Higher glutamate+glutamine and reduction of N-acetylaspartate in posterior cingulate according to age range in patients with cognitive impairment and/or pain

Understanding Proton Magnetic Resonance Spectroscopy Neurochemical Changes Using Alzheimer's Disease Biofluid, PET, Postmortem Pathology Biomarkers, and APOE Genotype

In vivo proton (1H) magnetic resonance spectroscopy (MRS) is a powerful non-invasive method that can measure Alzheimer's disease (AD)-related neuropathological alterations at the molecular level. AD biomarkers include amyloid-beta (Aβ) plaques and hyperphosphorylated tau neurofibrillary tangles. These biomarkers can be detected via postmortem analysis but also in living individuals through positron emission tomography (PET) or biofluid biomarkers of Aβ and tau. This review offers an overview of biochemical abnormalities detected by 1H MRS within the biologically defined AD spectrum. It includes a summary of earlier studies that explored the association of 1H MRS metabolites with biofluid, PET, and postmortem AD biomarkers and examined how apolipoprotein e4 allele carrier status influences brain biochemistry. Studying these associations is crucial for understanding how AD pathology affects brain homeostasis throughout the AD continuum and may eventually facilitate the development of potential novel therapeutic approaches.

Predicting performance in attention by measuring key metabolites in the PCC with 7T MRS

The posterior cingulate cortex (PCC) is a key hub of the default mode network and is known to play an important role in attention. Using ultra-high field 7 Tesla magnetic resonance spectroscopy (MRS) to quantify neurometabolite concentrations, this exploratory study investigated the effect of the concentrations of myo-inositol (Myo-Ins), glutamate (Glu), glutamine (Gln), aspartate or aspartic acid (Asp) and gamma-amino-butyric acid (GABA) in the PCC on attention in forty-six healthy participants. Each participant underwent an MRS scan and cognitive testing, consisting of a trail-making test (TMT A/B) and a test of attentional performance. After a multiple regression analysis and bootstrapping for correction, the findings show that Myo-Ins and Asp significantly influence (p < 0.05) attentional tasks. On one hand, Myo-Ins shows it can improve the completion times of both TMT A and TMT B. On the other hand, an increase in aspartate leads to more mistakes in Go/No-go tasks and shows a trend towards enhancing reaction time in Go/No-go tasks and stability of alertness without signal. No significant (p > 0.05) influence of Glu, Gln and GABA was observed.

Targeting Glutamate Neurotoxicity through Dietary Manipulation: Potential Treatment for Migraine

Glutamate, the main excitatory neurotransmitter in the central nervous system, is implicated in both the initiation of migraine as well as central sensitization, which increases the frequency of migraine attacks. Excessive levels of glutamate can lead to excitotoxicity in the nervous system which can disrupt normal neurotransmission and contribute to neuronal injury or death. Glutamate-mediated excitotoxicity also leads to neuroinflammation, oxidative stress, blood-brain barrier permeability, and cerebral vasodilation, all of which are associated with migraine pathophysiology. Experimental evidence has shown the protective effects of several nutrients against excitotoxicity. The current review focuses on the mechanisms behind glutamate's involvement in migraines as well as a discussion on how specific nutrients are able to work towards restoring glutamate homeostasis. Understanding glutamate's role in migraine is of vital importance for understanding why migraine is commonly comorbid with widespread pain conditions and for informing future research directions.

Neuroimaging modalities in the detection of Alzheimer's disease-associated biomarkers

Alzheimer's disease (AD) is the most common cause of dementia. Neuropathological changes in AD patients occur up to 10-20 years before the emergence of clinical symptoms. Specific diagnosis and appropriate intervention strategies are crucial during the phase of mild cognitive impairment (MCI) and AD. The detection of biomarkers has emerged as a promising tool for tracking the efficacy of potential therapies, making an early disease diagnosis, and prejudging treatment prognosis. Specifically, multiple neuroimaging modalities, including magnetic resonance imaging (MRI), positron emission tomography, optical imaging, and single photon emission-computed tomography, have provided a few potential biomarkers for clinical application. The MRI modalities described in this review include structural MRI, functional MRI, diffusion tensor imaging, magnetic resonance spectroscopy, and arterial spin labelling. These techniques allow the detection of presymptomatic diagnostic biomarkers in the brains of cognitively normal elderly people and might also be used to monitor AD disease progression after the onset of clinical symptoms. This review highlights potential biomarkers, merits, and demerits of different neuroimaging modalities and their clinical value in MCI and AD patients. Further studies are necessary to explore more biomarkers and overcome the limitations of multiple neuroimaging modalities for inclusion in diagnostic criteria for AD.

Excitation-Inhibition Imbalance in Migraine: From Neurotransmitters to Brain Oscillations

Migraine is among the most common and debilitating neurological disorders typically affecting people of working age. It is characterised by a unilateral, pulsating headache often associated with severe pain. Despite the intensive research, there is still little understanding of the pathophysiology of migraine. At the electrophysiological level, altered oscillatory parameters have been reported within the alpha and gamma bands. At the molecular level, altered glutamate and GABA concentrations have been reported. However, there has been little cross-talk between these lines of research. Thus, the relationship between oscillatory activity and neurotransmitter concentrations remains to be empirically traced. Importantly, how these indices link back to altered sensory processing has to be clearly established as yet. Accordingly, pharmacologic treatments have been mostly symptom-based, and yet sometimes proving ineffective in resolving pain or related issues. This review provides an integrative theoretical framework of excitation-inhibition imbalance for the understanding of current evidence and to address outstanding questions concerning the pathophysiology of migraine. We propose the use of computational modelling for the rigorous formulation of testable hypotheses on mechanisms of homeostatic imbalance and for the development of mechanism-based pharmacological treatments and neurostimulation interventions.

Tuina for peripherally-induced neuropathic pain: A review of analgesic mechanism

Peripherally-induced neuropathic pain (pNP) is a kind of NP that is common, frequent, and difficult to treat. Tuina, also known as massage and manual therapy, has been used to treat pain in China for thousands of years. It has been clinically proven to be effective in the treatment of pNP caused by cervical spondylosis, lumbar disc herniation, etc. However, its analgesic mechanism is still not clear and has been the focus of research. In this review, we summarize the existing research progress, so as to provide guidance for clinical and basic studies. The analgesic mechanism of tuina is mainly manifested in suppressing peripheral inflammation by regulating the TLR4 pathway and miRNA, modulating ion channels (such as P2X3 and piezo), inhibiting the activation of glial cells, and adjusting the brain functional alterations. Overall, tuina has an analgesic effect by acting on different levels of targets, and it is an effective therapy for the treatment of pNP. It is necessary to continue to study the mechanism of tuina analgesia.

