Review: does measurement of regional cerebral blood flow reflect synaptic activity? Implications for PET and fMRI

A deep learning model for generating [18F]FDG PET Images from early-phase [18F]Florbetapir and [18F]Flutemetamol PET images

INTRODUCTION

Amyloid-β (Aβ) plaques is a significant hallmark of Alzheimer's disease (AD), detectable via amyloid-PET imaging. The Fluorine-18-Fluorodeoxyglucose ([18F]FDG) PET scan tracks cerebral glucose metabolism, correlated with synaptic dysfunction and disease progression and is complementary for AD diagnosis. Dual-scan acquisitions of amyloid PET allows the possibility to use early-phase amyloid-PET as a biomarker for neurodegeneration, proven to have a good correlation to [18F]FDG PET. The aim of this study was to evaluate the added value of synthesizing the later from the former through deep learning (DL), aiming at reducing the number of PET scans, radiation dose, and discomfort to patients.

METHODS

A total of 166 subjects including cognitively unimpaired individuals (N = 72), subjects with mild cognitive impairment (N = 73) and dementia (N = 21) were included in this study. All underwent T1-weighted MRI, dual-phase amyloid PET scans using either Fluorine-18 Florbetapir ([18F]FBP) or Fluorine-18 Flutemetamol ([18F]FMM), and an [18F]FDG PET scan. Two transformer-based DL models called SwinUNETR were trained separately to synthesize the [18F]FDG from early phase [18F]FBP and [18F]FMM (eFBP/eFMM). A clinical similarity score (1: no similarity to 3: similar) was assessed to compare the imaging information obtained by synthesized [18F]FDG as well as eFBP/eFMM to actual [18F]FDG. Quantitative evaluations include region wise correlation and single-subject voxel-wise analyses in comparison with a reference [18F]FDG PET healthy control database. Dice coefficients were calculated to quantify the whole-brain spatial overlap between hypometabolic ([18F]FDG PET) and hypoperfused (eFBP/eFMM) binary maps at the single-subject level as well as between [18F]FDG PET and synthetic [18F]FDG PET hypometabolic binary maps.

RESULTS

The clinical evaluation showed that, in comparison to eFBP/eFMM (average of clinical similarity score (CSS) = 1.53), the synthetic [18F]FDG images are quite similar to the actual [18F]FDG images (average of CSS = 2.7) in terms of preserving clinically relevant uptake patterns. The single-subject voxel-wise analyses showed that at the group level, the Dice scores improved by around 13% and 5% when using the DL approach for eFBP and eFMM, respectively. The correlation analysis results indicated a relatively strong correlation between eFBP/eFMM and [18F]FDG (eFBP: slope = 0.77, R2 = 0.61, P-value < 0.0001); eFMM: slope = 0.77, R2 = 0.61, P-value < 0.0001). This correlation improved for synthetic [18F]FDG (synthetic [18F]FDG generated from eFBP (slope = 1.00, R2 = 0.68, P-value < 0.0001), eFMM (slope = 0.93, R2 = 0.72, P-value < 0.0001)).

CONCLUSION

We proposed a DL model for generating the [18F]FDG from eFBP/eFMM PET images. This method may be used as an alternative for multiple radiotracer scanning in research and clinical settings allowing to adopt the currently validated [18F]FDG PET normal reference databases for data analysis.

Hemodynamic signal changes during volitional swallowing in dysphagia patients with different unilateral hemispheric stroke and brainstem stroke: A near-infrared spectroscopy study

BACKGROUND AND OBJECTIVES

Strokes will result in decreased in cortical excitability and changed in the balance between the affected and unaffected hemispheres. Previous studies have focused on cortical changes in healthy subjects during swallowing, while they remain unknown in patients with stroke at different locations. Thus, the purpose of this study was to research cortical activation patterns of swallowing in patients with dysphagia and healthy subjects by the functional near-infrared spectroscopy (fNIRS). We also focus on the comparability of brain activation areas associated with swallowing between patients with different stroke locations and healthy subjects.

METHODS

total of 104 participants were invited to our study, involving 86 patients with dysphagic unilateral hemispheric stroke and 18 age and sex matched healthy controls. The stroke patients were categorized into patients with left unilateral stroke lesions (n = 30), patients with right unilateral stroke lesions (n = 32) and patients with brainstem injury (n = 24) according to different stroke sites. All patients underwent a series of clinical swallowing function assessments, such as the Fiberoptic endoscopic dysphagia severity scale (FEDSS), penetration-aspiration scale (PAS) of Rosenbek, the gugging swallowing screen (GUSS) and the functional oral Intake scale (FOIS) after informed consent has been signed. All participants received the fNIRS system assessment.

RESULTS

The results showed that extensive areas of the cerebral cortex activated during the swallowing tasks in healthy participants (P < FDR 0.05). For patients with left unilateral stroke lesions, the HbO concentration were strongest over the right hemisphere (P < FDR 0.05). In addition, a less severe activation was also observed in the left hemisphere. Comparable to patients with left unilateral stroke lesions, the strongest activation during swallowing task were found in the left hemisphere in patients with right unilateral stroke lesions (P < FDR 0.05). Similarly, the right hemisphere also has activated less. In contrast, patients with brain stem injury showed more bilaterally activation patterns.

CONCLUSION

Our finding states that cortical activation areas differ between patients with different stroke locations and healthy subjects during swallowing. There was a more bilateral activation in healthy participants and patients with lesions in the brainstem while more cortical activation in unaffected hemisphere in patients with unilateral hemispheric stroke. It also provides a basis for the future treatment of dysphagia after stroke.

The effects of nicotine use during adolescence and young adulthood on gray matter cerebral blood flow estimates

Nicotine and tobacco product (NTP) use remains prevalent in adolescence/young adulthood. The effects of NTPs on markers of brain health during this vulnerable neurodevelopmental period remain largely unknown. This report investigates associations between NTP use and gray matter cerebral blood flow (CBF) in adolescents/young adults. Adolescent/young adult (16-22 years-old) nicotine users (NTP; N = 99; 40 women) and non-users (non-NTP; N = 95; 56 women) underwent neuroimaging sessions including anatomical and optimized pseudo-continuous arterial spin labeling scans. Groups were compared on whole-brain gray matter CBF estimates and their relation to age and sex at birth. Follow-up analyses assessed correlations between identified CBF clusters and NTP recency and dependence measures. Controlling for age and sex, the NTP vs. non-NTP contrast revealed a single cluster that survived thresholding which included portions of bilateral precuneus (voxel-wise alpha < 0.001, cluster-wise alpha < 0.05; ≥7 contiguous voxels). An interaction between NTP group contrast and age was observed in two clusters including regions of the left posterior cingulate (PCC)/lingual gyrus and right anterior cingulate cortex (ACC): non-NTP exhibited positive correlations between CBF and age in these clusters, whereas NTP exhibited negative correlations between CBF and age. Lower CBF from these three clusters correlated with urine cotinine (rs=-0.21 - - 0.16; ps < 0.04) and nicotine dependence severity (rs=-0.16 - - 0.13; ps < 0.07). This is the first investigation of gray matter CBF in adolescent/young adult users of NTPs. The results are consistent with literature on adults showing age- and nicotine-related declines in CBF and identify the precuneus/PCC and ACC as potential key regions subserving the development of nicotine dependence.

Brain metabolic correlates of Locus Coeruleus degeneration in Alzheimer's disease: a multimodal neuroimaging study

Locus Coeruleus (LC) degeneration occurs early in Alzheimer's disease (AD) and this could affect several brain regions innervated by LC noradrenergic axon terminals, as these bear neuroprotective effects and modulate neurovascular coupling/neuronal activity. We used LC-sensitive Magnetic Resonance imaging (MRI) sequences enabling LC integrity quantification, and [18F]Fluorodeoxyglucose (FDG) PET, to investigate the association of LC-MRI changes with brain glucose metabolism in cognitively impaired patients (30 amnesticMCI and 13 demented ones). Fifteen cognitively intact age-matched controls (HCs) were submitted only to LC-MRI for comparison with patients. Voxel-wise regression analyses of [18F]FDG images were conducted using the LC-MRI parameters signal intensity (LC_CR) and LC-belonging voxels (LC_VOX). Both LC_CR and LC_VOX were significantly lower in patients compared to HCs, and were directly associated with [18F]FDG uptake in fronto-parietal cortical areas, mainly involving the left hemisphere (p < 0.001, kE > 100). These results suggest a possible association between LC degeneration and cortical hypometabolism in degenerative cognitive impairment with a prevalent left-hemispheric vulnerability, and that LC degeneration might be linked to large-scale functional network alteration in AD pathology.

Disruption in normal correlational patterns of metabolic networks in the limbic circuit during transient global amnesia

Transient global amnesia is characterized by the sudden apparition of severe episodic amnesia, mainly anterograde, associated with emotional changes. Even though the symptoms are stereotyped, cerebral mechanism underlying transient global amnesia remains unexplained and previous studies using positron emission tomography do not show any clear results or consensus on cerebral regions impacted during transient global amnesia. This study included a group of 10 transient global amnesic patients who underwent ¹⁸F-fluorodeoxyglucose positron emission tomography during the acute or recovery phase of the episode and 10 paired healthy controls. Episodic memory was evaluated with the encoding-storage-retrieval paradigm and a story recall test of the Wechsler's memory scale and anxiety was assessed with the Spielberger scale. We used statistical parametric mapping to identify modifications of whole-brain metabolism. Regarding hypometabolism, there was no brain region systematically affected in all transient global amnesic patients and the comparison between amnesic patients and controls did not show any significant differences. To better understand the specific implication of the limbic circuit in the pathophysiology of transient global amnesia, we then conducted a correlational analysis that included regions of this network. Our findings showed that in healthy controls, regions of the limbic circuit seem to operate in a synchronized way with all regions being highly correlated to each other. On the opposite, in transient global amnesic patients, we observed a clear disruption of this normal correlational patterns between regions with the medial temporal lobe (the hippocampus, parahippocampal gyrus and amygdala) included in one cluster and the orbitofrontal cortex, anterior and posterior cingulate gyrus and thalamus gathered in the other one. Given the individual variability in the time course of transient global amnesia, the direct comparison between a group of patients and controls does not seem to favour the identification of subtle and transient alterations in regional metabolism. The involvement of an extended network, such as the limbic circuit, seems more likely to explain the symptoms of patients. Indeed, the synchronization of regions within the limbic circuit seems to be altered during transient global amnesia, which could explain the amnesia and anxiety observed in transient global amnesic patients. The present study thus deepens our understanding of the mechanisms underlying not only amnesia but also the emotional component of transient global amnesia by considering it as a disruption in the normal correlational patterns within the limbic circuit.

