Hippocampal glutamate concentration predicts cerebral theta oscillations during cognitive processing

Laying the foundations for a theory of consciousness: the significance of critical brain dynamics for the formation of conscious states

Empirical evidence indicates that conscious states, distinguished by the presence of phenomenal qualities, are closely linked to synchronized neural activity patterns whose dynamical characteristics can be attributed to self-organized criticality and phase transitions. These findings imply that insight into the mechanism by which the brain controls phase transitions will provide a deeper understanding of the fundamental mechanism by which the brain manages to transcend the threshold of consciousness. This article aims to show that the initiation of phase transitions and the formation of synchronized activity patterns is due to the coupling of the brain to the zero-point field (ZPF), which plays a central role in quantum electrodynamics (QED). The ZPF stands for the presence of ubiquitous vacuum fluctuations of the electromagnetic field, represented by a spectrum of normal modes. With reference to QED-based model calculations, the details of the coupling mechanism are revealed, suggesting that critical brain dynamics is governed by the resonant interaction of the ZPF with the most abundant neurotransmitter glutamate. The pyramidal neurons in the cortical microcolumns turn out to be ideally suited to control this interaction. A direct consequence of resonant glutamate-ZPF coupling is the amplification of specific ZPF modes, which leads us to conclude that the ZPF is the key to the understanding of consciousness and that the distinctive feature of neurophysiological processes associated with conscious experience consists in modulating the ZPF. Postulating that the ZPF is an inherently sentient field and assuming that the spectrum of phenomenal qualities is represented by the normal modes of the ZPF, the significance of resonant glutamate-ZPF interaction for the formation of conscious states becomes apparent in that the amplification of specific ZPF modes is inextricably linked with the excitation of specific phenomenal qualities. This theory of consciousness, according to which phenomenal states arise through resonant amplification of zero-point modes, is given the acronym TRAZE. An experimental setup is specified that can be used to test a corollary of the theory, namely, the prediction that normally occurring conscious perceptions are absent under experimental conditions in which resonant glutamate-ZPF coupling is disrupted.

Glucose-oxygen coupling can serve as a biomarker for neuroinflammation-related genetic variants

The single-nucleotide polymorphism rs3197999 in the macrophage-stimulating protein 1 gene is a missense variant. Studies have indicated that macrophage-stimulating protein 1 mediates neuronal loss and synaptic plasticity damage, and overexpression of the macrophage-stimulating protein 1 gene leads to the excessive activation of microglial cells, thereby resulting in an elevation of cerebral glucose metabolism. Traditional diagnostic models may be disrupted by neuroinflammation, making it difficult to predict the pathological status of patients solely based on single-modal images. We hypothesize that the macrophage-stimulating protein 1 rs3197999 single-nucleotide polymorphism may lead to imbalances in glucose and oxygen metabolism, thereby influencing cognitive resilience and the progression of Alzheimer's disease. In this study, we found that among 121 patients with mild cognitive impairment, carriers of the macrophage-stimulating protein 1 rs3197999 risk allele showed a significant reduction in the coupling of glucose and oxygen metabolism in the dorsolateral prefrontal cortex region. However, the rs3197999 variant did not induce significant differences in glucose metabolism and neuronal activity signals. Furthermore, the rs3197999 risk allele correlated with a higher rate of increase in clinical dementia score, mediated by the coupling of glucose and oxygen metabolism.

HIGHLIGHT

Dissociation of energy connectivity and functional connectivity in Alzheimer's disease is associated with maintenance of cognitive performance

The correlation between functional connectivity (FC) network segregation, glucose metabolism and cognitive decline has been recently identified. The coupling relationship between glucose metabolism and the intensity of neuronal activity obtained using hybrid PET/MRI techniques can provide additional information on the physiological state of the brain in patients with AD and mild cognitive impairment (MCI). It is a valuable task to use the above rules for constructing biomarkers that are closely related to the cognitive ability of individuals to monitor the pathological status of patients. This study proposed the concept of the energy connectivity (EC) network and its construction method. We hypothesized that the dissociation between energy connectivity and functional connectivity of brain regions is a valid indicator of cognitive ability in patients with dementia. The number of EC-attenuated brain regions (EC-AR) and the number of FC-attenuated brain regions (FC-AR) are obtained by comparison with the normal group, and the dissociation between functional connectivity and energy connectivity is indicated using the ratio of FC-AR to EC-AR for individuals in the disease group. The findings suggest that FC-AR/EC-AR values are accurate predictors of cognitive performance, while taking into account the cognitive recovery due to compensatory effects of the brain. The cognitive ability of some patients with cognitive recovery can also be predicted more accurately. This also indicates that lower functional connectivity and higher energy connectivity between network modules may be one of the important features that maintain cognitive performance. The concept of energy connectivity also has potential to help explore the pathological state of AD.

Spontaneity matters! Network alterations before and after spontaneous and active facial self-touches: An EEG functional connectivity study

BACKGROUND

Despite humans frequently performing spontaneous facial self-touches (sFST), the function of this behavior remains speculative. sFST have been discussed in the context of self-regulation, emotional homeostasis, working memory processes, and attention focus. First evidence indicates that sFST and active facial self-touches (aFST) are neurobiologically different phenomena. The aim of the present analysis was to examine EEG-based connectivity in the course of sFST and aFST to test the hypotheses that sFST affect brain network interactions relevant for other than sensorimotor processes.

METHODS

To trigger spontaneous FST a previously successful setting was used: 60 healthy participants manually explored two haptic stimuli and held the shapes of the stimuli in memory for a 14 min retention interval. Afterwards the shapes were drawn on a sheet of paper. During the retention interval, artifact-free EEG-data of 97 sFST by 32 participants were recorded. At the end of the experiment, the participants performed aFST with both hands successively. For the EEG-data, connectivity was computed and compared between the phases before and after sFST and aFST and between the respective before-and the after-phases.

RESULTS

For the before-after comparison, brainwide distributed significant connectivity differences (p < .00079) were observed for sFST, but not for aFST. Additionally, comparing the before- and after-phases of sFST and aFST, respectively, revealed increased similarity between the after-phases than between the before-phases.

CONCLUSION

The results support the assumption that sFST and aFST are neurobiologically different phenomena. Furthermore, the aligned network properties of the after-phases compared to the before-phases indicate that sFST serve self-regulatory functions that aFST do not serve.

Neurofunctional correlates of glutamate and GABA imbalance in psychosis: A systematic review

Glutamatergic and GABAergic dysfunction are implicated in the pathophysiology of schizophrenia. Previous work has shown relationships between glutamate, GABA, and brain activity in healthy volunteers. We conducted a systematic review to evaluate whether these relationships are disrupted in psychosis. Primary outcomes were the relationship between metabolite levels and fMRI BOLD response in psychosis relative to healthy volunteers. 17 case-control studies met inclusion criteria (594 patients and 538 healthy volunteers). Replicated findings included that in psychosis, positive associations between ACC glutamate levels and brain activity are reduced during resting state conditions and increased during cognitive control tasks, and negative relationships between GABA and local activation in the ACC are reduced. There was evidence that antipsychotic medication may alter the relationship between glutamate levels and brain activity. Emerging literature is providing insights into disrupted relationships between neurometabolites and brain activity in psychosis. Future studies determining a link to clinical variables may develop this approach for biomarker applications, including development or targeting novel therapeutics.

Spatial and temporal frequency band changes during infarct induction, infarct progression, and spreading depolarizations in the gyrencephalic brain

Aim

To describe the spatial and temporal electrocorticographic (ECoG) changes after middle cerebral artery occlusion (MCAo), including those caused by spreading depolarization (SD) in the pig brain.

