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Metaphors Make Brains Touchy Feely

7 February 2012 5:02 pm
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Adapted from S. Lacey et al., Brain and Language, Online Publication (February 2, 2012)

Mapping metaphor. Touching different textures activates certain areas of the brain, shown in yellow and red. But a new study finds that textural metaphors trigger a reaction, too (shown in green and, where overlapping, brown), in the parietal operculum.

The right turn of phrase can activate the brain's sensory centers, a new study suggests. Researchers have found that textural metaphors—phrases such as "soft-hearted"—turn on a part of the brain that's important to the sense of touch. The result may help resolve a long-standing controversy over how the brain understands metaphors and may offer scientists a new way to study how different brain regions communicate.

Scientists have disagreed for decades about how the brain processes metaphors, those figures of speech that liken one thing to another without using "like" or "as." One camp claims that when we hear a metaphor—a friend tells us she's had a rough day—we understand the expression only because we've heard it so many times. The brain learns that "rough" means both "abrasive" and "bad," this camp says, and it toggles from one definition to the other. The other camp claims the brain calls on sensory experiences, such as what roughness feels like, to comprehend the metaphor. Researchers from both camps have scanned the brain for signs of sensory activity triggered by metaphors, but these past studies, which tested a variety of metaphors without targeting specific senses or regions of the brain, have come up dry.

Neurologist Krish Sathian of Emory University in Atlanta wondered whether using metaphors specific to only one of the senses might be a better strategy. He and his colleagues settled on touch and asked seven college students to distinguish between different textures while their brains were scanned using functional magnetic resonance imaging. This enabled them to map the brain regions each subject used to feel and classify textures. Then they scanned the subjects' brains again as they listened to a torrent of textural metaphors and their literal counterparts: "he is wet behind the ears" versus "he is naïve," for example, or "it was a hairy situation" versus "it was a precarious situation."

The language-processing parts of volunteers' brains became active regardless of whether the volunteers listened to the literal sentences or the metaphors. But textural metaphors also activated the parietal operculum, a region of the brain involved in feeling different textures through touch. That part of the brain didn't light up when listening to a literal sentence expressing the same meaning as the metaphor.

The result suggests the brain's grasp of metaphors is grounded in perception, the team reports online this month in Brain & Language. "We were really excited. This is pretty clear evidence" for the metaphor-through-perception camp, Sathian says.

"This is a very ingenious and elegant approach to the problem," says neuroscientist Vilayanur Ramachandran of the University of California, San Diego. But he says it doesn't quite show that sensory experiences are essential for getting metaphors. To rule out the possibility that the sensory activity is just an incidental byproduct, Ramachandran suggests the researchers try temporarily disabling the parietal operculum with a method called transcranial magnetic stimulation to see if that interferes with people's ability to grasp metaphors. Sathian already plans to pursue this. "These are difficult experiments," Ramachandran says, "but the authors have paved the way."

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