Evaluation of resting state gamma power as a response marker in schizophrenia

Schizophrenia diagnosis based on diverse epoch size resting-state EEG using machine learning

Schizophrenia is a severe mental disorder that impairs a person's mental, social, and emotional faculties gradually. Detection in the early stages with an accurate diagnosis is crucial to remedying the patients. This study proposed a new method to classify schizophrenia disease in the rest state based on neurologic signals achieved from the brain by electroencephalography (EEG). The datasets used consisted of 28 subjects, 14 for each group, which are schizophrenia and healthy control. The data was collected from the scalps with 19 EEG channels using a 250 Hz frequency. Due to the brain signal variation, we have decomposed the EEG signals into five sub-bands using a band-pass filter, ensuring the best signal clarity and eliminating artifacts. This work was performed with several scenarios: First, traditional techniques were applied. Secondly, augmented data (additive white Gaussian noise and stretched signals) were utilized. Additionally, we assessed Minimum Redundancy Maximum Relevance (MRMR) as the features reduction method. All these data scenarios are applied with three different window sizes (epochs): 1, 2, and 5 s, utilizing six algorithms to extract features: Fast Fourier Transform (FFT), Approximate Entropy (ApEn), Log Energy entropy (LogEn), Shannon Entropy (ShnEn), and kurtosis. The L2-normalization method was applied to the derived features, positively affecting the results. In terms of classification, we applied four algorithms: K-nearest neighbor (KNN), support vector machine (SVM), quadratic discriminant analysis (QDA), and ensemble classifier (EC). From all the scenarios, our evaluation showed that SVM had remarkable results in all evaluation metrics with LogEn features utilizing a 1-s window size, impacting the diagnosis of Schizophrenia disease. This indicates that an accurate diagnosis of schizophrenia can be achieved through the right features and classification model selection. Finally, we contrasted our results to recently published works using the same and a different dataset, where our method showed a notable improvement.

Optogenetic inhibition of the limbic corticothalamic circuit does not alter spontaneous oscillatory activity, auditory-evoked oscillations, and deviant detection

Aberrant neuronal circuit dynamics are at the core of complex neuropsychiatric disorders, such as schizophrenia (SZ). Clinical assessment of the integrity of neuronal circuits in SZ has consistently described aberrant resting-state gamma oscillatory activity, decreased auditory-evoked gamma responses, and abnormal mismatch responses. We hypothesized that corticothalamic circuit manipulation could recapitulate SZ circuit phenotypes in rodent models. In this study, we optogenetically inhibited the mediodorsal thalamus-to-prefrontal cortex (MDT-to-PFC) or the PFC-to-MDT projection in rats and assessed circuit function through electrophysiological readouts. We found that MDT-PFC perturbation could not recapitulate SZ-linked phenotypes such as broadband gamma disruption, altered evoked oscillatory activity, and diminished mismatch negativity responses. Therefore, the induced functional impairment of the MDT-PFC pathways cannot account for the oscillatory abnormalities described in SZ.

Gamma Oscillations and Potassium Channel Modulation in Schizophrenia: Targeting GABAergic Dysfunction

Impairments in gamma-aminobutyric acid (GABAergic) interneuron function lead to gamma power abnormalities and are thought to underlie symptoms in people with schizophrenia. Voltage-gated potassium 3.1 (Kv3.1) and 3.2 (Kv3.2) channels on GABAergic interneurons are critical to the generation of gamma oscillations suggesting that targeting Kv3.1/3.2 could augment GABAergic function and modulate gamma oscillation generation. Here, we studied the effect of a novel potassium Kv3.1/3.2 channel modulator, AUT00206, on resting state frontal gamma power in people with schizophrenia. We found a significant positive correlation between frontal resting gamma (35-45 Hz) power (n = 22, r = 0.613, P < .002) and positive and negative syndrome scale (PANSS) positive symptom severity. We also found a significant reduction in frontal gamma power (t13 = 3.635, P = .003) from baseline in patients who received AUT00206. This provides initial evidence that the Kv3.1/3.2 potassium channel modulator, AUT00206, may address gamma oscillation abnormalities in schizophrenia.

Differential Effects of Aripiprazole on Electroencephalography-Recorded Gamma-Band Auditory Steady-State Response, Spontaneous Gamma Oscillations and Behavior in a Schizophrenia Rat Model

The available antipsychotics for schizophrenia (SZ) only reduce positive symptoms and do not significantly modify SZ neurobiology. This has raised the question of the robustness and translational value of methods employed during drug development. Electroencephalography (EEG)-based measures like evoked and spontaneous gamma oscillations are considered robust translational biomarkers as they can be recorded in both patients and animal models to probe a key mechanism underlying all SZ symptoms: the excitation/inhibition imbalance mediated by N-methyl-D-aspartate receptor (NMDAr) hypofunction. Understanding the effects of commercialized atypical antipsychotics on such measures could therefore contribute to developing better therapies for SZ. Yet, the effects of such drugs on these EEG readouts are unknown. Here, we studied the effect of the atypical antipsychotic aripiprazole on the gamma-band auditory steady-state response (ASSR), spontaneous gamma oscillations and behavioral features in a SZ rat model induced by the NMDAr antagonist MK-801. Interestingly, we found that aripiprazole could not normalize MK-801-induced abnormalities in ASSR, spontaneous gamma oscillations or social interaction while it still improved MK-801-induced hyperactivity. Suggesting that aripiprazole is unable to normalize electrophysiological features underlying SZ symptoms, our results might explain aripiprazole's inefficacy towards the social interaction deficit in our model but also its limited efficacy against social symptoms in patients.

Potassium channel modulators and schizophrenia: an overview of investigational drugs

INTRODUCTION

Schizophrenia is severe mental illness comprised of positive, negative, and cognitive symptoms. Existing pharmacologic options exert their actions on the dopamine receptor but are largely ineffective at treating negative and cognitive symptoms. Alternative pharmacologic options that do not act directly on the dopamine receptor are being investigated, including potassium channel modulators. It has been hypothesized that dysfunctional fast-spiking parvalbumin-positive GABA interneurons, regulated by Kv 3.1 and Kv 3.2 potassium channels, contribute to the symptoms of schizophrenia, making potassium channels an area of clinical interest.

AREAS COVERED

This review will highlight potassium channel modulators for the treatment of schizophrenia, with a focus on AUT00206. Background on Kv3.1 and Kv3.2 potassium channels will be explored. Our search strategy included a literature review utilizing PubMed, Clinicaltrials.gov, and sources available on the manufacturer's website.

