This is an excerpt from Chapter 5 of the book: Incognito: The secret lives of the Brain, written by David Eagleman – The Neuroscientist. He talks about the Trolley-problem from the Neuroscience perspective. I found the dichotomy between the ‘rational’ and the ’emotional’ aspects of our brains pretty compelling.

“The battle between the rational and emotional systems is brought to light by what philosophers call the trolley dilemma. Consider this scenario: A trolley is barreling down the train tracks, out of control. Five workers are making repairs way down the track, and you, a bystander, quickly realize that they will all be killed by the trolley. But you also notice that there is a switch nearby that you can throw, and that will divert the trolley down a different track, where only a single worker will be killed. What do you do? (Assume there are no trick solutions or hidden information.)

If you are like most people, you will have no hesitation about throwing the switch: it’s far better to have one person killed than five, right? Good choice.

Now here’s an interesting twist to the dilemma: imagine that the same trolley is barreling down the tracks, and the same five workers are in harm’s way—but this time you are a bystander on a footbridge that goes over the tracks. You notice that there is an obese man standing on the footbridge, and you realize that if you were to push him off the bridge, his bulk would be sufficient to stop the train and save the five workers. Do you push him off? If you’re like most people, you bristle at this suggestion of murdering an innocent person. But wait a minute. What differentiates this from your previous choice? Aren’t you trading one life for five lives? Doesn’t the math work out the same way? What exactly is the difference in these two cases?

Philosophers working in the tradition of Immanuel Kant have proposed that the difference lies in how people are being used. In the first scenario, you are simply reducing a bad situation (the deaths of five people) to a less bad situation (the death of one). In the case of the man on the bridge, he is being exploited as a means to an end. This is a popular explanation in the philosophy literature. Interestingly, there may be a more brain-based approach to understand the reversal in people’s choices.

In the alternative interpretation, suggested by the neuroscientists Joshua Greene and Jonathan Cohen, the difference in the two scenarios pivots on the emotional component of actually touching someone—that is, interacting with him at a close distance. If the problem is constructed so that the man on the footbridge can be dropped, with the flip of switch, through a trapdoor, many people will vote to let him drop.

Something about interacting with the person up close stops most people from pushing the man to his death. Why? Because that sort of personal interaction activates the emotional networks. It changes the problem from an abstract, impersonal math problem into a personal, emotional decision. When people consider the trolley problem, here’s what brain imaging reveals: In the footbridge scenario, areas involved in motor planning and emotion become active. In contrast, in the track-switch scenario, only lateral areas involved in rational thinking become active. People register emotionally when they have to push someone; when they only have to tip a lever, their brain behaves like Star Trek’s Mr. Spock.


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