Magnetic resonance spectroscopy studies in migraine

This review summarizes major findings and recent advances in magnetic resonance spectroscopy (MRS) of migraine. A multi database search of PubMed, EMBASE, and Web of Science was performed with variations of magnetic resonance spectroscopy and headache until 20th September 2021. The search generated 2897 studies, 676 which were duplicates and 1836 were not related to headache. Of the remaining 385 studies examined, further exclusions for not migraine (n = 114), and not MRS of human brain (n = 128), and non-original contributions (n = 51) or conferences (n = 24) or case studies (n = 11) or non-English (n = 3), were applied. The manuscripts of all resulting reports were reviewed for their possible inclusion in this manuscript (n = 54). The reference lists of all included reports were carefully reviewed and articles relevant to this review were added (n = 2).Included are 56 studies of migraine with and without aura that involve magnetic resonance spectroscopy of the human brain. The topics are presented in the form of a narrative review. This review aims to provide a summary of the metabolic changes measured by MRS in patients with migraine. Despite the variability reported between studies, common findings focused on regions functionally relevant to migraine such as occipital cortices, thalamic nuclei, cerebellum and cingulate. The most reproducible results were decreased N-acetyl-aspartate (NAA) in cerebellum in patients with hemiplegic migraine and in the thalamus of chronic migraine patients. Increased lactate (Lac) in the occipital cortex was found for migraine with aura but not in subjects without aura. MRS studies support the hypothesis of impaired energetics and mitochondrial dysfunction in migraine. Although results regarding GABA and Glu were less consistent, studies suggest there might be an imbalance of these important inhibitory and excitatory neurotransmitters in the migraine brain. Multinuclear imaging studies in migraine with and without aura, predominantly investigating phosphorous, report alterations of PCr in occipital, parietal, and posterior brain regions. There have been too few studies to assess the diagnostic relevance of sodium imaging in migraine.

Inflammatory Blood Biomarker Kynurenine Is Linked With Elevated Neuroinflammation and Neurodegeneration in Older Adults: Evidence From Two 1H-MRS Post-Processing Analysis Methods

RATIONALE AND OBJECTIVES

Pro-inflammatory processes have been argued to play a role in conditions associated with cognitive decline and neurodegeneration, like aging and obesity. Only a limited number of studies have tried to measure both peripheral and central biomarkers of inflammation and examined their interrelationship. The primary aim of this study was to examine the hypothesis that chronic peripheral inflammation would be associated with neurometabolic changes that indicate neuroinflammation (the combined elevation of myoinositol and choline), brain gray matter volume decrease, and lower cognitive functioning in older adults.

MATERIALS AND METHODS

Seventy-four older adults underwent bio-impedance body composition analysis, cognitive testing with the Montreal Cognitive Assessment (MoCA), blood serum analysis of inflammatory markers interleukin-6 (IL-6) and kynurenine, magnetic resonance imaging (MRI), and proton magnetic resonance spectroscopy (¹H-MRS) of the brain. Neurometabolic findings from both Tarquin and LCModel ¹H-MRS post-processing software packages were compared. The regions of interest for MRI and ¹H-MRS measurements were dorsal posterior cingulate cortex (DPCC), left hippocampal cortex (HPC), left medial temporal cortex (MTC), left primary sensorimotor cortex (SM1), and right dorsolateral prefrontal cortex (DLPFC).

RESULTS

Elevated serum kynurenine levels were associated with signs of neuroinflammation, specifically in the DPCC, left SM1 and right DLPFC, and signs of neurodegeneration, specifically in the left HPC, left MTC and left SM1, after adjusting for age, sex and fat percentage (fat%). Elevated serum IL-6 levels were associated with increased Glx levels in left HPC, left MTC, and right DLPFC, after processing the ¹H-MRS data with Tarquin. Overall, the agreement between Tarquin and LCModel results was moderate-to-strong for tNAA, tCho, mIns, and tCr, but weak to very weak for Glx. Peripheral inflammatory markers (IL-6 and kynurenine) were not associated with older age, higher fat%, decreased brain gray matter volume loss or decreased cognitive functioning within a cohort of older adults.

CONCLUSION

Our results suggest that serum kynurenine may be used as a peripheral inflammatory marker that is associated with neuroinflammation and neurodegeneration, although not linked to cognition. Future studies should consider longitudinal analysis to assess the causal inferences between chronic peripheral and neuroinflammation, brain structural and neurometabolic changes, and cognitive decline in aging.

Mitochondrial dysfunction, oxidative stress, neuroinflammation, and metabolic alterations in the progression of Alzheimer's disease: A meta-analysis of in vivo magnetic resonance spectroscopy studies

Accumulating evidence demonstrates that metabolic changes in the brain associated with neuroinflammation, oxidative stress, and mitochondrial dysfunction play an important role in the pathophysiology of mild cognitive impairment (MCI) and Alzheimer's disease (AD). However, the neural signatures associated with these metabolic alterations and underlying molecular mechanisms are still elusive. Accordingly, we reviewed the literature on in vivo human brain 1H and 31P-MRS studies and use meta-analyses to identify patterns of brain metabolic alterations in MCI and AD. 40 and 39 studies on MCI and AD, respectively, were classified according to brain regions. Our results indicate decreased N-acetyl aspartate and creatine but increased myo-inositol levels in both MCI and AD, decreased glutathione level in MCI as well as disrupted energy metabolism in AD. In addition, the hippocampus shows the strongest alterations in most of these metabolites. This meta-analysis also illustrates progressive metabolite alterations from MCI to AD. Taken together, it suggests that 1) neuroinflammation and oxidative stress may occur in the early stages of AD, and likely precede neuron loss in its progression; 2) the hippocampus is a sensitive region of interest for early diagnosis and monitoring the response of interventions; 3) targeting bioenergetics associated with neuroinflammation/oxidative stress is a promising approach for treating AD.