EXPERT OPINION

Initial data on potassium channel modulators is promising, however, further study is needed, and existing evidence is limited. Early data suggests that dysfunctional GABA interneurons can be ameliorated through modulators of Kv3.1 and Kv3.2 channels. AUT00206 has been shown to improve dopaminergic dysfunction induced by ketamine and PCP, improve resting gamma power in patients with schizophrenia, impact dopamine synthesis capacity in a subgroup of individuals with schizophrenia, and affect reward anticipation-related neural activation.

Assessment of electroencephalography modification by antipsychotic drugs in patients with schizophrenia spectrum disorders using frontier orbital theory: A preliminary study

AIM

Schizophrenia is characterized by an abnormality in electroencephalography (EEG), which can be affected by antipsychotic drugs. Recently, the mechanism underlying these EEG alterations in schizophrenia patients was reframed from the perspective of redox abnormalities. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) can be calculated using a computational method and may be useful for evaluating the antioxidant/prooxidant effect of antipsychotic drugs. Thus, we examined the association between the effects of antipsychotic monotherapy on quantitative EEG and HOMO/LUMO energy.

METHODS

We used medical report data including EEG results of psychiatric patients admitted to Hokkaido University Hospital. We extracted the EEG records of patients diagnosed with a schizophrenia spectrum disorder undergoing antipsychotic monotherapy during the natural course of treatment (n = 37). We evaluated the HOMO/LUMO energy of all antipsychotic drugs using computational methods. Multiple regression analyses were used to examine the relationship between the HOMO/LUMO energy of all antipsychotic drugs and spectral band power in all patients. Statistical significance was set at p < 6.25 × 10^-4 adjusted with Bonferroni correction.

RESULTS

We showed that the HOMO energy of all antipsychotic drugs had weak positive correlations with delta- and gamma-band power (e.g., standardized β = 0.617 for delta in the F3 channel, p = 6.6 × 10^-5 ; standardized β = 0.563 for gamma in the O1 channel, p = 5.0 × 10^-4 ).

CONCLUSION

Although there may be unexpected bias and confounding factors, our findings suggest that the effect of antipsychotic drugs on EEG may be related to their antioxidant actions.

Decrease in gamma-band auditory steady-state response in patients with treatment-resistant schizophrenia

BACKGROUND

Thirty percent of patients with schizophrenia do not respond to non-clozapine antipsychotics and are termed treatment-resistant schizophrenia (TRS). The 40-Hz auditory steady-state response (ASSR) is a well-known to be reduced in patients with schizophrenia compared to healthy controls (HCs), suggesting impaired gamma oscillation in schizophrenia. Given no ASSR study on TRS, we aimed to examine the neurophysiological basis of TRS employing 40-Hz ASSR paradigm.

METHOD

We compared ASSR measures among HCs, patients with non-TRS, and patients with TRS. TRS criteria were defined by a score of 4 or higher on two items of the Positive and Negative Syndrome Scale (PANSS) positive symptoms despite standard antipsychotic treatment. Participants were examined for ASSR with 40-Hz click-train stimulus, and then time-frequency analysis was performed to calculate evoked power and phase-locking factor (PLF) of 40-Hz ASSR.

RESULTS

A total of 79 participants were included: 27 patients with TRS (PANSS = 92.6 ± 15.8); 27 patients with non-TRS (PANSS = 63.3 ± 14.7); and 25 HCs. Evoked power in 40-Hz ASSR was lower in the TRS group than in the HC group (F_2,79 = 8.37, p = 0.015; TRS vs. HCs: p = 0.012, d = 1.1) while no differences in PLF were found between the groups.

CONCLUSION

These results suggest that glutamatergic and GABAergic neurophysiological dysfunctions are involved in the pathophysiology of TRS. Our findings warrant more comprehensive and longitudinal studies for deep phenotyping of TRS.

Macroscale EEG characteristics in antipsychotic-naïve patients with first-episode psychosis and healthy controls

Electroencephalography in patients with a first episode of psychosis (FEP) may contribute to the diagnosis and treatment response prediction. Findings in the literature vary due to small sample sizes, medication effects, and variable illness duration. We studied macroscale resting-state EEG characteristics of antipsychotic naïve patients with FEP. We tested (1) for differences between FEP patients and controls, (2) if EEG could be used to classify patients as FEP, and (3) if EEG could be used to predict treatment response to antipsychotic medication. In total, we studied EEG recordings of 62 antipsychotic-naïve patients with FEP and 106 healthy controls. Spectral power, phase-based and amplitude-based functional connectivity, and macroscale network characteristics were analyzed, resulting in 60 EEG variables across four frequency bands. Positive and Negative Symptom Scale (PANSS) were assessed at baseline and 4-6 weeks follow-up after treatment with amisulpride or aripiprazole. Mann-Whitney U tests, a random forest (RF) classifier and RF regression were used for statistical analysis. Our study found that at baseline, FEP patients did not differ from controls in any of the EEG characteristics. A random forest classifier showed chance-level discrimination between patients and controls. The random forest regression explained 23% variance in positive symptom reduction after treatment in the patient group. In conclusion, in this largest antipsychotic- naïve EEG sample to date in FEP patients, we found no differences in macroscale EEG characteristics between patients with FEP and healthy controls. However, these EEG characteristics did show predictive value for positive symptom reduction following treatment with antipsychotic medication.

Neurexin1α knockout rats display oscillatory abnormalities and sensory processing deficits back-translating key endophenotypes of psychiatric disorders

Neurexins are presynaptic transmembrane proteins crucial for synapse development and organization. Deletion and missense mutations in all three Neurexin genes have been identified in psychiatric disorders, with mutations in the NRXN1 gene most strongly linked to schizophrenia (SZ) and autism spectrum disorder (ASD). While the consequences of NRXN1 deletion have been extensively studied on the synaptic and behavioral levels, circuit endophenotypes that translate to the human condition have not been characterized yet. Therefore, we investigated the electrophysiology of cortico-striatal-thalamic circuits in Nrxn1α-/- rats and wildtype littermates focusing on a set of translational readouts, including spontaneous oscillatory activity, auditory-evoked oscillations and potentials, as well as mismatch negativity-like (MMN) responses and responses to social stimuli. On the behavioral level Nrxn1α-/- rats showed locomotor hyperactivity. In vivo freely moving electrophysiology revealed pronounced increases of spontaneous oscillatory power within the gamma band in all studied brain areas and elevation of gamma coherence in cortico-striatal and thalamocortical circuits of Nrxn1α-/- rats. In contrast, auditory-evoked oscillations driven by chirp-modulated tones showed reduced power in cortical areas confined to slower oscillations. Finally, Nrxn1α-/- rats exhibited altered auditory evoked-potentials and profound deficits in MMN-like responses, explained by reduced prediction error. Despite deficits for auditory stimuli, responses to social stimuli appeared intact. A central hypothesis for psychiatric and neurodevelopmental disorders is that a disbalance of excitation-to-inhibition is underlying oscillatory and sensory deficits. In a first attempt to explore the impact of inhibitory circuit modulation, we assessed the effects of enhancing tonic inhibition via δ-containing GABAA receptors (using Gaboxadol) on endophenotypes possibly associated with network hyperexcitability. Pharmacological experiments applying Gaboxadol showed genotype-specific differences, but failed to normalize oscillatory or sensory processing abnormalities. In conclusion, our study revealed endophenotypes in Nrxn1α-/- rats that could be used as translational biomarkers for drug development in psychiatric disorders.

