Cerebrovascular Circulation
Research Papers
One-year aerobic exercise increases cerebral blood flow in cognitively normal older adults
The impact of aerobic exercise training (AET) on cerebral blood flow (CBF) regulation remains inconclusive. This study investigated the effects of one-year progressive, moderate-to-vigorous AET on CBF, central arterial stiffness, and cognitive performance in cognitively normal older adults. Seventy-three older adults were randomly assigned to AET or stretching-and-toning (SAT, active control) intervention. CBF was measured with 2D duplex ultrasonography. Central arterial stiffness, measured by carotid β-stiffness index, was assessed with the ultrasonography and applanation tonometry. Cerebrovascular resistance (CVR) was calculated as mean arterial pressure divided by CBF. A cognitive battery was administered with a focus on memory and executive function. Cardiorespiratory fitness was measured by peak oxygen consumption (V˙O2peak). One-year AET increased V˙O2peak and CBF and decreased CVR and carotid β-stiffness index. In the AET group, improved V˙O2peak was correlated with increased CBF (r = 0.621, p = 0.001) and decreased CVR (r = -0.412, p = 0.037) and carotid β-stiffness index (r = -0.478, p = 0.011). Further, increased Woodcock-Johnson recall score was associated with decreased CVR (r = -0.483, p = 0.012) and carotid β-stiffness index (r = -0.498, p = 0.008) in AET group (not in SAT group). In conclusion, one-year progressive, moderate-to-vigorous aerobic exercise training increased CBF and decreased carotid arterial stiffness and CVR which were associated with improved memory function in cognitively normal older adults.
View Full Paper →BOLD hemodynamic response function changes significantly with healthy aging
Functional magnetic resonance imaging (fMRI) has been used to infer age-differences in neural activity from the hemodynamic response function (HRF) that characterizes the blood-oxygen-level-dependent (BOLD) signal over time. BOLD literature in healthy aging lacks consensus in age-related HRF changes, the nature of those changes, and their implications for measurement of age differences in brain function. Between-study discrepancies could be due to small sample sizes, analysis techniques, and/or physiologic mechanisms. We hypothesize that, with large sample sizes and minimal analysis assumptions, age-related changes in HRF parameters could reflect alterations in one or more components of the neural-vascular coupling system. To assess HRF changes in healthy aging, we analyzed the large population-derived dataset from the Cambridge Center for Aging and Neuroscience (CamCAN) study (Shafto et al., 2014). During scanning, 74 younger (18-30 years of age) and 173 older participants (54-74 years of age) viewed two checkerboards to the left and right of a central fixation point, simultaneously heard a binaural tone, and responded via right index finger button-press. To assess differences in the shape of the HRF between younger and older groups, HRFs were estimated using FMRIB's Linear Optimal Basis Sets (FLOBS) to minimize a priori shape assumptions. Group mean HRFs were different between younger and older groups in auditory, visual, and motor cortices. Specifically, we observed increased time-to-peak and decreased peak amplitude in older compared to younger adults in auditory, visual, and motor cortices. Changes in the shape and timing of the HRF in healthy aging, in the absence of performance differences, support our hypothesis of age-related changes in the neural-vascular coupling system beyond neural activity alone. More precise interpretations of HRF age-differences can be formulated once these physiologic factors are disentangled and measured separately.
View Full Paper →Self-directed down-regulation of auditory cortex activity mediated by real-time fMRI neurofeedback augments attentional processes, resting cerebral perfusion, and auditory activation
In this work, we investigated the use of real-time functional magnetic resonance imaging (fMRI) with neurofeedback training (NFT) to teach volitional down-regulation of the auditory cortex (AC) using directed attention strategies as there is a growing interest in the application of fMRI-NFT to treat neurologic disorders. Healthy participants were separated into two groups: the experimental group received real feedback regarding activity in the AC; the control group was supplied sham feedback yoked from a random participant in the experimental group and matched for fMRI-NFT experience. Each participant underwent five fMRI-NFT sessions. Each session contained 2 neurofeedback runs where participants completed alternating blocks of "rest" and "lower" conditions while viewing a continuously-updated bar representing AC activation and listening to continuous noise. Average AC deactivation was extracted from each closed-loop neuromodulation run and used to quantify the control over AC (AC control), which was found to significantly increase across training in the experimental group. Additionally, behavioral testing was completed outside of the MRI on sessions 1 and 5 consisting of a subjective questionnaire to assess attentional control and two quantitative tests of attention. No significant changes in behavior were observed; however, there was a significant correlation between changes in AC control and attentional control. Also, in a neural assessment before and after fMRI-NFT, AC activity in response to continuous noise stimulation was found to significantly decrease across training while changes in AC resting perfusion were found to be significantly greater in the experimental group. These results may be useful in formulating effective therapies outside of the MRI, specifically for chronic tinnitus which is often characterized by hyperactivity of the primary auditory cortex and altered attentional processes. Furthermore, the modulation of attention may be useful in developing therapies for other disorders such as chronic pain.
