The Language Instinct: How the Mind Creates Language (53 page)

So is Broca’s area the grammar organ? Not really. Damage to Broca’s area alone usually does not produce long-lasting severe aphasia; the surrounding areas and underlying white matter (which connects Broca’s area to other brain regions) must be damaged as well. Sometimes symptoms of Broca’s aphasia can be produced by a stroke or Parkinson’s disease that damages the basal ganglia, complex neural centers buried inside the frontal lobes that are otherwise needed for skilled movement. The labored speech output of Broca’s aphasics may be distinct from the lack of grammar in their speech, and may implicate not Broca’s area but hidden parts of the cortex nearby that tend to be damaged by the same lesions. And, most surprisingly of all, some kinds of grammatical abilities seem to survive damage to Broca’s area. When asked to distinguish grammatical from ungrammatical sentences, some Broca’s aphasics can detect even subtle violations of the rules of syntax, as in pairs like these:

Still, aphasics do not detect all ungrammaticalities, nor do all aphasics detect them, so the role of Broca’s area in language is maddeningly unclear. Perhaps the area underlies grammatical processing by converting messages in mentalese into grammatical structures and vice versa, in part by communicating via the basal ganglia with the prefrontal lobes, which subserve abstract reasoning and knowledge.

Broca’s area is also connected by a band of fibers to a second language organ, Wernicke’s area. Damage to Wernicke’s area produces a very different syndrome of aphasia. Howard Gardner describes his encounter with a Mr. Gorgan:

Wernickc’s aphasia is in some ways the complement of Broca’s. Patients utter fluent streams of more-or-less grammatical phrases, but their speech makes no sense and is filled with neologisms and word substitutions. Unlike many Broca’s patients, Wernicke’s patients have consistent difficulty naming objects; they come up with related words or distortions of the sound of the correct one:

A striking symptom of Wernicke’s aphasia is that the patients show few signs of comprehending the speech around them. In a third kind of aphasia, the connection between Wernicke’s area and Broca’s is damaged, and these patients are unable to repeat sentences. In a fourth kind, Broca’s and Wernicke’s and the link between them are intact but they are an island cut off from the rest of the cortex, and these patients eerily repeat what they hear without understanding it or ever speaking spontaneously. For these reasons, and because Wernicke’s area is adjacent to the part of the cortex that processes sound, the area was once thought to underlie language comprehension. But that would not explain why the speech of these patients sounds so psychotic. Wernicke’s area seems to have a role in looking up words and funneling them to other areas, notably Broca’s, that assemble or parse them syntactically. Wernicke’s aphasia, perhaps, is the product of an intact Broca’s area madly churning out phrases without the intended message and intended words that Wernicke’s area ordinarily supplies. But to be honest, no one really knows what either Broca’s area or Wernicke’s area is for.

Wernicke’s area, together with the two shaded areas adjacent to it in the diagram (the angular and supramarginal gyri), sit at the crossroads of three lobes of the brain, and hence are ideally suited to integrating streams of information about visual shapes, sounds, bodily sensations (from the “somatosensory” strip), and spatial relations (from the parietal lobe). It would be a logical place to store links between the sounds of words and the appearance and geometry of what they refer to. Indeed, damage to this general vicinity often causes a syndrome that is called
anomia
, though a more mnemonic label might be “no-name-ia,” which is literally what it means. The neuropsychologist Kathleen Baynes describes “HW,” a business executive who suffered a stroke in this general area. He is highly intelligent, articulate, and conversationally adept but finds it virtually impossible to retrieve nouns from his mental dictionary, though he can understand them. Here is how he responded when Baynes asked him to describe a picture of a boy falling from a stool as he reaches into a jar on a shelf and hands a cookie to his sister:

HW uses noun phrases perfectly but cannot retrive the nouns to put inside them: he uses pronouns, gerunds like
falling down
, and a few generic nouns like
food
and
stuff
, referring to particular objects with convoluted circumlocutions. Verbs tend to pose less of a problem for anomics; they are much harder for Broca’s aphasics, presumably because verbs are intimately linked to syntax.

There are other indications that these regions in the rear of the pensylvian are implicated in storing and retrieving words. When people read perfectly grammatical sentences and come across a word that makes no sense, like
The boys heard Joe’s orange about Africa
, electrodes pasted near the back of the skull pick up a change in their EEG’s (although, as I have mentioned, it is only a guess that the blips are coming from below the electrodes). When people put their heads in the PET scanner, this general part of the brain lights up when they hear words (and pseudo-words, like
tweal
) and even when they read words on a screen and have to decide whether the words rhyme—a task requiring them to imagine the word’s sounds.