Methods

The left middle cerebral arteries (MCAs) were clipped in six pigs. The clipping procedure lasted between 8 and 12 min, achieving a permanent occlusion (MCAo). Five-contact ECoG stripes were placed bilaterally over the frontoparietal cortices corresponding to the irrigation territory of the MCA and anterior cerebral artery (ACA). ECoG recordings were performed around 24 h: 1 h before and 23 h after the MCAo, and SDs were quantified. Five-minute ECoG signal segments were sampled before, 5 min, and 4, 8, and 12 h after cerebral artery occlusion and before, during, and after the negative direct current shift of the SDs. The power spectrum of the signals was decomposed into delta, theta, alpha, beta, and gamma bands. Descriptive statistics, Wilcoxon matched-pairs signed-rank tests, and Friedman tests were performed.

Results

Electrodes close to the MCAo showed instant decay in all frequency bands and SD onset during the first 5 h. Electrodes far from the MCAo exhibited immediate loss of fast frequencies and progressive decline of slow frequencies with an increased SD incidence between 6 and 14 h. After 8 h, the ACA electrode reported a secondary reduction of all frequency bands except gamma and high SD incidence within 12-17 h. During the SD, all electrodes showed a decline in all frequency bands. After SD passage, frequency band recovery was impaired only in MCA electrodes.

Conclusion

ECoG can identify infarct progression and secondary brain injury. Severe disturbances in all the frequency bands are generated in the cortices where the SDs are passing by.

Abnormal Brain Oscillations in Developmental Disorders: Application of Resting State EEG and MEG in Autism Spectrum Disorder and Fragile X Syndrome

Autism Spectrum Disorder (ASD) and Fragile X Syndrome (FXS) are neurodevelopmental disorders with similar clinical and behavior symptoms and partially overlapping and yet distinct neurobiological origins. It is therefore important to distinguish these disorders from each other as well as from typical development. Examining disruptions in functional connectivity often characteristic of neurodevelopment disorders may be one approach to doing so. This review focuses on EEG and MEG studies of resting state in ASD and FXS, a neuroimaging paradigm frequently used with difficult-to-test populations. It compares the brain regions and frequency bands that appear to be impacted, either in power or connectivity, in each disorder; as well as how these abnormalities may result in the observed symptoms. It argues that the findings in these studies are inconsistent and do not fit neatly into existing models of ASD and FXS, then highlights the gaps in the literature and recommends future avenues of inquiry.

Using EEG to study sensorimotor adaptation

Sensorimotor adaptation, or the capacity to flexibly adapt movements to changes in the body or the environment, is crucial to our ability to move efficiently in a dynamic world. The field of sensorimotor adaptation is replete with rigorous behavioural and computational methods, which support strong conceptual frameworks. An increasing number of studies have combined these methods with electroencephalography (EEG) to unveil insights into the neural mechanisms of adaptation. We review these studies: discussing EEG markers of adaptation in the frequency and the temporal domain, EEG predictors for successful adaptation and how EEG can be used to unmask latent processes resulting from adaptation, such as the modulation of spatial attention. With its high temporal resolution, EEG can be further exploited to deepen our understanding of sensorimotor adaptation.

The relationship between synaptic density marker SV2A, glutamate and N-acetyl aspartate levels in healthy volunteers and schizophrenia: a multimodal PET and magnetic resonance spectroscopy brain imaging study

Glutamatergic excitotoxicity is hypothesised to underlie synaptic loss in schizophrenia pathogenesis, but it is unknown whether synaptic markers are related to glutamatergic function in vivo. Additionally, it has been proposed that N-acetyl aspartate (NAA) levels reflect neuronal integrity. Here, we investigated whether synaptic vesicle glycoprotein 2 A (SV2A) levels are related to glutamatergic markers and NAA in healthy volunteers (HV) and schizophrenia patients (SCZ). Forty volunteers (SCZ n = 18, HV n = 22) underwent [11C]UCB-J positron emission tomography and proton magnetic resonance spectroscopy (1H-MRS) imaging in the left hippocampus and anterior cingulate cortex (ACC) to index [11C]UCB-J distribution volume ratio (DVR), and creatine-scaled glutamate (Glu/Cr), glutamate and glutamine (Glx/Cr) and NAA (NAA/Cr). In healthy volunteers, but not patients, [11C]UCB-J DVR was significantly positively correlated with Glu/Cr, in both the hippocampus and ACC. Furthermore, in healthy volunteers, but not patients, [11C]UCB-J DVR was significantly positively correlated with Glx/Cr, in both the hippocampus and ACC. There were no significant relationships between [11C]UCB-J DVR and NAA/Cr in the hippocampus or ACC in healthy volunteers or patients. Therefore, an appreciable proportion of the brain 1H-MRS glutamatergic signal is related to synaptic density in healthy volunteers. This relationship is not seen in schizophrenia, which, taken with lower synaptic marker levels, is consistent with lower levels of glutamatergic terminals and/or a lower proportion of glutamatergic relative to GABAergic terminals in the ACC in schizophrenia.

Melamine Disrupts Acetylcholine-Mediated Neural Information Flow in the Hippocampal CA3-CA1 Pathway

Considering the cognitive and synaptic deficits following intragastric administration of melamine, the aim of the current investigation was to test whether the hippocampal oscillations were affected. The local field potential (LFP) was recorded in the hippocampal CA3–CA1 pathway of Wistar rats during a spatial-dependent Y-maze task. The general partial directed coherence (gPDC) method was used to assess the directionality of neural information flow (NIF) between the CA3 and CA1 regions. The levels of acetylcholine (ACh) and its esterolytic protease, acetylcholinesterase (AChE), were detected in the hippocampus (HPC) following the behavioral test. The values of phase synchronization between the CA3 and CA1 regions in delta, low theta, and high theta oscillations were reduced significantly in the melamine-treated group. Moreover, the coupling directional index and the strength of CA3 driving CA1 were critically decreased in the above three frequency bands as well. Meanwhile, a reduction in ACh expression and an enhancement in AChE activity were found in the HPC of melamine-treated rats. Intrahippocampal infusion with ACh could mitigate the weakened neural coupling and directional NIF in parallel with spatial learning improvements. However, infusion of scopolamine, an acetylcholine receptor antagonist, could block the mitigative effects of ACh treatment in melamine rats. These findings provide first evidence that ACh-mediated neuronal coupling and NIF in the CA3–CA1 pathway are involved in spatial learning deficits induced by chronic melamine exposure.

GABA, Glutamate and Neural Activity: A Systematic Review With Meta-Analysis of Multimodal 1H-MRS-fMRI Studies

Multimodal neuroimaging studies combining proton magnetic resonance spectroscopy (¹H-MRS) to quantify GABA and/or glutamate concentrations and functional magnetic resonance imaging (fMRI) to measure brain activity non-invasively have advanced understanding of how neurochemistry and neurophysiology may be related at a macroscopic level. The present study aimed to perform a systematic review and meta-analysis of available studies examining the relationship between ¹H-MRS glutamate and/or GABA levels and task-related fMRI signal in the healthy brain. Ovid (Medline, Embase, and PsycINFO) and Pubmed databases were systematically searched to identify articles published until December 2019. The primary outcome of interest was the association between resting levels of glutamate or GABA and task-related fMRI. Fifty-five papers were identified for inclusion in the systematic review. A further 22 studies were entered into four separate meta-analyses. These meta-analyses found evidence of significant negative associations between local GABA levels and (a) fMRI activation to visual tasks in the occipital lobe, and (b) activation to emotion processing in the medial prefrontal cortex (mPFC)/anterior cingulate cortex (ACC). However, there was no significant association between mPFC/ACC glutamate levels and fMRI activation to cognitive control tasks or to emotional processing, with the relationship to emotion processing related neural activity narrowly missing significance. Moreover, our systematic review also found converging evidence of negative associations between GABA levels and local brain activity, and positive associations between glutamate levels and distal brain activity, outside of the ¹H-MRS sampling region. Albeit less consistently, additional relationships between GABA levels and distal brain activity and between glutamate levels and local brain activity were found. It remains unclear if the absence of effects for other brain regions and other cognitive-emotional domains reflects study heterogeneity or potential confounding effects of age, sex, or other unknown factors. Advances in ¹H-MRS methodology as well as in the integration of ¹H-MRS readouts with other imaging modalities for indexing neural activity hold great potential to reveal key aspects of the pathophysiology of mental health disorders involving aberrant interactions between neurochemistry and neurophysiology such as schizophrenia.

