Metaphors and other figurative language are deeply woven into the fabric of human communication, as this very sentence actually demonstrates. But how do our brains translate these metaphors into something they can understand?
There's a longstanding debate among neuroscientists regarding that question. Let's look at the word "rotten", which literally means "spoiled" but whose metaphorical usage has expanded its definition to include anything bad or unpleasant. We're so used to these other usages that we might not even realize that they are metaphors, but we probably still can tell on an instinctual level that "these eggs are rotten" and "I've had a rotten time" are two fundamentally different usages.
One argument holds that the brain doesn't naturally understand the meaning of metaphors, and it's only through experience that it works out that certain words have multiple meanings that go beyond the literal definition. We come to understand that "rotten" can mean a couple different, albeit related, things, and our brain learns to switch between the definitions depending on context. A second possibility is that when the brain is presented with "rotten" in a metaphorical context, it uses its sensory experiences of rotten things — say, the smell of expired eggs — and works out a probable figurative definition for the word based on those memories.
That's an intriguing thought, but brain scans that have attempted to probe how the mind deals with metaphors have proven inconclusive. We may have reached a breakthrough, thanks to Emory University neurologist Krish Sathian, who zeroed in on how the brain deals with only one specific type of sense-related metaphor. ScienceNOW reports:
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.
These results suggest a strong link between our understanding of metaphors and our sensory perception, although it doesn't quite show that our ability to understand metaphors actually depends on the parietal operculum. Sathian says his next experiment will put this more directly to the test by temporarily disabling this part of the brain and then testing to see how well subjects can then understand these metaphors.