Intra-Regional Glu-GABA vs Inter-Regional Glu-Glu Imbalance: A 1H-MRS Study of the Neurochemistry of Auditory Verbal Hallucinations in Schizophrenia

Electroacupuncture inhibited carrageenan-induced pain aversion by activating GABAergic neurons in the ACC

Pain aversion is an avoidance response to painful stimuli. Previous research has indicated that the anterior cingulate cortex (ACC) is involved in pain aversion processing. However, as interneurons, the role of GABAergic neurons in the ACC (GABAACC neurons) in pain aversion is still unclear. Electroacupuncture (EA) has been shown to ameliorate pain aversion, but the mechanism is not clarified. The present study provided evidence that inhibition of GABAACC neurons contributed to pain aversion. EA alleviated pain aversion by activating GABAACC neurons in an intensity-dependent manner. Specifically, 0.3 mA EA stimulation showed better effects on pain aversion than 0.1 mA stimulation, which could be reversed by chemical genetic inhibition of GABAACC neurons. These results provide a novel mechanism by which EA alleviates pain aversion by reversing GABAACC neurons.

Comparative study about the therapeutic effect of cTBS and rTMS in the treatment of auditory verbal hallucinations in schizophrenia

OBJECTIVE

This study aims to compare the therapeutic effects of repetitive transcranial magnetic stimulation (rTMS) and continuous theta-burst stimulation (cTBS) treatment in schizophrenia patients with auditory verbal hallucinations (AVHs).

METHODS

We enrolled 64 schizophrenia patients with AVHs who were treated with either rTMS (n = 32) or cTBS (n = 32), and we compared the clinical outcomes by evaluating parameters from motor evoked potentials, Positive and Negative Syndrome Scale (PANSS), Auditory Hallucination Rating Scale (AHRS), and MATRICS Consensus Cognitive Battery (MCCB), as well as the changes of serum neurotrophic factors before and after the treatment.

RESULTS

After the treatment, both treatments resulted in reduced PANSS scores, with the cTBS group showing more substantial symptom improvement across positive, negative, and general symptoms, highlighting the enhanced efficacy of cTBS. Cognitive functions assessed by MCCB also improved in both groups, with cTBS showing a generally higher therapeutic effect. Serum levels of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) increased following treatment in both groups, with a more notable increase after cTBS, while GABA and glutamate levels remained unchanged. Cardiovascular indices were unaffected by either treatment, suggesting no significant impact on cardiovascular health.

CONCLUSIONS

Our study found that both rTMS and cTBS treatment can exhibit therapeutic effects in the management of AVHs in patients with schizophrenia. However, cTBS treatment generally shows a higher therapeutic effect than rTMS treatment.

Estradiol driven change in hallucination proneness across the menstrual cycle as studied with a white noise paradigm

The estrogen hypothesis for schizophrenia suggests neuroprotective effects of estrogen for the development of the disorder and for symptom severity, including auditory hallucinations. Furthermore, estrogen has shown enhancing effects on cognitive control, a function that is also implicated in auditory hallucinations. Whether estrogen affects the tendency to hallucinate in healthy participants, and the potential mediating role of cognitive control, has not yet been studied. Therefore, the current study aimed to test these relationships by using a white noise paradigm in combination with a N-back working memory task in which cognitive load could be manipulated. The paradigm used simulates a hallucinatory state by induction of negative emotions and drainage of cognitive resources. The simultaneous exposure to white noise elicit experiences of hearing voices (false alarms). In a between-subject design, forty-two participants were tested during the menstrual cycle in either the early follicular phase (low estradiol) or late follicular phase (high estradiol). A 2(Cycle Phase) x2(N-back task) ANOVA showed a main-effect of cycle phase on number of experienced hallucinations in the white noise task, with a significantly higher number of reported hallucinations in the early follicular phase. Furthermore, estradiol was found to predict number of hallucinations. No interaction effect of cycle phase and available cognitive resources was found. The results suggest an estradiol-related change in hallucination proneness across the menstrual cycle, but the idea that cognitive functioning mediates this relationship was not supported. Overall, the study supports protective effects of estradiol on hallucination proneness in line with the estrogen-hypothesis of schizophrenia, and that such effects are not specific to the disease.

