According to research led by V. S. Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego, a region of the brain known as the angular gyrus is probably at least partly responsible for the human ability to understand metaphor.
Ramachandran and colleagues tested four right-handed patients with damage to the left angular gyrus. Fluent in English and otherwise intelligent and mentally lucid, the patients showed gross deficits in comprehending such common proverbs as "the grass is always greener on the other side" and "an empty vessel makes more noise." Asked to explain the sayings, the patients tended give responses that were literal. The metaphorical meaning escaped them almost entirely.
When pressed to provide deeper or more general accounts, Ramachandran said, "the patients often came up with elaborate, even ingenious interpretations that were completely off the mark."
Patient SJ, for example, a former physician who could maintain the flow of normal conversation and even retained the ability to correctly diagnose descriptions of symptoms, got all 20 of the 20 proverbs he was tested on wrong. Prodded on "all that glitters is not gold," he finally said that it meant you had to be very careful when buying jewelry because you might get robbed.
The patients were equally bad at matching a bulbous, amoeboid shape to the sound "booba" and a jagged shape to "kiki." Whereas more than 90 percent of ordinary respondents succeed at this task of translating one sort of sensory information into another patients with damage to the angular gyrus performed at the level of chance.
Three age-matched control subjects, on the other hand, with lesions in other areas of the brain, performed normally both with proverbs and the booba/kiki test.