Neurovascular coupling is impaired in cerebral microangiopathy--An event-related Stroop study

Can white matter hyperintensities based Fazekas visual assessment scales inform about Alzheimer's disease pathology in the population?

BACKGROUND

White matter hyperintensities (WMH) are considered hallmark features of cerebral small vessel disease and have recently been linked to Alzheimer's disease (AD) pathology. Their distinct spatial distributions, namely periventricular versus deep WMH, may differ by underlying age-related and pathobiological processes contributing to cognitive decline. We aimed to identify the spatial patterns of WMH using the 4-scale Fazekas visual assessment and explore their differential association with age, vascular health, AD imaging markers, namely amyloid and tau burden, and cognition. Because our study consisted of scans from GE and Siemens scanners with different resolutions, we also investigated inter-scanner reproducibility and combinability of WMH measurements on imaging.

METHODS

We identified 1144 participants from the Mayo Clinic Study of Aging consisting of a population-based sample from Olmsted County, Minnesota with available structural magnetic resonance imaging (MRI), amyloid, and tau positron emission tomography (PET). WMH distribution patterns were assessed on FLAIR-MRI, both 2D axial and 3D, using Fazekas ratings of periventricular and deep WMH severity. We compared the association of periventricular and deep WMH scales with vascular risk factors, amyloid-PET, and tau-PET standardized uptake value ratio, automated WMH volume, and cognition using Pearson partial correlation after adjusting for age. We also evaluated vendor compatibility and reproducibility of the Fazekas scales using intraclass correlations (ICC).

RESULTS

Periventricular and deep WMH measurements showed similar correlations with age, cardiometabolic conditions score (vascular risk), and cognition, (p < 0.001). Both periventricular WMH and deep WMH showed weak associations with amyloidosis (R = 0.07, p = < 0.001), and none with tau burden. We found substantial agreement between data from the two scanners for Fazekas measurements (ICC = 0.82 and 0.74). The automated WMH volume had high discriminating power for identifying participants with Fazekas ≥ 2 (area under curve = 0.97) and showed poor correlation with amyloid and tau PET markers similar to the visual grading.

CONCLUSION

Our study investigated risk factors underlying WMH spatial patterns and their impact on global cognition, with no discernible differences between periventricular and deep WMH. We observed minimal impact of amyloidosis on WMH severity. These findings, coupled with enhanced inter-scanner reproducibility of WMH data, suggest the combinability of inter-scanner data assessed by harmonized protocols in the context of vascular contributions to cognitive impairment and dementia biomarker research.

Can white matter hyperintensities based Fazekas visual assessment scales inform about Alzheimer's disease pathology in the population?

Background

White matter hyperintensities (WMH) are considered hallmark features of cerebral small vessel disease and have recently been linked to Alzheimer's disease pathology. Their distinct spatial distributions, namely periventricular versus deep WMH, may differ by underlying age-related and pathobiological processes contributing to cognitive decline. We aimed to identify the spatial patterns of WMH using the 4-scale Fazekas visual assessment and explore their differential association with age, vascular health, Alzheimer's imaging markers, namely amyloid and tau burden, and cognition. Because our study consisted of scans from GE and Siemens scanners with different resolutions, we also investigated inter-scanner reproducibility and combinability of WMH measurements on imaging.

Methods

We identified 1144 participants from the Mayo Clinic Study of Aging consisting of older adults from Olmsted County, Minnesota with available structural magnetic resonance imaging (MRI), amyloid, and tau positron emission tomography (PET). WMH distribution patterns were assessed on FLAIR-MRI, both 2D axial and 3D, using Fazekas ratings of periventricular and deep WMH severity. We compared the association of periventricular and deep WMH scales with vascular risk factors, amyloid-PET and tau-PET standardized uptake value ratio, WMH volume, and cognition using Pearson partial correlation after adjusting for age. We also evaluated vendor compatibility and reproducibility of the Fazekas scales using intraclass correlations (ICC).

Results

Periventricular and deep WMH measurements showed similar correlations with age, cardiometabolic conditions score (vascular risk), and cognition, (p < 0.001). Both periventricular WMH and deep WMH showed weak associations with amyloidosis (R = 0.07, p = < 0.001), and none with tau burden. We found substantial agreement between data from the two scanners for Fazekas measurements (ICC = 0.78). The automated WMH volume had high discriminating power for identifying participants with Fazekas ≥ 2 (area under curve = 0.97).

Conclusion

Our study investigates risk factors underlying WMH spatial patterns and their impact on global cognition, with no discernible differences between periventricular and deep WMH. We observed minimal impact of amyloidosis on WMH severity. These findings, coupled with enhanced inter-scanner reproducibility of WMH data, suggest the combinability of inter-scanner data assessed by harmonized protocols in the context of vascular contributions to cognitive impairment and dementia biomarker research.

Vascular cognitive impairment - Past, present, and future challenges

Vascular cognitive impairment (VCI) is a lifelong process encompassing a broad spectrum of cognitive disorders, ranging from subtle or mild deficits to prodromal and fully developed dementia, originating from cerebrovascular lesions such as large and small vessel disease. Genetic predisposition and environmental exposure to risk factors such as unhealthy lifestyles, hypertension, cardiovascular disease, and metabolic disorders will synergistically interact, yielding biochemical and structural brain changes, ultimately culminating in VCI. However, little is known about the pathological processes underlying VCI and the temporal dynamics between risk factors and disease mechanisms (biochemical and structural brain changes). This narrative review aims to provide an evidence-based summary of the link between individual vascular risk/disorders and cognitive dysfunction and the potential structural and biochemical pathophysiological processes. We also discuss some key challenges for future research on VCI. There is a need to shift from individual risk factors/disorders to comorbid vascular burden, identifying and integrating imaging and fluid biomarkers, implementing a life-course approach, considering possible neuroprotective influences of positive life exposures, and addressing biological sex at birth and gender differences. Finally, this review highlights the need for future researchers to leverage and integrate multidimensional data to advance our understanding of the mechanisms and pathophysiology of VCI.

Cortical hemodynamic response during cognitive Stroop test in acute stroke patients assessed by fNIRS

BACKGROUND

Following acute ischemic stroke (AIS) many patients experience cognitive impairment which interferes neurorehabilitation. Understanding and monitoring pathophysiologic processes behind cognitive symptoms requires accessible methods during testing and training. Functional near-infrared spectroscopy (fNIRS) can assess activational hemodynamic responses in the prefrontal cortex (PFC) and feasibly be used as a biomarker to support stroke rehabilitation.

OBJECTIVE

Exploring the feasibility of fNIRS as a biomarker during the Stroop Color and Word Test (SCWT) assessing executive function in AIS patients.

METHODS

Observational study of 21 patients with mild to moderate AIS and 22 healthy age- and sex-matched controls (HC) examined with fNIRS of PFC during the SCWT. Hemodynamic responses were analyzed with general linear modeling.

RESULTS

The SCWT was performed worse by AIS patients than HC. Neither patients nor HC showed PFC activation, but an inverse activational pattern primarily in superolateral and superomedial PFC significantly lower in AIS. Hemodynamic responses were incoherent to test difficulty and performance. No other group differences or lateralization were found.

CONCLUSIONS

AIS patients had impaired executive function assessed by the SCWT, while both groups showed an inverse hemodynamic response significantly larger in HC. Investigations assessing the physiology behind inverse hemodynamic responses are warranted before deeming clinical implementation reasonable.

Association between carotid atherosclerosis and brain activation patterns during the Stroop task in older adults: An fNIRS investigation

There is an increasing body of evidence suggesting that vascular disease could contribute to cognitive decline and overt dementia. Of particular interest is atherosclerosis, as it is not only associated with dementia, but could be a potential mechanism through which cardiovascular disease directly impacts brain health. In this work, we evaluated the differences in functional near infrared spectroscopy (fNIRS)-based measures of brain activation, task performance, and the change in central hemodynamics (mean arterial pressure (MAP) and heart rate (HR)) during a Stroop color-word task in individuals with atherosclerosis, defined as bilateral carotid plaques (n = 33) and healthy age-matched controls (n = 33). In the healthy control group, the left prefrontal cortex (LPFC) was the only region showing evidence of activation when comparing the incongruous with the nominal Stroop test. A smaller extent of brain activation was observed in the Plaque group compared with the healthy controls (1) globally, as measured by oxygenated hemoglobin (p = 0.036) and (2) in the LPFC (p = 0.02) and left sensorimotor cortices (LMC)(p = 0.008) as measured by deoxygenated hemoglobin. There were no significant differences in HR, MAP, or task performance (both in terms of the time required to complete the task and number of errors made) between Plaque and control groups. These results suggest that carotid atherosclerosis is associated with altered functional brain activation patterns despite no evidence of impaired performance of the Stroop task or central hemodynamic changes.

