When Nina Strohminger was a teenager, her grandmother had dementia. “Before she got sick, she was not a very nice person,” Strohminger said. “One of the first things that went when this disease was taking hold is she became really, really nice. I just remember her stopping me one day and saying ‘Nina, your skin is so beautiful,’ and I was like ‘what is happening?’”

We spoke on the phone, both of us traveling—I paced outside of a Starbucks in Brooklyn while she packed her things to move from Durham, NC, where we both lived at the time, to New Haven, CT, where she’d be starting as a postdoctoral researcher at Yale University. (Full disclosure: Strohminger is a friend and collaborator of mine.) 

“She didn’t seem like the same person,” Strohminger went on. “She just seemed completely different.” This question, what makes someone seem like who they are?, is a fundamental one that philosophers and psychologists have always struggled to answer. Some thinkers have suggested that it’s our bodies that define us, while others argue that it’s our memories. In a forthcoming paper with University of Arizona philosopher Shaun Nichols, Strohminger advances  a novel solution: What makes us who we are is our moral character—whether we’re honest, what sorts of things we value, and how well we treat our grandchildren.

Strohminger’s research depends in part on an extremely rare type of brain cell, the spindle neuron. Outside of the sharpest mammals, like dolphins, elephants, and great apes, no other animal shares them with us. Typical neurons form dense canopies with their neighbors, connecting with one another across several clustered branches; spindle neurons, however, are skinny and long, arranged in parallel, with only one branch for receiving and transmitting information at either end. These neurological rarities appear in regions located near the front of the brain and around our temples—regions associated with self-control, emotion, and social behavior. 

Functional imaging of the brain regions they populate suggests that spindle neurons are integral to our emotional and social lives; they help make us human. Frontotemporal Dementia (FTD), a neurodegenerative disease second only to Alzheimer’s in prevalence, destroys more than 70 percent of them.

FTD is ugly. It blunts compassion and it lowers inhibition, leaving patients spouting racial slurs in public and cheating on their spouses. When self-control and self-restraint go, patients are left unlike themselves. It tends to hit earlier than Alzheimer’s, usually between someone’s 40s or early 60s, and there’s a large genetic component. Family history is the only known risk factor for the disease—it’s inherited in a third of all cases. 

Genevieve Wanucha, who writes about neurodegenerative disease research and treatment at the University of Washington, has a lot of experience with FTD. Her mother was diagnosed in 2009 at 58 (she died two years later, in 2011), and she’s currently working on a book that will profile five different patients living with FTD. We spoke briefly on the phone late last month.

“In the lab, researchers will ask patients in the early stages of this disease 'Is it okay to laugh at someone who fell down?' or 'Is it okay to steal a wallet?' or 'Is it okay to speed on the highway?" and usually they will be able to say 'No, that’s wrong.' But the fact is, outside in everyday life, they’re doing these things anyway,” Wanucha told me. “What that says to me is that they may still understand right or wrong, but they don’t care on an emotional level. They no longer care about the impact of their behavior on other people. They no longer care about how their behavior reflects back on them through other people’s eyes." Of course, this ability to step back and reflect on our actions—to see them as others see them—is one thing that separates us from most, if not all of our primate relatives. It's part of what makes us who are we. 

“Because of brain damage, they’ve lost this ability that they used to have to apply this emotional, intuitive knowledge about how they should act and put that into practice,” she went on. “I think that’s an important distinction to make because someone with FTD is not choosing to act this way, and these people—who used to be teachers, artists, athletes—can get into a lot of personal, legal, or financial trouble if others don't take responsibility and look out for them."

Before Strohminger and Nichols, few philosophers and psychologists seriously considered whether morality might play an important role in personal identity. “Most of the debates,” Strohminger told me, “have either located the self as being somewhere in the mind or just your mind in its entirety. If they’ve gone more specific than that, they’ve claimed that its memory, specifically your episodic or autobiographical memories, that really makes you who you are.”

This view, that our memory is what’s most essential to our identities, is most often credited to John Locke, a 17th century British philosopher. It’s difficult, though, to test this directly—after all, you can’t really ask someone who’s lost their memory whether or not they’re the same person as someone they no longer remember. To get around this requires some thought. In past work, Strohminger and Nichols tested Locke’s hypothesis with hypothetical scenarios: imagine someone seriously injured their head and lost their memories, or they lost their sight, or they lost their moral compass, and so on. Strohminger asked people to rate how different someone would be after these kinds of accidents. “What we find consistently, really no matter how we ask this question,” Strohminger told me, “is that moral traits are what matter the most.” 

“The problem with all those studies,” she continued, “is they tell us what people predict they would say, but what would they actually say if they were put in that situation?” So Strohminger and Nichols decided to find out. They went to families whose members had different neurodegenerative diseases.  What they were looking for, Strohminger told me, were  “the traits that cause us to say ‘I don’t even recognize them anymore. They’re a stranger to me.’”

