms (called "Change-N1m"). We investigated whether both the ASSR phase deviation and Change-N1m were affected by the magnitude of change in sound pressure. The ASSR and Change-N1m to 40 Hz click-trains (1000 ms duration, 70 dB), with and without an abrupt change (± 5, ± 10, or ± 15 dB) were recorded in ten healthy subjects. We used the source strength waveforms obtained by a two-dipole model for measurement of the ASSR phase deviation and Change-N1m values (peak amplitude and latency). As the magnitude of change increased, Change-N1m increased in amplitude and decreased in latency. Similarly, ASSR phase deviation depended on the magnitude of sound-pressure change. Thus, we suspect that both Change-N1m and the ASSR phase deviation reflect the sensitivity of the brain's neural change-detection system.

Visual Hyper-vigilance But Insufficient Mental Representation in Children with Overweight/Obesity: Event-related Potential Study with Visual Go/NoGo Test

PURPOSE

The neural processing of children with overweight/obesity (CWO), may affect their eating behavior. We investigated the visual information processing of CWO under response control condition, by event-related potential (ERP) study, an electrophysiologic study for cognitive mechanism.

METHODS

Seventeen CWO (mean age: 10.6±1.9), and 17 age-matched non-obese children (NOC), participated in the study. Neurocognitive function tests and visual ERP under Go/NoGo conditions, were implemented. Area amplitudes of major ERP components (P1, N1, P2, N2, and P3) from four scalp locations (frontal, central, parietal, and occipital), were analyzed.

RESULTS

For Go and NoGo conditions, CWO had significantly greater occipital P1, fronto-central N1, and P2 amplitudes compared with NOC. P2 amplitude was significantly greater in CWO, than in NOC, at the frontal location. N2 amplitude was not significantly different, between CWO and NOC. For CWO and NOC, Go P3 amplitude was highest at the parietal location, and NoGo P3 amplitude was highest at the frontal location. In Go and NoGo conditions, P3 amplitude of CWO was significantly less than in NOC.

CONCLUSION

The greater P1, N1, and P2 suggested hyper-vigilance to visual stimuli of CWO, but the smaller P3 suggested insufficient mental representation of them. Such altered visual processing, may affect the eating behavior of CWO.

Altered attentional processing of happy prosody in schizophrenia

BACKGROUND

Abnormalities in emotional prosody processing have been consistently reported in schizophrenia. Emotionally salient changes in vocal expressions attract attention in social interactions. However, it remains to be clarified how attention and emotion interact during voice processing in schizophrenia. The current study addressed this question by examining the P3b event-related potential (ERP) component.

METHOD

The P3b was elicited with a modified oddball task, in which frequent (p = .84) neutral stimuli were intermixed with infrequent (p = .16) task-relevant emotional (happy or angry) targets. Prosodic speech was presented in two conditions - with intelligible (semantic content condition - SCC) or unintelligible semantic content (prosody-only condition - POC). Fifteen chronic schizophrenia patients and 15 healthy controls were instructed to silently count the target vocal sounds.

RESULTS

Compared to controls, P3b amplitude was specifically reduced for happy prosodic stimuli in schizophrenia, irrespective of semantic status. Groups did not differ in the processing of neutral standards or angry targets.

DISCUSSION

The selectively reduced P3b for happy prosody in schizophrenia suggests top-down attentional resources were less strongly engaged by positive relative to negative prosody, reflecting alterations in the evaluation of the emotional salience of the voice. These results highlight the role played by higher-order processes in emotional prosody dysfunction in schizophrenia.