Increased Serum NSE and S100B Indicate Neuronal and Glial Alterations in Subjects Under 71 Years With Mild Neurocognitive Disorder/Mild Cognitive Impairment

Background

Mild cognitive impairment (MCI) is considered a pre-stage of different dementia syndromes. Despite diagnostic criteria refined by DSM-5 and a new term for MCI – “mild neurocognitive disorder” (mild NCD) – this diagnosis is still based on clinical criteria.

Methods

To link mild NCD to the underlying pathophysiology we assessed the degree of white matter hyperintensities (WMH) in the brain and peripheral biomarkers for neuronal integrity (neuron-specific enolase, NSE), plasticity (brain-derived neurotrophic factor, BDNF), and glial function (S100B) in 158 community-dwelling subjects with mild NCD and 82 healthy controls. All participants (63–79 years old) were selected from the Leipzig-population-based study of adults (LIFE).

Results

Serum S100B levels were increased in mild NCD in comparison to controls (p = 0.007). Serum NSE levels were also increased but remained non-significant after Bonferroni-Holm correction (p = 0.04). Furthermore, age by group interaction was significant for S100B. In an age-stratified sub-analysis, NSE and S100B were higher in younger subjects with mild NCD below 71 years of age. Some effects were inconsistent after controlling for potentially confounding factors. The discriminatory power of the two biomarkers NSE and S100B was insufficient to establish a pathologic threshold for mild NCD. In subjects with mild NCD, WMH load correlated with serum NSE levels (r = 0.20, p = 0.01), independently of age.

Conclusion

Our findings might indicate the presence of neuronal (NSE) and glial (S100B) injury in mild NCD. Future studies need to investigate whether younger subjects with mild NCD with increased biomarker levels are at risk of developing major NCD.

Impaired functional network properties contribute to white matter hyperintensity related cognitive decline in patients with cerebral small vessel disease

Background

White matter hyperintensity (WMH) is one of the typical neuroimaging manifestations of cerebral small vessel disease (CSVD), and the WMH correlates closely to cognitive impairment (CI). CSVD patients with WMH own altered topological properties of brain functional network, which is a possible mechanism that leads to CI. This study aims to identify differences in the characteristics of some brain functional network among patients with different grades of WMH and estimates the correlations between these different brain functional network characteristics and cognitive assessment scores.

Methods

110 CSVD patients underwent 3.0 T Magnetic resonance imaging scans and neuropsychological cognitive assessments. WMH of each participant was graded on the basis of Fazekas grade scale and was divided into two groups: (A) WMH score of 1–2 points (n = 64), (B) WMH score of 3–6 points (n = 46). Topological indexes of brain functional network were analyzed using graph-theoretical method. T-test and Mann–Whitney U test was used to compare the differences in topological properties of brain functional network between groups. Partial correlation analysis was applied to explore the relationship between different topological properties of brain functional networks and overall cognitive function.

Results

Patients with high WMH scores exhibited decreased clustering coefficient values, global and local network efficiency along with increased shortest path length on whole brain level as well as decreased nodal efficiency in some brain regions on nodal level (p < 0.05). Nodal efficiency in the left lingual gyrus was significantly positively correlated with patients' total Montreal Cognitive Assessment (MoCA) scores (p < 0.05). No significant difference was found between two groups on the aspect of total MoCA and Mini-mental State Examination (MMSE) scores (p > 0.05).

Conclusion

Therefore, we come to conclusions that patients with high WMH scores showed less optimized small-world networks compared to patients with low WMH scores. Global and local network efficiency on the whole-brain level, as well as nodal efficiency in certain brain regions on the nodal level, can be viewed as markers to reflect the course of WMH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12880-022-00769-7.

Cognitive impairment caused by hypoxia: from clinical evidences to molecular mechanisms

Hypoxia is a state of reduced oxygen supply and excessive oxygen consumption. According to the duration of hypoxic period, it can be classified as acute and chronic hypoxia. Both acute and chronic hypoxia could induce abundant neurological deficits. Although there have been significant advances in the pathophysiological injuries, few studies have focused on the cognitive dysfunction. In this review, we focused on the clinical evidences and molecular mechanisms of cognitive impairment under acute and chronic hypoxia. Hypoxia can impair several cognitive domains such as attention, learning and memory, procession speed and executive function, which are similar in acute and chronic hypoxia. The severity of cognitive deficit correlates with the duration and degree of hypoxia. Recovery can be achieved after acute hypoxia, while sequelae or even dementia can be observed after chronic hypoxia, perhaps due to the different molecular mechanisms. Cardiopulmonary compensatory response, glycolysis, oxidative stress, calcium overload, adenosine, mitochondrial disruption, inflammation and excitotoxicity contribute to the molecular mechanisms of cognitive deficit after acute hypoxia. During the chronic stage of hypoxia, different adaptive responses, impaired neurovascular coupling, apoptosis, transcription factors-mediated inflammation, as well as Aβ accumulation and tau phosphorylation account for the neurocognitive deficit. Moreover, brain structural changes with hippocampus and cortex atrophy, ventricle enlargement, senile plaque and neurofibrillary tangle deposition can be observed under chronic hypoxia rather than acute hypoxia.

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.

Graded fMRI Neurofeedback Training of Motor Imagery in Middle Cerebral Artery Stroke Patients: A Preregistered Proof-of-Concept Study

Ischemic stroke of the middle cerebral artery (MCA), a major brain vessel that supplies the primary motor and premotor cortex, is one of the most common causes for severe upper limb impairment. Currently available motor rehabilitation training largely lacks satisfying efficacy with over 70% of stroke survivors showing residual upper limb dysfunction. Motor imagery-based functional magnetic resonance imaging neurofeedback (fMRI-NF) has been suggested as a potential therapeutic technique to improve motor impairment in stroke survivors. In this preregistered proof-of-concept study (https://osf.io/y69jc/), we translated graded fMRI-NF training, a new paradigm that we have previously studied in healthy participants, to first-time MCA stroke survivors with residual mild to severe impairment of upper limb motor function. Neurofeedback was provided from the supplementary motor area (SMA) targeting two different neurofeedback target levels (low and high). We hypothesized that MCA stroke survivors will show (1) sustained SMA-region of interest (ROI) activation and (2) a difference in SMA-ROI activation between low and high neurofeedback conditions during graded fMRI-NF training. At the group level, we found only anecdotal evidence for these preregistered hypotheses. At the individual level, we found anecdotal to moderate evidence for the absence of the hypothesized graded effect for most subjects. These null findings are relevant for future attempts to employ fMRI-NF training in stroke survivors. The study introduces a Bayesian sequential sampling plan, which incorporates prior knowledge, yielding higher sensitivity. The sampling plan was preregistered together with a priori hypotheses and all planned analysis before data collection to address potential publication/researcher biases. Unforeseen difficulties in the translation of our paradigm to a clinical setting required some deviations from the preregistered protocol. We explicitly detail these changes, discuss the accompanied additional challenges that can arise in clinical neurofeedback studies, and formulate recommendations for how these can be addressed. Taken together, this work provides new insights about the feasibility of motor imagery-based graded fMRI-NF training in MCA stroke survivors and serves as a first example for comprehensive study preregistration of an (fMRI) neurofeedback experiment.