Subacute melamine exposure disrupts task-based hippocampal information flow via inhibiting the subunits 2 and 3 of AMPA glutamate receptors expression

Although melamine exposure induces cognitive deficits and dysfunctional neurotransmission in hippocampal Cornus Ammonis (CA) 1 region of rats, it is unclear whether the neural function, such as neural oscillations between hippocampal CA3-CA1 pathway and postsynaptic receptors involves in these effects. The levels of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) subunit glutamate receptor (GluR) 1 and GluR2/3 in CA1 region of melamine-treated rats, which were intragastric treated with 300 mg/kg/day for 4 weeks, were detected. Following systemic or intra-hippocampal CA1 injection with GluR2/3 agonist, spatial learning of melamine-treated rats was assessed in Morris water maze (MWM) task. Local field potentials were recorded in CA3-CA1 pathway before and during behavioral test. General Partial Directed Coherence approach was applied to determine directionality of neural information flow between CA3 and CA1 regions. Results showed that melamine exposure reduced GluR2/3 but not GluR1 level and systemic or intra-hippocampal CA1 injection with GluR2/3 agonist effectively mitigated the learning deficits. Phase synchronization between CA3 and CA1 regions were significantly diminished in delta, theta and alpha oscillations. Coupling directional index and strength of CA3 driving CA1 were marked reduced as well. Intra-hippocampal CA1 infusion with GluR2/3 agonist significantly enhanced the phase locked value and reversed the melamine-induced reduction in the neural information flow (NIF) from CA3 to CA1 region. These findings support that melamine exposure decrease the expression of GluR2/3 subunit involved in weakening directionality index of NIF, and thereby induced spatial learning deficits.

EXTENDED ATTENUATION OF CORTICOSTRIATAL POWER AND COHERENCE AFTER ACUTE EXPOSURE TO VAPOURIZED Δ9 TETRAHYDROCANNABINOL IN RATS

Introduction

Over 14% of Canadians use cannabis, with nearly 60% of these individuals reporting daily or weekly use. Inhalation of cannabis vapour has recently gained popularity, but the effects of this exposure on neural activity remain unknown. In this study, we assessed the impact of acute exposure to vapourized Δ9-tetrahydrocannabinol (THC) on neural circuit dynamics in rats.

Objectives

We aimed to characterize the changes in neural activity in the dorsal striatum (dStr), orbitofrontal cortex (OFC), and prefrontal cortex (PFC), after acute exposure to THC vapour.

Methods

Rats were implanted with electrode arrays targeting the dStr, OFC, and PFC. Rats were administered THC (or vehicle) using a Volcano® vapourizer and local field potential recordings were performed in a plexiglass chamber in a cross-over design with a week-long washout period.

Results

Decreased spectral power was observed within the dStr, OFC, and PFC in the gamma range (>32-100 Hz) following vapourized THC administration. Most changes in gamma were still present 7 days after THC administration. Decreased gamma coherence was also observed between the OFC-PFC and dStr-PFC region-pairs.

Conclusion

A single exposure to vapourized THC suppresses cortical and dorsal striatal gamma power and coherence, effects that appear to last at least a week. Given the role of gamma hypofunction in schizophrenia, these findings may provide mechanistic insights into the known psychotomimetic effects of THC.

Brain oscillatory activity and CT perfusion in hyper-acute ischemic stroke

OBJECTIVES

The combined use of perfusion neuroimaging and brain oscillatory activity may provide a better clinical picture of neurovascular coupling of the injured area in ischemic stroke. The aim is to assess stroke-related topographic electroencephalography (EEG) changes during the earliest phase of ischemic stroke and to compare them with hypoperfusion identified by computer tomography perfusion (CTP).

PATIENTS AND METHODS

The study included 15 patients with ischemic stroke, who underwent both CTP and EEG recording within 4.5 h. Topographic representation of power for each band was calculated and compared with hypoperfusion areas estimated by CTP maps.

RESULTS

Predominance of slow delta frequencies was found in all patients. The main finding is the agreement between slow rhythms hemispheric prevalence on EEG maps and cerebral hypoperfusion area identified using CTP.

CONCLUSION

The results of this preliminary study show that the combined use of EEG and CTP, as highly available techniques, in acute ischemic stroke may be helpful in clinical practice and provide information about functional and metabolic aspects of brain involvement. The joint use of these methodologies may give a better clinical insight of the functionality of injured area in the hyperacute phase.

Dyslexia and age related effects in the neurometabolites concentration in the visual and temporo-parietal cortex

Several etiological theories, in particular neuronal noise and impaired auditory sampling, predicted neurotransmission deficits in dyslexia. Neurometabolites also affect white matter microstructure, where abnormalities were previously reported in dyslexia. However findings from only few magnetic resonance spectroscopy studies using diverse age groups, different brain regions, data processing and reference scaling are inconsistent. We used MEGA-PRESS single-voxel spectroscopy in two ROIs: left temporo-parietal and occipital cortex in 36 adults and 52 children, where half in each group had dyslexia. Dyslexics, on average, had significantly lower total N-acetylaspartate (tNAA) than controls in the occipital cortex. Adults compared to children were characterized by higher choline and creatine in both areas, higher tNAA in left temporo-parietal and lower glutamate in the visual cortex, reflecting maturational changes in cortical microstructure and metabolism. Although the current findings do not support the proposed etiological theories of dyslexia, they show, for the first time, that tNAA, considered to be a neurochemical correlate of white matter integrity, is deficient in the visual cortex in both children and adults with dyslexia. They also point that several neurotransmitters, including ones previously used as reference, change with age.

Social isolation impairs the persistence of social recognition memory by disturbing the glutamatergic tonus and the olfactory bulb-dorsal hippocampus coupling

The absence of companion may jeopardize mental health in social animals. Here, we tested the hypothesis that social isolation impairs social recognition memory by altering the excitability and the dialog between the olfactory bulb (OB) and the dorsal hippocampus (dHIP). Adult male Swiss mice were kept grouped (GH) or isolated (SI) for 7 days. Social memory (LTM) was evaluated using social recognition test. SI increased glutamate release in the OB, while decreased in the dHIP. Blocking AMPA and NMDA receptors into the OB or activating AMPA into the dHIP rescued LTM in SI mice, suggesting a cause-effect relationship between glutamate levels and LTM impairment. Additionally, during memory retrieval, phase-amplitude coupling between OB and dHIP decreased in SI mice. Our results indicate that SI impaired the glutamatergic signaling and the normal communication between OB and HIP, compromising the persistence of social memory.

Cross-sectional Study of Glutamate in the Anterior Cingulate and Hippocampus in Schizophrenia

BACKGROUND

There has been growing support for dysfunctions of the excitatory glutamatergic system and its implications for the psychophysiology of schizophrenia. However, previous studies reported mixed results regarding glutamate concentrations in schizophrenia with varying deviations across brain regions.

METHODS

We used an optimized proton magnetic resonance spectroscopy procedure to measure absolute glutamate concentrations in the left hippocampal region and the anterior cingulate cortex (ACC) in 29 medicated patients with schizophrenia and in 29 control participants without mental disorder.

RESULTS

The glutamate concentrations were significantly lower in the ACC but higher in the hippocampus of patients compared to controls. ACC and hippocampal glutamate concentrations correlated positively in patients but not in controls. ACC glutamate was weakly associated with Clinical Global Impression score and duration of illness in patients.

