Resting cerebral blood flow, attention, and aging

The effect of multi-component exercise on cognition function in patients with diabetes: A systematic review and meta-analysis

BACKGROUND

This meta-analysis investigated the influence of exercise on cognitive function in people living with diabetes.

METHODS

Stringent criteria for literature inclusion and exclusion were defined. Searches were conducted across four English databases to gather randomized controlled trials investigating exercise interventions for cognitive function in people living with diabetes. Outcome indicators from 1193 subjects across 12 articles were analyzed using RevMan 5.4 software.

RESULTS

Exercise intervention demonstrated the ability to mitigate cognitive decline in people living with diabetes, with a combined effect size (standardized mean difference) of 0.91, 95% CI: 0.28, 1.54, P < 0.00001. The intervention effect showed significant modulation by intervention content (I2 = 95%), intervention duration (I2 = 95%), intervention frequency (I2 = 95%), and intervention cycle (I2 = 96%). Among these factors, multi-component exercise, sessions >40 minutes, exercise frequency >4 times per week, and sustained exercise for >6 months were paramount, all with P < 0.05.

CONCLUSION

Exercise intervention emerges as a viable strategy for delaying cognitive decline in people living with diabetes. Its efficacy is subject to modulation by various variables. Optimal intervention includes multi-component exercise, individual sessions lasting 40-60 minutes, exercising >4 times a week, and continuous exercise for over 6 months.

A multi-site 99mTc-HMPAO SPECT study of cerebral blood flow in a community sample of patients with major depression

Prior regional Cerebral Blood Flow (rCBF) studies in Major Depressive Disorder (MDD) have been limited by small, highly selective, non-representative samples that have yielded variable and poorly replicated findings. The aim of this study was to compare rCBF measures in a large, more representative community sample of adults with MDD and healthy control participants. This is a cross-sectional, retrospective multi-site cohort study in which clinical data from 338 patients 18-65 years of age with a primary diagnosis of MDD were retrieved from a central database for 8 privately owned, private-pay outpatient psychiatric centers across the United States. Two 99mTc-HMPAO SPECT brain scans, one at rest and one during performance of a continuous performance task, were acquired as a routine component of their initial clinical evaluation. In total, 103 healthy controls, 18-65 years old and recruited from the community were also assessed and scanned. Depressed patients had significantly higher rCBF in frontal, anterior cingulate, and association cortices, and in basal ganglia, thalamus, and cerebellum, after accounting for significantly higher overall CBF. Depression severity associated positively with rCBF in the basal ganglia, hippocampus, cerebellum, and posterior white matter. Elevated rCBF was especially prominent in women and older patients. Elevated rCBF likely represents pathogenic hypermetabolism in MDD, with its magnitude in direct proportion to depression severity. It is brain-wide, with disproportionate increases in cortical and subcortical attentional networks. Hypermetabolism may be a reasonable target for novel therapeutics in MDD.

Positive effects of brisk walking and Tai Chi on cognitive function in older adults: An fNIRS study

Exercise has shown to have beneficial effects on cognition in older adults. The purpose of this study was to investigate the cortical hemodynamic responses during the word-color Stroop test (WCST) prior and after acute walking and Tai Chi exercise by functional near-infrared spectroscopy (fNIRS). Twenty participants (9 males, mean age 62.8 ± 5.2), first underwent a baseline WCST test, after which they took three WCST tests in a randomized order, (a) after sitting rest (control), (b) after 6 minutes performing Tai Chi Quan, and (c) after a bout of 6 minutes brisk walking. During these four WCST tests cortical hemodynamic changes in the prefrontal area were monitored with fNIRS. Both brisk walking and Tai Chi enhanced hemodynamic activity during the Stroop incongruent tasks, leading to improved cognitive performance (quicker reaction time). Brisk walking induced a greater hemodynamic activity in the right dorsolateral prefrontal cortex (DLPFC) and ventrolateral prefrontal cortex (VLPFC) area, whereas Tai Chi induced a greater bilateral hemodynamic activity in the DLPFC and VLPFC areas. The present study provided empirical evidence of enhanced hemodynamic response in task- specific regions of the brain that can be achieved by a mere six minutes of brisk walking or Tai Chi in older adults.

Cerebrovascular Phenotype in Fabry Disease Patients Assessed by Ultrasound

OBJECTIVES

Fabry disease (FD) is a rare X-linked lysosomal storage disorder with variable phenotypes, including neurological symptoms. These can be influenced by vascular impairment. Extracranial and transcranial vascular sonography is an effective and noninvasive method for measuring arterial structures and blood flow. The study aims to investigate cerebrovascular phenotype characteristics in FD patients compared to controls using neurosonology.

METHODS

This is a single-center, cross-sectional study of 130 subjects-65 patients (38 females), with genetically confirmed FD, and 65 sex- and age-matched controls. Using ultrasonography, we measured structural and hemodynamic parameters, including distal common carotid artery intima-media thickness, inner vertebral artery diameter, resting blood flow velocity, pulsatility index, and cerebral vasoreactivity (CVR) in the middle cerebral artery. To assess differences between FD and controls and to identify factors influencing investigated outcomes, unadjusted and adjusted regression analyses were performed.

RESULTS

In comparison to sex- and age-matched controls, FD patients displayed significantly increased carotid artery intima-media thickness (observed FD 0.69 ± 0.13 mm versus controls 0.63 ± 0.12 mm; Padj  = .0014), vertebral artery diameter (observed FD 3.59 ± 0.35 mm versus controls 3.38 ± 0.33 mm; Padj  = .0002), middle cerebral artery pulsatility index (observed FD 0.98 ± 0.19 versus controls 0.87 ± 0.11; Padj  < .0001), and significantly decreased CVR (observed FD 1.21 ± 0.49 versus controls 1.35 ± 0.38; Padj  = .0409), when adjusted by age, BMI, and sex. Additionally, FD patients had significantly more variable CVR (0.48 ± 0.25 versus 0.21 ± 0.14; Padj  < .0001).

CONCLUSIONS

Our results suggest the presence of multiple vascular abnormalities and changes in hemodynamic parameters of cerebral arteries in patients with FD.

Alzheimer's genetic risk effects on cerebral blood flow across the lifespan are proximal to gene expression

Cerebrovascular dysregulation such as altered cerebral blood flow (CBF) can be observed in Alzheimer's disease (AD) and may precede symptom onset. Genome wide association studies show that AD has a polygenic aetiology, providing a tool for studying AD susceptibility across the lifespan. Here, we ascertain whether the AD genetic risk effects on CBF previously observed (Chandler et al., 2019) are also present in later life. Consistent with our prior observations, AD genetic risk score (AD-GRS) was associated with reduced CBF in the ADNI sample. The regional association between AD-GRS and CBF were also spatially similar. Furthermore, CBF was related to the regional mRNA transcript expression of AD risk genes proximal to AD-GRS risk loci. These observations suggest that AD risk alleles may reduce neurovascular process such as CBF, potentially via mechanisms such as regional expression of proximal AD risk genes as an antecedent AD pathophysiology. Our observations help establish processes that underpin AD genetic risk-related reductions in CBF as a therapeutic target prior to the onset of neurodegeneration.

Association of Arterial Spin Labeling Parameters With Cognitive Decline, Vascular Events, and Mortality in a Memory-Clinic Sample

BACKGROUND

Cognitive decline in older adults has been attributed to reduced cerebral blood flow (CBF). Recently, the spatial coefficient of variation (sCoV) of ASL has been proposed as a proxy marker of cerebrovascular insufficiency. We investigated the association between baseline ASL parameters with cognitive decline, incident cerebrovascular disease, and risk of vascular events and mortality.

DESIGN, SETTING, AND PARTICIPANTS

About 368 memory-clinic patients underwent three-annual neuropsychological assessments and brain MRI scans at baseline and follow-up. MRIs were graded for white matter hyperintensities (WMH), lacunes, cerebral microbleeds (CMBs), cortical infarcts, and intracranial stenosis. Baseline gray (GM) and white matter (WM) CBF and GM-sCoV were obtained with ExploreASL from 2D-EPI pseudo-continuous ASL images. Cognitive assessment was done using a validated neuropsychological battery. Data on incident vascular events (heart disease, stroke, transient ischemic attack) and mortality were obtained.

RESULTS

Higher baseline GM-sCoV was associated with decline in the memory domain over 3 years of follow-up. Furthermore, higher GM-sCoV was associated with a decline in the memory domain only in participants without dementia. Higher baseline GM-sCoV was associated with progression of WMH and incident CMBs. During a mean follow-up of 3 years, 29 (7.8%) participants developed vascular events and 18 (4.8%) died. Participants with higher baseline mean GM-sCoV were at increased risk of vascular events.

