by Sam Kean
While adjusting to his new, sedentary life in England, he earned an appointment as a Naval Knight of Windsor—which sounded grand, but in reality meant drear and tedium. His only duty was attending chapel twice a day and saying extra prayers for the king, his lords, and various toadies around Windsor Castle. The rest of the time he sat around his small apartment, alone, and did nothing; he couldn’t even read. Holman found life at Windsor such an existential torture that his physical health deteriorated, and a case of wanderlust gripped him. He soon fled England and spent much of the rest of his life roaming, plunging headlong into odd and often dangerous corners of the globe.
For one early trip, he got it into his head to cross Siberia. Thanks to the atrocious, teeth-rattling ruts on the roads, he ended up walking much of the way—strolling alongside the cart, holding on to a rope. But before reaching the Pacific he got kidnapped by officials of the tsar and deported as a spy, since no one believed that anyone would travel Siberia for fun. On later trips he chased down slave traders; mapped the Australian Outback; negotiated with headhunters; dodged forest fires; charged into war zones; and crossed the Indian Ocean on a ship carrying a cargo of sugar and champagne (it wasn’t all hardship). He also climbed Mount Vesuvius in mideruption, a jaunt that nearly burned the soles off his shoes but proved to him that he could handle anything, despite his handicap. Along the way he earned a reputation as quite a ladies’ man, and he did good enough scientific work (on the drifting of seeds among islands) to get elected to the Royal Society and cited by Charles Darwin. He rarely traveled in luxury—his pension amounted to just £84 yearly—and he stretched that further by packing his own meals (usually fruit, wine, and tongue, a cut-rate meat that didn’t spoil) and by wearing his old naval uniform everywhere. Altogether Holman and his naval jacket, straw hat, and cane traveled 250,000 miles*—equivalent to ten trips around the equator or one trip to the moon, making him the most prolific traveler the world had ever known.
He returned to England as little as possible, and whenever he did find himself marooned at home, he took advantage of his downtime to write travel books. Eclectic and rambling, they might include soy sauce recipes on one page, advice for hunting kangaroos on the next, and he was constantly quoting the many poems he’d had to memorize. (He also included plenty of gossip about robberies, affairs, and local customs like sponge baths.) Before Holman even finished writing a book, though, that old desire to roam would well up inside him. Indeed, with his first book, published in 1822, he scurried to leave England almost before he’d finished the page proofs. The book became a bestseller, but by the time the London literati got hold of it and could flip to the frontispiece to see a portrait of this curious author, Holman was a thousand miles distant.
Holman couldn’t have known it, but that frontispiece, while handsome overall, had one unsettling feature: his eyes, which seemed to look in different directions. Later portraits were even less flattering. In one book’s frontispiece he looked drugged, with eyes unfocused. A later oil portrait showed him with an unsightly Rip Van Winkle beard and, again, vacant white eyes. In another depiction Holman is shown with his hand draped over a blank white globe, as if embracing a giant, irisless eyeball. Portraying him with a globe devoid of all features seems baffling at first, since Holman had covered more of the earth’s surface than anyone alive. In truth, the blankness was fitting. Holman, you see, was blind.
His health troubles had started in the navy. His ship’s patrol route yo-yoed endlessly between Nova Scotia, where the wind practically froze icicles inside men’s noses, and the Caribbean, where the sunlight beat down hot enough to melt candles. Something about those extremes ruined his joints, and his ankles grew so stiff and sore that he could no longer pull on his boots, much less negotiate the rolling decks. He took shore leave and recovered, but more bitter nor’easters and more wilting afternoons finally broke him. Soon his eyes began to ache something awful: mere sunlight felt like needles piercing his retinas. His world gradually fell dark, and even though his doctors treated his eyes with leeches, poultices, opium, and lead ointments, nothing could rescue his vision. Segments of his optic nerves* finally died when he was twenty-five, severing that connection to the brain and leaving him permanently sightless. He would eventually set foot in nearly every country on earth, but would set eyes on none of them.
