Are you suggesting maybe giving Thornton some time off? Maybe clear the head and if it is an injury give him some time to heal? In the long run of the season that could help.
He may need time off but, if it is a TBI, I don't think that the doctors can diagnose that if Thornton wants to hide it. (I'm not suggesting that he's doing that but it is a possibility.) This is far from my area of expertise except for stuff I've read online bc of dealing with my own TBIs and a few in my family but I think most of the tests are pretty crude and many depend heavily on the patient's subjective symptoms (and such symptoms being conveyed to the doctor). Many of the symptoms are similar to other problems as well (e.g., Boyle's problems with sleep) or seem kind of vague (especially to someone whose judgment may be impaired bc of the TBI) so even if Thornton is not trying to hide symptoms, he may not have something that he connects with a TBI so never mentions it to the doctor.
I don't think that rest usually helps TBIs. It is better to not get another TBI while you are still healing from a TBI, though. AFAIK that's why players don't return before their concussion is fully healed. It's not like a torn ligament in that way. So I don't think rest will help him recover any quicker if it is a TBI of some sort.
If it takes longer for him to process things bc of a TBI, it might help to play against lesser competition bc it would give him a fraction of a second longer. That could help him play better bc it would give him a chance to adjust and maybe reinforce/kind of relearn things that have been affected (assuming it is a TBI), which might allow him to build on that.
I hope that he is seeing a neurologist and someone like a neuropsychologist and other experts. Even if it wasn't a TBI, something is going on. If he needs time off to recover, I'd be all for that too, just like I am for Couture.