Charles Whitman had a cancerous tumor in his brain when he wrote this:
"I don't quite understand what it is that compels me to type this letter. Perhaps it is to leave some vague reason for the actions I have recently performed. I don't really understand myself these days. I am supposed to be an average reasonable and intelligent young man. However, lately (I can't recall when it started) I have been a victim of many unusual and irrational thoughts"
Afterwords he went out and killed 15 people including his wife and mother.
Perhaps there are parasite's and various other things which can affect that region of the brain.
Of course I've had a few unusual and irrational thoughts in my day, never acted on them though. Is there a certain part of the brain that is strictly involved in making decisions?
