There’s a reason that we have a physical reaction to men like Arnold Schwarzenegger, Anthony Weiner, and John Edwards. There’s a reason why we can dismiss the death of Osama bin Laden with a, “he got what he deserved”, but seethe with hatred for someone like Dominique Strauss-Khan. It’s the same reason that liberals look at photos of Rush Limbaugh or Mitt Romney and become inflamed in the same way that conservatives may physically react to pictures of President Barack Obama. Our perceptions guide our moral and physical “disgust centers” in our brains, and often, those two neural networks overlap.

The widespread use of fMRI (functional magnetic imaging) has allowed researchers to watch as sensory stimuli literally “light up” various areas of the brain, which has lead to some very illuminating understandings of how our brains actually work. One of those areas, our “moral” center, is actually closely connected to the area of our brain in which physical revulsion is located. In other words, according to our brain circuitry, morality and disgust are closely related.

To illustrate this, researchers have conducted a commonplace study in which pairs of individuals are given $100 to share. However, only one of the individuals has the ability to decide how the cash is divided among them, with the other person having the ability to accept or reject the offer. If the offer is accepted, they both get the money. If the offer is rejected, they both get nothing. If the deal is rejected, fMRI scans show that the person rejecting the offer shows pronounced activity in the disgust center of the brain. Generally, any deal that offered the second person less than 43% of the pot was rejected, meaning the “rejecter” turned down a free $43 simply because the other person was going to get $57; a moral judgement that triggers feelings of physical disgust.

Jonathan Haidt, of the University of Virginia, told TIME, “There is literal disgust and moral disgust, and the two overlap. Betrayal, hypocrisy, certain kinds of baseness trigger the brain's moral response." In fact, so powerful is this mechanism in our brains that we even physically respond to witnessing someone else get cheated. The more honorably the victim responds to being taken advantage of, the more visceral our reactions are. In the case of John Edwards, who had an illegitimate child with his mistress while Elizabeth Edwards was dying of cancer, makes the bile rise in the back of the throat because we are powerfully morally reactive, and subsequently disgusted, by the behavior. In a sense, our physical reaction to those things which we deem immoral, serve to gird our moral code and make us even more morally reactive.

Perhaps this explains the vehemence and apparent inflexibility with which some, those who believe they are in the moral right, pursue their own personal, political, and social agendas. If we understand that the physical reaction is just a trick of brain chemistry, we may be able to approach moral questions more objectively, and more reasonably.