Increased spontaneous fronto-central oscillatory power during eye closing in patients with multiple somatic symptoms

Functional somatic symptoms (FSS) are typically associated with excessive thoughts, feelings and behaviors related to the physical symptoms whether these symptoms are unequivocally associated with a diagnosed medical condition. However, less evidence is available concerning the neurocognitive deficits underlying these features of FSS. This study aimed to examine the resting-state oscillatory activities during both eye-opening and eye-closure states in individuals with FSS. Sixty-six FSS patients screened with PHQ-15 received two 10-minute sessions of EEG assessments. All completed clinical measurements on depression, anxiety, and psychological measurements on personality traits and alexithymia. Patients scoring high on PHQ-15 (the multiple somatic symptom (MSS) or SS-high group) demonstrated increased powers in central channels (C3 and C4) in low-beta band and in the left-frontal channel (F3) in high-gamma band, during eye-closure states. Patients with higher scores in depression were more likely to be classified as the SS-high group. SS-high patients demonstrated increased difficulties in describing and identifying emotions, and less reduced day-dreaming. The combined findings in increased fronto-central high-frequency activities and alexithymia measures suggest MSS patients are associated with enhanced internally-oriented thinking and cognitive simulation which may lead to intensified feelings of simulated events and misattribution of symptoms. Future treatments should focus on eliminating cognitive bias and enhancing accuracy in interoceptive awareness.

A Role for Somatostatin-Positive Interneurons in Neuro-Oscillatory and Information Processing Deficits in Schizophrenia

Alterations in neocortical GABAergic interneurons (INs) have been affiliated with neuropsychiatric diseases, including schizophrenia (SZ). Significant progress has been made linking the function of a specific subtype of GABAergic cells, parvalbumin (PV) positive INs, to altered gamma-band oscillations, which, in turn, underlie perceptual and feedforward information processing in cortical circuits. Here, we review a smaller but growing volume of literature focusing on a separate subtype of neocortical GABAergic INs, somatostatin (SST) positive INs. Despite sharing similar neurodevelopmental origins, SSTs exhibit distinct morphology and physiology from PVs. Like PVs, SSTs are altered in postmortem brain samples from multiple neocortical regions in SZ, although basic and translational research into consequences of SST dysfunction has been relatively sparse. We highlight a growing body of work in rodents, which now indicates that SSTs may also underlie specific aspects of cortical circuit function, namely low-frequency oscillations, disinhibition, and mediation of cortico-cortical feedback. SSTs may thereby support the coordination of local cortical information processing with more global spatial, temporal, and behavioral context, including predictive coding and working memory. These functions are notably deficient in some cases of SZ, as well as other neuropsychiatric disorders, emphasizing the importance of focusing on SSTs in future translational studies. Finally, we highlight the challenges that remain, including subtypes within the SST class.

Quantitative Resting State Electroencephalography in Patients with Schizophrenia Spectrum Disorders Treated with Strict Monotherapy Using Atypical Antipsychotics

OBJECTIVE

The effect of antipsychotic drugs on quantitative electroencephalography (EEG) has been mainly examined by the administration of a single test dose or among patients using combinations of other psychotropic drugs. We therefore investigated the effects of strict monotherapy with antipsychotic drugs on quantitative EEG among schizophrenia patients.

METHODS

Data from 2,364 medical reports with EEG results from psychiatric patients admitted to the Hokkaido University Hospital were used. We extracted EEG records of patients who were diagnosed with schizophrenia spectrum disorders and who were either undergoing strict antipsychotic monotherapy or were completely free of psychotropic drugs. The spectral power was compared between drug-free patients and patients using antipsychotic drugs. We also performed multiple regression analysis to evaluate the relationship between spectral power and the chlorpromazine equivalent daily dose of antipsychotics in all the patients.

RESULTS

We included 31 monotherapy and 20 drug-free patients. Compared with drug-free patients, patients receiving antipsychotic drugs demonstrated significant increases in theta, alpha and beta power. When patients taking different types of antipsychotics were compared with drug-free patients, we found no significant change in any spectrum power for the aripiprazole or blonanserin groups. Patients taking risperidone demonstrated significant increases in alpha and beta power. Patients taking clozapine and olanzapine demonstrated significant slow wave increases. Multiple regression analysis revealed that the chlorpromazine equivalent dose was positively associated with theta power.

CONCLUSION

Use of any antipsychotic drug by patients was associated with a dose-dependent increase in theta power. However, each type of antipsychotic demonstrated different spectral power changes.

Effects of antipsychotic drugs and potassium channel modulators on spectral properties of local field potentials in mouse hippocampus and pre-frontal cortex

Local field potentials (LFPs) recorded intracranially display a range of location-specific oscillatory spectra which have been related to cognitive processes. Although the mechanisms producing LFPs are not completely understood, it is likely that voltage-gated ion channels which produce action potentials and patterned discharges play a significant role. It is also known that antipsychotic drugs (APDs) affect LFP spectra and a direct inhibitory effect on voltage-gated potassium channels has been reported. Additionally, voltage-gated potassium channels have been implicated in the pathophysiology of schizophrenia, a disorder for which APDs are primary therapies. In this study we sought to: i) better characterise the effects of two APDs on LFPs spectra and connectivity measures and ii) examine the effects of potassium channel modulators on LFPs and potential overlap of effects with APDs. Intracranial electrodes were implanted in hippocampus (HIP) and pre-frontal cortex (PFC) of C57BL/6J mice; power spectra, coherence and phase-amplitude cross-frequency coupling were measured. Drugs tested were APDs haloperidol and clozapine as well as voltage-gated potassium channel modulators (KVMs) 4-aminopyridine (4-AP), tetraethylammonium, retigabine and E-4031. Both APDs and KVMs significantly reduced gamma power except 4-AP, which conversely increased gamma power. Clozapine and retigabine additionally reduced gamma coherence between HIP and PFC, while 4-AP demonstrated the opposite effect. Phase-amplitude coupling between theta and gamma oscillations in HIP was significantly reduced by the administration of haloperidol and retigabine. These results provide previously undescribed effects of APDs on LFP properties and demonstrate novel modulation of LFP characteristics by KVMs that intriguingly overlap with the APD effects.