Meta-analysis and open-source database for in vivo brain Magnetic Resonance spectroscopy in health and disease

Proton (1H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo. Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Meta-analysis and Open-source Database for In Vivo Brain Magnetic Resonance Spectroscopy in Health and Disease

Proton ( 1 H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo . Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T 2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Spatial Distribution of Inhibitory Innervations of Excitatory Pyramidal Cells by Major Interneuron Subtypes in the Auditory Cortex

Mental disorders, characterized by the National Institute of Mental Health as disruptions in neural circuitry, currently account for 13% of the global incidence of such disorders. An increasing number of studies suggest that imbalances between excitatory and inhibitory neurons in neural networks may be a crucial mechanism underlying mental disorders. However, the spatial distribution of inhibitory interneurons in the auditory cortex (ACx) and their relationship with excitatory pyramidal cells (PCs) remain elusive. In this study, we employed a combination of optogenetics, transgenic mice, and patch-clamp recording on brain slices to investigate the microcircuit characteristics of different interneurons (PV, SOM, and VIP) and the spatial pattern of inhibitory inhibition across layers 2/3 to 6 in the ACx. Our findings revealed that PV interneurons provide the strongest and most localized inhibition with no cross-layer innervation or layer specificity. Conversely, SOM and VIP interneurons weakly regulate PC activity over a broader range, exhibiting distinct spatial inhibitory preferences. Specifically, SOM inhibitions are preferentially found in deep infragranular layers, while VIP inhibitions predominantly occur in upper supragranular layers. PV inhibitions are evenly distributed across all layers. These results suggest that the input from inhibitory interneurons to PCs manifests in unique ways, ensuring that both strong and weak inhibitory inputs are evenly dispersed throughout the ACx, thereby maintaining a dynamic excitation-inhibition balance. Our findings contribute to understanding the spatial inhibitory characteristics of PCs and inhibitory interneurons in the ACx at the circuit level, which holds significant clinical implications for identifying and targeting abnormal circuits in auditory system diseases.

Medial Frontal Cortex GABA Concentrations in Psychosis Spectrum and Mood Disorders: A Meta-analysis of Proton Magnetic Resonance Spectroscopy Studies

BACKGROUND

Abnormalities of GABAergic (gamma-aminobutyric acidergic) systems may play a role in schizophrenia and mood disorders. Magnetic resonance spectroscopy allows for noninvasive in vivo quantification of GABA; however, studies of GABA in schizophrenia have yielded inconsistent findings. This may stem from grouping together disparate voxels from functionally heterogeneous regions.

METHODS

We searched PubMed for magnetic resonance spectroscopy studies of GABA in the medial frontal cortex (MFC) in patients with schizophrenia, bipolar disorder, and depression and in individuals meeting criteria for ultra-high risk for psychosis. Voxel placements were classified as rostral-, rostral-mid-, mid-, or posterior MFC, and meta-analyses were conducted for each group for each subregion.

RESULTS

Of 341 screened articles, 23 studies of schizophrenia, 6 studies of bipolar disorder, 20 studies of depression, and 7 studies of ultra-high risk met the inclusion criteria. Meta-analysis revealed lower mid- (standardized mean difference [SMD] = -0.28, 95% CI, -0.48 to -0.07, p < .01) and posterior (SMD = -0.29, 95% CI, -0.49 to -0.09, p < .01) MFC GABA in schizophrenia and increased rostral MFC GABA in bipolar disorder (SMD = 0.76, 95% CI, 0.25 to -1.25, p < .01). In depression, reduced rostral MFC GABA (SMD = -0.36, 95% CI, -0.64 to -0.08, p = .01) did not survive correction for multiple comparisons. We found no evidence for GABA differences in individuals at ultra-high risk for psychosis.

