Johnathan Cohen asks Alan to make some difficult moral choices.

In this segment, researchers at Princeton University present Alan Alda with a dilemma — if a train was about to hit five people and you had a chance to throw the switch, change the train's course and save them, would you do it? The catch is, in doing so, you would kill a single person on the adjacent track. Most people, including Alan, almost immediately answer "yes." But what if you had to physically push this person in front of the train to save the five others? That's a far trickier situation and most people struggle, as Alan does, to make this tough decision.

Most People — including Alan — would sacrifice one life to save five.

Jonathan Cohen and his colleagues are hoping to discover what part of the brain helps us wrestle with emotional issues, and make rational decisions. By looking at people's brain activity with an MRI machine while asking them challenging questions like these, they have found that an area called the anterior cingulate helps us to focus during times when the frontal lobes - our primary decision-makers - are having a particularly difficult time.

Next Alan himself gets a MRI brain scan while playing a special game the Princeton team has divised involving fairness, compromise, and money. It turns out that, in decisions that involve emotion and reason, Alan and his anterior cingulate are most likely to choose the emotional path when making up Alan's mind.