In vivo measurements of glutamate, GABA, and NAAG in schizophrenia

The major excitatory and inhibitory neurotransmitters, glutamate (Glu) and gamma-aminobutyric acid (GABA), respectively, are implicated in the pathophysiology of schizophrenia. N-acetyl-aspartyl-glutamate (NAAG), a neuropeptide that modulates the Glu system, may also be altered in schizophrenia. This study investigated GABA, Glu + glutamine (Glx), and NAAG levels in younger and older subjects with schizophrenia. Forty-one subjects, 21 with chronic schizophrenia and 20 healthy controls, participated in this study. Proton magnetic resonance spectroscopy ((1)H-MRS) was used to measure GABA, Glx, and NAAG levels in the anterior cingulate (AC) and centrum semiovale (CSO) regions. NAAG in the CSO was higher in younger schizophrenia subjects compared with younger control subjects. The opposite pattern was observed in the older groups. Glx was reduced in the schizophrenia group irrespective of age group and brain region. There was a trend for reduced AC GABA in older schizophrenia subjects compared with older control subjects. Poor attention performance was correlated to lower AC GABA levels in both groups. Higher levels of CSO NAAG were associated with greater negative symptom severity in schizophrenia. These results provide support for altered glutamatergic and GABAergic function associated with illness course and cognitive and negative symptoms in schizophrenia. The study also highlights the importance of studies that combine MRS measurements of NAAG, GABA, and Glu for a more comprehensive neurochemical characterization of schizophrenia.

Differential impact of hyponatremia and hepatic encephalopathy on health-related quality of life and brain metabolite abnormalities in cirrhosis

BACKGROUND & AIMS

Hyponatremia (HN) and hepatic encephalopathy (HE) together can impair health-related quality of life (HRQOL) and cognition in cirrhosis. We aimed at studying the effect of hyponatremia on cognition, HRQOL, and brain MR spectroscopy (MRS) independent of HE.

METHODS

Four cirrhotic groups (no HE/HN, HE alone, HN alone (sodium <130 mEq/L), HE+HN) underwent cognitive testing, HRQOL using Sickness Impact Profile (SIP: higher score is worse; has psychosocial and physical sub-scores) and brain MRS (myoinositol (mI) and glutamate+glutamine (Glx)), which were compared across groups. A subset underwent HRQOL testing before/after diuretic withdrawal.

RESULTS

82 cirrhotics (30 no HE/HN, 25 HE, 17 HE+HN, and 10 HN, MELD 12, 63% hepatitis C) were included. Cirrhotics with HN alone and without HE/HN had better cognition compared to HE groups (median abnormal tests no-HE/HN: 3, HN: 3.5, HE: 6.5, HE+HN: 7, p=0.008). Despite better cognition, HN only patients had worse HRQOL in total and psychosocial SIP while both HN groups (with/without HE) had a significantly worse physical SIP (p<0.0001, all comparisons). Brain MRS showed the lowest Glx in HN and the highest in HE groups (p<0.02). mI levels were comparably decreased in the three affected (HE, HE+HN, and HN) groups compared to no HE/HN and were associated with poor HRQOL. Six HE+HN cirrhotics underwent diuretic withdrawal which improved serum sodium and total/psychosocial SIP scores.

CONCLUSIONS

Hyponatremic cirrhotics without HE have poor HRQOL despite better cognition than those with concomitant HE. Glx levels were lowest in HN without HE but mI was similar across affected groups. HRQOL improved after diuretic withdrawal. Hyponatremia has a complex, non-linear relationship with brain Glx and mI, cognition and HRQOL.

Brain mitochondrial oxidative metabolism during and after cerebral hypoxia-ischemia studied by simultaneous phosphorus magnetic-resonance and broadband near-infrared spectroscopy

BACKGROUND

Multimodal measurements combining broadband near-infrared spectroscopy (NIRS) and phosphorus magnetic resonance spectroscopy ((31)P MRS) assessed associations between changes in the oxidation state of cerebral mitochondrial cytochrome-c-oxidase (Δ[oxCCO]) and (31)P metabolite peak-area ratios during and after transient cerebral hypoxia-ischemia (HI) in the newborn piglet.