CONCLUSIONS

While limited by small numbers of published studies, these results substantiate the relevance of GABA in the pathophysiology of psychosis spectrum and mood disorders and underline the importance of voxel placement.

Language abnormalities in schizophrenia: binding core symptoms through contemporary empirical evidence

Both the ability to speak and to infer complex linguistic messages from sounds have been claimed as uniquely human phenomena. In schizophrenia, formal thought disorder (FTD) and auditory verbal hallucinations (AVHs) are manifestations respectively relating to concrete disruptions of those abilities. From an evolutionary perspective, Crow (1997) proposed that "schizophrenia is the price that Homo sapiens pays for the faculty of language". Epidemiological and experimental evidence points to an overlap between FTD and AVHs, yet a thorough investigation examining their shared neural mechanism in schizophrenia is lacking. In this review, we synthesize observations from three key domains. First, neuroanatomical evidence indicates substantial shared abnormalities in language-processing regions between FTD and AVHs, even in the early phases of schizophrenia. Second, neurochemical studies point to a glutamate-related dysfunction in these language-processing brain regions, contributing to verbal production deficits. Third, genetic findings further show how genes that overlap between schizophrenia and language disorders influence neurodevelopment and neurotransmission. We argue that these observations converge into the possibility that a glutamatergic dysfunction in language-processing brain regions might be a shared neural basis of both FTD and AVHs. Investigations of language pathology in schizophrenia could facilitate the development of diagnostic tools and treatments, so we call for multilevel confirmatory analyses focused on modulations of the language network as a therapeutic goal in schizophrenia.

Relating Glutamate, Conditioned, and Clinical Hallucinations via 1H-MR Spectroscopy

BACKGROUND AND HYPOTHESIS

Hallucinations may be driven by an excessive influence of prior expectations on current experience. Initial work has supported that contention and implicated the anterior insula in the weighting of prior beliefs.

STUDY DESIGN

Here we induce hallucinated tones by associating tones with the presentation of a visual cue. We find that people with schizophrenia who hear voices are more prone to the effect and using computational modeling we show they overweight their prior beliefs. In the same participants, we also measured glutamate levels in anterior insula, anterior cingulate, dorsolateral prefrontal, and auditory cortices, using magnetic resonance spectroscopy.

STUDY RESULTS

We found a negative relationship between prior-overweighting and glutamate levels in the insula that was not present for any of the other voxels or parameters.

CONCLUSIONS

Through computational psychiatry, we bridge a pathophysiological theory of psychosis (glutamate hypofunction) with a cognitive model of hallucinations (prior-overweighting) with implications for the development of new treatments for hallucinations.

Altered Coupling of Cerebral Blood Flow and Functional Connectivity Strength in First-Episode Schizophrenia Patients With Auditory Verbal Hallucinations

Objective

Auditory verbal hallucinations (AVHs) are a major symptom of schizophrenia and are connected with impairments in auditory and speech-related networks. In schizophrenia with AVHs, alterations in resting-state cerebral blood flow (CBF) and functional connectivity have been described. However, the neurovascular coupling alterations specific to first-episode drug-naïve schizophrenia (FES) patients with AVHs remain unknown.

Methods

Resting-state functional MRI and arterial spin labeling (ASL) was performed on 46 first-episode drug-naïve schizophrenia (FES) patients with AVHs (AVH), 39 FES drug-naïve schizophrenia patients without AVHs (NAVH), and 48 healthy controls (HC). Then we compared the correlation between the CBF and functional connection strength (FCS) of the entire gray matter between the three groups, as well as the CBF/FCS ratio of each voxel. Correlation analyses were performed on significant results between schizophrenia patients and clinical measures scale.

Results

The CBF/FCS ratio was reduced in the cognitive and emotional brain regions in both the AVH and NAVH groups, primarily in the crus I/II, vermis VI/VII, and cerebellum VI. In the AVH group compared with the HC group, the CBF/FCS ratio was higher in auditory perception and language-processing areas, primarily the left superior and middle temporal gyrus (STG/MTG). The CBF/FCS ratio in the left STG and left MTG positively correlates with the score of the Auditory Hallucination Rating Scale in AVH patients.

