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(Created page with "{{BioPsy}} {{expert}} {{Main|Functional magnetic resonance imaging}} [[Image:FMRI.jpg|thumb|right|A fMRI scan showing regions of activation in orange, including the [[primary ...")
 
 
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{{Main|Functional magnetic resonance imaging}}
 
{{Main|Functional magnetic resonance imaging}}
 
[[Image:FMRI.jpg|thumb|right|A fMRI scan showing regions of activation in orange, including the [[primary visual cortex]] (V1, BA17).]]
 
[[Image:FMRI.jpg|thumb|right|A fMRI scan showing regions of activation in orange, including the [[primary visual cortex]] (V1, BA17).]]
[[Functional MRI]] (fMRI) measures signal changes in the [[Human brain|brain]] that are due to changing [[neuron|neural]] activity. The brain is scanned at low resolution but at a rapid rate (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via ''T''{{su|p=*|b=2}} changes;<ref>{{cite journal |author=Thulborn KR, Waterton JC, Matthews PM, Radda GK |title=Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high field |journal=Biochim. Biophys. Acta |volume=714 |issue=2 |pages=265–70 |year=1982 |month=February |pmid=6275909 |doi=10.1016/0304-4165(82)90333-6}}</ref> this mechanism is referred to as the BOLD ([[blood-oxygen-level dependent]]) effect. Increased neural activity causes an increased demand for oxygen, and the [[blood vessel|vascular]] system actually overcompensates for this, increasing the amount of oxygenated [[hemoglobin]] relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.
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[[Functional MRI]] (fMRI) measures signal changes in the [[Human brain|brain]] that are due to changing [[neuron|neural]] activity. The brain is scanned at low resolution but at a rapid rate (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via ''T*2'' changes;<ref>{{cite journal |author=Thulborn KR, Waterton JC, Matthews PM, Radda GK |title=Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high field |journal=Biochim. Biophys. Acta |volume=714 |issue=2 |pages=265–70 |year=1982 |month=February |pmid=6275909 |doi=10.1016/0304-4165(82)90333-6}}</ref> this mechanism is referred to as the BOLD ([[blood-oxygen-level dependent]]) effect. Increased neural activity causes an increased demand for oxygen, and the [[blood vessel|vascular]] system actually overcompensates for this, increasing the amount of oxygenated [[hemoglobin]] relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.
   
 
While BOLD signal analysis is the most common method employed for neuroscience studies in human subjects, the flexible nature of MR imaging provides means to sensitize the signal to other aspects of the blood supply. Alternative techniques employ [[arterial spin labeling]] (ASL) or weighting the MRI signal by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method requires injection of a class of MRI contrast agents that are now in human clinical trials. Because this method has been shown to be far more sensitive than the BOLD technique in preclinical studies, it may potentially expand the role of fMRI in clinical applications. The CBF method provides more quantitative information than the BOLD signal, albeit at a significant loss of detection sensitivity.{{citation needed|date=July 2013}}
 
While BOLD signal analysis is the most common method employed for neuroscience studies in human subjects, the flexible nature of MR imaging provides means to sensitize the signal to other aspects of the blood supply. Alternative techniques employ [[arterial spin labeling]] (ASL) or weighting the MRI signal by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method requires injection of a class of MRI contrast agents that are now in human clinical trials. Because this method has been shown to be far more sensitive than the BOLD technique in preclinical studies, it may potentially expand the role of fMRI in clinical applications. The CBF method provides more quantitative information than the BOLD signal, albeit at a significant loss of detection sensitivity.{{citation needed|date=July 2013}}

Latest revision as of 19:26, October 3, 2013

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Main article: Functional magnetic resonance imaging
FMRI

A fMRI scan showing regions of activation in orange, including the primary visual cortex (V1, BA17).

Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity. The brain is scanned at low resolution but at a rapid rate (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via T*2 changes;[1] this mechanism is referred to as the BOLD (blood-oxygen-level dependent) effect. Increased neural activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated hemoglobin relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.

While BOLD signal analysis is the most common method employed for neuroscience studies in human subjects, the flexible nature of MR imaging provides means to sensitize the signal to other aspects of the blood supply. Alternative techniques employ arterial spin labeling (ASL) or weighting the MRI signal by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method requires injection of a class of MRI contrast agents that are now in human clinical trials. Because this method has been shown to be far more sensitive than the BOLD technique in preclinical studies, it may potentially expand the role of fMRI in clinical applications. The CBF method provides more quantitative information than the BOLD signal, albeit at a significant loss of detection sensitivity.[citation needed]


See alsoEdit

ReferencesEdit

  1. Thulborn KR, Waterton JC, Matthews PM, Radda GK (February 1982). Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high field. Biochim. Biophys. Acta 714 (2): 265–70.

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