In 1848, a company sought to clear some land for a railroad in Vermont. To clear land, foremen must explode rocks, and unsurprisingly, this procedure could be rather unsafe. So, in a case that is now famous among neurologists, a particularly competent foreman named Phineas Gage exploded a rock, and a tamping iron shot through his mouth and into his skull.

Miraculously, Gage survived the accident. The iron blasted through his left cheek and missed the parts of the brain necessary for functions such as breathing. However, the iron did hit his left frontal lobe, an area of the brain involved with emotional control.

Gage’s personality changed remarkably as a result of his injury. He could no longer execute plans and he was quite easily aggravated. In the words of his doctor: “He was gross, profane, coarse and vulgar, to such a degree that his society was intolerable to decent people.”

Gage’s story is not a comforting one to hear for people who believe in the persistence of personal identity. Personal identity refers to the idea that individuals have some essential characteristics that define them and continue to define them over time. Certain injuries can steal from us the aspects of ourselves we may regard as essential to who we are. Before his accident, Gage’s doctor and his friends described him as a “shrewd, smart business man” and a “favorite” among his co-workers. Yet after the accident, he hardly was familiar to his co-workers and friends.

The transformation of Gage’s personality calls into question how important our identities are to our being if they can be fundamentally altered. What kinds of characteristics might we call essential to someone’s identity, such that once they change, we regard that person as different? People often use morals as a way of defining their identity. For instance, people make claims such as “I would never cheat on a test because that is not the kind of person I am.” However, it turns out that brain diseases can claim our morals as well.

In 2002, neurologists from the University of Virginia reported a case of a man who suddenly began to follow child-pornographic websites and solicit prostitutes. The man was eventually sentenced to jail for child molestation. However, a MRI showed a massive tumor in his brain’s frontal lobe.

After the tumor was removed, he successfully completed a rehabilitation program and returned home. By that point, his pedophilic urges had stopped. However, a year later his pedophilia returned, but this time the doctors knew where to look: His tumor had reformed.

Evidently, our moral dispositions are subject to flux in the face of biological processes outside our control. While the two cases may seem like anomalies, moral transformation is common in patients who suffer from frontotemporal dementia — a neurodegenerative disorder characterized by sharp changes in personality. In fact, a recent study from Yale demonstrated that the disruption of a dementia patient’s morality contributes most strongly to whether that patient’s family members will start to see them as a different person.

Given the possibility that our identities have the potential to fundamentally change, to what extent should we prepare to become different people? We make decisions based on some sense of who we are, but our identities are malleable. It is usually impossible to predict exactly how we will change as we get older. But in the case of neurodegenerative disorders, the progressive loss of a patient’s mental abilities is quite predictable, and so it may make sense to prepare to lose those abilities ahead of time.

Ayan Mandal is a junior in the College. Brain History appears every other Tuesday