The Frontal Cortex

Is your right parahippocampal gyrus feeling a little tired? Then maybe you should stop being such a sarcastic smart ass. It turns out that this obscure brain area, tucked deep inside the right hemisphere, is largely responsible for the detection of sarcasm, a rather sophisticated element of social cognition:

Dr. Rankin, a neuropsychologist and assistant professor in the Memory and Aging Center at the University of California, San Francisco, used an innovative test developed in 2002, the Awareness of Social Inference Test, or Tasit. It incorporates videotaped examples of exchanges in which a person's words seem straightforward enough on paper, but are delivered in a sarcastic style so ridiculously obvious to the able-brained that they seem lifted from a sitcom.

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.

I'll be writing more about the right hemisphere in a future article, so I don't want to spill the beans, but I do think there's a newfound respect for the right side of the brain among neuroscientists.* We're beginning to realize that, although the left hemisphere excels at the generation of language and the categorization of particulars, and seems to have easier access to consciousness, the right hemisphere is essential for all sorts of cognitive talents that require a little more subtlety and circuitousness. As one scientist recently told me, the left hemisphere helps you see the trees, but the right hemisphere helps you see the forest. Sarcasm and humor, it turns out, require an ability to see the forest.

*It's a shame that the redemption of the right hemisphere has taken this long. Roger Sperry, in his 1981 Nobel lecture, summarized the prevailing view of the right hemisphere when he began studying it: "The right hemisphere was not only mute and agraphic, but also dyslexic, word deaf and apraxic, and lacking generally in higher cognitive function." But Sperry's research with split-brain patients was, at least for him, convincing evidence that the right hemisphere was not a mere accessory. Instead, it was busy doing its own computations, even if those computations were harder to test or investigate in a lab.