METHODS

Twenty-four piglets (aged<24 h) underwent transient HI (inspired oxygen fraction 9% and bilateral carotid artery occlusion for ~20 min). Whole-brain (31)P MRS and NIRS data were acquired every minute. Inorganic phosphate (Pi)/epp, phosphocreatine (PCr)/epp, and total nucleotide triphosphate (NTP)/epp were measured by (31)P MRS and were plotted against Δ[oxCCO] during HI and recovery (epp=exchangeable phosphate pool=Pi+PCr+2γ-NTP+β-NTP).

RESULTS

During HI Δ[oxCCO], PCr/epp and NTP/epp declined and Pi/epp increased. Significant correlations were seen between (31)P ratios and Δ[oxCCO]; during HI a threshold point was identified where the relationship between Δ[oxCCO] and both NTP/epp and Pi/epp changed significantly. Outcome at 48 h related to recovery of Δ[oxCCO] and (31)P ratios 1h post-HI (survived: 1-h NTP/epp 0.22 ± 0.02, Δ[oxCCO] -0.29 ± 0.50 μM; died: 1-h NTP/epp 0.10 ± 0.04, Δ[oxCCO] -2.41 ± 1.48 μM).

CONCLUSIONS

Both lowered Δ[oxCCO] and NTP/epp 1h post-HI indicated mitochondrial impairment. Animals dying before 48 h had slower recovery of both Δ[oxCCO] and (31)P ratios by 1 h after HI.

Frontal lobe γ-aminobutyric acid levels during adolescence: associations with impulsivity and response inhibition

BACKGROUND

The brain undergoes major remodeling during adolescence, resulting in improved cognitive control and decision-making and reduced impulsivity, components of behavior mediated in part by the maturing frontal lobe. γ-Aminobutyric acid (GABA), the main inhibitory neurotransmitter system, also matures during adolescence, with frontal lobe GABA receptors reaching adult levels late in adolescence. Thus, the objective of this study was to characterize in vivo developmental differences in brain GABA levels.

METHODS

Proton magnetic resonance spectroscopy was used at 4 T to acquire metabolite data from the anterior cingulate cortex (ACC) and the parieto-occipital cortex (POC) in adolescents (n=30) and emerging adults (n = 20).

RESULTS

ACC GABA/creatine (Cr) levels were significantly lower in adolescents relative to emerging adults, whereas no age differences were observed in the POC. Lower ACC GABA/Cr levels were significantly associated with greater impulsivity and worse response inhibition, with relationships being most pronounced for ACC GABA/Cr and No-Go response inhibition in adolescent males.

CONCLUSIONS

These data provide the first human developmental in vivo evidence confirming frontal lobe GABA maturation, which was linked to impulsiveness and cognitive control. These findings suggest that reduced GABA may be an important neurobiological mechanism in the immature adolescent brain, contributing to the reduced yet rapidly developing ability to inhibit risky behaviors and to make suboptimal decisions, which could compromise adolescent health and safety.

Neurochemical changes within human early blind occipital cortex

Early blindness results in occipital cortex neurons responding to a wide range of auditory and tactile stimuli. These changes in tuning properties are accompanied by an extensive reorganization of the occipital cortex that includes alterations in anatomical structure, neurochemical and metabolic pathways. Although it has been established in animal models that neurochemical pathways are heavily affected by early visual deprivation, the effects of blindness on these pathways in humans is still not well characterized. Here, using (1)H magnetic resonance spectroscopy in nine early blind and normally sighted subjects, we find that early blindness is associated with higher levels of creatine, choline and myo-Inositol and indications of lower levels of GABA within the occipital cortex. These results suggest that the cross-modal responses associated with early blindness may, at least in part, be driven by changes within occipital biochemical pathways.

Proteomics and metabolomics for mechanistic insights and biomarker discovery in cardiovascular disease

In the last decade, proteomics and metabolomics have contributed substantially to our understanding of cardiovascular diseases. The unbiased assessment of pathophysiological processes without a priori assumptions complements other molecular biology techniques that are currently used in a reductionist approach. In this review, we highlight some of the "omics" methods used to assess protein and metabolite changes in cardiovascular disease. A discrete biological function is very rarely attributed to a single molecule; more often it is the combined input of many proteins. In contrast to the reductionist approach, in which molecules are studied individually, "omics" platforms allow the study of more complex interactions in biological systems. Combining proteomics and metabolomics to quantify changes in metabolites and their corresponding enzymes will advance our understanding of pathophysiological mechanisms and aid the identification of novel biomarkers for cardiovascular disease.

