Some of the most important things we know about the brain come from people whose brains were damaged in unusual ways. Here are their stories. Click any case to read what happened.
In 1848, Phineas Gage was a 25-year-old railway construction foreman in Vermont, everyone who knew him described him as responsible, efficient, and well-liked. Then an accidental explosion drove a 1.1-metre iron tamping rod straight through his skull, entering under his left cheekbone and exiting through the top of his head.
He did not lose consciousness. He sat up and spoke within minutes. He walked to a cart that took him to a doctor. He survived, with no obvious paralysis and no loss of language or movement.
But within weeks, everyone around him noticed he was a completely different person. His doctor wrote that he was "fitful, irreverent, indulging at times in the grossest profanity... impatient of restraint or advice... capricious and vacillating." His friends said he was "no longer Gage."
The rod had destroyed most of his frontal lobe, specifically the prefrontal cortex. This was one of the first pieces of evidence that the frontal lobe is responsible for personality, impulse control, and social behaviour. Before Gage, scientists thought personality was fixed and had nothing to do with brain tissue. After him, they had proof that a physical structure was behind who we are.
Henry Molaison, who has been known for decades only as "H.M.", suffered from severe epilepsy. In 1953, at 27 years old, surgeons removed the hippocampus from both sides of his brain in an attempt to control his seizures. The surgery worked, and the seizures stopped.
But from that day forward, Henry could not form any new long-term memories. He could hold a thought for about 20 seconds before it vanished completely. Every conversation reset. Every person he met was a stranger, including the researchers who studied him almost daily for 55 years. He could not remember their names, their faces, or that he had ever met them.
He retained his personality, his intelligence, and memories from before the surgery. He knew who he was, remembered his childhood, and could hold a conversation. He just could not add anything new. When he looked in the mirror as an old man, he was always surprised, because he expected a 27-year-old face.
H.M. is the reason we know the hippocampus is essential for converting short-term memories into long-term ones. He could still learn physical skills (like tracing a star through a mirror) even though he had no memory of practising. This showed that different types of memory are stored in different places, while procedural memory is stored elsewhere. He became the most studied person in the history of neuroscience.
S.M. has a rare condition called Urbach-Wiethe disease, which gradually calcified, turned to stone, both of her amygdalae starting in childhood. By adulthood, the structures were completely destroyed.
Researchers discovered that she was literally incapable of experiencing fear. They showed her horror films, she found them interesting but not frightening. They took her to a pet store with exotic animals; she reached directly into the snake tank without hesitation. They took her to a haunted house; she walked through laughing, approached the costumed actors to chat, and at one point startled one of the performers.
But it was not just that she was brave. She also struggled to recognize fearful expressions on other people's faces. Fear, whether in herself or in others, did not seem to exist.
S.M. provided direct evidence that the amygdala is the brain's fear centre. Without it, fear as a feeling simply does not exist. This also raised a complex question: is a life without fear actually better? S.M. had a history of putting herself in dangerous situations she should have avoided. It turns out that, fear is a survival tool, and without it, that protection disappears.
Clive Wearing was a renowned conductor and musicologist in London, one of the most knowledgeable musicians in Britain. In 1985, he contracted a herpes virus that attacked his brain, devastating his hippocampus and parts of his cortex.
The result was one of the most extreme cases of amnesia ever recorded. His conscious memory lasted between 7 and 30 seconds. He kept a diary, and on page after page, in different handwriting at different times, he would write: "NOW I AM AWAKE." Then, a few minutes later, cross it out and write it again. He genuinely believed, every few seconds, that he had just woken up for the first time.
He did not recognise friends, doctors, or his house. Every time his wife Deborah entered the room, whether she had been gone 5 minutes or 5 hours, he greeted her with tears of joy, as though they had been separated for years. He loved her desperately. He just could not remember that she had been there before.
But sit him at a piano, and something else happened. He could play full concertos from memory, conduct a choir, sight-read music, with perfect fluency! But He couldn't tell you what he had played 2 minutes ago, but the music itself was intact.
Clive showed that memory is not one thing stored in 1 place. Conscious, declarative memory (facts, events, faces) depends on the hippocampus, but procedural memory (skills, muscle memory, musical ability) is stored differently, in the cerebellum and basal ganglia, which were largely undamaged.
Louis Leborgne was admitted to a Paris hospital in 1840 after losing the ability to speak. He was intelligent, understood everything said to him, and could communicate through gesture and expression. But whenever he tried to speak, only 1 syllable came out: "tan." He became known by this name throughout the ward.
He lived this way for 21 years. When he died in 1861, the neurologist Paul Broca performed an autopsy and found a lesion in the left frontal lobe (in a specific area we now call Broca's area).
Broca then examined other patients with similar speech difficulties. All had damage to the same region. He published his findings and made one of the most precise claims in neuroscience up to that point: language production is localised to a specific part of the brain's left hemisphere.
"Tan" gave us the first direct anatomical evidence of language localisation. Before Broca, it was assumed that all mental functions were distributed equally across the brain. After Tan, science knew that specific functions live in specific places. Broca's area in the frontal lobe now bears the name of the man who found it, and this is a discovery achieved through the lifetime of a man who could only speak 1 word.