CONCLUSION

Glutamate concentrations in schizophrenia deviate from controls and show associations with disease severity. A higher concentration of hippocampal glutamate in schizophrenia compared to controls is shown. The association between ACC and hippocampus glutamate concentrations in patients with schizophrenia suggests an abnormal coupling of excitatory systems compared to controls as predicted by previous glutamate models of schizophrenia.

[Significance of clinical electroencephalogram in psychiatry]

The generation of an electroencephalogram (EEG) provides a sensitive, non-invasive and inexpensive method for the investigation of brain function. This article critically reviews the significance of EEG examinations in clinical psychiatric practice and describes relevant applications and limitations. A summary of the basic principles of the production and interpretation of an EEG is followed by a survey of typical EEG patterns in healthy subjects and pathological alterations of EEG patterns. The importance of the EEG for the clinical diagnostics of Alzheimer's disease and acute delirium as well as the differentiation between psychiatric syndromes and non-convulsive status epilepticus is reviewed. Moreover, the usefulness of the EEG is highlighted with respect to the diagnostics and monitoring of the course of lithium intoxication. Finally, this article gives a brief insight into promising research approaches that are currently being followed in modern psychiatry using an EEG.

Perturbation of Brain Oscillations after Ischemic Stroke: A Potential Biomarker for Post-Stroke Function and Therapy

Brain waves resonate from the generators of electrical current and propagate across brain regions with oscillation frequencies ranging from 0.05 to 500 Hz. The commonly observed oscillatory waves recorded by an electroencephalogram (EEG) in normal adult humans can be grouped into five main categories according to the frequency and amplitude, namely δ (1-4 Hz, 20-200 μV), θ (4-8 Hz, 10 μV), α (8-12 Hz, 20-200 μV), β (12-30 Hz, 5-10 μV), and γ (30-80 Hz, low amplitude). Emerging evidence from experimental and human studies suggests that groups of function and behavior seem to be specifically associated with the presence of each oscillation band, although the complex relationship between oscillation frequency and function, as well as the interaction between brain oscillations, are far from clear. Changes of brain oscillation patterns have long been implicated in the diseases of the central nervous system including ischemic stroke, in which the reduction of cerebral blood flow as well as the progression of tissue damage have direct spatiotemporal effects on the power of several oscillatory bands and their interactions. This review summarizes the current knowledge in behavior and function associated with each brain oscillation, and also in the specific changes in brain electrical activities that correspond to the molecular events and functional alterations observed after experimental and human stroke. We provide the basis of the generations of brain oscillations and potential cellular and molecular mechanisms underlying stroke-induced perturbation. We will also discuss the implications of using brain oscillation patterns as biomarkers for the prediction of stroke outcome and therapeutic efficacy.

Effects of Hydrogen Sulfide on Modulation of Theta-Gamma Coupling in Hippocampus in Vascular Dementia Rats

Our previous study showed that hydrogen sulfide (H2S) could alleviate the cognitive deficits in vascular dementia (VD) rats associated with the improvement of synaptic plasticity. Neural oscillations are reported to interact with each other through either identical-frequency or cross-frequency coupling. This study examined whether impaired neural couplings could be alleviated by H2S in the hippocampal CA3-CA1 of VD rats and explored its possible mechanism. A VD rat model was established by two-vessel occlusion. Sodium hydrosulfide (NaHS), a kind of H2S donor, was administered intraperitoneally (5.6 mg/kg/day) for 3 weeks. Local field potentials were simultaneously collected in the hippocampal CA3 and CA1. The effects of NaHS on the modulation of theta-gamma coupling were evaluated by using the measurements of both phase-phase coupling and phase-amplitude coupling, while several other approaches including behavior, electrophysiology, western blot, immunofluorescence staining were also employed. The results showed that NaHS significantly prevented spatial learning and memory impairments (p < 0.01). NaHS considerably alleviated the impairment of neural coupling in VD rats in an identical-frequency rhythm and between cross-frequency bands. Moreover, the expression of cystathionine-β-synthase (CBS) was markedly attenuated in VD rats. NaHS elevated the expression of CBS to maintain the intrinsic balance of H2S. Interestingly, it was observed that NaHS increased the protein expression of N-methyl-D-aspartic acid receptor 2A (NMDAR2A) in VD rats. In conclusion, the data suggest that NaHS played the neuroprotective role partly via modulating the expression of NMDAR2A in order to alleviate the impairments of neural couplings in VD rats.

Frontal P3 event-related potential is related to brain glutamine/glutamate ratio measured in vivo

BACKGROUND

The auditory P3 event-related potential (ERP) is thought to index cognitive processing relevant to attention and working memory processes. Drug challenge studies suggest that glutamate neurotransmission plays an important role in modulating P3 ERP. However, while direct links between glutamate activity and P3 ERP response in humans are suspected, mechanistic details remain largely unknown. We investigated here the relationships between P3 ERP and indices of glutamatergic processing measured in vivo with proton magnetic resonance spectroscopy ((1)H MRS). We hypothesized that a higher index of glutamatergic processing (glutamine/glutamate ratio; abbreviated Gln/Glu) in the anterior cingulate (ACC) and in the parietal-occipital (POC) cortices would associate with larger frontal P3a and parietal P3b amplitudes, respectively.

METHODS

Frontal P3a (Fz) and parietal P3b (Pz) were collected from 32 healthy participants who performed an auditory oddball task. Resting glutamate (Glu), glutamine (Gln), and Gln/Glu (an index of glutamatergic processing) measures were obtained on a 4T MR scanner using J-resolved MR spectroscopy. Linear regression and partial correlations were used for statistical analysis.

RESULTS

Significant positive correlations were found between frontal P3a amplitude and ACC Gln/Glu ratio (partial R=0.57; P=0.001) and between frontal P3a amplitude and ACC Gln concentration (partial R=0.43; P=0.02). Relationships between parietal P3b and the glutamate indices in the POC were not significant.

CONCLUSIONS

These results indicate a specific connection between an index of glutamate neurotransmitter function in ACC and frontal P3 ERP, providing a novel insight into the neurochemistry underlying scalp recorded EEG response. Abnormalities in glutamate neurotransmission have been observed in schizophrenia and other psychiatric conditions and may underlie illness related deficits of P3 ERP.

1H-MRS glutamate level predicts auditory sensory gating in alcohol dependence: Preliminary results

Background:

Impairment in auditory sensory gating (ASG) has been documented in alcohol dependence [1]. Likewise, it has been shown that ASG becomes abnormal during alcohol administration in otherwise healthy individuals [2]. Patterns of gating abnormality associated with alcohol use are likely associated with an alcohol responsive neurochemical like glutamate (Glu), particularly since it is well-established that alcohol affects NMDA receptors and that glutamatergic functioning is abnormal in both acute alcohol use and in alcohol dependence [3]. Hence, a link between Glu metabolite levels and ASG was hypothesized. It was first hypothesized that Glu and ASG abnormality would be found in groups with alcohol dependence. A second hypothesis was that across groups, greater Glu would predict reduced ASG.

Methods:

Groups were comprised of healthy, non-drinking controls (Controls, N = 4), individuals with current alcohol dependence (AUD-current, N = 6), and with alcohol dependence in remission for at least 1 year (AUD-remission, N = 6). Participants underwent a diagnostic assessment for alcohol consumption, MRI, 1H-MRS for in vivo assessment of Glu and other metabolites, and MEG scanning during a paired click protocol. ASG was computed as the ratio of the source strength of the 50 ms component in the event related field (ERF) to the second click in the pair divided by the source strength of the 50 ms component to the first click in the pair.

Results:

Univariate MANOVAs controlling for age and gender revealed a significant effect for group on Glu and ASG, such that ASG ratios were significantly elevated, implying weakened gating. Glu concentration was reduced in AUD-current relative to the other two groups. Further analysis revealed that when additionally controlling for the group effect, reduced Glu predicted increasing impairment in ASG.

Conclusions:

The overall results were consistent with the hypothesis that differences in Glu metabolite levels associated with alcohol dependence result in impaired ASG.

