In the northwest corner of Colt Park, in downtown Hartford, Connecticut, a ten-foot-tall bronze statue of the park’s namesake rose from a granite pedestal. Engraved tributes to Samuel Colt, inventor of the Colt .45, covered one side of the pedestal, but the boy trudging toward it wouldn’t have been able to read them even if he’d wanted to, since he wasn’t wearing his glasses. It was dinnertime, July 3, and it was probably 1933 or 1934, though the exact year would be one of the things that scientists would argue about in the decades to come. His family’s second-floor walk-up apartment was about a quarter mile away. He was seven or eight years old and already he’d moved at least three times. His father was an electrician, didn’t make much money, had to go wherever the work was. It must have been confusing sometimes for the boy, all these homes flashing by, all those fresh starts. He had blond hair and bright blue eyes and a sweet, uncertain smile.

A steep road skirted the northern edge of the park, and if the boy cut across it and down some backstreets, he could shave a little time off his walk home. The boy’s eyesight may have been bad, but there was nothing wrong with his ears. He didn’t hear any cars coming. He stepped off the sidewalk and started crossing the road.

The bicyclist, coasting down the hill, didn’t see Henry until it was too late.

Hippocrates Asclepiades, a Greek physician born on the island of Cos in the fourth century B.C.E., is widely regarded as the father of modern medicine. Although his last name indicates a claimed family connection to Asclepius, the revered doctor-god of Greek myth, Hippocrates became famous by advancing the revolutionary argument that the gods had no place in medicine. Healers of one sort or another have existed for as long as humans have, but Hippocrates was one of the first to reject the magic and spiritualism and religion that most who came before him relied on. Instead he attempted to localize the sources of our ailments in our physical environment and inside our bodies themselves.

That approach was well illustrated in an essay he wrote called “On the Sacred Disease.” The title was a little misleading, since Hippocrates preferred to call the disease in question by a different name: epilepsy, from the Greek epilambanein, which means “to seize.” And the disease of epilepsy, he wrote, was “no more divine than others; but it has its nature such as other diseases have, and a cause whence it originates.” He criticized the “conjurors, purificators, mountebanks, and charlatans” who used “divinity as a pretext and screen of their own inability to afford any assistance,” and he ridiculed them for blaming the gods for the various ways epilepsy manifested itself in their patients: “For, if they imitate a goat, or grind their teeth, or if their right side be convulsed, they say that the mother of the gods is the cause. But if they speak in a sharper and more intense tone, they resemble this state to a horse, and say that Poseidon is the cause. Or if any excrement be passed, which is often the case, owing to the violence of the disease, the appellation of Enodia is adhibited; or if it be passed in smaller and denser masses, like a bird’s, it is said to be from Apollo Nomius. But if foam be emitted by the mouth, and the patient kick with his feet, Ares then gets the blame.”

After rejecting all the sacred explanations, Hippocrates presented a startling explanation of his own: “The brain is the cause of this affection,” he wrote, “as it is of other very great diseases, and in what manner and from what cause it is formed, I will now plainly declare.”

The details of Hippocrates’s subsequent explanation of the aetiology of epilepsy, of course, haven’t stood the test of time. In his view, the brain was a pneumatic organ, alternately pulsing with phlegm and bile. It was delicately attuned to the winds, and the wrong wind blowing on the wrong person at the wrong time could wreak havoc. If the west wind buffeted a constitutionally phlegmatic child, for example, it might cause the child’s brain to temporarily “melt,” at which point epileptic fits would occur. Hippocrates’s prescription for such children would be to shield them from the west wind and expose them instead to the north wind, which would, presumably, recongeal their brains and set them right.

What’s important about Hippocrates isn’t that he figured out epilepsy’s origins or its treatment—he did neither—but that he began looking in the right place: not up to the heavens or Mount Olympus but into the even more mysterious terrain inside our skulls.

In the years since, many doctors grappling with the problem of epilepsy followed Hippocrates’s lead, venturing deeper and deeper into the brain, seeking a secular understanding of the “sacred disease.”

By the early 1930s, when a bicyclist knocked down a young boy on a street in Hartford, Connecticut, they’d begun to find some answers.

Patient H.M.: A Story of Memory, Madness, and Family Secrets