Age-related differences in metabolites in the posterior cingulate cortex and hippocampus of normal ageing brain: A 1H-MRS study

Neurometabolite differences in Autism as assessed with Magnetic Resonance Spectroscopy: A systematic review and meta-analysis

1H-Magnetic Resonance Spectroscopy (MRS) is a non-invasive technique that can be used to quantify the concentrations of metabolites in the brain in vivo. MRS findings in the context of autism are inconsistent and conflicting. We performed a systematic review and meta-analysis of MRS studies measuring glutamate and gamma-aminobutyric acid (GABA), as well as brain metabolites involved in energy metabolism (glutamine, creatine), neural and glial integrity (e.g. n-acetyl aspartate (NAA), choline, myo-inositol) and oxidative stress (glutathione) in autism cohorts. Data were extracted and grouped by metabolite, brain region and several other factors before calculation of standardised effect sizes. Overall, we find significantly lower concentrations of GABA and NAA in autism, indicative of disruptions to the balance between excitation/inhibition within brain circuits, as well as neural integrity. Further analysis found these alterations are most pronounced in autistic children and in limbic brain regions relevant to autism phenotypes. Additionally, we show how study outcome varies due to demographic and methodological factors , emphasising the importance of conforming with standardised consensus study designs and transparent reporting.

The developmental trajectory of 1H-MRS brain metabolites from childhood to adulthood

Human brain development is ongoing throughout childhood, with for example, myelination of nerve fibers and refinement of synaptic connections continuing until early adulthood. 1H-Magnetic Resonance Spectroscopy (1H-MRS) can be used to quantify the concentrations of endogenous metabolites (e.g. glutamate and γ -aminobutyric acid (GABA)) in the human brain in vivo and so can provide valuable, tractable insight into the biochemical processes that support postnatal neurodevelopment. This can feasibly provide new insight into and aid the management of neurodevelopmental disorders by providing chemical markers of atypical development. This study aims to characterize the normative developmental trajectory of various brain metabolites, as measured by 1H-MRS from a midline posterior parietal voxel. We find significant non-linear trajectories for GABA+ (GABA plus macromolecules), Glx (glutamate + glutamine), total choline (tCho) and total creatine (tCr) concentrations. Glx and GABA+ concentrations steeply decrease across childhood, with more stable trajectories across early adulthood. tCr and tCho concentrations increase from childhood to early adulthood. Total N-acetyl aspartate (tNAA) and Myo-Inositol (mI) concentrations are relatively stable across development. Trajectories likely reflect fundamental neurodevelopmental processes (including local circuit refinement) which occur from childhood to early adulthood and can be associated with cognitive development; we find GABA+ concentrations significantly positively correlate with recognition memory scores.

sLASER and PRESS perform similarly at revealing metabolite-age correlations at 3 T

PURPOSE

To compare the respective ability of PRESS and sLASER to reveal biological relationships, using age as a validation covariate at 3 T.

METHODS

MRS data were acquired from 102 healthy volunteers using PRESS and sLASER in centrum semiovale and posterior cingulate cortex (PCC). Acquisition parameters included TR/TE = 2000/30 ms, 96 transients, and 2048 datapoints sampled at 2 kHz. Spectra were analyzed using Osprey. SNR, FWHM linewidth of total creatine, and metabolite concentrations were extracted. A linear model was used to compare SNR and linewidth. Paired t-tests were used to assess differences in metabolite measurements between PRESS and sLASER. Correlations were used to evaluate the relationship between PRESS and sLASER metabolite estimates, as well as the strength of each metabolite-age relationship. Coefficients of variation were calculated to assess inter-subject variability in each metabolite measurement.

RESULTS

SNR and linewidth were significantly higher (p < 0.01) for sLASER than PRESS in PCC. Paired t-tests showed significant differences between PRESS and sLASER in most metabolite measurements. PRESS-sLASER measurements were significantly correlated (p < 0.05) for most metabolites. Metabolite-age relationships were consistently identified using both methods. Similar coefficients of variation were observed for most metabolites.

CONCLUSION

The study results suggest strong agreement between PRESS and sLASER in identifying relationships between brain metabolites and age in centrum semiovale and PCC data acquired at 3 T. sLASER is technically desirable due to the reduced chemical shift displacement artifact; however, PRESS performed similarly in homogeneous brain regions at clinical field strength.

Metabolomics to Study Human Aging: A Review

In the last years, with the increase in the average life expectancy, the world's population is progressively aging, which entails social, health and economic problems. In this sense, the need to better understand the physiology of the aging process becomes an urgent need. Since the study of aging in humans is challenging, cellular and animal models are widely used as alternatives. Omics, namely metabolomics, have emerged in the study of aging, with the aim of biomarker discovering, which may help to uncomplicate this complex process. This paper aims to summarize different models used for aging studies with their advantages and limitations. Also, this review gathers the published articles referring to biomarkers of aging already discovered using metabolomics approaches, comparing the results obtained in the different studies. Finally, the most frequently used senescence biomarkers are described, along with their importance in understanding aging.

Microstructural and Metabolic Changes in Normal Aging Human Brain Studied with Combined Whole-Brain MR Spectroscopic Imaging and Quantitative MR Imaging

PURPOSE

This study aimed to detect age-related brain metabolic and microstructural changes in healthy human brains by the use of whole-brain proton magnetic resonance spectroscopic imaging (1H‑MRSI) and quantitative MR imaging (qMRI).

METHODS

In this study, 60 healthy participants with evenly distributed ages (between 21 and 69 years) and sex underwent MRI examinations at 3T including whole-brain 1H‑MRSI. The concentrations of the metabolites N‑acetylaspartate (NAA), choline-containing compounds (Cho), total creatine and phosphocreatine (tCr), glutamine and glutamate (Glx), and myo-inositol (mI), as well as the brain relaxation times T2, T2' and T1 were measured in 12 regions of interest (ROI) in each hemisphere. Correlations between measured parameters and age were estimated with linear regression analysis and Pearson's correlation test.

RESULTS

Significant age-related changes of brain regional metabolite concentrations and tissue relaxation times were found: NAA decreased in eight of twelve ROIs, Cho increased in three ROIs, tCr in four ROIs, and mI in three ROIs. Glx displayed a significant decrease in one ROI and an increase in another ROI. T1 increased in four ROIs and T2 in one ROI, while T2' decreased in two ROIs. A negative correlation of tCr concentrations with T2' relaxation time was found in one ROI as well as the positive correlations of age-related T1 relaxation time with concentrations of tCr, mI, Glx and Cho in another ROI.

CONCLUSION

Normal aging in human brain is associated with coexistent brain regional metabolic alterations and microstructural changes, which may be related to age-related decline in cognitive, affective and psychomotor domains of life in the older population.

White matter and neurochemical mechanisms underlying age-related differences in motor processing speed

Aging is associated with changes in the central nervous system and leads to reduced life quality. Here, we investigated the age-related differences in the CNS underlying motor performance deficits using magnetic resonance spectroscopy and diffusion MRI. MRS measured N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) concentrations in the sensorimotor and occipital cortex, whereas dMRI quantified apparent fiber density (FD) in the same voxels to evaluate white matter microstructural organization. We found that aging was associated with increased reaction time and reduced FD and NAA concentration in the sensorimotor voxel. Both FD and NAA mediated the association between age and reaction time. The NAA concentration was found to mediate the association between age and FD in the sensorimotor voxel. We propose that the age-related decrease in NAA concentration may result in reduced axonal fiber density in the sensorimotor cortex which may ultimately account for the response slowness of older participants.