Early Somatosensory Processing Over Time in Individuals at Risk to Develop Psychosis

Objective: Somatosensory evoked potentials (SEPs) enable the investigation of thalamocortical and early cortical processing. Previous studies reported alterations of SEPs in patients with schizophrenia as well as in individuals in the prodromal stage. Moreover, cannabis use as an environmental risk factor for the development of schizophrenia has been demonstrated to influence SEP parameters in individuals at risk to develop psychosis. The aim of this study was to explore the course of SEP changes and the impact of concomitant cannabis use in individuals at risk to develop psychosis who sought medical help. Methods: Median nerve SEPs including high-frequency oscillations (HFOs) superimposed on the primary cortical response (N20) were investigated using multichannel EEG in individuals (n = 54 at baseline) remaining at risk to develop psychosis at follow-up after 1 year (high-risk: n = 19; ultra-high-risk: n = 27) vs. subjects with conversion to psychosis (n = 8) and a healthy control group (n = 35). Longitudinal and cross-sectional analyses of SEP components as estimated by dipole source analysis were performed. Results: The longitudinal development of the N20 strength depended on cannabis use. In cannabis non-users, a greater decrease of N20 strengths over time was associated with more negative symptoms at baseline. At baseline, converters did not differ from subjects remaining at risk. At follow-up, converters showed increased low- and high-frequency activity than at-risk subjects and did not differ from controls. Conclusion: The results of this study lead to the suggestion that the deficits in early somatosensory processing in individuals at risk to develop psychosis may not represent a marker for a genetic risk for psychosis but rather reflect state-dependent factors such as negative symptoms. On the other hand, the transition to psychosis seems to represent an interstage between reduced sensory registration from the at-risk state and gating deficits in the chronic state.

Enhanced Auditory Steady-State Response Using an Optimized Chirp Stimulus-Evoked Paradigm

Objectives: It has been reported recently that gamma measures of the electroencephalogram (EEG) might provide information about the candidate biomarker of mental diseases like schizophrenia, Alzheimer's disease, affective disorder and so on, but as we know it is a difficult issue to induce visual and tactile evoked responses at high frequencies. Although a high-frequency response evoked by auditory senses is achievable, the quality of the recording response is not ideal, such as relatively low signal-to-noise ratio (SNR). Recently, auditory steady-state responses (ASSRs) play an essential role in the field of basic auditory studies and clinical uses. However, how to improve the quality of ASSRs is still a challenge which researchers have been working on. This study aims at designing a more comfortable and suitable evoked paradigm and then enhancing the quality of the ASSRs in healthy subjects so as to further apply it in clinical practice. Methods: Chirp and click stimuli with 40 Hz and 60 Hz were employed to evoke the gamma-ASSR respectively, and the sound adjusted to 45 dB sound pressure level (SPL). Twenty healthy subjects with normal-hearing participated, and 64-channel EEGs were simultaneously recorded during the experiment. Event-related spectral perturbation (ERSP) and SNR of the ASSRs were measured and analyzed to verify the feasibility and adaptability of the proposed evoked paradigm. Results: The results showed that the evoked paradigm proposed in this study could enhance ASSRs with strong feasibility and adaptability. 1) ASSR waves in time domain indicated that 40 Hz stimuli could significantly induce larger peak-to-peak values of ASSRs compared to 60 Hz stimuli (p < 0.01**); ERSP showed that obvious ASSRs were obtained at each lead for both 40 Hz and 60 Hz, as well as the click and chirp stimuli. 2) The SNR of the ASSRs were ⁻3.23 ± 1.68, ⁻2.44 ± 2.90, ⁻4.66 ± 2.09, and ⁻3.53 ± 3.49 respectively for 40 Hz click, 40 Hz chirp, 60 Hz click and 60 Hz chirp, indicating the chirp stimuli could induce significantly better ASSR than the click, and 40 Hz ASSRs had the higher SNR than 60 Hz (p < 0.01**). Limitation: In this study, sample size was small and the age span was not large enough. Conclusions: This study verified the feasibility and adaptability of the proposed evoked paradigm to improve the quality of the gamma-ASSR, which is significant in clinical application. The results suggested that 40 Hz ASSR evoked by chirp stimuli had the best performance and was expected to be used in clinical practice, especially in the field of mental diseases such as schizophrenia, Alzheimer's disease, and affective disorder.

