For the father of modern neuroscience, cellular anatomy was like the most exciting fiction.

Fiction is, by definition, a world away from fact—but Santiago Ramón y Cajal, often heralded as “the father of modern neuroscience,” used it to find objective truth. Cajal spent his days at the microscope, gazing down at faint, entangled fibers that appeared to his fellow anatomists as inscrutable labyrinths. Contrary to prevailing theory, the Spaniard discerned that the nervous system, including the brain, comprises distinctly individual cells (neurons), which, he theorized, must communicate across the infinitesimal spaces between them (synapses). It was Cajal who first applied the term plasticity to the brain; he went so far as to recommend “cerebral gymnastics” for mental enhancement, presaging twenty-first century insights and trends about brain exercise. “If he is so determined,” Cajal said, “every man can be the sculptor of his own brain.” If all Russian literature comes from Gogol’s “Overcoat,” and all modern American literature comes from “a book by Mark Twain called Huckleberry Finn,” then international brain research, including grand projects like the BRAIN Initiative and the Human Brain Project, emerges from the unlikely work of Santiago Ramón y Cajal.

Cajal was born in 1852, high in the mountains of northern Spain; his head always seemed to belong in the clouds. The landscape of his childhood was epic. Aragonese folklore echoed through dust-colored pueblos, swept through by the specters of conquests and kings. The young Cajal idolized these legendary figures, maybe because village life was incessantly prosaic. Alto Aragón was notoriously inhospitable; the highland region that Robert Hughes, in his biography of Goya (another native son), noted for its “sour wine, straw bedding, tough meat”—“semi-troglodytic conditions.” Almost nothing grew from the callous, fissured soil; Cajal’s home was a ramshackle pile of cobblestone. “Not a flower pot in the windows,” he recalls in his autobiography, Recollections of My Life: “not the smallest decoration on the fronts of the houses, nothing in a word, to indicate the slightest feeling for beauty.”

Cajal’s father was a man of facts, implacable and austere. The son of peasant farmers, he’d abandoned his home at age twelve, in search of less desolate fields. He apprenticed to a lowly barber-surgeon and went on to achieve a medical degree, the triumph of a grueling life. There was no time for leisure, for distractions from the path. The human mind, Cajal’s father believed, was made for obtaining knowledge. “He repudiated or despised all culture of a literary or of a purely ornamental or recreative nature,” Cajal recalls. Only medical books were allowed in the house—absolutely no fiction. Art, Cajal’s father believed, was the symptom of a devastating illness.

But Cajal’s mother, a covert romantic, kept cheap fantasy novels hidden at the bottom of a trunk and smuggled them into the hands of her children, to their delight. As the local surgeon, Cajal’s father was often away from home, and when he returned, his wife’s “excessive softness” enraged him; he was chagrined to recognize it in his son, too. He tried to eradicate the boy’s literary impulses, punishing him with whips, cudgels, and other instruments of torture often seen in “penny dreadful” horror tales and haunting children’s nightmares.

The abuse only seemed to embolden Cajal’s creative instincts. “Whenever I had finished supper,” he recalls, “I eagerly hastened to my little room and, until I fell asleep, spent my time giving form and life to the jumble of stains on the wall and the cobwebs of the ceiling, which I transformed, by the power of thought, into the wings of a magic stage, across which filed the cavalcade of my fantasies.” His mind transmuted shadows into story: a perceptual trick that would later help clarify his view of even more profound obscurities.

Cajal convinced his father that he needed a quiet room of his own in which to study. The pigeon house next to the family barn became the site of his first experiments, where he was free to imagine and explore. A window opened onto the roof of a neighbor, a pastry chef with slightly more elevated tastes. In the attic, among the sweetmeats and dried fruit, Cajal espied a smorgasbord of literary treats. He lost himself in Dumas, Hugo, Cervantes, and others. Long before peering through microscopes, Cajal trained his eyes to the pages of books. Reading novels primed his mind to explore more invisible realms.