N-acetyl-aspartate and Myo-inositol as Markers of White Matter Microstructural Organization in Mild Cognitive Impairment: Evidence from a DTI-1H-MRS Pilot Study

We implemented a multimodal approach to examine associations between structural and neurochemical changes that could signify neurodegenerative processes related to mild cognitive impairment (MCI). Fifty-nine older adults (60-85 years; 22 MCI) underwent whole-brain structural 3T MRI (T1W, T2W, DTI) and proton magnetic resonance spectroscopy (¹H-MRS). The regions of interest (ROIs) for ¹H-MRS measurements were the dorsal posterior cingulate cortex, left hippocampal cortex, left medial temporal cortex, left primary sensorimotor cortex, and right dorsolateral prefrontal cortex. The findings revealed that subjects in the MCI group showed moderate to strong positive associations between the total N-acetylaspartate to total creatine and the total N-acetylaspartate to myo-inositol ratios in the hippocampus and dorsal posterior cingulate cortex and fractional anisotropy (FA) of WM tracts crossing these regions-specifically, the left temporal tapetum, right corona radiata, and right posterior cingulate gyri. In addition, negative associations between the myo-inositol to total creatine ratio and FA of the left temporal tapetum and right posterior cingulate gyri were observed. These observations suggest that the biochemical integrity of the hippocampus and cingulate cortex is associated with a microstructural organization of ipsilateral WM tracts originating in the hippocampus. Specifically, elevated myo-inositol might be an underlying mechanism for decreased connectivity between the hippocampus and the prefrontal/cingulate cortex in MCI.

Brain total creatine differs between primary progressive aphasia (PPA) subtypes and correlates with disease severity

Primary progressive aphasia (PPA) is comprised of three subtypes: logopenic (lvPPA), non-fluent (nfvPPA), and semantic (svPPA). We used magnetic resonance spectroscopy (MRS) to measure tissue-corrected metabolite levels in the left inferior frontal gyrus (IFG) and right sensorimotor cortex (SMC) from 61 PPA patients. We aimed to: (1) characterize subtype differences in metabolites; and (2) test for metabolite associations with symptom severity. tCr differed by subtype across the left IFG and right SMC. tCr levels were lowest in lvPPA and highest in svPPA. tCr levels predicted lvPPA versus svPPA diagnosis. Higher IFG tCr and lower Glx correlated with greater disease severity. As tCr is involved in brain energy metabolism, svPPA pathology might involve changes in specific cellular energy processes. Perturbations to cellular energy homeostasis in language areas may contribute to symptoms. Reduced cortical excitatory capacity (i.e. lower Glx) in language regions may also contribute to symptoms. Thus, tCr may be useful for differentiating between PPA subtypes, and both tCr and Glx might have utility in understanding PPA mechanisms and tracking progression.

Neurometabolic correlates of posturography in normal aging and older adults with mild cognitive impairment: Evidence from a 1H-MRS study

Proton magnetic resonance spectroscopy (¹H-MRS) holds promise for revealing and understanding neurodegenerative processes associated with cognitive and functional impairments in aging. In the present study, we examined the neurometabolic correlates of balance performance in 42 cognitively intact older adults (healthy controls - HC) and 26 older individuals that were diagnosed with mild cognitive impairment (MCI). Neurometabolite ratios of total N-acetyl aspartate (tNAA), glutamate-glutamine complex (Glx), total choline (tCho) and myo-inositol (mIns) relative to total creatine (tCr) were assessed using single voxel ¹H-MRS in four different brain regions. Regions of interest were the left hippocampus (HPC), dorsal posterior cingulate cortex (dPCC), left sensorimotor cortex (SM1), and right dorsolateral prefrontal cortex (dlPFC). Center-of-pressure velocity (Vcop) and dual task effect (DTE) were used as measures of balance performance. Results indicated no significant group differences in neurometabolite ratios and balance performance measures. However, our observations revealed that higher tCho/tCr and mIns/tCr in hippocampus and dPCC were generic predictors of worse balance performance, suggesting that neuroinflammatory processes in these regions might be a driving factor for impaired balance performance in aging. Further, we found that higher tNAA/tCr and mIns/tCr and lower Glx/tCr in left SM1 were predictors of better balance performance in MCI but not in HC. The latter observation hints at the possibility that individuals with MCI may upregulate balance control through recruitment of sensorimotor pathways.

Neurometabolite alterations in traumatic brain injury and associations with chronic pain

Traumatic brain injury (TBI) can lead to a variety of comorbidities, including chronic pain. Although brain tissue metabolite alterations have been extensively examined in several chronic pain populations, it has received less attention in people with TBI. Thus, the primary aim of this study was to compare brain tissue metabolite levels in people with TBI and chronic pain (n = 16), TBI without chronic pain (n = 17), and pain-free healthy controls (n = 31). The metabolite data were obtained from participants using whole-brain proton magnetic resonance spectroscopic imaging (¹H-MRSI) at 3 Tesla. The metabolite data included N-acetylaspartate, myo-inositol, total choline, glutamate plus glutamine, and total creatine. Associations between N-acetylaspartate levels and pain severity, neuropathic pain symptom severity, and psychological variables, including anxiety, depression, post-traumatic stress disorder (PTSD), and post-concussive symptoms, were also explored. Our results demonstrate N-acetylaspartate, myo-inositol, total choline, and total creatine alterations in pain-related brain regions such as the frontal region, cingulum, postcentral gyrus, and thalamus in individuals with TBI with and without chronic pain. Additionally, NAA levels in the left and right frontal lobe regions were positively correlated with post-concussive symptoms; and NAA levels within the left frontal region were also positively correlated with neuropathic pain symptom severity, depression, and PTSD symptoms in the TBI with chronic pain group. These results suggest that neuronal integrity or density in the prefrontal cortex, a critical region for nociception and pain modulation, is associated with the severity of neuropathic pain symptoms and psychological comorbidities following TBI. Our data suggest that a combination of neuronal loss or dysfunction and maladaptive neuroplasticity may contribute to the development of persistent pain following TBI, although no causal relationship can be determined based on these data.

1H MR spectroscopy biomarkers of neuronal and synaptic function are associated with tau deposition in cognitively unimpaired older adults

Proton magnetic resonance spectroscopy (1H MRS) may provide information on pathophysiological changes associated with tau deposition in cognitively unimpaired older adults. In this study, the associations of posterior cingulate gyrus tau and amyloid beta (Aβ) deposition on PET with 1H MRS metabolite ratios acquired from bilateral posterior cingulate gyri were investigated in cognitively unimpaired older adults. Participants (n = 40) from the Mayo Clinic Study of Aging underwent single-voxel sLASER 1H MRS from the posterior cingulate gyrus at 3 Tesla, 18F-flortaucipir, and 11C- Pittsburgh Compound B (PiB) PET. An increase in posterior cingulate gyrus tau deposition, but not elevated Aβ, was associated with lower N-acetylaspartate/total creatine (tCr) and glutamate (Glu)/tCr ratios, and sex by tau interaction was observed in association with Glu/tCr. Higher tau levels in cognitively unimpaired older adults are associated with biomarkers of neural and synaptic injury even in the absence of cognitive impairment and these relationships appear to be stronger in women than in men.

A Neuroscience Primer for Integrating Geroscience With the Neurobiology of Aging

Neuroscience has a rich history of studies focusing on neurobiology of aging. However, much of the aging studies in neuroscience occur outside of the gerosciences. The goal of this primer is 2-fold: first, to briefly highlight some of the history of aging neurobiology and second, to introduce to geroscientists the broad spectrum of methodological approaches neuroscientists use to study the neurobiology of aging. This primer is accompanied by a corresponding geroscience primer, as well as a perspective on the current challenges and triumphs of the current divide across these 2 fields. This series of manuscripts is intended to foster enhanced collaborations between neuroscientists and geroscientists with the intent of strengthening the field of cognitive aging through inclusion of parameters from both areas of expertise.

The Brain Metabolic Signature in Superagers Using In Vivo 1H-MRS: A Pilot Study

BACKGROUND AND PURPOSE

Youthful memory performance in older adults may reflect an underlying resilience to the conventional pathways of aging. Subjects having this unusual characteristic have been recently termed "superagers." This study aimed to explore the significance of imaging biomarkers acquired by ¹H-MRS to characterize superagers and to differentiate them from their normal-aging peers.

MATERIALS AND METHODS

Fifty-five patients older than 80 years of age were screened using a detailed neuropsychological protocol, and 25 participants, comprising 12 superagers and 13 age-matched controls, were statistically analyzed. We used state-of-the-art 3T ¹H-MR spectroscopy to quantify 18 neurochemicals in the posterior cingulate cortex of our subjects. All ¹H-MR spectroscopy data were analyzed using LCModel. Results were further processed using 2 approaches to investigate the technique accuracy: 1) comparison of the average concentration of metabolites estimated with Cramer-Rao lower bounds <20%; and 2) calculation and comparison of the weighted means of metabolites' concentrations.

