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WORDS, SPOKEN AND OTHERWISE The exquisite specialization of neurons for processing very precise sorts of information -- moving but not still objects, the sensation of touch on a finger that isn't there anymore -- is perhaps at its most highly refined when it comes to language. As a result, brain-damaged patients can exhibit an astounding range of language problems. Some have trouble using and understanding just nouns. Others have trouble with verbs. Some patients can't produce language but comprehend it perfectly; others can speak normally but can't make any sense out of what they hear.
University of Washington neurosurgeon Dr. George Ojemann has discovered, by probing the brain with electrodes, that some neurons turn on when one is silently naming an object to oneself but not during reading and vice versa. In one bilingual patient he found neurons that were activated by Finnish but not English. In another he found neurons that changed activity with English but not Spanish. And, marvels Ojemann, "the neurons that are active when you hear a word are not active when you express it."
Until recently, scientists assumed that the brain processed language in two neatly defined boxes: Broca's area (for speech production) and Wernicke's area (for speech comprehension). The picture now emerging is far more complex. The University of Iowa's Damasio, along with his wife Hanna, also a neurologist, has recently constructed a model for how the brain processes language based on some 200 unusual case histories, most prominent among them a patient code-named Boswell. Boswell has no function in large areas of his brain, owing to an infection. One consequence is that he has no memory of recent events. Nonetheless, he is able to speak and understand language perfectly well-up to a point.
Prompted with "Denver," Boswell unfailingly responds, "Colorado." Asked to name a city in Colorado, however, he goes blank. Similarly, Boswell recognizes the category "horse" but cannot supply the example "Appaloosa." He knows "U.S. President" but not Harry Truman or Richard Nixon. Somewhere in his brain, the data may still exist, but he can no longer get at them. The reason, argue the Damasios, is that he has lost essential "convergence zones," mental switching stations that provide access to the information and relate it to other relevant data.
Using an MRI scanner, Hanna Damasio has examined the living brains of hundreds of patients, and she and her husband have identified regions they think may serve as convergence zones in the brain's left hemisphere. An area in the temporal lobe pulls together information about the names of objects, animals and people, for instance, while another area in the frontal cortex appears to act as the nexus for verbs. Yet a third oversees the task of assembling nouns and verbs into sentences.
CREATING THE SELF The Damasios suspect that convergence zones-thousands of them, spread through the cortex-do more than just process language. They may also coordinate every other sort of information the brain needs-perception, memory, emotion-to be fully functional. And if that's true, the convergence zones, merging disparate pieces of information into a semblance of a whole, could be responsible for that most elusive of brain phenomena: consciousness, the sense of being in the here and now.