We've all been mesmerized by them—those beautiful brain scan images that make us feel like we're on the cutting edge of scientifically decoding how we think. But as soon as one neuroscience study purports to show which brain region lights up when we are enjoying Coca-Cola, or looking at cute puppies, or thinking we have souls, some other expert claims that "it's just a correlation," and you wonder whether researchers will ever get it right.
But there's another approach to understanding how our minds work. In his new book, The Tale of the Dueling Neurosurgeons, Sam Kean tells the story of a handful of patients whose unique brains—rendered that way by surgical procedures, rare diseases, and unfortunate, freak accidents—taught us much more than any set of colorful scans. Kean recounts some of their unforgettable stories on the latest episode of the Inquiring Minds podcast.
"As I was reading these [case studies] I said, 'That's baloney! There's no way that can possibly be true,'" Kean remembers, referring to one particularly surprising case in which a woman's brain injury left her unable to recognize and distinguish between different kinds of animals. "But then I looked into it, and I realized that, not only is it true, it actually reveals some important things about how the brain works."
Here are five patients, from Kean's book, whose stories transformed neuroscience:
The Man Who Could Not Imagine the Future
Kent Cochrane (KC), pictured below, was a '70s wild child, playing in a rock band, getting into bar fights, and zooming around Toronto on his motorcycle. But in 1981, a motorcycle accident left him without two critical brain structures. Both of his hippocampi, the parts of the brain that allow us to form new long-term memories for facts and events in our lives, were lost. That's quite different from other amnesiacs, whose damage is either restricted to only one brain hemisphere, or includes large portions of regions outside of the hippocampus.
KC's case was similar to that of Henry Molaison, another famous amnesiac known as HM. HM taught us that conscious memories of things like which street you grew up on (personal semantic information or facts about yourself) and what happened on your prom night (episodic memories for events in your past) are stored independently from other types of nonconscious memories, of things like how to ride a bike or play the guitar. You can lose one type of memory without losing the other. But KC taught us still more: That our ability to imagine the future is tied to our ability to use our memories to reexperience the past.
"When he lost his past self," says Kean of KC, "he lost all sense of what he was going to do over the next hour, or over the next day, or over the next year. He couldn't project himself forward at all, and kind of realize that he would want to be doing something in a month or a year. He was kind of eternally trapped in the present tense."
Although it might sound obvious now, before KC came along, neuroscientists hadn't realized how closely tied, on a cognitive level, our future is to our past. "But if you think about it, it does make sense," explains Kean, "because the ultimate biological purpose of having a memory isn't just…to make you happy or something like that. The point of a memory is so that you can kind of keep track of what happened in your past, and then apply that to the future."
The Man Whose Vocabulary Was Reduced to One Word
In the late 18th century, the idea that different functions of the mind might be tied to specific parts of the brain first gained a foothold. Phrenology, as it came to be called, was based on the notion that bumps in the skull were markers of larger bits of brain, and that these bumps were clues as to what mental talents, or lack thereof, a person might possess. By the 1840s, however, many scientists dismissed phrenology (and rightly so) as rank pseudoscience.
So when Paul Broca, a French neuroanatomist, first proposed that there was a specific "language area" in the brain—and did so based on evidence from the brain of a patient nicknamed "Tan"—he was laughed out of a scientific meeting.
Tan—whose story is related in Kean's new book—suffered from epilepsy throughout his childhood. By age 31, he could only respond to questions by repeating the word "tan." Unless, that is, he was enraged. Then, he'd let out a cry of "Sacre nom de Dieu!" a French insult. Yet Tan still seemed to be able to understand spoken language, even if he could not to speak himself. Because his vocabulary was so impoverished, he became an expert at gesturing, expressing himself through mime.
So how was it possible that a man lost his ability to speak words, but not to understand them?
In 1861, gangrene took Tan's life—and Broca got his brain, which he proceeded to study. Broca found a lesion on the left side of the brain, near the front. This turned out to be the "language production" node; it is now known as Broca's area. From Tan and patients like him, neuroscientists thus learned that the speech production and speech comprehension regions of the brain are quite separable—and we need both, functioning properly, to communicate using language.
The Man Whose Brain Was Split in Two
In the 1940s, neurosurgeons developed a new procedure to treat patients with severe epilepsy. As a last resort when other less invasive treatments were ineffective, they would sever the major fiber tract, known as the corpus callosum, that connects the two hemispheres of the brain. That way, when the sparks of overexcited neurons started in one part of the brain, the seizure was at least confined to that hemisphere, limiting the damage of the electrical storm.
But as it happened, the patients involved didn't just have their epilepsy reduced: They also became marvels of science. Because these "split-brain" patients cannot send information from one hemisphere to the other, neuroscientists can learn from them which functions are limited to one side of the brain or the other.
One such patient, with the initials PS, was studied by neuroscientist Michael Gazzaniga. In experiments on PS and other split-brain patients, Gazzaniga devised a clever way of talking to each hemisphere independently. He would flash pictures on different sides of a screen, knowing that the visual system divides the world into two halves, and each hemisphere only sees one of them.
Thus in one experiment, Gazzaniga flashed an image of a snowy scene so that only PS's right hemisphere would perceive it, and an image of a chicken claw so that only his left hemisphere would pick it up. Then, Gazzaniga asked PS to choose, from an array of objects, those relevant to what he had seen. PS's left hand (governed by the right hemisphere) picked up a snow shovel, and his right hand (governed by the left hemisphere) chose a rubber chicken. So far, so good: That makes sense.
But when Gazzaniga asked him why he chose those objects, PS responded, "The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed," reports Kean. But of course, the shovel actually went with the snow scene. What was happening was that when it came to language, the left hemisphere is dominant. The right hemisphere, by contrast, has a barely functioning language capacity, but can express itself in other ways—by pointing with the left hand, for example, or by drawing or choosing objects with it.