RESULTS

The main finding observed was a higher total N-acetyl aspartate concentration in superagers than in age-matched controls using both approaches (P = .02 and P = .03 for the weighted means), reflecting a positive association of total N-acetyl aspartate with higher cognitive performance.

CONCLUSIONS

¹H-MR spectroscopy emerges as a promising technique to unravel neurochemical mechanisms related to cognitive aging in vivo and providing a brain metabolic signature in superagers. This may contribute to monitoring future interventional therapies to avoid or postpone the pathologic processes of aging.

Associations Between Neurochemistry and Gait Performance Following Concussion in Collegiate Athletes

OBJECTIVE

To evaluate the strength of associations between single-task and dual-task gait measures and posterior cingulate gyrus (PCG) neurochemicals in acutely concussed collegiate athletes.

SETTING

Participants were recruited from an NCAA Division 1 University.

PARTICIPANTS

Nineteen collegiate athletes acutely (<4 days) following sports-related concussion.

DESIGN

We acquired magnetic resonance spectroscopy (MRS) in the PCG and gait performance measurements in the participants, acutely following concussion. Linear mixed-effects models were constructed to measure the effect of gait performance, in the single- and dual-task settings, and sex on the 6 neurochemicals quantified with MRS in mmol. Correlation coefficients were also calculated to determine the direction and strength of the relationship between MRS neurochemicals and gait performance, postconcussion symptom score, and number of previous concussions.

MAIN MEASURES

Average gait speed, average cadence, N-acetyl aspartate, choline, myo-inositol, glutathione, glutamate plus glutamine, and creatine.

RESULTS

Single-task gait speed (P = .0056) and cadence (P = .0065) had significant effects on myo-inositol concentrations in the PCG, independent of sex, in concussed collegiate athletes. Single-task cadence (P = .047) also had a significant effect on glutathione in the PCG. No significant effects were observed between dual-task gait performance and PCG neurochemistry.

CONCLUSIONS

These findings indicate that increased concentrations of neuroinflammatory markers in the PCG are associated with slower single-task gait performance within 4 days of sports-related concussion.

Sensory and memory processing in old female and male Wistar rat brain, and its relationship with the cortical and hippocampal redox state

The brain is one of the most sensitive organs damaged during aging due to its susceptibility to the aging-related oxidative stress. Hence, in this study, the sensory nerve pathway integrity and the memory were evaluated and related to the redox state, the antioxidant enzymes function, and the protein oxidative damage in the brain cortex (Cx) and the hippocampus (Hc) of young (4-month-old) and old (24-month-old) male and female Wistar rats. Evoked potentials (EP) were performed for the auditory, visual, and somatosensory pathways. In both males and females, the old rat groups' latencies were larger in almost all waves when compared to the young same-sex animals. The novel object test was performed to evaluate memory. The superoxide dismutase and catalase antioxidant activity, as well as the protein oxidative damage, and the redox state were evaluated. Magnetic resonance (MR) imaging was used to obtain the diffusion tensor imaging, and the brain volume, while MR spectroscopy was used to obtain the brain metabolite concentrations (glutamine, glutamate, Myo-inositol, N-acetyl-aspartate, creatine) in the Cx and the Hc of young and old females. Our data suggest that, although there are limited variations regarding memory and nerve conduction velocity by sex, the differences concerning the redox status might be important to explain the dissimilar reactions during brain aging between males and females. Moreover, the increment in Myo-inositol levels in the Hc of old rats and the brain volume decrease suggest that redox state alterations might be correlated to neuroinflammation during brain aging.

Metabolite Signature of Alzheimer's Disease in Adults with Down Syndrome

OBJECTIVE

The purpose of this study was to examine the Alzheimer's disease metabolite signature through magnetic resonance spectroscopy in adults with Down syndrome and its relation with Alzheimer's disease biomarkers and cortical thickness.

METHODS

We included 118 adults with Down syndrome from the Down Alzheimer Barcelona Imaging Initiative and 71 euploid healthy controls from the Sant Pau Initiative on Neurodegeneration cohort. We measured the levels of myo-inositol (a marker of neuroinflammation) and N-acetyl-aspartate (a marker of neuronal integrity) in the precuneus using magnetic resonance spectroscopy. We investigated the changes with age and along the disease continuum (asymptomatic, prodromal Alzheimer's disease, and Alzheimer's disease dementia stages). We assessed the relationship between these metabolites and Aβ₄₂ /Aβ₄₀ ratio, phosphorylated tau-181, neurofilament light (NfL), and YKL-40 cerebrospinal fluid levels as well as amyloid positron emission tomography uptake using Spearman correlations controlling for multiple comparisons. Finally, we computed the relationship between cortical thickness and metabolite levels using Freesurfer.

RESULTS

Asymptomatic adults with Down syndrome had a 27.5% increase in the levels of myo-inositol, but equal levels of N-acetyl-aspartate compared to euploid healthy controls. With disease progression, myo-inositol levels increased, whereas N-acetyl-aspartate levels decreased in symptomatic stages of the disease. Myo-inositol was associated with amyloid, tau, and neurodegeneration markers, mainly at symptomatic stages of the disease, whereas N-acetyl-aspartate was related to neurodegeneration biomarkers in symptomatic stages. Both metabolites were significantly associated with cortical thinning, mainly in symptomatic participants.

INTERPRETATION

Magnetic resonance spectroscopy detects Alzheimer's disease related inflammation and neurodegeneration, and could be a good noninvasive disease-stage biomarker in Down syndrome. ANN NEUROL 2021.

The cross-sectional interplay between neurochemical profile and brain connectivity

Neurochemical profile and brain connectivity are both critical aspects of brain function. However, our knowledge of their interplay across development is currently poor. We combined single-voxel magnetic resonance spectroscopy and resting functional magnetic resonance imaging in a cross-sectional sample spanning from childhood to adulthood which was reassessed in ~1.5 years (N = 293). We revealed the developmental trajectories of 20 neurochemicals in two key developmental brain regions (the intraparietal sulcus, IPS, and the middle frontal gyrus, MFG). We found that certain neurochemicals exhibited similar developmental trajectories across the two regions, while other trajectories were region-specific. Crucially, we mapped the connectivity of the brain regions IPS and MFG to the rest of the brain across development as a function of regional glutamate and GABA concentration. We demonstrated that glutamate concentration within the IPS is modulated by age in explaining IPS connectivity with frontal, temporal and parietal regions. In mature participants, higher glutamate within the IPS was related to more negative connectivity while the opposite pattern was found for younger participants. Our findings offer specific developmental insights on the interplay between the brain's resting activity and the glutamatergic system both of which are crucial for regulating normal functioning and are dysregulated in several clinical conditions.

Bilingualism is a long-term cognitively challenging experience that modulates metabolite concentrations in the healthy brain

Cognitively demanding experiences, including complex skill acquisition and processing, have been shown to induce brain adaptations, at least at the macroscopic level, e.g. on brain volume and/or functional connectivity. However, the neurobiological bases of these adaptations, including at the cellular level, are unclear and understudied. Here we use bilingualism as a case study to investigate the metabolic correlates of experience-based brain adaptations. We employ Magnetic Resonance Spectroscopy to measure metabolite concentrations in the basal ganglia, a region critical to language control which is reshaped by bilingualism. Our results show increased myo-Inositol and decreased N-acetyl aspartate concentrations in bilinguals compared to monolinguals. Both metabolites are linked to synaptic pruning, a process underlying experience-based brain restructuring. Interestingly, both concentrations correlate with relative amount of bilingual engagement. This suggests that degree of long-term cognitive experiences matters at the level of metabolic concentrations, which might accompany, if not drive, macroscopic brain adaptations.