Modulation of induced frontocentral theta (Fm-θ) event-related (de-)synchronisation dynamics following mindfulness-based cognitive therapy in Major Depressive Disorder

Depressive severity has been associated with attenuated neocortical frontal midline theta (Fm-θ) power/evoked activity. Mindfulness-Based Cognitive Therapy (MBCT) has shown to be a successful novel intervention for Major Depressive Disorder (MDD), albeit precise working mechanisms remain elusive. We examined the hypothesis that MBCT would have modulating effects upon evoked Fm-θ power, in addition to investigating possible mediation of induced event-related de/synchronisation (ERD/ERS) dynamics. Fifty one patients with a primary diagnosis of MDD (26 exposed to MBCT vs. 25 wait-list/WL controls) undertook a Go/NoGo task consisting of positive, negative and neutral words, further stratified into abstract versus trait adjective matrices. Depressive symptom severity and rumination were also examined. A pattern of enhanced induced Fm-θ synchronisation during the latter 400-800 ms temporal-window pre-to-post MBCT was observed; the contrary in the WL. Modulated ERD/ERS dynamics correlated to amelioration in depressive and rumination symptoms in the MBCT group. We propose the primary action pathway alluded to a neural disengagement mechanism enacting upon tonic neuronal assemblies implicated in emotional and self-related processing. Due to the complexity and presently undiscovered complete unified scientific understanding of neuro-oscillatory-dynamics, and associated clinical interplays; we hypothesise that the electro-cortical and connected clinical working pathways of MBCT in depression are multi-levelled constituting nonlinear and interdependent mechanisms, represented by mediated EEG synchronisation dynamics.

Associations of regional GABA and glutamate with intrinsic and extrinsic neural activity in humans—a review of multimodal imaging studies

The integration of multiple imaging modalities is becoming an increasingly well used research strategy for studying the human brain. The neurotransmitters glutamate and GABA particularly lend themselves towards such studies. This is because these transmitters are ubiquitous throughout the cortex, where they are the key constituents of the inhibition/excitation balance, and because they can be easily measured in vivo through magnetic resonance spectroscopy, as well as with select positron emission tomography approaches. How these transmitters underly functional responses measured with techniques such as fMRI and EEG remains unclear though, and was the target of this review. Consistently shown in the literature was a negative correlation between GABA concentrations and stimulus-induced activity within the measured region. Also consistently found was a positive correlation between glutamate concentrations and inter-regional activity relationships, both during tasks and rest. These findings are outlined along with results from populations with mental disorders to give an overview of what brain imaging has suggested to date about the biochemical underpinnings of functional activity in health and disease. We conclude that the combination of functional and biochemical imaging in humans is an increasingly informative approach that does however require a number of key methodological and interpretive issues be addressed before can meet its potential.

Glutamate and choline levels predict individual differences in reading ability in emergent readers

Reading disability is a brain-based difficulty in acquiring fluent reading skills that affects significant numbers of children. Although neuroanatomical and neurofunctional networks involved in typical and atypical reading are increasingly well characterized, the underlying neurochemical bases of individual differences in reading development are virtually unknown. The current study is the first to examine neurochemistry in children during the critical period in which the neurocircuits that support skilled reading are still developing. In a longitudinal pediatric sample of emergent readers whose reading indicators range on a continuum from impaired to superior, we examined the relationship between individual differences in reading and reading-related skills and concentrations of neurometabolites measured using magnetic resonance spectroscopy. Both continuous and group analyses revealed that choline and glutamate concentrations were negatively correlated with reading and related linguistic measures in phonology and vocabulary (such that higher concentrations were associated with poorer performance). Correlations with behavioral scores obtained 24 months later reveal stability for the relationship between glutamate and reading performance. Implications for neurodevelopmental models of reading and reading disability are discussed, including possible links of choline and glutamate to white matter anomalies and hyperexcitability. These findings point to new directions for research on gene-brain-behavior pathways in human studies of reading disability.

Resting-state EEG oscillatory dynamics in fragile X syndrome: abnormal functional connectivity and brain network organization

Disruptions in functional connectivity and dysfunctional brain networks are considered to be a neurological hallmark of neurodevelopmental disorders. Despite the vast literature on functional brain connectivity in typical brain development, surprisingly few attempts have been made to characterize brain network integrity in neurodevelopmental disorders. Here we used resting-state EEG to characterize functional brain connectivity and brain network organization in eight males with fragile X syndrome (FXS) and 12 healthy male controls. Functional connectivity was calculated based on the phase lag index (PLI), a non-linear synchronization index that is less sensitive to the effects of volume conduction. Brain network organization was assessed with graph theoretical analysis. A decrease in global functional connectivity was observed in FXS males for upper alpha and beta frequency bands. For theta oscillations, we found increased connectivity in long-range (fronto-posterior) and short-range (frontal-frontal and posterior-posterior) clusters. Graph theoretical analysis yielded evidence of increased path length in the theta band, suggesting that information transfer between brain regions is particularly impaired for theta oscillations in FXS. These findings are discussed in terms of aberrant maturation of neuronal oscillatory dynamics, resulting in an imbalance in excitatory and inhibitory neuronal circuit activity.

Impairment of cognitive function and synaptic plasticity associated with alteration of information flow in theta and gamma oscillations in melamine-treated rats

Changes of neural oscillations at a variety of physiological rhythms are effectively associated with cognitive performance. The present study investigated whether the directional indices of neural information flow (NIF) could be used to symbolize the synaptic plasticity impairment in hippocampal CA3-CA1 network in a rat model of melamine. Male Wistar rats were employed while melamine was administered at a dose of 300 mg/kg/day for 4 weeks. Behavior was measured by the Morris water maze(MWM)test. Local field potentials (LFPs) were recorded before long-term potentiation (LTP) induction. Generalized partial directed coherence (gPDC) and phase-amplitude coupling conditional mutual information (PAC_CMI) were used to measure the unidirectional indices in both theta and low gamma oscillations (LG, ~ 30-50 Hz). Our results showed that melamine induced the cognition deficits consistent with the reduced LTP in CA1 area. Phase locking values (PLVs) showed that the synchronization between CA3 and CA1 in both theta and LG rhythms was reduced by melamine. In both theta and LG rhythms, unidirectional indices were significantly decreased in melamine treated rats while a similar variation trend was observed in LTP reduction, implying that the effects of melamine on cognitive impairment were possibly mediated via profound alterations of NIF on CA3-CA1 pathway in hippocampus. The results suggested that LFPs activities at these rhythms were most likely involved in determining the alterations of information flow in the hippocampal CA3-CA1 network, which might be associated with the alteration of synaptic transmission to some extent.

Glutamatergic correlates of gamma-band oscillatory activity during cognition: a concurrent ER-MRS and EEG study

Frequency specific synchronisation of neuronal firing within the gamma-band (30-70 Hz) appears to be a fundamental correlate of both basic sensory and higher cognitive processing. In-vitro studies suggest that the neurochemical basis of gamma-band oscillatory activity is based on interactions between excitatory (i.e. glutamate) and inhibitory (i.e. GABA) neurotransmitter concentrations. However, the nature of the relationship between excitatory neurotransmitter concentration and changes in gamma band activity in humans remains undetermined. Here, we examine the links between dynamic glutamate concentration and the formation of functional gamma-band oscillatory networks. Using concurrently acquired event-related magnetic resonance spectroscopy and electroencephalography, during a repetition-priming paradigm, we demonstrate an interaction between stimulus type (object vs. abstract pictures) and repetition in evoked gamma-band oscillatory activity, and find that glutamate levels within the lateral occipital cortex, differ in response to these distinct stimulus categories. Importantly, we show that dynamic glutamate levels are related to the amplitude of stimulus evoked gamma-band (but not to beta, alpha or theta or ERP) activity. These results highlight the specific connection between excitatory neurotransmitter concentration and amplitude of oscillatory response, providing a novel insight into the relationship between the neurochemical and neurophysiological processes underlying cognition.