Meta-Analysis of Neurochemical Changes Estimated via Magnetic Resonance Spectroscopy in Mild Cognitive Impairment and Alzheimer's Disease

The changes of neurochemicals in mild cognitive impairment (MCI) and Alzheimer's disease (AD) patients has been observed via magnetic resonance spectroscopy in several studies. However, whether it exists the consistent pattern of changes of neurochemicals in the encephalic region during the progression of MCI to AD were still not clear. The study performed meta-analysis to investigate the patterns of neurochemical changes in the encephalic region in the progress of AD. We searched the PubMed, Embase, Cochrane Library, and Web of Science databases, and finally included 63 studies comprising 1,086 MCI patients, 1,256 AD patients, and 1,907 healthy controls. It showed that during the progression from MCI to AD, N-acetyl aspartate (NAA) decreased continuously in the posterior cingulate (PC) (SMD: −0.42 [95% CI: −0.62 to −0.21], z = −3.89, P < 0.05), NAA/Cr (creatine) was consistently reduced in PC (SMD: −0.58 [95% CI: −0.86 to −0.30], z = −4.06, P < 0.05) and hippocampus (SMD: −0.65 [95% CI: −1.11 to −0.12], z = −2.44, P < 0.05), while myo-inositol (mI) (SMD: 0.44 [95% CI: 0.26–0.61], z = 4.97, P < 0.05) and mI/Cr (SMD: 0.43 [95% CI: 0.17–0.68], z = 3.30, P < 0.05) were raised in PC. Furthermore, these results were further verified by a sustained decrease in the NAA/mI of PC (SMD: −0.94 [95% CI: −1.24 to −0.65], z = −6.26, P < 0.05). Therefore, the levels of NAA and mI were associated with the cognitive decline and might be used as potentially biomarkers to predict the possible progression from MCI to AD.

Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO/, identifier: CRD42020200308.

Interictal pontine metabolism in migraine without aura patients: A 3 Tesla proton magnetic resonance spectroscopy study

In the pons, glutamatergic mechanisms are involved in regulating inhibitory descending pain modulation, serotoninergic neurotransmission as well as modulating the sensory transmission of the trigeminovascular system. Migraine involves altered pontine activation and structural changes, while biochemical, genetic and clinical evidence suggests that altered interictal pontine glutamate levels may be an important pathophysiological feature of migraine abetting to attack initiation. Migraine without aura patients were scanned outside attacks using a proton magnetic resonance spectroscopy protocol optimized for the pons at 3 Tesla. The measurements were performed on two separate days to increase accuracy and compared to similar repeated measurements in healthy controls. We found that interictal glutamate (i.e. Glx) levels in the pons of migraine patients (n = 33) were not different from healthy controls (n = 16) (p = 0.098), while total creatine levels were markedly increased in patients (9%, p = 0.009). There was no correlation of glutamate or total creatine levels to migraine frequency, days since the last attack, usual pain intensity of attacks or disease duration. In conclusion, migraine is not associated with altered interictal pontine glutamate levels. However, the novel finding of increased total creatine levels suggests that disequilibrium in the pontine energy metabolism could be an important feature of migraine pathophysiology.

Increased GABA+ in People With Migraine, Headache, and Pain Conditions- A Potential Marker of Pain

Treatment outcomes for migraine and other chronic headache and pain conditions typically demonstrate modest results. A greater understanding of underlying pain mechanisms may better inform treatments and improve outcomes. Increased GABA+ has been identified in recent studies of migraine, however, it is unclear if this is present in other headache, and pain conditions. We primarily investigated GABA+ levels in the posterior cingulate gyrus (PCG) of people with migraine, whiplash-headache and low back pain compared to age- and sex-matched controls, GABA+ levels in the anterior cingulate cortex (ACC) and thalamus formed secondary aims. Using a cross-sectional design, we studied people with migraine, whiplash-headache or low back pain (n = 56) and compared them with a pool of age- and sex-matched controls (n = 22). We used spectral-edited magnetic resonance spectroscopy at 3T (MEGA-PRESS) to determine levels of GABA+ in the PCG, ACC and thalamus. PCG GABA+ levels were significantly higher in people with migraine and low back pain compared with controls (eg, migraine 4.89 IU ± 0.62 vs controls 4.62 IU ± 0.38; P = .02). Higher GABA+ levels in the PCG were not unique to migraine and could reflect a mechanism of chronic pain in general. A better understanding of pain at a neurochemical level informs the development of treatments that target aberrant brain neurochemistry to improve patient outcomes. PERSPECTIVE: This study provides insights into the underlying mechanisms of chronic pain. Higher levels of GABA+ in the PCG may reflect an underlying mechanism of chronic headache and pain conditions. This knowledge may help improve patient outcomes through developing treatments that specifically address this aberrant brain neurochemistry.

3D magnetic resonance spectroscopic imaging reveals links between brain metabolites and multidimensional pain features in fibromyalgia

BACKGROUND

Fibromyalgia is a centralized multidimensional chronic pain syndrome, but its pathophysiology is not fully understood.

METHODS

We applied 3D magnetic resonance spectroscopic imaging (MRSI), covering multiple cortical and subcortical brain regions, to investigate the association between neuro-metabolite (e.g. combined glutamate and glutamine, Glx; myo-inositol, mIno; and combined (total) N-acetylaspartate and N-acetylaspartylglutamate, tNAA) levels and multidimensional clinical/behavioural variables (e.g. pain catastrophizing, clinical pain severity and evoked pain sensitivity) in women with fibromyalgia (N = 87).

RESULTS

Pain catastrophizing scores were positively correlated with Glx and tNAA levels in insular cortex, and negatively correlated with mIno levels in posterior cingulate cortex (PCC). Clinical pain severity was positively correlated with Glx levels in insula and PCC, and with tNAA levels in anterior midcingulate cortex (aMCC), but negatively correlated with mIno levels in aMCC and thalamus. Evoked pain sensitivity was negatively correlated with levels of tNAA in insular cortex, MCC, PCC and thalamus.

CONCLUSIONS

These findings support single voxel placement targeting nociceptive processing areas in prior ¹ H-MRS studies, but also highlight other areas not as commonly targeted, such as PCC, as important for chronic pain pathophysiology. Identifying target brain regions linked to multidimensional symptoms of fibromyalgia (e.g. negative cognitive/affective response to pain, clinical pain, evoked pain sensitivity) may aid the development of neuromodulatory and individualized therapies. Furthermore, efficient multi-region sampling with 3D MRSI could reduce the burden of lengthy scan time for clinical research applications of molecular brain-based mechanisms supporting multidimensional aspects of fibromyalgia.

SIGNIFICANCE

This large N study linked brain metabolites and pain features in fibromyalgia patients, with a better spatial resolution and brain coverage, to understand a molecular mechanism underlying pain catastrophizing and other aspects of pain transmission. Metabolite levels in self-referential cognitive processing area as well as pain-processing regions were associated with pain outcomes. These results could help the understanding of its pathophysiology and treatment strategies for clinicians.