Changes in beta and high-gamma power in resting-state electrocorticogram induced by repetitive transcranial magnetic stimulation of primary motor cortex in unanesthetized macaque monkeys

Repetitive transcranial magnetic stimulation (rTMS) is now widely used as a means of neuromodulation, but the details of the mechanisms by which rTMS works remain unclarified. As a step forward to unveiling the neural phenomena occurring underneath the TMS coil, we conducted an electrophysiological study using awake and unanesthetized monkeys with subdural electrocorticogram (ECoG) electrodes implanted over the primary motor cortex (MI). We evaluated the effects of low-frequency (1 Hz) and high-frequency (10 Hz) rTMS on the resting-state ECoG signals in the stimulated MI, as well as the motor evoked potentials (MEPs) in the contralateral hand. Following the 1-Hz rTMS application, the ECoG beta band power and the MEP amplitude were significantly decreased. Following the 10-Hz rTMS application, the ECoG high-gamma power and the MEP amplitude significantly increased. Given that beta and high-gamma activities in the ECoG reflect the synchronous firing and the firing frequency of cell assemblies, respectively, in local neural circuits, these results suggest that low-frequency rTMS inhibits neural activity by desynchronizing the firing activity of local circuits, whereas high-frequency rTMS facilitates neural activity by increasing the firing rate of cell assemblies in the local circuits.

Resting state quantitative electroencephalogram gamma power spectra in patients with first episode psychosis: An observational study

INTRODUCTION

Electrophysiological abnormalities, especially in the gamma frequency range, have been well documented in schizophrenia. This study was aimed to investigate the gamma spectral power of the brain in patients with first episode psychosis, using high-resolution electroencephalography.

METHODOLOGY

Twenty-nine neuroleptic naïve/free male patients with non-affective psychosis as per ICD 10 DCR clinical criteria were compared with thirty age, sex, education and handedness matched healthy individuals as controls. All participants underwent 192-channel resting electroencephalography (EEG) recording. Gamma spectral power was calculated for low (31-50 Hz) and high-gamma (51-70 and 71-100 Hz) bands and compared between two groups using MANOVA and supplementary one-way ANOVA. Pearson correlation and linear regression analyses were conducted between spectral power parameters and various clinical variables.

RESULTS

The gamma spectral power in 31-50 Hz and 51-70 Hz frequency bands was found to be significantly higher in patients in most brain regions. Duration of illness predicted the gamma spectral power in both right and left frontal regions of the brain in the frequency range 31-50 Hz and 71-100 Hz, as well as in the right temporal region in 71-100 Hz range, where it was negatively correlated.

CONCLUSION

Patients with first episode psychosis have increased gamma spectral power, which might be indirectly related to the duration of illness.

Dynamic Changes of Brain Networks during Working Memory Tasks in Schizophrenia

Electroencephalograph (EEG) signals and graph theory measures have been widely used to characterize the brain functional networks of healthy individuals and patients by calculating the correlations between different electrodes over an entire time series. Although EEG signals have a high temporal resolution and can provide relatively stable results, the process of constructing and analyzing brain functional networks is inevitably complicated by high time complexity. Our goal in this research was to distinguish the brain function networks of schizophrenia patients from those of healthy participants during working memory tasks. Consequently, we utilized a method involving microstates, which are each characterized by a unique topography of electric potentials over an entire channel array, to reduce the dimension of the EEG signals during working memory tasks and then compared and analyzed the brain functional networks using the microstates time series (MTS) and original time series (OTS) of the schizophrenia patients and healthy individuals. We found that the right frontal and parietal-occipital regions neurons of the schizophrenia patients were less active than those of the healthy participants during working memory tasks. Notably, compared with OTS, the time needed to construct the brain functional networks was significantly reduced by using MTS. In conclusion, our results show that, like OTS, MTS can well distinguish the brain functional network of schizophrenia patients from those of healthy individuals during working memory tasks while greatly decreasing time complexity. MTS can thus provide a method for characterizing the original time series for the construction and analysis of EEG brain functional networks.

Patient, interrupted: MEG oscillation dynamics reveal temporal dysconnectivity in schizophrenia

Current theories of schizophrenia emphasize the role of altered information integration as the core dysfunction of this illness. While ample neuroimaging evidence for such accounts comes from investigations of spatial connectivity, understanding temporal disruptions is important to fully capture the essence of dysconnectivity in schizophrenia. Recent electrophysiology studies suggest that long-range temporal correlation (LRTC) in the amplitude dynamics of neural oscillations captures the integrity of transferred information in the healthy brain. Thus, in this study, 25 schizophrenia patients and 25 controls (8 females/group) were recorded during two five-minutes of resting-state magnetoencephalography (once with eyes-open and once with eyes-closed). We used source-level analyses to investigate temporal dysconnectivity in patients by characterizing LRTCs across cortical and sub-cortical brain regions. In addition to standard statistical assessments, we applied a machine learning framework using support vector machine to evaluate the discriminative power of LRTCs in identifying patients from healthy controls. We found that neural oscillations in schizophrenia patients were characterized by reduced signal memory and higher variability across time, as evidenced by cortical and subcortical attenuations of LRTCs in the alpha and beta frequency bands. Support vector machine significantly classified participants using LRTCs in key limbic and paralimbic brain areas, with decoding accuracy reaching 82%. Importantly, these brain regions belong to networks that are highly relevant to the symptomology of schizophrenia. These findings thus posit temporal dysconnectivity as a hallmark of altered information processing in schizophrenia, and help advance our understanding of this pathology.

