fMRI: a very critical review, again (Introduction)

by David Turell , Wednesday, July 13, 2016, 14:49 (3057 days ago) @ David Turell

This paper is a review of the statistical results that come from the software that analyzes scans. Essentially not reliable:-http://www.theregister.co.uk/2016/07/03/mri_software_bugs_could_upend_years_of_research/-"A whole pile of “this is how your brain looks like” fMRI-based science has been potentially invalidated because someone finally got around to checking the data.-"The problem is simple: to get from a high-resolution magnetic resonance imaging scan of the brain to a scientific conclusion, the brain is divided into tiny “voxels”. Software, rather than humans, then scans the voxels looking for clusters.-"When you see a claim that “scientists know when you're about to move an arm: these images prove it”, they're interpreting what they're told by the statistical software.-"Now, boffins from Sweden and the UK have cast doubt on the quality of the science, because of problems with the statistical software: it produces way too many false positives.-"In this paper at PNAS, they write: “the most common software packages for fMRI analysis (SPM, FSL, AFNI) can result in false-positive rates of up to 70%. These results question the validity of some 40,000 fMRI studies and may have a large impact on the interpretation of neuroimaging results.”-"For example, a bug that's been sitting in a package called 3dClustSim for 15 years, fixed in May 2015, produced bad results (3dClustSim is part of the AFNI suite; the others are SPM and FSL).-"That's not a gentle nudge that some results might be overstated: it's more like making a bonfire of thousands of scientific papers.-"Further: “Our results suggest that the principal cause of the invalid cluster inferences is spatial autocorrelation functions that do not follow the assumed Gaussian shape”.-From the paper itself:-http://www.pnas.org/content/113/28/7900.full-"Significance-Functional MRI (fMRI) is 25 years old, yet surprisingly its most common statistical methods have not been validated using real data. Here, we used resting-state fMRI data from 499 healthy controls to conduct 3 million task group analyses. Using this null data with different experimental designs, we estimate the incidence of significant results. In theory, we should find 5% false positives (for a significance threshold of 5%), but instead we found that the most common software packages for fMRI analysis (SPM, FSL, AFNI) can result in false-positive rates of up to 70%. These results question the validity of some 40,000 fMRI studies and may have a large impact on the interpretation of neuroimaging results." -Comment: I'm not surprised. The fMRI is a shorthand trick to look at areas of the brain that light up with thought activity. All this does is give us a hint of which areas of the most complex organ in the universe are assigned to do the work, nothing more.