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In JoVE (1)
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Articles by Waqas Majeed in JoVE
JoVE Neuroscience
एक साथ और कृंतक मस्तिष्क में fMRI इलैक्ट्रोफिजियोलॉजी
1Biomedical Engineering, Emory University, 2Biomedical Engineering, Georgia Institute of Technology, 3Biology, Emory University
हम एक साथ कार्यात्मक चुंबकीय अनुनाद इमेजिंग और कृंतक मस्तिष्क में electrophysiological रिकॉर्डिंग के लिए एक विधि विकसित की है, तंत्रिका गतिविधि और रक्त oxygenation स्तर निर्भर (बोल्ड) एमआरआई संकेत के बीच संबंधों की जांच के लिए एक मंच प्रदान.
Other articles by Waqas Majeed on PubMed
Spatiotemporal Dynamics of Low Frequency Fluctuations in BOLD FMRI of the Rat
To examine spatiotemporal dynamics of low frequency fluctuations in rat cortex.
Comparison of Alpha-chloralose, Medetomidine and Isoflurane Anesthesia for Functional Connectivity Mapping in the Rat
Functional connectivity measures based upon low-frequency blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) signal fluctuations have become a widely used tool for investigating spontaneous brain activity in humans. Still unknown, however, is the precise relationship between neural activity, the hemodynamic response and fluctuations in the MRI signal. Recent work from several groups had shown that correlated low-frequency fluctuations in the BOLD signal can be detected in the anesthetized rat - a first step toward elucidating this relationship. Building on this preliminary work, through this study, we demonstrate that functional connectivity observed in the rat depends strongly on the type of anesthesia used. Power spectra of spontaneous fluctuations and the cross-correlation-based connectivity maps from rats anesthetized with alpha-chloralose, medetomidine or isoflurane are presented using a high-temporal-resolution imaging sequence that ensures minimal contamination from physiological noise. The results show less localized correlation in rats anesthetized with isoflurane as compared with rats anesthetized with alpha-chloralose or medetomidine. These experiments highlight the utility of using different types of anesthesia to explore the fundamental physiological relationships of the BOLD signal and suggest that the mechanisms contributing to functional connectivity involve a complicated relationship between changes in neural activity, neurovascular coupling and vascular reactivity.
Functional Connectivity in Blood Oxygenation Level-dependent and Cerebral Blood Volume-weighted Resting State Functional Magnetic Resonance Imaging in the Rat Brain
To directly compare functional connectivity and spatiotemporal dynamics acquired with blood oxygenation level-dependent (BOLD) and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) in anesthetized rats.
Spatiotemporal Dynamics of Low Frequency BOLD Fluctuations in Rats and Humans
Most studies involving spontaneous fluctuations in the BOLD signal extract connectivity patterns that show relationships between brain areas that are maintained over the length of the scanning session. In this study, however, we examine the spatiotemporal dynamics of the BOLD fluctuations to identify common patterns of propagation within a scan. A novel pattern finding algorithm was developed for detecting repeated spatiotemporal patterns in BOLD fMRI data. The algorithm was applied to high temporal resolution T2*-weighted multislice images obtained from rats and humans in the absence of any task or stimulation. In rats, the primary pattern consisted of waves of high signal intensity, propagating in a lateral to medial direction across the cortex, replicating our previous findings (Majeed et al., 2009a). These waves were observed primarily in sensorimotor cortex, but also extended to visual and parietal association areas. A secondary pattern, confined to subcortical regions consisted of an initial increase and subsequent decrease in signal intensity in the caudate-putamen. In humans, the most common spatiotemporal pattern consisted of an alteration between activation of areas comprising the "default-mode" (e.g., posterior cingulate and anterior medial prefrontal cortices) and the "task-positive" (e.g., superior parietal and premotor cortices) networks. Signal propagation from focal starting points was also observed. The pattern finding algorithm was shown to be reasonably insensitive to the variation in user-defined parameters, and the results were consistent within and between subjects. This novel approach for probing the spontaneous network activity of the brain has implications for the interpretation of conventional functional connectivity studies, and may increase the amount of information that can be obtained from neuroimaging data.