Antipsychotics-Induced Changes in Synaptic Architecture and Functional Connectivity: Translational Implications for Treatment Response and Resistance

Schizophrenia is a severe mental illness characterized by alterations in processes that regulate both synaptic plasticity and functional connectivity between brain regions. Antipsychotics are the cornerstone of schizophrenia pharmacological treatment and, beyond occupying dopamine D2 receptors, can affect multiple molecular targets, pre- and postsynaptic sites, as well as intracellular effectors. Multiple lines of evidence point to the involvement of antipsychotics in sculpting synaptic architecture and remodeling the neuronal functional unit. Furthermore, there is an increasing awareness that antipsychotics with different receptor profiles could yield different interregional patterns of co-activation. In the present systematic review, we explored the fundamental changes that occur under antipsychotics' administration, the molecular underpinning, and the consequences in both acute and chronic paradigms. In addition, we investigated the relationship between synaptic plasticity and functional connectivity and systematized evidence on different topographical patterns of activation induced by typical and atypical antipsychotics.

Simultaneous electroencephalography-functional magnetic resonance imaging for assessment of human brain function

Electroencephalography (EEG) and functional Magnetic Resonance Imaging (MRI) have long been used as tools to examine brain activity. Since both methods are very sensitive to changes of synaptic activity, simultaneous recording of EEG and fMRI can provide both high temporal and spatial resolution. Therefore, the two modalities are now integrated into a hybrid tool, EEG-fMRI, which encapsulates the useful properties of the two. Among other benefits, EEG-fMRI can contribute to a better understanding of brain connectivity and networks. This review lays its focus on the methodologies applied in performing EEG-fMRI studies, namely techniques used for the recording of EEG inside the scanner, artifact removal, and statistical analysis of the fMRI signal. We will investigate simultaneous resting-state and task-based EEG-fMRI studies and discuss their clinical and technological perspectives. Moreover, it is established that the brain regions affected by a task-based neural activity might not be limited to the regions in which they have been initiated. Advanced methods can help reveal the regions responsible for or affected by a developed neural network. Therefore, we have also looked into studies related to characterization of structure and dynamics of brain networks. The reviewed literature suggests that EEG-fMRI can provide valuable complementary information about brain neural networks and functions.

Early-phase 18F-Florbetapir and 18F-Flutemetamol images as proxies of brain metabolism in a memory clinic setting

Background: Alzheimer's disease (AD) neuropathologic changes are β-amyloid (Aβ) deposition, pathologic tau, and neurodegeneration. Dual-phase amyloid-PET might be able to evaluate Aβ deposition and neurodegeneration with a single tracer injection. Early-phase amyloid-PET scans provide a proxy for cerebral perfusion, which has shown good correlations with neural dysfunction measured through metabolic consumption, while the late frames depict amyloid distribution. Our study aims to assess the comparability between early-phase amyloid-PET scans and 18F-fluorodeoxyglucose (18F-FDG)-PET brain topography at the individual level, and their ability to discriminate patients. Methods: 166 subjects evaluated at the Geneva Memory Center, ranging from cognitively unimpaired to Mild Cognitive Impairment (MCI) and dementia, underwent early-phase amyloid-PET - using either 18F-florbetapir (eFBP) (n = 94) or 18F-flutemetamol (eFMM) (n = 72) - and 18F-FDG-PET. Aβ status was assessed. Standardized uptake value ratios (SUVR) were extracted to evaluate the correlation of eFBP/eFMM and their respective 18F-FDG-PET scans. The single-subject procedure was applied to investigate hypometabolism and hypoperfusion maps and their spatial overlap by Dice coefficient. Receiver operating characteristic analyses were performed to compare the discriminative power of eFBP/eFMM, and 18F-FDG-PET SUVR in AD-related metaROI between Aβ-negative healthy controls and cases in the AD continuum. Results: Positive correlations were found between eFBP/eFMM and 18F-FDG-PET SUVR independently of Aβ status and Aβ radiotracer (R>0.72, p<0.001). eFBP/eFMM single-subject analysis revealed clusters of significant hypoperfusion with good correspondence to hypometabolism topographies, independently of the underlying neurodegenerative patterns. Both eFBP/eFMM and 18F-FDG-PET SUVR significantly discriminated AD patients from controls in the AD-related metaROIs (AUCFBP = 0.888; AUCFMM=0.801), with 18F-FDG-PET performing slightly better, however not significantly (all p-value higher than 0.05), than others (AUCFDG=0.915 and 0.832 for subjects evaluated with 18F-FBP and 18F-FMM, respectively). Conclusion: The distribution of perfusion was comparable to that of metabolism at the single-subject level by parametric analysis, particularly in the presence of a high neurodegeneration burden. Our findings indicate that eFBP/eFMM imaging can replace 18F-FDG-PET imaging, as they reveal typical neurodegenerative patterns, or allow to exclude the presence of neurodegeneration. The finding shows cost-saving capacities of amyloid-PET and supports the routine use of the modality for individual classification in clinical practice.

Alzheimer's disease pattern derived from relative cerebral flow as an alternative for the metabolic pattern using SSM/PCA

BACKGROUND

2-Deoxy-2-[¹⁸F]fluoroglucose (FDG) PET is an important tool for the identification of Alzheimer's disease (AD) patients through the characteristic neurodegeneration pattern that these patients present. Regional cerebral blood flow (rCBF) images derived from dynamic ¹¹C-labelled Pittsburgh Compound B (PIB) have been shown to present a similar pattern as FDG. Moreover, multivariate analysis techniques, such as scaled subprofile modelling using principal component analysis (SSM/PCA), can be used to generate disease-specific patterns (DP) that may aid in the classification of subjects. Therefore, the aim of this study was to compare rCBF AD-DPs with FDG AD-DP and their respective performances. Therefore, 52 subjects were included in this study. Fifteen AD and 16 healthy control subjects were used to generate four AD-DP: one based on relative cerebral trace blood (R₁), two based on time-weighted average of initial frame intervals (ePIB), and one based on FDG images. Furthermore, 21 subjects diagnosed with mild cognitive impairment were tested against these AD-DPs.

RESULTS

In general, the rCBF and FDG AD-DPs were characterized by a reduction in cortical frontal, temporal, and parietal lobes. FDG and rCBF methods presented similar score distribution.

CONCLUSION

rCBF images may provide an alternative for FDG PET scans for the identification of AD patients through SSM/PCA.

Incremental diagnostic value of 18F-Fluetemetamol PET in differential diagnoses of Alzheimer's Disease-related neurodegenerative diseases from an unselected memory clinic cohort

To evaluate the incremental diagnostic value of 18F-Flutemetamol PET following MRI measurements on an unselected prospective cohort collected from a memory clinic. A total of 84 participants was included in this study. A stepwise study design was performed including initial analysis (based on clinical assessments), interim analysis (revision of initial analysis post-MRI) and final analysis (revision of interim analysis post-18F-Flutemetamol PET). At each time of evaluation, every participant was categorized into SCD, MCI or dementia syndromal group and further into AD-related, non-AD related or non-specific type etiological subgroup. Post 18F-Flutemetamol PET, the significant changes were seen in the syndromal MCI group (57%, p < 0.001) involving the following etiological subgroups: AD-related MCI (57%, p < 0.01) and non-specific MCI (100%, p < 0.0001); and syndromal dementia group (61%, p < 0.0001) consisting of non-specific dementia subgroup (100%, p < 0.0001). In the binary regression model, amyloid status significantly influenced the diagnostic results of interim analysis (p < 0.01). 18F-Flutemetamol PET can have incremental value following MRI measurements, particularly reflected in the change of diagnosis of individuals with unclear etiology and AD-related-suspected patients due to the role in complementing AD-related pathological information.

Hyper-connectivity between the left motor cortex and prefrontal cortex is associated with the severity of dysfunction of the descending pain modulatory system in fibromyalgia

Introduction

The association between descending pain modulatory system (DPMS) dysfunction and fibromyalgia has been previously described, but more studies are required on its relationship with aberrant functional connectivity (FC) between the motor and prefrontal cortices.

Objectives

The objective of this cross-sectional observational study was to compare the intra- and interhemispheric FC between the bilateral motor and prefrontal cortices in women with fibromyalgia, comparing responders and nonresponders to the conditioned pain modulation (CPM) test.

Methods

A cross-sectional sample of 37 women (23 responders and 14 nonresponders to the CPM test) with fibromyalgia diagnosed according to the American College of Rheumatology criteria underwent a standardized clinical assessment and an FC analysis using functional near-infrared spectroscopy. DPMS function was inferred through responses to the CPM test, which were induced by hand immersion in cold water (0–1°C). A multivariate analysis of covariance for main effects between responders and nonresponders was conducted using the diagnosis of multiple psychiatric disorders and the use of opioid and nonopioid analgesics as covariates. In addition, we analyzed the interaction between the CPM test response and the presence of multiple psychiatric diagnoses.

