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How good is blood flow (BOLD signal) as a measure of actual neural activity? What deficiencies exist?

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Could you write a little more...if i answer this as it is its going to be deleted again – user3832 Feb 10 '14 at 21:11
That wouldn't be the OP's fault. However, Mark (welcome to cogsci.SE BTW!), have you considered any of the information on Wikipedia's page on criticism and limitations of BOLD? I'll excerpt some into an answer in case you care to respond to it or to see what the community thinks of it. – Nick Stauner Feb 10 '14 at 23:29
Nick and caseyr547, thanks for the responses (-1 on my first cogsci.SE question, eek)—is there a specific cs.SE rule that I'm not following here? My mistake if this is not the kind of question that should be asked. I did take a look at that Wikipedia page, but I am looking for more specific data and more recent data since it looks like the info on that Wikiepdia page dates back to '94, '95, and an article from 2008. – Mark Bao Feb 11 '14 at 3:23
That there is no new criticism of BOLD does not mean that the old criticism has been invalidated. The world is still round, even though the criticism of the flat world theory is at least two thousand years old ;-) – what Feb 11 '14 at 11:34
My only guess as to why your question might've received that downvote is the same reason I haven't given it an upvote: no demonstration of research effort. Your comment improves that by explaining why the info I've given isn't satisfactory; if you edit that in to make your question more specific (and you let me know or I happen to notice), I'll toss you an upvote :) I tend to agree with @what, since Raichle clearly still believed what he was saying in 2010...but I think there's value in newer critiques—since BOLD is still in use—so ask away! – Nick Stauner Feb 11 '14 at 16:04

From Wikipedia's page on criticism and limitations of BOLD:

Although most fMRI research uses BOLD contrast imaging as a method to determine which parts of the brain is most active, because the signals are relative, and not individually quantitative, some question its rigor. Other methods which propose to measure neural activity directly have been attempted (for example, measurement of the Oxygen Extraction Fraction, or OEF, in regions of the brain, which measures how much of the oxyhemoglobin in the blood has been converted to deoxyhemoglobin[(Yablonskiy & Haacke, 1994)]), but because the electromagnetic fields created by an active or firing neuron are so weak, the signal-to-noise ratio is extremely low and statistical methods used to extract quantitative data have been largely unsuccessful so far.

The wisdom of discarding the low-frequency signals in BOLD-contrast imaging came into question in 1995, when it was observed that the “noise” in the area of the brain that controls right-hand movement fluctuated in unison with similar activity in the area on the opposite side of the brain associated with left-hand movement [(Raichle, 2006, 2010)]. BOLD-contrast imaging is only sensitive to differences between two brain states.


Raichle, M. E. (2006). The brain's dark energy. Science, 314, 1249–1250.

Raichle, M. E. (March 2010). The brain's dark energy. Scientific American: Mind & Brain. Retrieved from:

Yablonskiy, D. A., & Haacke, E. M. (1994). Theory of NMR signal behavior in magnetically inhomogeneous tissues: The static dephasing regime. Magnetic Resonance in Medicine, 32(6), 749–763. Retrieved from:

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