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.
Highlights
The current review provides an overview of the motivation to investigate white matter Functional magnetic resonance imaging (fMRI) activation, as well as the published evidence of this phenomenon
In Section Understanding why reports of white matter fMRI activation are uncommon, we describe the challenges that may explain the paucity of observations of white matter fMRI activation, including technical, physiological, and philosophical issues
Functional MRI is a tremendous technique that has allowed for noninvasive visualization of functional dynamics in the human brain
Summary
Tettamanti et al (2002) published a key report of white matter fMRI activation, in which a cluster was observed in the genu of the corpus callosum associated with a visuo-motor interhemispheric transfer task, the Poffenberger paradigm. Frontiers in Neuroscience | Brain Imaging Methods fMRI White Matter Review activation, used a Poffenberger interhemispheric transfer task and detected a cluster of activation in the anterior corpus callosum.
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