Global brain volume and N-acetyl-aspartate decline over seven decades of normal aging

We characterize the whole-brain N-acetyl-aspartate (WBNAA) and brain tissue fractions across the adult lifespan and test the hypothesis that, despite age-related atrophy, neuronal integrity (reflected by WBNAA) is preserved in normal aging. Two-hundred-and-seven participants: 133 cognitively intact older adults (73.6 ± 7.4 mean ± standard deviation, range: 60-90 year old) and 84 young (37.9 ± 11, range: 21-59 year old) were scanned with proton magnetic resonance spectroscopy and T₁-weighted MRI. Their WBNAA, fractional brain parenchyma, and gray and white matter volumes (fBPV, fGM, and fWM) were compared and modeled as functions of age and sex. Compared with young, older-adults' WBNAA was lower by ~35%, and fBPV, fGM and fWM were lower by ~10%. Linear regressions found 0.5%/year WBNAA and 0.2%/year fBPV and fGM declines, whereas fWM rose to age ~40 years, and declined thereafter. fBPV and fGM were 1.8% and 4% higher in women, with no sex decline rates difference. We conclude that contrary to our hypothesis, atrophy was accompanied by WBNAA decline. Across the entire age range, women's brains showed less atrophy than men's. Formulas to estimate WBNAA and brain tissue fractions in healthy adults are provided to help differentiate normal from abnormal aging.

Regional Myo-Inositol, Creatine, and Choline Levels Are Higher at Older Age and Scale Negatively with Visuospatial Working Memory: A Cross-Sectional Proton MR Spectroscopy Study at 7 Tesla on Normal Cognitive Ageing

Proton MR spectroscopy (¹H-MRS) has been used to assess regional neurochemical brain changes during normal ageing, but results have varied. Exploiting the increased sensitivity at ultra-high field, we performed ¹H-MRS in 60 healthy human volunteers to asses age-related differences in metabolite levels and their relation to cognitive ageing. Sex was balanced, and participants were assigned to a younger, middle, and older group according to their age, ranging from 18 to 79 years. They underwent 7T ¹H-MRS of the ACC, DLPFC, hippocampus, and thalamus and performed a visuospatial working memory task outside the scanner. A multivariate ANCOVA revealed a significant overall effect of age group on metabolite levels in all regions. Higher levels in the middle than the younger group were observed for myo-inositol (mIns) in DLPFC and hippocampus and total choline (tCho) in ACC. Higher levels in the older than the younger group were observed for mIns in hippocampus and thalamus, total creatine (tCr) and tCho in ACC and hippocampus; lower levels of glutamate (Glu) were observed in DLPFC. Higher levels in the older than the middle group were observed for mIns in hippocampus, tCr in ACC and hippocampus, tCho in hippocampus, and total N-acetyl aspartate (tNAA) in hippocampus. Working memory performance correlated negatively with tCr and tCho levels in ACC and mIns levels in hippocampus and thalamus, but not with tNAA or glutamate levels. As NAA and Glu are commonly regarded to reflect neuronal health and function and concentrations of mIns, tCr, and tCho are higher in glia than neurons, the findings of this study suggest a potential in vivo connection between cognitive ageing and higher regional levels of glia-related metabolites.SIGNIFICANCE STATEMENT Neurochemical ageing is an integral component of age-related cognitive decline. Proton MR spectroscopy (¹H-MRS) studies of in vivo neurochemical changes across the lifespan have, however, yielded inconclusive results. ¹H-MRS at ultra-high field strength can potentially improve the consistency of findings. Using 7T ¹H-MRS, we assessed levels of mIns, tCr, and tCho (glia-related metabolites) and tNAA and Glu (neuron-related metabolites) in ACC, DLPFC, hippocampus, and thalamus. We found higher levels of glia-related metabolites in all brain regions in older individuals. Working memory performance correlated negatively with regional levels of glia-related metabolites. This study is the first to investigate normal ageing in these brain regions using 7T ¹H-MRS and findings indicate that glia-related metabolites could be valuable in cognitive ageing studies.

Transcranial magnetic stimulation and magnetic resonance spectroscopy: Opportunities for a bimodal approach in human neuroscience

Over the last decade, there has been an increasing number of studies combining transcranial magnetic stimulation (TMS) and magnetic resonance spectroscopy (MRS). MRS provides a manner to non-invasively investigate molecular concentrations in the living brain and thus identify metabolites involved in physiological and pathological processes. Particularly the MRS-detectable metabolites glutamate, the major excitatory neurotransmitter, and gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter, are of interest when combining TMS and MRS. TMS is a non-invasive brain stimulation technique that can be applied either as a neuromodulation or neurostimulation tool, specifically targeting glutamatergic and GABAergic mechanisms. The combination of TMS and MRS can be used to evaluate alterations in brain metabolite levels following an interventional TMS protocol such as repetitive TMS (rTMS) or paired associative stimulation (PAS). MRS can also be combined with a variety of non-interventional TMS protocols to identify the interplay between brain metabolite levels and measures of excitability or receptor-mediated inhibition and facilitation. In this review, we provide an overview of studies performed in healthy and patient populations combining MRS and TMS, both as a measurement tool and as an intervention. TMS and MRS may reveal complementary and comprehensive information on glutamatergic and GABAergic neurotransmission. Potentially, connectivity changes and dedicated network interactions can be probed using the combined TMS-MRS approach. Considering the ongoing technical developments in both fields, combined studies hold future promise for investigations of brain network interactions and neurotransmission.

Examining brain maturation during adolescence using graph Laplacian learning based Fourier transform

BACKGROUND

Longitudinal neuroimaging studies have demonstrated that adolescence is a crucial developmental period of continued brain growth and change. Motivated by both achievements in graph signal processing and recent evidence that some brain areas act as hubs connecting functionally specialized systems, we propose an approach to detect these regions from a spectral analysis perspective. In particular, as the human brain undergoes substantial development throughout adolescence, we evaluate functional network difference among age groups from functional magnetic resonance imaging (fMRI) measurements.

NEW METHODS

We treated these measurements as graph signals defined on the parcellated functional brain regions and proposed a graph Laplacian learning based Fourier transform (GLFT) to transform the original graph signals into the frequency domain. Eigen-analysis was conducted afterwards to study the behaviors of the corresponding brain regions, which enabled the characterization of brain maturation.

RESULT

We first evaluated our method on the synthetic data and then applied it to resting state and task fMRI data from the Philadelphia Neurodevelopmental Cohort (PNC) dataset, comprised of normally developing adolescents from 8 to 22 years of age. The method provided an accuracy of 94.9% in distinguishing different adolescent stages and we detected 13 hubs from resting state fMRI and 16 hubs from task fMRI related to brain maturation.

COMPARISON WITH EXISTING METHODS

The proposed GLFT demonstrated its superiority over conventional graph Fourier transform and alternative graph Fourier transform with high predictive power.

CONCLUSION

The method provides a powerful approach for extracting brain connectivity patterns and identifying hub regions.

Alcohol consumption is associated with reduced creatine levels in the hippocampus of older adults

Besides its well established susceptibility to ageing, the hippocampus has also been shown to be affected by alcohol consumption. Proton spectroscopy (¹H-MRS) of the hippocampus, particularly at high-field 7T MRI, may further our understanding of these associations. Here, we aimed to examine how hippocampal metabolites varied with age and alcohol consumption. Hippocampal metabolite spectra were acquired in 37 older adults using 7T ¹H-MRS, from which we determined the absolute concentration of N-acetylaspartate (NAA), creatine, choline, myo-inositol, glutamate and glutamine. Thirty participants (mean age = 70.4 ± 4.7 years) also had self-reported data on weekly alcohol consumption. Total choline inversely correlated with age, although this did not survive multiple comparisons correction. Crucially, adults with a higher weekly alcohol consumption had significantly lower levels of creatine, suggesting a deficit in their hippocampal metabolism. These findings add to an increasing body of evidence linking alcohol to hippocampal function.