Results

Nonresponders showed increased FC between the left motor cortex (lMC) and the left prefrontal cortex (lPFC) (t = −2.476, p = 0.01) and right prefrontal cortex (rPFC) (t = −2.363, p = 0.02), even when both were considered as covariates in the regression analysis (lMC–lPFC: β = −0.127, t = −2.425, p = 0.021; lMC–rPFC: β = −0.122, t = −2.222, p = 0.033). Regarding main effects, a significant difference was only observed for lMC–lPFC (p = 0.035). A significant interaction was observed between the psychiatric disorders and nonresponse to the CPM test in lMC−lPFC (β = −0.222, t = −2.275, p = 0.03) and lMC−rPFC (β = −0.211, t = −2.2, p = 0.035). Additionally, a significant interaction was observed between the CPM test and FC in these two region-of-interest combinations, despite the psychiatric diagnoses (lMC−lPFC: β = −0.516, t = −2.447, p = 0.02; lMC−rPFC: β = −0.582, t = −2.805, p = 0.008).

Conclusions

Higher FC between the lMC and the bilateral PFC may be a neural marker of DPMS dysfunction in women with fibromyalgia, although its interplay with psychiatric diagnoses also seems to influence this association.

Repetitive Transcranial Magnetic Stimulation-Associated Changes in Neocortical Metabolites in Major Depression: A Systematic Review

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We reviewed 12 studies that measured metabolites pre and post rTMS in MDD.

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Frontal lobe Glu, Gln, NAA, and GABA increased after rTMS.

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Increases in metabolites were often associated with MDD symptom improvement.

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We propose novel intracellular mechanisms by which metabolites are altered by rTMS.

Introduction

Repetitive Transcranial magnetic stimulation (rTMS) is an FDA approved treatment for major depressive disorder (MDD). However, neural mechanisms contributing to rTMS effects on depressive symptoms, cognition, and behavior are unclear. Proton magnetic resonance spectroscopy (MRS), a noninvasive neuroimaging technique measuring concentrations of biochemical compounds within the brain in vivo, may provide mechanistic insights.

Methods

This systematic review summarized published MRS findings from rTMS treatment trials to address potential neurometabolic mechanisms of its antidepressant action. Using PubMed, Google Scholar, Web of Science, and JSTOR, we identified twelve empirical studies that evaluated changes in MRS metabolites in a within-subjects, pre- vs. post-rTMS treatment design in patients with MDD.

Results

rTMS protocols ranged from four days to eight weeks duration, were applied at high frequency to the left dorsolateral prefrontal cortex (DLPFC) in most studies, and were conducted in patients aged 13-to-70. Most studies utilized MRS point resolved spectroscopy acquisitions at 3 Tesla in the bilateral anterior cingulate cortex and DLPFC. Symptom improvements were correlated with rTMS-related increases in the concentration of glutamatergic compounds (glutamate, Glu, and glutamine, Gln), GABA, and N-acetylated compounds (NAA), with some results trend-level.

Conclusions

This is the first in-depth systematic review of metabolic effects of rTMS in individuals with MDD. The extant literature suggests rTMS stimulation does not produce changes in neurometabolites independent of clinical response; increases in frontal lobe glutamatergic compounds, N-acetylated compounds and GABA following high frequency left DLPFC rTMS therapy were generally associated with clinical improvement. Glu, Gln, GABA, and NAA may mediate rTMS treatment effects on MDD symptomatology through intracellular mechanisms.

Long term effects of chronic intranasal oxytocin on adult pair bonding behavior and brain glucose uptake in titi monkeys (Plecturocebus cupreus)

Intranasal oxytocin (IN OXT) administration has been proposed as a pharmacological treatment for a range of biomedical conditions including neurodevelopmental disorders. However, studies evaluating the potential long-lasting effects of chronic IN OXT during development are still scarce. Here we conducted a follow-up study of a cohort of adult titi monkeys that received intranasal oxytocin 0.8 IU/kg (n = 15) or saline (n = 14) daily for six months during their juvenile period (12 to 18 months of age), with the goal of evaluating the potential long-lasting behavioral and neural effects one year post-treatment. Subjects were paired with an opposite-sex mate at 30 months of age (one year post-treatment). We examined pair affiliative behavior in the home cage during the first four months and tested for behavioral components of pair bonding at one week and four months post-pairing. We assessed long-term changes in brain glucose uptake using ¹⁸FDG positron emission tomography (PET) scans. Our results showed that OXT-treated animals were more affiliative across a number of measures, including tail twining, compared to SAL treated subjects (tail twining is considered the "highest" type of affiliation in titi monkeys). Neuroimaging showed no treatment differences in glucose uptake between SAL and OXT-treated animals; however, females showed higher glucose uptake in whole brain at 23 months, and in both the whole brain and the social salience network at 33 months of age compared to males. Our results suggest that chronic IN OXT administration during development can have long-term effects on adult social behavior.

Assessment of the In Vivo Relationship Between Cerebral Hypometabolism, Tau Deposition, TSPO Expression, and Synaptic Density in a Tauopathy Mouse Model: a Multi-tracer PET Study

Cerebral glucose hypometabolism is a typical hallmark of Alzheimer’s disease (AD), usually associated with ongoing neurodegeneration and neuronal dysfunction. However, underlying pathological processes are not fully understood and reproducibility in animal models is not well established. The aim of the present study was to investigate the regional interrelation of glucose hypometabolism measured by [¹⁸F]FDG positron emission tomography (PET) with various molecular targets of AD pathophysiology using the PET tracers [¹⁸F]PI-2620 for tau deposition, [¹⁸F]DPA-714 for TSPO expression associated with neuroinflammation, and [¹⁸F]UCB-H for synaptic density in a transgenic tauopathy mouse model. Seven-month-old rTg4510 mice (n = 8) and non-transgenic littermates (n = 8) were examined in a small animal PET scanner with the tracers listed above. Hypometabolism was observed throughout the forebrain of rTg4510 mice. Tau pathology, increased TSPO expression, and synaptic loss were co-localized in the cortex and hippocampus and correlated with hypometabolism. In the thalamus, however, hypometabolism occurred in the absence of tau-related pathology. Thus, cerebral hypometabolism was associated with two regionally distinct forms of molecular pathology: (1) characteristic neuropathology of the Alzheimer-type including synaptic degeneration and neuroinflammation co-localized with tau deposition in the cerebral cortex, and (2) pathological changes in the thalamus in the absence of other markers of AD pathophysiology, possibly reflecting downstream or remote adaptive processes which may affect functional connectivity. Our study demonstrates the feasibility of a multitracer approach to explore complex interactions of distinct AD-pathomechanisms in vivo in a small animal model. The observations demonstrate that multiple, spatially heterogeneous pathomechanisms can contribute to hypometabolism observed in AD mouse models and they motivate future longitudinal studies as well as the investigation of possibly comparable pathomechanisms in human patients.

Metabolic Imaging of Deep Brain Stimulation in Meige Syndrome

Objectives

The subthalamic nucleus (STN) has been shown to be a safe and effective deep brain stimulation (DBS) surgical target for the treatment of Meige syndrome. The aim of this study was to compare changes in brain metabolism before and 6 months after STN-DBS surgery.

Methods

Twenty-five patients with primary Meige syndrome underwent motor function assessment, including the Burke–Fahn–Marsden Dystonia Rating Scale movement (BFMDRS-M) and disability subscale (BFMDRS-D) and positron emission tomography with an 18[F]-fluorodeoxyglucose scan before and 6 months after STN-DBS surgery. For the voxelwise metabolic change assessment, the p-value was controlled for multiple comparisons using the familywise error rate.

Results

There was a significant decrease in BFMDRS-M scores 6 months after STN-DBS, from 10.02 ± 3.99 to 4.00 ± 2.69 (p &lt; 0.001). The BFMDRS-D scores also decreased significantly from 4.52 ± 2.90 to 0.64 ± 1.29 (p &lt; 0.001). In the left hemisphere, hypermetabolism was found in the occipital lobe, superior parietal gyrus, postcentral gyrus and thalamus. In the right hemisphere, hypermetabolism was found in the lentiform nucleus, precuneus and precentral gyrus in patients with Meige syndrome receiving DBS. In addition, the bilateral inferior temporal gyrus and middle frontal gyrus exhibited glucose hypermetabolism.

Conclusion

Our findings indicate that STN-DBS has a significant effect on metabolic level in the brain, which may be an important mechanism for the treatment of Meige syndrome using STN-DBS.