Altered hippocampal astroglial metabolism is associated with aging and preserved spatial learning and memory

An age-related decrease in hippocampal metabolism correlates with cognitive decline. Hippocampus-dependent learning and memory requires glutamatergic neurotransmission supported by glutamate-glutamine (GLU-GLN) cycling between neurons and astrocytes. We examined whether GLU-GLN cycling in hippocampal subregions (dentate gyrus and CA1) in Fischer 344 rats was altered with age and cognitive status. Hippocampal slices from young adult, aged cognitively-unimpaired (AU) and aged cognitively-impaired (AI) rats were incubated in artificial cerebrospinal fluid (aCSF) containing 1-13C-glucose to assess neural metabolism. Incorporation of 13C-glucose into glutamate and glutamine, measured by mass spectroscopy/liquid chromatography tandem mass spectroscopy, did not significantly differ between groups. However, when 13C-acetate, a preferential astrocytic metabolite, was used, a significant increase in 13C-labeled glutamate was observed in slices from AU rats. Taken together, the data suggest that resting state neural metabolism and GLU-GLN cycling may be preserved during aging when sufficient extracellular glucose is available, but that enhanced astroglial metabolism can occur under resting state conditions. This may be an aging-related compensatory change to maintain hippocampus-dependent cognitive function.

Elevated Brain Glutamate Levels in Bipolar Disorder and Pyruvate Carboxylase-Mediated Anaplerosis

In vivo ¹H magnetic resonance spectroscopy studies have found elevated brain glutamate or glutamate + glutamine levels in bipolar disorder with surprisingly high reproducibility. We propose that the elevated glutamate levels in bipolar disorder can be explained by increased pyruvate carboxylase-mediated anaplerosis in brain. Multiple independent lines of evidence supporting increased pyruvate carboxylase-mediated anaplerosis as a common mechanism underlying glutamatergic hyperactivity in bipolar disorder and the positive association between bipolar disorder and obesity are also described.

Altered thalamic neurotransmitters metabolism and functional connectivity during the development of chronic constriction injury induced neuropathic pain

Background

To investigate the thalamic neurotransmitters and functional connections in the development of chronic constriction injury (CCI)-induced neuropathic pain.

Methods

The paw withdrawal threshold was measured by mechanical stimulation the right hind paw with the von frey hair in the rats of CCI-induced neuropathic pain. The N-acetylaspartate (NAA) and Glutamate (Glu) in thalamus were detected by magnetic resonance spectrum (MRS) process. The thalamic functional connectivity with other brain regions was scanned by functional magnetic resonance image (fMRI).

Results

The paw withdrawal threshold of the ipsilateral side showed a noticeable decline during the pathological process. Increased concentrations of Glu and decreased levels of NAA in the thalamus were significantly correlated with mechanical allodynia in the neuropathic pain states. The thalamic regional homogeneity (ReHo) decreased during the process of neuropathic pain. The functional connectivity among the thalamus with the insula and somatosensory cortex were significantly increased at different time points (7, 14, 21 days) after CCI surgery.

Conclusion

Our study suggests that dynamic changes in thalamic NAA and Glu levels contribute to the thalamic functional connection hyper-excitation during CCI-induced neuropathic pain. Enhanced thalamus-insula functional connection might have a significant effect on the occurrence of neuropathic pain.

Magnetic Resonance Imaging in Pediatric Migraine

This literature review provides an overview of the research using magnetic resonance imaging (MRI) in pediatric migraine and compares findings with the adult migraine literature. A literature search using PubMed was conducted using all relevant sources up to February 2019. Using MRI methods to categorize and explain pediatric migraine in comparison with adult migraine is important, in order to recognize and appreciate the differences between the two entities, both clinically and physiologically. We aim to demonstrate the differences and similarities between pediatric and adult migraine using data from white matter and gray matter structural studies, cerebral perfusion, metabolites, and functional MRI (fMRI) studies, including task-based and resting-state blood oxygen level-dependent studies. By doing this we identify areas that need further research, as well as possible areas where intervention could alter outcomes.

Reduced excitatory neurotransmitter levels in anterior insulae are associated with abdominal pain in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a visceral pain condition with psychological comorbidity. Brain imaging studies in IBS demonstrate altered function in anterior insula (aINS), a key hub for integration of interoceptive, affective, and cognitive processes. However, alterations in aINS excitatory and inhibitory neurotransmission as putative biochemical underpinnings of these functional changes remain elusive. Using quantitative magnetic resonance spectroscopy, we compared women with IBS and healthy women (healthy controls [HC]) with respect to aINS glutamate + glutamine (Glx) and γ-aminobutyric acid (GABA+) concentrations and addressed possible associations with symptoms. Thirty-nine women with IBS and 21 HC underwent quantitative magnetic resonance spectroscopy of bilateral aINS to assess Glx and GABA+ concentrations. Questionnaire data from all participants and prospective symptom-diary data from patients were obtained for regression analyses of neurotransmitter concentrations with IBS-related and psychological parameters. Concentrations of Glx were lower in IBS compared with HC (left aINS P < 0.05, right aINS P < 0.001), whereas no group differences were detected for GABA+ concentrations. Lower right-lateralized Glx concentrations in patients were substantially predicted by longer pain duration, while less frequent use of adaptive pain-coping predicted lower Glx in left aINS. Our findings provide first evidence for reduced excitatory but unaltered inhibitory neurotransmitter levels in aINS in IBS. The results also indicate a functional lateralization of aINS with a stronger involvement of the right hemisphere in perception of abdominal pain and of the left aINS in cognitive pain regulation. Our findings suggest that glutaminergic deficiency may play a role in pain processing in IBS.

Advanced Imaging in the Evaluation of Migraine Headaches

The use of advanced imaging in routine diagnostic practice appears to provide only limited value in patients with migraine who have not experienced recent changes in headache characteristics or symptoms. However, advanced imaging may have potential for studying the biological manifestations and pathophysiology of migraine headaches. Migraine with aura appears to have characteristic spatiotemporal changes in structural anatomy, function, hemodynamics, metabolism, and biochemistry, whereas migraine without aura produces more subtle and complex changes. Large, controlled, multicenter imaging-based observational trials are needed to confirm the anecdotal evidence in the literature and test the scientific hypotheses thought to underscore migraine pathophysiology.

