How Removing Half of Someone's Brain Can Improve Their Life

McZusatz, Wikimedia Commons // CC BY-SA 3.0
McZusatz, Wikimedia Commons // CC BY-SA 3.0 / McZusatz, Wikimedia Commons // CC BY-SA 3.0

From the outside, Elena del Peral seems to be like any other high-achieving college senior. She goofs around the campus quad of Massachusetts’ Curry College with her classmates and posts pictures on Facebook of birthday drinks with girlfriends. She holds a philanthropic job at a childhood cancer foundation and is on the dean’s list. She's friendly, bright, and fit. Outwardly, perhaps the most provocative thing about her is that she’ll wear both a Yankees cap and a Red Sox jersey at the same time—a peacemaker among the long-standing rivals.

But beneath her cap is one remarkable mind. Elena del Peral has only half a brain.

Image courtesy of Elena del Peral

Shortly after her birth in 1992, Elena’s parents started to notice that she was favoring her right side. By the time she was a toddler, she was solely using her left arm to shimmy along the floor, with her right arm tucked in to her chest. Within 18 months she began to suffer severe seizures, and at age two she had a massive tonic-clonic episode while vacationing in the Adirondack Mountains. Desperate to determine what was causing these intractable seizures and the hemiparesis, her parents, Sonya and Casiano, jockeyed from specialist to specialist throughout the northeast.

It turns out that Elena had suffered a left-sided congenital stroke in utero, which was sparking electric storms in her brain that spread from the diseased area across the corpus callosum—the great communicator between the two cerebral hemispheres—to the healthy right side of her brain. For the next four years, she took every epileptic medication in the book. They dulled her senses but didn’t stop the seizures.

At age six, del Peral underwent a battery of tests including MRIs, EEGs, and CAT scans. A team including neurologists and neurosurgeons pored over the results. They said her condition fit the criteria for a rare surgery that seemed radical but had yielded promising results in the past for people like her. It was called a hemispherectomy: “hemisphere,” half the brain; “-ectomy,” surgically removing it. In short, they wanted to remove half of Elena’s brain.

Dr. Howard Weiner, a pediatric neurosurgeon and professor of neurological surgery and pediatrics at the NYU Langone Medical Center and NYU School of Medicine, has been performing these types of surgeries on children for decades—including on Elena. He explained to mental_floss­ that when it comes to cases like hers, the normal part of the brain is impaired when it is bombarded by overly active impulses sent over from the damaged side. These children can suffer cognitive developmental impairment, partial paralysis, behavioral issues, social isolation, and a laundry list of other problems. Once that transmission is cut, the unharmed hemisphere can start functioning without all of that charged disruption.

Soon after, Weiner performed a left-sided hemispherectomy on Elena, removing the left half of her brain. Recovery after a hemispherectomy is very positive. With aggressive occupational therapy and physical therapy, children can usually lead normal, productive lives. Elena recalls to mental_floss, “Things suddenly got easy. I became smart. I made friends. I became social. I just need a little extra help.”

Her parents capitalized on her go-getter attitude and inner motivation. She attended special programs for children with disabilities and then attended Darrow School, a co-ed boarding school in New York, where her talents were fostered. Over the years, she excelled.


The first hemispherectomies—at least ones that patients actually survived—date back to the 1920s, when neurosurgery pioneer Walter Dandy removed entire halves of the brain to treat cerebral glioma, a type of brain tumor. In 1938, Canadian neurosurgeon K.G. McKenzie performed a similar procedure to treat a patient with left hemiplegia (paralysis on the left side of the body) and epilepsy; the patient's seizures eased after the right hemisphere was removed. Various techniques have been performed over the years, from cutting out small portions of the afflicted area to removing entire hemispheres.

In the past 25 years, the procedure has evolved, thanks to a better understanding of complications such as hydrocephalus, an abnormal accumulation of cerebral spinal fluid in the empty part of the brain cavity; improved surgical methods to prevent recurring seizures; accurate mapping and isolation of the unhealthy area; and a deeper knowledge of the brain’s plasticity. In fact, 2016 Republican presidential candidate and pediatric neurosurgeon Ben Carson revived the surgery in the 1980s at Johns Hopkins Hospital—the very hospital where Dandy operated.