EEG alpha activity increased in response to transcutaneous electrical nervous stimulation in young healthy subjects but not in the healthy elderly

Transcutaneous Electrical Nerve Stimulation (TENS) is used not only in the treatment of pain but also in the examination of sensory functions. With aging, there is decreased sensitivity to somatosensory stimuli. It is essential to examine the effect of TENS application on the sensory functions in the brain by recording the spontaneous electroencephalogram (EEG) activity and the effect of aging on the sensory functions of the brain during the application. The present study aimed to investigate the effect of the application of TENS on the brain’s electrical activity and the effect of aging on the sensory functions of the brain during application of TENS. A total of 15 young (24.2 ± 3.59) and 14 elderly (65.64 ± 4.92) subjects were included in the study. Spontaneous EEG was recorded from 32 channels during TENS application. Power spectrum analysis was performed by Fast Fourier Transform in the alpha frequency band (8–13 Hz) for all subjects. Repeated measures of analysis of variance was used for statistical analysis (p < 0.05). Young subjects had increased alpha power during the TENS application and had gradually increased alpha power by increasing the current intensity of TENS (p = 0.035). Young subjects had higher alpha power than elderly subjects in the occipital and parietal locations (p = 0.073). We can, therefore, conclude that TENS indicated increased alpha activity in young subjects. Young subjects had higher alpha activity than elderly subjects in the occipital and somatosensory areas. To our knowledge, the present study is one of the first studies examining the effect of TENS on spontaneous EEG in healthy subjects. Based on the results of the present study, TENS may be used as an objective method for the examination of sensory impairments, and in the evaluative efficiency of the treatment of pain conditions.

Age-related Brain Metabolic Changes up to Seventh Decade in Healthy Humans : Whole-brain Magnetic Resonance Spectroscopic Imaging Study

PURPOSE

To study brain metabolic changes under normal aging and to collect reference data for the study of neurodegenerative diseases.

METHODS

A total of 55 healthy subjects aged 20-70 years (n ≥ 5 per age decade for each gender) underwent whole-brain magnetic resonance spectroscopic imaging at 3T after completing a DemTect test and the Beck depressions inventory II to exclude cognitive impairment and mental disorder. Regional concentrations of N-acetylaspartate (NAA), choline-containing compounds (Cho), total creatine (tCr), glutamine and glutamate (Glx), and myo-inositol (mI) were determined in 12 brain regions of interest (ROIs). The two-sided t‑test was used to estimate gender differences and linear regression analysis was carried out to estimate age dependence of brain regional metabolite contents.

RESULTS

Brain regional metabolite concentrations changed with age in the majority of selected brain regions. The NAA decreased in 8 ROIs with a rate varying from -4.9% to -1.9% per decade, reflecting a general reduction of brain neuronal function or volume and density in older age; Cho increased in 4 ROIs with a rate varying from 4.3% to 6.1%; tCr and mI increased in one ROI (4.2% and 8.2% per decade, respectively), whereas Glx decreased in one ROI (-5.1% per decade), indicating an inhomogeneous increase of cell membrane turnover (Cho) with altered energy metabolism (tCr) and glutamatergic neuronal activity (Glx) as well as function of glia cell (mI) in normal aging brain.

CONCLUSION

Healthy aging up to the seventh decade of life is associated with regional dependent alterations of brain metabolism. These results provide a reference database for future studies of patients.

Sensorimotor cortex neurometabolite levels as correlate of motor performance in normal aging: evidence from a 1H-MRS study

Aging is associated with gradual alterations in the neurochemical characteristics of the brain, which can be assessed in-vivo with proton-magnetic resonance spectroscopy (¹H-MRS). However, the impact of these age-related neurochemical changes on functional motor behavior is still poorly understood. Here, we address this knowledge gap and specifically focus on the neurochemical integrity of the left sensorimotor cortex (SM1) and the occipital lobe (OCC), as both regions are main nodes of the visuomotor network underlying bimanual control. ¹H-MRS data and performance on a set of bimanual tasks were collected from a lifespan (20-75 years) sample of 86 healthy adults. Results indicated that aging was accompanied by decreased levels of N-acetylaspartate (NAA), glutamate-glutamine (Glx), creatine ​+ ​phosphocreatine (Cr) and myo-inositol (mI) in both regions, and decreased Choline (Cho) in the OCC region. Lower NAA and Glx levels in the SM1 and lower NAA levels in the OCC were related to poorer performance on a visuomotor bimanual coordination task, suggesting that NAA could serve as a potential biomarker for the integrity of the motor system supporting bimanual control. In addition, lower NAA, Glx, and mI levels in the SM1 were found to be correlates of poorer dexterous performance on a bimanual dexterity task. These findings highlight the role for ¹H-MRS to study neurochemical correlates of motor performance across the adult lifespan.

Regional Striatal Cholinergic Involvement in Human Behavioral Flexibility

Animal studies have shown that the striatal cholinergic system plays a role in behavioral flexibility but, until recently, this system could not be studied in humans due to a lack of appropriate noninvasive techniques. Using proton magnetic resonance spectroscopy, we recently showed that the concentration of dorsal striatal choline (an acetylcholine precursor) changes during reversal learning (a measure of behavioral flexibility) in humans. The aim of the present study was to examine whether regional average striatal choline was associated with reversal learning. A total of 22 participants (mean age = 25.2 years, range = 18-32 years, 13 female) reached learning criterion in a probabilistic learning task with a reversal component. We measured choline at rest in both the dorsal and ventral striatum using magnetic resonance spectroscopy. Task performance was described using a simple reinforcement learning model that dissociates the contributions of positive and negative prediction errors to learning. Average levels of choline in the dorsal striatum were associated with performance during reversal, but not during initial learning. Specifically, lower levels of choline in the dorsal striatum were associated with a lower number of perseverative trials. Moreover, choline levels explained interindividual variance in perseveration over and above that explained by learning from negative prediction errors. These findings suggest that the dorsal striatal cholinergic system plays an important role in behavioral flexibility, in line with evidence from the animal literature and our previous work in humans. Additionally, this work provides further support for the idea of measuring choline with magnetic resonance spectroscopy as a noninvasive way of studying human cholinergic neurochemistry.SIGNIFICANCE STATEMENT Behavioral flexibility is a crucial component of adaptation and survival. Evidence from the animal literature shows that the striatal cholinergic system is fundamental to reversal learning, a key paradigm for studying behavioral flexibility, but this system remains understudied in humans. Using proton magnetic resonance spectroscopy, we showed that choline levels at rest in the dorsal striatum are associated with performance specifically during reversal learning. These novel findings help to bridge the gap between animal and human studies by demonstrating the importance of cholinergic function in the dorsal striatum in human behavioral flexibility. Importantly, the methods described here cannot only be applied to furthering our understanding of healthy human neurochemistry, but also to extending our understanding of cholinergic disorders.

Artificial intelligence based discovery of the association between depression and chronic fatigue syndrome

BACKGROUND

Both of the modern medicine and the traditional Chinese medicine classify depressive disorder (DD) and chronic fatigue syndrome (CFS) to one type of disease. Unveiling the association between depressive and the fatigue diseases provides a great opportunity to bridge the modern medicine with the traditional Chinese medicine.

METHODS

In this work, 295 general participants were recruited to complete Zung Self-Rating Depression Scales and Chalder Fatigue Scales, and meanwhile, to donate plasma and urine samples for ¹H NMR-metabolic profiling. Artificial intelligence methods was used to analysis the underlying association between DD and CFS. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to analyze the metabolic profiles with respect to gender and age. Variable importance in projection and t-test were employed in conjunction with the PLS-DA models to identify the metabolite biomarkers. Considering the asymmetry and complexity of the data, convolutional neural networks (CNN) model, an artificial intelligence method, was built to analyze the data characteristics between each groups.

RESULTS

The results showed the gender- and age-related differences for the candidate biomarkers of the DD and the CFS diseases, and indicated the same and different biomarkers of the two diseases. PCA analysis for the data characteristics reflected that DD and CFS was separated completely in plasma metabolite. However, DD and CFS was merged into one group.

LIMITATION

Lack of transcriptomic analysis limits the understanding of the association of the DD and the CFS diseases on gene level.

CONCLUSION

The unmasked candidate biomarkers provide reliable evidence to explore the commonality and differences of the depressive and the fatigue diseases, and thereby, bridge over the traditional Chinese medicine with the modern medicine.

