With the help of the New York Times, neuropsychologist Katherine P. Rankin dissects for us what it means to recognize sarcasm.

In one videotaped exchange, a man walks into the room of a colleague named Ruth to tell her that he cannot take a class of hers that he had previously promised to take. “Don’t be silly, you shouldn’t feel bad about it,” she replies, hitting the kind of high and low registers of a voice usually reserved for talking to toddlers. “I know you’re busy — it probably wasn’t fair to expect you to squeeze it in,” she says, her lips curled in derision.

Although people with mild Alzheimer’s disease perceived the sarcasm as well as anyone, it went over the heads of many of those with semantic dementia, a progressive brain disease in which people forget words and their meanings.

“You would think that because they lose language, they would pay close attention to the paralinguistic elements of the communication,” Dr. Rankin said.

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 of the brain, 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.

Well then. That just explains everything, doesn’t it? I hope the very important Dr. Rankin knows how much we all appreciate her contribution to civil discourse.