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Does functional MRI detect activation in white matter? A review of emerging evidence, issues, and future directions.

Gawryluk JR, Mazerolle EL, D'Arcy RC - Front Neurosci (2014)

Bottom Line: There are two main reasons white matter fMRI remains controversial: (1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in white matter than gray matter and (2) fMRI signal has been associated with post-synaptic potentials (mainly localized in gray matter) as opposed to action potentials (the primary type of neural activity in white matter).White matter fMRI activation has the potential to greatly expand the breadth of brain connectivity research, as well as improve the assessment and diagnosis of white matter and connectivity disorders.We end with a discussion of future basic and clinical research directions in the study of white matter fMRI.

View Article: PubMed Central - PubMed

Affiliation: Division of Medical Sciences, Department of Psychology, University of Victoria Victoria, BC, Canada.

ABSTRACT
Functional magnetic resonance imaging (fMRI) is a non-invasive technique that allows for visualization of activated brain regions. Until recently, fMRI studies have focused on gray matter. There are two main reasons white matter fMRI remains controversial: (1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in white matter than gray matter and (2) fMRI signal has been associated with post-synaptic potentials (mainly localized in gray matter) as opposed to action potentials (the primary type of neural activity in white matter). Despite these observations, there is no direct evidence against measuring fMRI activation in white matter and reports of fMRI activation in white matter continue to increase. The questions underlying white matter fMRI activation are important. White matter fMRI activation has the potential to greatly expand the breadth of brain connectivity research, as well as improve the assessment and diagnosis of white matter and connectivity disorders. The current review provides an overview of the motivation to investigate white matter fMRI activation, as well as the published evidence of this phenomenon. We speculate on possible neurophysiologic bases of white matter fMRI signals, and discuss potential explanations for why reports of white matter fMRI activation are relatively scarce. We end with a discussion of future basic and clinical research directions in the study of white matter fMRI.

No MeSH data available.


3D views of white matter fMRI activation co-localized to functionally-guided tractography in two subjects. An interhemispheric transfer task was used to elicit gray and white matter activation (rainbow color scale). Tracts (black) were seeded from regions of gray matter activation to determine whether the white matter activation was structurally connected to activation in gray matter. This work provided evidence for the anatomic basis of white matter activation; that is, regions of white matter activation are structurally connected to the activated network in gray matter. A discussion of individual variability in the location of callosal activation can be found in (Mazerolle et al., 2010). Figures were generated from data selected from (Mazerolle et al., 2010).
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Figure 3: 3D views of white matter fMRI activation co-localized to functionally-guided tractography in two subjects. An interhemispheric transfer task was used to elicit gray and white matter activation (rainbow color scale). Tracts (black) were seeded from regions of gray matter activation to determine whether the white matter activation was structurally connected to activation in gray matter. This work provided evidence for the anatomic basis of white matter activation; that is, regions of white matter activation are structurally connected to the activated network in gray matter. A discussion of individual variability in the location of callosal activation can be found in (Mazerolle et al., 2010). Figures were generated from data selected from (Mazerolle et al., 2010).

Mentions: In order to better understand the relationship between white matter activation and the activated network in gray matter, functionally-guided tractography has been applied. Mazerolle et al. (2010) used tractography to verify that regions of callosal activation were structurally connected to cortical regions activated by an interhemispheric transfer task (Figure 3). Thus, there is an anatomic basis for the notion that white matter fMRI activation corresponds with activated distributed brain networks. These findings also highlighted the potential value of combining white matter fMRI activation and diffusion tensor imaging (DTI) tractography methods for brain connectivity research, an approach subsequently adopted by Fabri and Polonara (2013) for an expanded set of functional domains.


Does functional MRI detect activation in white matter? A review of emerging evidence, issues, and future directions.

Gawryluk JR, Mazerolle EL, D'Arcy RC - Front Neurosci (2014)

3D views of white matter fMRI activation co-localized to functionally-guided tractography in two subjects. An interhemispheric transfer task was used to elicit gray and white matter activation (rainbow color scale). Tracts (black) were seeded from regions of gray matter activation to determine whether the white matter activation was structurally connected to activation in gray matter. This work provided evidence for the anatomic basis of white matter activation; that is, regions of white matter activation are structurally connected to the activated network in gray matter. A discussion of individual variability in the location of callosal activation can be found in (Mazerolle et al., 2010). Figures were generated from data selected from (Mazerolle et al., 2010).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4125856&req=5

Figure 3: 3D views of white matter fMRI activation co-localized to functionally-guided tractography in two subjects. An interhemispheric transfer task was used to elicit gray and white matter activation (rainbow color scale). Tracts (black) were seeded from regions of gray matter activation to determine whether the white matter activation was structurally connected to activation in gray matter. This work provided evidence for the anatomic basis of white matter activation; that is, regions of white matter activation are structurally connected to the activated network in gray matter. A discussion of individual variability in the location of callosal activation can be found in (Mazerolle et al., 2010). Figures were generated from data selected from (Mazerolle et al., 2010).
Mentions: In order to better understand the relationship between white matter activation and the activated network in gray matter, functionally-guided tractography has been applied. Mazerolle et al. (2010) used tractography to verify that regions of callosal activation were structurally connected to cortical regions activated by an interhemispheric transfer task (Figure 3). Thus, there is an anatomic basis for the notion that white matter fMRI activation corresponds with activated distributed brain networks. These findings also highlighted the potential value of combining white matter fMRI activation and diffusion tensor imaging (DTI) tractography methods for brain connectivity research, an approach subsequently adopted by Fabri and Polonara (2013) for an expanded set of functional domains.

Bottom Line: There are two main reasons white matter fMRI remains controversial: (1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in white matter than gray matter and (2) fMRI signal has been associated with post-synaptic potentials (mainly localized in gray matter) as opposed to action potentials (the primary type of neural activity in white matter).White matter fMRI activation has the potential to greatly expand the breadth of brain connectivity research, as well as improve the assessment and diagnosis of white matter and connectivity disorders.We end with a discussion of future basic and clinical research directions in the study of white matter fMRI.

View Article: PubMed Central - PubMed

Affiliation: Division of Medical Sciences, Department of Psychology, University of Victoria Victoria, BC, Canada.

ABSTRACT
Functional magnetic resonance imaging (fMRI) is a non-invasive technique that allows for visualization of activated brain regions. Until recently, fMRI studies have focused on gray matter. There are two main reasons white matter fMRI remains controversial: (1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in white matter than gray matter and (2) fMRI signal has been associated with post-synaptic potentials (mainly localized in gray matter) as opposed to action potentials (the primary type of neural activity in white matter). Despite these observations, there is no direct evidence against measuring fMRI activation in white matter and reports of fMRI activation in white matter continue to increase. The questions underlying white matter fMRI activation are important. White matter fMRI activation has the potential to greatly expand the breadth of brain connectivity research, as well as improve the assessment and diagnosis of white matter and connectivity disorders. The current review provides an overview of the motivation to investigate white matter fMRI activation, as well as the published evidence of this phenomenon. We speculate on possible neurophysiologic bases of white matter fMRI signals, and discuss potential explanations for why reports of white matter fMRI activation are relatively scarce. We end with a discussion of future basic and clinical research directions in the study of white matter fMRI.

No MeSH data available.