Fecal microbial metabolism of polyphenols and its effects on human gut microbiota

We investigated the biotransformation of four common dietary polyphenols, rutin, quercetin, chlorogenic acid and caffeic acid, in an in vitro mixed culture model of human intestinal microbiota, to determine effects on human gut bacteria. All four compounds were biotransformed rapidly, disappearing from the medium within 0.5 h and later replaced by known phenolic acid breakdown products, at concentrations up to hundreds of micromolar, much higher than in no-polyphenol control experiments. Quantitative PCR was used to measure effects of the polyphenols on the balance between the major groups of intestinal bacteria that are known to influence gut health, i.e., Bifidobacterium spp., Bacteroidetes, and Firmicutes. Fermentation of polyphenols stimulated proliferation of bifidobacteria and decreased the ratio of Firmicutes to Bacteroidetes, relative to controls. Polyphenols also stimulated short chain fatty acid production by the bacteria. Pure bifidobacterial cultures were treated separately with either fermented media isolated from the incubations, the pure test polyphenols, or the biotransformation products detected in the fermentations. Growth stimulation was observed only with fermented polyphenol media and the pure biotransformation products. It appears that dietary polyphenols may have the ability to modify the gut microbial balance, but this effect is indirect, i.e., it is mediated by biotransformation products, rather than the original plant compounds.

Astrocytic energetics during excitatory neurotransmission: What are contributions of glutamate oxidation and glycolysis?

Astrocytic energetics of excitatory neurotransmission is controversial due to discrepant findings in different experimental systems in vitro and in vivo. The energy requirements of glutamate uptake are believed by some researchers to be satisfied by glycolysis coupled with shuttling of lactate to neurons for oxidation. However, astrocytes increase glycogenolysis and oxidative metabolism during sensory stimulation in vivo, indicating that other sources of energy are used by astrocytes during brain activation. Furthermore, glutamate uptake into cultured astrocytes stimulates glutamate oxidation and oxygen consumption, and glutamate maintains respiration as well as glucose. The neurotransmitter pool of glutamate is associated with the faster component of total glutamate turnover in vivo, and use of neurotransmitter glutamate to fuel its own uptake by oxidation-competent perisynaptic processes has two advantages, substrate is supplied concomitant with demand, and glutamate spares glucose for use by neurons and astrocytes. Some, but not all, perisynaptic processes of astrocytes in adult rodent brain contain mitochondria, and oxidation of only a small fraction of the neurotransmitter glutamate taken up into these structures would be sufficient to supply the ATP required for sodium extrusion and conversion of glutamate to glutamine. Glycolysis would, however, be required in perisynaptic processes lacking oxidative capacity. Three lines of evidence indicate that critical cornerstones of the astrocyte-to-neuron lactate shuttle model are not established and normal brain does not need lactate as supplemental fuel: (i) rapid onset of hemodynamic responses to activation delivers oxygen and glucose in excess of demand, (ii) total glucose utilization greatly exceeds glucose oxidation in awake rodents during activation, indicating that the lactate generated is released, not locally oxidized, and (iii) glutamate-induced glycolysis is not a robust phenotype of all astrocyte cultures. Various metabolic pathways, including glutamate oxidation and glycolysis with lactate release, contribute to cellular energy demands of excitatory neurotransmission.

The Effects of Psychopharmacologic and Therapeutic Approaches on Neuro-imaging in Obsessive-compulsive Disorder

The neurobiological etiopathogenesis of OCD is still obscure. Neuroimaging studies have been very influential in shaping neurobiological models of OCD. Investigations performed within last twenty years have revealed some important findings and proposed that specific cortico-striato-thalamic circuits are involved in the mediation of its symptoms. The effects of antiobsessional drugs and cognitive behavioral therapy on structural and functional imaging have been evaluated in limited size of investigations. In structural investigations, in summary, it was found key brain regions in the pathophysiology of OCD and amygdala to change volumetrically by treatment. In functional and neurochemical investigations, by using different treatment modalities, cortico-striatal function disablements and NAA changes in a variety of brain regions were reported. In this paper, these limited data are reviewed. It is clear that there is so many things to be performed in the future researches on the effects of therapy on brains of the patients with OCD.

