Stanislas Dehaene tries to explain how when we read a word, the brain gathers and relays information to multiple networks:
Take the verb “bite.” As you remember what it means, your mind briskly evokes the body parts involved: the mouth and teeth, their movements, and perhaps also the pain associated with being bitten. All of these fragments of gesture, motion, and sensation are bound together under the heading “bite.” This link works in both directions: we pronounce the word whenever we talk about this peculiar series of events, but to hear or read the word brings on a swarm of meanings…
Perhaps the easiest way to describe how activation spreads through the dozens of fragments of meaning dispersed in the brain is to compare it to a tidal bore. Some rivers are subject, twice a day, at high tide, to a peculiar phenomenon whereby the leading edge of a massive wave reaches deep into their estuaries. If conditions are right, the wave can travel dozens of miles upstream. No salt water ever reaches this far inland—the tidal bore simply relays a distant rise in water level that spreads in synchrony into the river’s entire system. Only an airplane or satellite can get the true measure of this beautiful natural phenomenon. For a few minutes, a whole network of streams is simultaneously swollen by a powerful surge of water, simply because they all flow into the same sea.
A written or spoken word probably activates fragments of meaning in the brain in much the same way that a tidal bore invades a whole riverbed. If you compare a word like “cheese” with a non-word like “croil,” the only difference lies in the size of the cortical tidal wave that they can bring on. A known word resonates in the temporal lobe networks and produces a massive wave of synchronized oscillations that rolls through millions of neurons. This tidal bore goes even as far as the more distant regions of the cortex as it successively contacts the many assemblies of neurons that each encode a fragment of the word’s meaning. An unknown word, however, even if it gets through the first stages of visual analysis, finds no echo in the cortex and the wave it triggers is quickly broken down into inarticulate cerebral foam.
What a metaphor! A wave, like a thought, consists of countless micro-events which appear to us as a single complex phenomenon. If a stray thought is a wave, then reading is the wave of waves, transversing a network of networks — or a tidal bore.
Which reminds me: So far in the book, Dehaene hasn’t talked about how the brain processes metaphor. It might not be directly tied to reading, but man, I’d love to hear what he has to say. Until then, I guess I’m sticking with that other great French neuroscientist, Marcel Proust.