CONCLUSIONS

Higher baseline GM-sCoV of ASL was associated with a decline in memory and risk of cerebrovascular disease and vascular events, suggesting that cerebrovascular insufficiency may contribute to accelerated cognitive decline and worse clinical outcomes in memory clinic participants.

Passive exercise increases cerebral blood flow velocity and supports a postexercise executive function benefit

Executive function entails high-level cognitive control supporting activities of daily living. Literature has shown that a single-bout of exercise involving volitional muscle activation (i.e., active exercise) improves executive function and that an increase in cerebral blood flow (CBF) may contribute to this benefit. It is, however, unknown whether non-volitional exercise (i.e., passive exercise) wherein an individual's limbs are moved via an external force elicits a similar executive function benefit. This is a salient question given that proprioceptive and feedforward drive from passive exercise increases CBF independent of the metabolic demands of active exercise. Here, in a procedural validation participants (n = 2) used a cycle ergometer to complete separate 20-min active and passive (via mechanically driven flywheel) exercise conditions and a non-exercise control condition. Electromyography showed that passive exercise did not increase agonist muscle activation or increase ventilation or gas exchange variables (i.e., V̇O₂ and V̇CO₂ ). In a main experiment participants (n = 28) completed the same exercise and control conditions and transcranial Doppler ultrasound showed that active and passive exercise (but not the control condition) increased CBF through the middle cerebral artery (ps <.001); albeit the magnitude was less during passive exercise. Notably, antisaccade reaction times prior to and immediately after each condition showed that active (p < .001) and passive (p = .034) exercise improved an oculomotor-based measure of executive function, whereas no benefit was observed in the control condition (p = .85). Accordingly, results evince that passive exercise 'boosts' an oculomotor-based measure of executive function and supports convergent evidence that increased CBF mediates this benefit.

A Systematic Review of the Impact of Physical Exercise-Induced Increased Resting Cerebral Blood Flow on Cognitive Functions

Brain perfusion declines with aging. Physical exercise represents a low-cost accessible form of intervention to increase cerebral blood flow; however, it remains unclear if exercise-induced amelioration of brain perfusion has any impact on cognition. We aimed to provide a state-of-the art review on this subject. A comprehensive search of the PubMed (MEDLINE) database was performed. On the basis of the inclusion and exclusion criteria, 14 studies were included in the analysis. Eleven of the studies conducted well-controlled exercise programs that lasted 12–19 weeks for 10–40 participants and two studies were conducted in much larger groups of subjects for more than 5 years, but the exercise loads were indirectly measured, and three of them were focused on acute exercise. Literature review does not show a direct link between exercise-induced augmentation of brain perfusion and better cognitive functioning. However, in none of the reviewed studies was such an association the primary study endpoint. Carefully designed clinical studies with focus on cognitive and perfusion variables are needed to provide a response to the question whether exercise-induced cerebral perfusion augmentation is of clinical importance.

Biological sex differences in afferent-mediated inhibition of motor responses evoked by TMS

Sensorimotor integration can be assessed by pairing electrical peripheral nerve stimulation with transcranial magnetic stimulation (TMS). The resulting afferent inhibition is observed when TMS precedes nerve stimulation by ∼ 20-25 ms, termed short-latency afferent inhibition (SAI), or by 200 ms, termed long-latency afferent inhibition (LAI). The purpose of this study was to determine whether biological sex influences the magnitude of SAI or LAI. SAI and LAI were assessed in fifteen males (21.5 ± 2.7 years) and fifteen females (20.2 ± 2.3 years). TMS was delivered to the primary motor cortex (M1) following stimulation of the contralateral median nerve at the wrist or digital nerve of the index finger, and motor-evoked potentials (MEPs) were obtained from the right first dorsal interosseous (FDI) muscle. SAI evoked by median and digital nerve stimulation, and LAI evoked by median nerve stimulation, were not different between males and females. LAI evoked by digital nerve stimulation was increased in females compared to males, but this difference between sexes was no longer present following the removal of datapoints where inhibition was not observed. This study is the first to investigate biological sex differences in afferent inhibition.

Exercise intensity-specific changes to cerebral blood velocity do not modulate a postexercise executive function benefit

Executive function is transiently improved (i.e., <60-min) following a single bout of aerobic exercise. A candidate mechanism for this improvement is an exercise-mediated increase in cerebral blood flow (CBF). Further, it has been proposed that an increase in CBF across the continuum of increasing exercise intensities improves the magnitude of a postexercise executive function benefit (i.e., drive theory); however, this proposal has not been empirically tested. Here, participants completed four experimental sessions: a V̇O_2peak test to determine cardiorespiratory fitness and estimated lactate threshold (LT), followed by separate 10-min sessions of light- (i.e., 25 W), moderate- (i.e., 80% estimated LT), and heavy-intensity (i.e., 15% of the difference between LT and V̇O_2peak) aerobic exercise. An estimate of CBF during exercise was achieved via transcranial Doppler ultrasound and near-infrared spectroscopy to quantify blood velocity (BV) through the middle cerebral artery and deoxygenated hemoglobin (HHb), respectively. Executive function was assessed before and after each session via the executive-mediated antisaccade task (i.e., saccade mirror-symmetrical to a target). Results demonstrated that BV increased in relation to increasing exercise intensity, whereas HHb decreased by a comparable magnitude independent of intensity. In terms of executive function, null hypothesis and equivalence tests indicated a comparable magnitude postexercise reduction in antisaccade reaction time across exercise intensities. Accordingly, the magnitude of CBF change during exercise does not impact the magnitude of a postexercise executive function benefit.

Does task complexity impact the neurovascular coupling response similarly between males and females?

BACKGROUND

While previous studies have demonstrated a complex visual scene search elicits a robust neurovascular coupling (NVC) response, it is unknown how the duration of visual stimuli presentation influences NVC metrics. This study examined how stimuli duration, in addition to biological sex and self-reported engagement impact NVC responses.

METHODS

Participants (n = 20, female = 10) completed four visual paradigms. Three involved simple visual shapes presented at 0.5-, 2-, and 4-s intervals in randomized orders. The fourth paradigm was a complex visual scene search ("Where's Waldo?"). Participants completed eight cycles of 20-s eyes-closed followed by 40-s eyes-open. Transcranial Doppler ultrasound indexed posterior and middle cerebral artery velocities (PCA and MCA). Participants self-reported their engagement following each task (1 [minimal] to 10 [maximal]).

RESULTS

The "Where's Waldo?" task evoked greater PCA percent increase (all p < 0.001) and area under the curve during the first 30-s of the task (all p < 0.001) compared to simple shapes. Females displayed greater absolute baseline and peak PCA and MCA velocities across all tasks (all p < 0.002). Subjective engagement displayed moderate correlation levels with PCA percent increase (Spearman ρ = 0.58) and area under the curve (Spearman ρ = 0.60) metrics in males, whereas these were weak for females (Spearman ρ = 0.43 and ρ = 0.38, respectively).

CONCLUSIONS

The complex visual paradigm "Where's Waldo?" greatly augmented the signal-to-noise ratio within the PCA aspects of the NVC response compared to simple shapes. While both sexes had similar NVC responses, task engagement was more related to NVC metrics in males compared to females. Therefore, future NVC investigations should consider task engagement when designing studies.

Age-related alterations in the cerebrovasculature affect neurovascular coupling and BOLD fMRI responses: Insights from animal models of aging

The present and future research efforts in cognitive neuroscience and psychophysiology rely on the measurement, understanding, and interpretation of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to effectively investigate brain function. Aging and age-associated pathophysiological processes change the structural and functional integrity of the cerebrovasculature which can significantly alter how the BOLD signal is recorded and interpreted. In order to gain an improved understanding of the benefits, drawbacks, and methodological implications for BOLD fMRI in the context of cognitive neuroscience, it is crucial to understand the cellular and molecular mechanism of age-related vascular pathologies. This review discusses the multifaceted effects of aging and the contributions of age-related pathologies on structural and functional integrity of the cerebral microcirculation as they has been investigated in animal models of aging, including age-related alterations in neurovascular coupling responses, cellular and molecular mechanisms involved in microvascular damage, vascular rarefaction, blood-brain barrier disruption, senescence, humoral deficiencies as they relate to, and potentially introduce confounding factors in the interpretation of BOLD fMRI.

