LIFE WITH A HALF BRAIN.

Kacie Caves, 15, of Tulsa, Oklahoma, can't wait to get behind the wheel of a car, For practice, she zooms around her backyard in the family golf cart. She also jets in their motorboat on a nearby lake, and loves to swim, snorkel, and dive. When not on the fast tract, Kacie hits the high notes in her church choir and whips up a family dinner. Her favorite subject in school? "Math, definitely," Kacie answers.

Pretty amazing, considering Kacie has only half a brain.

Two years ago, on November 12, surgeons at Johns Hopkins Children's Center in Baltimore, Maryland, surgically split open Kacie's skull and operated for 12 hours to remove the left side of her brain. For almost four years, that portion of her brain had been ravaged with seizures--electrical disturbances that led to uncontrollable twitching in the right side of her face and body. The seizures sometimes attacked Kacie 100 times a day, leaving her virtually paralyzed and unable even to talk.

Kacie suffered from an extremely rare form of epilepsy (recurring seizures), called Rasmussen's encephalitis (ras-MYOU-sens in-se-fuh-LY-tis)--a brain disorder that strikes children under 10. About 2.5 million Americans suffer from some form of epilepsy; fewer than 1 in 1,000 is diagnosed with Rasmussen's.

MIND GAMES

Scientists still don't know for sure what causes Rasmussen's encephalitis. "It's probably an autoimmune disease, in which the body destroys its own brain tissue," speculates Dr. John Freeman, director of the Johns Hopkins Pediatric Epilepsy Center. Researchers do know that Rasmussen's patients carry antibodies (substances produced by the body to destroy bacteria or other foreign organisms) to specific brain proteins called glutamate receptors. When they enter the brain, these antibodies attack the receptors, triggering seizures. For Kacie, it started with a pounding headache when she was 10. "It was May of '93," her mom, Regina, recalls. "That night, Kacie went into a seizure. She was walking around the room, snapping and grabbing things out of the air that weren't there." Her parents immediately rushed Kacie to the hospital. An electroencephalogram (ih-LEK-troh-in-SE-fuh-luh-gram), which measures electrical activity in the brain, determined that the seizure was centered on her brain's left side.

As Kacie's seizures worsened, her parents sought out one hospital after another, searching for a cure. At one point, Kacie's doctors removed a very small section of the frontal brain where they thought the seizures originated. But the seizures continued in full fury.

The Caves finally turned to Dr. Freeman, who suggested a procedure so drastic the Caves were horrified. His recommendation: take out the entire left half of the brain--a procedure called a hemispherectomy (he-muh-sfir-EK-tuh-mee). The operation, first developed in the 1920s, was soon abandoned--too many patients died during surgery.

But new medical techniques and advanced brain scans in the 1980s have revived the procedure.

WHAT THE BRAIN KNOWS

The cerebrum, the largest part of the brain, is divided into two hemispheres, right and left (see miniposter p. 12). Each half controls the opposite side of the body--the reason why electrical disturbances in Kacie's left hemisphere rendered the right side of her body useless. For reasons doctors still don't know, Rasmussen's spreads through only one hemisphere, but doesn't cross over to the brain's other side.

Nearly half of all hemispherectomies are performed on children with Rasmussen's encephalitis. Surgeons also operate on children with cortical dysplasia (dis-PLAY-zhuh), or irregular brain development, and Sturge-Weber syndrome (abnormal blood-vessel formation that causes one side of the brain to shrink). When doctors remove the diseased half, spinal fluid fills the empty space--one teaspoon every five minutes. Several dozen hemispherectomies are performed each year in the U.S.

Children, especially preteens, prove the best candidates for hemispherectomies: Up to about age 12, the human brain continues to grow and develop. Brain cells called neurons form, and dendrites--threadlike extensions that grow out of neuron--forge connections between cells, enabling brain communication. That means that during brain development, even when one hemisphere is removed, the other half compensates by quickly forming new neurons and dendrites.

Memory and understanding seem to be coded on both sides of the brain. "When you take out half of the brain, you don't forget anything you've learned before and you're still able to understand things perfectly well," says Dr. Freeman. Skills that reside on one side of the brain--for example, math and language on the left--automatically shift to the other side.

Can such transfers still happen when the patient is older? By the time the Caves family decided to go ahead with the hemispherectomy, Kacie was almost 14 years old.

"What concerned us about Kacie was her language," Dr. Freeman explains. "We know that language transfers very well at 8 or 10. At 13, we had concerns."

To her doctors' amazement, Kacie came out of surgery speaking. But while she understood everything said to her, she couldn't communicate a thought. "She could say `yes,' `no,' `thank you,'" Kacie's mom says. "But she might have known that something was blue, and couldn't say the word `blue.'" Kacie went for occupational therapy, physical therapy, and speech therapy every day until spring of the following year. Last fall.

Kacie returned to school as a high school freshman. The operation has left her right hand practically useless, and she walks with a slight limp. Now a sophomore, Kacie still has trouble verbally expressing her thoughts. But when Science World asked Kacie how she feels two years after the operation, she responded, "I feel great! Really good." And the seizures? "Good, really no seizures. And I'm glad with that."

RELATED ARTICLE: How Seizures Spread Through the Brain

Seizures that accompany Rasmussen's encephalitis often start in a small part of the brain, then spread throughout the entire hemisphere.

1. A seizure in the brain's motor strip, which controls the body's motion, could set off one finger twitching.

2. Soon the seizures spreads to include all fingers.

3. As the disease progresses, the entire hand will start twitching, them the arm and face, until one side of the body is ravaged with epileptic seizures.