Reduction in LFP cross-frequency coupling between theta and gamma rhythms associated with impaired STP and LTP in a rat model of brain ischemia

The theta-gamma cross-frequency coupling (CFC) in hippocampus was reported to reflect memory process. In this study, we measured the CFC of hippocampal local field potentials (LFPs) in a two-vessel occlusion (2VO) rat model, combined with both amplitude and phase properties and associated with short and long-term plasticity indicating the memory function. Male Wistar rats were used and a 2VO model was established. STP and LTP were recorded in hippocampal CA3-CA1 pathway after LFPs were collected in both CA3 and CA1. Based on the data of relative power spectra and phase synchronization, it suggested that both the amplitude and phase coupling of either theta or gamma rhythm were involved in modulating the neural network in 2VO rats. In order to determine whether the CFC was also implicated in neural impairment in 2VO rats, the coupling of CA3 theta–CA1 gamma was measured by both phase-phase coupling (n:m phase synchronization) and phase-amplitude coupling. The attenuated CFC strength in 2VO rats implied the impaired neural communication in the coordination of theta-gamma entraining process. Moreover, compared with modulation index (MI) a novel algorithm named cross frequency conditional mutual information (CF-CMI), was developed to focus on the coupling between theta phase and the phase of gamma amplitude. The results suggest that the reduced CFC strength probably attributed to the disruption of the phase of CA1 gamma envelop. In conclusion, it implied that the phase coupling and CFC of hippocampal theta and gamma played an important role in supporting functions of neural network. Furthermore, synaptic plasticity on CA3-CA1 pathway was reduced in line with the decreased CFC strength from CA3 to CA1. It partly supported our hypothesis that directional CFC indicator might probably be used as a measure of synaptic plasticity.

Alteration of phase-phase coupling between theta and gamma rhythms in a depression-model of rats

Alterations in oscillatory brain activity are strongly correlated with cognitive performance in various physiological rhythms, especially the theta and gamma rhythms. In this study, we investigated the coupling relationship of neural activities between thalamus and medial prefrontal cortex (mPFC) by measuring the phase interactions between theta and gamma oscillations in a depression model of rats. The phase synchronization analysis showed that the phase locking at theta rhythm was weakened in depression. Furthermore, theta-gamma phase locking at n:m (1:6) ratio was found between thalamus and mPFC, while it was diminished in depression state. In addition, the analysis of coupling direction based on phase dynamics showed that the unidirectional influence from thalamus to mPFC was diminished in depression state only in theta rhythm, while it was partly recovered after the memantine treatment in a depression model of rats. The results suggest that the effects of depression on cognitive deficits are modulated via profound alterations in phase information transformation of theta rhythm and theta-gamma phase coupling.

Multimodal analysis of the hippocampus in schizophrenia using proton magnetic resonance spectroscopy and functional magnetic resonance imaging

BACKGROUND

Studies have shown that individuals with schizophrenia suffer from memory impairments. In this study, we combined proton magnetic resonance spectroscopy (¹H-MRS) and functional magnetic resonance imaging (fMRI) to clarify the neurobiology of memory deficits in schizophrenia.

METHODS

We used single-voxel MRS acquired in the left hippocampus and fMRI during performance of a memory task to obtain measures of neurochemistry and functional response in 28 stable, medicated participants with schizophrenia (SZ) and 28 matched healthy controls (HC).

RESULTS

The SZ group had significantly decreased blood oxygen level-dependent (BOLD) signal in left inferior frontal gyrus (IFG) during encoding and in the anterior cingulate cortex (ACC) and superior temporal gyrus (STG) during retrieval. We did not find significant differences in N-acetylaspartate/creatine (NAA/Cr) or glutamate+glutamine (Glx/Cr) levels between the groups, but did find a significant positive correlation between NAA/Cr and Glx/Cr in the HC group that was absent in the SZ group. There were no significant correlations between BOLD and MRS measured in the hippocampus. Further analyses revealed a negative correlation between left IFG BOLD and task performance in the SZ group. Finally, in the HC group, the left IFG BOLD was positively correlated with Glx/Cr.

CONCLUSIONS

We replicated findings of reduced BOLD signal in left IFG and of an altered relationship between IFG BOLD response and task performance in the SZ. The absence of correlation between NAA/Cr and Glx/Cr levels in patients might suggest underlying pathologies of the glutamate-glutamine cycle and/or mitochondria.

Decreased thalamo-cortical connectivity by alteration of neural information flow in theta oscillation in depression-model rats

Alterations in oscillatory brain activity are strongly correlated with cognitive performance in various physiological rhythms. The present study investigated whether the directionality of neural information flow (NIF) could be used to characterize the synaptic plasticity in thalamocortical (TC) pathway, and examined which frequency field oscillations were mostly related to the cognitive deficiency in depression. Two novel algorithms were employed to determine the coupling interaction between the LD thalamus and medial prefrontal cortex (mPFC) in five frequency bands, using the phase signals of local field potentials (LFP) in these two regions. The results showed that the power of neural activity in mPFC was increased in delta, theta and beta frequency bands in depression. However, the nonlinear characteristics of LFP activity were weakened in depression by means of sample entropy measurements. In the analysis of phase dynamics, the phase synchronization values were reduced in theta rhythm in stressed rats. Importantly, the coupling direction index d and the unidirectional influence from LD thalamus to mPFC were significantly reduced at the theta rhythm in rats in depression, and increased after memantine treatment, which were associated with the LTP alterations and cognitive impairment in our previous report. Moreover, the fact that the reduced entropy value was only found in mPFC might implicate postsynaptic effect involved in synaptic plasticity alteration in the depression model. The results suggest that the effects of depression on cognitive deficits are mediated via profound alterations in information flow in the TC pathway, and the directional index at theta rhythm could be used as a measurement of synaptic plasticity.

Event-Related Oscillations in Alcoholism Research: A Review

Alcohol dependence is characterized as a multi-factorial disorder caused by a complex interaction between genetic and environmental liabilities across development. A variety of neurocognitive deficits/dysfunctions involving impairments in different brain regions and/or neural circuitries have been associated with chronic alcoholism, as well as with a predisposition to develop alcoholism. Several neurobiological and neurobehavioral approaches and methods of analyses have been used to understand the nature of these neurocognitive impairments/deficits in alcoholism. In the present review, we have examined relatively novel methods of analyses of the brain signals that are collectively referred to as event-related oscillations (EROs) and show promise to further our understanding of human brain dynamics while performing various tasks. These new measures of dynamic brain processes have exquisite temporal resolution and allow the study of neural networks underlying responses to sensory and cognitive events, thus providing a closer link to the physiology underlying them. Here, we have reviewed EROs in the study of alcoholism, their usefulness in understanding dynamical brain functions/dysfunctions associated with alcoholism as well as their utility as effective endophenotypes to identify and understand genes associated with both brain oscillations and alcoholism.

Neurochemical and electrophysiological changes induced by paradoxical sleep deprivation in rats

The present study aims to investigate the effects of paradoxical sleep deprivation (PSD) on the waking EEG and amino acid neurotransmitters in the hippocampus and cortex of rats. Animals were deprived of paradoxical sleep for 72h by using the multiple platform method. The EEG power spectral analysis was carried out to assess the brain's electrophysiological changes due to sleep deprivation. The concentrations of amino acid neurotransmitters were assessed in the hippocampus and cortex using HPLC. Control data showed slight differences from normal animals in the delta, theta and alpha waves while an increase in the beta wave was obtained. After 24h of PSD, delta relative power increased and the rest of EEG wave's power decreased with respect to control. After 48h and 72h the spectral power analysis showed non-significant changes to control. The amino acid neurotransmitter analysis revealed a significant increase in cortical glutamate, glycine and taurine levels while in the hippocampus, glutamate, aspartate, glutamine and glycine levels increased significantly. Both the waking EEG and neurotransmitter analyses suggest that PSD induced neurochemical and electrophysiological changes that may affect brain proper functionality.