Big GABA II: Water-referenced edited MR spectroscopy at 25 research sites

Accurate and reliable quantification of brain metabolites measured in vivo using ¹H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited γ-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference. Data from 284 volunteers scanned across 25 research sites were collected using GABA+ (GABA + co-edited macromolecules (MM)) and MM-suppressed GABA editing. The unsuppressed water signal from the volume of interest was acquired for concentration referencing. Whole-brain T₁-weighted structural images were acquired and segmented to determine gray matter, white matter and cerebrospinal fluid voxel tissue fractions. Water-referenced GABA measurements were fully corrected for tissue-dependent signal relaxation and water visibility effects. The cohort-wide coefficient of variation was 17% for the GABA + data and 29% for the MM-suppressed GABA data. The mean within-site coefficient of variation was 10% for the GABA + data and 19% for the MM-suppressed GABA data. Vendor differences contributed 53% to the total variance in the GABA + data, while the remaining variance was attributed to site- (11%) and participant-level (36%) effects. For the MM-suppressed data, 54% of the variance was attributed to site differences, while the remaining 46% was attributed to participant differences. Results from an exploratory analysis suggested that the vendor differences were related to the unsuppressed water signal acquisition. Discounting the observed vendor-specific effects, water-referenced GABA measurements exhibit similar levels of variance to creatine-referenced GABA measurements. It is concluded that quantification using internal tissue water referencing is a viable and reliable method for the quantification of in vivo GABA levels.

From fetus to older age: A review of brain metabolic changes across the lifespan

INTRODUCTION

The knowledge of metabolic changes across the lifespan is poorly understood. Thus we systematically reviewed the available literature to determine the changes in brain biochemical composition from fetus to older age and tried to explain them in the context of neural, cognitive, and behavioural changes.

METHODS

The search identified 1262 articles regarding proton magnetic resonance spectroscopy (1H MRS) examinations through December 2017. The following data was extracted: age range of the subjects, number of subjects studied, brain regions studied, MRS sequence used, echo time, MR system, method of statistical analysis, metabolites analyzed, significant differences in metabolites concentrations with age as well as the way of presentation of the results.

RESULTS

82 studies that described brain metabolite changes with age were identified. Reports on metabolic changes related to healthy aging were analyzed and discussed among six basic age groups: fetuses, infants, children, adolescents, adults, and the elderly as well as between groups and during the whole lifetime.

DISCUSSION

The results presented in the reviewed papers provide evidence that normal aging is associated with a number of metabolic changes characteristic for every period of life. Therefore, it can be concluded that the age matching is essential for comparative studies of disease states using 1H MRS.

Alteration of regional homogeneity and white matter hyperintensities in amnestic mild cognitive impairment subtypes are related to cognition and CSF biomarkers

Amnestic mild cognitive impairment can be further classified as single-domain aMCI (SD-aMCI) with isolated memory deficit, or multi-domain aMCI (MD-aMCI) if memory deficit is combined with impairment in other cognitive domains. Prior studies reported these clinical subtypes presumably differ in etiology. Thus, we aimed to explore the possible mechanisms between different aMCI subtypes by assessing alteration in brain activity and brain vasculature, and their relations with CSF AD biomarkers. 49 healthy controls, 32 SD-aMCI, and 32 MD-aMCI, who had undergone structural scans, resting-state functional MRI (rsfMRI) scans and neuropsychological evaluations, were identified. Regional homogeneity (ReHo) was employed to analyze regional synchronization. Periventricular white matter hyperintensities (PWMH) and deep WMH (DWMH) volume of each participant was quantitatively assessed. AD biomarkers from CSF were also measured. SD-aMCI showed decreased ReHo in medial temporal gyrus (MTG), and increased ReHo in lingual gyrus (LG) and superior temporal gyrus (STG) relative to controls. MD-aMCI showed decreased ReHo, mostly located in precuneus (PCu), LG and postcentral gyrus (PCG), relative to SD-aMCI and controls. As for microvascular disease, MD-aMCI patients had more PWMH burden than SD-aMCI and controls. Correlation analyses indicated mean ReHo in differenced regions were related with memory, language, and executive function in aMCI patients. However, no significant associations between PWMH and behavioral data were found. The Aβ level was related with the ReHo value of STG in SD-aMCI. MD-aMCI displayed different patterns of abnormal regional synchronization and more severe PWMH burden compared with SD-aMCI. Therefore aMCI is not a uniform disease entity, and MD-aMCI group may show more complicated pathologies than SD-aMCI group.

Impact of Aging on the Auditory System and Related Cognitive Functions: A Narrative Review

Age-related hearing loss (ARHL), presbycusis, is a chronic health condition that affects approximately one-third of the world's population. The peripheral and central hearing alterations associated with age-related hearing loss have a profound impact on perception of verbal and non-verbal auditory stimuli. The high prevalence of hearing loss in the older adults corresponds to the increased frequency of dementia in this population. Therefore, researchers have focused their attention on age-related central effects that occur independent of the peripheral hearing loss as well as central effects of peripheral hearing loss and its association with cognitive decline and dementia. Here we review the current evidence for the age-related changes of the peripheral and central auditory system and the relationship between hearing loss and pathological cognitive decline and dementia. Furthermore, there is a paucity of evidence on the relationship between ARHL and established biomarkers of Alzheimer's disease, as the most common cause of dementia. Such studies are critical to be able to consider any causal relationship between dementia and ARHL. While this narrative review will examine the pathophysiological alterations in both the peripheral and central auditory system and its clinical implications, the question remains unanswered whether hearing loss causes cognitive impairment or vice versa.

Functional neurochemical imaging of the human striatal cholinergic system during reversal learning

Animal studies have shown that acetylcholine (ACh) levels in the dorsal striatum play a role in reversal learning. However, this has not been studied in humans due to a lack of appropriate non-invasive techniques. Proton magnetic resonance spectroscopy (¹ H-MRS) can be used to measure metabolite levels in humans in vivo. Although it cannot be used to study ACh directly, ¹ H-MRS can be used to study choline, an ACh precursor, which is linked to activity-dependent ACh release. The aim of this study was to use functional-¹ H-MRS (fMRS) to measure changes in choline levels in the human dorsal striatum during performance of a probabilistic reversal learning task. We demonstrate a task-dependent decrease in choline, specifically during reversal, but not initial, learning. We interpret this to reflect a sustained increase in ACh levels, which is in line with findings from the animal literature. This task-dependent change was specific to choline and was not observed in control metabolites. These findings provide support for the use of fMRS in the in vivo study of the human cholinergic system.

Metabolic abnormality in the right dorsolateral prefrontal cortex in patients with obsessive-compulsive disorder: proton magnetic resonance spectroscopy

OBJECTIVE

Proton magnetic resonance spectroscopy (1H-MRS) was used to evaluate metabolic changes in the dorsolateral prefrontal cortex (DLPFC) in patients with obsessive-compulsive disorder (OCD).

METHODS

In total, 14 OCD patients (mean age 28.9±7.2 years) and 14 healthy controls (mean age 32.6±7.1 years) with no history of neurological and psychiatric illness participated in this study. Brain metabolite concentrations were measured from a localised voxel on the right DLPFC using a 3-Tesla 1H-MRS.

RESULTS

The metabolic concentration of myo-inositol in patients with OCD increased significantly by 52% compared with the healthy controls, whereas glutamine/glutamate was decreased by 11%. However, there were no significant differences in N-acetylaspartate, choline, lactate and lipid between the two groups.

CONCLUSION

These findings would be helpful to understand the pathophysiology of OCD associated with the brain metabolic abnormalities in the right DLPFC.