Conclusion

These findings point to the difference in neurovascular coupling failure between AVH and NAVH patients. The dysfunction of the forward model based on the predictive and computing role of the cerebellum may increase the excitability in the auditory cortex, which may help to understand the neuropathological mechanism of AVHs.

Deficits in Sense of Body Ownership, Sensory Processing, and Temporal Perception in Schizophrenia Patients With/Without Auditory Verbal Hallucinations

It has been claimed that individuals with schizophrenia have difficulty in self-recognition and, consequently, are unable to identify the sources of their sensory perceptions or thoughts, resulting in delusions, hallucinations, and unusual experiences of body ownership. The deficits also contribute to the enhanced rubber hand illusion (RHI; a body perception illusion, induced by synchronous visual and tactile stimulation). Evidence based on RHI paradigms is emerging that auditory information can make an impact on the sense of body ownership, which relies on the process of multisensory inputs and integration. Hence, we assumed that auditory verbal hallucinations (AVHs), as an abnormal auditory perception, could be linked with body ownership, and the RHI paradigm could be conducted in patients with AVHs to explore the underlying mechanisms. In this study, we investigated the performance of patients with/without AVHs in the RHI. We administered the RHI paradigm to 80 patients with schizophrenia (47 with AVHs and 33 without AVHs) and 36 healthy controls. We conducted the experiment under two conditions (synchronous and asynchronous) and evaluated the RHI effects by both objective and subjective measures. Both patient groups experienced the RHI more quickly and strongly than HCs. The RHI effects of patients with AVHs were significantly smaller than those of patients without AVHs. Another important finding was that patients with AVHs did not show a reduction in RHI under asynchronous conditions. These results emphasize the disturbances of the sense of body ownership in schizophrenia patients with/without AVHs and the associations with AVHs. Furthermore, it is suggested that patients with AVHs may have multisensory processing dysfunctions and internal timing deficits.

Negative valence of hallucinatory voices as predictor of cortical glutamatergic metabolite levels in schizophrenia patients

OBJECTIVES

Negative emotional valence of auditory verbal hallucinations (AVHs) in schizophrenia can be a source of distress and is considered a strong predictor of illness severity. Previous studies have found glutamate to mediate AVH severity in frontal and temporal brain regions, however, they do not specifically address emotional valence of AVH. The role of glutamate for the experience of negative- versus positive emotional valence of AVH is therefore unknown and was investigated in the current study.

METHODS

Using magnetic resonance spectroscopy (MRS), 37 schizophrenia patients had Glx (glutamate+glutamine) measured in the left superior temporal gyrus (STG), and additionally in the anterior cingulate cortex (ACC) and the right STG, or in the left inferior frontal gyrus (IFG). Self-reported emotional valence in AVH was measured with the Beliefs About Voices Questionnaire (BAVQ-R).

RESULTS

Results from linear mixed models showed that negative emotional valence was associated with reduced Glx levels across all four measured brain regions in the frontal and temporal lobe. More specifically, voices that were experienced to be omnipotent (p = 0.04) and that the patients attempted to resist (p = 0.04) were related to lower Glx levels. Follow-up analysis of the latter showed that voices that evoked emotional resistance (i.e., fear, sadness, anger), rather than behavioral resistance, was a significant predictor of reduced glutamate (p = 0.02).

CONCLUSION

The findings could indicate aberrant glutamatergic signaling, or increased NMDA-receptor hypoactivity in patients who experience their voices to be more emotionally negative. Overall, the study provides support for the glutamate hypothesis of schizophrenia.