Holman almost never got the chance to travel, thanks to his pseudo-ennoblement. Naval Knight bylaws said that he and his six fellow knights could not be absent from England more than ten days per year. Holman obeyed at first, but the monotony of life at Windsor proved unendurable, and after just a few months there his fevers returned and his flying gout began clawing at him again. He needed activity, stimulation, and his doctors begged the two wardens of the Naval Knights to let him catch the next ship out. The wardens, sympathetic at first, let Holman go, and the travel worked wonders. When he returned to Windsor, though, and the tedium descended, his aches and pains started to torment him anew. He got another travel visa and immediately felt better. But the illness started right up again after the next homecoming. And the next, and the next. Writing books allayed the pain a little—memory is a powerful analgesic—but each time he finished a manuscript he felt worse, and needed more leave to recover. After Holman missed some state funerals and coronations, the Windsor wardens began to grumble.
They weren’t the only ones. After each book appeared, pundits would challenge the very idea that a blind man had, or even could have, traveled so widely. As we’ll see, modern neuroscience lends credence to Holman, but in the early 1800s, society treated blind people pretty shabbily. Most blind folk simply scrounged up a bowl and started begging for farthings. The luckier ones (arguably) worked in traveling carnivals, where they were dressed up in donkey ears and/or huge fake eyeglasses and shoved onstage. There, they stumbled around without any real script; the entertainment lay in watching the production fall to shambles. Beggars and buffoons were what people thought of when they thought of the blind, not circumnavigation and adventure.
Even those who didn’t dismiss Holman condescended to him. “I am constantly asked…” he once wrote, “what is the use of travelling to one who cannot see?” Some idiots questioned whether Holman had really left England, since all seven continents must look the same to him. Holman gritted his teeth and explained that foreign lands sounded different, smelled different, had different weather patterns and different daily rhythms. And in fact, Holman rarely neglected other senses in his writing. Timbers squeal and crockery gets smashed and ships pitch about seasickeningly in storms. Holman eats monkeys “cooked in the manner of an Irish stew” and describes touching everything from snakeskin to statues in the Vatican museum. You don’t need two good eyes to describe the horrors of dysentery, or of swarms of flies and mosquitoes so thick that he needed chain mail to protect himself. And in some ways, Holman argued, his handicap made him a superior traveler:* instead of relying on a superficial view of a scene, his blindness forced him to talk to people and ask questions.
Still, Holman did have some practical tricks, tactics for navigating a world he couldn’t see. Instead of indistinguishable paper bills, he demanded coins for currency. He acquired a special pocket watch whose hands he could trace without interfering with its ticking. To record his observations, he used an inkless dictation machine called a Noctograph,* a wooden slab with wires strung every half inch to guide his hand across the paper. And in exchange for free passage on ships, he often bartered his services—especially storytelling, like Homer of old—to relieve the tedium of ocean travel. One story he no doubt related involved a short excursion (1,400 miles) that he took with a friend—who happened to be deaf. “The circumstance was somewhat droll,” he later wrote. “We were not infrequently exposed to a jest on the subject, which we generally participated in, and sometimes contributed to improve.” All travelers need a sense of humor.
Blind explorer James Holman. Notice the unfocused eyes and Noctograph dictation machine.
Perhaps
most important, James Holman succeeded in traveling the world by himself because he took advantage of neuroscience. Like most blind people, Holman explored his immediate environment with his hands. (For this reason women found Holman alluring—they adored his heightened sense of touch and often granted him permission to “look over” their faces and even bodies.) For navigating the world at large, however—for dodging poles and trees, for negotiating crowded bazaars—Holman relied not on his hands but on his hickory cane. He didn’t use the cane the way blind people do today, as a sort of extended finger to feel his way along. His cane was too short, too heavy, too inflexible for that. Instead, he clicked the metal nib onto the pavement every few steps, and listened.
Whenever he clicked the cane, sound waves ricocheted off any nearby objects, and the echoes arrived back in each ear at slightly different times. After some practice, his brain learned to triangulate those time differences and determine the layout of the scene confronting him. The echoes also revealed details about an object’s size, shape, and texture—hard, skinny statues sound different from soft, broad horses. Mastering this sensory capacity—called echolocation, the same sense that bats use—took years of determined work, but determination was James Holman’s long suit. And once he’d perfected it, he could navigate everything from Vatican art galleries to Mount Vesuvius mideruption. Like flicks of a flashlight in a dark room, these cane clicks became Holman’s sight.