A very gross anatomy of the language sub-organs within the perisylvian might be: front of the perisylvian (including Broca’s area), grammatical processing; rear of the perisylvian (including Wernicke’s and the three-lobe junction), the sounds of words, especially nouns, and some aspects of their meaning. Can we zoom in still closer, and locate smaller areas of brain that carry out more circumscribed language tasks? The answer is no and yes. No, there are no smaller patches of brain that one can draw a line around and label as some linguistic module—at least, not today. But yes, there must be portions of cortex that carry out circumscribed tasks, because brain damage can lead to language deficits that are startlingly specific. It is an intriguing paradox.

Here are some examples. Although impairments of what I have been calling the sixth sense, speech perception, can arise from damage to most areas of the left perisylvian (and speech perception causes several parts of the perisylvian to light up in PET studies), there is a specific syndrome called Pure Word Deafness that is exactly what it sounds like: the patients can read and speak, and can recognize environmental sounds like music, slamming doors, and animal cries, but cannot recognize spoken words; words are as meaningless as if they were from a foreign language. Among patients with problems in grammar, some do not display the halting articulation of Broca’s aphasia but produce fluent ungrammatical speech. Some aphasics leave out verbs, inflections, and function words; others use the wrong ones. Some cannot comprehend complicated sentences involving traces (like
The man
who the woman kissed
(trace)
hugged the child
) but can comprehend complex sentences involving reflexives (like
The girl said that the woman washed herself
). Other patients do the reverse. There are Italian patients who mangle their language’s inflectional suffixes (similar to the -
ing, -s
, and -
ed
of English) but are almost flawless with its derivational suffixes (similar to -
able, -ness
, and -
er
).

The mental thesaurus, in particular, is sometimes torn into pieces with clean edges. Among anomic patients (those who have trouble using nouns), different patients have problems with different kinds of nouns. Some can use concrete nouns but not abstract nouns. Some can use abstract nouns but not concrete nouns. Some can use nouns for nonliving things but have trouble with nouns for living things; others can use nouns for living things but have trouble with nouns for nonliving things. Some can name animals and vegetables but not foods, body parts, clothing, vehicles, or furniture. There are patients who have trouble with nouns for anything but animals, patients who cannot name body parts, patients who cannot name objects typically found indoors, patients who cannot name colors, and patients who have trouble with proper names. One patient could not name fruits or vegetables: he could name an abacus and a sphinx but not an apple or a peach. The psychologist Edgar Zurif, jesting the neurologist’s habit of giving a fancy name to every syndrome, has suggested that it be called anomia for bananas, or “banananomia.”

Does this mean that the brain has a produce section? No one has found one, nor centers for inflections, traces, phonology, and so on. Pinning brain areas to mental functions has been frustrating. Frequently one finds two patients with lesions in the same general area but with different kinds of impairment, or two patients with the same impairment but lesions in different areas. Sometimes a circumscribed impairment, like the inability to name animals, can be caused by massive lesions, brain-wide degeneration, or a blow to the head. And about ten percent of the time a patient with a lesion in the general vicinity of Wernicke’s area can have a Broca-like aphasia, and a patient with lesions near Broca’s area can have a Wernicke-like aphasia.

Why has it been so hard to draw an atlas of the brain with areas for different parts of language? According to one school of thought, it is because there aren’t any; the brain is a meatloaf. Except for sensation and movement, mental processes are patterns of neuronal activity that are widely distributed, hologram-style, all over the brain. But the meatloaf theory is hard to reconcile with the amazingly specific deficits of many brain-damaged patients, and it is becoming obsolete in this “decade of the brain.” Using tools that are getting more sophisticated each month, neurobiologists are charting vast territories that once bore the unhelpful label “association cortex” in the old textbooks, and are delineating dozens of new regions with their own functions or styles of processing, like visual areas specializing in object shape, spatial layout, color, 3D stereo-vision, simple motion, and complex motion.

For all we know, the brain might have regions dedicated to processes as specific as noun phrases and metrical trees; our methods for studying the human brain are still so crude that we would be unable to find them. Perhaps the regions look like little polka dots or blobs or stripes scattered around the general language areas of the brain. They might be irregularly shaped squiggles, like gerrymandered political districts. In different people, the regions might be pulled and stretched onto different bulges and folds of the brain. (All of these arrangements are found in brain systems we understand better, like the visual system.) If so, the enormous bomb craters that we call brain lesions, and the blurry snapshots we call PET scans, would leave their whereabouts unknown.