<p>From <a href="https://en.wikipedia.org/wiki/Blood-oxygen-level_dependent#Criticism_and_limitations" rel="nofollow noreferrer">Wikipedia's page on criticism and limitations of BOLD</a>:</p>
<blockquote>
<p>Although most fMRI research uses BOLD contrast imaging as a method to determine which parts of the brain is most active, because <strong>the signals are relative, and not individually quantitative</strong>, 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[(<a href="http://siba.unipv.it/fisica/articoli/M/MagneticResonanceInMedicine1994_32_6_749.pdf" rel="nofollow noreferrer">Yablonskiy &amp; Haacke, 1994</a>)]), 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.</p>
<p>The wisdom of discarding the low-frequency signals in BOLD-contrast imaging came into question in 1995, when it was observed that the <strong>“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, <a href="http://www.scientificamerican.com/article/the-brains-dark-energy/" rel="nofollow noreferrer">2010</a>)]. BOLD-contrast imaging is only sensitive to differences between two brain states</strong>.</p>
</blockquote>
<p><strong>Reference</strong></p>
<p>Raichle, M. E. (2006). The brain's dark energy. <em>Science, 314</em>, 1249–1250.</p>
<p>Raichle, M. E. (March 2010). The brain's dark energy. <em>Scientific American: Mind &amp; Brain</em>. Retrieved from: <a href="http://www.scientificamerican.com/article/the-brains-dark-energy/" rel="nofollow noreferrer">http://www.scientificamerican.com/article/the-brains-dark-energy/</a>.</p>
<p>Yablonskiy, D. A., &amp; Haacke, E. M. (1994). Theory of NMR signal behavior in magnetically inhomogeneous tissues: The static dephasing regime. <em>Magnetic Resonance in Medicine, 32</em>(6), 749–763. Retrieved from: <a href="http://siba.unipv.it/fisica/articoli/M/MagneticResonanceInMedicine1994_32_6_749.pdf" rel="nofollow noreferrer">http://siba.unipv.it/fisica/articoli/M/MagneticResonanceInMedicine1994_32_6_749.pdf</a>.</p>

CC BY-SA 3.0
2014-02-10T23:29:24.973Z
2014-02-10T23:29:24.973Z
2020-06-17T09:55:31.633Z
Nick Stauner
<p>How good is blood flow (BOLD signal) as a measure of actual neural activity? What deficiencies exist?</p>

CC BY-SA 3.0
2014-02-10T23:29:18.443Z
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](https://en.wikipedia.org/wiki/Blood-oxygen-level_dependent#Criticism_and_limitations)? 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
CC BY-SA 3.0
2014-02-11T03:23:07.057Z
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
CC BY-SA 3.0
2014-02-11T16:04:24.103Z
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](http://cogsci.stackexchange.com/posts/5704/edit) 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
<neuroscience>
What is the current consensus on if fMRI studies in blood flow actually match brain activity?
Mark Bao
# What is the current consensus on if fMRI studies in blood flow actually match brain activity?

(Asked by: username_0 on 2014-02-10)

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

**Tags:** neuroscience

> **Comments:**
> **username_1**: 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](https://en.wikipedia.org/wiki/Blood-oxygen-level_dependent#Criticism_and_limitations)? I'll excerpt some into an answer in case you care to respond to it or to see what the community thinks of it.  
> **username_0**: 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.  
> **username_1**: 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](http://cogsci.stackexchange.com/posts/5704/edit) 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!  

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## 1 answers

### Answer by username_1 on 2014-02-10. Score: 2

From [Wikipedia's page on criticism and limitations of BOLD](https://en.wikipedia.org/wiki/Blood-oxygen-level_dependent#Criticism_and_limitations):

> 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](http://siba.unipv.it/fisica/articoli/M/MagneticResonanceInMedicine1994_32_6_749.pdf))]), 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](http://www.scientificamerican.com/article/the-brains-dark-energy/))]. BOLD-contrast imaging is only sensitive to differences between two brain states**.

**Reference**

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: <http://www.scientificamerican.com/article/the-brains-dark-energy/>.

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: <http://siba.unipv.it/fisica/articoli/M/MagneticResonanceInMedicine1994_32_6_749.pdf>.


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