Protective effects of edaravone on white matter pathology in a novel mouse model of Alzheimer's disease with chronic cerebral hypoperfusion

White matter lesions (WMLs) caused by cerebral chronic hypoperfusion (CCH) may contribute to the pathophysiology of Alzheimer's disease (AD). However, the underlying mechanisms and therapeutic approaches have yet to be totally identified. In the present study, we investigated a potential therapeutic effect of the free radical scavenger edaravone (EDA) on WMLs in our previously reported novel mouse model of AD (APP23) plus CCH with motor and cognitive deficits. Relative to AD with CCH mice at 12 months (M) of age, EDA strongly improved CCH-induced WMLs in the corpus callosum of APP23 mice at 12 M by improving the disruption of white matter integrity, enhancing the proliferation of oligodendrocyte progenitor cells, attenuating endothelium/astrocyte unit dysfunction, and reducing neuroinflammation and oxidative stress. The present study demonstrates that the long-term administration of EDA may provide a promising therapeutic approach for WMLs in AD plus CCH disease with cognitive deficits.

Anterior Cingulate Structure and Perfusion is Associated with Cerebrospinal Fluid Tau among Cognitively Normal Older Adult APOEɛ4 Carriers

Evidence suggests the ɛ4 allele of the apolipoprotein E (APOE) gene may accelerate an age-related process of cortical thickening and cerebral blood flow (CBF) reduction in the anterior cingulate cortex (ACC). Although the neural basis of this association remains unclear, evidence suggests it might reflect early neurodegenerative processes. However, to date, associations between cerebrospinal fluid (CSF) biomarkers of neurodegeneration, such as CSF tau, and APOE-related alterations in ACC cortical thickness (CTH) and CBF have yet to be explored. The current study explored the interaction of CSF tau and APOE genotype (ɛ4+, ɛ4-) on FreeSurfer-derived CTH and arterial spin labeling MRI-measured resting CBF in the ACC (caudal ACC [cACC] and rostral ACC [rACC]) among a sample of 45 cognitively normal older adults. Secondary analyses also examined associations between APOE, CTH/CBF, and cognitive performance. In the cACC, higher CSF tau was associated with higher CTH and lower CBF in ɛ4+, whereas these relationships were not evident in ɛ4-. In the rACC, higher CSF tau was associated with higher CTH for both ɛ4+ and ɛ4-, and with lower CBF only in ɛ4+. Significant interactions of CSF tau and APOE on CTH/CBF were not observed in two posterior reference regions implicated in Alzheimer's disease. Secondary analyses revealed a negative relationship between cACC CTH and executive functioning in ɛ4+ and a positive relationship in ɛ4-. Findings suggest the presence of an ɛ4-related pattern of increased CTH and reduced CBF in the ACC that is associated with biomarkers of neurodegeneration and subtle decrements in cognition.

Defining Hypoperfusion in Chronic Aphasia: An Individualized Thresholding Approach

Within the aphasia literature, it is common to link location of lesioned brain tissue to specific patterns of language impairment. This has provided valuable insight into the relationship between brain structure and function, but it does not capture important underlying alterations in function of regions that remain structurally intact. Research has demonstrated that in the chronic stage of aphasia, variable patterns of reduced cerebral blood flow (CBF; hypoperfusion) in structurally intact regions of the brain contribute to persisting language impairments. However, one consistent issue in this literature is a lack of clear consensus on how to define hypoperfusion, which may lead to over- or underestimation of tissue functionality. In the current study, we conducted an exploratory analysis in six individuals with chronic aphasia (>1 year post-onset) using perfusion imaging to (1) suggest a new, individualized metric for defining hypoperfusion; (2) identify the extent of hypoperfused tissue in perilesional bands; and (3) explore the relationship between hypoperfusion and language impairment. Results indicated that our individualized metric for defining hypoperfusion provided greater precision when identifying functionally impaired tissue and its effects on language function in chronic aphasia. These results have important implications for intervention approaches that target intact (or impaired) brain tissue.

Hemodynamic and behavioral changes in older adults during cognitively demanding dual tasks

INTRODUCTION

Executive functions play a fundamental role in walking by integrating information from cognitive-motor pathways. Subtle changes in brain and behavior may help identify older adults who are more susceptible to executive function deficits with advancing age due to prefrontal cortex deterioration. This study aims to examine how older adults mitigate executive demands while walking during cognitively demanding tasks.

METHODS

Twenty healthy older adults (M = 71.8 years, SD = 6.4) performed simple reaction time (SRT), go/no-go (GNG), n-back (NBK), and double number sequence (DNS) cognitive tasks of increasing difficulty while walking (i.e., dual task). Functional near infra-red spectroscopy (fNIRS) was used to measure the hemodynamic response (i.e., oxy- [HbO2] and deoxyhemoglobin [HbR]) changes in the prefrontal cortex (PFC) during dual and single tasks (i.e., walking alone). In addition, performance was measured using gait speed (m/s), response time (s), and accuracy (% correct).

RESULTS

Using repeated measures ANOVAs, neural findings demonstrated a main effect of task such that ∆HbO2 (p = .047) and ∆HbR (p = .040) decreased between single and dual tasks. An interaction between task and cognitive difficulty (p = .014) revealed that gait speed decreased in the DNS between single and dual tasks. A main effect of task in response time indicated that the SRT response time was faster than all other difficulty levels (p < .001). Accuracy performance declined between single and dual tasks (p = .028) and across difficulty levels (p < .001) but was not significantly different between the NBK and DNS.

CONCLUSION

Findings suggest that a healthy older adult sample might mitigate executive demands using an automatic locomotor control strategy such that shifting conscious attention away from walking during the dual tasks resulted in decreased ∆HbO2 and ∆HbR. However, decreased prefrontal activation was inefficient at maintaining response time and accuracy performance and may be differently affected by increasing cognitive demands.

Transcranial laser stimulation: Mitochondrial and cerebrovascular effects in younger and older healthy adults

BACKGROUND

Transcranial laser stimulation is a novel method of noninvasive brain stimulation found safe and effective for improving prefrontal cortex neurocognitive functions in healthy young adults. This method is different from electric and magnetic stimulation because it causes the photonic oxidation of cytochrome-c-oxidase, the rate-limiting enzyme for oxygen consumption and the major intracellular acceptor of photons from near-infrared light. This photobiomodulation effect promotes mitochondrial respiration, cerebrovascular oxygenation and neurocognitive function. Pilot studies suggest that transcranial photobiomodulation may also induce beneficial effects in aging individuals.

OBJECTIVES

Randomized, sham-controlled study to test photobiomodulation effects caused by laser stimulation on cytochrome-c-oxidase oxidation and hemoglobin oxygenation in the prefrontal cortex of 68 healthy younger and older adults, ages 18-85.

METHODS

Broadband near-infrared spectroscopy was used for the noninvasive quantification of bilateral cortical changes in oxidized cytochrome-c-oxidase and hemoglobin oxygenation before, during and after 1064-nm wavelength laser (IR-A laser, area: 13.6 cm², power density: 250 mW/cm²) or sham stimulation of the right anterior prefrontal cortex (Brodmann Area 10).

RESULTS

As compared to sham control, there was a significant laser-induced increase in oxidized cytochrome-c-oxidase during laser stimulation, followed by a significant post-stimulation increase in oxygenated hemoglobin and a decrease in deoxygenated hemoglobin. Furthermore, there was a greater laser-induced effect on cytochrome-c-oxidase with increasing age, while laser-induced effects on cerebral hemodynamics decreased with increasing age. No adverse laser effects were found.

CONCLUSION

The findings support the use of transcranial photobiomodulation for cerebral oxygenation and alleviation of age-related decline in mitochondrial respiration. They justify further research on its therapeutic potential in neurologic and psychiatric diseases.

Investigating the effects of healthy cognitive aging on brain functional connectivity using 4.7 T resting-state functional magnetic resonance imaging

Functional changes in the aging human brain have been previously reported using functional magnetic resonance imaging (fMRI). Earlier resting-state fMRI studies revealed an age-associated weakening of intra-system functional connectivity (FC) and age-associated strengthening of inter-system FC. However, the majority of such FC studies did not investigate the relationship between age and network amplitude, without which correlation-based measures of FC can be challenging to interpret. Consequently, the main aim of this study was to investigate how three primary measures of resting-state fMRI signal-network amplitude, network topography, and inter-network FC-are affected by healthy cognitive aging. We acquired resting-state fMRI data on a 4.7 T scanner for 105 healthy participants representing the entire adult lifespan (18-85 years of age). To study age differences in network structure, we combined ICA-based network decomposition with sparse graphical models. Older adults displayed lower blood-oxygen-level-dependent (BOLD) signal amplitude in all functional systems, with sensorimotor networks showing the largest age differences. Our age comparisons of network topography and inter-network FC demonstrated a substantial amount of age invariance in the brain's functional architecture. Despite architecture similarities, old adults displayed a loss of communication efficiency in our inter-network FC comparisons, driven primarily by the FC reduction in frontal and parietal association cortices. Together, our results provide a comprehensive overview of age effects on fMRI-based FC.

