by Sam Kean
The meeting had all the makings of high scientific drama. Broca entered with Tan’s freshly disembodied brain—confronting a skeptical audience, yet armed with the first solid evidence, ever, of brain localization. It might have been Huxley versus Wilberforce part deux, and indeed, Broca’s latter-day disciples have infused his talk that day with an almost supernatural significance. In truth, Broca did little more than present the brain for inspection and summarize Tan’s medical history; he mentioned his conclusion about the language node only briefly, without pressing it. His would-be opponents all but yawned, and as soon as Broca finished they delved into a much juicier debate about race, brain size, and intelligence.
Race, brain size, and intelligence obsessed Broca, too, and he had much to contribute to the discussion, which ended up dominating the society’s agenda for months. Nevertheless, Broca kept mentioning Tan’s brain here and there at subsequent meetings, and one cog in his own brain kept turning over Tan’s “aphasia,” as the neurological loss of speech is now known. He preserved Tan’s brain in alcohol, then placed the pickled mass in a jar for future study. Meanwhile he scouted around for other aphasics, and soon encountered a patient who deserves to be every bit as famous as Tan.
Like Tan, “Lelo” earned his nickname based on what little he could say. An octogenarian ditchdigger, Monsieur Lelong had suffered a stroke eighteen months before Broca met him in October 1861. He’d lost all ability to speak, save for five words: “Lelo,” his name for himself; “oui”; “non”; “tois,” for trois, three, which stood for all numbers; and “toujours,” always, which stood for the rest of the dictionary. Ask him how many daughters he’d sired, and he’d say “tois” and hold up two fingers. Ask him what he did for a living, and he’d say “toujours,” and mime shoveling dirt.
History records little else about Lelo, except that complications from a broken femur soon killed him. But when he died, Broca performed probably the most important brain autopsy since Henri II’s. Going in, Broca felt anxious, edgy: if he found no lesion in Lelo’s brain—or a lesion in the wrong place—he’d be mocked. He sawed the skull carefully and cracked open the shell. He needn’t have worried. Whereas Tan’s brain looked pulverized, with widespread putrefaction, Lelong’s brain had a single BB hole of damage. And Broca himself must have cried Sacré nom de Dieu! upon seeing the location: near the back of the frontal lobe. This location* is now known as Broca’s area.
Broca’s announcement of a language node inside the human brain caused no big stir among the public. (Paris newspapers were tittering instead about the underwhelming premiere—full of catcalls and raspberries—of Richard Wagner’s Tannhäuser.) But the discovery ricocheted through the learned societies of Europe, leaving scientists agog. Could localization be real? Two subsequent developments suggested yes. First, Broca confirmed his initial findings in more patients. After 1861 doctors started referring aphasics to Broca for further study, and by 1864 he’d done autopsies on twenty-five of them. Every victim save one had a lesion in the rear frontal lobe. Moreover, the nature of the damage—tumors, strokes, syphilis, trauma—didn’t matter, only its location, location, location.
The second development had even more profound consequences for understanding how language works inside the brain. In 1876 a twenty-six-year-old German medical student named Karl Wernicke (of Wernicke-Korsakoff fame) discovered a new type of aphasia. Specifically, Wernicke found that lesions near the back of the temporal lobe—well distant from Broca’s area—destroyed the meaning of language for people. Whereas Broca’s aphasics knew what they wanted to say but sputtered in saying it, Wernicke’s aphasics could string together sentences of Proustian length, with quite fetching rhythms; the sentences just didn’t make sense. (Some neuroscientists call this a word salad—random chunks of phrases tossed together. I’d call it Finnegans Wake syndrome.) And unlike Broca-type aphasics, who get quite frustrated, Wernicke-type aphasics remain oblivious; doctors can spout gibberish right back at them, and they’ll nod and grin. Generally speaking, a broken Broca’s area knocks out speech production, while a wrecked Wernicke’s area impairs speech comprehension.