Structural and functional abnormalities of the insular cortex in trigeminal neuralgia: a multimodal magnetic resonance imaging analysis

Trigeminal neuralgia (TN) is a chronic neuropathic pain disorder characterized by intense, lancinating attacks of facial pain. Increasing evidence suggests that TN is accompanied by abnormalities in brain morphology, white matter microstructure, and function. However, whether these abnormalities are linked or reflect independent etiologies remains unknown. Using multimodal magnetic resonance imaging data of 20 patients with TN and 21 healthy controls, we investigated cortical gyrification abnormalities, their relationships with abnormalities of the underlying white matter microstructure and gray matter morphology, as well as their functional significance in TN. Compared with controls, patients with TN showed significant local gyrification index (LGI) reductions predominantly in the left insular cortex, which were negatively correlated with pain intensity. In this cluster, patients with TN had concurrent cortical thickness reductions but unaltered cortical surface area. Meanwhile, LGI of this cluster was not correlated with overlying cortical thickness or surface area but was positively correlated with the fractional anisotropy of 2 nearby white matter clusters, suggesting that insular LGI reductions may be primarily driven by microstructural abnormalities of the underlying white matter tracts, rather than by abnormalities in cortical thickness and surface area. In addition, patients with TN exhibited increased insula functional connectivity to the left posterior cingulate cortex and thalamus, which was positively correlated with disease duration. These findings provide new evidence for the involvement of insular abnormalities in the pathophysiology of TN.

Inflammation, Glutamate, and Cognition in Bipolar Disorder Type II: A Proof of Concept Study

Background: Two current theories regarding the neuroscientific bases of mood disorders involve alterations in glutamatergic neurotransmission and excessive activation of inflammatory pathways. We hypothesized that glutamate (Glu) levels and peripheral inflammatory markers would be associated with cognitive function, in patients with Bipolar Disorder Type II (BP-II), and that such factors would be associated with psychological treatment outcomes. Aims: The primary aim of this study was to explore the relationship between the neurotransmitter Glu, cytokines (CRP, IL_6, and TNFa) and neuropsychological and related functioning. The secondary aim was to assess cognitive functioning as a predictor of poor response to psychological therapy. Methods: Proton magnetic resonance spectroscopy data were acquired from the anterior cingulate cortex (ACC) of 15 participants with BP-II, and 13 healthy controls in a 3T magnetic resonance imaging scanner. The Digit Symbol Task (DST) for processing speed, TMT-B for executive function and Rey Auditory Verbal Learning Test (RAVLT) were administered to assess cognitive domains. Results: There was no significant difference in anterior cingulate Glu, or inflammatory markers between groups. Furthermore, we found no significant difference between groups in any cognitive tests. Scores on the DST were found to be significantly associated with poor response to psychological therapy. Conclusions: This study may highlight an association between neuropsychological dysfunction and treatment outcome in euthymic patients with BP-II. We did not find any association between peripheral inflammatory markers and brain Glu levels. This may have been in part due to the small sample size.

Metabolite Profile of Alzheimer's Disease in the Frontal Cortex as Analyzed by HRMAS 1H NMR

Background: Investigation on neurochemical changes in the frontal cortex in individuals with Alzheimer’s disease (AD) and different Apolipoprotein E (APOE) genotypes, using ex vivo solid-state high-resolution NMR analysis, may lead to a better understanding of the neurochemistry associated with AD as well as new AD-specific metabolite biomarkers that might potentially improve the clinical diagnosis of AD.

Methods: Intact tissue samples of the frontal cortex were obtained from 11 patients and 11 age-matched non-demented controls. Metabolite profiles in all samples were analyzed ex vivo, using solid-state high-resolution magic angle spinning (HRMAS) 600 MHz ¹H nuclear magnetic resonance (NMR). A logistic regression analysis was used to rank metabolites based on their level of contribution in differentiating the AD patient tissues and the controls, and different AD-associated APOE genotypes (APOE ε4 vs. APOE ε3).

Results: Tissue samples from the AD patients showed significantly lower NAA/Cr (p = 0.011), Ace/Cr (p = 0.027), GABA/Cr (p = 0.005), Asp/Cr (p < 0.0001), mI/Cr (p < 0.0001), and Tau/Cr (p = 0.021), and higher PCho/Cr (p < 0.0001), GPCho/Cr (p < 0.0001), and α&β-Glc/Cr (p < 0.0001) than the controls did. Specifically, a newly observed resonance at 3.71 ppm, referred to as α&β-Glc, was observed in 90.9% of the AD samples (10/11). Samples with APOE ε4 also exhibited higher PCho/Cr (p = 0.0002), GPCho/Cr (p = 0.0001), α&β-Glc/Cr (p < 0.0001), and lower Asp/Cr (p = 0.004) and GABA/Cr (p = 0.04) than the samples with APOE ε3 did. In the logistic regression analysis, PCho, GPCho, ASP, and α&β-Glc were found to be the most relevant metabolites for differentiating the AD patient tissues and the controls, and different APOE genotypes.

Conclusion: HRMAS ¹H NMR with high spectral resolution and sensitivity offers a powerful tool to gain quantitative information on AD associated neurochemical changes. There are important neurochemical differences in the frontal cortex between the AD patient tissues and the controls, and between those with different APOE genotypes. The resonance (α&β-Glc) found at 3.71 ppm in the AD patient tissues may be further investigated for its potential in the diagnosis and monitoring of AD.

Measuring Glutamate Levels in the Brains of Fibromyalgia Patients and a Potential Role for Glutamate in the Pathophysiology of Fibromyalgia Symptoms: A Systematic Review

OBJECTIVES

The aim of this study was to systematically review the literature concerning proton magnetic resonance spectroscopy (H-MRS) measured glutamate levels in specific brain regions of fibromyalgia (FM) patients to determine if there is a correlation between raised glutamate levels and the presentation of FM.

MATERIALS AND METHODS

The electronic databases-MEDLINE, EMBASE Classic+Embase, PsychINFO, Cochrane Database of Systematic Reviews, Cochrane Database of Abstracts of Reviews of Effect, Cochrane Central Register of Controlled Trials-were searched to find original studies that used H-MRS to measure glutamate concentrations in the brains of FM patients.

RESULTS

Nine studies with a total of 482 participants were selected for inclusion in the review. Seven of the 8 studies that investigated an association between cerebral glutamate levels and FM, showed a positive association. Brain regions identified as having increased glutamate levels include the posterior cingulate gyrus, posterior insula, ventrolateral prefrontal cortex, and amygdala. One study reported a decrease in glutamate levels in the hippocampus of FM patients compared with healthy controls. Seven of the 8 studies that analyzed the correlations between cerebral glutamate levels and FM symptoms, found a significant positive correlation.

