The sign on the door to his office reads, “Warning! Zombie Contagion / Do Not Enter!” Carnegie Mellon University’s Timothy Verstynen, 35, is quick to call himself a nerd — in the confident way of someone who knows that nerd is the new cool. An assistant professor in psychology at CMU and the Center for the Neural Basis of Cognition (a joint venture of CMU and the University of Pittsburgh), he is engaged in science outreach that combines two of his favorite things — horror movies and brains.