As someone who used to work at the Cognitive Neurophysiology Lab in the Scripts Institute-- doing some work on functional brain image-- I can confirm this was not news even thirty years ago. I guess this is trying to make some point to lay people?
Herting, M. M., Gautam, P., Chen, Z., Mezher, A., & Vetter, N. C. (2018). Test-retest reliability of longitudinal task-based fMRI: Implications for developmental studies. Developmental Cognitive Neuroscience, 33, 17–26. https://doi.org/10.1016/j.dcn.2017.07.001
It's not at all clear to me that teenagers' brains OR behaviours should be stable across years, especially when it involves decision-making or emotions. Their Figure 3 shows that sensory experiments are a lot more consistent, which seems reasonable.
The technical challenges (registration, motion, etc) like things that will improve and there are some practical suggestions as well (counterbalancing items, etc).
I agree it makes a lot of sense though the sensory experiments are more consistent, somatosensory and sensorimotor localization results generally seem to the be most consistent fMRI findings. I am not sure registration or motion correction is really going to help much here, I suspect the reality is just that the BOLD response is a lot less longitudinally stable than we thought (brain is changing more often and more quickly than we expected).
Or if we do get better at this, it will be more sophisticated "correction" methods (e.g. deep-learners that can predict typical longitudinal BOLD changes, and those better allow such changes to be "subtracted out", or something like that). But I am skeptical about progress here given the amount of data needed to develop any kind of corrective improvements in cases where there are such low longitudinal reliabilities.
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> Using ICCs [intraclass correlation coefficients], recent efforts have examined test-retest reliability of task-based fMRI BOLD signal in adults. Bennett and Miller performed a meta-analysis of 13 fMRI studies between 2001 and 2009 that reported ICCs. ICC values ranged from 0.16 to 0.88, with the average reliability being 0.50 across all studies. Others have also suggested a minimal acceptable threshold of task-based fMRI ICC values of 0.4–0.5 to be considered reliable [...] Moreover, Bennett and Miller, as well as a more recent review, highlight that reliability can change on a study-by-study basis depending on several methodical considerations.
These can be measured themselves separately (that's exactly what they did here!) and if there's a spatial component, which the figures sort of suggest, you can also look at what a particular spot tends to do. It may also be interesting/important to understand why different parts of the brain seem to use different strategies to meet that demand.
Ekstrom, A. (2010). How and when the fMRI BOLD signal relates to underlying neural activity: The danger in dissociation. Brain Research Reviews, 62(2), 233–244. https://doi.org/10.1016/j.brainresrev.2009.12.004, https://scholar.google.ca/scholar?cluster=642045057386053841...
Hasty post. I apologize.
They are indeed coupled, but the coupling is complicated and may be situationally dependent.
Honestly, it's hard to imagine many aggregate measurements that aren't. For example, suppose you learn that the average worker's pay increased. Is it because a) the economy is booming or b) the economy crashed and lower-paid workers have all been laid off (and are no longer counted).