DISCUSSION

Although the cause of FM remains inconclusive, there is converging data in favor of a dysregulation of pain processing in the central nervous system of FM patients, particularly associated with an increase in cerebral glutamate levels. Furthermore, there is evidence to support an association between increased glutamate levels and an increase in FM symptoms.

Could dietary glutamate be contributing to the symptoms of obsessive-compulsive disorder?

A 50-year-old man who had suffered from daily obsessive-compulsive disorder (OCD) symptoms for 39 years, in addition to fibromyalgia and irritable bowel syndrome symptoms, was enrolled in a randomized double-blind placebo-controlled clinical trial to test the effects of a low-glutamate diet on fibromyalgia/irritable bowel syndrome symptoms. After 1 month on the low-glutamate diet all of his symptoms remitted, including his OCD, which had previously been nonresponsive to pharmacological treatment. This case study is limited by self-report of symptoms; however, glutamatergic neurotransmission appears to be dysregulated in OCD, suggesting biological plausibility for this observation. Future research is needed.

Reduced cognitive function, increased blood-brain-barrier transport and inflammatory responses, and altered brain metabolites in LDLr -/-and C57BL/6 mice fed a western diet

Recent work suggests that diet affects brain metabolism thereby impacting cognitive function. Our objective was to determine if a western diet altered brain metabolism, increased blood-brain barrier (BBB) transport and inflammation, and induced cognitive impairment in C57BL/6 (WT) mice and low-density lipoprotein receptor null (LDLr -/-) mice, a model of hyperlipidemia and cognitive decline. We show that a western diet and LDLr -/- moderately influence cognitive processes as assessed by Y-maze and radial arm water maze. Also, western diet significantly increased BBB transport, as well as microvessel factor VIII in LDLr -/- and microglia IBA1 staining in WT, both indicators of activation and neuroinflammation. Interestingly, LDLr -/- mice had a significant increase in ¹⁸F- fluorodeoxyglucose uptake irrespective of diet and brain ¹H-magnetic resonance spectroscopy showed increased lactate and lipid moieties. Metabolic assessments of whole mouse brain by GC/MS and LC/MS/MS showed that a western diet altered brain TCA cycle and β-oxidation intermediates, levels of amino acids, and complex lipid levels and elevated proinflammatory lipid mediators. Our study reveals that the western diet has multiple impacts on brain metabolism, physiology, and altered cognitive function that likely manifest via multiple cellular pathways.

A pilot study of the metabolomic profiles of saliva from female orthodontic patients with external apical root resorption

BACKGROUND

Orthodontically induced external apical root resorption (OIEARR) is one of the most severe complications of orthodontic treatment, which is hard to diagnose at early stage by merely radiographic examination. This study aimed to identify salivary metabolic products using unbiased metabolic profiling in order to discover biomarkers that may indicate OIEARR.

MATERIALS AND METHODS

Unstimulated saliva samples were analyzed from 19 healthy orthodontic patients with EARR (n=8) and non-EARR (n=11). Metabolite profiling was performed using ¹H Nuclear Magnetic Resonance (NMR) spectroscopy.

RESULTS

A total of 187 metabolites were found in saliva samples. With supervised partial least squares discriminant analysis and regression analysis, samples from 2 groups were well separated, attributed by a series of metabolites of interest, including butyrate, propane-1,2-diol, α-linolenic acid (Ala), α-glucose, urea, fumarate, formate, guanosine, purine, etc. Indicating the increased inflammatory responses in the periodontal tissues possibly associated with energy metabolism and oxidative stress.

CONCLUSIONS

The effective separation capacity of ¹H NMR based metabolomics suggested potential feasibility of clinical application in monitoring periodontal and apical condition in orthodontic patients during treatment and make early diagnosis of OIEARR. Metabolites detected in this study need further validation to identify exact biomarkers of OIEARR. Saliva biomarkers may assist in diagnosis and monitoring of this disease.

Lower brain and blood nutrient status in Alzheimer's disease: Results from meta-analyses

INTRODUCTION

Alzheimer's disease (AD) patients are at risk of nutritional insufficiencies because of physiological and psychological factors. Recently, we showed the results of the meta-analyses indicating lower plasma levels of vitamins A, B12, C, E, and folate in AD patients compared with cognitively intact elderly controls (controls). Now, additional and more extensive literature searches were performed selecting studies which compare blood and brain/cerebrospinal fluid (CSF) levels of vitamins, minerals, trace elements, micronutrients, and fatty acids in AD patients versus controls.

METHODS

The literature published after 1980 in Cochrane Central Register of Controlled Trials, Medline, and Embase electronic databases was systematically analyzed using Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines to detect studies meeting the selection criteria. Search terms used are as follows: AD patients, Controls, vitamins, minerals, trace elements, micronutrients, and fatty acids. Random-effects meta-analyses using a linear mixed model with correction for age differences between AD patients and controls were performed when four or more publications were retrieved for a specific nutrient.

RESULTS

Random-effects meta-analyses of 116 selected publications showed significant lower CSF/brain levels of docosahexaenoic acid (DHA), choline-containing lipids, folate, vitamin B12, vitamin C, and vitamin E. In addition, AD patients showed lower circulatory levels of DHA, eicosapentaenoic acid, choline as phosphatidylcholine, and selenium.

CONCLUSION

The current data show that patients with AD have lower CSF/brain availability of DHA, choline, vitamin B12, folate, vitamin C, and vitamin E. Directionally, brain nutrient status appears to parallel the lower circulatory nutrient status; however, more studies are required measuring simultaneously circulatory and central nutrient status to obtain better insight in this observation. The brain is dependent on nutrient supply from the circulation, which in combination with nutrient involvement in AD-pathophysiological mechanisms suggests that patients with AD may have specific nutritional requirements. This hypothesis could be tested using a multicomponent nutritional intervention.

