I've been studying lately about brains, brain tumors, and traumatic brain injury. In my searches for appealing books, I came across "Trigger" by Susan Vaught, a fictional account of a teenager with traumatic brain injury after a failed suicide attempt.
The voice Susan created for Jersey, her main brain-damaged character, was completely authentic to me. After reading medical accounts of recovering from brain injury, it was very believable to follow the struggle of Jersey making his way back into life. The book was gripping and I read it all in a few hours. If you want to read a book that will give you insight into the world of brain damage, plus show you an authentic out-of-the-norm voice for a character, I highly recommend it.
Just by way of warning: there is some amount of swearing in the book. Not a lot, but some. Probably a strong PG rating for it.