This is why I love this site. You get input from so many specialized folks! I appreciate you contributing your expertise and I also appreciate you calling out the limits to that knowledge.

Two points I'm hoping you can help clarify:

> Researchers ... found that an increased fMRI signal is associated with reduced brain activity in around 40 percent of cases.

So it's not just that they found it was uncorrelated, they found it was anticorrelated in 40% of cases?

And you are suggesting that conclusion suffers from the same potential issues as these fMRI studies in general?

Like you mention, it seems to me if we wanted to really validate the model, we'd have to run the same experiment with two, three, or maybe even more different modalities (fMRI, PET with different tracers, etc).