Higher visceral fat is associated with lower cerebral N-acetyl-aspartate ratios in middle-aged adults

Excessive adipose tissue, particularly with a central distribution, consists of visceral fat, which is metabolically active and could impinge upon central nervous system functioning. The aim of the current study was to examine levels of visceral adiposity in relation to key cerebral metabolite ratios localized in the occipitoparietal grey matter. Seventy-three adults, aged between 40 and 60 years, underwent structural magnetic resonance imaging and single voxel ¹H Magnetic Resonance Spectroscopy (¹H MRS). Visceral fat was assessed using Dual Energy X Ray Absorptiometry (DXA). Individuals with higher visceral fat mass and volume had significantly lower ratios of N-acetyl-aspartate to total creatine (phosphocreatine + creatine, PCr + Cr) (NAA/PCr + Cr) (β = -0.29, p = 0.03, β = -0.28, p = 0.04). They also had significantly higher ratios of myo-inositol to total creatine (mI/PCr + Cr ) (β = 0.36, p = 0.01, β = 0.36, p = 0.01). Visceral fat mass and volume were not significantly related to ratios of glutamate to total creatine (Glu/PCr + Cr). While future studies are necessary, these results indicate central adiposity is associated with metabolic changes that could impinge upon the central nervous system in middle age.

Structural Brain Imaging in People With Low Back Pain

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

The aim of this study was to determine whether low back pain (subacute and chronic) is related to differences in brain volume.

SUMMARY OF BACKGROUND DATA

Inconsistent findings have been reported about the effect of chronic low back pain on brain volume, and the effect of subacute low back pain on brain volume has not been sufficiently investigated.

METHODS

A total of 130 participants were included (23 subacute and 68 chronic low back pain; 39 healthy controls). The main outcome measure was whole and regional brain volume. Clinical outcome measures included pain duration, pain intensity, fear avoidance belief questionnaire, Oswestry Disability Index, and Beck's Depression Inventory.

RESULTS

Decrease in brain volume in several regions was observed in chronic low back pain when compared with health subjects; however, after correcting for multiple comparisons, no significant differences were detected between any of the three groups in whole-brain volume. Regionally, we detected less gray matter volume in two voxels in the middle frontal gyrus in chronic low back pain participants compared with healthy controls. None of the clinical outcome measures were correlated with brain volume measurements.

CONCLUSION

Low back pain (subacute or chronic) is not related to significant differences in brain volume after correction for multiple comparisons. The effect size was too small to detect possible subtle changes unless much larger sample sizes are examined, or it is possible that low back pain does not affect brain volume.

LEVEL OF EVIDENCE

5.

Region-specific aging of the human brain as evidenced by neurochemical profiles measured noninvasively in the posterior cingulate cortex and the occipital lobe using 1H magnetic resonance spectroscopy at 7 T

The concentrations of fourteen neurochemicals associated with metabolism, neurotransmission, antioxidant capacity, and cellular structure were measured noninvasively from two distinct brain regions using ¹H magnetic resonance spectroscopy. Seventeen young adults (age 19-22years) and sixteen cognitively normal older adults (age 70-88years) were scanned. To increase sensitivity and specificity, ¹H magnetic resonance spectra were obtained at the ultra-high field of 7T and at ultra-short echo time. The concentrations of neurochemicals were determined using water as an internal reference and accounting for gray matter, white matter, and cerebrospinal fluid content of the volume of interest. In the posterior cingulate cortex (PCC), the concentrations of neurochemicals associated with energy (i.e., creatine plus phosphocreatine), membrane turnover (i.e., choline containing compounds), and gliosis (i.e., myo-inositol) were higher in the older adults while the concentrations of N-acetylaspartylglutamate (NAAG) and phosphorylethanolamine (PE) were lower. In the occipital cortex (OCC), the concentration of N-acetylaspartate (NAA), a marker of neuronal viability, concentrations of the neurotransmitters Glu and NAAG, antioxidant ascorbate (Asc), and PE were lower in the older adults while the concentration of choline containing compounds was higher. Altogether, these findings shed light on how the human brain ages differently depending on region.

Magnetic resonance spectroscopy and brain volumetry in mild cognitive impairment. A prospective study

OBJECTIVE

To assess the accuracy of magnetic resonance spectroscopy (1H-MRS) and brain volumetry in mild cognitive impairment (MCI) to predict conversion to probable Alzheimer's disease (AD).

METHODS

Forty-eight patients fulfilling the criteria of amnestic MCI who underwent a conventional magnetic resonance imaging (MRI) followed by MRS, and T1-3D on 1.5 Tesla MR unit. At baseline the patients underwent neuropsychological examination. 1H-MRS of the brain was carried out by exploring the left medial occipital lobe and ventral posterior cingulated cortex (vPCC) using the LCModel software. A high resolution T1-3D sequence was acquired to carry out the volumetric measurement. A cortical and subcortical parcellation strategy was used to obtain the volumes of each area within the brain. The patients were followed up to detect conversion to probable AD.

RESULTS

After a 3-year follow-up, 15 (31.2%) patients converted to AD. The myo-inositol in the occipital cortex and glutamate+glutamine (Glx) in the posterior cingulate cortex predicted conversion to probable AD at 46.1% sensitivity and 90.6% specificity. The positive predictive value was 66.7%, and the negative predictive value was 80.6%, with an overall cross-validated classification accuracy of 77.8%. The volume of the third ventricle, the total white matter and entorhinal cortex predict conversion to probable AD at 46.7% sensitivity and 90.9% specificity. The positive predictive value was 70%, and the negative predictive value was 78.9%, with an overall cross-validated classification accuracy of 77.1%. Combining volumetric measures in addition to the MRS measures the prediction to probable AD has a 38.5% sensitivity and 87.5% specificity, with a positive predictive value of 55.6%, a negative predictive value of 77.8% and an overall accuracy of 73.3%.

CONCLUSION

Either MRS or brain volumetric measures are markers separately of cognitive decline and may serve as a noninvasive tool to monitor cognitive changes and progression to dementia in patients with amnestic MCI, but the results do not support the routine use in the clinical settings.

Magnetic Resonance Spectroscopy in Alzheimer's Disease: Systematic Review and Meta-Analysis

BACKGROUND

The application of non-invasive proton magnetic resonance spectroscopy (1H-MRS) could potentially identify changes in cerebral metabolites in the patients with Alzheimer's disease (AD). However, whether these metabolites can serve as biomarkers for the diagnosis of AD remains unclear.

OBJECTIVE

Using meta-analysis, we aimed to investigate the patterns of cerebral metabolite changes in several cerebral regions that are strongly associated with cognitive decline in AD patients.

METHODS

Using Hedges' g effect size, a systematic search was performed in PubMed, Cochrane Library, Ovid, Embase, and EBSCO, and 38 studies were integrated into the final meta-analysis.