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.

Deciphering Alzheimer's Disease Pathogenic Pathway: Role of Chronic Brain Hypoperfusion on p-Tau and mTOR

This review examines new biomolecular findings that lend support to the hemodynamic role played by chronic brain hypoperfusion (CBH) in driving a pathway to Alzheimer's disease (AD). CBH is a common clinical feature of AD and the current topic of intense investigation in AD models. CBH is also the basis for the vascular hypothesis of AD which we originally proposed in 1993. New biomolecular findings reveal the interplay of CBH in increasing tau phosphorylation (p-Tau) in the hippocampus and cortex of AD mice, damaging fast axonal transport, increasing signaling of mammalian target of rapamycin (mTOR), impairing learning-memory function, and promoting the formation of neurofibrillary tangles, a neuropathologic hallmark of AD. These pathologic elements have been singularly linked with neurodegeneration and AD but their abnormal, collective participation during brain aging have not been fully examined. The format for this review will provide a consolidated analysis of each pathologic phase contributing to cognitive decline and AD onset, summarized in nine chronological steps. These steps galvanize each factor's active participation and contribution in constructing a biomolecular pathway to AD onset generated by CBH.

Coupling of cerebral blood flow and functional connectivity is decreased in healthy aging

Aging leads to cerebral perfusion and functional connectivity changes that have been assessed using various neuroimaging techniques. In addition, a link between these two parameters has been demonstrated in healthy young adults. In this work, we employed arterial spin labeling (ASL) fMRI to measure global and voxel-wise differences in cerebral blood flow (CBF) and intrinsic connectivity contrast (ICC) in the resting state in a group of cognitively normal elderly subjects and a group of cognitively normal young subjects, in order to assess the effects of aging on CBF-ICC coupling, which had not been previously evaluated. Our results showed age-related global and regional CBF decreases in prefrontal mesial areas, lateral frontal regions, insular cortex, lateral parietal areas, precuneus and occipital regions. Subcortically, perfusion was reduced in the medial thalamus and caudate nucleus. ICC was also found reduced with age in prefrontal cortical areas and insular cortex, affecting key nodes of the default mode and salience networks. Areas of ICC and CBF decrease partially overlapped, however, the CBF reduction was more extensive and encompassed more areas. This dissociation was accompanied by a decrease in CBF-ICC coupling. These results suggest that aging leads to a disruption in the relationship between CBF and intrinsic functional connectivity that could be due to neurovascular dysregulation.

Reduced cerebral pressure-flow responses are associated with electrophysiological markers of attention in healthy older adults

The aim of this study was to determine the effect of age on the relationship between cerebrovascular function and the neural bases of sustained attention. Twenty-seven healthy young adults (aged 18-30 years) and 24 older adults (60-75 years) underwent assessments of cerebrovascular function and sustained attention. Blood flow velocity of the middle cerebral artery was assessed via Transcranial Doppler Ultrasound, during seated rest, in response to hypocapnic breathing (cerebrovascular reactivity) and during a repeated sit-to-stand procedure (pressure-flow response). Attentional processing was assessed using the N2 and P3 components of the event-related potential during a two-tone auditory oddball task. Poorer pressure-flow responses were significantly associated with reductions in N2 and P3 amplitude in the old group (b = -0.50, p = .029 and b = -0.46, p = .045), but not the young group. These results suggest that alterations in the brain's capacity to combat reductions in perfusion pressure are associated with age-related differences in attentional processing, supporting the hypothesis that cerebrovascular hemodynamic disturbances play a role in age-related cognitive decline.

Lower Thalamic Blood Flow Is Associated With Slower Stride Velocity in Older Adults

Background

Gait deficits are associated with brain atrophy and white matter hyperintensities (WMH) - both markers of underlying cerebral small vessel disease (SVD). Given reduced subcortical cerebral blood flow (CBF) is prevalent in SVD, we tested the hypothesis that regional CBF is positively associated with gait performance among older adults.

Methods

Thirty-two older adults (55-80 years) with at least one vascular risk factor were recruited. We assessed gait during 2 consecutive walking sequences using a GAITRite system: (1) at a self-selected pace, and (2) while performing a serial subtraction dual-task challenge. We quantified CBF using pseudo-continuous arterial spin labeling MRI within 4 regions of interest: putamen, pallidum, thalamus, and hippocampus. We investigated associations between gait characteristics and overall CBF adjusting for age, sex, and height in an omnibus approach using multivariate analysis of variance, followed by regression analysis with each individual region. We also conducted further regression analyses to investigate associations between gait characteristics and frontal lobe CBF. Sensitivity analyses examined how the observed associations were modified by WMH, executive function, and depressive symptoms. A change of 10% in the model's adjusted r² and effect size was considered as a threshold for confounding.

Results

Overall subcortical CBF was not associated with self-paced gait. When examining individual ROI, gait velocity was directly related to thalamic CBF (p = 0.026), and across all gait variables the largest effect sizes were observed in relation to thalamic CBF. In the dual-task condition, gait variables were not related to CBF in either the omnibus approach or individual multiple regressions. Furthermore, no significant associations were observed between frontal CBF and gait variables in either the self-paced or dual-task condition. Sensitivity analyses which were restricted to examine the association of velocity and thalamic CBF identified a cofounding effect of depressive symptoms which increased the effect size of the CBF-gait association by 12%.

Conclusion

Subcortical hypoperfusion, particularly in regions that comprise central input/output tracts to the cortical tissue, may underlie the association between gait deficits and brain aging.

Gulf War Illness: Mechanisms Underlying Brain Dysfunction and Promising Therapeutic Strategies

Gulf War Illness (GWI), a chronic multisymptom health problem, afflicts ~30% of veterans served in the first GW. Impaired brain function is among the most significant symptoms of GWI, which is typified by persistent cognitive and mood impairments, concentration problems, headaches, chronic fatigue, and musculoskeletal pain. This review aims to discuss findings from animal prototypes and veterans with GWI on mechanisms underlying its pathophysiology and emerging therapeutic strategies for alleviating brain dysfunction in GWI. Animal model studies have linked brain impairments to incessantly elevated oxidative stress, chronic inflammation, inhibitory interneuron loss, altered lipid metabolism and peroxisomes, mitochondrial dysfunction, modified expression of genes relevant to cognitive function, and waned hippocampal neurogenesis. Furthermore, the involvement of systemic alterations such as the increased intensity of reactive oxygen species and proinflammatory cytokines in the blood, transformed gut microbiome, and activation of the adaptive immune response have received consideration. Investigations in veterans have suggested that brain dysfunction in GWI is linked to chronic activation of the executive control network, impaired functional connectivity, altered blood flow, persistent inflammation, and changes in miRNA levels. Lack of protective alleles from Class II HLA genes, the altered concentration of phospholipid species and proinflammatory factors in the circulating blood have also been suggested as other aiding factors. While some drugs or combination therapies have shown promise for alleviating symptoms in clinical trials, larger double-blind, placebo-controlled trials are needed to validate such findings. Based on improvements seen in animal models of GWI, several antioxidants and anti-inflammatory compounds are currently being tested in clinical trials. However, reliable blood biomarkers that facilitate an appropriate screening of veterans for brain pathology need to be discovered. A liquid biopsy approach involving analysis of brain-derived extracellular vesicles in the blood appears efficient for discerning the extent of neuropathology both before and during clinical trials.

Clinical and Pathological Benefits of Edaravone for Alzheimer's Disease with Chronic Cerebral Hypoperfusion in a Novel Mouse Model

Alzheimer's disease (AD) and chronic cerebral hypoperfusion (CCH) often coexist in dementia patients in aging societies. The hallmarks of AD including amyloid-β (Aβ)/phosphorylated tau (pTau) and pathology-related events such as neural oxidative stress and neuroinflammation play critical roles in pathogenesis of AD with CCH. A large number of lessons from failures of drugs targeting a single target or pathway on this so complicated disease indicate that disease-modifying therapies targeting multiple key pathways hold potent potential in therapy of the disease. In the present study, we used a novel mouse model of AD with CCH to investigate a potential therapeutic effect of a free radical scavenger, Edaravone (EDA) on AD with CCH via examining motor and cognitive capacity, AD hallmarks, neural oxidative stress, and neuroinflammation. Compared with AD with CCH mice at 12 months of age, EDA significantly improved motor and cognitive deficits, attenuated neuronal loss, reduced Aβ/pTau accumulation, and alleviated neural oxidative stress and neuroinflammation. These findings suggest that EDA possesses clinical and pathological benefits for AD with CCH in the present mouse model and has a potential as a therapeutic agent for AD with CCH via targeting multiple key pathways of the disease pathogenesis.

