The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

There is no simple answer to this question, but we do know that some very specific brain mechanisms—even specific brain regions—might be critical, because the ability to use metaphors can be selectively lost in certain neurological and psychiatric disorders. For instance, in addition to experiencing difficulty using words and numbers, there are hints that people with damage to the left inferior parietal lobule (IPL) often also lose the ability to interpret metaphors and become extremely literal minded. This hasn’t been “nailed down” yet, but the evidence is compelling.

If asked, “What does ‘a stitch in time saves nine’ mean?” a patient with an IPL stroke might say, “It’s good to stitch up a hole in your shirt before it gets too large.” He will completely miss the metaphorical meaning of the proverb even when told explicitly that it is a proverb. This leads me to wonder whether the angular gyrus may have originally evolved for mediating cross-sensory associations and abstractions but then, in humans, was coopted for making all kinds of associations, including metaphorical ones. Metaphors seem paradoxical: On the one hand, a metaphor isn’t literally true, and yet on the other hand a well-turned metaphor seems to strike like lightning, revealing the truth more deeply or directly than a drab, literal statement.

I get chills whenever I hear Macbeth’s immortal soliloquy from Act 5, Scene 5:

Out, out, brief candle!

Life’s but a walking shadow, a poor player

That struts and frets his hour upon the stage,

And then is heard no more. It is a tale

Told by an idiot, full of sound and fury,

Signifying nothing.

Nothing he says is literal. He is not actually talking about candles or stagecraft or idiots. If taken literally, these lines really would be the ravings of an idiot. And yet these words are one of the most profound and deeply moving remarks about life that anyone has ever made!

Puns, on the other hand, are based on superficial associations. Schizophrenics, who have miswired brains, are terrible at interpreting metaphors and proverbs. Yet according to clinical folklore, they are very good at puns. This seems paradoxical because, after all, both metaphors and puns involve linking seemingly unrelated concepts. So why should schizophrenics be bad at the former but good with the latter? The answer is that even though the two appear similar, puns are actually the opposite of metaphor. A metaphor exploits a surface-level similarity to reveal a deep hidden connection. A pun is a surface-level similarity that masquerades as a deep one—hence its comic appeal. (“What fun do monks have on Christmas?” Answer: “Nun.”) Perhaps a preoccupation with “easy” surface similarities erases or deflects attention from deeper connections. When I asked a schizophrenic what an elephant had in common with a man, he answered “They both carry a trunk” alluding maybe to the man’s penis (or maybe to an actual trunk used for storage).

Leaving puns aside, if my ideas about the link between synesthesia and metaphor are correct, then why isn’t every synesthete highly gifted or every great artist or poet a synesthete? The reason may be that synesthesia might merely predispose you to be creative, but this does not mean other factors (both genetic and environmental) aren’t involved in the full flowering of creativity. Even so, I would suggest that similar—though not identical—brain mechanisms might be involved in both phenomena, and so understanding one might help us understand the other.