The present and future use of functional near-infrared spectroscopy (fNIRS) for cognitive neuroscience

The past few decades have seen a rapid increase in the use of functional near-infrared spectroscopy (fNIRS) in cognitive neuroscience. This fast growth is due to the several advances that fNIRS offers over the other neuroimaging modalities such as functional magnetic resonance imaging and electroencephalography/magnetoencephalography. In particular, fNIRS is harmless, tolerant to bodily movements, and highly portable, being suitable for all possible participant populations, from newborns to the elderly and experimental settings, both inside and outside the laboratory. In this review we aim to provide a comprehensive and state-of-the-art review of fNIRS basics, technical developments, and applications. In particular, we discuss some of the open challenges and the potential of fNIRS for cognitive neuroscience research, with a particular focus on neuroimaging in naturalistic environments and social cognitive neuroscience.

Small Vessel Disease-Related Dementia: An Invalid Neurovascular Coupling?

The arteriosclerosis-dependent alteration of brain perfusion is one of the major determinants in small vessel disease, since small vessels have a pivotal role in the brain's autoregulation. Nevertheless, as far as we know, endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia that is related to small vessel disease (SVD), also being defined as subcortical vascular dementia (sVAD), as well as microglia activation, chronic hypoxia and hypoperfusion, vessel-tone dysregulation, altered astrocytes, and pericytes functioning blood-brain barrier disruption. The molecular basis of this pathology remains controversial. The apparent consequence (or a first event, too) is the macroscopic alteration of the neurovascular coupling. Here, we examined the possible mechanisms that lead a healthy aging process towards subcortical dementia. We remarked that SVD and white matter abnormalities related to age could be accelerated and potentiated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors, which are, to the best of our knowledge, mostly unknown. Metabolic demands, active neurovascular coupling, correct glymphatic process, and adequate oxidative and inflammatory responses could be bulwarks in defense of the correct aging process; their impairments lead to a potentially catastrophic and non-reversible condition.

B Vitamins and Fatty Acids: What Do They Share with Small Vessel Disease-Related Dementia?

Many studies have been written on vitamin supplementation, fatty acid, and dementia, but results are still under debate, and no definite conclusion has yet been drawn. Nevertheless, a significant amount of lab evidence confirms that vitamins of the B group are tightly related to gene control for endothelium protection, act as antioxidants, play a co-enzymatic role in the most critical biochemical reactions inside the brain, and cooperate with many other elements, such as choline, for the synthesis of polyunsaturated phosphatidylcholine, through S-adenosyl-methionine (SAM) methyl donation. B-vitamins have anti-inflammatory properties and act in protective roles against neurodegenerative mechanisms, for example, through modulation of the glutamate currents and a reduction of the calcium currents. In addition, they also have extraordinary antioxidant properties. However, laboratory data are far from clinical practice. Many studies have tried to apply these results in everyday clinical activity, but results have been discouraging and far from a possible resolution of the associated mysteries, like those represented by Alzheimer's disease (AD) or small vessel disease dementia. Above all, two significant problems emerge from the research: No consensus exists on general diagnostic criteria-MCI or AD? Which diagnostic criteria should be applied for small vessel disease-related dementia? In addition, no general schema exists for determining a possible correct time of implementation to have effective results. Here we present an up-to-date review of the literature on such topics, shedding some light on the possible interaction of vitamins and phosphatidylcholine, and their role in brain metabolism and catabolism. Further studies should take into account all of these questions, with well-designed and world-homogeneous trials.

Small vessel disease to subcortical dementia: a dynamic model, which interfaces aging, cholinergic dysregulation and the neurovascular unit

Background

Small vessels have the pivotal role for the brain’s autoregulation. The arteriosclerosis-dependent alteration of the brain perfusion is one of the major determinants in small vessel disease. Endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia (sVAD). sVAD increases morbidity and disability. Epidemiological studies have shown that sVAD shares with cerebrovascular disease most of the common risk factors. The molecular basis of this pathology remains controversial.

Purpose

To detect the possible mechanisms between small vessel disease and sVAD, giving a broad vision on the topic, including pathological aspects, clinical and laboratory findings, metabolic process and cholinergic dysfunction.

Methods

We searched MEDLINE using different search terms (“vascular dementia”, “subcortical vascular dementia”, “small vessel disease”, “cholinergic afferents”, etc). Publications were selected from the past 20 years. Searches were extended to Embase, Cochrane Library, and LILIACS databases. All searches were done from January 1, 1998 up to January 31, 2018.

Results

A total of 560 studies showed up, and appropriate studies were included. Associations between traditional vascular risk factors have been isolated. We remarked that SVD and white matter abnormalities are seen frequently with aging and also that vascular and endothelium changes are related with age; the changes can be accelerated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors.

Conclusion

Small vessel disease and the related dementia are two pathologies that deserve attention for their relevance and impact in clinical practice. Hypertension might be a historical problem for SVD and SVAD, but low pressure might be even more dangerous; CBF regional selective decrease seems to be a critical factor for small vessel disease-related dementia. In those patients, endothelium damage is a super-imposed condition. Several issues are still debatable, and more research is needed.

The importance of comorbidities in ischemic stroke: Impact of hypertension on the cerebral circulation

Comorbidities are a hallmark of stroke that both increase the incidence of stroke and worsen outcome. Hypertension is prevalent in the stroke population and the most important modifiable risk factor for stroke. Hypertensive disorders promote stroke through increased shear stress, endothelial dysfunction, and large artery stiffness that transmits pulsatile flow to the cerebral microcirculation. Hypertension also promotes cerebral small vessel disease through several mechanisms, including hypoperfusion, diminished autoregulatory capacity and localized increase in blood-brain barrier permeability. Preeclampsia, a hypertensive disorder of pregnancy, also increases the risk of stroke 4-5-fold compared to normal pregnancy that predisposes women to early-onset cognitive impairment. In this review, we highlight how comorbidities and concomitant disorders are not only risk factors for ischemic stroke, but alter the response to acute ischemia. We focus on hypertension as a comorbidity and its effects on the cerebral circulation that alters the pathophysiology of ischemic stroke and should be considered in guiding future therapeutic strategies.

The brain's hemodynamic response function rapidly changes under acute psychosocial stress in association with genetic and endocrine stress response markers

Ample evidence links dysregulation of the stress response to the risk for psychiatric disorders. However, we lack an integrated understanding of mechanisms that are adaptive during the acute stress response but potentially pathogenic when dysregulated. One mechanistic link emerging from rodent studies is the interaction between stress effectors and neurovascular coupling, a process that adjusts cerebral blood flow according to local metabolic demands. Here, using task-related fMRI, we show that acute psychosocial stress rapidly impacts the peak latency of the hemodynamic response function (HRF-PL) in temporal, insular, and prefrontal regions in two independent cohorts of healthy humans. These latency effects occurred in the absence of amplitude effects and were moderated by regulatory genetic variants of KCNJ2, a known mediator of the effect of stress on vascular responsivity. Further, hippocampal HRF-PL correlated with both cortisol response and genetic variants that influence the transcriptional response to stress hormones and are associated with risk for major depression. We conclude that acute stress modulates hemodynamic response properties as part of the physiological stress response and suggest that HRF indices could serve as endophenotype of stress-related disorders.

White matter hyperintensities associated with small vessel disease impair social cognition beside attention and memory

Age-related white matter hyperintensities (WMH) are a manifestation of white matter damage seen on magnetic resonance imaging (MRI). They are related to vascular risk factors and cognitive impairment. This study investigated the cognitive profile at different stages of WMH in a large community-dwelling sample; 849 subjects aged 21 to 79 years were classified on the 4-stage Fazekas scale according to hyperintense lesions seen on individual T2-weighted fluid-attenuated inversion recovery MRI scans. The evaluation of cognitive functioning included seven domains of cognitive performance and five domains of subjective impairment, as proposed by the DSM-5. For the first time, the impact of age-related WMH on Theory of Mind was investigated. Differences between Fazekas groups were analyzed non-parametrically and effect sizes were computed. Effect sizes revealed a slight overall cognitive decline in Fazekas groups 1 and 2 relative to healthy subjects. Fazekas group 3 presented substantial decline in social cognition, attention and memory, although characterized by a high inter-individual variability. WMH groups reported subjective cognitive decline. We demonstrate that extensive WMH are associated with specific impairment in attention, memory, social cognition, and subjective cognitive performance. The detailed neuropsychological characterization of WMH offers new therapeutic possibilities for those affected by vascular cognitive decline.

