The Anatomy of Sarcasm

There was nothing very interesting in Katherine P. Rankin’s study of sarcasm . 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 requires the ability to figure out what others are thinking. Those who lose that ability, whether through a head injury or through frontotemporal dementia , just do not get it when someone says during a hurricane, “Nice weather we’re having.
“ 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, Minnesota. “It’s very disturbing for family members, but neurologists haven’t had good tools for measuring it.”
Dr. Rankin, a neuropsychologist and assistant professor in the Memory and Aging Center at the University of California, San Francisco, used a test developed in 2002, the Awareness of Social Inference Test, or Tasit. It incorporates videotaped examples of exchanges in which a person’s words are delivered in a sarcastic style that is ridiculously obvious to the able-brained .
Although people with mild Alzheimer’s disease perceived the sarcasm as well as anyone, many of those with semantic dementia, a progressive brain disease in which people forget words and their meanings, did not.
To her surprise, though, the magnetic resonance scans revealed that the part of the brain lost among those who failed to perceive sarcasm was not in the left hemisphere , which specializes in language and social interactions, but in a part of the right hemisphere previously identified as important only to detecting contextual background changes in visual tests.
“The right parahippocampal gyrus must be involved in detecting more than just visual context - it perceives social context as well, Dr. Rankin said.
The discovery fits with an increasingly nuanced view of the right hemisphere’s role, said Dr. Anjan Chatterjee, an associate professor in the Center for Cognitive Neuroscience at the University of Pennsylvania.
“The left hemisphere does language in the narrow sense, understanding of individual words and sentences, Dr. Chatterjee said. “But it’s now thought that the appreciation of humor and language that is not literal, puns and jokes, requires the right hemisphere.
Dr. Boeve, at the Mayo Clinic, said that the study offered hope that a test like Tasit could help in the diagnosis of frontotemporal dementia. Short of giving such a test, he said, the best way to diagnose such problems is by talking with family members about changes in the person’s behavior.
After a presentation of her findings at the American Academy of Neurology’s annual meeting in April, Dr. Rankin was asked whether even those with intact brains might have differences in brain areas that explain how well they pick up on sarcasm.
“There may be volume-based differences in certain regions that explain variations in all sorts of cognitive abilities, she said.