Altered parahippocampal gyrus activation and its connectivity with resting-state network areas in schizophrenia: An EEG study

Synchronized and coherent activity in resting-networks during normal brain functioning could be altered in disconnection syndrome like schizophrenia. Study of neural oscillations as assessed by EEG appears to be a promising proposition to understand the pathophysiology of schizophrenia in patients and their first-degree relatives, where disturbances in neural oscillations point towards genetic predisposition. Therefore, present study aims at establishing EEG based biomarkers for early detection and management strategies. Thirty-two patients with schizophrenia, 28 first-degree relatives and 31 healthy controls (HC) participated in the study. Resting brain activity was recorded using 128-channel electroencephalography. After pre-processing and independent component analysis (ICA), an equivalent current dipole was estimated for each IC. Total of 1551 independent and localizable EEG components across all groups were used in subsequent analysis. Power spectral density and source coherence between IC clusters were computed. Patients and first-degree relatives displayed significantly higher power spectral density (PSD) than HC for all frequency bands in left parahippocampal gyrus (PHG) (-7, -26, 8; BA 27). Another region within left deep PHG (-4, -28, 1), however, distinguished patients from first-degree relatives and HC in terms of significantly lower PSD in higher frequency bands. Functional connectivity (FC) was found to be lower in patients and higher in relatives compared to HC between different resting-state network areas. In patients, connectivity was lower compared to first-degree relatives. Altered activity within left PHG and FC of primarily this with other areas in resting-state network can serve as state and trait markers of schizophrenia.

Modulation of frontal gamma oscillations improves working memory in schizophrenia

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Cognitive deficits, a core symptom of schizophrenia, are difficult to treat with available therapies.

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Abnormal neural dynamics of frontal gamma oscillations contribute to these deficits.

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Neurofeedback has been used previously to alter brain oscillations.

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Gamma band neurofeedback can impact brain and behavioral markers of cognition.

Schizophrenia is a debilitating mental disorder that is associated with cognitive deficits. Impairments in cognition occur early in the course of illness and are associated with poor functional outcome, but have been difficult to treat with conventional treatments. Recent studies have implicated abnormal neural network dynamics and impaired connectivity in frontal brain regions as possible causes of cognitive deficits. For example, high-frequency, dorsal-lateral prefrontal oscillatory activity in the gamma range (30–50 Hz) is associated with impaired working memory in individuals with schizophrenia. In light of these findings, it may be possible to use EEG neurofeedback (EEG-NFB) to train individuals with schizophrenia to enhance frontal gamma activity to improve working memory and cognition. In a single-group, proof-of-concept study, 31 individuals with schizophrenia received 12 weeks of twice weekly EEG-NFB to enhance frontal gamma band response. EEG-NFB was well-tolerated, associated with increased gamma training threshold, and significant increases in frontal gamma power during an n-back working memory task. Additionally, EEG-NFB was associated with significant improvements in n-back performance and working memory, speed of processing, and reasoning and problem solving on neuropsychological tests. Change in gamma power was associated with change in cognition. Significant improvements in psychiatric symptoms were also found. These encouraging findings suggest EEG-NFB targeting frontal gamma activity may provide a novel effective approach to cognitive remediation in schizophrenia, although placebo-controlled trials are needed to assess the effects of non-treatment related factors.

Auditory EEG Biomarkers in Fragile X Syndrome: Clinical Relevance

Sensory hypersensitivities are common and distressing features of Fragile X Syndrome (FXS). While there are many drug interventions that reduce behavioral deficits in Fmr1 mice and efforts to translate these preclinical breakthroughs into clinical trials for FXS, evidence-based clinical interventions are almost non-existent potentially due to lack of valid neural biomarkers. Local circuit function in sensory networks is dependent on the dynamic balance of activity in inhibitory/excitatory synapses. Studies are needed to examine the association of electrophysiological alterations in neural systems with sensory and other clinical features of FXS to establish their clinical relevance. Adolescents and adults with FXS (n = 38, Mean age = 25.5, std = 10.1; 13 females) and age matched typically developing controls (n = 40, Mean age = 27.7, std = 12.1; 17 females) completed auditory chirp and auditory habituation tasks while undergoing dense array electroencephalography (EEG). Amplitude, latency, and percent change (habituation) in N1 and P2 event-related potential (ERP) components were characterized for the habituation task; time-frequency calculations using Morlet wavelets characterized phase-locking and single trial power for the habituation and chirp tasks. FXS patients showed increased amplitude but some evidence for reduced habituation of the N1 ERP, and reduced phase-locking in the low and high gamma frequency range and increased low gamma power to the chirp stimulus. FXS showed increased theta power in both tasks. While the habituation finding was weaker than previously found, the remaining findings replicate our previous work in a new sample of patients with FXS. Females showed less deficit in the chirp task but not the habituation task. Abnormal increases in gamma power were related to more severe behavioral and psychiatric features as well as reductions in neurocognitive abilities. Replicating electrophysiological deficits in a new group of patients using different EEG equipment at a new data collection site with differing levels of environmental noise that were robust to data processing techniques utilizing multiple researchers, indicates a potential for scalability to multi-site clinical trials. Given the robust replicability, relevance to clinical measures, and preclinical evidence for sensitivity of these EEG measures to pharmacological intervention, the observed abnormalities may provide novel translational markers of target engagement and potentially outcome measures in large-scale studies evaluating new treatments targeting neural hyperexcitability in FXS.

Oscillations in cortico-basal ganglia circuits: implications for Parkinson’s disease and other neurologic and psychiatric conditions

Cortico-basal ganglia circuits are thought to play a crucial role in the selection and control of motor behaviors and have also been implicated in the processing of motivational content and in higher cognitive functions. During the last two decades, electrophysiological recordings in basal ganglia circuits have shown that several disease conditions are associated with specific changes in the temporal patterns of neuronal activity. In particular, synchronized oscillations have been a frequent finding suggesting that excessive synchronization of neuronal activity may be a pathophysiological mechanism involved in a wide range of neurologic and psychiatric conditions. We here review the experimental support for this hypothesis primarily in relation to Parkinson’s disease but also in relation to dystonia, essential tremor, epilepsy, and psychosis/schizophrenia.

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.

Unsuccessful reduction of high-frequency alpha activity during cognitive activation in schizophrenia

AIMS

Electroencephalogram (EEG) alpha activity during resting state reflects the 'readiness' of an individual to respond to the environment; this includes the performance of cognitive processes. Alpha activity is reported to be attenuated in schizophrenia (SCZ). Understanding the interaction between alpha activity during rest and when cognitively engaged may provide insights into the neural circuitry, which is dysfunctional in SCZ. This study investigated the changes of alpha activity between resting state and cognitive engagement in SCZ patients.

METHODS

Thirty-four SCZ patients and 29 healthy controls (HC) were recruited. EEG was performed in the resting state and during an auditory P300 task. All experimental procedures followed the relevant institutional guidelines and regulations.