Repetition suppression in aging: A near-infrared spectroscopy study on the size-congruity effect

Age-related changes in the hemodynamic response regarding inhibition capacity and repetition suppression were examined using a modified version of the numerical Stroop task. Young (20-38 yrs; M = 28 yrs; N = 18), middle-aged (47-59 yrs; M = 52 yrs; N = 17), and older participants (60-78 yrs; M = 69 yrs; N = 19) solved a physical and numerical version of the size-congruity task, in which trials from the same experimental condition were presented in triplets. Response times revealed a strong Stroop effect in both tasks (faster reaction times during neutral than during incongruent trials) and increased with participants' age. Reaction times decreased with item repetition. In line with previous studies, the hemodynamic response (relative concentration changes in oxygenated and deoxygenated hemoglobin) assessed with near-infrared spectroscopy was comparable across incongruent and neutral trials. Strong repetition suppression of the oxygenated hemoglobin response was observed in frontal brain regions as well as in the left parietal region in all age groups. In middle and right parietal regions, repetition suppression decreased with age and was absent among older participants. These results indicate a reduced adaptation of the hemodynamic response in middle and right parietal regions of older individuals' brains in response to repeated interference control.

Prefrontal cortex-mediated executive function as assessed by Stroop task performance associates with weight loss among overweight and obese adolescents and young adults

People with cognitive deficits or executive dysfunction are often overweight or obese. Several human neuroimaging studies have found that executive function (EF) predicts food intake and weight gain; however, fewer studies have investigated the relationship between EF and weight loss. The Stroop task is a classic measure of EF that is used in many neuroimaging studies. In the present work, functional near infrared spectroscopy (fNIRS) data were collected during performance of the Stroop task from a sample of overweight or obese adolescents and young adults (n=31) who participated in a summer fitness and weight loss camp. We assessed the Stroop effect by interference in the reaction time (RT) to visual challenges, and by alterations in levels of oxygenated hemoglobin, as detected by fNIRS. In line with previous studies, we found that the Stroop effect was successfully induced by different visual task conditions among obese/overweight individuals. Moreover, our results reveal that better Stroop task performance is correlated with greater weight loss over a4-weekfitness intervention. Indeed, behavioral data demonstrated that reduced RT interference predicted a greater percentage of weight loss. Moreover, overweight/obese individuals with a greater hemodynamic response in the left ventrolateral and bilateral dorsolateral prefrontal cortex due to the Stroop effect lost more weight during the short-term fitness intervention than participants with lower levels of activation of these neural regions. Overall, our results support a role for prefrontal cortex-mediated EF in influencing food intake and weight loss outcomes in a population of a previously unstudied age.

The effects of hemodynamic lag on functional connectivity and behavior after stroke

Stroke disrupts the brain's vascular supply, not only within but also outside areas of infarction. We investigated temporal delays (lag) in resting state functional magnetic resonance imaging signals in 130 stroke patients scanned two weeks, three months and 12 months post stroke onset. Thirty controls were scanned twice at an interval of three months. Hemodynamic lag was determined using cross-correlation with the global gray matter signal. Behavioral performance in multiple domains was assessed in all patients. Regional cerebral blood flow and carotid patency were assessed in subsets of the cohort using arterial spin labeling and carotid Doppler ultrasonography. Significant hemodynamic lag was observed in 30% of stroke patients sub-acutely. Approximately 10% of patients showed lag at one-year post-stroke. Hemodynamic lag corresponded to gross aberrancy in functional connectivity measures, performance deficits in multiple domains and local and global perfusion deficits. Correcting for lag partially normalized abnormalities in measured functional connectivity. Yet post-stroke FC-behavior relationships in the motor and attention systems persisted even after hemodynamic delays were corrected. Resting state fMRI can reliably identify areas of hemodynamic delay following stroke. Our data reveal that hemodynamic delay is common sub-acutely, alters functional connectivity, and may be of clinical importance.

Intra-individual lap time variation of the 400-m walk, an early mobility indicator of executive function decline in high-functioning older adults?

Higher intra-individual lap time variation (LTV) of the 400-m walk is cross-sectionally associated with poorer attention in older adults. Whether higher LTV predicts decline in executive function and whether the relationship is accounted for by slower walking remain unanswered. The main objective of this study was to examine the relationship between baseline LTV and longitudinal change in executive function. We used data from 347 participants aged 60 years and older (50.7% female) from the Baltimore Longitudinal Study of Aging. Longitudinal assessments of executive function were conducted between 2007 and 2013, including attention (Trails A, Digit Span Forward Test), cognitive flexibility and set shifting (Trails B, Delta TMT: Trials B minus Trials A), visuoperceptual speed (Digit Symbol Substitution Test), and working memory (Digit Span Backward Test). LTV and mean lap time (MLT) were obtained from the 400-m walk test concurrent with the baseline executive function assessment. LTV was computed as variability of lap time across ten 40-m laps based on individual trajectories. A linear mixed-effects model was used to examine LTV in relation to changes in executive function, adjusted for age, sex, education, and MLT. Higher LTV was associated with greater decline in performance on Trails B (β = 4.322, p < 0.001) and delta TMT (β = 4.230, p < 0.001), independent of covariates. Findings remained largely unchanged after further adjustment for MLT. LTV was not associated with changes in other executive function measures (all p > 0.05). In high-functioning older adults, higher LTV in the 400-m walk predicts executive function decline involving cognitive flexibility and set shifting over a long period of time. High LTV may be an early indicator of executive function decline independent of MLT.

Endothelial Dysfunction and Amyloid-β-Induced Neurovascular Alterations

Alzheimer's disease (AD) and cerebrovascular diseases share common vascular risk factors that have disastrous effects on cerebrovascular regulation. Endothelial cells, lining inner walls of cerebral blood vessels, form a dynamic interface between the blood and the brain and are critical for the maintenance of neurovascular homeostasis. Accordingly, injury in endothelial cells is regarded as one of the earliest symptoms of impaired vasoregulatory mechanisms. Extracellular buildup of amyloid-β (Aβ) is a central pathogenic factor in AD. Aβ exerts potent detrimental effects on cerebral blood vessels and impairs endothelial structure and function. Recent evidence implicates vascular oxidative stress and activation of the non-selective cationic channel transient receptor potential melastatin (TRPM)-2 on endothelial cells in the mechanisms of Aβ-induced neurovascular dysfunction. Thus, Aβ triggers opening of TRPM2 channels in endothelial cells leading to intracellular Ca(2+) overload and vasomotor dysfunction. The cerebrovascular dysfunction may contribute to AD pathogenesis by reducing the cerebral blood supply, leading to increased susceptibility to vascular insufficiency, and by promoting Aβ accumulation. The recent realization that vascular factors contribute to AD pathobiology suggests new targets for the prevention and treatment of this devastating disease.

Coupling mechanism and significance of the BOLD signal: a status report

Functional magnetic resonance imaging (fMRI) provides a unique view of the working human mind. The blood-oxygen-level-dependent (BOLD) signal, detected in fMRI, reflects changes in deoxyhemoglobin driven by localized changes in brain blood flow and blood oxygenation, which are coupled to underlying neuronal activity by a process termed neurovascular coupling. Over the past 10 years, a range of cellular mechanisms, including astrocytes, pericytes, and interneurons, have been proposed to play a role in functional neurovascular coupling. However, the field remains conflicted over the relative importance of each process, while key spatiotemporal features of BOLD response remain unexplained. Here, we review current candidate neurovascular coupling mechanisms and propose that previously overlooked involvement of the vascular endothelium may provide a more complete picture of how blood flow is controlled in the brain. We also explore the possibility and consequences of conditions in which neurovascular coupling may be altered, including during postnatal development, pathological states, and aging, noting relevance to both stimulus-evoked and resting-state fMRI studies.

Early small vessel disease affects frontoparietal and cerebellar hubs in close correlation with clinical symptoms--a resting-state fMRI study

Cerebral small vessel disease, mainly characterized by white matter lesions and lacunes, has a high clinical impact as it leads to vascular dementia. Recent studies have shown that this disease impairs frontoparietal networks. Here, we apply resting-state magnetic resonance imaging and data-driven whole-brain imaging analysis methods (eigenvector centrality) to investigate changes of the functional connectome in early small vessel disease. We show reduced connectivity in frontoparietal networks, whereas connectivity increases in the cerebellum. These functional changes are closely related to white matter lesions and typical neuropsychological deficits associated with small vessel disease.