MR-Spectroscopy of GABA and Glutamate/Glutamine Concentrations in Auditory Cortex in Clinical High-Risk for Psychosis Individuals

Psychosis involves changes in GABAergic and glutamatergic neurotransmission in auditory cortex that could be important for understanding sensory deficits and symptoms of psychosis. However, it is currently unclear whether such deficits are present in participants at clinical high-risk for psychosis (CHR-P) and whether they are associated with clinical outcomes. Magnetic Resonance Spectroscopy (MEGAPRESS, 1H-MRS at 3 Tesla) was used to estimate GABA, glutamate, and glutamate-plus-glutamine (Glx) levels in auditory cortex in a large sample of CHR-P (n = 99), CHR-N (clinical high-risk negative, n = 32), and 45 healthy controls. Examined were group differences in metabolite concentrations as well as relationships with clinical symptoms, general cognition, and 1-year follow-up clinical and general functioning in the CHR-P group. Results showed a marginal (p = 0.039) main group effect only for Glx, but not for GABA and glutamate concentrations, and only in left, not right, auditory cortex. This effect did not survive multiple comparison correction, however. Exploratory post-hoc tests revealed that there were significantly lower Glx levels (p = 0.029, uncorrected) in the CHR-P compared to the CHR-N group, but not relative to healthy controls (p = 0.058, uncorrected). Glx levels correlated with the severity of perceptual abnormalities and disorganized speech scores. However, in the CHR-P group, Glx levels did not predict clinical or functional outcomes. Accordingly, the findings from the present study suggest that MRS-measured GABA, glutamate and Glx levels in auditory cortex of CHR-P individuals are largely intact.

Glutamatergic and GABAergic metabolite levels in schizophrenia-spectrum disorders: a meta-analysis of 1H-magnetic resonance spectroscopy studies

BACKGROUND

The glutamate (Glu) and gamma aminobutyric acid (GABA) hypotheses of schizophrenia were proposed in the 1980s. However, current findings on those metabolite levels in schizophrenia have been inconsistent, and the relationship between their abnormalities and the pathophysiology of schizophrenia remains unclear. To summarize the nature of the alterations of glutamatergic and GABAergic systems in schizophrenia, we conducted meta-analyses of proton magnetic resonance spectroscopy (¹H-MRS) studies examining these metabolite levels.

METHODS

A systematic literature search was conducted using Embase, Medline, PsycINFO, and PubMed. Original studies that compared four metabolite levels (Glu, glutamine [Gln], Glx [Glu+Gln], and GABA), as measured by ¹H-MRS, between individuals at high risk for psychosis, patients with first-episode psychosis, or patients with schizophrenia and healthy controls (HC) were included. A random-effects model was used to calculate the effect sizes for group differences in these metabolite levels of 18 regions of interest between the whole group or schizophrenia group and HC. Subgroup analysis and meta-regression were performed based on the status of antipsychotic treatment, illness stage, treatment resistance, and magnetic field strength.

RESULTS

One-hundred-thirty-four studies met the eligibility criteria, totaling 7993 participants with SZ-spectrum disorders and 8744 HC. 14 out of 18 ROIs had enough numbers of studies to examine the group difference in the metabolite levels. In the whole group, Glx levels in the basal ganglia (g = 0.32; 95% CIs: 0.18-0.45) were elevated. Subgroup analyses showed elevated Glx levels in the hippocampus (g = 0.47; 95% CIs: 0.21-0.73) and dorsolateral prefrontal cortex (g = 0.25; 95% CIs: 0.05-0.44) in unmedicated patients than HC. GABA levels in the MCC were decreased in the first-episode psychosis group compared with HC (g = -0.40; 95% CIs: -0.62 to -0.17). Treatment-resistant schizophrenia (TRS) group had elevated Glx and Glu levels in the MCC (Glx: g = 0.7; 95% CIs: 0.38-1.01; Glu: g = 0.63; 95% CIs: 0.31-0.94) while MCC Glu levels were decreased in the patient group except TRS (g = -0.17; 95% CIs: -0.33 to -0.01).

CONCLUSIONS

Increased glutamatergic metabolite levels and reduced GABA levels indicate that the disruption of excitatory/inhibitory balance may be related to the pathophysiology of schizophrenia-spectrum disorders.

