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A child’s brain can recover even after half a hemisphere is removed. Getty Images
  • A new study looked at the long-term effects of having a hemispherectomy, where the right or left half of the brain is surgically removed or disconnected.
  • The procedure is done mainly in very young children with severe epilepsy in an effort to protect their cognitive development.
  • Researchers are learning how the plasticity of younger brains helps children avoid severe impairment.

Seizures can have a devastating effect on brain development in children, and in some severe cases, physicians have even removed part of the brain to help stop them.

In these cases surgeons perform a hemispherectomy, where the right or left half of the brain is surgically removed or disconnected from the other healthier half.

But what happens to a growing child when half their brain is removed?

A new small case study published this week in the journal Cell Reports focused on these children and their development into adults. The findings suggests that the remaining half of the brain may form unusually strong connections between different functional brain networks. This may help the body work as if the brain was intact.

The reason this occurs is that if the patient is young enough, their body may compensate by shifting some neural functions from the damaged, disconnected, or missing half of their brain to the other half.

“The people with hemispherectomies that we studied were remarkably high functioning,” Dorit Kliemann, PhD, first author of the study and a postdoctoral scholar at the California Institute of Technology, said in a statement.

“When I sit in front of the computer and see these MRI images showing only half a brain,” she continued, “I still marvel that the images are coming from the same human being who I just saw talking and walking and who has chosen to devote his or her time to research.”

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This MRI scan shows the brain of an adult who had an entire hemisphere removed during childhood due to epilepsy. Image via Caltech Brain Imaging Center

To conduct this study, Kliemann and colleagues recruited six high-functioning adults who had undergone hemispherectomy in childhood to treat epileptic seizures. They also recruited six healthy adults who hadn’t undergone hemispherectomy.

They asked each participant to lie down and relax in a functional MRI (fMRI) machine, which created images of the participant’s brain activity.

When they compared the brain activity of people who had undergone hemispherectomy to those who hadn’t, they found that both had similar connections within brain regions that are typically involved in the same functional brain network. However, people who had undergone hemispherectomy had unusually high brain connectivity between different functional networks.

Although more research is needed, it’s possible that between-network connections might help the brain compensate for loss of function in one hemisphere.

“We’re just beginning to think about how the connections in the remaining hemisphere reorganize and how they work,” Dr. William Bingaman, head of the epilepsy surgery section at Cleveland Clinic in Cleveland, told Healthline.

“I think this an important study to help us think about how that happens,” Bingaman, who was not involved in the study, added.

Although brain surgery may seem like a drastic treatment approach, it can have substantial benefits for children who continue to experience seizures after trying multiple medications.

“There’s really only one circumstance [where we consider surgery], and that’s where somebody has what we call intractable epilepsy, meaning seizures that cannot be controlled with medication,” Dr. Sean Lew, medical director of neurosurgery at the Children’s Hospital of Wisconsin, said.

“If those seizures are coming from a large area in one hemisphere [of the brain], then [hemispherectomy] is the only procedure that’s going to stop those seizures,” he continued.

If left untreated, seizures can cause more damage to a child’s brain and disrupt their cognitive development. This can lead to more severe disability.

Hemispherectomy can potentially stop the seizures. This can give the brain a chance to reorganize and develop without ongoing disruption.

Anyone who undergoes hemispherectomy will have some functional limitations.

For example, when half of the brain is damaged, disconnected, or removed, it causes weakness on the opposite side of the body. In particular, the foot and hand on one side will be weaker. It also causes vision loss on one side of the visual field.

But in many cases, children who are candidates for hemispherectomy have already lost some neurological function as a result of the brain injury or disorder that’s causing their seizures.

Without effective treatment, they’re at risk of losing even more function.

“For a parent who’s putting their child through hemispherectomy, one of their biggest questions is, ‘What’s my child going to be like 15 or 20 years from now?’” Bingaman said.

“And the main indicator of that is stopping the seizures. We know that if we don’t stop the seizures, cognition suffers and outcome suffers,” he continued.

The outcomes of hemispherectomy tend to be best when it’s performed early in life, Lew and Bingaman said.

That’s because the brain seems to be more plastic when it’s developing in early childhood. As a result, younger brains are more likely to shift some neurological functions from one side to the other.

For example, language function typically develops on the left side of the brain. If the left side is damaged, disconnected, or missing, language function can potentially shift to the right side — but that’s more likely to happen when the change is triggered in early childhood.

“If you have a left-sided hemispherectomy when you’re older, you probably won’t be able to speak because it’s too late. These functions have been laid down in the left side and then you disconnect it,” Lew said.

“But if you do it on a 3-year-old, their brain is still plastic enough that it can develop language on the right side of the brain,” he continued.

Although hemispherectomy tends to be more effective in younger patients, many parents are hesitant to choose surgery.

“For the lay public, these surgeries can seem very dramatic and dangerous, and that perception prevents a lot of people from getting treated at a younger age,” Lew said.

“But kids who have the surgery when they’re 2 [years old] will have a much better quality of life than kids who have the surgery when they’re 16 [years old],” he added.

Bingaman hopes that studies on hemispherectomy may help increase understanding of brain plasticity and the potential benefits of epilepsy surgery.

“It’s a fantastic surgery, and there’s a lot of kids out there that can benefit,” Bingaman said.

“I think these kind of studies are helping to get the word out there and help us understand how the brain can reorganize,” he continued. “The brain is a remarkable organ.”