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Trends Cogn Sci Journal of Affective Disorders Drug Alcohol Depend Brain Res Rev Google Scholar , Crossref , Medline. A meta-analysis and critical review. Neurosci Biobehav Rev World Journal of Biological Psychiatry Hum Brain Mapp The procedure is similar to MRI but uses the change in magnetization between oxygen-rich and oxygen-poor blood as its basic measure. This measure is frequently corrupted by noise from various sources and hence statistical procedures are used to extract the underlying signal.
Research Summary
The resulting brain activation can be presented graphically by color-coding the strength of activation across the brain or the specific region studied. The technique can localize activity to within millimeters but, using standard techniques, no better than within a window of a few seconds.
FMRI is used both in research, and to a lesser extent, in clinical settings. The physiological blood-flow response largely decides the temporal sensitivity, how well neurons that are active can be measured in BOLD fMRI.
Resting state fMRI
The basic time resolution parameter is the sampling rate , or TR, which dictates how often a particular brain slice is excited and allowed to lose its magnetization. TRs could vary from the very short ms to the very long 3 seconds. For fMRI specifically, the haemodynamic response is assumed to last over 10 seconds, rising multiplicatively that is, as a proportion of current value , peaking at 4 to 6 seconds, and then falling multiplicatively. Changes in the blood-flow system, the vascular system, integrate responses to neuronal activity over time.
Because this response is a smooth continuous function, sampling with faster TRs helps only to map faster fluctuations like respiratory and heart rate signals.
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While fMRI strives to measure the neuronal activity in the brain, the BOLD signal can be influenced by many other physiological factors other than neuronal activity. For example, respiratory fluctuations and cardiovascular cycles affect the BOLD signal being measured in the brain and therefore are usually tried to be removed during processing of the raw fMRI data.
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Due to these sources of noise, there have been many experts who have approached the idea of resting state fMRI very skeptically during the early uses of fMRI. It has only been very recently that researchers have become confident that the signal being measured is not an artifact caused by other physiological function. Resting state functional connectivity between spatially distinct brain regions reflects the repeated history of co-activation patterns within these regions, thereby serving as a measure of plasticity.
Functional connectivity is the connectivity between brain regions that share functional properties.
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More specifically, it can be defined as the temporal correlation between spatially remote neurophysiological events, expressed as deviation from statistical independence across these events in distributed neuronal groups and areas. While functional connectivity can refer to correlations across subjects, runs, blocks, trials, or individual time points, resting state functional connectivity focuses on connectivity assessed across individual BOLD time points during resting conditions.
The connectivity of brain regions that are physically or anatomically attached to one another is referred to as structural connectivity. Regions of the brain do not have to be structurally connected to have functional connectivity, and a structural connection does not necessarily signify a functional link. Many programs exist for the processing and analyzing of resting state fMRI data.
There are many methods of both acquiring and processing rsfMRI data. The most popular methods of analysis focus either on independent components or on regions of correlation. Other methods for characterizing resting-state networks include partial correlation, coherence and partial coherence, phase relationships, dynamic time warping distance, clustering, and graph theory.
Resting-state functional magnetic resonance imaging rfMRI can image low-frequency fluctuations in the spontaneous brain activities, representing a popular tool for macro-scale functional connectomics to characterize inter-individual differences in normal brain function, mind-brain associations, and the various disorders. This suggests reliability and reproducibility for commonly used rfMRI-derived measures of the human brain functional connectomics.
These metrics hold great potentials of accelerating biomarker identification for various brain diseases, which call the need of addressing reliability and reproducibility at first place. Many imaging experts feel that in order to obtain the best combination of spatial and temporal information from brain activity, both fMRI as well as electroencephalography EEG should be used simultaneously. The clinical value of these findings is the subject of ongoing investigations, but recent researches suggest an acceptable reliability for EEG-fMRI studies and better sensitivity in higher field scanner.
Outside the field of epilepsy, EEG-fMRI has been used to study event-related triggered by external stimuli brain responses and provided important new insights into baseline brain activity in during resting wakefulness and sleep.
Resting state fMRI - Wikipedia
Transcranial magnetic stimulation TMS uses small and relatively precise magnetic fields to stimulate regions of the cortex without dangerous invasive procedures. When these magnetic fields stimulate an area of the cortex, focal blood flow increases at the site of stimulation as well as at distant sites anatomically connected to the stimulated location.
Positron emission tomography PET can then be used to image the brain and changes in blood flow and results show very similar regions of connectivity confirming networks found in fMRI studies and TMS can also be used to support and provide more detailed information on the connected regions. Potential pitfalls when using rsfMRI to determine functional network integrity are contamination of the BOLD signal by sources of physiological noise such as heart rate, respiration , [42] [43] and head motion.
Also, it has been shown that the use of global signal regression can produce artificial correlations between a small number of signals e. Research using resting state fMRI has the potential to be applied in clinical context, including use in the assessment of many different diseases and mental disorders. Other types of current and future clinical applications for resting state fMRI include identifying group differences in brain disease, obtaining diagnostic and prognostic information, longitudinal studies and treatment effects, clustering in heterogeneous disease states, and pre-operative mapping and targeting intervention.
From Wikipedia, the free encyclopedia. This article is about resting state networks and functional imaging.