Neuroscientist James Fallon discovered through his work that he has the brain of a psychopath, and subsequently learned a lot about the role of genes in personality and how his brain affects his life

Judith Ohikuare in The Atlantic:

In 2005, James Fallon's life started to resemble the plot of a well-honed joke or big-screen thriller: A neuroscientist is working in his laboratory one day when he thinks he has stumbled upon a big mistake. He is researching Alzheimer's and using his healthy family members' brain scans as a control, while simultaneously reviewing the fMRIs of murderous psychopaths for a side project. It appears, though, that one of the killers' scans has been shuffled into the wrong batch.

The scans are anonymously labeled, so the researcher has a technician break the code to identify the individual in his family, and place his or her scan in its proper place. When he sees the results, however, Fallon immediately orders the technician to double check the code. But no mistake has been made: The brain scan that mirrors those of the psychopaths is his own.

After discovering that he had the brain of a psychopath, Fallon delved into his family tree and spoke with experts, colleagues, relatives, and friends to see if his behavior matched up with the imaging in front of him. He not only learned that few people were surprised at the outcome, but that the boundary separating him from dangerous criminals was less determinate than he presumed. Fallon wrote about his research and findings in the book The Psychopath Inside: A Neuroscientist's Personal Journey Into the Dark Side of the Brain, and we spoke about the idea of nature versus nurture, and what—if anything—can be done for people whose biology might betray their behavior.

More here.