PROFILE BOOKS, NOVEMBER 2017Most of what we know about the human brain comes from trial and error, often more on the error side of that pairing. Some of the biggest breakthroughs in neuroscience have come from investigations no more sophisticated than shoving a finger inside a hole in someone’s head, hanging around Victorian insane asylums and, of course, lots of swearing.

By cataloging the functions and the structure of the brain, neuroscience has helped us to understand how and why we swear. It’s a two-way street, though: understanding how and why we swear has helped us to reverse-engineer the structure of the brain. Take one of the first and most famous case studies in the history of neuroscience, that of railway foreman Phineas Gage.

One late September afternoon in 1848, Phineas Gage was hard at work blasting rock faces apart, deep in the heart of Vermont. By...

Gage’s team were busy drilling holes in the rock face so they could blast a path for the railway. The process was a dicey one: first the hole was drilled, then it was filled with explosives and a fuse. Finally, sand was poured on top of the explosives so that everything could be “tamped down”—compacted with a meter-long, six-kilogram rod of iron. No one quite knows what went wrong that day, but as Gage drove his tamping iron into the hole it seems to have caused a spark that detonated the blasting powder and shot the metal rod straight through his head and a further twenty-five meters before it finally landed.

The first doctor on the scene, Dr. Edward H. Williams, later wrote that the damage was so bad that he could see the gaping hole in Gage’s head even before he stepped out of his carriage, “the pulsations of the brain being very distinct,” he wrote. You’d expect someone with a head wound of that magnitude, at best, to be sitting very quietly feeling sorry for himself but Phineas Gage was—according to Dr. Williams and several of Mr. Gage’s colleagues—sitting up and chat- ting with his workmates, regaling them with the details of the accident.

“Mr. Gage persisted in saying that the bar went through his head,” wrote Williams. At first, the doctor didn’t believe the story, thinking instead that Gage had been hit in the face with a flying lump of rock. But then, Mr. Gage “got up and vomited; the effort of vomiting pressed out about half a teacupful of the brain which fell upon the floor.” That’s quite an evocative picture, even if “half a teacupful” isn’t the most rigorous unit of measurement. And even after that incident, he still remained very much awake and alive.

Perhaps the most interesting thing about this accident is not that Gage survived, but that this railway foreman became an essential part of the emerging debate on the structure of the human brain. Gage’s accident occurred during a monumental shift in how people thought about the brain, when a debate was raging between those scientists who believed that the brain was like a trifle and others who thought it was more like a blancmange. To explain this dessert-based metaphor, the “blancmange” theory (not an official name) held that our brains are an undifferentiated mass. Each bit is just like the other bits—like a blancmange. But the “trifle” school of thought held that the brain is made up of different parts, each one with a different role to play. If you take away a third of a blancmange you still have blancmange. If you take away one of the layers of a trifle you end up with something even more depressing than trifle. Knowing what we do about brain structure these days, it might seem astounding that the question was ever up for debate, but in 1848 there was no means of scanning the brains of living people, and not many survivors of brain injuries that could be observed in close detail, so the debate raged on.

Most of what we know about Gage’s condition results from the observations of Dr. John Martyn Harlow, who took over the case. He wrote two papers that describe in detail Gage’s injury and the aftermath: the compellingly titled “Passage of an Iron Rod through the Head” and the equally inventively named sequel, “Recovery from the Passage of an Iron Bar through the Head.”

Harlow had an inquisitive mind, a strong stomach, and what must have been a really persuasive bedside manner because he left notes explaining how he literally got inside Gage’s head to try to figure out—by touch alone—the exact shape of the damage done by the bar. He wanted to check whether there were any bits of bone or shrapnel in the wound and so, around three hours after the accident, he decided to use his finger:

“I passed in [to the hole in the top of Gage’s head] the index finger its whole length, without the least resistance, in the direction of the wound in the cheek which received the other [index] finger in like manner.”

It’s a striking image: Harlow poking one finger up through the hole in Gage’s cheek and another through the hole in the top of Gage’s head like a pair of Chinese finger cuffs. This was only the first of many painstaking measurements he made. Over the coming years Gage would be sketched, have plaster casts made of his head, and be measured countless times. Harlow eventually concluded that Gage’s left frontal lobe was destroyed (that fateful half a teacupful) but that the right side was completely intact.

We now know that Harlow’s description of Gage’s injury was spot on. His observations were confirmed in 2004 when doctors from the Brigham and Women’s Hospital in Boston, Massachusetts, made a 3D computer model from Gage’s skull—which Gage’s family had bequeathed to Harlow when Gage died—showing the exact path of the tamping iron through his head. The damage corresponds perfectly with Harlow’s records.

The painstaking nature of Harlow’s observations are vitally important because they helped us to understand how much brain structure matters. After the accident, Gage made an excellent physical recovery but he seemed to be a different man, so much so that the same bosses who thought him a “smart and capable” and “shrewd” man before his accident refused to hire him when he reapplied for his old job as a foreman in 1849. At the time of his death, twelve years after his accident, he was working as an itinerant farmhand. One of a whole range of symptoms he experienced was a newfound compulsion to swear. Dr. Harlow wrote that Gage had become “fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom).”

For these reasons, Gage provided an important bit of evidence in the pudding wars. If the blancmange theory was correct, Gage could lose a chunk of his brain and still be left with all of his faculties intact. His brain would be the same as before—just smaller. However, Gage seemed to come out of the experience a very different person—and in a way that seemed both too profound and too specialized to be the psychological effect of having a six-kilogram missile take a shortcut through your noggin. “The equilibrium or balance, so to speak, between his intellectual faculties and his animal propensities, seems to have been destroyed,” wrote Harlow. Gage’s intelligence, memory, and skills were intact, but his self-control was shattered. His new habit of swearing—of using “gross profanities”—appeared to show that a vital ingredient of Gage’s personality used to reside in the destroyed left frontal lobe.

Excerpted from Swearing is Good for You: The Amazing Science of Bad Language by Emma Byrne. Copyright © 2017 by Emma Byrne. Used with permission of the publisher, W.W. Norton & Company, Inc. All rights reserved.

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