[Sethomas]

What I basically meant by "external influences" is any stimulus that provokes thinking or actions inconsistent with the brain's usual activity.

I guess the fundamental point is that most cases of clinical depression are not external influences, since they reflect the nature of the mind itself. If you go into a line of infinite causations, then ultimately EVERYTHING has roots in external causes, but I think it's easy enough to know when to draw the line. This provokes the question, why are depressed people so much more visible now, and why are they killing themselves?

On the general question of "madness", it's been my assumption that until the Victorian Era or so most people who were "mad" simply found ways to blend in with their society, unto the point of their being batshit insane. Perhaps violent crimes were more prevalent because of this; it wouldn't be surprising, but I haven't seen statistics either way. An interesting statement that Augustine posed is that "Man would rather be unhappy and sane than joyful and mad". I've always wondered if that's the case for myself.