Effect of age and the APOE gene on metabolite concentrations in the posterior cingulate cortex

Proton magnetic resonance spectroscopy (1H-MRS) has provided valuable information about the neurochemical profile of Alzheimer's disease (AD). However, its clinical utility has been limited in part by the lack of consistent information on how metabolite concentrations vary in the normal aging brain and in carriers of apolipoprotein E (APOE) ε4, an established risk gene for AD. We quantified metabolites within an 8cm3 voxel within the posterior cingulate cortex (PCC)/precuneus in 30 younger (20-40 years) and 151 cognitively healthy older individuals (60-85 years). All 1H-MRS scans were performed at 3T using the short-echo SPECIAL sequence and analyzed with LCModel. The effect of APOE was assessed in a sub-set of 130 volunteers. Older participants had significantly higher myo-inositol and creatine, and significantly lower glutathione and glutamate than younger participants. There was no significant effect of APOE or an interaction between APOE and age on the metabolite profile. Our data suggest that creatine, a commonly used reference metabolite in 1H-MRS studies, does not remain stable across adulthood within this region and therefore may not be a suitable reference in studies involving a broad age-range. Increases in creatine and myo-inositol may reflect age-related glial proliferation; decreases in glutamate and glutathione suggest a decline in synaptic and antioxidant efficiency. Our findings inform longitudinal clinical studies by characterizing age-related metabolite changes in a non-clinical sample.

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.

Proton magnetic resonance spectroscopy reveals significant decline in the contents of N-acetylaspartylglutamate in the hippocampus of aged healthy subjects

INTRODUCTION

To characterize the contents of choline (Cho), creatine (Cr) and N-acetylaspartylglutamate (NAA) in the hippocampus of healthy volunteers, we investigated the contents and their correlationship with age, gender and laterality.

MATERIAL AND METHODS

Volunteers were grouped into a young, a middle and an old age. The Cho, Cr and NAA contents were determined with proton magnetic resonance spectroscopy (1H-MRS), and the correlationship was analyzed with Pearson correlation.

RESULTS

The concentration of NAA in the bilateral hippocampi was markedly lower in the old than in the young and the middle (LSD test, all p < 0.025). Furthermore, NAA/Cr in the bilateral hippocampi head (left: 1.10 ±0.40 vs. 1.54 ±0.49 or 1.43 ±0.49; right: 1.04 ±0.42 vs. 1.35 ±0.40 or 1.30 ±0.42), region 1 of the bilateral hippocampal body (left: 1.24 ±0.53 vs. 1.58 ±0.58 or 1.35 ±0.44; right: 1.30 ±0.43 vs. 1.54 ±0.51 or 1.35 ±0.51) and region 2 of the left hippocampal body (1.21 ±0.32 vs. 1.46 ±0.36 or 1.36 ±0.44) and the left hippocampal tail (1.11 ±0.40 vs. 1.36 ±0.47 or 1.15 ±0.32) was significantly higher in the old than in the young and the middle, respectively (all p < 0.026). The NAA content in the bilateral hippocampal head, body and tail negatively correlated with age. Moreover, the NAA, Cho and Cr contents in the hippocampal body and the tail were higher in the right than the left.

CONCLUSIONS

The NAA content of the hippocampal head, body and tail were significantly decreased in the old compared with younger persons, and it negatively correlates with age. The NAA, Cho and Cr contents exhibit laterality in the hippocampal body and tail.

Volume, metabolites and neuroinflammation of the hippocampus in bipolar disorder - A combined magnetic resonance imaging and positron emission tomography study

BACKGROUND

The hippocampus is one of the brain regions that is involved in several pathophysiological theories about bipolar disorder (BD), such as the neuroinflammation theory and the corticolimbic metabolic dysregulation theory. We compared hippocampal volume and hippocampal metabolites in bipolar I disorder (BD-I) patients versus healthy controls (HCs) with magnetic resonance imaging (MRI) and spectroscopy (MRS). We post hoc investigated whether hippocampal volume and hippocampal metabolites were associated with microglial activation and explored if potential illness modifying factors affected these hippocampal measurements and whether these were associated with experienced mood and functioning.

MATERIALS AND METHODS

Twenty-two BD-I patients and twenty-four HCs were included in the analyses. All subjects underwent psychiatric interviews as well as an MRI scan, including a T1 scan and PRESS magnetic resonance spectroscopy (MRS). Volumetric analysis was performed with Freesurfer. MRS quantification was performed with LC Model. A subgroup of 14 patients and 11 HCs also underwent a successful [(11)C]-(R)-PK11195 neuroinflammation positron emission tomography scan.

RESULTS

In contrast to our hypothesis, hippocampal volumes were not decreased in patients compared to HC after correcting for individual whole-brain volume variations. We demonstrated decreased N-acetylaspartate (NAA)+N-acetyl-aspartyl-glutamate (NAAG) and creatine (Cr)+phosphocreatine (PCr) concentrations in the left hippocampus. In the explorative analyses in the left hippocampus we identified positive associations between microglial activation and the NAA+NAAG concentration, between alcohol use and NAA+NAAG concentration, between microglial activation and the depression score and a negative relation between Cr+PCr concentration and experienced occupational disability. Duration of illness associated positively with volume bilaterally.

CONCLUSION

Compared to HCs, the decreased NAA+NAAG concentration in the left hippocampus of BD-I patients suggests a decreased neuronal integrity in this region. In addition we found a positive relation between microglial activation and neuronal integrity in vivo, corresponding to a differentiated microglial function where some microglia induce apoptosis while others stimulate neurogenesis.

Correlation of iron deposition and change of gliocyte metabolism in the basal ganglia region evaluated using magnetic resonance imaging techniques: an in vivo study

INTRODUCTION

We assessed the correlation between iron deposition and the change of gliocyte metabolism in healthy subjects' basal ganglia region, by using 3D-enhanced susceptibility weighted angiography (ESWAN) and proton magnetic resonance spectroscopy ((1)H-MRS).

MATERIAL AND METHODS

Seventy-seven healthy volunteers (39 female and 38 male subjects; age range: 24-82 years old) were enrolled in the experiment including ESWAN and proton MRS sequences, consent for which was provided by themselves or their guardians. For each subject, the mean phase value gained by ESWAN was used to evaluate the iron deposition; choline/creatine (Cho/Cr) and mI/Cr ratios gained by (1)H-MRS were used to evaluate gliocyte metabolism in the basal ganglia region of both sides. The paired t test was used to test the difference between the two sides of the basal ganglia region. Linear regression was performed to evaluate the relation between mean phase value and age. Pearson's correlation coefficient was calculated to analyze the relationship between the result of ESWAN and (1)H-MRS.

RESULTS

There was no difference between the two sides of the basal ganglia region in the mean phase value and Cho/Cr. But in mI/Cr the mean phase value of each nucleus in bilateral basal ganglia decreased with increasing age. There are 16 r-values between the mean phase value and Cho/Cr and mI/Cr in bilateral basal ganglia region. And each of all p-values is less than 0.001 (p < 0.001).

CONCLUSIONS

Iron deposition in the bilateral basal ganglia is associated with the change of gliocyte metabolism with increasing age. Iron deposition in each nucleus of the basal ganglia region changes with age.

Myocardial Metabolic Abnormality in a Primary Left Atrial Rhabdomyosarcoma: Localized 1H MR Spectroscopy

We report a 73-year-old woman with primary left atrial rhabdomyosarcoma and its 1H MR spectroscopy (MRS) findings. The tumor showed a 2.8 cm sized lesion in the posteroinferior atrial wall on MRI. 1H MR spectra were acquired using a point-resolved spectroscopy (PRESS) sequence with electrocardiographic (ECG) gating and respiratory motion. The use of 1H-MRS allowed the quantification of triglyceride (TG) peak groups at 0.9 and 1.3 ppm, and unsaturated group of lipids at 2.1 ppm, creatine (Cr) at 3.0 ppm, and choline (Cho) at 3.2 ppm. The percentages of the myocardial metabolites based on water-peak in the interventricular septum were TG 18.4%, Cr 1.6%, Cho 3.3% and unsaturated group 4.0%, whereas the rhabdomyosarcoma showed TG 118.8%, unsaturated group 5.1%, Cr 1.3%, Cho 3.5% and the olefinic components of fatty acid at 5.4 ppm 24.5%. This case demonstrates that 1H-MRS is potentially useful to diagnose the rhabdomyosarcoma by quantifying the myocardial metabolites which are important biomarkers for heart function and diseases.