Quantifying the excitatory-inhibitory balance: A comparison of SemiLASER and MEGA-SemiLASER for simultaneously measuring GABA and glutamate at 7T

The importance of the excitatory-inhibitory (E/I) balance in a wide range of cognitive and behavioral processes has prompted a commensurate interest in methods for reliably quantifying it. Proton Magnetic Resonance Spectroscopy (¹H-MRS) remains the only method capable of safely and non-invasively measuring the concentrations of the brain's major excitatory (glutamate) and inhibitory (γ-aminobutyric-acid, GABA) neurotransmitters in-vivo. MRS relies on spectral Mescher-Garwood (MEGA) editing techniques at 3T to distinguish GABA from its overlapping resonances. However, with the increased spectral resolution at ultrahigh field strengths of 7T and above, non-edited spectroscopic techniques become potential viable alternatives to MEGA based approaches, and also address some of their shortcomings, such as signal loss, sensitivity to transmitter inhomogeneities and temporal resolution. We present a comprehensive comparison of both edited and non-edited strategies at 7T for simultaneously quantifying glutamate and GABA from the dorsal anterior cingulate cortex (dACC), and evaluate their reproducibility and relative bias. The combined root-mean-square test-retest reproducibility of Glu and GABA (CV_E/I) was as low as 13.3% for unedited MRS at TE=80 ms using SemiLASER localization, while edited MRS at TE=80 ms yielded CV_E/I=20% and 21% for asymmetric and symmetric MEGA editing, respectively. An unedited SemiLASER acquisition using a shorter echo time of TE=42 ms yielded CV_E/I as low as 24.9%. Our results show that non-edited sequences at an echo time of 80 ms provide better reproducibility than either edited sequences at the same TE, or non-edited sequences at a shorter TE of 42 ms. This is supported by numerical simulations and is driven in part by a pseudo-singlet appearance of the GABA multiplets at TE=80 ms, and the excellent spectral resolution at 7T. Our results uphold a transition to non-edited MRS for monitoring the E/I balance at ultrahigh fields, and stress the importance of using a properly-optimized echo time.

The Etiology of Auditory Hallucinations in Schizophrenia: From Multidimensional Levels

Enormous efforts have been made to unveil the etiology of auditory hallucinations (AHs), and multiple genetic and neural factors have already been shown to have their own roles. Previous studies have shown that AHs in schizophrenia vary from those in other disorders, suggesting that they have unique features and possibly distinguishable mechanisms worthy of further investigation. In this review, we intend to offer a comprehensive summary of current findings related to AHs in schizophrenia from aspects of genetics and transcriptome, neurophysiology (neurometabolic and electroencephalogram studies), and neuroimaging (structural and functional magnetic resonance imaging studies and transcriptome–neuroimaging association study). Main findings include gene polymorphisms, glutamate level change, electroencephalographic alterations, and abnormalities of white matter fasciculi, cortical structure, and cerebral activities, especially in multiple regions, including auditory and language networks. More solid and comparable research is needed to replicate and integrate ongoing findings from multidimensional levels.

Frontal neural metabolite changes in schizophrenia and their association with cognitive control: A systematic review

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GABA levels are decreased in medial frontal brain areas of schizophrenia patients.

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Glutamate levels are lower in medial and lateral frontal areas in chronic patients.

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Working memory performance is associated with frontal GABA and Glu.

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Prediction errors are associated Glu and medial frontal GABA.

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Processing speed correlates with medial frontal GABA levels.

A large proportion of patients with schizophrenia exhibit deficits in cognitive control functions including working memory, processing speed and inhibitory control, which have been associated with frontal brain areas. In this systematic review, we investigated differences between chronic schizophrenia patients, first-episode (FEP) patients and healthy control groups in the neurometabolite levels of GABA, glutamate, glutamine and Glx in frontal brain areas. Additionally, we reviewed correlations between cognitive control functions or negative symptoms and these neurometabolite levels. Several studies reported decreased GABA or glutamate concentrations in frontal lobe areas, particularly in chronic schizophrenia patients, while the results were mixed for FEP patients. Working memory performance and prediction errors have been associated with frontal GABA and glutamate levels, and processing speed with frontomedial GABA levels in chronic patients. The relationship between metabolites and negative symptom severity was somewhat inconsistent. Future studies should take the participants' age, medication status or responsivity, disease stage and precise anatomical location of the voxel into account when comparing neurometabolite levels between schizophrenia patients and healthy controls.