RESULTS

In SCZ, high-frequency alpha activity was reduced in the resting state. High-frequency alpha source density was decreased in both the resting-state and a P300 task condition in patients, compared to HC. HC, but not SCZ patients, showed a reduction in high-frequency alpha source density during the P300 task compared to the resting state. The negative correlation between high-frequency alpha source density in the resting state and positive symptoms was significant.

CONCLUSIONS

High-frequency alpha activity in SCZ patients and its unsuccessful reduction during cognitive processing may be biological markers of SCZ.

EEG Frequency Bands in Psychiatric Disorders: A Review of Resting State Studies

A significant proportion of the electroencephalography (EEG) literature focuses on differences in historically pre-defined frequency bands in the power spectrum that are typically referred to as alpha, beta, gamma, theta and delta waves. Here, we review 184 EEG studies that report differences in frequency bands in the resting state condition (eyes open and closed) across a spectrum of psychiatric disorders including depression, attention deficit-hyperactivity disorder (ADHD), autism, addiction, bipolar disorder, anxiety, panic disorder, post-traumatic stress disorder (PTSD), obsessive compulsive disorder (OCD) and schizophrenia to determine patterns across disorders. Aggregating across all reported results we demonstrate that characteristic patterns of power change within specific frequency bands are not necessarily unique to any one disorder but show substantial overlap across disorders as well as variability within disorders. In particular, we show that the most dominant pattern of change, across several disorder types including ADHD, schizophrenia and OCD, is power increases across lower frequencies (delta and theta) and decreases across higher frequencies (alpha, beta and gamma). However, a considerable number of disorders, such as PTSD, addiction and autism show no dominant trend for spectral change in any direction. We report consistency and validation scores across the disorders and conditions showing that the dominant result across all disorders is typically only 2.2 times as likely to occur in the literature as alternate results, and typically with less than 250 study participants when summed across all studies reporting this result. Furthermore, the magnitudes of the results were infrequently reported and were typically small at between 20% and 30% and correlated weakly with symptom severity scores. Finally, we discuss the many methodological challenges and limitations relating to such frequency band analysis across the literature. These results caution any interpretation of results from studies that consider only one disorder in isolation, and for the overall potential of this approach for delivering valuable insights in the field of mental health.

High Frequencies in QEEG Are Related to the Level of Insight in Patients With Schizophrenia

Lack of insight is a neurocognitive problem commonly encountered in patients with psychotic disorders that negatively affects treatment compliance and prognosis. Measurement of insight is based on self-report scales, which are limited due to subjectivity. This study aimed to determine the correlation between resting state beta and gamma power in 23 patients with schizophrenia and insight. It was observed that as beta and gamma power measured via qualitative electroencephalography (qEEG) increased the level of insight decreased. Negative correlation was found in F3, C3, Cz for gamma activity and in F3 and C3 for beta activity. This finding indicates that resting state qEEG could be used to evaluate the level of insight in patients with schizophrenia.

Social anhedonia and gamma band abnormalities as a composite/multivariate endophenotype for schizophrenia: a dense array EEG study

AIM

Social anhedonia and gamma band oscillations are proposed as a promising endophenotype for schizophrenia (SZ). The aim was to assess whether social anhedonia and spontaneous gamma band oscillations could be used as multivariate/composite endophenotypic measures for SZ.

METHODS

Sixty consented subjects, of which 20 remitted SZ patients, 20 unaffected siblings of patients with schizophrenia (US) and 20 healthy controls (HC) were recruited for the study. The Revised Social Anhedonia Scale, Temporal Experience of Pleasure Scale and the Schizotypal Personality Questionnaire assessed social anhedonia, temporal experience of pleasure and schizotypal features. All participants underwent awake, resting state 192-channel dense array electroencephalographic recording. Gamma spectral power and coherence were calculated. We performed chi-square test, one-way analysis of variance, Pearsons correlation coefficient and step-by-step linear discriminant functional analysis.

RESULTS

Social anhedonia was significantly higher and anticipatory aspects of pleasure were significantly lower in both SZ and US compared with HC. US scored significantly higher than HC in the Schizotypal Personality Questionnaire. Spectral power of high gamma band (>70 Hz) was significantly lower over the right temporo-parietal and midline regions in both SZ and US than HC. We accurately classified (85%) three groups when social anhedonia, high gamma band spectral power of midline, right frontal and right fronto-temporal interhemispheric gamma coherence were considered as composite measures rather than each variable representing independently.

CONCLUSION

We propose region-specific high gamma spectral 'power and coherence' and social anhedonia as composite/multivariate measures could be a useful measure in distinguishing schizophrenia patients and unaffected siblings from healthy controls.

The impact of cognitive training on spontaneous gamma oscillations in schizophrenia

Schizophrenia patients exhibit less gamma-frequency EEG/MEG activity (>30 Hz), a finding interpreted as evidence of poor temporal neural organization and functional network communication. Research has shown that neuroplasticity-oriented training can improve task-related oscillatory dynamics, indicating some reorganization capacity in schizophrenia. Demonstrating a generalization of such task training effects to spontaneous oscillations at rest would not only enrich understanding of this neuroplastic potential but inform the interpretation of spontaneous gamma oscillations in the service of normal cognitive function. In the present study, neuromagnetic resting-state oscillatory brain activity and cognitive performance were assessed before and after training in 61 schizophrenia patients, who were randomly assigned to 4 weeks of neuroplasticity-oriented targeted cognitive training or treatment as usual (TAU). Gamma power of 40-90 Hz increased after training, but not after TAU, in a frontoparietal network. Across two types of training, this increase was related to improved cognitive test performance. These results indicate that abnormal oscillatory dynamics in schizophrenia patients manifested in spontaneous gamma activity can be changed with neuroplasticity-oriented training parallel to cognitive performance.

Schizophrenia: A review of potential biomarkers

OBJECTIVES

Understanding the biological process and progression of schizophrenia is the first step to developing novel approaches and new interventions. Research on new biomarkers is extremely important when the goal is an early diagnosis (prediction) and precise theranostics. The objective of this review is to understand the research on biomarkers and their effects in schizophrenia to synthesize the role of these new advances.

METHODS

In this review, we search and review publications in databases in accordance with established limits and specific objectives. We look at particular endpoints such as the category of biomarkers, laboratory techniques and the results/conclusions of the selected publications.

RESULTS

The investigation of biomarkers and their potential as a predictor, diagnosis instrument and therapeutic orientation, requires an appropriate methodological strategy. In this review, we found different laboratory techniques to identify biomarkers and their function in schizophrenia.

CONCLUSION

The consolidation of this information will provide a large-scale application network of schizophrenia biomarkers.

