The operation known as a hemispherectomy—the removal of half the brain-sounds too radical to ever consider, much less perform. In the past century, however, surgeons have done it hundreds of times for disorders that cannot be controlled any other way. Perhaps surprisingly, the surgery has no apparent effect on personality or memory. Does that mean a person needs only half a brain Yes and no. People can survive and function pretty well after the procedure, but they will have some physical disabilities. The first known hemispherectomy was performed on a dog in 1888 by German physiologist Friedrich Goltz. Neurosurgeon Walter Dandy pioneered the use of the procedure on humans at Johns Hopkins University in 1923, operating on a patient who had a brain tumor. That man lived for more than three years before ultimately dying from cancer. In 1938, after performing a hemispherectomy on a 16-year-old girl, Canadian neurosurgeon Kenneth McKenzie reported that it could stop seizures, a neurological disorder in the brain. And today brain surgeons perform hemispherectomies on patients who undergo dozens of seizures daily that resist all medication and stem from conditions that primarily afflict one hemisphere. "These disorders are often progressive and damage the rest of the brain if not treated," explains neurosurgeon Gary W. Mathern of the University of California, Los Angeles. The surgery takes two forms. Anatomical hemispherectomies involve the removal of an entire hemisphere, whereas functional hemispherectomies take out only parts of a hemisphere—as well as severing the connections between the two halves of the brain. Doctors often prefer anatomical hemispherectomies because "leaving even a little bit of brain behind can lead seizures to return," says neurologist John Freeman of Johns Hopkins, which specializes in the procedure. On the other hand, functional hemispherectomies, which U.C.LA. surgeons usually perform, lead to less blood loss. "Our patients are usually under two years of age, so they have less blood to lose," Mathern says. Neurosurgeons have performed the functional operation on children as young as three months old. In these tiny patients, memory and personality develop normally. Most Johns Hopkins hemispherectomy patients are older than five years. A recent study found that 86 percent of the 111 children who underwent the procedure at Johns Hopkins between 1975 and 2001 are either seizure-free or have non-disabling seizures that do not require medication. Another study found that children who underwent a hemispherectomy often improved academically once their seizures stopped. "One was champion bowler of her class, one was chess champion of his state, and others are in college doing very nicely," Freeman notes. From Paragraph 2 and Paragraph 3, we learn that

A. hemispherectomy has become a common procedure since 1888.
B. the first patient performed with hemispherectomy finally conquered cancer.
C. the entire hemisphere must be removed once diagnosed with seizures.
D. seizures are hazardous because they can spread to the entire hemisphere.