Reduced GABAergic neuropil and interneuron profiles in schizophrenia: Complementary analysis of disease course-related differences

BACKGROUND

GABAergic interneuron dysfunction has been implicated in the pathophysiology of schizophrenia. Expression of glutamic acid decarboxylase (GAD), a key enzyme in GABA synthesis, may also be altered. Here, we have simultaneously evaluated GAD-immunoreactive (GAD-ir) neuropil and cell profiles in schizophrenia-relevant brain regions, and analysed disease-course related differences.

METHODS

GAD65/67 immunoreactivity was quantified in specific brain regions for profiles of fibres and cell bodies of interneurons by automated digital image analysis in post-mortem brains of 16 schizophrenia patients from paranoid (n = 10) and residual (n = 6) diagnostic subgroups and 16 matched controls. Regions of interest were superior temporal gyrus (STG) layers III and V, mediodorsal (MD) and laterodorsal (LD) thalamus, and hippocampal CA1 and dentate gyrus (DG) regions.

RESULTS

A reduction in GAD-ir neuropil profiles (p < 0.001), particularly in STG layer V (p = 0.012) and MD (p = 0.001), paralleled decreased GAD-ir cell profiles (p = 0.029) in schizophrenia patients compared to controls. Paranoid schizophrenia patients had lower GAD-ir neuron cell profiles in STG layers III (p = 0.007) and V (p = 0.001), MD (p = 0.002), CA1 (p = 0.001) and DG (p = 0.043) than residual patients. There was no difference in GAD-ir neuropil profiles between paranoid and residual subgroups (p = 0.369).

CONCLUSIONS

These results support the hypothesis of GABAergic dysfunction in schizophrenia. They show a more prominent reduction of GAD-ir interneurons in paranoid versus residual patients, suggestive of more pronounced GABAergic dysfunction in the former. Fully automated analyses of histological sections represent a step towards user-independent assessment of brain structure.

Medial Prefrontal Cortex Glutamate Is Reduced in Schizophrenia and Moderated by Measurement Quality: A Meta-analysis of Proton Magnetic Resonance Spectroscopy Studies

BACKGROUND

Magnetic resonance spectroscopy studies measuring brain glutamate separately from glutamine are helping elucidate schizophrenia pathophysiology. An expanded literature and improved methodologies motivate an updated meta-analysis examining effects of measurement quality and other moderating factors in characterizing abnormal glutamate levels in schizophrenia.

METHODS

Searching previous meta-analyses and the MEDLINE database identified 83 proton magnetic resonance spectroscopy datasets published through March 25, 2020. Three quality metrics were extracted-Cramér-Rao lower bound (CRLB), line width, and coefficient of variation. Pooled effect sizes (Hedges' g) were calculated with random-effects, inverse variance-weighted models. Moderator analyses were conducted using quality metrics, field strength, echo time, medication, age, and stage of illness.

RESULTS

Across 36 datasets (2086 participants), medial prefrontal cortex glutamate was significantly reduced in patients (g = -0.19, confidence interval [CI] = -0.07 to -0.32). CRLB and coefficient of variation quality subgroups significantly moderated this effect. Glutamate was significantly more reduced in studies with lower CRLB or coefficient of variation (g = -0.44, CI = -0.29 to -0.60, and g = -0.43, CI = -0.29 to -0.57, respectively). Studies using echo time ≤20 ms also showed significantly greater reduction in glutamate (g = -0.41, CI = -0.26 to -0.55). Across 11 hippocampal datasets, group differences and moderator effects were nonsignificant. Group effects in thalamus and dorsolateral prefrontal cortex were also nonsignificant.