Decoding Saccadic Directions Using Epidural ECoG in Non-Human Primates

A brain-computer interface (BCI) can be used to restore some communication as an alternative interface for patients suffering from locked-in syndrome. However, most BCI systems are based on SSVEP, P300, or motor imagery, and a diversity of BCI protocols would be needed for various types of patients. In this paper, we trained the choice saccade (CS) task in 2 non-human primate monkeys and recorded the brain signal using an epidural electrocorticogram (eECoG) to predict eye movement direction. We successfully predicted the direction of the upcoming eye movement using a support vector machine (SVM) with the brain signals after the directional cue onset and before the saccade execution. The mean accuracies were 80% for 2 directions and 43% for 4 directions. We also quantified the spatial-spectro-temporal contribution ratio using SVM recursive feature elimination (RFE). The channels over the frontal eye field (FEF), supplementary eye field (SEF), and superior parietal lobule (SPL) area were dominantly used for classification. The α-band in the spectral domain and the time bins just after the directional cue onset and just before the saccadic execution were mainly useful for prediction. A saccade based BCI paradigm can be projected in the 2D space, and will hopefully provide an intuitive and convenient communication platform for users.

Neural synchronization deficits linked to cortical hyper-excitability and auditory hypersensitivity in fragile X syndrome

Background

Studies in the fmr1 KO mouse demonstrate hyper-excitability and increased high-frequency neuronal activity in sensory cortex. These abnormalities may contribute to prominent and distressing sensory hypersensitivities in patients with fragile X syndrome (FXS). The current study investigated functional properties of auditory cortex using a sensory entrainment task in FXS.

Methods

EEG recordings were obtained from 17 adolescents and adults with FXS and 17 age- and sex-matched healthy controls. Participants heard an auditory chirp stimulus generated using a 1000-Hz tone that was amplitude modulated by a sinusoid linearly increasing in frequency from 0–100 Hz over 2 s.

Results

Single trial time-frequency analyses revealed decreased gamma band phase-locking to the chirp stimulus in FXS, which was strongly coupled with broadband increases in gamma power. Abnormalities in gamma phase-locking and power were also associated with theta-gamma amplitude-amplitude coupling during the pre-stimulus period and with parent reports of heightened sensory sensitivities and social communication deficits.

Conclusions

This represents the first demonstration of neural entrainment alterations in FXS patients and suggests that fast-spiking interneurons regulating synchronous high-frequency neural activity have reduced functionality. This reduced ability to synchronize high-frequency neural activity was related to the total power of background gamma band activity. These observations extend findings from fmr1 KO models of FXS, characterize a core pathophysiological aspect of FXS, and may provide a translational biomarker strategy for evaluating promising therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-017-0140-1) contains supplementary material, which is available to authorized users.

Electroencephalogram alpha-to-theta ratio over left fronto-temporal region correlates with negative symptoms in schizophrenia

BACKGROUND

Negative symptoms impair outcomes on occupational functioning, social interaction and interpersonal relationships in patients with schizophrenia. Past researchers have reported reduced alpha and increased theta and delta spectral powers on quantitative EEG recordings in those with prominent negative symptoms.

AIM

Present analysis aimed at exploring the relationships between lower-frequency EEG powers and negative symptoms, in schizophrenia, over a period of naturalistic antipsychotic treatment.

METHOD

Fifteen right-handed drug-free/drug-naïve schizophrenia patients (N=15;M=12,F=3) were recruited and assessed on PANSS. Spontaneous 192-channel resting-state EEG was recorded at baseline, and PANSS rating was repeated at 4 weeks. Baseline EEGs of patients were compared to 15 age-sex-handedness matched controls.

RESULTS

Non-significant differences emerged between patient and controls in terms of socio-demographic characteristics. Over left frontal and left temporal regions, baseline ratio of alpha/theta power (bATR) was significantly lower (p<0.001) in patients, correlated negatively with baseline PANSS negative score (PNS) (p<0.05); and over 4-weeks of antipsychotic treatment, left temporal bATR correlated positively with relative improvements in PNS.

CONCLUSION

Reduced alpha power over frontal regions might imply altered arousal and/or impaired attentional process, while abnormal theta range oscillations may relate to impairments in working memory via their influences on theta-gamma coupling. Our findings suggest left-predominant deficiencies in these processes might mediate negative symptoms. Further, since ATR might reflect integrity of certain cognitive processes, those with a higher bATR might possess better cognitive resource at baseline and therefore experience greater improvement in negative symptoms with antipsychotic treatments, at least during the first 4 weeks.

A Neurophysiological Perspective on a Preventive Treatment against Schizophrenia Using Transcranial Electric Stimulation of the Corticothalamic Pathway

Schizophrenia patients are waiting for a treatment free of detrimental effects. Psychotic disorders are devastating mental illnesses associated with dysfunctional brain networks. Ongoing brain network gamma frequency (30–80 Hz) oscillations, naturally implicated in integrative function, are excessively amplified during hallucinations, in at-risk mental states for psychosis and first-episode psychosis. So, gamma oscillations represent a bioelectrical marker for cerebral network disorders with prognostic and therapeutic potential. They accompany sensorimotor and cognitive deficits already present in prodromal schizophrenia. Abnormally amplified gamma oscillations are reproduced in the corticothalamic systems of healthy humans and rodents after a single systemic administration, at a psychotomimetic dose, of the glutamate N-methyl-d-aspartate receptor antagonist ketamine. These translational ketamine models of prodromal schizophrenia are thus promising to work out a preventive noninvasive treatment against first-episode psychosis and chronic schizophrenia. In the present essay, transcranial electric stimulation (TES) is considered an appropriate preventive therapeutic modality because it can influence cognitive performance and neural oscillations. Here, I highlight clinical and experimental findings showing that, together, the corticothalamic pathway, the thalamus, and the glutamatergic synaptic transmission form an etiopathophysiological backbone for schizophrenia and represent a potential therapeutic target for preventive TES of dysfunctional brain networks in at-risk mental state patients against psychotic disorders.

Safety and Efficacy of Adjunctive Θ Burst Repetitive Transcranial Magnetic Stimulation to Right Inferior Parietal Lobule in Schizophrenia Patients With First-Rank Symptoms: A Pilot, Exploratory Study

BACKGROUND

First-rank symptoms (FRS) in schizophrenia have been found to be associated with various cognitive and biological markers. Repetitive transcranial magnetic stimulation (rTMS) has been shown to modulate such factors. We hypothesized that rTMS adjunctive to antipsychotics will be safe and effective in treatment of FRS in schizophrenia.