Functionally, Broca’s area helps the mouth form and articulate words, so when this area falters, sentences get choppy and people have to pause frequently. Moreover, it helps generate proper syntax, so Broca aphasics use almost no syntax or conjunctions to string concepts together: “Dog—bit—girl.” Wernicke’s area, in contrast, links words to their meanings—it fuses signifier with signified inside your brain. To see how the areas work together, imagine that the person next to you suddenly says “Zeppelin.” First your ear relays this input to your auditory cortex, which in turn relays it to Wernicke’s area. Wernicke’s then dredges up the proper associations in your memory, causing you to glance skyward, hear a guitar riff, or think, “Oh, the humanity!” Sound and meaning are thereby united. If you decide to repeat “zeppelin” aloud (and why not?), Wernicke’s area first matches up the concept of “zeppelin” with the auditory representation stored in your brain. Wernicke’s then sends out a signal that arouses Broca’s area, which in turn arouses the strip of motor cortex that controls your lips and tongue. If your Wernicke’s cannot match up the words and ideas, it’s word salad time. (Infants cannot produce or understand language in part because their Wernicke’s area hasn’t matured.) If Broca’s area fouls up, you sputter.
Beyond finding a new language node, Wernicke made a more general point about language inside the brain, a point worth italicizing: there is no single “language spot” up there. As with memory, many different regions contribute to understanding and producing language, which explains why people can lose the ability to speak without losing the ability to comprehend, or vice versa. If other language nodes crumble, or if the white-matter cables between two language nodes get severed, language skills can break down in other ways as well, some of them startlingly specific.
Some stroke victims can remember nouns but not verbs, or vice versa. People fluent in two languages can lose either one after trauma, since first and second languages* draw on distinct neural circuits. Language deficits can even interfere with math. We seem to have a natural “number circuit” in the parietal lobe that handles comparisons and magnitudes—the basis of most arithmetic. But we learn some things (like the times tables) linguistically, by rote memorization. So if language goes kaput, so too will those linguistically based skills.
More strikingly, some people who struggle to string even three words together can sing just fine. For whatever reason, melody and rhythm can bypass broken circuits and jump-start language production—allowing someone who stammers through “I—like—ham” to rip through “The Battle Hymn of the Republic” moments later. (After being shot in the brain, former congresswoman Gabrielle Giffords learned how to speak again by practicing with song lyrics, including “Girls Just Wanna Have Fun.”) Similarly, emotions can also resurrect dead language circuits: many aphasics (like Tan) can swear if provoked, but never intentionally. The dissociations between singing, speaking, and swearing imply, again, that our brains don’t have a single language spot; there’s no neurological “pantry” where we keep our words.
Perhaps the most startling example of language disconnect is called alexia sine agraphia, a reading disorder. Reading actually requires a higher degree of neurological dexterity than speaking does. Printed words enter our brains through the visual cortex easily enough, but because we humans started reading so late in our evolutionary history—around 3000 BC—the visual cortex doesn’t naturally wire itself up to Wernicke’s area. (Why would it?) A little training with Dick and Jane can nevertheless rewire the brain and patch those two areas together—allowing us to conjure up concepts and stories from mere dashes of ink. Reading changes the way our brains work.
People with alexia sine agraphia, however, cannot read a lick, because of broken axons in the visual cortex: the curves and shapes of letters get into their brains just fine, but the data never reach Wernicke’s area and never get co
nverted into meaningful information. As a result, sentences look like they’re written in or . Yet these people can write just fine, because the brain’s meaning centers can still access downstream motor circuits that control handwriting. This leads to the farcical situation of someone being able to write down a sentence—“I’m allergic to beer”—but not being able to read what he just wrote.
As much as anything, language makes us human, and Broca earned his bust on the Mount Rushmore of modern neuroscience largely for discovering the first language node. Truth be told, though, Wernicke’s idea of language circuits is more in harmony with our current understanding of language. And while Broca also usually gets credit for discovering brain localization, Auburtin* and even the phrenologists pushed the idea of localization first, and pushed it harder. It was simply Broca’s eminence, his vivid clinical reports, and especially his luck in finding Tan and Lelo that transformed those other scientists’ intuitions into scientific fact.