MRS in early and presymptomatic carriers of a novel octapeptide repeat insertion in the prion protein gene

To evaluate the proton magnetic resonance (MR) spectroscopy ((1) H MRS) changes in carriers of a novel octapeptide repeat insertion in the prion protein gene (PRNP) and family history of frontotemporal dementia with ataxia. Four at-risk mutation carriers and 13 controls were compared using single voxel, short TE, (1) H MRS from the posterior cingulate gyrus. The mutation carriers had an increased choline/creatine, P = .003 and increased myoinositol/creatine ratio, P = .003. (1) H MRS identified differences in markers of glial activity and choline metabolism in pre- and early-symptomatic carriers of a novel PRNP gene octapeptide insertion. These findings expand the possible diagnostic utility of (1) H MRS in familial prion disorders.

1H-MR spectroscopy metabolite levels correlate with executive function in vascular cognitive impairment

BACKGROUND

White matter hyperintensities (WMHs) are associated with vascular cognitive impairment (VCI) but fail to correlate with neuropsychological measures. As proton MR spectroscopy ((1)H-MRS) can identify ischaemic tissue, we hypothesised that MRS detectable brain metabolites would be superior to WMHs in predicting performance on neuropsychological tests.

METHODS

60 patients with suspected VCI underwent clinical, neuropsychological, MRI and CSF studies. They were diagnosed as having subcortical ischaemic vascular disease (SIVD), multiple infarcts, mixed dementia and leukoaraiosis. We measured brain metabolites in a white matter region above the lateral ventricles with (1)H-MRS and WMH volume in this region and throughout the brain.

RESULTS

We found a significant correlation between both total creatine (Cr) and N-acetylaspartyl compounds (NAA) and standardised neuropsychological test scores. Cr levels in white matter correlated significantly with executive function (p=0.001), attention (p=0.03) and overall T score (p=0.007). When lesion volume was added as a covariate, NAA also showed a significant correlation with executive function (p=0.003) and overall T score (p=0.015). Furthermore, while metabolite levels also correlated with total white matter lesion volume, adjusting the Cr levels for lesion volume did not diminish the strength of the association between Cr levels and neuropsychological scores. The lowest metabolite levels and neuropsychological scores were found in the SIVD group. Finally, lesion volume alone did not correlate significantly with any neuropsychological test score.

CONCLUSION

These results suggest that estimates of neurometabolite levels provide additional and useful information concerning cognitive function in VCI not obtainable by measurements of lesion load.

Late onset GM2 gangliosidosis mimicking spinal muscular atrophy

A case of late onset GM2 gangliosidodis with spinal muscular atrophy phenotype followed by cerebellar and extrapyramidal symptoms is presented. Genetic analysis revealed compound heterozygous mutation in exon 10 of the HEXA gene. Patient has normal intelligence and emotional reactivity. Neuroimaging tests of the brain showed only cerebellar atrophy consistent with MR spectroscopy (MRS) abnormalities. (18)F-fluorodeoxyglucose positron emission tomography (18)F-FDG PET/CT of the brain revealed glucose hypometabolism in cerebellum and in temporal and occipital lobes bilaterally.

Feedback field control improves linewidths in in vivo magnetic resonance spectroscopy

PURPOSE

Magnetic resonance spectroscopy (MRS) experiments rely on a homogeneous and stable magnetic field within the sample. Field homogeneity is typically optimized by static B0 shimming while reproducible effects from dynamic field variation are commonly diminished by means of gradient system calibration as well as calibration based on non-water suppressed reference data. However, residual encoding deficiencies from incomplete calibration and nonreproducible field perturbations deteriorate the quality of the obtained data. To overcome this problem, we propose to adapt higher-order feedback field control based on NMR field probes for its application in MRS.

METHODS

To allow for field measurements simultaneously with the spectroscopy readout, radiofrequency-shielded field probes were employed. The setup was evaluated in vitro and tested in vivo for single-voxel MRS at 7T to correct for field perturbations that occur due to subject breathing and limb motion.

RESULTS

The in vitro experiments showed an effective field control during the MRS sequence. The resulting spectroscopy data were free of spurious signal and the achieved field stabilization improved the spectral resolution in vitro and in vivo.

CONCLUSION

High-field MRS is limited by nonreproducible field perturbations for which spatiotemporal field feedback provides a solution without compromising sequence timing and efficiency.