Longitudinal Single Photon Emission Computed Tomography Neuroimaging as an Indication of Improvement in Psychiatric Disorders in a Community Psychiatric Practice

In the community, there is a need to more objectively evaluate the response of common chronic psychiatric disorders to treatment. Brain single photon emission computed tomography (SPECT) indirectly measures cerebral functional activity by uptake of a radiotracer, which follows regional cerebral blood flow. Brain 3D Thresholded SPECT scans are thresholded three dimensional images derived from brain SPECT data. A retrospective community study of longitudinal (before and after treatment) brain 3D Thresholded SPECT scans of 73 patients with all-cause psychiatric disorders (most frequent diagnostic clusters: attention-deficit hyperactivity disorder, post-mild traumatic brain injury, affective disorders, psychotic disorders, post-viral chronic syndromes), shows these baseline SPECT scans predict improvement (non-worsening to large improvement) in clinical functioning with a sensitivity of 94% (95% confidence interval 86-98%) and a specificity of 67% (95% confidence interval 21-94%). In contrast, contemporaneous analysis by the same radiologist of conventional 2D reading of the same before and after treatment brain SPECT scan data of the same 73 patients, predicted improvement (non-worsening to large improvement) in clinical functioning with a sensitivity of only 26% (95% confidence interval 17-37%) although with a specificity of 100% (95% confidence interval 44-100%). These data suggest 3D Thresholded SPECT scans can provide the clinician with a more objective measure for verifying improvement in psychiatric disorders seen in the community, consistent with prior studies of SPECT as a measure of neurobiological change. Furthermore, these data suggest 3D Thresholded SPECT scans may have clinical application in guiding treatment and potentially improving outcomes.

rTMS Therapy Reduces Hypofrontality in Patients With Depression as Measured by fNIRS

Multichannel functional near-infrared spectroscopy (fNIRS) is a tool used to capture changes in cerebral blood flow. A consistent result for depression is a decrease in blood flow in the frontal cortex leading to hypofrontality, which indicates multidomain functional impairment. Repetitive transcranial magnetic stimulation (rTMS) and elective convulsive therapy (ECT) are alternatives to antidepressant drugs for the treatment of depression but the underlying mechanism is yet to be elucidated. The aim of the current study was to evaluate cerebral blood flow using fNIRS following rTMS treatment in patients with depression. The cerebral blood flow of 15 patients with moderate depression after rTMS treatment was measured using fNIRS. While there was clear hypofrontality during pre-treatment (5 ± 2.5), a notable increase in oxygenated hemoglobin was observed after 30 sessions with rTMS (50 ± 15). This increased blood flow was observed in a wide range of channels in the frontal cortex; however, the centroid values were similar between the treatments. Increased blood flow leads to the activation of neuronal synapses, as noted with other neuromodulation treatments such as electroconvulsive therapy. This study describes the rTMS-induced modulation of blood oxygenation response over the prefrontal cortex in patients with depression, as captured by fNIRS. Future longitudinal studies are needed to assess cerebral blood flow dynamics during rTMS treatment for depression.

Impact of multisession 40Hz tACS on hippocampal perfusion in patients with Alzheimer's disease

Background

Alzheimer’s disease (AD) is associated with alterations in cortical perfusion that correlate with cognitive impairment. Recently, neural activity in the gamma band has been identified as a driver of arteriolar vasomotion while, on the other hand, gamma activity induction on preclinical models of AD has been shown to promote protein clearance and cognitive protection.

Methods

In two open-label studies, we assessed the possibility to modulate cerebral perfusion in 15 mild to moderate AD participants via 40Hz (gamma) transcranial alternating current stimulation (tACS) administered 1 h daily for 2 or 4 weeks, primarily targeting the temporal lobe. Perfusion-sensitive MRI scans were acquired at baseline and right after the intervention, along with electrophysiological recording and cognitive assessments.

Results

No serious adverse effects were reported by any of the participants. Arterial spin labeling MRI revealed a significant increase in blood perfusion in the bilateral temporal lobes after the tACS treatment. Moreover, perfusion changes displayed a positive correlation with changes in episodic memory and spectral power changes in the gamma band.

Conclusions

Results suggest 40Hz tACS should be further investigated in larger placebo-controlled trials as a safe, non-invasive countermeasure to increase fast brain oscillatory activity and increase perfusion in critical brain areas in AD patients.

Trial registration

Studies were registered separately on ClinicalTrials.gov (NCT03290326, registered on September 21, 2017; NCT03412604, registered on January 26, 2018).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00922-4.

Associations between Brain Reserve Proxies and Clinical Progression in Alzheimer's Disease Dementia

The purpose of this study was to investigate whether brain and cognitive reserves were associated with the clinical progression of AD dementia. We included participants with AD dementia from the Alzheimer’s Disease Neuroimaging Initiative, provided they were followed up at least once, and candidate proxies for cognitive (education for early-life reserve and Adult Reading Test for late-life reserve) or brain reserve (intracranial volume [ICV] for early-life reserve and the composite value of [¹⁸F] fluorodeoxyglucose positron emission tomography regions of interest (FDG-ROIs) for late-life reserve) were available. The final analysis included 120 participants. Cox proportional hazards model revealed that FDG-ROIs were the only significant predictor of clinical progression. Subgroup analysis revealed a significant association between FDG-ROIs and clinical progression only in the larger ICV group (HR = 0.388, p = 0.028, 95% CI 0.167–0.902). Our preliminary findings suggest that relatively preserved cerebral glucose metabolism might delay further clinical progression in AD dementia, particularly in the greater ICV group. In addition to ICV, cerebral glucose metabolism could play an important role as a late-life brain reserve in the process of neurodegeneration. Distinguishing between early- and late-life reserves, and considering both proxies simultaneously, would provide a wider range of factors associated with the prognosis of AD dementia.

Coupling relationship between glucose and oxygen metabolisms to differentiate preclinical Alzheimer's disease and normal individuals

The discovery of preclinical Alzheimer's disease (preAD) provides a wide time window for the early intervention of AD. The coupling relationships between glucose and oxygen metabolisms from hybrid PET/MRI can provide complementary information on the brain's physiological state for preAD. In this study, we purpose to explore the change of coupling relationship among 27 normal controls (NCs), 20 preADs, and 15 cognitive impairments (CIs). For each subject, we calculated the Spearman partial correlation between the fractional amplitude of low-frequency fluctuations (fALFF) and the regional homogeneity (ReHo) from functional image (fMRI), and the standard uptake value ratio (SUVR) from [18F] fluorodeoxyglucose positron emission tomography (18 F-FDG PET), in the whole-brain and default mode network (DMN) as a novel potential biomarker. The diagnostic performance of this biomarker was evaluated by the receiver operating characteristic analysis. Significant Spearman correlations between the FDG SUVR and the fALFF/ReHo were found in 98% of subjects. For the DMN-based biomarker, there was a significant decreasing trend for the preAD and CI groups compared to the NC group, whereas no significant difference in preAD based on whole-brain. The correlation ρ value for the FDG SUVR/ReHo showed the highest area under curve of the preAD classification (0.787). The results imply the coupling relationship changed during the preAD stage in the DMN area.

Regional metabolic and network changes in Meige syndrome

To contribute to the understanding of the aetiology and pathogenesis of Meige syndrome, the metabolic networks of patients with Meige syndrome were investigated using 18F-fluoro-D-glucose positron emission tomography (18F-FDG-PET) imaging of cerebral glucose metabolism. Fifty right-handed and unmedicated primary Meige syndrome patients enrolled between September 2017 and September 2020 at the Department of Neurosurgery, Peking University People’s Hospital, and 50 age- and sex-matched healthy control subjects participated in the study. Metabolic connectivity and graph theory analysis were used to investigate metabolic network differences based on 18F-FDG-PET images. Glucose hypometabolism was detected in the left internal globus pallidus and parietal lobe, right frontal lobe and postcentral gyrus, and bilateral thalamus and cerebellum of patients with Meige syndrome. Clustering coefficients (Cps) (density threshold: 16–28%; P < 0.05) and shortest path lengths (Lps) (density threshold: 10–15%; P < 0.05) were higher in Meige syndrome patients than in healthy controls. Small-worldness was lower in Meige syndrome patients than in healthy controls, and centrality was significantly lower in the right superior occipital gyrus and pallidum and higher in the right thalamus. Hypometabolism in the globus pallidus and thalamus may indicate basal ganglia-thalamocortical motor circuit abnormalities as a pathogenic mechanism of Meige syndrome, providing a possible explanation for the efficacy of deep brain stimulation (DBS) in improving symptoms. Meige syndrome patients had abnormal small-world properties. Centrality changes in the right pallidus and thalamus verified the important roles of these regions in the pathogenesis of Meige syndrome.

Disease Burden Affects Aging Brain Function

BACKGROUND

Most older adults live with multiple chronic disease conditions, yet the effect of multiple diseases on brain function remains unclear.

METHODS

We examine the relationship between disease multimorbidity and brain activity using regional cerebral blood flow (rCBF) 15O-water PET scans from 97 cognitively normal participants (mean baseline age 76.5) in the Baltimore Longitudinal Study of Aging (BLSA). Multimorbidity index scores, generated from the presence of 13 health conditions, were correlated with PET data at baseline and in longitudinal change (n=74) over 5.05 (2.74 SD) years.

RESULTS

At baseline, voxel-based analysis showed that higher multimorbidity scores were associated with lower relative activity in orbitofrontal, superior frontal, temporal pole and parahippocampal regions, and greater activity in lateral temporal, occipital and cerebellar regions. Examination of the individual health conditions comprising the index score showed hypertension and chronic kidney disease individually contributed to the overall multimorbidity pattern of altered activity. Longitudinally, both increases and decreases in activity were seen in relation to increasing multimorbidity over time. These associations were identified in orbitofrontal, lateral temporal, brainstem, and cerebellar areas.

CONCLUSION

Together, these results show that greater multimorbidity is associated with widespread areas of altered brain activity, supporting a link between health and changes in aging brain function.

The Usefulness of Functional Near-Infrared Spectroscopy for the Assessment of Post-Stroke Depression

Background: Post-stroke depression (PSD) is the most common mood disorder following stroke and is also the main factor that limits the recovery and rehabilitation of patients with stroke. The prevalence of PSD is ~30%. Since there is no gold standard for the diagnosis and evaluation of PSD, it is important to raise awareness of PSD and to establish methods for its evaluation, early diagnosis, and treatment. In the field of psychiatry, functional near-infrared spectroscopy (fNIRS) has been used as a diagnostic tool for the measurement of oxygenated hemoglobin (oxy-Hb). This study aimed to assess whether fNIRS could be applied in the diagnosis and evaluation of PSD.