A critical role for the vascular endothelium in functional neurovascular coupling in the brain

Background

The functional modulation of blood flow in the brain is critical for brain health and is the basis of contrast in functional magnetic resonance imaging. There is evident coupling between increases in neuronal activity and increases in local blood flow; however, many aspects of this neurovascular coupling remain unexplained by current models. Based on the rapid dilation of distant pial arteries during cortical functional hyperemia, we hypothesized that endothelial signaling may play a key role in the long‐range propagation of vasodilation during functional hyperemia in the brain. Although well characterized in the peripheral vasculature, endothelial involvement in functional neurovascular coupling has not been demonstrated.

Methods and Results

We combined in vivo exposed‐cortex multispectral optical intrinsic signal imaging (MS‐OISI) with a novel in vivo implementation of the light‐dye technique to record the cortical hemodynamic response to somatosensory stimulus in rats before and after spatially selective endothelial disruption. We demonstrate that discrete interruption of endothelial signaling halts propagation of stimulus‐evoked vasodilation in pial arteries, and that wide‐field endothelial disruption in pial arteries significantly attenuates the hemodynamic response to stimulus, particularly the early, rapid increase and peak in hyperemia.

Conclusions

Involvement of endothelial pathways in functional neurovascular coupling provides new explanations for the spatial and temporal features of the hemodynamic response to stimulus and could explain previous results that were interpreted as evidence for astrocyte‐mediated control of functional hyperemia. Our results unify many aspects of blood flow regulation in the brain and body and prompt new investigation of direct links between systemic cardiovascular disease and neural deficits.

Serum S100B represents a new biomarker for mood disorders

Recently, mood disorders have been discussed to be characterized by glial pathology. The protein S100B, a growth and differentiation factor, is located in, and may actively be released by astro- and oligodendrocytes. This protein is easily assessed in human serum and provides a useful parameter for glial activation or injury. Here, we review studies investigating the glial marker S100B in serum of patients with mood disorders. Studies consistently show that S100B is elevated in mood disorders; more strongly in major depressive than bipolar disorder. Consistent with the glial hypothesis of mood disorders, serum S100B levels interact with age with higher levels in elderly depressed subjects. Successful antidepressive treatment has been associated with serum S100B reduction in major depression, whereas there is no evidence of treatment effects in mania. In contrast to the glial marker S100B, the neuronal marker protein neuron-specific enolase is unaltered in mood disorders. Recently, serum S100B has been linked to specific imaging parameters in the human white matter suggesting a role for S100B as an oligodendrocytic marker protein. In sum, serum S100B can be regarded as a promising in vivo biomarker for mood disorders deepening the understanding of the pathogenesis and plasticity-changes in these disorders. Future longitudinal studies combining serum S100B with other cell-specific serum parameters and multimodal imaging are warranted to further explore this serum protein in the development, monitoring and treatment of mood disorders.

Late-onset epilepsy and occult cerebrovascular disease

The interface between cerebrovascular disease (CVD) and epilepsy is complex and multifaceted. Late-onset epilepsy (LOE) is increasingly common and is often attributed to CVD, and is indeed associated with an increased risk of stroke. This relationship is easily recognizable where there is a history of stroke, particularly involving the cerebral cortex. However, the relationship with otherwise occult, subcortical CVD is currently less well established yet causality is often invoked. In this review, we consider the diagnosis of LOE in clinical practice--including its behaviour as a potential mimic of acute ischemic stroke and transient ischemic attack; evidence for an association between occult CVD and LOE; and potential mechanisms of epileptogenesis in occult CVD, including potential interrelationships between disordered cerebral metabolism and perfusion, disrupted neurovascular unit integrity, blood-brain barrier dysfunction, and inflammation. We also discuss recently recognized issues concerning antiepileptic drug treatment and vascular risk and consider a variety of less common CVD entities associated with seizures.

Visually evoked blood flow responses and interaction with dynamic cerebral autoregulation: correction for blood pressure variation

Visually evoked flow responses recorded using transcranial Doppler ultrasonography are often quantified using a dynamic model of neurovascular coupling. The evoked flow response is seen as the model's response to a visual step input stimulus. However, the continuously active process of dynamic cerebral autoregulation (dCA) compensating cerebral blood flow for blood pressure fluctuations may induce changes of cerebral blood flow velocity (CBFV) as well. The effect of blood pressure variability on the flow response is evaluated by separately modeling the dCA-induced effects of beat-to-beat measured blood pressure related CBFV changes. Parameters of 71 subjects are estimated using an existing, well-known second order dynamic neurovascular coupling model proposed by Rosengarten et al., and a new model extending the existing model with a CBFV contributing component as the output of a dCA model driven by blood pressure as input. Both models were evaluated for mean and systolic CBFV responses. The model-to-data fit errors of mean and systolic blood pressure for the new model were significantly lower compared to the existing model: mean: 0.8%±0.6 vs. 2.4%±2.8, p<0.001; systolic: 1.5%±1.2 vs. 2.2%±2.6, p<0.001. The confidence bounds of all estimated neurovascular coupling model parameters were significantly (p<0.005) narrowed for the new model. In conclusion, blood pressure correction of visual evoked flow responses by including cerebral autoregulation in model fitting of averaged responses results in significantly lower fit errors and by that in more reliable model parameter estimation. Blood pressure correction is more effective when mean instead of systolic CBFV responses are used. Measurement and quantification of neurovascular coupling should include beat-to-beat blood pressure measurement.

Effects of blood flow to the prefrontal cortex on high-intensity exercise combined with high-decibel music

We studied the effects of high-intensity exercise (70-75% of VO2 max) combined with high-decibel music (100 dB) on cognitive function (measured by the Stroop test) and related blood flow changes to the prefrontal cortex (measured by Oxy-hemoglobin (Hb), Deoxy-Hb, tissue oxygen index (TOI), and normalized tissue hemoglobin index (nTHI)). The subjects of the study were 28 healthy female university students in their early 20s. Subjects were categorized into control group (CG), music group (MG), exercise group (Ex), and music and exercise group (MnEx). A crossover design was implemented so that all subjects participated in all test groups. We found no significant difference in reaction time between CG and MG for the neutral and incongruent tasks of Stroop test. However, there were significant improvements in the neutral and incongruent tasks for both the Ex (p < 0.01) and MnEx (p < 0.01) groups. Oxy-Hb measurements in the prefrontal cortex of the brain supported the Stroop test data. We found no difference between Ex and MnEx in the TOI; however, there was a significant decrease (p < 0.05) in MnEx compared to Ex. In addition, Ex resulted in a significant increase (p < 0.05) in nTHI as compared to CG. These results indicate that high decibel music could negatively affect prefrontal cortex activation of the brain during exercise.

Are the neural correlates of subitizing and estimation dissociable? An fNIRS investigation

Human performance in visual enumeration tasks typically shows two distinct patterns as a function of set size. For small sets, usually up to 4 items, numerosity judgments are extremely rapid, precise and confident, a phenomenon known as subitizing. When this limit is exceeded and serial counting is precluded, exact enumeration gives way to estimation: performance becomes error-prone and more variable. Surprisingly, despite the importance of subitizing and estimation in numerical cognition, only few neuroimaging studies have examined whether the neural activity related to these two phenomena can be dissociated. In the present work, we used multi-channel near-infrared spectroscopy (fNIRS) to measure hemodynamic activity of the bilateral parieto-occipital cortex during a visual enumeration task. Participants had to judge the numerosity of dot arrays and indicate it by means of verbal response. We observed a different hemodynamic pattern in the parietal cortex, both in terms of amplitude modulation and temporal profile, for numerosities below and beyond the subitizing range. Crucially, the neural dissociation between subitizing and estimation was strongest at the level of right IPS. The present findings confirm that fNIRS can be successfully used to detect subtle temporal differences in hemodynamic activity and to produce inferences on the neural mechanisms underlying cognitive functions.