Biomarkers in Parkinson's disease (recent update)

Parkinson's disease (PD) is the second most common neurodegenerative disorder mostly affecting the aging population over sixty. Cardinal symptoms including, tremors, muscle rigidity, drooping posture, drooling, walking difficulty, and autonomic symptoms appear when a significant number of nigrostriatal dopaminergic neurons are already destroyed. Hence we need early, sensitive, specific, and economical peripheral and/or central biomarker(s) for the differential diagnosis, prognosis, and treatment of PD. These can be classified as clinical, biochemical, genetic, proteomic, and neuroimaging biomarkers. Novel discoveries of genetic as well as nongenetic biomarkers may be utilized for the personalized treatment of PD during preclinical (premotor) and clinical (motor) stages. Premotor biomarkers including hyper-echogenicity of substantia nigra, olfactory and autonomic dysfunction, depression, hyposmia, deafness, REM sleep disorder, and impulsive behavior may be noticed during preclinical stage. Neuroimaging biomarkers (PET, SPECT, MRI), and neuropsychological deficits can facilitate differential diagnosis. Single-cell profiling of dopaminergic neurons has identified pyridoxal kinase and lysosomal ATPase as biomarker genes for PD prognosis. Promising biomarkers include: fluid biomarkers, neuromelanin antibodies, pathological forms of α-Syn, DJ-1, amyloid β and tau in the CSF, patterns of gene expression, metabolomics, urate, as well as protein profiling in the blood and CSF samples. Reduced brain regional N-acetyl-aspartate is a biomarker for the in vivo assessment of neuronal loss using magnetic resonance spectroscopy and T2 relaxation time with MRI. To confirm PD diagnosis, the PET biomarkers include [(18)F]-DOPA for estimating dopaminergic neurotransmission, [(18)F]dG for mitochondrial bioenergetics, [(18)F]BMS for mitochondrial complex-1, [(11)C](R)-PK11195 for microglial activation, SPECT imaging with (123)Iflupane and βCIT for dopamine transporter, and urinary salsolinol and 8-hydroxy, 2-deoxyguanosine for neuronal loss. This brief review describes the merits and limitations of recently discovered biomarkers and proposes coenzyme Q10, mitochondrial ubiquinone-NADH oxidoreductase, melatonin, α-synculein index, Charnoly body, and metallothioneins as novel biomarkers to confirm PD diagnosis for early and effective treatment of PD.

Different stages of white matter changes in the original HDLS family revealed by advanced MRI techniques

BACKGROUND

The temporal evolution of white matter (WM) changes on MR examinations in hereditary diffuse leukoencephalopathy with spheroids (HDLS) is largely unknown. Our purpose was to investigate the evolution of these WM changes with diffusion weighted/tensor imaging (DWI/DTI) and MR Spectroscopy (MRS).

METHODS

A newly diagnosed patient with HDLS from the original Swedish family was followed prospectively with 5 MRI as well as DWI/DTI and MRS examinations during 16 months.

RESULTS

The DTI eigenvalues demonstrated changes that suggested early myelin and axonal disturbances in the normal appearing WM (NAWM). DWI/DTI showed a rim of decreased diffusion progressively expanding through the WM from the initial frontal periventricular zones, and indicated complete destruction of axons and myelin in the area behind the front. MRS findings were suggestive of axonal destruction in the NAWM.

CONCLUSION

We describe HDLS changes in three temporal stages of development corresponding to lesions outside, in the vicinity of, and behind a characteristic rim centrifugally progressing from the ventricular horns. The axonal disturbances indicated by MRS changes in the NAWM support a primary axonal degeneration, as proposed in the original HDLS report, rather than axonal degeneration secondary to demyelination. These findings could help in differential diagnosis of HDLS.

Metabolomic approach to human brain spectroscopy identifies associations between clinical features and the frontal lobe metabolome in multiple sclerosis

Proton magnetic resonance spectroscopy ((1)H-MRS) is capable of noninvasively detecting metabolic changes that occur in the brain tissue in vivo. Its clinical utility has been limited so far, however, by analytic methods that focus on independently evaluated metabolites and require prior knowledge about which metabolites to examine. Here, we applied advanced computational methodologies from the field of metabolomics, specifically partial least squares discriminant analysis and orthogonal partial least squares, to in vivo (1)H-MRS from frontal lobe white matter of 27 patients with relapsing-remitting multiple sclerosis (RRMS) and 14 healthy controls. We chose RRMS, a chronic demyelinating disorder of the central nervous system, because its complex pathology and variable disease course make the need for reliable biomarkers of disease progression more pressing. We show that in vivo MRS data, when analyzed by multivariate statistical methods, can provide reliable, distinct profiles of MRS-detectable metabolites in different patient populations. Specifically, we find that brain tissue in RRMS patients deviates significantly in its metabolic profile from that of healthy controls, even though it appears normal by standard MRI techniques. We also identify, using statistical means, the metabolic signatures of certain clinical features common in RRMS, such as disability score, cognitive impairments, and response to stress. This approach to human in vivo MRS data should promote understanding of the specific metabolic changes accompanying disease pathogenesis, and could provide biomarkers of disease progression that would be useful in clinical trials.