The use of polygenic risk scores to identify phenotypes associated with genetic risk of schizophrenia: Systematic review

Studying the phenotypic manifestations of increased genetic liability for schizophrenia can increase our understanding of this disorder. Specifically, information from alleles identified in genome-wide association studies can be collapsed into a polygenic risk score (PRS) to explore how genetic risk is manifest within different samples. In this systematic review, we provide a comprehensive assessment of studies examining associations between schizophrenia PRS (SZ-PRS) and several phenotypic measures. We searched EMBASE, Medline and PsycINFO (from August 2009-14th March 2016) plus references of included studies, following PRISMA guidelines. Study inclusion was based on predetermined criteria and data were extracted independently and in duplicate. Overall, SZ-PRS was associated with increased risk for psychiatric disorders such as depression and bipolar disorder, lower performance IQ and negative symptoms. SZ-PRS explained up to 6% of genetic variation in psychiatric phenotypes, compared to <0.7% in measures of cognition. Future gains from using the PRS approach may be greater if used for examining phenotypes that are more closely related to biological substrates, for scores based on gene-pathways, and where PRSs are used to stratify individuals for study of treatment response. As it was difficult to interpret findings across studies due to insufficient information provided by many studies, we propose a framework to guide robust reporting of PRS associations in the future.

Top-Down Disconnectivity in Schizophrenia During P300 Tasks

Cognitive deficits in schizophrenia are correlated with the dysfunctions of distinct brain regions including anterior cingulate cortex (ACC) and prefrontal cortex (PFC). Apart from the dysfunctions of the intrinsic connectivity of related areas, how the coupled neural populations work is also crucial in related processes. Twenty-four patients with schizophrenia (SZs) and 24 matched healthy controls (HCs) were recruited in our study. Based on the electroencephalogram (EEG) datasets recorded, the Dynamic Causal Modeling (DCM) was then adopted to estimate how the brain architecture adapts among related areas in SZs and to investigate the mechanism that accounts for their cognitive deficits. The distinct winning models in SZs and HCs consistently emphasized the importance of ACC in regulating the elicitations of P300s. Specifically, comparing to that in HCs, the winning model in SZs uncovered a compensatory pathway from dorsolateral PFC to intraparietal sulcus that promised the SZs' accomplishing P300 tasks. The findings demonstrated that the “disconnectivity hypothesis” is helpful and useful in explaining the cognitive deficits in SZs, while the brain architecture adapted with related compensatory pathway promises the limited brain cognitions in SZs. This study provides a new viewpoint that deepens our understanding of the cognitive deficits in schizophrenia.

Prepulse Inhibition of the Auditory Off-Response: A Magnetoencephalographic Study

A weak preceding sound stimulus attenuates the startle response evoked by an intense sound stimulus. Like startle reflexes, change-related auditory responses are suppressed by a weak leading stimulus (ie, a prepulse). We aim to examine whether a prepulse inhibits cerebral responses to the sound offset and how the prepulse magnitude affects the degree of the prepulse inhibition (PPI). Using magnetoencephalography, we recorded the Off-P50m elicited by an offset of a train sound of 100-Hz clicks in 12 healthy subjects. A single click slightly louder (+1.5, +3, or +5 dB) than the background sound of 80 dB was inserted 50 ms before the sound offset as a prepulse. We performed a dipole source analysis of the Off-P50m, and we measured its latency and amplitude using the source strength waveforms. The origin of the Off-P50m was estimated to be the auditory cortex on both hemispheres. The Off-P50m was clearly attenuated by the prepulses, and the degree of PPI was greater with a louder prepulse. The Off-P50m is considered to be a simple change-related response, which does not overlap with a processing of incoming sounds. Thus, the Off-P50m and its PPI comprise a valuable tool for investigating the neural inhibitory system.

Disordered high-frequency oscillation in face processing in schizophrenia patients

Schizophrenia is a complex disorder characterized by marked social dysfunctions, but the neural mechanism underlying this deficit is unknown. To investigate whether face-specific perceptual processes are influenced in schizophrenia patients, both face detection and configural analysis were assessed in normal individuals and schizophrenia patients by recording electroencephalogram (EEG) data. Here, a face processing model was built based on the frequency oscillations, and the evoked power (theta, alpha, and beta bands) and the induced power (gamma bands) were recorded while the subjects passively viewed face and nonface images presented in upright and inverted orientations. The healthy adults showed a significant face-specific effect in the alpha, beta, and gamma bands, and an inversion effect was observed in the gamma band in the occipital lobe and right temporal lobe. Importantly, the schizophrenia patients showed face-specific deficits in the low-frequency beta and gamma bands, and the face inversion effect in the gamma band was absent from the occipital lobe. All these results revealed face-specific processing in patients due to the disorder of high-frequency EEG, providing additional evidence to enrich future studies investigating neural mechanisms and serving as a marked diagnostic basis.