Strohminger and Nichols recruited family members from online support networks for three different diseases: Alzheimer’s, for testing changes in memory; FTD, for changes in morality, and Amytotrophic lateral sclerosis—better known as ALS or Lou Gerhig’s disease—for a control, because it causes only physical changes. The participants listed their loved one’s symptoms and answered questions like “Does the patient ever seem like a stranger to you?” and “Do you still feel like you know who the patient is?” The results were exactly in line with what their past work predicted.

“What we found,” Strohminger told me, “was the ALS patients were seen as changing the least, the FTD patients were seen as changing the most, and the Alzheimer’s patients were somewhere in between.” 

These results are suggestive of the importance of morality for identity, but neurological diseases are messier. Alzheimer’s does more than just affect memory, and FTD isn’t only a disease of morality—the symptoms bleed into one another, so it’s difficult to tell which change matters for identity. Strohminger and Nichols thought some more about how to parse the impact of each disease, and went back to the symptoms families claimed changed the sufferer’s identity.

“The only symptoms that predict identity change are those that are related to moral change,” Strohminger told me. “The extent to which an Alzheimer’s patient seems different is predicted almost entirely by the extent to which their moral traits changed and not at all by their memory loss.” In other words, a patient with Alzheimer’s may seem like a different person, but it’s not because their memories have gone.

This is surprising, since there seems to be an unmatched cultural anxiety about Alzheimer’s and memory loss. Strohminger, though, says our personal experiences can be misleading. “It’s evident that someone with dementia doesn’t seem like the same person, and one of the most salient symptoms they have is loss of memory,” she told me. “Perhaps what we've been doing is falsely inferring a causal relationship where there was none.” Perhaps we should be more afraid of our morals deteriorating than our memories.

Popular culture doesn’t do much better in giving us accurate representation of neurodegenerative disease; it most often seems to be deployed as a dramatic, romantic plot twist. The Notebook uses an elderly woman’s advanced Alzheimer’s as a plot device, so that an elderly man—her husband— could remind her how they fell in love. In 2010’s Love and Other Drugs, Anne Hathaway’s character suffers from early onset Parkinson’s disease, and her paramour, a pharmaceuticals sales rep played by Jake Gyllenhaal, struggles with the idea of a life spent caring for someone with a chronic, debilitating illness. 

One notable exception is last year’s Still Alice, where Julia Moore (who won an Oscar for her role) plays a Columbia University linguistics professor suffering from Alzheimer’s disease. The movie grapples honestly with the realities of illness, and its title is suggestive—for all the ravages of Alzheimer’s, it suggests, something of the person is still there.

It’s hard to imagine, though, a love story where a character has FTD; Alice isn’t Alice when her moral character goes. While the families Strohminger surveyed seemed to agree in their responses, two insights in particular stood out. “One is that they all were angry that no one ever talked about FTD, and it was always ‘Alzheimer’s, Alzheimer’s, Alzheimer’s,’” Strohminger told me. The second, she went on, was FTD’s specific kind of devastation. Families were “ especially aware that the thing that makes this disease particularly devastating is that it’s really hard to still love this person who has become a moral monster.”

During the study, family members rated how much their relationship with the patient deteriorated; Strohminger found that only moral decay had an impact. “Any other sorts of mental deterioration probably won’t, at least according to the data, impact your ability to love and care for this person whose mind is slowly going.”

Wanucha, the science writer whose mother died from FTD, told me a more personal story. “I often hear doctors tell me about patients who lose empathy, which is the most painful part of the disease to loved ones. A wife cuts her finger in the kitchen, and the husband just kind of shrugs and goes and watches television. An adult daughter doesn't show the normal concern or grief over a death in the family, that kind of thing," she said. 

“The best you can do,” she continued, “is to learn all you can about the disease so you can create a supportive environment and structure home life such that these patients don't have access to bank accounts, credit cards, or keys to the car, and are kept as comfortable and safe as possible.” It’s important to remember that patients aren’t consciously choosing to act the way they do, Wanucha told me.“Responding everyday with patience and compassion in these situations doesn't come naturally—it's a real choice and takes a village.”

Though FTD and Alzheimer’s are very different diseases, Strohminger’s findings have important implications for both illnesses. Alzheimer’s is still a particularly devastating disease, and it’s relevant to the more than 15 million people in the U.S. caring for those patients that Strohminger did find some sufferers do experience moral changes. But those caretakers may find some solace in the idea that memory loss doesn’t fundamentally change the person they love. 

One of my academic mentors, Felipe De Brigard, a philosopher and neuroscientist at Duke University, illustrated this for me with a story. De Brigard started his career as a student in Columbia doing clinical work with patients suffering memory loss. He recalled to me a man in his 70s who used to come into the lab as a control subject. This man didn’t have Alzheimer’s, but his wife did. “He told me, ‘There’s something about the way she interacts with me that makes me realize she knows who I am, even though she can’t remember me,” De Brigard said. “And I asked him, ‘Can you give me an example?’ He said, ‘Yeah, every night when I put her to bed, she asks me to stay.’”