Age-related change of neurochemical abnormality in attention-deficit hyperactivity disorder: a meta-analysis

Prevalence and symptoms of attention-deficit hyperactivity disorder (ADHD) change with advancing age. However, neurochemical background of such age-related change is yet to be elucidated. We therefore conducted a meta-analysis of 16 proton magnetic resonance spectroscopy studies comprising 270 individuals with ADHD and 235 controls. Standardized mean differences were calculated and used as an effect size. Sensitivity analyses and meta-regression to explore the effect of age on neurochemical abnormality were performed. A random effects model identified a significantly higher-than-normal N-acetylaspartate (NAA) in the medial prefrontal cortex (mPFC), but no significant differences of other metabolites in that area. No significant difference in metabolite levels was demonstrated in any other region. Sensitivity analysis of children with ADHD revealed significantly higher-than-normal NAA, whereas no significant difference was found in adults with ADHD. Meta-regression revealed significant correlation between advanced age and normal levels of NAA in the mPFC, suggesting that age-dependent abnormality of NAA level in the mPFC is a potential neural basis of age-related change of symptoms of ADHD.

Differentiation between idiopathic and atypical parkinsonian syndromes using three-dimensional magnetic resonance spectroscopic imaging

OBJECTIVES

Degeneration of dopaminergic neurons in the substantia nigra (SN) pars compacta is the primary cause of idiopathic Parkinson's disease (iPD). In early stages of disease in particular, presentation of symptoms is non-specific leading to difficulties in differentiating between iPD and atypical parkinsonian syndromes (aPS). The aim of this study was to evaluate the feasibility of three-dimensional magnetic resonance spectroscopic imaging (MRSI) of the SN region for differentiation between iPD and aPS.

METHODS

20 patients with iPD, 10 with aPS and 22 controls were examined on a 3 T MR scanner using three-dimensional MRSI with a voxel size of 0.252 ml and an echo time of 30 ms. Excitation volume was positioned in such a way that in each hemisphere 1 voxel defines the rostral and 1 voxel the caudal SN region. Using a fully automatic spectra evaluation, the metabolite ratios of N-acetyl aspartate/creatine (NAA/Cr) were calculated.

RESULTS

In all cases spectra with good quality were obtained. Differences in rostral to caudal NAA/Cr ratios were significant between controls and iPD patients, as well as between iPD and aPS patients (p<0.001 for both). For controls, rostral NAA/Cr was greater than caudal, whereas in iPD patients this ratio was reversed. aPS patients showed similar ratios as controls.

CONCLUSIONS

Typical reversed rostral to caudal NAA/Cr ratios in iPD patients suggests that they could be linked to specific pathology of neuronal loss in the SN pars compacta. Therefore, the results suggest that MRSI may support the differential diagnosis of patients with clinically unclassifiable parkinsonian syndromes who do not yet fulfil the established clinical criteria.

GABA estimation in the brains of children on the autism spectrum: measurement precision and regional cortical variation

(1)H magnetic resonance spectroscopy ((1)H MRS) and spectral editing methods, such as MEGA-PRESS, allow researchers to investigate metabolite and neurotransmitter concentrations in-vivo. Here we address the utilization of (1)H MRS for the investigation of GABA concentrations in the ASD brain, in three locations; motor, visual and auditory areas. An initial repeatability study (5 subjects, 5 repeated measures separated by ~5days on average) indicated no significant effect of reference metabolite choice on GABA quantitation (p>0.6). Coefficients of variation for GABA+/NAA, GABA+/Cr and GABA+/Glx were all of the order of 9-11%. Based on these findings, we investigated creatine-normalized GABA+ ratios (GABA+/Cr) in a group of (N=17) children with autism spectrum disorder (ASD) and (N=17) typically developing children (TD) for Motor, Auditory and Visual regions of interest (ROIs). Linear regression analysis of gray matter (GM) volume changes (known to occur with development) revealed a significant decrease of GM volume with Age for Motor (F(1,30)=17.92; p<0.001) and Visual F(1,16)=14.41; p<0.005 but not the Auditory ROI (p=0.55). Inspection of GABA+/Cr changes with Age revealed a marginally significant change for the Motor ROI only (F(1,30)=4.11; p=0.054). Subsequent analyses were thus conducted for each ROI separately using Age and GM volume as covariates. No group differences in GABA+/Cr were observed for the Visual ROI between TD vs. ASD children. However, the Motor and Auditory ROI showed significantly reduced GABA+/Cr in ASD (Motor p<0.05; Auditory p<0.01). The mean deficiency in GABA+/Cr from the Motor ROI was approximately 11% and Auditory ROI was approximately 22%. Our novel findings support the model of regional differences in GABA+/Cr in the ASD brain, primarily in Auditory and to a lesser extent Motor but not Visual areas.