But we have to look back to the 19th century to understand why we ever thought taking away half a patient’s brain might make her better off—and specifically to Phineas Gage, perhaps neuroscience’s most famous patient, who clued us in to the remarkable resiliency and adaptability of the human brain. In 1848, while he was working on a railroad-building site in Vermont, an explosion blasted a 43-inch tamping iron through Gage’s head, entering through his left cheek and exiting straight out of the top of his head.

Not only did Gage live to tell the tale, but he had a relatively normal life for another 12 years, working as a stagecoach driver in Chile before returning to San Francisco to live with relatives. Gage had some neurological deficits and major personality changes—he became an avid user of profanity and had little sense of social propriety, among other things—but various reports suggest that, all in all, his brain regained much of its function. In this studio portrait, Gage is said to be holding the iron rod that pierced his skull.

Wikimedia Commons // CC BY-SA 3.0

Gage’s case is only one of several historical incidents in which individuals sustained massive brain injuries yet largely recovered. Immensely complex, the brain is more than a collection of neurons and glial cells. It is the body’s primary controller, with highly specialized areas wired to command thoughts, movement, and action. For example, Broca’s area, located in the frontal lobe of the left hemisphere, controls the ability to speak. But the brain compensates. Despite the left side of her brain being gone, del Peral speaks without any difficulty—and quite eloquently.

Gage's and del Peral’s cases are prime examples of neuroplasticity, the brain’s ability to rewire networks and reorganize cellular or neural function to take place somewhere else.

“Language sets up shop by age two, three, and four, at which time we are learning how to speak,” Dr. Weiner says. “When the area that controls language is damaged, it can move. The earlier the insult, the more likely it is to move—the more plasticity.” That’s what happened in del Peral’s case. The left side of her brain was damaged in the womb, so language and motor function shifted to the right side before she was even born. At the time of her surgery, the left side of her brain, the source of her epilepsy, was doing more harm than good.


Hemispherectomies can reduce or eliminate seizures up to 89 percent of the time in children with certain neurological disorders, including infarcts (brain necrosis), malformations of the cortical development, Rasmussen’s encephalitis (an inflammatory condition that attacks only half of the brain), and Sturge-Weber syndrome (a vascular abnormality).

The trend now is to perform the surgery on younger children, and even babies, to take advantage of the brain’s plasticity as early as possible. For example, if the left hemisphere is removed around age 10 or after, the child will likely never speak again, as speech is already fixed.

Today, the operation can be much less invasive, with more vascularized brain left intact. In fact, surgeons are increasingly referring to the procedure as a hemispherotomy because they may not have to remove an entire half of the brain. In one diagnostic test, subdural electrode grids are surgically applied before the actual hemispherectomy in order to help neurologists and neurosurgeons map out the bad tissue. Once surgery begins and the brain is exposed, they work carefully from the inside out, following the corpus callosum to then functionally disconnect the communication link between the two halves of the brain. Highly technical microscopes and micro-surgical instruments—wielded with a lot of skill—are used to excise the problematic matter. Any hole that is left naturally fills in with cerebral spinal fluid, which protects the tissue left inside.

Disconnect is the key word,” says Dr. Weiner. “We went from resecting [complete removal] to simply disconnecting.”

By disengaging the damaged portion of the brain, the electrical storms stop traveling to the healthy side of the brain. Many patients like Elena can stop having seizures altogether and cease taking epileptic medications for good.

According to data collected by the Kids' Inpatient Database (KID) every three years from 2000 to 2009, 552 hospital admissions were documented for hemispherectomies in the U.S. during that time period, with a mean patient age of 6.7 years old. Currently, approximately 42 hospitals in the United States and 13 facilities abroad perform the surgery. The demand outpaces the supply; at the time he spoke to mental_floss, Dr. Weiner was en route to Panama to operate on children with intractable seizures.

Next spring, del Peral will graduate from Curry College, where she has made the dean’s list every semester since freshman year. “I have to work 10 times more than the average person, but it’s worth it,” she says. “No one has a story like mine. Living with half a brain? I don’t want this to define who I am.”