Increased cerebral blood flow supports a single-bout postexercise benefit to executive function: evidence from hypercapnia

A single bout of aerobic exercise improves executive function; however, the mechanism for the improvement remains unclear. One proposal asserts that an exercise-mediated increase in cerebral blood flow (CBF) enhances the efficiency of executive-related cortical structures. To examine this, participants completed separate 10-min sessions of moderate- to heavy-intensity aerobic exercise, a hypercapnic environment (i.e., 5% CO₂), and a nonexercise and nonhypercapnic control condition. The hypercapnic condition was included because it produces an increase in CBF independent of metabolic demands. An estimate of CBF was achieved via transcranial Doppler ultrasound and near-infrared spectroscopy that provided measures of middle cerebral artery blood velocity (BV) and deoxygenated hemoglobin (HHb), respectively. Exercise intensity was adjusted to match participant-specific changes in BV and HHb associated with the hypercapnic condition. Executive function was assessed before and after each session via antisaccades (i.e., saccade mirror-symmetrical to a target) because the task is mediated via the same executive networks that demonstrate task-dependent modulation following single and chronic bouts of aerobic exercise. Results showed that hypercapnic and exercise conditions were associated with comparable BV and HHb changes, whereas the control condition did not produce a change in either metric. In terms of antisaccade performance, the exercise and hypercapnic, but not control, conditions demonstrated improved postcondition reaction times (RT), and the magnitude of the hypercapnic and exercise-based increase in estimated CBF was reliably related to the postcondition improvement in RT. Accordingly, results evince that an increase in CBF represents a candidate mechanism for a postexercise improvement in executive function.NEW & NOTEWORTHY Single-bout aerobic exercise "boosts" executive function, and increased cerebral blood flow (CBF) has been proposed as a mechanism for the benefit. In this study, participants completed 10 min of aerobic exercise and 10 min of inhaling a hypercapnic gas, a manipulation known to increase CBF independently of metabolic demands. Both exercise and hypercapnic conditions improved executive function for at least 20 min. Accordingly, an increase in CBF is a candidate mechanism for the postexercise improvement in executive function.

Physical exercise in the prevention and treatment of Alzheimer's disease

Dementia is one of the greatest global challenges for health and social care in the 21st century. Alzheimer's disease (AD), the most common type of dementia, is by no means an inevitable consequence of growing old. Several lifestyle factors may increase, or reduce, an individual's risk of developing AD. Much has been written over the ages about the benefits of exercise and physical activity. Among the risk factors associated with AD is a low level of physical activity. The relationship between physical and mental health was established several years ago. In this review, we discuss the role of exercise (aerobic and resistance) training as a therapeutic strategy for the treatment and prevention of AD. Older adults who exercise are more likely to maintain cognition. We address the main protective mechanism on brain function modulated by physical exercise by examining both human and animal studies. We will pay especial attention to the potential role of exercise in the modulation of amyloid β turnover, inflammation, synthesis and release of neurotrophins, and improvements in cerebral blood flow. Promoting changes in lifestyle in presymptomatic and predementia disease stages may have the potential for delaying one-third of dementias worldwide. Multimodal interventions that include the adoption of an active lifestyle should be recommended for older populations.

Long-term effects of resveratrol on cognition, cerebrovascular function and cardio-metabolic markers in postmenopausal women: A 24-month randomised, double-blind, placebo-controlled, crossover study

Ageing and menopause contribute to endothelial dysfunction, causing impaired cerebral perfusion, which is in turn associated with accelerated cognitive decline. In a 14-week pilot study, we showed that supplementation with low-dose resveratrol, a phytoestrogen that can enhance endothelial function, improved cerebrovascular and cognitive functions in postmenopausal women. We sought to confirm these benefits in a larger, longer-term trial. A 24-month randomized, placebo-controlled crossover trial was undertaken in 125 postmenopausal women, aged 45-85 years, who took 75 mg trans-resveratrol or placebo twice-daily for 12 months and then crossover to the alternative treatment for another 12 months. We evaluated within individual differences between each treatment period in measures of cognition (primary outcome), cerebrovascular function in the middle cerebral artery (cerebral blood flow velocity: CBFV, cerebrovascular responsiveness: CVR) and cardio-metabolic markers as secondary outcomes. Subgroup analyses examined effects of resveratrol by life stages. Compared to placebo, resveratrol supplementation resulted a significant 33% improvement in overall cognitive performance (Cohen's d = 0.170, P = 0.005). Women ≥65 years of age showed a relative improvement in verbal memory with resveratrol compared to those younger than 65 years. Furthermore, resveratrol improved secondary outcomes including resting mean CBFV (d = 0.275, P = 0.001), CVR to hypercapnia (d = 0.307, P = 0.027), CVR to cognitive stimuli (d = 0.259, P = 0.032), fasting insulin (d = 0.174, P = 0.025) and insulin resistance index (d = 0.102, P = 0.034). Regular supplementation with low-dose resveratrol can enhance cognition, cerebrovascular function and insulin sensitivity in postmenopausal women. This may translate into a slowing of the accelerated cognitive decline due to ageing and menopause, especially in late-life women. Further studies are warranted to observe whether these cognitive benefits of resveratrol can reduce the risk of dementia.

Interpersonal early life trauma is associated with increased cerebral perfusion and poorer memory performance in post-9/11 veterans

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IP-ELT is associated with greater cerebral perfusion in the right inferior/middle temporal gyrus.

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Cerebral perfusion mediates the relationship between IP-ELT and memory, not attention or executive function.

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PTSD diagnosis and severity were not significantly associated with cerebral perfusion.

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Other factors relevant to perfusion did not influence the relationship between IP-ELT and cerebral perfusion.

Cerebral blood flow (CBF) is critically important in the overall maintenance of brain health, and disruptions in normal flow have been linked to the degradation of the brain’s structural integrity and function. Recent studies have highlighted the potential role of CBF as a link between psychiatric disorders and brain integrity. Although interpersonal early life trauma (IP-ELT) is a risk factor for the development of psychiatric disorders and has been linked to disruptions in brain structure and function, the mechanisms through which IP-ELT alters brain integrity and development remain unclear. The goal of this study was to understand whether IP-ELT was associated with alterations in CBF assessed during adulthood. Further, because the cognitive implications of perfusion disruptions in IP-ELT are also unclear, this study sought to investigate the relationship between IP-ELT, perfusion, and cognition. Methods: 179 Operations Enduring Freedom/Iraqi Freedom/New Dawn (OEF/OIF/OND) Veterans and military personnel completed pseudo-continuous arterial spin labeling (pCASL) imaging, clinical interviews, the Traumatic Life Events Questionnaire (TLEQ), and a battery of neuropsychological tests that were used to derive attention, memory, and executive function cognitive composite scores. To determine whether individuals were exposed to an IP-ELT, events on the TLEQ that specifically queried interpersonal trauma before the age of 18 were tallied for each individual. Analyses compared individuals who reported an interpersonal IP-ELT (IP-ELT+, n = 48) with those who did not (IP-ELT-, n = 131). Results: Whole brain analyses revealed that IP-ELT+ individuals had significantly greater CBF in the right inferior/middle temporal gyrus compared to those in the IP-ELT- group, even after controlling for age, sex, and posttraumatic stress disorder (PTSD). Further, perfusion in the right inferior/middle temporal gyrus significantly mediated the relationship between IP-ELT and memory, not attention or executive function, such that those with an IP-ELT had greater perfusion, which, in turn, was associated with poorer memory. Examination of other clinical variables such as current PTSD diagnosis and severity as well as the interaction between IP-ELT and PTSD yielded no significant effects. Conclusions: These results extend prior work demonstrating an association between ELT and cerebral perfusion by suggesting that increased CBF may be an important neural marker with cognitive implications in populations at risk for psychiatric disorders.

ABBaH: Activity Breaks for Brain Health. A Protocol for a Randomized Crossover Trial

Introduction: Extended periods of sitting may have detrimental effects on brain health. However, the effects of breaking up prolonged sedentary periods with frequent, short physical activity bouts on mechanisms to improve brain health remain unclear. Therefore, this study aims to investigate the immediate effects of uninterrupted sitting and frequent, short bouts of physical activity on cerebral blood flow and cognitive function in the prefrontal cortex in middle-aged adults.