View Full Paper →Active pain coping is associated with the response in real-time fMRI neurofeedback during pain
Real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback is used as a tool to gain voluntary control of activity in various brain regions. Little emphasis has been put on the influence of cognitive and personality traits on neurofeedback efficacy and baseline activity. Here, we assessed the effect of individual pain coping on rt-fMRI neurofeedback during heat-induced pain. Twenty-eight healthy subjects completed the Coping Strategies Questionnaire (CSQ) prior to scanning. The first part of the fMRI experiment identified target regions using painful heat stimulation. Then, subjects were asked to down-regulate the pain target brain region during four neurofeedback runs with painful heat stimulation. Functional MRI analysis included correlation analysis between fMRI activation and pain ratings as well as CSQ ratings. At the behavioral level, the active pain coping (first principal component of CSQ) was correlated with pain ratings during neurofeedback. Concerning neuroimaging, pain sensitive regions were negatively correlated with pain coping. During neurofeedback, the pain coping was positively correlated with activation in the anterior cingulate cortex, prefrontal cortex, hippocampus and visual cortex. Thermode temperature was negatively correlated with anterior insula and dorsolateral prefrontal cortex activation. In conclusion, self-reported pain coping mechanisms and pain sensitivity are a source of variance during rt-fMRI neurofeedback possibly explaining variations in regulation success. In particular, active coping seems to be associated with successful pain regulation.
View Full Paper →Area-specific information processing in prefrontal cortex during a probabilistic inference task: a multivariate fMRI BOLD time series analysis
INTRODUCTION: Discriminating spatiotemporal stages of information processing involved in complex cognitive processes remains a challenge for neuroscience. This is especially so in prefrontal cortex whose subregions, such as the dorsolateral prefrontal (DLPFC), anterior cingulate (ACC) and orbitofrontal (OFC) cortices are known to have differentiable roles in cognition. Yet it is much less clear how these subregions contribute to different cognitive processes required by a given task. To investigate this, we use functional MRI data recorded from a group of healthy adults during a "Jumping to Conclusions" probabilistic reasoning task. METHODS: We used a novel approach combining multivariate test statistics with bootstrap-based procedures to discriminate between different task stages reflected in the fMRI blood oxygenation level dependent signal pattern and to unravel differences in task-related information encoded by these regions. Furthermore, we implemented a new feature extraction algorithm that selects voxels from any set of brain regions that are jointly maximally predictive about specific task stages. RESULTS: Using both the multivariate statistics approach and the algorithm that searches for maximally informative voxels we show that during the Jumping to Conclusions task, the DLPFC and ACC contribute more to the decision making phase comprising the accumulation of evidence and probabilistic reasoning, while the OFC is more involved in choice evaluation and uncertainty feedback. Moreover, we show that in presumably non-task-related regions (temporal cortices) all information there was about task processing could be extracted from just one voxel (indicating the unspecific nature of that information), while for prefrontal areas a wider multivariate pattern of activity was maximally informative. CONCLUSIONS/SIGNIFICANCE: We present a new approach to reveal the different roles of brain regions during the processing of one task from multivariate activity patterns measured by fMRI. This method can be a valuable tool to assess how area-specific processing is altered in psychiatric disorders such as schizophrenia, and in healthy subjects carrying different genetic polymorphisms.
View Full Paper →Spontaneous low-frequency oscillations decline in the aging brain
It is well known that aging leads to a degeneration of the vascular system. Hence, one may hypothesize that spontaneous oscillations decrease in the cerebral microvasculature with aging. Accordingly, the authors investigated the age dependency of spontaneous oscillations in the visual cortex during rest and functional activation. Functional near-infrared spectroscopy was used because it is particularly sensitive to the microvasculature. Visual stimulation led to an increase of oxyhemoglobin, total hemoglobin, and a decrease of deoxyhemoglobin, without any influence of age. Peaks of normalized power spectral density were detected for spontaneous low-frequency (0.07 to 0.11 Hz) and very-low-frequency (0.01 to 0.05 Hz) oscillations, with a higher amplitude for oxyhemoglobin than for deoxyhemoglobin. Spontaneous low-frequency oscillations of oxyhemoglobin and deoxyhemoglobin declined strongly with aging during both rest and visual stimulation. Reduction of spontaneous low-frequency oscillations might indicate a declining spontaneous activity in microvascular smooth muscle cells, in conjunction with an increased vessel stiffness with aging.
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