Scientists often call the human brain the most elaborate machine that ever existed. It contains some hundred billion neurons, and the tip of an average axon wires itself up to thousands of neighbors, producing an inordinate number of connections for analyzing data. (There are so many connections that neurons seem to obey the famed “six degrees of separation” law: no two neurons are separated by more than six steps.) And cases like James Holman’s reveal even more intricacies, since they show how the human brain can deviate from the standard wiring plan and sometimes even rewire itself, by changing its wiring patterns over time. Some of these changes sound as fantastical as a blind man climbing volcanoes, but all of them give us insight into the incredible plasticity of our neural circuits.
To see how brain circuits work, imagine a noise—like a clack on a cobblestone—arriving at James Holman’s ear. The clack vibrates various bones and membranes inside his ear canal, and the sound wave eventually transfers its energy to a fluid in his inner ear. That fluid sloshes over rows of tiny hair cells and (depending on the sound) bends some of them to a greater or lesser extent. These hairs are connected to the dendrites of nearby nerve cells, which immediately fire and transmit electrical signals down their long axon “wires” toward the brain. Upon reaching the brain, the signal causes the axon to squirt a chemical soup into a nearby synapse. This finally arouses neurons in the auditory cortex, a patch of gray matter in the temporal lobe that analyzes the sound’s pitch, volume, and rhythm.
Reaching the auditory cortex is only the start, though. For Holman to consciously recognize the clack or navigate with it, the signal has to circulate to other patches of gray matter for further processing. And reaching those other patches of gray matter requires going subterranean—diving beneath the gray matter surface and into the brain’s white matter.
White matter consists largely of high-speed axon cables that zip information from one gray matter node to another, at speeds up to 250 miles per hour. These axons can shuttle information around so quickly because they’re fatter than normal axons, and because they’re sheathed in a fatty substance called myelin. Myelin acts like rubber insulation on wires and prevents the signal from petering out: in whales, giraffes, and other stretched creatures, a sheathed neuron can send a signal multiple yards with little loss of fidelity. (In contrast, diseases that fray myelin, like multiple sclerosis, destroy communication between different nodes in the brain.) In sum, you can think about the gray matter as a patchwork of chips that analyze different types of information, and about the white matter as cables that transmit information between those chips.
(And before we go further, I should point out that “gray” and “white” are misnomers. Gray matter looks pinkish-tan inside a living skull, while white matter, which makes up the bulk of the brain, looks pale pink. The white and gray colors appear only after you soak the brain in preservatives. Preservatives also harden the brain, which is normally tapioca-soft. This explains why the brain you might have dissected in biology class way back when didn’t disintegrate between your fingers.)
A message traveling through a white-matter cable can either stir other neurons to life (pay attention!) or anesthetize them (pay no attention!). But given the inordinate number of neurons we have, and given the bazillions of pathways that run between different patches of neurons, one key question in neuroscience is how the clack signal “knows” which path to follow, and which neighbors to excite and which to inhibit. The answer turns out to be fairly simple: like James Holman’s cart through Siberia, brain signals follow ruts.
Start with two neurons. If one neuron causes another to fire in quick succession over and over, the synapse between them actually changes in response. The axon tip of neuron one swells larger and starts packing in more bubbles of neurotransmitters to flood the synapse between them; wholly new axon branches might even sprout up. Neuron two can then make listening to neuron one a priority by extending more dendrite receptors back toward it. This allows neuron two to respond to even low-intensity prompts. Overall, just as a wagon wheel will carve a rut into the road after repeated journeys, repeated neuron firings will carve ruts into the brain that make signals much more likely to follow some neural tracks than others.
