The political scene can sometimes be seen like a contest of how loudly everyone is shouting, with everyone seemingly talking past one another. While in halcyon days past, people may have been able to have reasonable dialogue, it can often appear that people on either side of the political aisle cannot even agree on the same starting point.

In hot-button issues like abortion, for example, one person might believe that life starts at conception, while another believes that life starts when the fetus is viable. When presented with the same set of facts, how can both sides feel so certain that they are correct?

The answer lies in the brain structure. Gary Lewis, a postdoctoral research fellow at the University of California, Santa Barbara, and his colleagues have identified that brains that align with particular moral values have different amounts of gray matter. Gray matter consists of neuronal cell bodies, and is found in regions of the brain that control things like memory, emotions, and perception. According to the article, this discovery "suggest[s] a biological basis for moral sentiment."

First, the experiment took brain scans of 70 participants from the University College London, all healthy and in their late twenties. Then the investigators administered a test called the Moral Foundations Questionnaire, which asks respondents how much they agree with statements like "People should not do things that are disgusting, even if no one is harmed" and " I think it’s morally wrong that rich children inherit a lot of money while poor children inherit nothing". The questionnaire asks questions pertaining to five moral areas: harm, fairness, loyalty, authority, and purity.

Researchers found a clear correlation between the sizes of certain regions of the brain and the way that they answered certain questions. People who have a strong interest in maintaining fairness and of avoiding harm had larger left dorsal medial prefrontal cortexes, which have been linked to the guiding of basic behavior. People who scored highly on the purity index had higher volumes of anterior insula, which is strongly related to disgust.

Of course, researchers say that the shape of the brain is less important than environmental influence that shapes you. But if you or a family member grew up in a conservative household or area, and then came back from college having changed their ideology, something had probably been nagging them all along: their left dorsal medial prefrontal cortexes.

The study was published in the Journal of Cognitive Neuroscience.