There are 2 doors in the intro level (Outer Cerebrum): the first one is where you install the elevator disc for the 2nd time and the occupant talks about the coming brain storm, the second one is next door (go up on the roof, across the bridge, down the stairs, and the door is immediately next to the stairs) and there is no answer.
Cerebrum City has: Reason, Nerves, Party, Optimism, Anger, Compassion (behind the ground level pencil stairs on the right side of town), Pride, Nostalgia, Destruction, Apathy, Stress, and Order.