Insulin-like growth factor-1 in CNS and cerebrovascular aging

Insulin-like growth factor-1 (IGF-1) is an important anabolic hormone that decreases with age. In the past two decades, extensive research has determined that the reduction in IGF-1 is an important component of the age-related decline in cognitive function in multiple species including humans. Deficiency in circulating IGF-1 results in impairment in processing speed and deficiencies in both spatial and working memory. Replacement of IGF-1 or factors that increase IGF-1 to old animals and humans reverses many of these cognitive deficits. Despite the overwhelming evidence for IGF-1 as an important neurotrophic agent, the specific mechanisms through which IGF-1 acts have remained elusive. Recent evidence indicates that IGF-1 is both produced by and has important actions on the cerebrovasculature as well as neurons and glia. Nevertheless, the specific regulation and actions of brain- and vascular-derived IGF-1 is poorly understood. The diverse effects of IGF-1 discovered thus far reveal a complex endocrine and paracrine system essential for integrating many of the functions necessary for brain health. Identification of the mechanisms of IGF-1 actions will undoubtedly provide critical insight into regulation of brain function in general and the causes of cognitive decline with age.

Dynamic exercise improves cognitive function in association with increased prefrontal oxygenation

The Stroop test was performed before and after ergometer exercise for 15 min at 20, 40, and 60 % of maximum voluntary exercise (EXmax), in order to examine whether dynamic exercise is capable of improving cognitive function and whether the changes in regional cerebral blood flow of the prefrontal cortex are associated with the cognitive improvement. Subjects were asked to answer the displayed color of incongruent color words as quickly as possible. The total time period and the number of errors for the Stroop test were measured as an index of cognitive function. The concentrations of oxygenated-hemoglobin (Oxy-Hb) and deoxygenated-hemoglobin (Deoxy-Hb) in the cerebral prefrontal area were measured with near-infrared spectroscopy to determine the changes in regional cerebral blood flow. Ergometer exercise at 40 % of EXmax, but not 20 and 60 % of EXmax, shortened (P < 0.05) the total time period for the Stroop test by 6.6 ± 1.5 % as compared to the time control. In contrast, the number of errors was not altered by exercise at any intensity. The Oxy-Hb in bilateral prefrontal cortices increased during the Stroop test, while the Deoxy-Hb in those areas was unchanged. Ergometer exercise at 40 % of EXmax, but not at 20 and 60 % of EXmax, significantly augmented the response in the prefrontal Oxy-Hb during the Stroop test. The magnitude of the increased prefrontal Oxy-Hb response tended to correlate with the reduction in total time period for the Stroop test. Thus, it is likely that ergometer exercise at moderate intensity for 15 min may improve cognitive function through the increased neural activity in the prefrontal cortex.

NIRS in clinical neurology - a 'promising' tool?

Near-infrared spectroscopy (NIRS) has become a relevant research tool in neuroscience. In special populations such as infants and for special tasks such as walking, NIRS has asserted itself as a low resolution functional imaging technique which profits from its ease of application, portability and the option to co-register other neurophysiological and behavioral data in a 'near natural' environment. For clinical use in neurology this translates into the option to provide a bed-side oximeter for the brain, broadly available at comparatively low costs. However, while some potential for routine brain monitoring during cardiac and vascular surgery and in neonatology has been established, NIRS is largely unknown to clinical neurologists. The article discusses some of the reasons for this lack of use in clinical neurology. Research using NIRS in three major neurologic diseases (cerebrovascular disease, epilepsy and headache) is reviewed. Additionally the potential to exploit the established position of NIRS as a functional imaging tool with regard to clinical questions such as preoperative functional assessment and neurorehabilitation is discussed.

Number-space interactions in the human parietal cortex: Enlightening the SNARC effect with functional near-infrared spectroscopy

Interactions between numbers and space have become a major issue in cognitive neuroscience, because they suggest that numerical representations might be deeply rooted in cortical networks that also subserve spatial cognition. The spatial-numerical association of response codes (SNARC) is the most robust and widely replicated demonstration of the link between numbers and space: in magnitude comparison or parity judgments, participants' reaction times to small numbers are faster with left than right effectors, whereas the converse is found for large numbers. However, despite the massive body of research on number-space interactions, the nature of the SNARC effect remains controversial and no study to date has identified its hemodynamic correlates. Using functional near-infrared spectroscopy, we found a hemodynamic signature of the SNARC effect in the bilateral intraparietal sulcus, a core region for numerical magnitude representation, and left angular gyrus (ANG), a region implicated in verbal number processing. Activation of intraparietal sulcus was also modulated by numerical distance. Our findings point to number semantics as cognitive locus of number-space interactions, thereby revealing the intrinsic spatial nature of numerical magnitude representation. Moreover, the involvement of left ANG is consistent with the mediating role of verbal/cultural factors in shaping interactions between numbers and space.

Identifying the neural correlates of executive functions in early cerebral microangiopathy: a combined VBM and DTI study

Cerebral microangiopathy (CMA) has been associated with executive dysfunction and fronto-parietal neural network disruption. Advances in magnetic resonance imaging allow more detailed analyses of gray (e.g., voxel-based morphometry-VBM) and white matter (e.g., diffusion tensor imaging-DTI) than traditional visual rating scales. The current study investigated patients with early CMA and healthy control subjects with all three approaches. Neuropsychological assessment focused on executive functions, the cognitive domain most discussed in CMA. The DTI and age-related white matter changes rating scales revealed convergent results showing widespread white matter changes in early CMA. Correlations were found in frontal and parietal areas exclusively with speeded, but not with speed-corrected executive measures. The VBM analyses showed reduced gray matter in frontal areas. All three approaches confirmed the hypothesized fronto-parietal network disruption in early CMA. Innovative methods (DTI) converged with results from conventional methods (visual rating) while allowing greater spatial and tissue accuracy. They are thus valid additions to the analysis of neural correlates of cognitive dysfunction. We found a clear distinction between speeded and nonspeeded executive measures in relationship to imaging parameters. Cognitive slowing is related to disease severity in early CMA and therefore important for early diagnostics.

Executive deficits are related to the inferior frontal junction in early dementia

Executive functions describe a wide variety of higher order cognitive processes that allow the flexible modification of thought and behaviour in response to changing cognitive or environmental contexts. Their impairment is common in neurodegenerative disorders. Executive deficits negatively affect everyday activities and hamper the ability to cope with other deficits, such as memory impairment in Alzheimer's disease or behavioural disorders in frontotemporal lobar degeneration. Our study aimed to characterize the neural correlates of executive functions by relating respective deficits to regional hypometabolism in early dementia. Executive functions were assessed with two classical tests, the Stroop and semantic fluency test and various subtests of the behavioural assessment of the dysexecutive syndrome test battery capturing essential aspects of executive abilities relevant to daily living. Impairments in executive functions were correlated with reductions in brain glucose utilization as measured by [(18)F]fluorodeoxyglucose positron emission tomography and analysed voxelwise using statistical parametric mapping in 54 subjects with early dementia, mainly Alzheimer's disease and frontotemporal lobar degeneration, and its prodromal stages: subjective and mild cognitive impairment. Although the analysis revealed task-specific frontoparietal networks, it consistently showed that hypometabolism in one region in the left lateral prefrontal cortex-the inferior frontal junction area-was related to performance in the various neuropsychological tests. This brain region has recently been related to the three component processes of cognitive control-working memory, task switching and inhibitory control. Group comparisons additionally showed hypometabolism in this area in Alzheimer's disease and frontotemporal lobar degeneration. Our study underlines the importance of the inferior frontal junction area for cognitive control in general and for executive deficits in early dementia.

Forebrain-dominant deficit in cerebrovascular reactivity in Alzheimer's disease

Epidemiologic evidence and postmortem studies of cerebral amyloid angiopathy suggest that vascular dysfunction may play an important role in the pathogenesis of Alzheimer's disease (AD). However, alterations in vascular function under in vivo conditions are poorly understood. In this study, we assessed cerebrovascular-reactivity (CVR) in AD patients and age-matched controls using CO(2)-inhalation while simultaneously acquiring Blood-Oxygenation-Level-Dependent (BOLD) MR images. Compared with controls, AD patients had widespread reduction in CVR in the rostral brain including prefrontal, anterior cingulate, and insular cortex (p < 0.01). The deficits could not be explained by cardiovascular risk factors. The spatial distribution of the CVR deficits differed drastically from the regions of cerebral blood flow (CBF) deficits, which were found in temporal and parietal cortices. Individuals with greater CVR deficit tended to have a greater volume of leukoaraiosis as seen on FLAIR MRI (p = 0.004). Our data suggest that early AD subjects have evidence of significant forebrain vascular contractility deficits. The localization, while differing from CBF findings, appears to be spatially similar to PIB amyloid imaging findings.

