Who knew a hole in the head could unlock brain’s secrets?

It took centuries for scientists to figure out that the brain’s frontal cortex, which sits just behind the forehead, governs emotions and reasoning. One important early clue came from an accident a young railroad worker suffered in 1848. The worker, Phineas Gage, went on to become one of the most famous brain-injury patients of all time.

Hard-working and well-liked, the 25-year-old foreman was blasting through granite to lay track in Vermont when he dropped his tamping iron into a hole filled with blasting powder. The iron -- a meter-long, 13-pound tapered rod -- created a spark that ignited the powder, and the pole shot out of the hole and right through Gage’s head.

The iron entered under his left eye and exited through the top of Gage’s skull, landing a few feet away. But Gage, on the ground, was still conscious. He joked that he should probably see the doctor, then he asked his co-workers to hand him the log book so he could sign out for the day.

Local doctor John Harlow patched and bandaged the hole in Gage’s head, predicted he wouldn’t live and had him measured for a coffin. Gage held on for two weeks, barely conscious. Then slowly he rebounded and, save for weakened vision in his left eye, within weeks seemed cured. For the most part.

Just more than a month after the accident, Harlow returned from a short trip to find Gage wandering barefoot in the rain, ignoring medical advice and cursing left and right. He was acting, by all accounts, like a rash, ill-tempered and impulsive child with no sense of self-restraint.

“The balance of his mind,” Harlow concluded, “was gone.”

Still, Gage was alive and functioning -- which made him a medical curiosity. In 1850, Harlow took the patient to Harvard to discuss his case, sending doctors there into a tizzy.

Some refused to believe he had suffered the injury at all. But proponents of phrenology, which held that specific areas of the brain governed the various aspects of a person’s character, rejoiced. The phrenologists pointed out that the iron had damaged the brain regions, located just above the left eye, that they believed to be associated with kindness and respect. And Gage’s new personality certainly bore this out.

Gage went to New Hampshire to work in a stable then to Chile to drive a stagecoach. In 1859, frail and sickly, he showed up at his mother’s new home in San Francisco. Over the next few months, he began suffering seizures and, in 1860, finally died.

Two years later, scientists began to show that -- somewhat akin to the phrenologists’ beliefs -- specific areas of the brain do govern specific tasks. French doctor Paul Broca identified a spot on the left frontal lobe that governs speech, and German scientist Carl Wernicke pinpointed a nearby spot that governs the ability to understand it. Other curious brain damage cases cropped up -- ones strangely similar to that of Gage. A good-natured Swiss builder became aggressive and mean after falling from the fourth story of a house he was building. An autopsy later revealed his frontal cortex had been destroyed. A 45-year-old teacher in France suffered a similar change in disposition; in her case, a frontal lobe tumor was found.

Looking at these and similar cases, Swiss doctor Lenore Welt came to a conclusion: When the frontal lobe is damaged, a change in personality ensues.

In 1866, curious as to what had happened to his old frontal lobe patient, Dr. Harlow contacted Gage’s mother, only to learn of his death. He requested -- and soon received -- Gage’s exhumed and disembodied skull and the tamping iron, which had been buried with Gage in his coffin.

Gage’s body was dug up again in 1940, when the cemetery in which he lay was forced to give way to new housing. The bodies were moved to a mass grave outside the city, and the tombstones converted to landfill.

Gage’s skull and iron, though, have been granted more lasting veneration: Since Harlow’s request, they’ve been on display at Harvard.