This is what I got from this article: Researchers looked at MRI scans of people listening to a Podcast on their daily commute. The researchers don't know what any of it means.
"Oh! Cache is lighting up!"
It's from 2009, so things have improved, but still.
Dead salmon, though they may be, light-sensitive organs the eyes still are.
And provided that the salmon were probably preserved on ice, much of the carcasses probably remained fairly chemically stable, so while the electron pumps in the electron transport chains of the multi-polar neurons were deactivated, I bet the whole pipeline from salmon's visual cortex to its eyeball probably was still slightly capable of transmitting photo-sensitivity.
Then, it probably came down to the fMRI imaging software being so fine-tuned as to notice that differentiation, and amplify it into statistical significance!