Reduced prefrontal oxygenation during object and spatial visual working memory in unpolar and bipolar depression

Altered prefrontal brain activity (e.g. hypofrontality) during cognitive tasks such as working memory is a core neuroimaging marker in unipolar (UNI) and bipolar (BI) depression. The present study investigated for the first time UNI (n=16) and BI patients (n=14) in a working memory task including different processes (storage and matching) and components (object and spatial visual) with functional near-infrared spectroscopy (fNIRS) over the prefrontal cortex. In healthy controls (n=15) comparable to both patient groups, changes of oxygenated and deoxygenated haemoglobin indicated increased ventro-lateral, dorso-lateral prefrontal and superior frontal cortex activity for object and spatial visual working memory storage as compared to the control condition. In contrast, both patient groups showed diminished brain activity in all working memory conditions. Results revealed unspecific deficits that did not allow the differentiation between unipolar and bipolar depression in dependence of working memory processes or components. However, fNIRS can be considered as a valid, easy manageable, low cost and rapid tool for measuring (diminished) prefrontal cortex functions.

Non-invasive optical imaging of stroke

The acute onset of a neurological deficit is the key clinical feature of stroke. In most cases, however, pathophysiological changes in the cerebral vasculature precede the event, often by many years. Persisting neurological deficits may also require long-term rehabilitation. Hence, stroke may be considered a chronic disease, and diagnostic and therapeutic efforts must include identification of specific risk factors, and the monitoring of and interventions in the acute and subacute stages, and should aim at a pathophysiologically based approach to optimize the rehabilitative effort. Non-invasive optical techniques have been experimentally used in all three stages of the disease and may complement the established diagnostic and monitoring tools. Here, we provide an overview of studies using the methodology in the context of stroke, and we sketch perspectives of how they may be integrated into the assessment of the highly dynamic pathophysiological processes during the acute and subacute stages of the disease and also during rehabilitation and (secondary) prevention of stroke.

Occult cerebrovascular disease and late-onset epilepsy: could loss of neurovascular unit integrity be a viable model?

Late-onset epilepsy (LOE) first occurs after 60 years of age and may be due to occult cerebrovascular disease (CVD) which confers an increased risk of stroke. However, patients with late-onset epilepsy are not currently consistently investigated or treated for cerebrovascular risk factors. We discuss how abnormalities of neurovascular unit function, namely, changes in regional cerebral blood flow and blood brain barrier disruption, may be caused by occult cerebrovascular disease but present clinically as late-onset epilepsy. We describe novel magnetic resonance imaging methods to detect abnormal neurovascular unit function in subjects with LOE and controls. We hypothesise that occult CVD may cause LOE as a result of neurovascular unit dysfunction.

Pleasant mood intensifies brain processing of cognitive control: ERP correlates

The present study investigated the impact of auditory-induced mood on brain processing of cognitive control using a Stroop color-word interference task. A total of 135 positive, negative, and neutral sounds (45 of each) were presented in separate blocks for a mood induction procedure, which was then followed by a Stroop color-word task in each trial. Event-related potentials (ERPs) were recorded for color-word congruent, incongruent and neutral (color-word irrelevant) words and subjects named the printed colors of the words by pressing the appropriate key (irrespective of word meaning). Response latency was delayed during incongruent vs. neutral trials, and this cost did not interact significantly with mood states. ERP data showed prolonged peak latencies in the P200 component and more negative deflections in the Late Positive Component (LPC, 450-550 ms) during incongruent vs. neutral conditions, regardless of mood states. Moreover, the negative deflections (N450) in the 450-550 ms interval of the incongruent- neutral difference waves, which index cognitive control effect in brain potentials, was more pronounced in the pleasant, but not in the unpleasant, mood state when compared with the neutral mood state. These data suggest that, pleasant mood intensifies brain processing of cognitive control, in a situation requiring effective inhibition of task-irrelevant distracting information. In addition, N450 component serves as an affective marker, embodying not only cognitive control effect in the brain but also its interaction with mood states.

A hemodynamic correlate of lateralized visual short-term memories

Neuroimaging studies attempting to isolate the neural substrate of visual short-term memory in humans have concentrated on the behavior of neurons populating the posterior part of the parietal cortex as a possible source of visual short-term memory capacity limits. Using a standard change-detection task, fMRI studies have shown that maintenance of bilaterally encoded objects elicited bilateral increases of hemodynamic activation in the intra-parietal and intra-occipital sulci (IPS-IOS) proportional to the number of objects retained in visual short-term memory. We used a spatially cued variant of the change-detection task to record hemodynamic responses to unilaterally encoded objects using functional near-infrared spectroscopy (fNIRS). Electrophysiological studies that employed this task have shown that maintenance of unilaterally encoded objects elicited posterior unilateral (contralateral) increase in event-related negativity proportional to the number of objects retained in visual short-term memory. We therefore examined whether contralateral increases in oxy-hemoglobin concentration correlated with the number of retained objects. Contrary to the idea that bilateral increases in BOLD responses and unilateral increases in event-related negativity may be different reflections of the same underlying neural/functional processing, memory-related increases in oxy-hemoglobin concentration were found bilaterally even when objects had to be encoded unilaterally. The present findings suggest that EEG and fMRI/fNIRS techniques reveal distinct neural signatures of the mechanisms supporting visual short-term memory.

Bayesian filtering of human brain hemodynamic activity elicited by visual short-term maintenance recorded through functional near-infrared spectroscopy (fNIRS)

Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique that measures changes in oxy-hemoglobin (ΔHbO) and deoxy-hemoglobin (ΔHbR) concentration associated with brain activity. The signal acquired with fNIRS is naturally affected by disturbances engendering from ongoing physiological activity (e.g., cardiac, respiratory, Mayer wave) and random measurement noise. Despite its several drawbacks, the so-called conventional averaging (CA) is still widely used to estimate the hemodynamic response function (HRF) from noisy signal. One such drawback is related to the number of trials necessary to derive stable HRF functions adopting the CA approach, which must be substantial (N >> 50). In this work, a pre-processing procedure to remove artifacts followed by the application of a non-parametric Bayesian approach is proposed that capitalizes on a priori available knowledge about HRF and noise. Results with the proposed Bayesian approach were compared with CA and with a straightforward band-pass filtering approach. On simulated data, a five times lower estimation error on HRF was obtained with respect to that obtained by CA, and 2.5 times lower than that obtained by band pass filtering. On real data, the improvement achieved by the present method was attested by an increase in the contrast to noise ratio (CNR) and by a reduced variability in single trial estimation. An application of the present Bayesian approach is illustrated that was optimized to monitor changes in hemodynamic activity reflecting variations in visual short-term memory load in humans, which are notoriously hard to detect using functional magnetic resonance imaging (fMRI). In particular, statistical analyses of HRFs recorded during a memory task established with high reliability the crucial role of the intraparietal sulcus and the intra-occipital sulcus in posterior areas of the human brain in visual short-term memory maintenance.

Quantitative analysis of hemodynamic and metabolic changes in subcortical vascular dementia using simultaneous near-infrared spectroscopy and fMRI measurements

Subcortical vascular dementia (SVD) is a form of vascular dementia from small vessel disease with white matter lesions and lacunes. We hypothesized that hemodynamic and metabolic changes in the cortex during a simple motor task may reflect the impaired neurovascular coupling in SVD. We used fMRI and near-infrared spectroscopy (NIRS) simultaneously, which together provided multiple hemodynamic responses as well as a robust estimation of the cerebral metabolic rate of oxygen (CMRO(2)). During the task periods, the oxy-hemoglobin, total-hemoglobin, blood oxygenation level-dependent (BOLD) response, cerebral blood flow (CBF), and CMRO(2) decreased statistically significantly in the primary motor and somatosensory cortices of SVD patients, whereas the oxygen extraction fraction increased when compared with controls. Notably, the flow-metabolism coupling ratio, n representing the ratio of oxygen supply to its utilization, showed a robust reduction in the SVD patient group (n(Control)=1.99 ± 0.23; n(SVD)=1.08 ± 0.24), which implies a loss of metabolic reserve. These results support the pathological small vessel compromise, including an increased vessel stiffness, impaired vascular reactivity, and impaired neurovascular coupling in SVD. In conclusion, simultaneous measurement by NIRS and fMRI can reveal various hemodynamic and metabolic changes and may be used for as an early detection or monitoring of SVD.