Methods: We recruited 45 patients with stroke, who were admitted to Nagasaki Kita Hospital between May 2015 and April 2019. The 17-item Hamilton Rating Scale for Depression (HAMD17), which is considered to be a useful screening and evaluation tool for PSD, was used for the assessment of patients after stroke; moreover, oxy-Hb was measured in the pre-frontal cortex. The subjects were divided into two groups: the depressed group (n = 13) and the non-depressed group (n = 32). We evaluated the correlation between the oxy-Hb integral values and HAMD17 scores.

Results: We investigated the relationship between the oxy-Hb integral values and HAMD17 total scores, and found a negative correlation between them (ρ = −0.331, P < 0.005). There was a significant difference in the oxy-Hb integral values during the activation task period between the depressed and non-depressed groups (3.16 ± 2.7 and 1.71 ± 2.4, respectively; P = 0.040). The results indicated that the patients of the depressed group showed lower oxy-Hb integral values and lower activation in the frontal lobe in comparison with the patients of the non-depressed group.

Conclusion: The present study highlights that the measurement of oxy-Hb by using fNIRS is a useful methodology for the diagnosis of PSD in patients after stroke.

Feasibility of pharmacokinetic parametric PET images in scaled subprofile modelling using principal component analysis

Scaled subprofile model using principal component analysis (SSM/PCA) is a multivariate analysis technique used, mainly in [¹⁸F]-2-fluoro-2-deoxy-d-glucose (FDG) PET studies, for the generation of disease-specific metabolic patterns (DP) that may aid with the classification of subjects with neurological disorders, like Alzheimer’s disease (AD). The aim of this study was to explore the feasibility of using quantitative parametric images for this type of analysis, with dynamic [¹¹C]-labelled Pittsburgh Compound B (PIB) PET data as an example. Therefore, 15 AD patients and 15 healthy control subjects were included in an SSM/PCA analysis to generate four AD-DPs using relative cerebral blood flow (R₁), binding potential (BP_ND) and SUVR images derived from dynamic PIB and static FDG-PET studies. Furthermore, 49 new subjects with a variety of neurodegenerative cognitive disorders were tested against these DPs. The AD-DP was characterized by a reduction in the frontal, parietal, and temporal lobes voxel values for R₁ and SUVR-FDG DPs; and by a general increase of values in cortical areas for BP_ND and SUVR-PIB DPs. In conclusion, the results suggest that the combination of parametric images derived from a single dynamic scan might be a good alternative for subject classification instead of using 2 independent PET studies.

Mapping the orbitofrontal cortex using temporal fluctuations in cerebral blood flow

INTRODUCTION

The orbitofrontal cortex (OFC) is involved in diverse cognitive and behavioral processes including incentive valuation, decision-making, and reinforcement learning. Anatomic and cytoarchitectonic studies divide the OFC along both medial-lateral and rostral-caudal axes. OFC regions diverge in structure and function, assessed in vivo using white matter tractography and blood oxygenation level-dependent (BOLD) MRI, respectively. However, interpretation of T₂ *-weighted BOLD is limited by susceptibility artifacts in the inferior frontal lobes, with the spatial pattern of these artifacts frequently assuming the geometry of OFC organization. Here, we utilize a novel perfusion-weighted arterial spin labeling (ASL) functional connectivity approach, which is minimally susceptibility-weighted, to test the hypothesis that OFC topology reflects correlated temporal hemodynamic activity.

METHODS

In healthy participants (n = 20; age = 29.5 ± 7.3), 3D ASL scans were acquired (TR/TE = 3,900/13 ms; spatial resolution = 3.8 mm isotropic). To evaluate reproducibility, follow-up scanning on a separate day was performed on a participant subset (n = 8). ASL-based connectivity was modeled for gray matter OFC voxels, and k-means clustering (k = 2-8) applied to correlation statistics.

RESULTS

These approaches revealed both medial-lateral and rostral-caudal OFC divisions, confirming our hypothesis. Longitudinal reproducibility testing revealed 84% voxel clustering agreement between sessions for the k = 2 solution.

CONCLUSION

To our knowledge, this constitutes the first in vivo cortical parcellation based on perfusion fluctuations. Our approach confirms functional OFC subdivisions predicted from anatomy using a less susceptibility-sensitive method than the conventional approach.

FDG-PET assessment of the locus coeruleus in Alzheimer's disease

Sensitive and reliable in vivo imaging of the locus coeruleus (LC) is important to develop and evaluate its potential as a biomarker in neurodegenerative diseases such as Alzheimer's disease (AD). It is not known whether AD-related alterations in LC integrity can be detected using 18F-labelled fluoro-2-deoxyglucose (FDG) positron emission tomography (PET). Mean FDG-PET images from AD patients (N ​= ​193) and controls (N ​= ​256) from the ADNI database were co-registered to a study-wise anatomical template. Regional LC median standardized uptake value ratio (SUVR) values were obtained using four previously published LC masks and normalized to values from pons and cerebellar vermis reference regions. To support the validity of our methods, other regions previously reported to be most and least affected metabolically in AD were also compared to controls. The LC did not show between-group differences in FDG-PET signal, whereas the mammillary bodies did, despite these regions having comparable volumes and SUVR ranges. Brain regions previously reported to be most and least affected metabolically in AD compared to controls showed medium-to-large and small effect sizes for SUVR differences respectively. The results do not support the current application of LC FDG-PET signal as an in vivo biomarker for AD. Methodological and demographic factors potentially contributing to these findings are discussed. Future research may investigate age-related differences in LC FDG-PET signal and higher resolution images to fully explore its biomarker potential.

Towards chronic deep brain stimulation in freely moving hemiparkinsonian rats: Applicability and functionality of a fully implantable stimulation system

Objective This study aimed at investigating a novel fully implantable deep brain stimulation system and its ability to modulate brain metabolism and behavior through subthalamic nucleus stimulation in a hemiparkinsonian rat model. Approach Twelve male rats were unilaterally lesioned with 6-hydroxydopamine in the medial forebrain bundle and received a fully implantable deep brain stimulation system aiming at the ipsilesional subthalamic nucleus. Each rat underwent three cylinder tests to analyze front paw use: A PRE test before any surgical intervention, an OFF test after surgery but before stimulation onset and an ON test under deep brain stimulation. To visualize brain glucose metabolism in the awake animal, two [18F]FDG scans were conducted in the OFF and ON condition. At least four weeks after surgery, an [18F]FDOPA scan was used to check for dopaminergic integrity. Main results In general, STN DBS increased [18F]FDG uptake ipsilesionally and decreased it contralesionally. More specifically, bilateral orbitofrontal cortex, ipsilateral caudate putamen, sensorimotor cortex and nucleus accumbens showed significantly higher tracer uptake in ON compared to OFF condition. Contralateral cingulate and secondary motor cortex, caudate putamen, amygdala, hippocampus, retrosplenial granular cortex, superior colliculus, and parts of the cerebellum exhibited significantly higher [18F]FDG uptake in the OFF condition. On the behavioral level, stimulation was able improve use of the contralesional affected front paw suggesting an effective stimulation produced by the implanted system. Significance The fully implantable stimulation system developed by us and presented here offers the output of arbitrary user-defined waveforms, patterns and stimulation settings and allows tracer accumulation in freely moving animals. It is therefore a suitable device for implementing behavioral PET studies. It contributes immensely to the possibilities to characterize and unveil the effects and mechanisms of deep brain stimulation offering valuable clues for future improvements of this therapy.

Sex and age-related differences in cerebral blood flow investigated using pseudo-continuous arterial spin labeling magnetic resonance imaging

Adequate cerebral blood flow (CBF) is essential to a healthy central nervous system (CNS). Previous work suggests that CBF differs between men and women, and declines with age and certain pathologies, but a highly controlled systematic study across a wide age range, and incorporating white matter (WM) regions, has not been undertaken. Here, we investigate age- and sex-related differences in CBF in gray matter (GM) and WM regions in a cohort (N = 80) of cognitively unimpaired individuals over a wide age range. In agreement with literature, we find that GM regions exhibited lower CBF with age. In contrast, WM regions exhibited higher CBF with age in various cerebral regions. We attribute this new finding to increased oligodendrocyte metabolism to maintain myelin homeostasis in the setting of increased myelin turnover with age. Further, consistent with prior studies, we found that CBF was higher in women than in men in all brain structures investigated. Our work provides new insights into the effects of age and sex on CBF. In addition, our results provide reference CBF values for the standard ASL protocol recommended by the ISMRM Perfusion Study Group and the European ASL in Dementia consortium. Thus, these results provide a foundation for further investigations of CNS perfusion in a variety of settings, including aging, cerebrovascular diseases, and dementias.

The effects of nicotine and cannabis co-use during adolescence and young adulthood on white matter cerebral blood flow estimates

RATIONALE

Co-use of cannabis and nicotine is common among adolescents/young adults and is associated with poorer psychological and physical outcomes, compared with single substance use. Little is known about the impact of co-use on the developing brain.

OBJECTIVES

Preliminary investigation of the effects of nicotine on white matter (WM) cerebral blood flow (CBF) in adolescents/young adults and its potential moderation by cannabis use.

METHODS

Adolescent/young adult (16-22 years old) nicotine and tobacco product users (NTP; N = 37) and non-nicotine users (non-NTP; N = 26) underwent a neuroimaging session comprised of anatomical, optimized pseudo-continuous arterial spin labeling, and diffusion tensor imaging scans. Groups were compared on whole-brain WM CBF estimates and their relation to past-year cannabis use. Follow-up analyses assessed correlations between identified CBF clusters and corresponding fractional anisotropy (FA) values.

