that you have to avoid? >> yes. i have to limit those things very carefully. >> reporter: the everyday emotional moments that most of us cherish are land mines to matt. the walls of their oregon home are nearly bare. only a few family pictures remain. but mostly out of sight. it can be a hellish existence. we witness how even the simplest things become threatening for matt. like the new dog trish got so she'd have somewhere to express her love. >> i want someone to play with, yeah. >> reporter: there are two things matt has no problem doing. one, surprisingly, is driving. it helps him focus and stay awake. >> as long as i carefully avoid emotional topics, the risk of having an unprovoked, unexpected attack is nil. >> reporter: and the second thing is work. the deep irony in all of this is matt is a neuroscientist. he runs his own lab at the oregon health sciences