Cannabinoid modulations of resting state EEG θ power and working memory are correlated in humans

Object representations in working memory depend on neural firing that is phase-locked to oscillations in the theta band (4-8 Hz). Cannabis intake disrupts synchronicity of theta oscillations and interferes with memory performance. Sixteen participants smoked cigarettes containing 0.0, 29.3, 49.1, or 69.4 mg Delta(9)-tetrahydrocannabinol (THC) in a randomized crossover design and performed working memory and general attention tasks. Dose-dependent effects of THC were observed for resting state EEG theta and beta power, working memory (per-item search time), and attentional performance (percent errors and RT). The THC effects on EEG theta power and memory performance were correlated, whereas other EEG and behavioral effects were not. These findings confirm and extend previous results in rodents and humans, and corroborate a neurocomputational model that postulates that temporal aspects of information processing in working memory depend causally on nested oscillations in the theta and gamma (>30 Hz) bands.

No observable relationship between the 12 genes of nervous system and reasoning skill in a young Chinese Han population

Reasoning skill is an advanced cognitive ability which is needed for drawing inferences from given information. It is well known that the ability depends on the neural network of the frontal and parietal brain regions. In this study, we hypothesized that some genes involved in neurotransmitter systems were related to reasoning skill. To confirm this hypothesis, we examined the effects of 13 genes (BDNF, NRSF, COMT, DBH, DRD(2), DRD(3), DAT(1), MAOA, GRM(1), GRIN2B, TPH(2), 5-HT(2A), and 5-HT(6)) in neurotransmitter systems on the non-verbal reasoning and verbal reasoning skills. The results indicated there were on significant effects of the 17 functional variants of these genes on the performance of non-verbal reasoning and verbal analogical reasoning skills (χ(2) > 3.84, df = 1, P > 0.05). This study suggests that some of the functional variations in BDNF, COMT, DBH, DRD(2), DRD(3), MAOA, 5-HT(2A), 5-HT(6), GRM(1), and GRIN2B have no observable effects on the certain reasoning skills in a young healthy Chinese Han population.

The impact of blood pressure on hippocampal glutamate and mnestic function

Hypertension is associated with an increased risk of cognitive decline, which is generally regarded as a consequence of advanced cerebral atherosclerosis. Many hypertensive patients, however, suffer from cognitive decline long before they have any signs of cerebrovascular disease. Therefore, this study examines direct effects of blood pressure on neurotransmitter status in the hippocampus, a vulnerable cerebral structure relevant for memory consolidation. Absolute glutamate concentration and N-acetylaspartate (NAA) concentration as an alternative marker of neuronal integrity were determined in the hippocampus and the cerebral cortex (anterior cingulate cortex; ACC) by 3-T proton magnetic resonance spectroscopy in 16 probands without any history of cerebrovascular disease. Memory function was tested by the auditory verbal learning test (AVLT) and the rivermead behavioural memory test (RBMT). Arterial stiffness was assessed by augmentation index (AI). Mean arterial pressure showed a significant negative age-adjusted correlation to absolute glutamate concentrations in the hippocampus (R=-0.655, P=0.011), but not in the ACC. There was no significant correlation of mean arterial pressure and NAA in either hippocampus or ACC. AI did not affect hippocampal glutamate. Moreover, there was a significant negative correlation between mean arterial pressure and AVLT (r=-0.558, P=0.025) and RBMT score (r=-0.555, P=0.026). There is an inverse relation between blood pressure and the concentration of hippocampal glutamate. Glutamate is essential for long-term potentiation, the neurobiological correlate for memory formation in the hippocampus. Thus, hypertension-associated cognitive decline may not only be mediated by structural atherosclerotic wall changes, but also by functional changes in neurotransmission.

Metabolic correlatives of brain activity in a FOS epilepsy patient

The correlation and the interactions between neuronal activity and underlying metabolic dynamics are still a matter of debate, especially in pathological conditions. This study reports findings obtained on a subject suffering from fixation-off sensitivity (FOS) epilepsy, exploited as a model system of triggerable anomalous electrical activity. Functional Magnetic Resonance Spectroscopy was used to investigate the metabolic response to visual spike-inducing stimuli in a single voxel placed in the temporo-occipital lobe of a FOS epilepsy patient. MRS measurements were additionally performed on a control group of five healthy volunteers. The FOS patient also underwent an EEG session with the same stimulus paradigm. Uniquely in the FOS patient, glutamate and glutamine concentration increased during the first 10 min of stimulation and then returned to baseline. On the other hand, FOS-induced epileptic activity (spiking) endured throughout all the stimulation epoch. The observed metabolic dynamics may be likely linked to a complex interplay between alterations of the metabolic pathways of glutamate and modulation of the neuronal activity.

Glutamate as a spectroscopic marker of hippocampal structural plasticity is elevated in long-term euthymic bipolar patients on chronic lithium therapy and correlates inversely with diurnal cortisol

While an excess of glucocorticoids is associated with hippocampal pathology in mood disorders, lithium exerts robust neuroprotective and neurotrophic effects. Here, 21 stably remitted bipolar I patients who had been on chronic lithium maintenance therapy, on average, for more than a decade, and 19 carefully matched healthy controls were studied using 3 T (1)H-magnetic resonance spectroscopy of left and right hippocampus. Salivary cortisol samples were obtained to assess activity of the hypothalamus-pituitary-adrenal system. Absolute concentrations of N-acetylaspartate (NAA), choline-containing compounds and total creatine were similar in euthymic bipolar patients and healthy controls. Hippocampal glutamate concentrations were significantly increased as an effect of patient status (patients>controls) and laterality (left hippocampus>right hippocampus). Hippocampal glutamate content (Glu) was strongly correlated with NAA. Across groups and within the patient group, diurnal saliva cortisol levels showed a significant inverse relationship with both Glu and NAA. Taken together, these results add to the concept of bipolar disorder as an illness involving disturbed hippocampal structural plasticity under the opposing influences of lithium and glucocorticoids.

Association of single nucleotide polymorphisms in a glutamate receptor gene (GRM8) with theta power of event-related oscillations and alcohol dependence

Evidence suggests the P3 amplitude of the event-related potential and its underlying superimposed event-related oscillations (EROs), primarily in the theta (4-5 Hz) and delta (1-3 Hz) frequencies, as endophenotypes for the risk of alcoholism and other disinhibitory disorders. Major neurochemical substrates contributing to theta and delta rhythms and P3 involve strong GABAergic, cholinergic and glutamatergic system interactions. The aim of this study was to test the potential associations between single nucleotide polymorphisms (SNPs) in glutamate receptor genes and ERO quantitative traits. GRM8 was selected because it maps at chromosome 7q31.3-q32.1 under the peak region where we previously identified significant linkage (peak LOD = 3.5) using a genome-wide linkage scan of the same phenotype (event-related theta band for the target visual stimuli). Neural activities recorded from scalp electrodes during a visual oddball task in which rare target elicited P3s were analyzed in a subset of the Collaborative Study on the Genetics of Alcoholism (COGA) sample comprising 1,049 Caucasian subjects from 209 families (with 472 DSM-IV alcohol dependent individuals). The family-based association test (FBAT) detected significant association (P < 0.05) with multiple SNPs in the GRM8 gene and event-related theta power to target visual stimuli, and also with alcohol dependence, even after correction for multiple comparisons by false discovery rate (FDR). Our results suggest that variation in GRM8 may be involved in modulating event-related theta oscillations during information processing and also in vulnerability to alcoholism. These findings underscore the utility of electrophysiology and the endophenotype approach in the genetic study of psychiatric disorders.

