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this headline is a bit misleading on the first read, since it only affects functional (f)MRI, which is controversial since a longer time. a prominent example is

this headline is a bit misleading on the first read, since it only affects functional (f)MRI, which is controversial since a longer time. a prominent example is the activity that has been detected in a dead salmon

kspacewalk2 10mo ago
It's not that fMRI itself is controversial, it's that it is prone to statistical abuse unless you're careful in how you analyse the data. That's what the dead salmon study showed - some voxels will appear "active" purely by statistical chance, so without correction you will get spurious activations.
- tsimionescu 10mo ago
  This study questions the fMRI method itself, not the statistical analysis (you're right that the dead salmon study was challenging the way statistical analysis is done). Basically, this study claims that the association between the BOLD signal measured by fMRI and actual brain activity is quite weak, and they are even anti-correlated in 40% of cases. There is no statistical analysis that can save you if your interpretation of a signal is wrong (for example, you can't get information about personality from phrenology, regardless of what statistical analysis you try to apply to the data). That's not to say that we need to just trust this study implicitly - I'm just trying to describe how serious of a problem to the field their claim is.
kgarten 10mo ago
wondering why you are downvoted. You are right, though it's kind of inferred that the author means fMRI as the title focuses on brain activity only.
freehorse 10mo ago
Structural MRI does not record brain activity, because it is, like, structural, not functional. Structural MRI is even more abused, where people find "differences" between 2 groups with ridiculously small sample sizes.
giancarlostoro 10mo ago
So, is fMRI like "fast" MRI? Can someone fill the rest of us mortals in on this? :)
- jawilson2 10mo ago
  f is functional. MRIs are basically huge magnets used for imaging. When you apply a strong magnetic field, different tissue types and densities will react differently, and the MRI is basically measuring how those tissues react to the magnet. It is very good for imaging soft tissues, but not so much bone. Someone figured out that you can measure blood flow using the MRI, because blood cells react in a magnetic field, then "relax" at a known rate. Since we can measure blood flow, that is correlated with increased brain activity, i.e. since more neurons are firing, they require more energy, and therefore more blood. So, fMRI is using blood flow as a proxy for brain activity.
  - parpfish 10mo ago
    Fmri doesn’t measure blood flow, it measures the oxygen level in the blood. Hemoglobin molecules change shape when they carry oxygen and the different shapes react differently to magnets, which is a real stroke of luck
    - jawilson2 10mo ago
      Yep, this is why it's also called BOLD imaging, for blood-oxygenation-level-dependent fMRI. I did my PhD is BME and brain-computer interfaces, but it has been a while since I worked in the field.
    - physPop 10mo ago
      it doesn't measure the oxygen level directly either. the bold signal is correlated to dephasing induced by the oxy/deoxy hg ratio that isn't even necessarially localized to the voxel (flow or long range magnetic susceptibility perturbations from nearby accumulated deoxyhg (veins)).
- ErroneousBosh 10mo ago
SubiculumCode 10mo ago
The dead salmon was just a lesson in failing to correct for multiple comparisons.
- prefrontal 10mo ago
  As the first author of the salmon paper, yes, this was exactly our point. fMRI can be an amazing tool, but if you are going to trust the results you need to have proper statistical corrections along the way.
  - SubiculumCode 10mo ago
    Cheers!
ErroneousBosh 10mo ago
If you apply enough gain and filtering to an unknown signal, eventually you'll pull something out of it that you can convince yourself is what you're looking for.

kspacewalk2 10mo ago

It's not that fMRI itself is controversial, it's that it is prone to statistical abuse unless you're careful in how you analyse the data. That's what the dead salmon study showed - some voxels will appear "active" purely by statistical chance, so without correction you will get spurious activations.

tsimionescu 10mo ago
This study questions the fMRI method itself, not the statistical analysis (you're right that the dead salmon study was challenging the way statistical analysis is done). Basically, this study claims that the association between the BOLD signal measured by fMRI and actual brain activity is quite weak, and they are even anti-correlated in 40% of cases. There is no statistical analysis that can save you if your interpretation of a signal is wrong (for example, you can't get information about personality from phrenology, regardless of what statistical analysis you try to apply to the data). That's not to say that we need to just trust this study implicitly - I'm just trying to describe how serious of a problem to the field their claim is.

kgarten 10mo ago

wondering why you are downvoted. You are right, though it's kind of inferred that the author means fMRI as the title focuses on brain activity only.

freehorse 10mo ago

Structural MRI does not record brain activity, because it is, like, structural, not functional. Structural MRI is even more abused, where people find "differences" between 2 groups with ridiculously small sample sizes.

giancarlostoro 10mo ago

So, is fMRI like "fast" MRI? Can someone fill the rest of us mortals in on this? :)

jawilson2 10mo ago
f is functional. MRIs are basically huge magnets used for imaging. When you apply a strong magnetic field, different tissue types and densities will react differently, and the MRI is basically measuring how those tissues react to the magnet. It is very good for imaging soft tissues, but not so much bone. Someone figured out that you can measure blood flow using the MRI, because blood cells react in a magnetic field, then "relax" at a known rate. Since we can measure blood flow, that is correlated with increased brain activity, i.e. since more neurons are firing, they require more energy, and therefore more blood. So, fMRI is using blood flow as a proxy for brain activity.
- parpfish 10mo ago
  Fmri doesn’t measure blood flow, it measures the oxygen level in the blood. Hemoglobin molecules change shape when they carry oxygen and the different shapes react differently to magnets, which is a real stroke of luck
  - jawilson2 10mo ago
    Yep, this is why it's also called BOLD imaging, for blood-oxygenation-level-dependent fMRI. I did my PhD is BME and brain-computer interfaces, but it has been a while since I worked in the field.
  - physPop 10mo ago
    it doesn't measure the oxygen level directly either. the bold signal is correlated to dephasing induced by the oxy/deoxy hg ratio that isn't even necessarially localized to the voxel (flow or long range magnetic susceptibility perturbations from nearby accumulated deoxyhg (veins)).
ErroneousBosh 10mo ago

SubiculumCode 10mo ago

The dead salmon was just a lesson in failing to correct for multiple comparisons.

prefrontal 10mo ago
As the first author of the salmon paper, yes, this was exactly our point. fMRI can be an amazing tool, but if you are going to trust the results you need to have proper statistical corrections along the way.
- SubiculumCode 10mo ago
  Cheers!

ErroneousBosh 10mo ago

If you apply enough gain and filtering to an unknown signal, eventually you'll pull something out of it that you can convince yourself is what you're looking for.