RESULTS

Group by cannabis effects were observed in five clusters (voxel-wise alpha < 0.001, cluster-wise alpha < 0.05; ≥ 11 contiguous voxels): non-NTP exhibited positive correlations between CBF and cannabis use in all clusters, whereas no significant relationships were observed for NTP. Greater CBF extracted from one cluster (including portions of right superior longitudinal fasciculus) was associated with reduced FA for non-NTP group only.

CONCLUSIONS

This is the first investigation of WM health as indexed by CBF, and its association with FA, in adolescents/young adults with nicotine and/or cannabis use. Results suggest that cannabis use by itself may be related to increased CBF in WM fiber tracts demonstrating poorer structural intergrity, yet the occurrence of even infrequent NTP use (greater than once per month) appears to diminish this relationship.

Local syntactic violations evoke fast mismatch-related neural activity detected by optical neuroimaging

It remains to be investigated whether syntax-related mismatch activity would be evoked in event-related optical signals by syntactic violations that deviate from our language knowledge and expectations. In the current study, we have employed fast optical neuroimaging with a frequency-domain oximeter to examine whether syntactic violations of English bare infinitives in the non-finite complement clause would trigger syntax-related mismatch effects. Recorded sentences of bare or full infinitive structures (without or with the 'to' infinitival marker) with syntactically correct or incorrect versions and non-syntactic lexical items (verbs) were presented to native speakers of English (n = 8) during silent movie viewing as a passive oddball task. The analysis of source strength (i.e., minimum norm current amplitudes) revealed that the syntactic category violations of bare object infinitives led to significantly more robust optical mismatch effects than the other syntactic violation and non-structural, lexical elements. This mismatch response had a peak latency of 186 ms in the left anterior superior temporal gyrus. In combination with our prior MEG report (Kubota et al. in Neurosci Lett 662:195-204, 2018), the present optical neuroimaging findings show that syntactic marking (unmarked-to-marked) violations of the bare object infinitive against the rule of the mental grammar enhance the signal strength exactly in the same manner seen with MEG scanning, including the peak latency of mismatch activity and the activated area of the brain.

Lasting consequences of concussion on the aging brain: Findings from the Baltimore Longitudinal Study of Aging

Studies suggest that concussions may be related to increased risk of neurodegenerative diseases, such as Chronic Traumatic Encephalopathy and Alzheimer’s Disease. Most neuroimaging studies show effects of concussionsin frontal and temporal lobes of the brain, yet the long-term impacts of concussions on the aging brain have not been well studied. We examined neuroimaging data from 51 participants (mean age at first imaging visit = 65.1±11.23) in the Baltimore Longitudinal Study of Aging (BLSA) who reported a concussion in their medical history an average of 23 years prior to the first imaging visit, and compared them to 150 participants (mean age at first imaging visit = 66.6 ± 10.97) with no history of concussion. Participants underwent serial structural MRI overa mean of 5.17 ± 6.14 years and DTI over a mean of 2.92 ± 2.22 years to measure brain structure, as well as ¹⁵O-water PET over a mean of 5.33 ± 2.19 years to measure brain function. A battery of neuropsychological tests was also administered over a mean of 11.62 ± 7.41 years. Analyses of frontal and temporal lobe regions were performed to examine differences in these measures between the concussion and control groups at first imaging visit and in change over time. Compared to those without concussion, participants with a prior concussion had greater brain atrophy in temporal lobe white matter and hippocampus at first imaging visit, which remained stable throughout the follow-up visits. Those with prior concussion also showed differences in white matter microstructure using DTI, including increased radial and axial diffusivity in the fornix/stria terminalis, anterior corona radiata, and superior longitudinal fasciculus at first imaging visit. In ¹⁵O-water PET, higher resting cerebral blood flow was seen at first imaging visit in orbitofrontal and lateral temporal regions, and both increases and decreases were seen in prefrontal, cingulate, insular, hippocampal, and ventral temporal regions with longitudinal follow-up. There were no significant differences in neuropsychological performance between groups. Most of the differences observed between the concussed and non-concussed groups were seen at the first imaging visit, suggesting that concussions can produce long-lasting structural and functional alterations in temporal and frontal regions of the brain in older individuals. These results also suggest that many of the reported short-term effects of concussion may still be apparent later in life.

Effect of post-labeling delay on regional cerebral blood flow in arterial spin-labeling MR imaging

BACKGROUND

Investigating the effect of post-labeling delay (PLD) on regional cerebral blood flow (CBF) in adults and optimizing the PLD for arterial spin-labeling (ASL) magnetic resonance (MR) imaging are important.

METHODS

Pseudo-continuous ASL imaging with a three PLDs protocol was performed in 90 healthy adult volunteers from January 2018 to February 2019. Healthy subjects were divided into youth group (mean age, 30.63 years; age range, 20-44 years), middle-aged group (mean age, 52.16 years; age range 45-59 years) and elderly group (mean age, 66.07 years; age range, 60-77 years). After preprocessing, analyses of variance (ANOVA) and volume-of-interest (VOI) were conducted to compare the CBF in each brain region. According to the trends of CBF changing with PLD and the results of ANOVA, we optimized the PLD for ASL imaging in different brain regions and age groups.

RESULTS

The CBF values of 87 VOIs [global gray matter (global GM) and other 86 VOIs] for each subject were obtained. Young people had less statistically significant VOIs than middle-aged and elderly people [Numbers of VOIs which had statistical significance (P < .05) in the analysis of ANOVA: 42 (youth group), 79 (middle-aged group), and 71 (elderly group)]. In youth group, the deep GM, occipital lobe and temporal lobe were more affected by PLDs than limbic system, frontal lobe and parietal lobe [VOIs with statistical significance (P < .05)/total VOIs: 8/8 (deep GM) > 8/12 (occipital lobe) > (8/14) (temporal lobe) > 5/12 (limbic system) > 11/28 (frontal lobe) > (2/12) parietal lobe]. In middle-aged group, the limbic system, deep GM and temporal lobe were more affected by PLDs than parietal lobe, frontal lobe and occipital lobe [VOIs with statistical significance (P < 0.05)/total VOIs: 12/12 (limbic system) = 8/8 (deep GM) > (13/14) (temporal lobe) > (11/12) parietal lobe > 25/28 (frontal lobe) > 9/12 (occipital lobe)]. In elderly group, the temporal lobe, parietal lobe, and frontal lobe were more affected by PLDs than occipital lobe, limbic system, and deep GM [VOIs with statistical significance (P < .05)/total VOIs: 14/14 (temporal lobe) > 12/12 (parietal lobe) > 22/28 (frontal lobe) > 9/12 (occipital lobe) > 8/12 (limbic system) > 5/8 (deep GM)]. The optimal PLD for most VOIs in youth group was 1525 ms. However, for middle-aged and elderly group, the optimal PLD for most VOIs was 2525 ms.

CONCLUSION

Young people are less affected by PLDs than middle-aged and elderly people. The middle-aged people are most affected by PLDs. In addition, the spatial distributions of PLD effect were different among the three age groups. Optimizing the PLD for ASL imaging according to age and brain regions can obtain more accurate and reliable CBF values.

Cortical Excitation:Inhibition Imbalance Causes Abnormal Brain Network Dynamics as Observed in Neurodevelopmental Disorders

Abnormal brain development manifests itself at different spatial scales. However, whether abnormalities at the cellular level can be diagnosed from network activity measured with functional magnetic resonance imaging (fMRI) is largely unknown, yet of high clinical relevance. Here a putative mechanism reported in neurodevelopmental disorders, that is, excitation-to-inhibition ratio (E:I), was chemogenetically increased within cortical microcircuits of the mouse brain and measured via fMRI. Increased E:I caused a significant "reduction" of long-range connectivity, irrespective of whether excitatory neurons were facilitated or inhibitory Parvalbumin (PV) interneurons were suppressed. Training a classifier on fMRI signals, we were able to accurately classify cortical areas exhibiting increased E:I. This classifier was validated in an independent cohort of Fmr1y/- knockout mice, a model for autism with well-documented loss of parvalbumin neurons and chronic alterations of E:I. Our findings demonstrate a promising novel approach towards inferring microcircuit abnormalities from macroscopic fMRI measurements.

Direct prospective comparison of 18F-FDG PET and arterial spin labelling MR using simultaneous PET/MR in patients referred for diagnosis of dementia

PURPOSE

¹⁸F-FDG PET is routinely used as an imaging marker in the early and differential diagnosis of dementing disorders and has incremental value over the clinical neurological and neuropsychological evaluation. Perfusion MR imaging by means of arterial spin labelling (ASL) is an alternative modality to indirectly measure neuronal functioning and could be used as complement measurement in a single MR session in the workup of dementia. Using simultaneous PET-MR, we performed a direct head-to-head comparison between enhanced multiplane tagging ASL (eASL) and ¹⁸F-FDG PET in a true clinical context of subjects referred for suspicion of neurodegenerative dementia.

METHODS

Twenty-seven patients underwent a 20-min ¹⁸F-FDG PET/MR and simultaneously acquired eASL on a GE Signa PET/MR. Data were compared with 30 screened age- and gender-matched healthy controls. Both integral eASL and ¹⁸F-FDG datasets were analysed visually by two readers unaware of the final clinical diagnosis, either in normal/abnormal classes, or full differential diagnosis (normal, Alzheimer type dementia [AD], dementia with Lewy Bodies [LBD], frontotemporal dementia [FTD] or other). Reader confidence was assessed with a rating scale (range 1-4). Data were also analysed semiquantitatively by VOI and voxel-based analyses.