Wavelet analysis of the frontal auditory evoked potentials obtained in the passive oddball paradigm in healthy subjects and schizophrenics

The goal of the present study was to apply the oscillatory brain dynamics model to the structural and quantitative analysis of neurocognitive functions considered as a potential marker of schizophrenia. This was achieved in tests of the detection of auditory events deviating in the regular auditory stream (oddball paradigm, MMN effect). It was hypothesized that the post-stimulus peaks of the oscillation power localized in post-stimulus time in the definite EEG oscillators represented neuro-electrical 'events' evoked in the specific neuronal nets characterized by this oscillation frequency band. We suggest that the time-frequency destination of these events related to the activation of the functional neuronal nets could be used for the determination of specific neurocognitive functions. Thus it was an attempt to distinguish the different neuro-functional parts of auditory processing and to compare these results between healthy subjects and patients with schizophrenia. The present results demonstrate the significant difference between the frontal averaged EEG oscillatory dynamics in healthy subjects and patients with schizophrenia related to neurocognitive function marked by the MMN and orienting response N200/P300a.

Identifying the neural circuitry of alcohol craving and relapse vulnerability

With no further intervention, relapse rates in detoxified alcoholics are high and usually exceed 80% of all detoxified patients. It has been suggested that stress and exposure to priming doses of alcohol and to alcohol-associated stimuli (cues) contribute to the relapse risk after detoxification. This article focuses on neuronal correlates of cue responses in detoxified alcoholics. Current brain imaging studies indicate that dysfunction of dopaminergic, glutamatergic and opioidergic neurotransmission in the brain reward system (ventral striatum including the nucleus accumbens) can be associated with alcohol craving and functional brain activation in neuronal systems that process attentional relevant stimuli, reward expectancy and experience. Increased functional brain activation elicited by such alcohol-associated cues predicted an increased relapse risk, whereas high brain activity elicited by affectively positive stimuli may represent a protective factor and was correlated with a decreased prospective relapse risk. These findings are discussed with respect to psychotherapeutic and pharmacological treatment options.

Prefrontal cortex glutamate correlates with mental perspective-taking

Background

Dysfunctions in theory of mind and empathic abilities have been suggested as core symptoms in major psychiatric disorders including schizophrenia and autism. Since self monitoring, perspective taking and empathy have been linked to prefrontal (PFC) and anterior cingulate cortex (ACC) function, neurotransmitter variations in these areas may account for normal and pathological variations of these functions. Converging evidence indicates an essential role of glutamatergic neurotransmission in psychiatric diseases with pronounced deficits in empathy. However, the role of the glutamate system for different dimensions of empathy has not been investigated so far.

Methodology/Principal Findings

Absolute concentrations of cerebral glutamate in the ACC, left dorsolateral PFC and left hippocampus were determined by 3-tesla proton magnetic resonance spectroscopy (1H-MRS) in 17 healthy individuals. Three dimensions of empathy were estimated by a self-rating questionnaire, the Interpersonal Reactivity Index (IRI). Linear regression analysis showed that dorsolateral PFC glutamate concentration was predicted by IRI factor “perspective taking” (T = −2.710, p = 0.018; adjusted alpha-level of 0.017, Bonferroni) but not by “empathic concern” or “personal distress”. No significant relationship between IRI subscores and the glutamate levels in the ACC or left hippocampus was detected.

Conclusions/Significance

This is the first study to investigate the role of the glutamate system for dimensions of theory of mind and empathy. Results are in line with recent concepts that executive top-down control of behavior is mediated by prefrontal glutamatergic projections. This is a preliminary finding that needs a replication in an independent sample.

A review of brain oscillations in cognitive disorders and the role of neurotransmitters

The analysis of the functional correlates of "brain oscillations" has become an important branch of neuroscience. Although research on the functional correlates of brain oscillation has progressed to a high level, studies on cognitive disorders are rare and mainly limited to schizophrenia patients. The present review includes the results of the changes in brain oscillations in patients with Alzheimer's, schizophrenia, bipolar disorders, mild cognitive impairment, attention-deficit hyperactivity disorder (ADHD), alcoholism and those with genetic disorders. Furthermore, the effects of pharmaca and the influence of neurotransmitters in patients with cognitive disorders are also reviewed. Following the review, a short synopsis is given related to the analysis of brain oscillations.

Uncovering genes for cognitive (dys)function and predisposition for alcoholism spectrum disorders: a review of human brain oscillations as effective endophenotypes

Brain oscillations provide a rich source of potentially useful endophenotypes (intermediate phenotypes) for psychiatric genetics, as they represent important correlates of human information processing and are associated with fundamental processes from perception to cognition. These oscillations are highly heritable, are modulated by genes controlling neurotransmitters in the brain, and provide links to associative and integrative brain functions. These endophenotypes represent traits that are less complex and more proximal to gene function than either diagnostic labels or traditional cognitive measures, providing a powerful strategy in searching for genes in psychiatric disorders. These intermediate phenotypes identify both affected and unaffected members of an affected family, including offspring at risk, providing a more direct connection with underlying biological vulnerability. Our group has utilized heritable neurophysiological features (i.e., brain oscillations) as endophenotypes, making it possible to identify susceptibility genes that may be difficult to detect with diagnosis alone. We have discussed our findings of significant linkage and association between brain oscillations and genes in GABAergic, cholinergic and glutamatergic systems (GABRA2, CHRM2, and GRM8). We have also shown that some oscillatory indices from both resting and active cognitive states have revealed a common subset of genetic foci that are shared with the diagnosis of alcoholism and related disorders. Implications of our findings have been discussed in the context of physiological and pharmacological studies on receptor function. These findings underscore the utility of quantitative neurophysiological endophenotypes in the study of the genetics of brain function and the genetic diathesis underlying complex psychiatric disorders.

Applications of magnetic resonance spectroscopy to tinnitus research: initial data, current issues, and future perspectives

Conducting tinnitus research on humans poses challenges for investigators because of its subjective nature, the complexities involved in establishing underlying generator sites, the diversity of potential causes, and the inherent difficulties in dissociating reactive changes in the central nervous system (CNS), secondary to peripheral hearing loss, from those effects that may be due to tinnitus. One area of considerable interest concerns biomarker development, particularly in the areas of metabolism and biochemistry. Establishing a biomarker or a profile of metabolic and neurobiochemical constituents of tinnitus-related activity within the CNS could be of considerable importance for understanding the fundamental properties of this disorder. Therefore, in an effort to gain greater insight into mechanisms of tinnitus, magnetic resonance spectroscopy (MRS) is being proposed as one of the several tools that can address pertinent issues. Apart from its long-standing use in analytical chemistry and physics, MRS is also being applied with greater frequency in the neurosciences to gain insight into human brain function under normal and pathological states. By considering the history of this method and advances made to date, MRS has the potential to: (1) identify unique in vivo metabolic and neurobiochemical biomarkers associated with tinnitus in specific regions of the CNS, (2) clarify and track disease pathogenesis, (3) monitor short and long-term treatment effects, and (4) serve as a tool in testing of drugs that may be used in treatment of tinnitus.

The -181 A/C polymorphism in the excitatory amino acid transporter-2 gene promoter affects the personality trait of reward dependence in healthy subjects

There have been some animal and human data suggesting that excitatory amino acid transporter (EAAT)-2, the major subtype of EAAT, is involved in human mental function and behavior. Recently, it has been shown that the -181 A/C polymorphism in the EAAT2 gene promoter affects plasma glutamate concentrations in humans. In the present study, the association of this genetic polymorphism with personality traits was examined in 575 Japanese healthy volunteers. Personality traits were assessed by the Temperament and Character Inventory, and the EAAT2 polymorphism was detected by a PCR-RFLP method. The scores of reward dependence were significantly (p=0.017) lower in the group with the A allele (A/A and A/C) than in that without this allele (C/C). When males and females were analyzed separately, the significant difference between the two genotype groups was observed in females (p=0.021) but not in males. The present study thus suggests that the -181 A/C polymorphism in the EAAT2 gene promoter affects the personality trait of reward dependence in healthy subjects.