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High dimensional geometry is transforming the MRI industry (2017) [pdf]

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Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#11

Post by mattkrause »

FL33TW00D wrote: post #8
yummybrainz wrote: post #7

If folks are interested, I recently published a paper [1] demonstrating that fMRI activity in the visual cortex is remarkably high-dimensional! Specifically, using a linear approach (like PCA, but slightly fancier), we find that stimulus-related information is present along many, many dimensions of the neural response---much more than previously expected/reported. [1] https://journals.plos.org/ploscompbiol/article?id…

Hasn't fMRI as a whole been called into question? https://www.nature.com/articles/s41593-025-02132-9

I wouldn't say "called into question", as if the whole idea is bunk.

MRI is, in general, a lot harder than people often imagine. It uses complicated physics to measure convoluted physiological changes to indirectly measure brain activity, which is obviously stupifying involved--and then relate that to other, often complicated factors like behavior, lifestyle or disease state.

I think it's reasonably well-known that the BOLD response is complex and doesn't directly reflect "average" spiking activity. Some studies find that it's sensitive to the amount of synchrony (=more neurons firing together in time) rather than the rate. The paper you mention shows another dissociation: neurons can get more fuel by extracting oxygen more efficiently OR have having more overall oxygen to extract at the same rate. Thus, it's not noise, but it is complicated.

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#12

Post by observationist »

FL33TW00D wrote: post #8
yummybrainz wrote: post #7

If folks are interested, I recently published a paper [1] demonstrating that fMRI activity in the visual cortex is remarkably high-dimensional! Specifically, using a linear approach (like PCA, but slightly fancier), we find that stimulus-related information is present along many, many dimensions of the neural response---much more than previously expected/reported. [1] https://journals.plos.org/ploscompbiol/article?id…

Hasn't fMRI as a whole been called into question? https://www.nature.com/articles/s41593-025-02132-9

fMRI is noisy, but there is definitely signal.

https://medarc-ai.github.io/mindeye/

Recent studies have demonstrated using fMRI data to reconstruct the images of what the person being scanned is seeing. There's enough information there to produce a highly plausible reconstruction - if someone is seeing a picture of a zebra, the software shows a zebra, but it's not going to get the stripe patterns exactly right.

fMRI provides a great proxy and noisy set of signals. Fortunately, the brain is redundant enough that a bunch of regions getting activated creates a sufficiently differentiable pattern at large that you can get enough good information to do things like MindEye and so on. Fortunately, recent AI breakthroughs have allowed extremely high dimensional geometry to be handled relatively simply, with millions or billions of dimensions being processed into semantically useful tools.

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#13

Post by throwaway34018 »

Having worked through Geometric Tomography by Gardner, one of the big names in the field, I am pretty confident in asserting that the folks in the field have little to no interest in tomography or other applications. It's merely a grant winning ruse. The same field rebrands as "high dimensional probability/stats" by casting the uniform measure on convex bodies in the language of log-concave densities, but you talk to the folks themselves and they smirk about the extent to which they care about whether their work has any relation to the applications they claim.

There are some notable exceptions -- Donoho, Vershynin -- but most of them are doing good old fashioned Brunn-Minkowski theory, which is fundamental but a hard sell in its most truthful form.

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#14

Post by Vexs »

It's worth reading this one to the end- the point of this paper isn't about the math involved, it's that this math was the result of the federal funding of maths research.

> The cost-benefit ratio of Mathematical research has been off-scale. The Federal government spends about $250 Million/year on mathematics research. Yet in the US there are 40 Million MRI scans per year, incurring tens of billions in Medicaid, Medicare and other Federal costs. The financial benefits of the roughly 10-to-1 productivity improvements now being seen in MRI could soon far exceed the annual NSF budget for mathematics research

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#15

Post by Lerc »

yummybrainz wrote: post #10
FL33TW00D wrote: post #8

Earlier quoted context omitted.

Hasn't fMRI as a whole been called into question? https://www.nature.com/articles/s41593-025-02132-9

Yeah, there's a ton of criticism of fMRI as a method, largely because of a lot of results that are statistically unsound (to say the least)! I tend to think of fMRI data as some highly nonlinear transform of whatever neural activity is occurring in a particular region of the brain, at pretty coarse spatial resolution (~1-3 mm) and pretty bad temporal resolution (~5-15 s). Sure, it's no direct measure of neurons firin…

It sounds like it's a claim along the lines that you can't tell "I love Lucy" is on because you are listening to the audio and not looking at the screen.

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#16

Post by fcortes »

A couple of months ago I wrote a small post [1] (in Spanish) about subsampled MRI image reconstruction using compressed sensing and how it relates to government funding issues. At the time Tao had written some posts [2] about how the IPAM, where Terrence Tao was working, was losing some funding because UCLA wouldn't follow some new federal government policies.

[1] https://fintualist.com/chile/ciencia/los-efectos-de-las-pole... [2] https://mathstodon.xyz/@tao/114956840959338146

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#17

Post by rtkwe »

Vexs wrote: post #14

It's worth reading this one to the end- the point of this paper isn't about the math involved, it's that this math was the result of the federal funding of maths research. > The cost-benefit ratio of Mathematical research has been off-scale. The Federal government spends about $250 Million/year on mathematics research. Yet in the US there are 40 Million MRI scans per year, incurring tens of billions in Medicaid, Medi…

It's the thing people don't get when they see odd studies being funded and try to judge if they're worthy of being funded. Either it's just they don't understand where the study fits into a larger problem or simply that esoteric studies sometimes leads to surprising findings that are far more useful than anyone could reasonable predict.

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#18

Post by CGMthrowaway »

Vexs wrote: post #14

It's worth reading this one to the end- the point of this paper isn't about the math involved, it's that this math was the result of the federal funding of maths research. > The cost-benefit ratio of Mathematical research has been off-scale. The Federal government spends about $250 Million/year on mathematics research. Yet in the US there are 40 Million MRI scans per year, incurring tens of billions in Medicaid, Medi…

Sounds more like the point is that math research has high ROI compared to most federally funded research

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#19

Post by djoldman »

yummybrainz wrote: post #10
FL33TW00D wrote: post #8

Earlier quoted context omitted.

Hasn't fMRI as a whole been called into question? https://www.nature.com/articles/s41593-025-02132-9

Yeah, there's a ton of criticism of fMRI as a method, largely because of a lot of results that are statistically unsound (to say the least)! I tend to think of fMRI data as some highly nonlinear transform of whatever neural activity is occurring in a particular region of the brain, at pretty coarse spatial resolution (~1-3 mm) and pretty bad temporal resolution (~5-15 s). Sure, it's no direct measure of neurons firin…

Could you share your thoughts about neuralink? Is there enough signal for this to really work?

Re: High dimensional geometry is transforming the MRI industry (2017) [pdf]

#20

Post by CGMthrowaway »

Lerc wrote: post #15
yummybrainz wrote: post #10

Earlier quoted context omitted.

Yeah, there's a ton of criticism of fMRI as a method, largely because of a lot of results that are statistically unsound (to say the least)! I tend to think of fMRI data as some highly nonlinear transform of whatever neural activity is occurring in a particular region of the brain, at pretty coarse spatial resolution (~1-3 mm) and pretty bad temporal resolution (~5-15 s). Sure, it's no direct measure of neurons firin…

It sounds like it's a claim along the lines that you can't tell "I love Lucy" is on because you are listening to the audio and not looking at the screen.

fMRI is a step above dowsing rods. It's plugging a multimeter into an outlet and guessing what type and brand of appliances you are running in your house.
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