CONCLUSIONS

High-quality measurements reveal consistently reduced medial prefrontal cortex glutamate in schizophrenia. Stricter CRLB criteria and reduced nuisance variance may increase the sensitivity of future studies examining additional regions and the pathophysiological significance of abnormal glutamate levels in schizophrenia.

Glutamate- and GABA-Modulated Connectivity in Auditory Hallucinations-A Combined Resting State fMRI and MR Spectroscopy Study

Background: Auditory verbal hallucinations (AVH) have been linked to aberrant interhemispheric connectivity between the left and the right superior temporal gyrus (STG), labeled the interhemispheric miscommunication theory. The present study investigated if interhemispheric miscommunication is modulated at the neurochemical level by glutamate (Glu) and gamma-aminobutyric acid (GABA) concentrations in temporal and prefrontal lobe areas, as proposed by the theory. Methods: We combined resting-state fMRI connectivity with MR spectroscopy (MRS) in a sample of 81 psychosis patients, comparing patients with high hallucination severity (high-AVH) and low hallucination severity (low-AVH) groups. Glu and GABA concentrations were acquired from the left STG and the anterior cingulate cortex (ACC), an area of cognitive control that has been proposed to modulate STG functioning in AVH. Results: Functional connectivity showed significant interaction effects between AVH Group and ACC-recorded Glu and GABA metabolites. Follow-up tests showed that there was a significant positive association for Glu concentration and interhemispheric STG connectivity in the high-AVH group, while there was a significant negative association for GABA concentration and interhemispheric STG connectivity in the low-AVH group. Conclusion: The results show neurochemical modulation of STG interhemispheric connectivity, as predicted by the interhemispheric miscommunication hypothesis. Furthermore, the findings are in line with an excitatory/inhibitory imbalance model for AVH. By combining different neuroimaging modalities, the current results provide a more comprehensive insight into the neural correlates of AVH.

Glutamatergic modulation of auditory cortex connectivity with attentional brain networks in unpredictable perceptual environment

In a stable environment the brain can minimize processing required for sensory input by forming a predictive model of the surrounding world and suppressing neural response to predicted stimuli. Unpredicted stimuli lead to a prediction error signal propagation through the perceptual network, and resulting adjustment to the predictive model. The inter-regional plasticity which enables the model-building and model-adjustment is hypothesized to be mediated via glutamatergic receptors. While pharmacological challenge studies with glutamate receptor ligands have demonstrated impact on prediction-error indices, it is not clear how inter-individual differences in the glutamate system affect the prediction-error processing in non-medicated state. In the present study we examined 20 healthy young subjects with resting-state proton MRS spectroscopy to characterize glutamate + glutamine (rs-Glx) levels in their Heschl’s gyrus (HG), and related this to HG functional connectivity during a roving auditory oddball protocol. No rs-Glx effects were found within the frontotemporal prediction-error network. Larger rs-Glx signal was related to stronger connectivity between HG and bilateral inferior parietal lobule during unpredictable auditory stimulation. We also found effects of rs-Glx on the coherence of default mode network and frontoparietal network during unpredictable auditory stimulation. Our results demonstrate the importance of Glx in modulating long-range connections and wider networks in the brain during perceptual inference.

Local and Interregional Neurochemical Associations Measured by Magnetic Resonance Spectroscopy for Studying Brain Functions and Psychiatric Disorders

Magnetic resonance spectroscopy (MRS) studies have found significant correlations among neurometabolites (e.g., between glutamate and GABA) across individual subjects and altered correlations in neuropsychiatric disorders. In this article, we discuss neurochemical associations among several major neurometabolites which underpin these observations by MRS. We also illustrate the role of spectral editing in eliminating unwanted correlations caused by spectral overlapping. Finally, we describe the prospects of mapping macroscopic neurochemical associations across the brain and characterizing excitation-inhibition balance of neural networks using glutamate- and GABA-editing MRS imaging.