If the hospital did an EEG then it's documented. If they didn't, and it would be typical if they didn't, they were idiots. That last part was just my personal opinion because it's one of my biggest medical pet peeves.
I'll explain and this might take a minute...
My 20 year old daughter is a recovering opiate addict. Her addiction was born in a perfect storm. She always suffered anxiety and panic attacks since she was a little girl. Later on, she suffered PTSD from two things and they feed the anxiety/panic. The first time was accidentally being shot with an air rifle by a neighbor; it penetrated the skin and tissue, then slid by her heart missing it by 1/4 inch. The second time was after watching a friend die in a car accident.
Between those two incidents, she was a passenger in a car wreck and slammed her head into the dash. She also separated her shoulder and that's when she started abusing opiates. Another time, when she was pulled over by the police, she stepped out of the car and had a panic attack. She passed out and her head bounced on the pavement. They took her to the ER but no EEG's were done.
Fast forward to about six months ago and she went to a psychiatrist for anxiety meds. He's into diagnostics and did an EEG on her to match her meds to her brain function. It's a new tool and it's called rEEG. A few unexpected things showed up, and traumatic brain injury was one of them.
Doctors know that even mild concussions can cause adverse side effects years later. But for some reason not enough testing or even questioning is being done. Luckily we found the only psychiatrist in our area that does look at the whole picture.
She started doing neurofeedback to treat it and it definitely helped, but she's not done yet. She still has problems connecting the dots so to speak. She was always something of a dingbat but after the TBI's it was a lot worse. Now, she's almost back to her normal.
She always said opiates gave her clarity, and her psychiatrist and a neurologist gave me the medical reason why but for the life of me I can't remember it right now. Opiates also stopped the panic attacks.
Anyway, when you add all this up that's why I said it was a perfect storm. Going by what you said, it sounds like your brother had one of those storms, too.
If you brother had an EEG today and a CT scan, it would show any previous brain injury and the specific location.
I don't know how you'd talk him into it, if for nothing else the process of elimination. I had to explain the tests and the necessity to my daughter about three times, and each time was like the first time to her. Thankfully she got past the confusion and agreed.
Addiction is bad enough but when other physiological issues are going on, it requires special treatment and care beyond the norm.