RESULTS

According to the observational studies, N-acetyl aspartate (NAA) in AD patients was significantly reduced in the posterior cingulate (PC) (effect size (ES) =-0.924, p <  0.005) and bilateral hippocampus (left hippocampus: ES =-1.329, p <  0.005; right hippocampus: ES =-1.287, p <  0.005). NAA/Cr (creatine) ratio decreased markedly in the PC (ES =-1.052, p <  0.005). Simultaneously, significant elevated myo-inositol (mI)/Cr ratio was found not only in the PC but also in the parietal gray matter. For lack of sufficient data, we failed to elucidate the efficacy of pharmacological interventions with the metabolites changes.

CONCLUSION

The available data indicates that NAA, mI, and the NAA/Cr ratio might be potential biomarkers of brain dysfunction in AD subjects. Choline (Cho)/Cr and mI/NAA changes might also contribute toward the diagnostic process. Thus, large, well-designed studies correlated with cerebral metabolism are needed to better estimate the cerebral extent of alterations in brain metabolite levels in AD patients.

The Association Between Clinical Characteristics of Migraine and Brain GABA Levels: An Exploratory Study

Migraine is prevalent and disabling yet is poorly understood. One way to better understand migraine is to examine its clinical characteristics and potential biomarkers such as gamma-aminobutyric acid (GABA). The primary objective of this study was to explore whether relevant disease characteristics of migraine are associated with brain GABA levels. Twenty adults fulfilling the established diagnostic criteria for migraine and 20 age- and gender-matched controls completed this cross-sectional study. Pain, central sensitization, negative emotional state, and perceived disability were measured using Short-form McGill Pain Questionnaire-2, Central Sensitization Inventory, Depression Anxiety Stress Scales-21, and Headache Impact Test-6, respectively. Secondary analysis of brain GABA levels of the same cohort measured using proton magnetic resonance spectroscopy was conducted. The migraine group had significantly higher scores than the control group on pain, central sensitization, and disability. Correlation analyses showed fair positive association between GABA levels and pain and central sensitization scores. No association was found between GABA levels and emotional state and disability. These findings are preliminary evidence supporting the use of questionnaires and GABA levels in characterizing migraine better and broadening the diagnostic process. These findings also strengthen the rationale for the role of GABA in migraine pathophysiology and corroborate the potential of GABA as a migraine biomarker.

PERSPECTIVE

Higher pain and central sensitization scores were associated with increased brain GABA levels in individuals with migraine. These findings offer preliminary evidence for the usefulness of measuring pain and central sensitization in migraine and provide some support for the possible role of GABA in migraine pathophysiology and its potential as a diagnostic marker.

Nutrient intake and cerebral metabolism in healthy middle-aged adults: Implications for cognitive aging

OBJECTIVES

Growing evidence suggests dietary factors influence cognition, but the effects of nutrient intake on cerebral metabolism in adults are currently unknown. The present study investigated the relationship between major macronutrient intake (fat, carbohydrate, and protein) and cerebral neurochemical profiles in middle-aged adults.

METHODS

Thirty-six adults recorded dietary intake for 3 days prior to completing cognitive testing and a proton magnetic resonance spectroscopy (¹H-MRS) scan. ¹H-MRS of occipitoparietal gray matter was used to assess glutamate (Glu), N-acetyl-aspartate (NAA), choline (Cho), and myo-inositol (mI) relative to creatine (Cr) levels.

RESULTS

Regression analyses revealed that high intake of polyunsaturated fatty acids (PUFAs) was associated with lower cerebral Glu/Cr (P = 0.005), and high intake of saturated fat (SFA) was associated with poorer memory function (P = 0.030) independent of age, sex, education, estimated intelligence, total caloric intake, and body mass index.

DISCUSSION

In midlife, greater PUFA intake (ω-3 and ω-6) may be associated with lower cerebral glutamate, potentially indicating more efficient cellular reuptake of glutamate. SFA intake, on the other hand, was linked with poorer memory performance. These results suggest that dietary fat intake modification may be an important intervention target for the prevention of cognitive decline.

State-of-art neuroanatomical target analysis of high-definition and conventional tDCS montages used for migraine and pain control

Although transcranial direct current stimulation (tDCS) studies promise to modulate cortical regions associated with pain, the electric current produced usually spreads beyond the area of the electrodes' placement. Using a forward-model analysis, this study compared the neuroanatomic location and strength of the predicted electric current peaks, at cortical and subcortical levels, induced by conventional and High-Definition-tDCS (HD-tDCS) montages developed for migraine and other chronic pain disorders. The electrodes were positioned in accordance with the 10-20 or 10-10 electroencephalogram (EEG) landmarks: motor cortex-supraorbital (M1-SO, anode and cathode over C3 and Fp2, respectively), dorsolateral prefrontal cortex (PFC) bilateral (DLPFC, anode over F3, cathode over F4), vertex-occipital cortex (anode over Cz and cathode over Oz), HD-tDCS 4 × 1 (one anode on C3, and four cathodes over Cz, F3, T7, and P3) and HD-tDCS 2 × 2 (two anodes over C3/C5 and two cathodes over FC3/FC5). M1-SO produced a large current flow in the PFC. Peaks of current flow also occurred in deeper brain structures, such as the cingulate cortex, insula, thalamus and brainstem. The same structures received significant amount of current with Cz-Oz and DLPFC tDCS. However, there were differences in the current flow to outer cortical regions. The visual cortex, cingulate and thalamus received the majority of the current flow with the Cz-Oz, while the anterior parts of the superior and middle frontal gyri displayed an intense amount of current with DLPFC montage. HD-tDCS montages enhanced the focality, producing peaks of current in subcortical areas at negligible levels. This study provides novel information regarding the neuroanatomical distribution and strength of the electric current using several tDCS montages applied for migraine and pain control. Such information may help clinicians and researchers in deciding the most appropriate tDCS montage to treat each pain disorder.

Neuroimaging of chronic pain

Chronic pain is an important public health problem, and there is a need to understand the mechanisms that lead to pain chronification. From a neurobiological perspective, the mechanisms contributing to the transition from acute to subacute and chronic pain are heterogeneous and are thought to take place at various levels of the peripheral and central nervous system. In the past decade, brain imaging studies have shed light on neural correlates of pain perception and pain modulation, but they have also begun to disentangle neural mechanisms that underlie chronic pain. This review summarizes important and recent findings in pain research using magnetic resonance tomography. Especially new developments in functional, structural and neurochemical imaging such as resting-state connectivity and γ-aminobutyric acid (GABA) spectroscopy, which have advanced our understanding of chronic pain and which can potentially be integrated in clinical practice, will be discussed.