Differentiating sensitivity of post-stimulus undershoot under diffusion weighting: implication of vascular and neuronal hierarchy.
Abstract
The widely used blood oxygenation level dependent (BOLD) signal during brain activation,
as measured in typical fMRI methods, is composed of several distinct phases, the last
of which, and perhaps the least understood, is the post-stimulus undershoot. Although
this undershoot has been consistently observed, its hemodynamic and metabolic sources
are still under debate, as evidences for sustained blood volume increases and metabolic
activities have been presented. In order to help differentiate the origins of the
undershoot from vascular and neuronal perspectives, we applied progressing diffusion
weighting gradients to investigate the BOLD signals during visual stimulation. Three
distinct regions were established and found to have fundamentally different properties
in post-stimulus signal undershoot. The first region, with a small but focal spatial
extent, shows a clear undershoot with decreasing magnitude under increasing diffusion
weighting, which is inferred to represent intravascular signal from larger vessels
with large apparent diffusion coefficients (ADC), or high mobility. The second region,
with a large continuous spatial extent in which some surrounds the first region while
some spreads beyond, also shows a clear undershoot but no change in undershoot amplitude
with progressing diffusion weighting. This would indicate a source based on extravascular
and small vessel signal with smaller ADC, or lower mobility. The third region shows
no significant undershoot, and is largely confined to higher order visual areas. Given
their intermediate ADC, it would likely include both large and small vessels. Thus
the consistent observation of this third region would argue against a vascular origin
but support a metabolic basis for the post-stimulus undershoot, and would appear to
indicate a lack of sustained metabolic rate likely due to a lower oxygen metabolism
in these higher visual areas. Our results are the first, to our knowledge, to suggest
that the post-stimulus undershoots have a spatial dependence on the vascular and neuronal
hierarchy, and that progressing flow-sensitized diffusion weighting can help delineate
these dependences.
Type
Journal articleSubject
Blood Flow VelocityBlood Vessels
Brain
Brain Mapping
Cerebrovascular Circulation
Humans
Magnetic Resonance Imaging
Neurons
Oxygen
Photic Stimulation
Signal Transduction
Permalink
https://hdl.handle.net/10161/13718Published Version (Please cite this version)
10.1371/journal.pone.0002914Publication Info
Harshbarger, Todd B; & Song, Allen W (2008). Differentiating sensitivity of post-stimulus undershoot under diffusion weighting:
implication of vascular and neuronal hierarchy. PLoS One, 3(8). pp. e2914. 10.1371/journal.pone.0002914. Retrieved from https://hdl.handle.net/10161/13718.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
Collections
More Info
Show full item recordScholars@Duke
Todd B Harshbarger
Assistant Professor in Radiology
Allen W Song
Professor in Radiology
The research in our lab is concerned with advancing structural and functional MRI
methodologies (e.g. fast and high-resolution imaging techniques) for human brain imaging.
We also aim to improve our understanding of functional brain signals, including spatiotemporal
characterizations of the blood oxygenation level dependent contrast and alternative
contrast mechanisms that are more directly linked to the neuronal activities. Additional
effort is invested in applying and validating the de
Alphabetical list of authors with Scholars@Duke profiles.

Articles written by Duke faculty are made available through the campus open access policy. For more information see: Duke Open Access Policy
Rights for Collection: Scholarly Articles
Works are deposited here by their authors, and represent their research and opinions, not that of Duke University. Some materials and descriptions may include offensive content. More info