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.

Cannabinoids and Vanilloids in Schizophrenia: Neurophysiological Evidence and Directions for Basic Research

Much of our knowledge of the endocannabinoid system in schizophrenia comes from behavioral measures in rodents, like prepulse inhibition of the acoustic startle and open-field locomotion, which are commonly used along with neurochemical approaches or drug challenge designs. Such methods continue to map fundamental mechanisms of sensorimotor gating, hyperlocomotion, social interaction, and underlying monoaminergic, glutamatergic, and GABAergic disturbances. These strategies will require, however, a greater use of neurophysiological tools to better inform clinical research. In this sense, electrophysiology and viral vector-based circuit dissection, like optogenetics, can further elucidate how exogenous cannabinoids worsen (e.g., tetrahydrocannabinol, THC) or ameliorate (e.g., cannabidiol, CBD) schizophrenia symptoms, like hallucinations, delusions, and cognitive deficits. Also, recent studies point to a complex endocannabinoid-endovanilloid interplay, including the influence of anandamide (endogenous CB₁ and TRPV₁ agonist) on cognitive variables, such as aversive memory extinction. In fact, growing interest has been devoted to TRPV₁ receptors as promising therapeutic targets. Here, these issues are reviewed with an emphasis on the neurophysiological evidence. First, we contextualize imaging and electrographic findings in humans. Then, we present a comprehensive review on rodent electrophysiology. Finally, we discuss how basic research will benefit from further combining psychopharmacological and neurophysiological tools.

Revealing the Dysfunction of Schematic Facial-Expression Processing in Schizophrenia: A Comparative Study of Different References

The use of event-related potential (ERP) recording technology during perceptual and cognitive processing has been studied in order to develop objective diagnostic indexes for people with neuropsychiatric disorders. For example, patients with schizophrenia exhibit consistent abnormalities in face-evoked early components of ERPs and mismatch negativities (MMNs). In most studies, the choice of reference has been the average reference (AVE), but whether this is the most suitable choice is still unknown. The aim of this study was to systematically compare the AVE and reference electrode standardization technique (REST) methods for assessing expressional face-evoked early visual ERPs and visual MMNs (vMMNs) in patients with schizophrenia and healthy controls. The results showed that both the AVE and REST methods could: (1) obtain primary visual-evoked ERPs in the two groups, (2) reveal the neutral and emotional expression discrimination deficit of the P1 component in the patients, which was normal in the healthy controls, (3) reflect reductions of happy vMMNs in the patients compared to the healthy controls, and (4) show right-dominant sad vMMNs only in the patients. On the other hand, compared to the energy distributions of the AVE-obtained potentials, those of REST-obtained early visual ERPs and vMMNs were more concentrated around the temporo-occipital areas. Furthermore, only the REST-obtained vMMNs revealed a significant difference between happy and sad mismatch stimuli in patients with schizophrenia. These results demonstrate that REST technology might provide new insights into neurophysiological factors associated with neuropsychiatric disorders.

Abnormal N400 Semantic Priming Effect May Reflect Psychopathological Processes in Schizophrenia: A Twin Study

OBJECTIVE

Activation of semantic networks is indexed by the N400 effect. We used a twin study design to investigate whether N400 effect abnormalities reflect genetic/trait liability or are related to psychopathological processes in schizophrenia.

METHODS

We employed robust linear regression to compare N400 and behavioral priming effects across 36 monozygotic twin pairs (6 pairs concordant for schizophrenia/schizoaffective disorder, 11 discordant pairs, and 19 healthy control pairs) performing a lexical decision task. Moreover, we examined the correlation between Brief Psychiatric Rating Scale (BPRS) score and the N400 effect and the influence of medication status on this effect.