METHODS

Schizophrenia patients with FRS randomly received either active or sham-magnetic resonance imaging navigated continuous Θ burst stimulation (cTBS)-rTMS to right inferior parietal lobule for 2 weeks; assessments were repeated. While primary outcome variables were safety profile, FRS and overall psychopathology; secondary outcomes were γ oscillatory activity, brain-derived neurotrophic factor levels, and self-monitoring function.

RESULTS

No significant adverse events were reported in either group. None of the outcome measures showed sufficient power on the time by group analysis.

CONCLUSIONS

This study fails to demonstrate whether or not adjunctive cTBS to right inferior parietal lobule could significantly alleviate FRS. We also fail to provide evidence for whether this protocol has any effect on brain-derived neurotrophic factor levels, self-monitoring function, and right hemispheric γ oscillations.

Hyper-coherence and increased energy of gamma oscillations in patient with first onset schizophrenia and cerebral white matter damage

Background: According to current knowledge, gamma frequency is closely related to the functioning of neural networks underlying the basic activity of the brain and mind. Disorders in mechanisms synchronizing brain activity observed in patients diagnosed with schizophrenia are at the roots of neurocognitive disorders and psychopathological symptoms of the disease. Synchronization mechanisms are also related to the structure and functional effectiveness of the white matter. So far, not many analysis has been conducted concerning changes in the image of high frequency in patients with comorbid schizophrenia and white matter damage. The aim of this research was to present specific features of gamma waves in subjects with different psychiatric diagnoses and condition of brain structure.

Methods: Quantitative analysis of an EEG record registered from a patient diagnosed with schizophrenia and comorbid white matter hyperintensities (SCH+WM), a patient with an identical diagnosis but without structural brain changes present in the MRI (SCH-WM) of a healthy control (HC). The range of gamma waves has been obtained by using analogue filters. In order to obtain precise analysis, gamma frequencies have been divided into three bands: 30-50Hz, 50-70Hz, 70-100Hz. Matching Pursuit algorithm has been used for signal analysis enabling assessing the changes in signal energy. Synchronization effectiveness of particular areas of the brain was measured with the aid of coherence value for selected pairs of electrodes.

Results: The electrophysiological signals recorded for the SCH+WM patient showed the highest signal energy level identified for all the analyzed bands compared to the results obtained for the same pairs of electrodes of the other subjects. Coherence results revealed hipercompensation for the SCH+WM patient and her level differed substantially compared to the results of the other subjects.

Conclusions: The coexistence of schizophrenia with white matter damage can significantly disturb parameters of neural activity with high frequencies. The paper discusses possible explanations for the obtained results.

Increased BOLD Signals Elicited by High Gamma Auditory Stimulation of the Left Auditory Cortex in Acute State Schizophrenia

Recent MRI studies have shown that schizophrenia is characterized by reductions in brain gray matter, which progress in the acute state of the disease. Cortical circuitry abnormalities in gamma oscillations, such as deficits in the auditory steady state response (ASSR) to gamma frequency (> 30-Hz) stimulation, have also been reported in schizophrenia patients. In the current study, we investigated neural responses during click stimulation by BOLD signals.

We acquired BOLD responses elicited by click trains of 20, 30, 40 and 80-Hz frequencies from 15 patients with acute episode schizophrenia (AESZ), 14 symptom-severity-matched patients with non-acute episode schizophrenia (NASZ), and 24 healthy controls (HC), assessed via a standard general linear-model-based analysis. The AESZ group showed significantly increased ASSR-BOLD signals to 80-Hz stimuli in the left auditory cortex compared with the HC and NASZ groups. In addition, enhanced 80-Hz ASSR-BOLD signals were associated with more severe auditory hallucination experiences in AESZ participants. The present results indicate that neural over activation occurs during 80-Hz auditory stimulation of the left auditory cortex in individuals with acute state schizophrenia. Given the possible association between abnormal gamma activity and increased glutamate levels, our data may reflect glutamate toxicity in the auditory cortex in the acute state of schizophrenia, which might lead to progressive changes in the left transverse temporal gyrus.

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We investigated neural responses during click stimulation by BOLD signals.

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We evaluated patients with acute and non-acute schizophrenia, and healthy controls.

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80-Hz auditory stimulation activated the left auditory cortex in acute schizophrenia.

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Our data may reflect left auditory cortex glutamate toxicity in acute schizophrenia.

Recent MRI studies show that schizophrenia is characterized by reduced brain gray matter, which deteriorates in the acute state of the disease. Periodic auditory click trains elicit auditory steady-state responses (ASSRs), and ASSR abnormalities are reported in schizophrenia. We investigated neural responses during click stimulation using BOLD signals, which may reflect glutamate toxicity. Compared with non-acute schizophrenia patients and healthy controls, acute episode schizophrenia patients showed significantly increased ASSR-BOLD to 80-Hz stimuli in the left auditory cortex. Our data demonstrate neuronal over activation in terms of the BOLD pattern in acute state schizophrenia, which might reflect progressive volume reduction in the left superior temporal cortex by glutamate toxicity during the acute phase of schizophrenia.

Schneiderian first rank symptoms in schizophrenia: A developmental neuroscience evaluation

INTRODUCTION

Self disorders in schizophrenia have been suggested to have distinct neurobiological underpinnings. Using comprehensive neuro-scientific assessments including a neurophysiological, a neurochemical and a neuropsychological marker, this study assesses disordered-"self" in schizophrenia.

METHODS

Twenty schizophrenia patients with first rank symptoms (FRS;FRS+), 20 patients without FRS (FRS-) and 20 healthy controls (HC) were assessed for psychopathology, especially on specially designed FRS score sheets with a narrow and a broad definition. Resting state electroencephalography was acquired using 256-electrodes; gamma spectral-power was measured in 8 regions of interest. Serum BDNF and self-monitoring were also assessed. Comparative and correlation analysis were conducted in addition to a step-wise discriminant function analysis.

RESULTS

FRS+ group with greater positive symptom score and a lower negative symptom score, showed significantly increased gamma spectral power, especially on right hemispheric regions, along with lower BDNF levels and lower scores on self-monitoring compared to FRS- and HC. Serum BDNF levels and gamma spectral power in the region corresponding right inferior parietal lobule were identified as predictors that most accurately classified the defined groups.

CONCLUSIONS

Schizophrenia patients satisfying the criteria of presence of first rank symptoms represent a distinct neurodevelopmental subgroup with associated features of predominantly positive symptoms, significantly lower neurotrophin levels, aberrant resting state brain activity in the heteromodal association cortex and performing poorer on self-monitoring tasks.