After high school, Cajal’s father enrolled him in medical school, where the only subject that held his interest was anatomy. Though it had emerged decades earlier, cell theory was revolutionizing—or scandalizing—the field then. Reading about it, Cajal encountered literary metaphors that drew him in, such as the famous line from the German pathologist Rudolf Virchow: “The body is a state in which every cell is a citizen.” Cajal’s first look through a microscope confirmed this idea, showing him, in his own words, “captivating scenes from life of the infinitely small.” For twenty continuous hours—or so he claimed—he watched the movement of a leucocyte away from a capillary, akin, in his vivid imagination, to high-stakes escape. He even wrote and illustrated a novel about a miniature man—about the size of a cell—traveling through bodies of gargantuan beings on Jupiter.

Cellular anatomy, for Cajal, was like the most exciting fiction. He became a researcher, setting up a makeshift laboratory—not unlike the old pigeon house—in his parents’ attic. Later, he witnessed a demonstration of the so-called black reaction, an erratic chemical stain—which other biologists had abandoned—that had the power to reveal whole hidden elements beneath the discriminating light of the microscope. Cajal was stunned by the clarity of the results; the arcane forms reminded him of ink on paper. He immediately applied the technique to the nervous system—the holy grail of human anatomy—hoping to uncover “the material course of thought and will.”

Cajal modeled his scientific quest after literary heroes from his childhood. He cast himself in the mold of Crusoe, envisioning the brain as “a world consisting of a number of unexplored continents and vast stretches of unknown territory,” and devoting his work to “islands of discovery.” In 1888, working alone at the microscope in his home laboratory, Cajal observed the endpoint of a nerve fiber, a nearly imperceptible phenomenon that led him to declare that nerve cells were independent—thus beginning the saga of modern neuroscience. “The job of the anatomist,” Cajal writes, “is to separate the apparent from the real.” Like his beloved Don Quixote, he believed in an alternative view of the world; unlike Quixote, he succeeded in rallying the people around him, who eventually celebrated his foresight.

How did Cajal see what others could not? To anthropomorphize was his genius—yet such an approach seemed unscientific, to say the least. “Cajal treated the microscopic scene as though it were alive,” recalled Charles Sherrington, his lifelong friend and fellow Nobel Laureate, “and were inhabited by beings which felt and did and hoped and tried even as we do.” Sherrington saw that fantasy aided the unorthodox Spaniard’s ability to visualize the brain. “If we would enter adequately into Cajal’s thought in this field,” Sherrington continues, “we must suppose his entrance, through the microscope, into a world populated by tiny beings actuated by motives and striving and satisfactions not very remotely different from our own.” Cajal highlighted that subject and object—the brain scientist and the neuron—descended from the same evolutionary ancestor, contained the same physical material, and were beholden to the same mortal laws.

The world of the infinitely small, like novels of his youth, seemed more real to Cajal than everyday existence. How else could he routinely spend up to fifteen hours a day, for almost fifty years, alone in the laboratory? He claimed to have observed a million neurons, witnessing them in every phase of their lives: birth, development, movement, relationships, adversity, trauma, decline, and death. On thumbnail sheets of dead brain tissue, the Spaniard’s cherished stories came to life. He imagined neurons as protagonists in an intense cerebral drama. Their fibers “groped to find another.” Their aching contacts became “protoplasmic kisses”—“the final ecstasy of an epic love story.”

More than a century after his 1906 Nobel Prize, Cajal’s portraits are iconic. It might be natural to assume that these drawings are copies of what he saw through the eyepiece, like cerebral still lifes. Yet his illustrations were strikingly interpretative and deeply personal, blurring the line between abstraction and representation. After viewing many cells, Cajal distilled their features to a type. His images are composites, highlights, even exaggerations of actual neurons; I’ve heard it said that he often drew from memory after taking long walks through the park. Cajal called them “pieces of reality,” these tactfully fictionalized depictions. Had he listened to his father, forsaking literature, he might never have recognized the truth. The human brain contains around eighty billion neurons, we now know, each of which may interact with up to ten thousand others. One might wonder: Do we tell their ephemeral stories, or do they, somehow, tell ours?

Benjamin Ehrlich is the author of The Dreams of Santiago Ramón Cajal.