They put people in an MRI and then asked them to decide between various discounts and buy-one-get-one-free offers like they would face in a supermarket.
fMRI studies are largely bullshit in the best of times. Using it to study an abstract effect is doubly so.
> Some people like to use the salmon study as proof that fMRI is woo, but this isn't the case, it's actually a study to show the importance of correcting your stats.