Probing astrocyte metabolism in vivo: proton magnetic resonance spectroscopy in the injured and aging brain

Following a brain injury, the mobilization of reactive astrocytes is part of a complex neuroinflammatory response that may have both harmful and beneficial effects. There is also evidence that astrocytes progressively accumulate in the normal aging brain, increasing in both number and size. These astrocyte changes in normal brain aging may, in the event of an injury, contribute to the exacerbated injury response and poorer outcomes observed in older traumatic brain injury (TBI) survivors. Here we present our view that proton magnetic resonance spectroscopy (¹H-MRS), a neuroimaging approach that probes brain metabolism within a defined region of interest, is a promising technique that may provide insight into astrocyte metabolic changes in the injured and aging brain in vivo. Although ¹H-MRS does not specifically differentiate between cell types, it quantifies certain metabolites that are highly enriched in astrocytes (e.g., Myo-inositol, mlns), or that are involved in metabolic shuttling between astrocytes and neurons (e.g., glutamate and glutamine). Here we focus on metabolites detectable by ¹H-MRS that may serve as markers of astrocyte metabolic status. We review the physiological roles of these metabolites, discuss recent ¹H-MRS findings in the injured and aging brain, and describe how an astrocyte metabolite profile approach might be useful in clinical medicine and clinical trials.

In Vitro Metabolomic Approach to Hippocampal Neurodegeneration Induced by Trimethyltin

Search for indicators of neurodegenerative disorders is a hot topic where much research remains to be done. Our aim was to determine proton nuclear magnetic resonance ((1)H-NMR) spectra of brain metabolites in the trimethyltin (TMT) model of neurodegeneration. Male Wistar rats were subjected to TMT or saline and were sacrificed on day 3 or 24 after administration. (1)H-NMR spectrum was measured on the 600 MHz Varian VNMRS spectrometer in nano-probe in the volume of 40 μl of hippocampal extracts. TMT administration resulted in reduction of the hippocampal weight on day 24. Of the sixteen identified metabolite spectra, decreased aspartate and increased glutamine contents were observed in the initial asymptomatic stage of neurodegeneration on day 3 in hippocampal extracts of TMT exposed rats compared to sham animals. Increased myo-inositol content was observed on day 24. The presented data provide further knowledge about this experimental model and putative indicators of neuronal damage.

Regional metabolite concentrations in the brain of healthy dogs measured by use of short echo time, single voxel proton magnetic resonance spectroscopy at 3.0 Tesla

OBJECTIVE

To investigate regional differences of relative metabolite concentrations in the brain of healthy dogs with short echo time, single voxel proton magnetic resonance spectroscopy ((1)H MRS) at 3.0 T.

ANIMALS

10 Beagles.

PROCEDURES

Short echo time, single voxel (1)H MRS was performed at the level of the right and left basal ganglia, right and left thalamus, right and left parietal lobes, occipital lobe, and cerebellum. Data were analyzed with an automated fitting method (linear combination model). Metabolite concentrations relative to water content were obtained, including N-acetyl aspartate, total choline, creatine, myoinositol, the sum of glutamine and glutamate (glutamine-glutamate complex), and glutathione. Metabolite ratios with creatine as the reference metabolite were calculated. Concentration differences between right and left hemispheres and sexes were evaluated with a Wilcoxon signed rank test and among various regions of the brain with an independent t test and 1-way ANOVA.

RESULTS

No significant differences were detected between sexes and right and left hemispheres. All metabolites, except the glutamine-glutamate complex and glutathione, had regional concentrations that differed significantly. The creatine concentration was highest in the basal ganglia and cerebellum and lowest in the parietal lobes. The N-acetyl aspartate concentration was highest in the parietal lobes and lowest in the cerebellum. Total choline concentration was highest in the basal ganglia and lowest in the occipital lobe.

CONCLUSIONS AND CLINICAL RELEVANCE

Metabolite concentrations differed among brain parenchymal regions in healthy dogs. This study may provide reference values for clinical and research studies involving (1)H MRS performed at 3.0 T.

Evaluation of Myo-Inositol as a Potential Biomarker for Depression in Schizophrenia

Depression is highly prevalent in patients with schizophrenia and is associated with significant clinical consequences, but there is no known biomarker for depression in schizophrenia. One of the putative neurochemical biomarkers for depression in major depressive disorder (MDD) is reduced cerebral concentration of myo-Inositol. We examined whether myo-Inositol levels provide a potential marker for depressive symptoms in schizophrenia similar to that in MDD and are informative regarding causal biological pathways underlying both depression and schizophrenia. We used proton magnetic resonance spectroscopy to examine myo-Inositol levels in the anterior cingulate cortex (ACC) in 59 schizophrenia spectrum disorder (SSD) patients and 69 matched community comparison participants. Participants completed the Maryland Trait and State Depression (MTSD) scale to measure symptoms of depression experienced around time of assessment ('State' subscale) and longitudinally ('Trait' subscale). Myo-Inositol in the ACC was negatively correlated with MTSD-Trait scores in both patients (ρ=-0.336, p=0.009) and community comparison samples (ρ=-0.328, p=0.006). Furthermore, patients with a diagnosis of schizoaffective disorder or a history of at least one major depressive episode had lower levels of myo-Inositol compared with schizophrenia patients without a current or past affective diagnosis (p=0.012). Since reduced brain myo-Inositol is associated with MDD, myo-Inositol may be a biochemical marker of depressive mood symptoms across diagnostic boundaries. If confirmed, this finding may aid investigation of the pathophysiology and therapeutics of depression common between depression, schizophrenia and other psychiatric diagnoses.

Metabolic change in the right dorsolateral prefrontal cortex and its correlation with symptom severity in patients with generalized anxiety disorder: Proton magnetic resonance spectroscopy at 3 Tesla

AIMS

A few neuroimaging studies have demonstrated the key brain areas associated with generalized anxiety disorder (GAD). However, the brain metabolic changes in the dorsolateral prefrontal cortex (DLPFC) of patients with GAD are unclear. This study utilized 3-Tesla proton magnetic resonance spectroscopy ((1) H-MRS) to assess the DLPFC metabolic change and its correlation with symptom severity in patients with GAD.

METHODS

Patients with GAD diagnosed using the DSM-IV-TR and age-matched healthy controls participated in this study. Brain metabolite concentrations were measured from a localized voxel on the DLPFC using 3-Tesla (1) H-MRS. Also, the volumetric composition of the gray matter and white matter volumes was assessed using voxel-based morphometry.

RESULTS

The choline/creatine and choline/N-acetylaspartate ratios were significantly lower in patients than in controls. However, there were no significant differences in other metabolite ratios between the two groups. Choline concentrations were negatively correlated with anxiety levels as measured by the Hamilton Anxiety Rating Scale and the Generalized Anxiety Disorder Scale 7. There was no significant difference in the gray matter and white matter volumes in the MRS voxel between the two groups.

CONCLUSIONS

The present study demonstrates that GAD is associated with low a level of choline/N-acetylaspartate in the DLPFC, which is closely related with symptom severity and cognitive dysfunction. This finding will be useful for an understanding of the neural mechanism associated with GAD.

A quantitative analysis of (1)H-MR spectroscopy at 3.0 T of three brain regions from childhood to middle age

OBJECTIVE

To study age-related metabolic changes in different brain regions.

METHODS

Point-resolved spectroscopy (repetition time/echo time = 2000 ms/30 ms) was performed in the left and right hippocampus, the left thalamus and the left centrum semiovale of 80 healthy subjects (37 females and 43 males aged 7-64 years). Analysis of covariance and linear regression were used for statistical analysis. Both metabolite concentration ratios with respect to total creatine (tCr) and absolute metabolite concentrations were included for analysis.

RESULTS

Ins (myo-inositol)/tCr (p < 0.001) and absolute Ins concentration (p = 0.031) were significantly increased with age after adolescence. NAA (N-acetylaspartic acid)/tCr (p < 0.001) and absolute NAA concentration (p = 0.010) significantly declined with age after adolescence.

CONCLUSION

Age-related increase of Ins and decline of NAA are found in all three regions, especially at the hippocampus, indicating possible gliosis in the ageing brain.

ADVANCES IN KNOWLEDGE

We could use NAA/tCr and Ins/tCr as an indicator to estimate the neurons-to-glial cells ratio at the thalamus. This may be an index to distinguish normal tissues from gliosis.