Acting is half shame, half glory. Shame at exhibiting yourself, glory when you can forget yourself.
Unlike life, you've got more or less complete control over what's going on in your stories. That's not to say you can make characters do whatever you want them to - they usually have a life of their own if you've done your job properly.
For somebody who has injured their brain, every single thing they say and think will be the subject of their own questioning.