Methods: This is a protocol article to describe a randomized crossover study. We will collect data from 13 healthy adults, aged between 40 and 60 years old, with a body mass index <35 kg/m². Participants will be required to come into the laboratory on three occasions, sit for 3 h, and perform a different type of break for 3 min every 30 min at each visit in a random order, being either: (1) a social break; (2) brisk walk on a treadmill; or (3) simple resistance activities. Before and after each experimental condition, cerebral blood flow (primary outcome) will be measured using functional near-infrared spectroscopy (fNIRS), with short-separation channels, and working memory (1-, 2-, and 3-back on the computer) will be assessed. The following additional secondary outcomes will be collected: psychological factors (questionnaires); arterial stiffness; salivary cortisol levels; and blood glucose levels.

Conclusion: The results from this randomized crossover study will determine the effects of uninterrupted sitting and frequent, short bouts of physical activity on cerebral blood flow and cognitive performance. Publication of this study protocol emphasizes the importance of registration and publication of protocols in the field of sedentary behavior research.

Age-related prefrontal cortex activation in associative memory: An fNIRS pilot study

Older adults typically perform more poorly than younger adults in free recall memory tests. This age-related deficit has been linked to decline of brain activation and brain prefrontal lateralization, which may be the result of compensatory mechanisms. In the present pilot study, we investigated the effect of age on prefrontal cortex (PFC) activation during performance of a task that requires memory associations (temporal vs. spatial clustering), using functional Near-Infrared Spectroscopy (fNIRS). Ten younger adults, ten cognitively high-performing older individuals, and ten low-performing older individuals completed a free recall task, where either a temporal or spatial strategy (but not both simultaneously) could be employed to retrieve groups of same-category stimuli, whilst changes in PFC hemodynamics were recorded by means of a 12-channel fNIRS system. The results suggest PFC activation, and right lateralization specific to younger adults. Moreover, age did not affect use of memory organization, given that temporal clustering was preferred over spatial clustering in all groups. These findings are in line with previous literature on the aging brain and on temporal organization of memory. Our results also suggest that the PFC may be specifically involved in memory for temporal associations. Future research may consider whether age-related deficits in temporal organization may be an early sign of PFC pathology and possible neurodegeneration.

Repository Describing an Aging Population to Inform Physiologically Based Pharmacokinetic Models Considering Anatomical, Physiological, and Biological Age-Dependent Changes

BACKGROUND

Aging is characterized by anatomical, physiological, and biological changes that can impact drug kinetics. The elderly are often excluded from clinical trials and knowledge about drug kinetics and drug-drug interaction magnitudes is sparse. Physiologically based pharmacokinetic modeling can overcome this clinical limitation but detailed descriptions of the population characteristics are essential to adequately inform models.

OBJECTIVE

The objective of this study was to develop and verify a population database for aging Caucasians considering anatomical, physiological, and biological system parameters required to inform a physiologically based pharmacokinetic model that included population variability.

METHODS

A structured literature search was performed to analyze age-dependent changes of system parameters. All collated data were carefully analyzed, and descriptive mathematical equations were derived.

RESULTS

A total of 362 studies were found of which 318 studies were included in the analysis as they reported rich data for anthropometric parameters and specific organs (e.g., liver). Continuous functions could be derived for most system parameters describing a Caucasian population from 20 to 99 years of age with variability. Areas with sparse data were identified such as tissue composition, but knowledge gaps were filled with plausible qualified assumptions. The developed population was implemented in Matlab^® and estimated system parameters from 1000 virtual individuals were in accordance with independent observed data showing the robustness of the developed population.

CONCLUSIONS

The developed repository for aging subjects provides a singular specific source for key system parameters needed for physiologically based pharmacokinetic modeling and can in turn be used to investigate drug kinetics and drug-drug interaction magnitudes in the elderly.

The short-term effects of sedentary behaviour on cerebral hemodynamics and cognitive performance in older adults: a cross-over design on the potential impact of mental and/or physical activity

BACKGROUND

Sedentary behaviour might be a potential risk factor for cognitive decline. However, the short-term effects of sedentary behaviour on (cerebro) vascular and cognitive performance in older people are unknown.

METHODS

We used a cross-over design with 22 older adults (78 years, 9 females) to assess the short-term hemodynamic and cognitive effects of three hours uninterrupted sitting and explored if these effects can be counteracted with regular (every 30 min) two-minute walking breaks. In addition, we investigated if low versus high mental activity during the three hours of sitting modified these effects. Before and after each condition, alertness, executive functioning, and working memory were assessed with the Test of Attentional Performance battery. Additionally, cerebral blood flow velocity (Transcranial Doppler) and blood pressure (Finapres) were measured in rest, and during sit-to-stand and CO₂ challenges to assess baroreflex sensitivity, cerebral autoregulation, and cerebral vasomotor reactivity.

RESULTS

No short-term differences were observed in cognitive performance, cerebral blood flow velocity, baroreflex sensitivity, cerebral autoregulation, or cerebral vasomotor reactivity across time, or between conditions. Blood pressure and cerebrovascular resistance increased over time (8.6 mmHg (5.0;12.1), p < 0.001), and 0.23 in resistance (0.01;0.45), p = 0.04). However, these effects were not mitigated by mental activity or by short walking breaks to interrupt sitting.

CONCLUSIONS

In older individuals, three hours of sitting did not influence cognitive performance or cerebral perfusion. However, the sitting period increased blood pressure and cerebrovascular resistance, which are known to negatively impact brain health in the long-term. Importantly, we found that these effects in older individuals cannot be mitigated by higher mental activity and/or regular walking breaks.

TRIAL REGISTRATION

Clinical trial registration URL: https://www.toetsingonline.nl/. Unique identifier: NL64309.091.17. Date of registration: 06-02-2018.

Hippocampal vascular reserve associated with cognitive performance and hippocampal volume

Medial temporal lobe dependent cognitive functions are highly vulnerable to hypoxia in the hippocampal region, yet little is known about the relationship between the richness of hippocampal vascular supply and cognition. Hippocampal vascularization patterns have been categorized into a mixed supply from both the posterior cerebral artery and the anterior choroidal artery or a single supply by the posterior cerebral artery only. Hippocampal arteries are small and affected by pathological changes when cerebral small vessel disease is present. We hypothesized, that hippocampal vascularization patterns may be important trait markers for vascular reserve and modulate (i) cognitive performance; (ii) structural hippocampal integrity; and (iii) the effect of cerebral small vessel disease on cognition. Using high-resolution 7 T time-of-flight angiography we manually classified hippocampal vascularization patterns in older adults with and without cerebral small vessel disease in vivo. The presence of a mixed supplied hippocampus was an advantage in several cognitive domains, including verbal list learning and global cognition. A mixed supplied hippocampus also was an advantage for verbal memory performance in cerebral small vessel disease. Voxel-based morphometry showed higher anterior hippocampal grey matter volume in mixed, compared to single supply. We discuss that a mixed hippocampal supply, as opposed to a single one, may increase the reliability of hippocampal blood supply and thereby provide a hippocampal vascular reserve that protects against cognitive impairment.

Cerebrovascular Correlates of Subclinical Attentional Disturbances in Non-stroke Cardiovascular Disease

Evidence suggests that cerebrovascular hemodynamic disturbances underlie cognitive deterioration secondary to cardiovascular disease (CVD), including manifestations other than stroke, but the mechanisms remain unclear. To date, the majority of studies have used neuropsychological measures validated for the detection of clinically significant cognitive decline but lack the sensitivity to accurately detect subclinical or subtle cognitive changes. The N2 and P3 components of the event-related potential are sensitive markers of attention and cognitive processing, and are valuable in the assessment of age-related cognitive changes and neurodegenerative disease. The aims of this study were to test (a) the sensitivity of N2 and P3 components in differentiating older adults with CVD from healthy controls, and (b) whether cerebrovascular hemodynamics are associated with alterations in attention in persons with non-stroke CVD. Older adults with CVD (n = 20) and healthy older adults (n = 20) without cognitive impairment or history of stroke and matched for age, were recruited. Cerebral blood flow velocity of the middle cerebral artery (MCAv) and Gosling's Pulsatility Index (PI) were assessed using Transcranial Doppler ultrasound (TCD). ERPs were elicited using a two-tone auditory oddball task. N2 amplitude was significantly reduced in the CVD group at midline frontal, central and parietal sites (p < .05, d > 0.6). No significant group differences were observed in N2 latency, P3 amplitude, or P3 latency. Further, MCAv and PI were strongly associated with N2 amplitude in the CVD group, such that greater MCAv was associated with reductions in N2 amplitude (b = -0.58, p = .018), whilst PI was associated with increases in N2 amplitude (b = 0.66, p = .006). No relationships between MCAv or PI with N2 or P3 ERP components were observed in the healthy control group. The data reported here suggest that a reduction in N2 amplitude may be an important objective indicator of subclinical cognitive and attentional alterations in non-stroke CVD, and support the notion that cerebrovascular hemodynamic disturbances play a role in the pathogenesis of cognitive deterioration secondary to non-stroke CVD.