RESULTS

Regression yielded a significant main effect of group on the N400 effect only in the direct priming condition (p = 0.003). Indirect condition and behavioral priming effect showed no significant effect of group. Planned contrasts with the control group as a reference group revealed that affected concordant twins had significantly reduced N400 effect compared to controls, and discordant affected twins had a statistical trend for reduced N400 effect compared to controls. The unaffected twins did not differ significantly from the controls. There was a trend for correlation between reduced N400 effect and higher BPRS scores, and the N400 effect did not differ significantly between medicated and unmedicated patients.

CONCLUSIONS

Reduced N400 effect may reflect disease-specific processes in schizophrenia implicating frontotemporal brain network in schizophrenia pathology.

Beta/Gamma Oscillations and Event-Related Potentials Indicate Aberrant Multisensory Processing in Schizophrenia

Recent behavioral and neuroimaging studies have suggested multisensory processing deficits in patients with schizophrenia (SCZ). Thus far, the neural mechanisms underlying these deficits are not well understood. Previous studies with unisensory stimulation have shown altered neural oscillations in SCZ. As such, altered oscillations could contribute to aberrant multisensory processing in this patient group. To test this assumption, we conducted an electroencephalography (EEG) study in 15 SCZ and 15 control participants in whom we examined neural oscillations and event-related potentials (ERPs) in the sound-induced flash illusion (SIFI). In the SIFI multiple auditory stimuli that are presented alongside a single visual stimulus can induce the illusory percept of multiple visual stimuli. In SCZ and control participants we compared ERPs and neural oscillations between trials that induced an illusion and trials that did not induce an illusion. On the behavioral level, SCZ (55.7%) and control participants (55.4%) did not significantly differ in illusion rates. The analysis of ERPs revealed diminished amplitudes and altered multisensory processing in SCZ compared to controls around 135 ms after stimulus onset. Moreover, the analysis of neural oscillations revealed altered 25–35 Hz power after 100 to 150 ms over occipital scalp for SCZ compared to controls. Our findings extend previous observations of aberrant neural oscillations in unisensory perception paradigms. They suggest that altered ERPs and altered occipital beta/gamma band power reflect aberrant multisensory processing in SCZ.

Sluggishness of Early-Stage Face Processing (N170) Is Correlated with Negative and General Psychiatric Symptoms in Schizophrenia

Patients with schizophrenia consistently exhibit abnormalities in the N170 event-related potential (ERP) component evoked by images of faces. However, the relationship between these face-specific N170 abnormalities in patients with schizophrenia and the clinical characteristics of this disorder has not been elucidated. Here, ERP recordings were conducted for patients with schizophrenia and healthy controls. The amplitude and latency of the N170 component were recorded while participants passively viewed face and non-face (table) images to explore the correlation between face-specific processing and clinical characteristics in schizophrenia. The results provided evidence for a face-specific N170 latency delay in patients with schizophrenia. The N170 latency in patients with schizophrenia was significantly longer than that in healthy controls when images of faces were presented in both upright and inverted orientations. Importantly, the face-related N170 latencies of the left temporo-occipital electrodes (P7 and PO7) were positively correlated with both negative and general psychiatric symptoms in these patients. The N170 amplitudes were weaker in patients than in controls for inverted images of both faces and non-faces (tables), with a left-hemisphere dominance. The face inversion effect (FIE), meaning the difference in N170 amplitude between upright and inverted faces, was absent in patients with schizophrenia, suggesting an abnormality of holistic face processing. Together, these results revealed a marked symptom-relevant neural delay associated with face-specific processing in patients with schizophrenia, providing additional evidence to support the demyelination hypothesis of schizophrenia.