Scientists use a different metaphor to explain how neural connections grow stronger over time: neurons that fire together wire together. And usually it’s not just two or three neurons firing and wiring together. Once a rut gets established, circuits of many thousands of neurons will fire in sequence.*
Thanks to white matter cables, these circuits can link together even distant patches of gray matter, allowing the brain to carry out complicated actions automatically. We’re all born with circuits in our lower brain, for example, that control reflexes like sneezing, gagging, and yawning: as soon as the first neurons in the sequence fire, all the others follow, like a row of dominoes. That’s why the steps involved in a sneeze or yawn rarely vary. Circuits in the higher brain work in the same way. After tons of practice, we all learned to link the letters d-o-g in our Dick and Jane primer with both an image of a fuzzy quadruped and with the sound duh-aw-guh. Eventually, any one of that triad automatically evokes the others. Negative experiences can wire neurons together, too. Enter an alley where you once had a fright, and its smells and shadows will reawaken your terror circuits.
All human brains subscribe to a standard wiring plan, which ensures that certain patches of neurons can always talk to certain other patches—and good thing. Your eyes better be able to rouse your fear circuits, and your fear circuits better be able to tell your legs to skedaddle, or you won’t last long outdoors. This general wiring scheme gets laid down during our fetal days, when axons begin to bud and grow like shoots. That said, the general wiring diagram can vary in its details from person to person. One dramatic example of this is synesthesia, a condition in which people’s senses blend together in trippy ways.
For most people, one sensory input produces just one sensory experience. Cherries simply taste like cherries, and rubbing sandpaper on the skin simply feels scratchy. For people with synesthesia, one sensory input leads to multiple outputs—the expected cherry taste, plus, say, a phantom tone. These superadded sensations are involuntary and consistent: each time the synesthete hears G-sharp, the exact same unaccountable pepper smell floods her nose. Synesthesia is idiosyncratic as well: while one person always sees the number 5 as fuchsia, another insists it’s key-lime-pie green.
The most common type of synesthesia produces a symphony of color, especially when people hear certain sounds or see certain letters and numbers. Rich
ard Feynman saw ecru j’s, indigo n’s, and chocolate x’s inside equations. Vladimir Nabokov once said that for him, the long vowel aaah has “the tint of weathered wood,” while the shorter ah “evokes polished ebony.” Franz Liszt used to berate his orchestra—who could only stare back, bewildered—for playing his music the wrong color: “Gentlemen, a little bluer, please, the tone depends on it!” Another time he implored: “That is a deep violet [passage]!… Not so rose.”
Color-sound and color-letter synesthesia are the most common types because of brain geography: some of the regions that analyze sounds, letters, and colors lie right near each other, so signals can easily leak across the border. In theory, though, synesthesia can link any two sensations in the brain, and sixty known types exist. Hearing-motion synesthetes might hear a siren song emerging from a simple screen saver of moving dots. Touch-emotion synesthetes might feel silk as calming, oranges as shocking, wax as embarrassing, and denim as morose (so much for your favorite jeans). To touch-taste synesthetes, wrought-iron fences might taste salty, or certain kinds of meat “pointy.” (One man pouted before a dinner party that the chicken he’d fricasseed came out too “spherical.”) Sexual synesthetes might see colored shapes floating in front of them during coitus. Color-time synesthetes can experience days of the week, months of the year, or even stages of life as a patchwork of shades and hues. Imagine listening to Jacques’s “seven ages of man” speech from As You Like It, and watching a rainbow envelop the stage.
Synesthesia probably has a genetic component, since it runs in families and pops up in most cultures. Importantly, too, neurologists have ruled out the idea that synesthetes are just talking metaphorical jive, the way the rest of us speak of “loud shirts” and “sharp cheddar.” These people’s brains actually work differently, as tests reveal. One experiment involved filling a piece of paper with a bunch of alarm-clock fives (5), but also scattering a few blocky twos (2) in there. Normal people find it nearly impossible to pick out the 2s without hunting one by one. To synesthetes, each 2 pops out in Technicolor, instantly. (It’s similar to the way numbers pop out automatically on color-blind tests.) As another trick, if you show a synesthete, say, a giant numeral 4 made up of rows and rows of tiny 8s, the figure’s color will flip depending on whether she focuses on the whole (the 4) or the pixels (the 8s). Other tests make synesthetes squirm. Normal people have no trouble reading text of basically any color. For synesthetes, numbers or letters that are the “wrong” color can disorient or repel them, since the colors on the page do battle with the colors in their minds.