Contralateral Hemispheric Cerebral Blood Flow Measured With Arterial Spin Labeling Can Predict Outcome in Acute Stroke

Background and Purpose- Imaging is frequently used to select acute stroke patients for intra-arterial therapy. Quantitative cerebral blood flow can be measured noninvasively with arterial spin labeling magnetic resonance imaging. Cerebral blood flow levels in the contralateral (unaffected) hemisphere may affect capacity for collateral flow and patient outcome. The goal of this study was to determine whether higher contralateral cerebral blood flow (cCBF) in acute stroke identifies patients with better 90-day functional outcome. Methods- Patients were part of the prospective, multicenter iCAS study (Imaging Collaterals in Acute Stroke) between 2013 and 2017. Consecutive patients were enrolled after being diagnosed with anterior circulation acute ischemic stroke. Inclusion criteria were ischemic anterior circulation stroke, baseline National Institutes of Health Stroke Scale score ≥1, prestroke modified Rankin Scale score ≤2, onset-to-imaging time <24 hours, with imaging including diffusion-weighted imaging and arterial spin labeling. Patients were dichotomized into high and low cCBF groups based on median cCBF. Outcomes were assessed by day-1 and day-5 National Institutes of Health Stroke Scale; and day-30 and day-90 modified Rankin Scale. Multivariable logistic regression was used to test whether cCBF predicted good neurological outcome (modified Rankin Scale score, 0-2) at 90 days. Results- Seventy-seven patients (41 women) met the inclusion criteria with median (interquartile range) age of 66 (55-76) yrs, onset-to-imaging time of 4.8 (3.6-7.7) hours, and baseline National Institutes of Health Stroke Scale score of 13 (9-20). Median cCBF was 38.9 (31.2-44.5) mL per 100 g/min. Higher cCBF predicted good outcome at day 90 (odds ratio, 4.6 [95% CI, 1.4-14.7]; P=0.01), after controlling for baseline National Institutes of Health Stroke Scale, diffusion-weighted imaging lesion volume, and intra-arterial therapy. Conclusions- Higher quantitative cCBF at baseline is a significant predictor of good neurological outcome at day 90. cCBF levels may inform decisions regarding stroke triage, treatment of acute stroke, and general outcome prognosis. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT02225730.

APOE modifies the interaction of entorhinal cerebral blood flow and cortical thickness on memory function in cognitively normal older adults

OBJECTIVE

The ε4 allele of the apolipoprotein E (APOE) gene increases risk for cognitive decline in normal and pathologic aging. However, precisely how APOE ε4 exerts its negative impact on cognition is poorly understood. The present study aimed to determine whether APOE genotype (ε4+ vs. ε4-) modifies the interaction of medial temporal lobe (MTL) resting cerebral blood flow (CBF) and brain structure (cortical thickness [CT], volume [Vo]) on verbal memory performance.

METHODS

Multiple linear regression models were employed to investigate relationships between APOE genotype, arterial spin labeling MRI-measured CBF and FreeSurfer-based CT and Vo in four MTL regions of interest (left and right entorhinal cortex and hippocampus), and verbal memory performance among a sample of 117 cognitively normal older adults (41 ε4+, 76 ε4-) between the ages of 64 and 89 (mean age ​= ​73).

RESULTS

Results indicated that APOE genotype modified the interaction of CBF and CT on memory in the left entorhinal cortex, such that the relationship between entorhinal CBF and memory was negative (lower CBF was associated with better memory) in non-carriers with higher entorhinal CT, positive (higher CBF was associated with better memory) in non-carriers with lower entorhinal CT, and negative (higher CBF was associated with worse memory) in ε4 carriers with lower entorhinal CT.

CONCLUSIONS

Findings suggest that older adult APOE ε4 carriers may experience vascular dysregulation and concomitant morphological alterations in the MTL that interact to negatively affect memory even in the absence overt clinical symptoms, providing potential insight into the mechanistic link between APOE ε4 and detriments in cognition. Moreover, findings suggest a distinct multimodal neural signature in ε4 carriers (higher CBF and lower CT in the entorhinal cortex) that could aid in the identification of candidates for future clinical trials aimed at preventing or slowing cognitive decline. Differential findings with respect to ε4 carriers and non-carriers are discussed in the context of neurovascular compensation.

The Effect of Daily Low Dose Tadalafil on Cerebral Perfusion and Cognition in Patients with Erectile Dysfunction and Mild Cognitive Impairment

Objective

The aims of this study were to investigate the effects of daily low-dose tadalafil on cognitive function and to examine whether there was a change in cerebral blood flow (CBF) in patients with erectile dysfunction (ED) and mild cognitive impairment.

Methods

Male patients aged 50 to 75 years with at least three months of ED (International Index of Erectile Function [IIEF]-5 score ≤ 21) and mild cognitive impairment (Montreal Cognitive Assessment [MoCA] score ≤ 22) were included in the study. The subjects were prescribed a low-dose PDE5 inhibitor (tadalafil 5 mg) to be taken once daily for eight weeks. Changes in MoCA score and single-photon emission computed tomography (SPECT) study between the two time-points were assessed by paired t tests.

Results

Overall, 30 male patients were assigned to the treatment group in this study and 25 patients completed the eight-week treatment course. Five patients were withdrawn due to adverse events such as myalgia and dizziness. Mean baseline IIEF and MoCA scores were 7.52 ± 4.84 and 18.92 ± 1.78. After the eight-week treatment, mean IIEF and MoCA scores were increased to 12.92 ± 7.27 (p < 0.05) and 21.8 ± 1.71 (p < 0.05), respectively. Patients showed increased relative regional CBF in the postcentral gyrus, precuneus, and brainstem after tadalafil administration versus at baseline (p < 0.001).

Conclusion

The results of this prospective clinical study suggest that daily use of tadalafil 5 mg increases some regional CBF and improves cognitive function in patients with ED and mild cognitive impairment.

Regulating effect of CBF on memory in cognitively normal older adults with different ApoE genotype: the Alzheimer's Disease Neuroimaging Initiative (ADNI)

Apolipoprotein E (ApoE) ε4 allele and cerebral blood flow (CBF) changes are related to the increased risk of cognitive impairment independently. However, whether there are interactions between ApoE ε4 and CBF on memory performance in older adults with normal cognition remains unknown. This study determined whether the association between CBF and memory performance could be moderated by ApoE ε4 within a sample of cognitively normal older adults from the ADNI. 62 participants, including 23 with ApoE ε4 (ApoE ε4+) and 39 without ApoE ε4 (ApoE ε4-), underwent resting CBF measurement and memory testing. CBF was measured by arterial spin labeling MRI and memory performance was evaluated by the Rey Auditory Verbal Learning Test. By using linear regression models, CBF was negatively associated with memory function in ApoE ε4+ group, whereas positively in ApoE ε4- group by contrast. This study suggests that different CBF-memory relationships can be detected in cognitively normal ApoE ε4 carriers compared to ApoE ε4 non-carriers. Associations between hyperperfusion and worse memory performance in ApoE ε4 carriers may reflect vascular and/or cellular dysfunction.

The Effectiveness of Exercise on Cognitive Performance in Individuals with Known Vascular Disease: A Systematic Review

Patients with known vascular disease are at increased risk for cognitive impairments. Exercise has been shown to improve cognition in healthy elderly populations and those with mild cognitive impairments. We explored the literature to understand exercise as a modality to improve cognition in those with vascular disease, focusing on dose-responses. A systematic review was conducted through 2017 using Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane, Ovid Embase, and Ovid MEDLINE databases. Eligible studies examined effects of exercise on memory and cognition in cardiovascular (CVD) or cerebrovascular disease (CBVD). Data extracted included group characteristics, exercise dosage and outcomes measures employed. Twenty-two studies (12 CVD, 10 CBVD) met the inclusion criteria. Interventions included aerobic, resistance, or mixed training, with neuropsychological test batteries assessing cognition. In CVD populations, five studies demonstrated improved cardiovascular fitness and cognition with aerobic training, and another seven studies suggested a dose-response. In CBVD trials, four studies reported improved cognition, with no effects observed in the fifth study. Another study found enhanced cognition with resistance training and four demonstrated a positive association between functional capacity and cognition following combined aerobic and resistance training. Exercise is able to positively affect cognitive performance in those with known vascular disease. There is evidence to suggest a dose–response relationship. Further research is required to optimize prescription.

