You’ve probably heard the old myth that humans only use ten percent of their brains. It’s total nonsense. We use all of it. But here is the kicker: we don’t necessarily need all of it to be ourselves.
Imagine waking up and realizing a surgeon literally scooped out 50 percent of the grey matter inside your skull. It sounds like a horror movie plot or a freakish Victorian experiment. Yet, for hundreds of people living today, having half a brain is a medical reality that saved their lives. This procedure, known as a hemispherectomy, is one of the most radical surgeries in existence. It’s not just some fringe theory. It’s a standard, albeit last-resort, treatment for catastrophic epilepsy.
The brain is weird. It’s stubborn. It’s also incredibly lazy until it’s forced to be a hero.
Why Surgeons Actually Remove Half a Brain
Nobody goes under the knife for this because they want to. It’s a choice made in the face of absolute desperation. Usually, it’s for kids. Imagine a three-year-old having 50, 60, or even 100 seizures a day. Their brain is essentially a lightning storm that never stops. This usually happens because of things like Rasmussen’s encephalitis—an inflammatory disease that attacks one side of the brain—or Sturge-Weber syndrome.
The sick half isn’t just useless; it’s actively sabotaging the healthy half. By removing or disconnecting the "bad" side, surgeons allow the "good" side to finally breathe.
Dr. Ben Carson, long before his political career, became famous for refining this at Johns Hopkins. He wasn't the first, though. Walter Dandy tried it back in the 1920s on a patient with a brain tumor. It was messy back then. Now, it’s refined. Sometimes they don't even take the tissue out anymore; they just cut the "cables" (the white matter) so the two halves can’t talk. It's called a functional hemispherectomy. Same result. The seizures stop. Life starts.
The Mystery of Plasticity
How does a person walk, talk, or tell a joke with only half a brain?
The answer is neuroplasticity. It’s a buzzword these days, but in this context, it’s literal magic. When a child has this surgery, their remaining hemisphere begins a massive "remodeling" project. The brain doesn't just keep doing its old job; it takes over the chores of the missing side.
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If the left side—the side usually responsible for language—is removed in a very young child, the right side often just shrugs and learns how to speak. It’s not perfect. There’s usually a bit of a limp or limited use of one hand. But the person is there. Their personality remains intact. They still love pizza, hate math, and remember their grandmother’s name.
A study published in Cell Reports in 2019 looked at adults who had hemispherectomies as kids. Researchers at Caltech found that these individuals had incredibly strong brain connections. Their neural networks were actually more connected than people with full brains. It’s like the brain realizes it’s short-staffed, so it makes every remaining employee work twice as hard and communicate twice as fast.
The Physical Reality of Living "Half-Empty"
Let's be real for a second. It isn't a miracle cure without a cost.
If you lose your right hemisphere, you’re going to have trouble with the left side of your body. That’s just how the wiring works. Your left hand might be permanently clenched or just weak. You lose peripheral vision in both eyes on that left side. This is called hemianopsia. It sucks. You’ll probably bump into doorframes.
But the brain fills in the gaps.
Patients often describe it as a "new normal." They aren't walking around feeling like half a person. They feel whole. The empty space in the skull doesn't stay a vacuum, by the way. It fills up with cerebrospinal fluid. It’s basically a salty water balloon where the brain used to be.
A Case Study: Michelle Mack
You might have heard of Michelle Mack. She’s one of the most famous examples, though her case was natural, not surgical. She was born without much of her left hemisphere due to a pre-birth stroke. Nobody even knew until she was 27. She grew up with some learning disabilities and a bit of physical struggle, but she graduated high school and lived a relatively normal life.
Her brain essentially "rewired" itself in the womb. The right side took over the verbal processing. It’s a testament to how flexible our biology is. We think of the brain as a hard drive, but it’s actually more like a muscle or a piece of clay.
The Cognitive Trade-offs
Is there a "soul" in the left or right side?
Old-school psychology used to talk about "left-brained" people being logical and "right-brained" being creative. If that were strictly true, someone with half a brain would be a robot or a flighty artist. But they aren't.
They are nuanced.
However, subtle things do change. People who lose their right hemisphere might struggle to catch sarcasm or read deep emotional cues in someone’s voice. They might be very literal. Those who lose the left side might struggle more with the mechanics of speech (aphasia), even if they understand everything you say.
The interesting part is that IQ scores often increase after the surgery. Why? Because the constant seizures were dragging the score down. Once you stop the internal electrical fire, the remaining half can finally focus on learning.
The Future of "Half-Brain" Research
We are moving away from the "scooping out" method. Modern neurosurgery is getting more surgical—literally.
At places like Cleveland Clinic or UCLA, they are using laser interstitial thermal therapy (LITT). Basically, they use a tiny laser to zap the specific pathways causing seizures without removing the whole lobe. It’s less invasive. It preserves more tissue.
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But the "radical" hemispherectomy will likely stay in the books for a long time. Why? Because it works. It has an 80-90% success rate for stopping seizures. In medicine, those are Hall of Fame numbers.
Common Misconceptions
People think you’ll be a "vegetable."
False. Many go to college.
People think your head will look lopsided.
False. The fluid keeps the pressure equal.
People think you lose your memory.
Partially false. You might lose some specific things, but your identity and "core" memories are usually distributed or moved.
Actionable Insights for Families and Patients
If you or a loved one are facing the prospect of a hemispherectomy, the "scare factor" is usually higher than the clinical risk. It is a massive surgery, but the long-term outcomes for quality of life are statistically staggering.
- Early Intervention Matters: The younger the brain, the better it adapts. Plasticity peaks in childhood. If a surgery is necessary, waiting often does more harm than good because the seizures continue to damage the "healthy" side.
- Post-Op Is a Marathon: Surgery is just day one. The real work happens in physical and occupational therapy. This is where the brain is "taught" to use its new connections.
- Vision Support: Seek out specialists for hemianopsia early. Learning "scanning" techniques can prevent accidents and make driving (which is possible for some!) a reality.
- Connect with the Community: Organizations like the Brain Recovery Project provide peer-reviewed data and support groups for families. You aren't the first person to go through this.
The human brain is arguably the most complex object in the known universe. But as it turns out, it’s also incredibly redundant. We can lose half of our most precious organ and still keep our humor, our memories, and our "us-ness." It’s a reminder that we are more than just a sum of our biological parts. We are the patterns those parts create, and those patterns are remarkably hard to break.