There was nothing very interesting in Katherine P. Rankin’s study of sarcasm  at least, nothing worth your important time. All she did was use an M.R.I. to find the place in the brain where the ability to detect sarcasm resides. But then, you probably already knew it was in the right parahippocampal gyrus.

What you may not have realized is that perceiving sarcasm, the smirking put-down that buries its barb by stating the opposite, requires a nifty mental trick that lies at the heart of social relations: figuring out what others are thinking. Those who lose the ability, whether through a head injury or the frontotemporal dementias afflicting the patients in Dr. Rankin’s study, just do not get it when someone says during a hurricane, “Nice weather we’re having.”

“A lot of the social cognition we take for granted and learn through childhood, the ability to appreciate that someone else is being ironic or sarcastic or angry  the so-called theory of mind that allows us to get inside someone else’s head  is characteristically lost very early in the course of frontotemporal dementia,” said Dr. Bradley F. Boeve, a behavioral neurologist at the Mayo Clinic in Rochester, Minn.

“It’s very disturbing for family members, but neurologists haven’t had good tools for measuring it,” he went on. “That’s why I found this study by Kate Rankin and her group so fascinating.”