Real-time automated spectral assessment of the BOLD response for neurofeedback at 3 and 7T

Echo-planar imaging is the dominant functional MRI data acquisition scheme for evaluating the BOLD signal. To date, it remains the only approach providing neurofeedback from spatially localized brain activity. Real-time functional single-voxel proton spectroscopy (fSVPS) may be an alternative for spatially specific BOLD neurofeedback at 7T because it allows for a precise estimation of the local T2* signal, EPI-specific artifacts may be avoided, and the signal contrast may increase. In order to explore and optimize this alternative neurofeedback approach, we tested fully automated real-time fSVPS spectral estimation procedures to approximate T2* BOLD signal changes from the unsuppressed water peak, i.e. lorentzian non-linear complex spectral fit (LNLCSF) in frequency and frequency-time domain. The proposed approaches do not require additional spectroscopic localizers in contrast to conventional T2* approximation based on linear regression of the free induction decay (FID). For methods comparison, we evaluated quality measures for signals from the motor and the visual cortex as well as a real-time feedback condition at high (3T) and at ultra-high (7T) magnetic field strengths. Using these methods, we achieved reliable and fast water peak spectral parameter estimations. At 7T, we observed an absolute increase of spectra line narrowing due to the BOLD effect, but quality measures did not improve due to artifactual line broadening. Overall, the automated fSVPS approach can be used to assess dynamic spectral changes in real-time, and to provide localized T2* neurofeedback at 3 and 7T.

Neuroimaging biomarkers for epilepsy: advances and relevance to glial cells

Glial cells play an important role in normal brain function and emerging evidence would suggest that their dysfunction may be responsible for some epileptic disease states. Neuroimaging of glial cells is desirable, but there are no clear methods to assess neither their function nor localization. Magnetic resonance imaging (MRI) is now part of a standardized epilepsy imaging protocol to assess patients. Structural volumetric and T2-weighted imaging changes can assist in making a positive diagnosis in a majority of patients. The alterations reported in structural and T2 imaging is predominantly thought to reflect early neuronal loss followed by glial hypertrophy. MR spectroscopy for myo-inositol is a being pursued to identify glial alterations along with neuronal markers. Diffusion weighted imaging (DWI) is ideal for acute epileptiform events, but is not sensitive to either glial cells or neuronal long-term changes found in epilepsy. However, DWI variants such as diffusion tensor imaging or q-space imaging may shed additional light on aberrant glial function in the future. The sensitivity and specificity of PET radioligands, including those targeting glial cells (translocator protein) hold promise in being able to image glial cells. As the role of glial function/dysfunction in epilepsy becomes more apparent neuroimaging methods will evolve to assist the clinician and researcher in visualizing their location and function.

Application of 31P MR spectroscopy to the brain tumors

Objective

To evaluate the clinical feasibility and obtain useful parameters of ³¹P magnetic resonance spectroscopy (MRS) study for making the differential diagnosis of brain tumors.

Materials and Methods

Twenty-eight patients with brain tumorous lesions (22 cases of brain tumor and 6 cases of abscess) and 11 normal volunteers were included. The patients were classified into the astrocytoma group, lymphoma group, metastasis group and the abscess group. We obtained the intracellular pH and the metabolite ratios of phosphomonoesters/phosophodiesters (PME/PDE), PME/inorganic phosphate (Pi), PDE/Pi, PME/adenosine triphosphate (ATP), PDE/ATP, PME/phosphocreatine (PCr), PDE/PCr, PCr/ATP, PCr/Pi, and ATP/Pi, and evaluated the statistical significances.