By all rights Broca should also share credit for the other major discovery usually attributed to him, brain lateralization. By the mid-1800s scientists knew that the left hemisphere controls the right side of the body and vice versa. But scientists still believed, deeply, in brain symmetry—the idea that both halves of the brain worked the same way. After all, each hemisphere looked identical, and in no other paired body part (eyes, kidneys, gonads) did lefty and righty function differently. So when doing autopsies on aphasics, Broca ignored any hemispherical differences and concentrated solely on longitude and latitude. Only in early 1863 did he realize that all his aphasics so far had left frontal lobe damage. He chewed on the potential meaning of this in private—could the left hemisphere control language? “But I could not easily resign myself,” he later admitted, “to such a subversive consequence.”
Others proved less timid. In March 1863, while Broca hemmed and hawed, an obscure country physician named Gustave Dax submitted a three-decades-old manuscript to the Académie Nationale de Médecine in Paris, hoping to publish it. In an accompanying letter Dax explained that the manuscript belonged to his late father, Dr. Marc Dax, who had compiled case reports on dozens of patients who’d lost the ability to speak after suffering frontal lobe damage. Dax père had then presented the manuscript at a conference in Montpellier in 1836, but had been unjustly ignored ever since. Because all his patients had injuries in roughly the same place, the elder Dax concluded that the frontal lobe contained a language spot—exactly what Broca had proposed only two years before. Furthermore, since all these lesions appeared on the left side, the left hemisphere must control language—exactly the idea Broca was playing around with now.
The history of science is full of examples of two or more people discovering something independently—oxygen, sunspots, calculus, the periodic table. But few priority disputes have proved as messy as the Broca-Dax affair. Broca made his first tentative public statement about the left hemisphere being the seat of language in early April 1863, just days after the Dax manuscript surfaced in Paris. The contents of a manuscript submitted to the Académie were supposedly confidential, but Broca had friends there, and almost certainly knew of its conclusions ahead of time. What’s more, the Académie took its sweet time reviewing the paper for publication, first referring it to committee (that ultimate tool of bureaucratic obstruction) and then holding it for over a year. Dax eventually had to publish the manuscript himself, and the delay gave Broca time to develop his ideas.
However, the younger Dax—by all accounts an obnoxious fellow—didn’t take this subterfuge lying down. He railed against the Académie’s stall tactics and rallied support among scientists in southern France, who generally resented their snooty Parisian colleagues. Dax also accused Broca of stealing his dear father’s ideas, by purposely failing to cite his father’s work. Broca took this charge seriously and began to hunt down other scientists who’d attended the Montpellier conference in 1836, to ask about Dax’s presentation there.
Oddly, though, none of the attendees remembered Dax’s work. And after a few months of dead ends, Broca came away unsure whether Dax had even attended the conference, much less presented there. As a matter of fact, the only evidence that the elder Dax had ever studied language lesions was the original draft of the manuscript, which supposedly dated from the 1830s. That provenance, however, depended on the younger Dax’s word, and Broca naturally grew suspicious. He even analyzed the writing style of both Daxes, to see if Dax fils had tried to pass off a forgery. (Broca ruled the document authentic, but he was no linguist.)
The Broca-Dax affair remains clouded today. There’s no question Broca was the superior scientist. Like Darwin with natural selection or Mendeleev with the periodic table, Broca didn’t discover lateralization alone; but also like those men, his work was an order of magnitude more developed than any rival claim. Dax didn’t even confirm the location of his patient’s lesions with autopsies; he simply guessed, based on where patients said they’d been smacked. Nevertheless, Dax got it right—the left brain does control language—and in science, getting it right first often counts for everything.