RESULTS

The ground truth diagnosis for the patient group resulted in 14 patients with a neurodegenerative cognitive disorder (AD, FTD, LBD) and 13 patients with no arguments for an underlying neurodegenerative cause. Visual analysis resulted in equal specificity (0.70) for differentiating normal and abnormal cases between the two modalities, but in a higher sensitivity (0.93), confidence rating (0.64) and interobserver agreement for ¹⁸F-FDG PET compared with eASL. The same was true for assigning a specific differential diagnosis (sensitivity: and 0.39 for ¹⁸F-FDG PET and eASL, respectively). Semiquantitative analyses revealed prototypical patterns for AD and FTD, with both higher volumes of abnormality and intensity differences on ¹⁸F-FDG PET.

CONCLUSION

In a direct head-to-head comparison on a simultaneous GE Signa PET/MR, ¹⁸F-FDG PET performed better compared with ASL in terms of sensitivity and reader confidence, as well as volume and intensity of abnormalities. However, using pure semiquantitative analysis, similar diagnostic accuracy between the two modalities was obtained. Therefore, ASL may still serve as complement to neuroreceptor or protein deposition PET studies when a single simultaneous investigation is warranted.

Distinct Neural Correlates of Executive Function by Amyloid Positivity and Associations with Clinical Progression in Mild Cognitive Impairment

PURPOSE

This study aimed to identify the neural basis of executive function (EF) in amnestic mild cognitive impairment (aMCI) according to beta-amyloid (Aβ) positivity. Furthermore, we explored if the identified brain areas could serve as predictors for clinical progression.

MATERIALS AND METHODS

We included individuals with aMCI using data from [¹⁸F]-florbetapir-positron emission tomography (PET), fluorodeoxyglucose-PET, and EF scores, as well as follow-up clinical severity scores at 1 and 5 years from baseline from the Alzheimer's Disease Neuroimaging Initiative database. The correlations between EF score and regional cerebral glucose metabolism (rCMglc) were analyzed separately for aMCI with low Aβ burden (aMCI Aβ-, n=230) and aMCI with high Aβ burden (aMCI Aβ+, n=268). Multiple linear regression analysis was conducted to investigate the associations between rCMglc and clinical progression.

RESULTS

Longitudinal courses differed between aMCI Aβ- and aMCI Aβ+ groups. On average, aMCI Aβ- subjects maintained their level of clinical severity, whereas aMCI Aβ+ subjects showed progression. EF impairment in aMCI Aβ- was related to the anterior cingulate cortex (ACC), whereas that in aMCI Aβ+ was related to Alzheimer's Disease-vulnerable brain regions. ACC and the posterior cingulate cortex were associated with clinical progression in aMCI Aβ- and aMCI Aβ+, respectively.

CONCLUSION

Our findings suggest that although MCI subjects showed similar behavioral phenotypes at the time of diagnosis, EF and further progression were associated with different brain regions according to Aβ burden. Clarification of the etiologies and nature of EF impairment in aMCI are critical for disease prognosis and management.

The Vascular Hypothesis of Alzheimer's Disease: A Key to Preclinical Prediction of Dementia Using Neuroimaging

The vascular hypothesis of Alzheimer's disease (VHAD) was proposed 24 years ago from observations made in our laboratory using aging rats subjected to chronic brain hypoperfusion. In recent years, VHAD has become a mother-lode to numerous neuroimaging studies targeting cerebral hemodynamic changes, particularly brain hypoperfusion in elderly patients at risk of developing Alzheimer's disease (AD). There is a growing consensus among neuroradiologists that brain hypoperfusion is likely involved in the pathogenesis of AD and that disturbed cerebral blood flow (CBF) can serve as a key biomarker for predicting conversion of mild cognitive impairment to AD. The use of cerebral hypoperfusion as a preclinical predictor of AD is becoming decisive in stratifying low and high risk patients that may develop cognitive decline and for assessing the effectiveness of therapeutic interventions. There is currently an international research drive from neuroimaging groups to seek new perspectives that can broaden our understanding of AD and improve lifestyle. Diverse neuroimaging methods are currently being used to monitor normal and dyscognitive brain activity. Some techniques are very powerful and can detect, diagnose, quantify, prognose, and predict cognitive decline before AD onset, even from a healthy cognitive state. Multimodal imaging offers new insights in the treatment and prevention of cognitive decline during advanced aging and better understanding of the functional and structural organization of the human brain. This review discusses the impact the VHAD and CBF are having on the neuroimaging technology that can usher practical strategies to help prevent AD.

Simultaneous EEG-fMRI for Functional Neurological Assessment

The increasing incidence of neurodegenerative and psychiatric diseases requires increasingly sophisticated tools for their diagnosis and monitoring. Clinical assessment takes advantage of objective parameters extracted by electroencephalogram and magnetic resonance imaging (MRI) among others, to support clinical management of neurological diseases. The complementarity of these two tools can be now emphasized by the possibility of integrating the two technologies in a hybrid solution, allowing simultaneous acquisition of the two signals by the novel EEG-fMRI technology. This review will focus on simultaneous EEG-fMRI technology and related early studies, dealing about issues related to the acquisition and processing of simultaneous signals, and including critical discussion about clinical and technological perspectives.

Diagnostic performance of regional cerebral blood flow images derived from dynamic PIB scans in Alzheimer's disease

BACKGROUND

In clinical practice, visual assessment of glucose metabolism images is often used for the diagnosis of Alzheimer's disease (AD) through 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) scans. However, visual assessment of the characteristic AD hypometabolic pattern relies on the expertise of the reader. Therefore, user-independent pipelines are preferred to evaluate the images and to classify the subjects. Moreover, glucose consumption is highly correlated with cerebral perfusion. Regional cerebral blood flow (rCBF) images can be derived from dynamic 11C-labelled Pittsburgh Compound B PET scans, which are also used for the assessment of the deposition of amyloid-β plaques on the brain, a fundamental characteristic of AD. The aim of this study was to explore whether these rCBF PIB images could be used for diagnostic purposes through the PMOD Alzheimer's Discrimination Tool.

RESULTS

Both tracer relative cerebral flow (R1) and early PIB (ePIB) (20-130 s) uptake presented a good correlation when compared to FDG standardized uptake value ratio (SUVR), while ePIB (1-8 min) showed a worse correlation. All receiver operating characteristic curves exhibited a similar shape, with high area under the curve values, and no statistically significant differences were found between curves. However, R1 and ePIB (1-8 min) had the highest sensitivity, while FDG SUVR had the highest specificity.

CONCLUSION

rCBF images were suggested to be a good surrogate for FDG scans for diagnostic purposes considering an adjusted threshold value.

Alterations of cerebral perfusion and functional brain connectivity in medication-naïve male adults with attention-deficit/hyperactivity disorder

Aims

Functional brain abnormalities, including altered cerebral perfusion and functional connectivities, have been illustrated in adults with attention‐deficit/hyperactivity disorder (aADHD). The present study attempted to explore the alterations of cerebral blood flow (CBF) and resting‐state functional connectivity (RSFC) simultaneously to understand the neural mechanisms for adults with ADHD comprehensively.

Methods

Resting‐state arterial spin labeling (ASL) and blood oxygenation level‐dependent (BOLD) magnetic resonance imaging (MRI) data were acquired for 69 male aADHD and 69 matched healthy controls (HCs). The altered CBFs associated with aADHD were explored based on both categorical (aADHD vs HCs) and dimensional (correlation with aADHD core symptoms) perspectives. Then, the seed‐based RSFC analyses were developed for the regions showing significant alterations of CBF.

Results

Significantly decreased CBF in the large‐scale resting‐state networks regions (eg, ventral attentional network, somatomotor network, limbic network) and subcortical regions was indicated in aADHD compared with HCs. The correlation analyses indicated that the hypoperfusion in left putamen/global pallidum and left amygdala/hippocampus was correlated with ADHD inattentive and total symptoms, respectively. Further, weaker negative functional connectivity between left amygdala and bilateral supplementary motor area, bilateral superior frontal gyrus, and left medial frontal gyrus was found in adults with ADHD.

Conclusion

The present findings suggested alterations of both cerebral perfusion and functional connectivity for the left amygdala in aADHD. The combination of CBF and RSFCs may help to interpret the neuropathogenesis of ADHD more comprehensively.

Frequency-Dependent Relationship Between Resting-State fMRI and Glucose Metabolism in the Elderly

Both glucose metabolism and resting-state fMRI (RS-fMRI) signal reflect hemodynamic features. The objective of this study was to investigate their relationship in the resting-state in healthy elderly participants (n = 18). For RS-fMRI signal, regional homogeneity (ReHo), amplitude of low frequency fluctuations (ALFF), fractional ALFF (fALFF), and degree of centrality (DC) maps were generated in multiple frequency bands. Glucose uptake was acquired with ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET). Linear correlation of each pair of the FDG-PET and RS-fMRI metrics was explored both in across-voxel way and in across-subject way. We found a significant across-voxel correlation between the FDG-PET and BOLD-fMRI metrics. However, only a small portion of voxels showed significant across-subject correlation between FDG-PET and BOLD-fMRI metrics. All these results were similar across all frequency bands of RS-fMRI data. The current findings indicate that FDG-PET and RS-fMRI metrics share similar spatial pattern (significant across-voxel correlation) but have different underlying physiological importance (non-significant across-subject correlation). Specifically, FDG-PET measures the mean glucose metabolism over tens of minutes, while RS-fMRI measures the dynamic characteristics. The combination of FDG-PET and RS-fMRI provides complementary information to reveal the underlying mechanisms of the brain activity and may enable more comprehensive interpretation of clinical PET-fMRI studies. Future studies would attempt to reduce the artifacts of RS-fMRI and to analyze the dynamic feature of PET signal.

Elevated Markers of Inflammation Are Associated With Longitudinal Changes in Brain Function in Older Adults

Background

Chronic inflammation has been linked to memory and other cognitive impairments, as well as Alzheimer's disease. Here, we investigate the association between inflammatory markers and changes in brain activity measured by regional cerebral blood flow (rCBF) to assess the relationship between inflammation and brain function in older individuals.