Results

The brain tumors had a tendency of alkalization (pH = 7.28 ± 0.27, p = 0.090), especially the pH of the lymphoma was significantly increased (pH = 7.45 ± 0.32, p = 0.013). The brain tumor group showed increased PME/PDE ratio compared with that in the normal control group (p = 0.012). The ratios of PME/PDE, PDE/Pi, PME/PCr and PDE/PCr showed statistically significant differences between each brain lesion groups (p < 0.05). The astrocytoma showed an increased PME/PDE and PME/PCr ratio. The ratios of PDE/Pi, PME/PCr, and PDE/PCr in lymphoma group were lower than those in the control group and astrocytoma group. The metastasis group showed an increased PME/PDE ratio, compared with that in the normal control group.

Conclusion

We have obtained the clinically applicable ³¹P MRS, and the pH, PME/PDE, PDE/Pi, PME/PCr, and PDE/PCr ratios are helpful for differentiating among the different types of brain tumors.

Combined neurostimulation and neuroimaging in cognitive neuroscience: past, present, and future

Modern neurostimulation approaches in humans provide controlled inputs into the operations of cortical regions, with highly specific behavioral consequences. This enables causal structure–function inferences, and in combination with neuroimaging, has provided novel insights into the basic mechanisms of action of neurostimulation on distributed networks. For example, more recent work has established the capacity of transcranial magnetic stimulation (TMS) to probe causal interregional influences, and their interaction with cognitive state changes. Combinations of neurostimulation and neuroimaging now face the challenge of integrating the known physiological effects of neurostimulation with theoretical and biological models of cognition, for example, when theoretical stalemates between opposing cognitive theories need to be resolved. This will be driven by novel developments, including biologically informed computational network analyses for predicting the impact of neurostimulation on brain networks, as well as novel neuroimaging and neurostimulation techniques. Such future developments may offer an expanded set of tools with which to investigate structure–function relationships, and to formulate and reconceptualize testable hypotheses about complex neural network interactions and their causal roles in cognition.

Methodology for improved detection of low concentration metabolites in MRS: optimised combination of signals from multi-element coil arrays

State of the art magnetic resonance imaging (MRI) scanners are generally equipped with multi-element receive coils; 16 or 32 channel coils are common. Their development has been predominant for parallel imaging to enable faster scanning. Less consideration has been given to localized magnetic resonance spectroscopy (MRS). Multinuclear studies, for example (31)P or (13)C MRS, are often conducted with a single element coil located over the region of interest. (1)H MRS studies have generally employed the same multi-element coils used for MRI, but little consideration has been given as to how the spectroscopic data from the different channels are combined. In many cases it is simply co-added with detrimental effect on the signal to noise ratio. In this study, we derive the optimum method for combining multi-coil data, namely weighting with the ratio of signal to the square of the noise. We show that provided that the noise is uncorrelated, this is the theoretical optimal combination. The method is demonstrated for in vivo proton MRS data acquired using a 32 channel receive coil at 7T in four different brain areas; left motor and right motor, occipital cortex and medial frontal cortex.

GABA in the insula - a predictor of the neural response to interoceptive awareness

The insula has been identified as a key region involved in interoceptive awareness. Whilst imaging studies have investigated the neural activation patterns in this region involved in intero- and exteroceptive awareness, the underlying biochemical mechanisms still remain unclear. In order to investigate these, a well-established fMRI task targeting interoceptive awareness (heartbeat counting) and exteroceptive awareness (tone counting) was combined with magnetic resonance spectroscopy (MRS). Controlling for physiological noise, neural activity in the insula during intero- and exteroceptive awareness was confirmed in an independent data sample using the same fMRI design. Focussing on MRS values from the left insula and combining them with neural activity during intero- and exteroceptive awareness in the same healthy individuals, we demonstrated that GABA concentration in a region highly involved in interoceptive processing is correlated with neural responses to interoceptive stimuli, as opposed to exteroceptive stimuli. In addition, both GABA and interoceptive signal changes in the insula predicted the degree of depressed affect, as measured by the Beck Hopelessness Scale. On the one hand, the association between GABA concentration and neural activity during interoceptive awareness provides novel insight into the biochemical underpinnings of insula function and interoception. On the other, through the additional association of both GABA and neural activity during interoception with depressed affect, these data also bear potentially important implications for psychiatric disorders like depression and anxiety, where GABAergic deficits, altered insula function and abnormal affect coincide.