This is the second of two stories born out of an afternoon at UCSF's Memory and Aging Center, where a team of scientists, led by Dr. Bruce Miller, is trying to tease out the differences between as many as 200 dementias that affect aging brains.

The two stories have a lot in common: Both introduce us to people who have lived with extremely difficult degenerative diseases: ALS in "Decoding the Emotional Brain," and frontotemporal dementia in this week's story. Both open up provocative questions about human nature. And neither would have happened without the generosity of a Northern California family – in this case, Cassandra Shafer, who drove down from Forestville with her daughter, Columbia, to tell me about Cassandra's husband and Columbia's father, Keith Jordan.

In these video clips, you meet Keith Jordan in the second half of his disease, after doctors at UC Davis and UCSF diagnosed him with frontotemporal dementia. The videos were taken at UCSF over the course of many hours doctors spent studying Keith and his symptoms. In them, we glimpse of two of Keith's FTD-caused obsessions: joke telling and music. (We also see one of the first symptoms to have emerged: his Jerry Garcia hairdo.)

At first glance, Keith's behavior might strike you as more eccentric than brain-damaged, which is precisely why FTD can take so long to diagnose. If you're a doctor with a 15-minute appointment slot, frontotemporal dementia might just look like a midlife crisis. What we don't see in the video clips are the five heartbreaking years that Cassandra spent trying to figure out what was happening to her husband – a search that included marriage and career counseling, the full gamut of conventional western specialists, yoga, meditation, chelation therapy, replacing every household cleaning product, every pot and pan, all the way to shamanic soul retrieval and exorcism – all while his behavior grew more erratic and difficult to be around. It's impossible to overstate the drain – both emotional and financial — that this search brought on Keith's family.

Keith died in May and Cassandra is still, she says, "inching her way" out of the "foreign land" that FTD plunged her into. As unlikely as it sounds, I think she takes some comfort in the fact that Keith's illness also gave doctors a chance to explore profound questions about human nature and the extent to which the structure of our brains determines who we are.

FTD can turn Democrats into Republicans, and vice versa. People with no interest in art begin to paint obsessively. As the neurons in Keith's right frontotemporal lobe (just behind the right eyebrow) died, his taste in music, his sense of humor, his relationships with his family members and friends changed completely. Our self, in other words, may owe much more to the way our brains are built than we'd care to acknowledge.

And what to make of the fact that this same part of the brain that shapes personality is also responsible for reading other people's reactions? People with some forms of FTD can't empathize with others (hear more about this in our slide show about FTD and art) or read the emotion on another person's face. Not only do they experience radical personality changes, but they lose the ability to sense others' reactions to them. In other words, how we define ourselves – whether we consider ourselves funny, smart, ambitious — seems to have everything to do with how others define us. We are all, in other words, people people.

Which begs the question: What about people raised in isolation, without the critical feedback loop of social interaction? What does FTD tell us, for example, about children who have been deeply neglected in orphanages? Or – taking another angle entirely — autistic people, who have trouble empathizing with others? What does self-perception look like in those who can’t perceive those around them?

If all this is giving you a headache, you might spend some time exploring the web extras we've produced for these two stories. Here, Bruce Miller explains why frontotemporal dementia can bring with it an artistic renaissance. And here, we introduce you to Matt Cheney and find out what his compulsive laughing and crying jags might reveal about emotion and the human brain.

Then use our blog, below, to let us know what you think.

Listen to the Beyond Alzheimer's radio report online, and watch our Web Extra: Dementia and Artistic Renaissance slideshow.

There are many others also working in the field. The Alzheimer's Association has information about current treatments available. The National Institute on Aging gives a good overview of what avenues of research are being pursued to better diagnose the disease and find a cure. A team of health professionals at the UC Davis Alzheimer's Disease Center can provide a diagnostic work-up, as well as enroll patients in several ongoing clinical trials.

Watch the "Alzheimer's: Is the Cure in the Genes?" TV Story online, as well as find additional links and resources.

Gabriela Quirós is a Segment Producer for KQED-TV, and is the producer for this story.