Concussions seem to be pretty physiological - first they're a brain bleed, and blood doesn't seem to pump the same as it did before the concussion... resulting in different symptoms.

That might be what you're referring to as functional?

Metabolically, or otherwise, if the brain can't operate, other things in the body such as metabolism would be impacted for sure when it can't oversee and run as it normally can?

While I'm not sure if a concussion directly is visible or not (some have sizeable enough brain bleeds that can be visible), concussions to the extent that they are a change in blood circulation changes and issues, can be visualized on fMRI, etc, where it's not regular, those areas suffer in a brain.

Things luckily have progressed and quite exciting.

Out of convenience, I'll share one I know about (no affiliation) that lay out their therapies and the science behind it as well.

Effectively (I hope I'm getting this accurately) it seems the blood vessels in the brain also have signalling from the blood and oxygen that gets affected which affects things downstream from there.

These guys do an fMRI baseline, have you jump on a bike, fMRI again, see what's not getting blood, and then give you exercises and activites for those regions of the brain. It's pretty interesting.

https://www.cognitivefxusa.com/treatment

Some reported patient outcomes: https://www.cognitivefxusa.com/our-patients

Blog links to research: https://www.cognitivefxusa.com/blog

Independently of this I've heard QEEGs can do a similar thing of seeing where brain activity is/isn't baseline.