Association of Common Polymorphisms in the Nicotinic Acetylcholine Receptor Alpha4 Subunit Gene with an Electrophysiological Endophenotype in a Large Population-Based Sample

Variation in genes coding for nicotinic acetylcholine receptor (nAChR) subunits affect cognitive processes and may contribute to the genetic architecture of neuropsychiatric disorders. Single nucleotide polymorphisms (SNPs) in the CHRNA4 gene that codes for the alpha4 subunit of alpha4/beta2-containing receptors have previously been implicated in aspects of (mostly visual) attention and smoking-related behavioral measures. Here we investigated the effects of six synonymous but functional CHRNA4 exon 5 SNPs on the N100 event-related potential (ERP), an electrophysiological endophenotype elicited by a standard auditory oddball. A total of N = 1,705 subjects randomly selected from the general population were studied with electroencephalography (EEG) as part of the German Multicenter Study on nicotine addiction. Two of the six variants, rs1044396 and neighboring rs1044397, were significantly associated with N100 amplitude. This effect was pronounced in females where we also observed an effect on reaction time. Sequencing of the complete exon 5 region in the population sample excluded the existence of additional/functional variants that may be responsible for the observed effects. This is the first large-scale population-based study investigation the effects of CHRNA4 SNPs on brain activity measures related to stimulus processing and attention. Our results provide further evidence that common synonymous CHRNA4 exon 5 SNPs affect cognitive processes and suggest that they also play a role in the auditory system. As N100 amplitude reduction is considered a schizophrenia-related endophenotype the SNPs studied here may also be associated with schizophrenia outcome measures.

Mismatch negativity: Alterations in adults from the general population who report subclinical psychotic symptoms

BACKGROUND

Deficits of mismatch negativity (MMN) in schizophrenia and individuals at risk for psychosis have been replicated many times. Several studies have also demonstrated the occurrence of subclinical psychotic symptoms within the general population. However, none has yet investigated MMN in individuals from the general population who report subclinical psychotic symptoms.

METHODS

The MMN to duration-, frequency-, and intensity deviants was recorded in 217 nonclinical individuals classified into a control group (n=72) and three subclinical groups: paranoid (n=44), psychotic (n=51), and mixed paranoid-psychotic (n=50). Amplitudes of MMN at frontocentral electrodes were referenced to average. Based on a three-source model of MMN generation, we conducted an MMN source analysis and compared the amplitudes of surface electrodes and sources among groups.

RESULTS

We found no significant differences in MMN amplitudes of surface electrodes. However, significant differences in MMN generation among the four groups were revealed at the frontal source for duration-deviant stimuli (P=0.01). We also detected a trend-level difference (P=0.05) in MMN activity among those groups for frequency deviants at the frontal source.

CONCLUSIONS

Individuals from the general population who report psychotic symptoms are a heterogeneous group. However, alterations exist in their frontal MMN activity. This increased activity might be an indicator of more sensitive perception regarding changes in the environment for individuals with subclinical psychotic symptoms.

Differentiation between major depressive disorder and bipolar disorder by auditory steady-state responses

BACKGROUND

The auditory steady-state response (ASSR) elicited by gamma band neural oscillations has received considerable interest as a biomarker of psychiatric disorders. Although recent ASSR studies have reported that patients with bipolar disorder (BD) show altered ASSRs, little is known about ASSRs in patients with major depressive disorder (MDD). The aim of this study was to evaluate whether ASSRs in MDD subjects differed from those in BD subjects or normal controls (NC).

METHOD

We analyzed ASSRs in 14 MDD patients, 19 BD patients, and 29 normal control subjects. We used whole-head 306-channel magnetoencephalography to evaluate ASSR power and phase-locking factors (PLF) elicited by 20-, 30-, 40-, and 80-Hz click trains. We determined optimal sensitivity and specificity of ASSR power and PLF for the diagnosis of MDD or BD via receiver operating characteristic (ROC) curve analysis using a nonparametric approach.

RESULTS

MDD patients exhibited no significant differences in ASSR power or PLF compared with NC subjects, while BD patients showed deficits on the ASSR measures. MDD patients showed significantly larger ASSR power and PLF for 30-, 40-, and 80-Hz stimuli compared with BD patients. The area under the curve (AUC) for the ROC analysis (MDD vs. BD) was 0.81 [95% CI=0.66-0.96, p=0.003] concerning 40-Hz ASSR power.

LIMITATIONS

We could not exclude the effect of medication and the sample size of the current study is relatively small.

CONCLUSIONS

We could differentiate between MDD and BD subjects in terms of gamma band ASSR. Our data suggest that the 40-Hz ASSR may be a potential biomarker for differentiation between MDD and BD patients.