Methods

Annual 15O water resting-state positron emission tomography (PET) scans collected over a 5-year period were assessed in 138 cognitively normal older participants (77 males; mean age at baseline = 71.3; mean scans per participant = 3.5) in the Baltimore Longitudinal Study of Aging. Voxel-wise linear mixed models were used to investigate associations between rCBF and C-reactive protein (CRP) and interleukin-6 (IL-6) at the time of scanning. We examined relationships between baseline CRP and IL-6 levels and baseline rCBF, and relationships between baseline and mean inflammatory levels over time and longitudinal rCBF changes.

Results

Higher baseline CRP and IL-6 were each associated with lower baseline rCBF primarily in frontal and occipital regions, with only the lingual gyrus surviving atrophy correction. Higher baseline and mean CRP were also associated with greater rCBF declines over time in anterior cingulate and hippocampal regions, whereas higher baseline and mean IL-6 levels were associated with greater rCBF declines in orbitofrontal and hippocampal regions.

Conclusions

Higher levels of inflammation are associated with longitudinal changes in brain function in regions important for cognition. These results, along with previous studies, suggest that chronic inflammation in older adults may contribute to age-associated declines in cognitive function.

The Relationship Between Regional Cerebral Blood Flow Estimates and Alcohol Problems at 5-Year Follow-Up: The Role of Level of Response

BACKGROUND

Acute alcohol consumption is associated with temporarily increased regional cerebral blood flow (CBF). The extent of this increase appears to be moderated by individual differences in the level of response (LR) to alcohol's subjective effects. The low LR phenotype is a known risk factor for the development of alcohol problems. This study investigates how the low LR phenotype relates to the relationship between alcohol-related changes in CBF and alcohol problems 5 years later.

METHODS

Young adults (ages 18 to 25) were selected based on their LR to alcohol and underwent a neuroimaging protocol including arterial spin labeling and functional scans. These participants were recontacted ~5 years later and assessed on alcohol outcomes. A final sample of 107 subjects (54 low and 53 high LR subjects) was included in the analyses. Whole-brain analysis revealed 5 clusters of significant alcohol-induced, versus placebo-induced, CBF changes that were consistent with a previous report. Peak alcohol-placebo CBF response was extracted from these regions and, along with the LR group, submitted to a hierarchical linear regression predicting alcohol problems. Analyses controlled for age, sex, and baseline alcohol problems.

RESULTS

In the regression analysis, greater alcohol-placebo CBF difference in the right middle/superior/inferior frontal gyri and bilateral anterior cingulate gyri clusters predicted greater future alcohol problems for the low LR group, whereas this relationship was not found to be significant in the high LR group.

CONCLUSIONS

This study demonstrates a clinically important relationship between CBF and future alcohol problems, particularly in individuals with a low LR phenotype. These initial results help to elucidate the neurobiological pathways involved in the development of alcohol use disorders for individuals with low LR.

The dark matter of the brain

The bulk of brain energy expenditure is allocated for maintenance of perpetual intrinsic activity of neurons and neural circuits. Long-term electrophysiological and neuroimaging studies in anesthetized and behaving animals show, however, that the great majority of nerve cells in the intact brain do not fire action potentials, i.e., are permanently silent. Herein, I review emerging data suggesting massive redundancy of nerve cells in mammalian nervous system, maintained in inhibited state at high energetic costs. Acquired in the course of evolution, these collections of dormant neurons and circuits evade routine functional undertakings, and hence, keep out of the reach of natural selection. Under penetrating stress and disease, however, they occasionally switch in active state and drive a variety of neuro-psychiatric symptoms and behavioral abnormalities. The increasing evidence for widespread occurrence of silent neurons warrants careful revision of functional models of the brain and entails unforeseen reserves for rehabilitation and plasticity.

Relative cerebral flow from dynamic PIB scans as an alternative for FDG scans in Alzheimer's disease PET studies

In Alzheimer's Disease (AD) dual-tracer positron emission tomography (PET) studies with 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) and 11C-labelled Pittsburgh Compound B (PIB) are used to assess metabolism and cerebral amyloid-β deposition, respectively. Regional cerebral metabolism and blood flow (rCBF) are closely coupled, both providing an index for neuronal function. The present study compared PIB-derived rCBF, estimated by the ratio of tracer influx in target regions relative to reference region (R1) and early-stage PIB uptake (ePIB), to FDG scans. Fifteen PIB positive (+) patients and fifteen PIB negative (-) subjects underwent both FDG and PIB PET scans to assess the use of R1 and ePIB as a surrogate for FDG. First, subjects were classified based on visual inspection of the PIB PET images. Then, discriminative performance (PIB+ versus PIB-) of rCBF methods were compared to normalized regional FDG uptake. Strong positive correlations were found between analyses, suggesting that PIB-derived rCBF provides information that is closely related to what can be seen on FDG scans. Yet group related differences between method's distributions were seen as well. Also, a better correlation with FDG was found for R1 than for ePIB. Further studies are needed to validate the use of R1 as an alternative for FDG studies in clinical applications.

Brain network changes and memory decline in aging

One theory of age-related cognitive decline proposes that changes within the default mode network (DMN) of the brain impact the ability to successfully perform cognitive operations. To investigate this theory, we examined functional covariance within brain networks using regional cerebral blood flow data, measured by ¹⁵O-water PET, from 99 participants (mean baseline age 68.6 ± 7.5) in the Baltimore Longitudinal Study of Aging collected over a 7.4 year period. The sample was divided in tertiles based on longitudinal performance on a verbal recognition memory task administered during scanning, and functional covariance was compared between the upper (improvers) and lower (decliners) tertile groups. The DMN and verbal memory networks (VMN) were then examined during the verbal memory scan condition. For each network, group differences in node-to-network coherence and individual node-to-node covariance relationships were assessed at baseline and in change over time. Compared with improvers, decliners showed differences in node-to-network coherence and in node-to-node relationships in the DMN but not the VMN during verbal memory. These DMN differences reflected greater covariance with better task performance at baseline and both increasing and declining covariance with declining task performance over time for decliners. When examined during the resting state alone, the direction of change in DMN covariance was similar to that seen during task performance, but node-to-node relationships differed from those observed during the task condition. These results suggest that disengagement of DMN components during task performance is not essential for successful cognitive performance as previously proposed. Instead, a proper balance in network processes may be needed to support optimal task performance.

Early-Life Cognitive Activity Is Related to Reduced Neurodegeneration in Alzheimer Signature Regions in Late Life

Background: Although increased cognitive activity (CA), both current and past, is known to be associated with a decreased occurrence of Alzheimer’s disease (AD) dementia in older adults, the exact neural mechanisms underlying the association between CA during different stages of life and human dementia remain unclear. Therefore, we investigated whether CA during different life stages is associated with cerebral amyloid-beta (Aβ) pathology and AD-related neurodegeneration in non-demented older adults.

Methods: Cross-sectional analyses of data collected between April 2014 and March 2016 from the Korean Brain Aging Study for Early Diagnosis and Prediction of Alzheimer’s Disease (KBASE), an ongoing prospective cohort. In total, 321 community-dwelling, non-demented older adults were involved in this study. Cerebral Aβ deposition and Aβ positivity were measured using ¹¹C-Pittsburgh compound B (PiB)-positron emission tomography (PET). AD-signature region cerebral glucose metabolism (AD-CMglu) and AD-signature region neurodegeneration (AD-ND) positivity were measured using ¹⁸F-fluorodeoxyglucose (FDG)-PET. In addition, CA in early, mid, and late life was systematically evaluated using a structured questionnaire.

Results: Of the 321 participants, 254 were cognitively normal (CN) and 67 had mild cognitive impairment (MCI). The mean age of participants was 69.6 years old [standard deviation (SD) = 8.0]. Higher early-life CA (CA_early) was associated with significantly increased AD-CMglu (B = 0.035, SE = 0.013, P = 0.009) and a decreasing trend of AD-ND positivity (OR = 0.65, 95% CI 0.43–0.98, P = 0.04) but was not associated with Aβ deposition or positivity. We observed no association between midlife CA (CA_mid) and any AD-related brain changes. Late-life CA (CA_late) showed an association with both global Aβ deposition and AD-CMglu, although it was not statistically significant. Sensitivity analyses controlling for current depression or conducted only for CN individuals revealed similar results.

Conclusion: Our results suggest that CA in early life may be protective against late-life AD-related neurodegeneration, independently of cerebral Aβ pathology.

Vascular-metabolic and GABAergic Inhibitory Correlates of Neural Variability Modulation. A Combined fMRI and PET Study

Neural activity varies continually from moment to moment. Such temporal variability (TV) has been highlighted as a functionally specific brain property playing a fundamental role in cognition. We sought to investigate the mechanisms involved in TV changes between two basic behavioral states, namely having the eyes open (EO) or eyes closed (EC) in vivo in humans. To these ends we acquired BOLD fMRI, ASL, and [¹⁸F]-fluoro-deoxyglucose PET in a group of healthy participants (n = 15), along with BOLD fMRI and [¹⁸F]-flumazenil PET in a separate group (n = 19). Focusing on an EO- vs EC-sensitive region in the occipital cortex (identified in an independent sample), we show that TV is constrained in the EO condition compared to EC. This reduction is correlated with an increase in energy consumption and with regional GABA_A receptor density. This suggests that the modulation of TV by behavioral state involves an increase in overall neural activity that is related to an increased effect from GABAergic inhibition in addition to any excitatory changes. These findings contribute to our understanding of the mechanisms underlying activity variability in the human brain and its control.