Half of our brains can be removed by surgery with no apparent effect on personality or memory.
The operation known as hemispherectomy—where half the brain is removed—sounds too radical to ever consider, much less perform. In the last century, however, surgeons have performed it hundreds of times for disorders uncontrollable in any other way. Unbelievably, the surgery has no apparent effect on personality or memory.
The first known hemispherectomy was performed on a dog in 1888 by German physiologist Friedrich Goltz. In humans, neurosurgeon Walter Dandy pioneered the operation at Johns Hopkins University in 1923 on a brain tumor patient. (That man lived for more than three years before ultimately succumbing to cancer.) The procedure is among the most drastic kinds of brain surgery—"You can't take more than half. If you take the whole thing, you've got a problem," Johns Hopkins neurologist John Freeman quips.
One side effect Canadian neurosurgeon Kenneth McKenzie reported in 1938 after a hemispherectomy on a 16-year-old girl who suffered a stroke was that her seizures stopped.
Nowadays, the surgery is performed on patients who suffer dozens of seizures every day that resist all medication, and which are due to conditions that mostly afflict one hemisphere. "These disorders are often progressive and damage the rest of the brain if not treated," University of California, Los Angeles, neurosurgeon Gary Mathern says. Freeman concurs: "Hemispherectomy is something that one only does when the alternatives are worse."
Anatomical hemispherectomies involve the removal of the entire hemisphere, whereas functional hemispherectomies only take out parts of a hemisphere, as well as severing the corpus callosum, the fiber bundle that connects the two halves of the brain. The evacuated cavity is left empty, filling with cerebrospinal fluid in a day or so.