A decrease in protein level and a missense polymorphism of KIF17 are associated with schizophrenia

It has been shown that the dysfunction of N-methyl-d-asparate (NMDA) receptors-mediated neurotransmission plays a role in the pathophysiology of schizophrenia. Especially, GluN2B, a subunit of NMDA receptors, associated trafficking complex is altered in the prefrontal cortex of schizophrenia. The kinesin superfamily motor protein 17 (KIF17) is known as a transporter of NR2B.Previous studies showed that a structural variant of KIF17 gene is associated with a schizophrenic phenotype. Therefore, here we investigated KIF17 levels in postmortem prefrontal cortex in schizophrenia and the association of a missense polymorphism (Ile341Val) in KIF17 with schizophrenia. The protein expression of KIF17 in schizophrenic postmortem brains was significantly lower than that in controls. Next, the association of missense polymorphisms (rs631375, rs13375609, rs522496 and rs2296225) of KIF17 gene in 567 schizophrenia and 710 healthy subjects was examined. Both genotypic distribution and allelic frequency of rs2296225 polymorphism were significantly different between the chronic schizophrenia subjects and controls. However, our findings described above were not replicated with the independent subjects (555 schizophrenia and 814 healthy controls). Furthermore, the two alleles of rs2296225 polymorphism did not affect the mRNA expression of KIF17. These results suggest that the dysfunction of KIF17 might be involved in the pathophysiology of schizophrenia.

Endophenotypes in Schizophrenia for the Perinatal Period: Criteria for Validation

Endophenotypes are disease-associated phenotypes that are thought to reflect the neurobiological or other mechanisms that underlie the more overt symptoms of a psychiatric illness. Endophenotypes have been critical in understanding the genetics, neurobiology, and treatment of schizophrenia. Because psychiatric illnesses have multiple causes, including both genetic and nongenetic risk factors, an endophenotype linked to one of the mechanisms may be expressed more frequently than the disease itself. However, in schizophrenia research, endophenotypes have almost exclusively been studied in older adolescents or adults who have entered or passed through the age of risk for the disorder. Yet, schizophrenia is a neurodevelopmental disorder where prenatal development starts a cascade of brain changes across the lifespan. Endophenotypes have only minimally been utilized to explore the perinatal development of vulnerability. One major impediment to the development of perinatally-useful endophenotypes has been the established validity criteria. For example, the criterion that the endophenotype be more frequently present in those with disease than those without is difficult to demonstrate when there can be a decades-long period between endophenotype measurement and the age of greatest risk for onset of the disorder. This article proposes changes to the endophenotype validity criteria appropriate to perinatal research and reviews how application of these modified criteria helped identify a perinatally-usable phenotype of risk for schizophrenia, P50 sensory gating, which was then used to propose a novel perinatal primary prevention intervention.

Electrophysiological endophenotypes in rodent models of schizophrenia and psychosis

Schizophrenia is caused by a diverse array of risk factors and results in a similarly diverse set of symptoms. Electrophysiological endophenotypes lie between risks and symptoms and have the potential to link the two. Electrophysiological studies in rodent models, described here, demonstrate that widely differing risk factors result in a similar set of core electrophysiological endophenotypes, suggesting the possibility of a shared neurobiological substrate.

Sleep in patients with schizophrenia

Numerous electrophysiological and neuroimaging studies have reported neurophysiological and cognitive deficits in schizophrenia patients during wakefulness. However, these findings have been inconsistently replicated across different groups of patients, thus complicating the identification of underlying neuronal defects. Sleep minimizes possible waking-related confounds, including decreased motivation and presence of active symptoms. Additionally, the two main sleep rhythms, slow waves and spindles, reflect the intrinsic activity of corticothalamic circuits and are associated with cognitive activities, including learning and memory, occurring during wakefulness. In this review I will present the most relevant sleep findings in schizophrenia, with particular emphasis on several recent studies that have consistently reported sleep spindle deficits in patients with schizophrenia. I will then elaborate on how these findings may contribute to a better understanding of the neurobiology of schizophrenia as well as to the development of novel pharmacological and non-pharmacological interventions to ameliorate the symptoms and cognitive impairments of schizophrenia patients.