JUDY WOODRUFF:

Now: part two of our series War on the Brain.

Tonight, special correspondent Soledad O'Brien reports from North Carolina on the difficulty in diagnosing PTSD and how that complicates treatment.

SGT. 1ST CLASS MICHAEL RODRIGUEZ (RET.), U.S. Army: Sometimes, it's fear. Sometimes, I'm scared of — of everything. Sometimes, I feel sad. Sometimes, I feel overwhelmed. The biggest trigger I have is myself.

I don't like the way I smell. I frequently bathe, at least four or five times a day.