Cerebral tissue pO2 response to stimulation is preserved with age in awake mice

Compromised oxygen supply to cerebral tissue could be an important mechanism contributing to age-related cognition decline. We recently showed in awake mice that resting cerebral tissue pO₂ decreases with age, a phenomenon that manifests mainly after middle-age. To extend these findings, here we aimed to study how tissue pO₂ response to neuronal stimulation is affected by aging. We used two-photon phosphorescence lifetime microscopy to directly measure the brain tissue pO₂ response to whisker stimulation in healthy awake young, middle-aged and old mice. We show that despite a decrease in baseline tissue pO₂, the amplitude of the tissue pO₂ response to stimulation is well preserved with age. However, the response dynamics are altered towards a slower response with reduced post-stimulus undershoot in older ages, possibly due to stiffer vessel wall among other factors. An estimation of the net oxygen consumption rate using a modified Krogh model suggests that the O₂ overshoot during stimulation may be necessary to secure a higher capillary O₂ delivery to the tissue proportional to increased CMRO₂ to maintain the capillary tissue pO₂. It was observed that the coupling between the CMRO₂ and capillary O₂ delivery is preserved with age.

Normal Cerebral Oxygen Consumption Despite Elevated Cerebral Blood Flow in Adolescents With Bipolar Disorder: Putative Neuroimaging Evidence of Anomalous Energy Metabolism

Background: Regional cerebral blood flow (CBF) is reportedly altered in both adolescents and adults with bipolar disorder (BD). Whether these CBF differences are part of an overall imbalance in cerebral energy homeostasis remains unknown. Therefore, we examined global cerebral metabolic rate of oxygen consumption (CMRO₂) as a physiological index of brain metabolism in adolescents with and without BD. Methods: One hundred and fifteen adolescents (mean age 17.3 ± 1.4 years), including 58 BD (type I, II, or not otherwise specified [NOS]) and 57 age-matched healthy controls (HCs) participated in this magnetic resonance imaging (MRI) study. Global estimates for venous blood oxygenation (Y_v) and grey matter CBF were measured using T2-relaxation-under-spin-tagging (TRUST) and arterial spin labeling (ASL) MRI, respectively. CMRO₂ was calculated using the Fick principle of arteriovenous difference to test for a group difference. We also examined CMRO₂ in relation to mood states (i.e. euthymic, depressed, or hypomanic/mixed). Results: Although CBF was significantly higher in BD compared to HCs, there was no group difference in global CMRO₂, nor Y_v. Meanwhile, Y_v significantly decreased with age, and females tended to have greater CBF and CMRO₂ in comparison to males. Lastly, there was no significant association between CMRO₂ and mood states. Conclusions: Our results indicate a potential mismatch between cerebral blood supply and oxygen metabolism in BD, suggesting inefficiency in energy homeostasis in the brain. Mapping CMRO₂ would provide the spatial resolution to investigate regional alterations in metabolism, particularly in the brain regions where CBF is increased.

Can Blood Oxygenation Level Dependent Functional Magnetic Resonance Imaging Be Used Accurately to Compare Older and Younger Populations? A Mini Literature Review

A wealth of research has investigated the aging brain using blood oxygenation level dependent functional MRI [Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI)]. However, many studies do not consider the aging of the cerebrovascular system, which can influence the BOLD signal independently from neural activity, limiting what can be inferred when comparing age groups. Here, we discuss the ways in which the aging neurovascular system can impact BOLD fMRI, the consequences for age-group comparisons and possible strategies for mitigation. While BOLD fMRI is a valuable tool in this context, this review highlights the importance of consideration of vascular confounds.

Dynamic cerebral autoregulation is impaired in Veterans with Gulf War Illness: A case-control study

Neurological dysfunction has been reported in Gulf War Illness (GWI), including abnormal cerebral blood flow (CBF) responses to physostigmine challenge. However, it is unclear whether the CBF response to normal physiological challenges and regulation is similarly dysfunctional. The goal of the present study was to evaluate the CBF velocity response to orthostatic stress (i.e., sit-to-stand maneuver) and increased fractional concentration of carbon dioxide. 23 cases of GWI (GWI+) and 9 controls (GWI) volunteered for this study. Primary variables of interest included an index of dynamic autoregulation and cerebrovascular reactivity. Dynamic autoregulation was significantly lower in GWI+ than GWI- both for autoregulatory index (2.99±1.5 vs 4.50±1.5, p = 0.017). In addition, we observed greater decreases in CBF velocity both at the nadir after standing (-18.5±6.0 vs -9.8±4.9%, p = 0.001) and during steady state standing (-5.7±7.1 vs -1.8±3.2%, p = 0.042). In contrast, cerebrovascular reactivity was not different between groups. In our sample of Veterans with GWI, dynamic autoregulation was impaired and consistent with greater cerebral hypoperfusion when standing. This reduced CBF may contribute to cognitive difficulties in these Veterans when upright.

Regular walking breaks prevent the decline in cerebral blood flow associated with prolonged sitting

Decreased cerebrovascular blood flow and function are associated with lower cognitive functioning and increased risk of neurodegenerative diseases. Prolonged sitting impairs peripheral blood flow and function, but its effects on the cerebrovasculature are unknown. This study explored the effect of uninterrupted sitting and breaking up sitting time on cerebrovascular blood flow and function of healthy desk workers. Fifteen participants (10 male, 35.8 ± 10.2 yr, body mass index: 25.5 ± 3.2 kg/m2) completed, on separate days, three 4-h conditions in a randomized order: 1) uninterrupted sitting (SIT), 2) sitting with 2-min light-intensity walking breaks every 30 min (2WALK), or 3) sitting with 8-min light-intensity walking breaks every 2 h (8WALK). At baseline and 4 h, middle cerebral artery blood flow velocity (MCAv) and CO2 reactivity (CVR) of the MCA and carotid artery were measured using transcranial Doppler (TCD) and duplex ultrasound, respectively. Cerebral autoregulation (CA) was assessed with TCD using a squat-stand protocol and analyzed to generate values of gain and phase in the very low, low, and high frequencies. There was a significant decline in SIT MCAv (−3.2 ± 1.2 cm/s) compared with 2WALK (0.6 ± 1.5 cm/s, P = 0.02) but not between SIT and 8WALK (−1.2 ± 1.0 cm/s, P = 0.14). For CA, the change in 2WALK very low frequency phase (4.47 ± 4.07 degrees) was significantly greater than SIT (−3.38 ± 2.82 degrees, P = 0.02). There was no significant change in MCA or carotid artery CVR ( P > 0.05). Results indicate that prolonged uninterrupted sitting in healthy desk workers reduces cerebral blood flow; however, this is offset when frequent short-duration walking breaks are incorporated.

NEW & NOTEWORTHY Prolonged uninterrupted sitting in healthy desk workers reduces cerebral blood flow. However, this reduction in cerebral blood flow is offset when frequent short-duration walking breaks are incorporated into this sitting period. For those who engage in long periods of sedentary behavior, chronically breaking up these sitting periods with frequent active break strategies may have important implications for cerebrovascular health; however, further research should explore this hypothesis.

Aging-associated changes in cerebral vasculature and blood flow as determined by quantitative optical coherence tomography angiography

Normal aging is associated with significant alterations in brain's vascular structure and function, which can lead to compromised cerebral circulation and increased risk of neurodegeneration. The in vivo examination of cerebral blood flow (CBF), including capillary beds, in aging brains with sufficient spatial detail remains challenging with current imaging modalities. In the present study, we use 3-dimensional (3-D) quantitative optical coherence tomography angiography (OCTA) to examine characteristic differences of the cerebral vasculatures and hemodynamics at the somatosensory cortex between old (16 months old) and young mice (2 months old) in vivo. The quantitative metrics include cortical vascular morphology, CBF, and capillary flow velocity. We show that compared with young mice, the pial arterial tortuosity increases by 14%, the capillary vessel density decreases by 15%, and the CBF reduces by 33% in the old mice. Most importantly, changes in capillary velocity and heterogeneity with aging are quantified for the first time with sufficiently high statistical power between young and old populations, with a 21% (p < 0.05) increase in capillary mean velocity and 19% (p ≤ 0.05) increase in velocity heterogeneity in the latter. Our findings through noninvasive imaging are in line with previous studies of vascular structure modification with aging, with additional quantitative assessment in capillary velocity enabled by advanced OCTA algorithms on a single imaging platform. The results offer OCTA as a promising neuroimaging tool to study vascular aging, which may shed new light on the investigations of vascular factors contributing to the pathophysiology of age-related neurodegenerative disorders.