The tougher debate is how much Broca knew and when he knew it. The younger Dax’s bitching notwithstanding, Broca almost certainly didn’t rip off his father wholesale. But did the manuscript influence Broca? Perhaps it was a coincidence that Broca felt confident enough to start speaking about left-side specialization shortly after the manuscript arrived in Paris. Or perhaps hearing of the manuscript convinced Broca that he was on the right track. Most historians agree that Marc Dax and Paul Broca probably did discover left-right lateralization independently. But good luck determining how much Dax influenced Broca, or whether Dax gave him the courage to pursue an avenue he might not have.
Amid all this squabbling, Broca withdrew somewhat from neuroscience, and after about 1866 he decided to focus more on other scientific topics, such as skulls. In 1867 he wowed the world by determining that a pre-Columbian skull from Peru—which had a square hole carved into it—was evidence of ancient neurosurgery. Broca even declared, correctly, that the patient had survived the operation, based on healing scars around the hole’s rim. Around the same time he saved a man’s life by performing the first neurosurgery based on localization theory. A patient had lost the ability to speak after head trauma, and instead of removing half the man’s skull to explore, Broca opened a small hole over his eponymous area and relieved the pressure.
Meanwhile, Broca began dabbling in politics. During a tumultuous coup attempt in 1871, he smuggled 75 million francs’ worth of gold to Versailles in a hay cart (some sources say a potato cart), to help the exiled government. The powers that be never rewarded him, but the French people did elect Broca a “lifetime Senator” in 1880. Before he could really enjoy the honor, though, he died a few months later at age fifty-six—fittingly, of brain trouble, a hemorrhage.
After his untimely death scientists more or less beatified Broca, and brain lateralization became a pillar of twentieth-century neuroscience. In fact, as so often happens, this former heresy became the new orthodoxy: by the 1950s most neuroscientists had declared the left hemisphere home to not just language but all of our highest faculties and skills. Humankind was its left brain. And not content to merely praise the left brain, scientists simultaneously demeaned the right brain, dismissing it as the left’s slower, imbecilic, even “retarded” twin. It would take one pissed-off Nazi, and decades of follow-up work, to prove otherwise.
In 1944 a thirty-year-old American officer, W.J., leapt out of a plane over Holland to help liberate the Dutch. His parachute opened only partway, and he hit the ground like a sandbag, breaking his leg and knocking himself unconscious. Upon waking he began pissing blood, and soon became a Nazi captive. At some point—perhaps while being herded around a POW camp—he enraged a guard, who wound up and cracked him on the skull with his rifle butt. W.J. crumpled, and probably suffered a brain hemorrhage. He barely got any treatment over the next year, and lost almost a hundred pounds.
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bsp; After the war W.J. found work as a payroll courier in Los Angeles. But he started having what are called “absences”: he’d start his car, pull out—then find himself fifty miles away, having no idea how he’d got there. He began having seizures, too. His aura felt like a Ferris wheel rumbling to life inside him, and his head would jerk left; he’d grimace and occasionally yell “Bail out, Jerry!” before collapsing. He didn’t soil himself, but he banged and scraped his head a lot and once fell into a fire. Perhaps worst, the frequency of seizures—up to twenty per day by the later 1950s—left him mentally dazed. Whereas before the war he’d read Greek history and Victor Hugo with enthusiasm, now he could manage only newspaper headlines. So in 1962 he agreed to let two L.A. surgeons perform an operation every bit as desperate as H.M.’s surgery a decade earlier. They proposed slicing clean through W.J.’s corpus callosum.
You can’t see the corpus callosum unless you peel the brain’s two halves apart and peer into the gully. It looks like a bundle of off-white twine, and it connects the two hemispheres like Siamese twins. It’s one of the few brain structures we have just one of, and in past centuries at least a few scientists pinned the indivisible human soul there for this reason. By the 1900s scientists didn’t view the corpus callosum as a sanctum sanctorum anymore, but damn them if they knew what it did do. It consists of 200 million white-matter fibers, which implied a role in interhemispheric communication. (The next beefiest bundle connecting the hemispheres contains just 50 thousand fibers.) Still, X-rays showed that some people were born without a corpus callosum, and they seemed fine.