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A comment on 40 percent of fMRI signals do not correspond to actual brain activity. Parent comment

Re:40 percent of fMRI signals do not correspond to actual br... by parpfish on Tuesday December 16, 2025 @09:51AM (#46289226)
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
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Re:40 percent of fMRI signals do not correspond to actual br... by jawilson2 on Tuesday December 16, 2025 @12:54PM (#46291766)
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.
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Re:40 percent of fMRI signals do not correspond to actual br... by physPop on Wednesday December 17, 2025 @01:47PM (#46303721)
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)).
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