Pathophysiological interference with neurovascular coupling - when imaging based on hemoglobin might go blind

Assessing neuronal activity by non-invasive functional brain imaging techniques which are based on the hemodynamic response depends totally on the physiological cascade of metabolism and blood flow. At present, functional brain imaging with near infrared spectroscopy (NIRS) or BOLD-fMRI is widely used in cognitive neuroscience in healthy subjects where neurovascular coupling and cerebrovascular reactivity can be assumed to be intact. Local activation studies as well as studies investigating functional connectivity between brain regions of the resting brain provide a rapidly increasing body of knowledge on brain function in humans and animals. Furthermore, functional NIRS and MRI techniques are increasingly being used in patients with severe brain diseases and this use might gain more and more importance for establishing their use in the clinical routine. However, more and more experimental evidence shows that changes in baseline physiological parameters, pharmacological interventions, or disease-related vascular changes may significantly alter the normal response of blood flow and blood oxygenation and thus may lead to misinterpretation of neuronal activity. In this article we present examples of recent experimental findings on pathophysiological changes of neurovascular coupling parameters in animals and discuss their potential implications for functional imaging based on hemodynamic signals such as fNIRS or BOLD-fMRI. To enable correct interpretation of neuronal activity by vascular signals, future research needs to deepen our understanding of the basic mechanisms of neurovascular coupling and the specific characteristics of disturbed neurovascular coupling in the diseased brain.

The overlap between neurodegenerative and vascular factors in the pathogenesis of dementia

There is increasing evidence that cerebrovascular dysfunction plays a role not only in vascular causes of cognitive impairment but also in Alzheimer's disease (AD). Vascular risk factors and AD impair the structure and function of cerebral blood vessels and associated cells (neurovascular unit), effects mediated by vascular oxidative stress and inflammation. Injury to the neurovascular unit alters cerebral blood flow regulation, depletes vascular reserves, disrupts the blood-brain barrier, and reduces the brain's repair potential, effects that amplify the brain dysfunction and damage exerted by incident ischemia and coexisting neurodegeneration. Clinical-pathological studies support the notion that vascular lesions aggravate the deleterious effects of AD pathology by reducing the threshold for cognitive impairment and accelerating the pace of the dementia. In the absence of mechanism-based approaches to counteract cognitive dysfunction, targeting vascular risk factors and improving cerebrovascular health offers the opportunity to mitigate the impact of one of the most disabling human afflictions.

Executive and behavioral deficits share common neural substrates in frontotemporal lobar degeneration - a pilot FDG-PET study

Behavioral and executive dysfunctions are typical symptoms of frontotemporal lobar degeneration, associated with its subtypes frontotemporal and semantic dementia. Although both functions depend on the frontal lobes, no study has yet compared their neural correlates in frontotemporal lobar degeneration. Accordingly, we correlated clinical scores of behavioral and executive deficits with glucose utilization as measured by [(18)F]fluorodeoxyglucose positron emission tomography in 17 patients with frontotemporal lobar degeneration and 9 age- and sex-matched control subjects. Impairment in executive functions was measured by the Behavioral Assessment of the Dysexecutive Syndrome, a modified Stroop paradigm and/or the Tower of Toronto Test. Behavioral deficits were examined with the Neuropsychiatric Inventory. Executive dysfunction was correlated with diminished glucose utilization in frontomedial and frontolateral cortices. Brain regions included the anterior cingulate and midcingulate gyri, anterior medial frontal cortex, and left frontolateral cortex. Behavioral deficits were associated with mainly frontomedial networks, particularly the anterior medial frontal cortex, gyrus rectus, and area subcallosa. Our pilot study reveals partially overlapping neural correlates of executive and behavioral dysfunction in frontotemporal lobar degeneration. The results suggest that some behavioral deficits, namely disinhibition and appetite and eating abnormalities, are particularly related to executive dysfunction. This hypothesis might be further explored in studies involving larger patient groups.

Traumatic brain injury affects the frontomedian cortex--an event-related fMRI study on evaluative judgments

Traumatic brain injuries represent the leading cause of death and disability in young adults in industrialized countries. Recently, it has been suggested that dysfunctions of the frontomedian cortex, which enables social cognition, are responsible for clinical deficits in the long-term. To validate this hypothesis, we examined brain activation in seven young adults suffering from diffuse axonal injury during a cognitive task that specifically depends on frontomedian structures, namely evaluative judgments, contrasted with semantic memory retrieval. Brain activation in patients was compared with healthy age and gender matched control subjects using event-related functional magnetic resonance imaging. Evaluative judgments were related to a neural network discussed in the context of self-referential processing and theory of mind. More precisely, the neural network consisted of frontomedian regions, the temporal pole, and the posterior superior temporal gyrus and sulcus/angular gyrus. Patients showed higher activations in this network and the inferior frontal gyrus, whereas healthy control subjects activated more dopaminergic structures, namely the ventral tegmental area, during evaluative judgments. One possible interpretation of the data is that deficits in the ventral tegmental area, and consequently the mesocorticolimbic projection system, have to be compensated for by higher brain activations in the frontomedian and anterior cingulate cortex in patients with diffuse axonal injury. In conclusion, our study supports the hypothesis that traumatic brain injury is characterized by frontomedian dysfunctions, which may be responsible for clinical deficits in the long-term and which might be modified by rehabilitative strategies in the future.

Right prefrontal brain activation due to Stroop interference is altered in attention-deficit hyperactivity disorder - A functional near-infrared spectroscopy study

Attention-deficit hyperactivity disorder is a common finding in school children. Because it was suggested to be related to frontal lobe dysfunction, we hypothesized that brain activation would be altered during an event-related color-word matching Stroop task in comparison to a healthy control group. Twelve medication-free boys suffering from attention-deficit hyperactivity disorder were compared with 12 education- and age-matched healthy boys. As an imaging method we applied functional near-infrared spectroscopy, because it is particularly insensitive to movement artifacts and, accordingly, well suited for studies in children. Generally, the Stroop task led to activations in the lateral prefrontal cortex of both patients and control subjects. Moreover, data suggest that Stroop interference elicited (presumably compensatory) higher oxygen consumption and brain activation in the right dorsolateral prefrontal cortex of boys with attention-deficit hyperactivity disorder. This effect was not confounded by behavioral differences, because boys with attention-deficit hyperactivity disorder showed only a non-specifically increased reaction time in comparison with control subjects. In sum, our results indicate that attention-deficit hyperactivity disorder is characterized by functional impairments of the dorsolateral prefrontal cortex. Our study further establishes functional near-infrared spectroscopy as an imaging tool for studies in neurodevelopment and child and adolescent psychiatry.

Intact neurovascular coupling during executive function in migraine without aura: Interictal near-infrared spectroscopy study

An altered neurovascular coupling has been proposed in migraine. We aimed to investigate neurovascular coupling during a mental task interictally in patients with migraine without aura (MO) by near-infrared spectroscopy (NIRS). Twelve migraineurs and 12 healthy controls were included. Using NIRS, we recorded the magnitude and latency of cortical changes in oxyhaemoglobin (HbO2) and deoxyhaemoglobin (Hb) during the colour-word matching Stroop test via 16 channels covering the forehead. We found no differences in the magnitude of responses between migraineurs and healthy subjects in the incongruent Stroop task subtracted by the neutral Stroop task on either side of the frontal cortex for HbO2 (left, P = 0.984; right, P = 0.406) or Hb (left, P = 0.689; right, P = 0.406) values. No differences in error rate ( P = 0.611) or reaction time ( P = 0.936) were found between healthy subjects and MO patients for incongruent tasks. The present study suggests that vascular reactivity and oxygen supply during a mental task in patients with MO are intact interictally.