Removing Half the Brain Appears to Boost Brain Connectivity

Six adults had half of their brain removed when they were children. Years later, and brain scans show that not only were the connections comparable to healthy controls with both brain hemispheres intact—they were, in almost all cases, "markedly" stronger.

Researchers writing in Cell Reports describe how the brain can reshuffle and adapt in the face of major surgery to enable the body, at least as far as brain connectivity is concerned, to function and perform as if it was a whole organ.

"Somehow the existing networks of the brain compensated for the extreme condition people find themselves in after surgery," Wael Assad, an associate professor of neuroscience at Brown University's Carney Institute for Brain Science who was not involved in the research, told Newsweek.

"We know that children's brains are typically a little bit more plastic or reorganizable, so to see this is one way in which that reorganization would be happening is interesting."

The six volunteers who underwent a hemispherectomy did so to prevent debilitating seizures triggered by epilepsy. But despite essentially having only half a brain, they are high-functioning with intact language skills. According to Web MD, "Most people feel normal and can go back to work, school, and their usual lives about 6 to 8 weeks after surgery."

"You can almost forget their condition when you meet them for the first time," first author Dorit Kliemann, a postdoc 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, 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."

Brain scan
This picture shows an fMRI scan showing one single slice through the brain of an adult who had an entire hemisphere removed during childhood due to epilepsy. Caltech Brain Imaging Center

Brain scans of the six volunteers at rest were compared to those of six healthy controls, as well as data collected by the Brain Genomics Superstruct Project pertaining to 1,500 typical brains.

The researchers then analyzed regions of the brain associated with functions including vision, movement, emotion and cognition by studying temporal correlations of blood-oxygenation-level-dependent-signal (BOLD). These correlations served an indirect measure of functional connectivity.

The scans revealed the opposite of what had originally been expected. Instead of finding weaker connections as initially assumed—several of the networks studied involve two hemispheres in people with typical brains—they found that many were stronger.

"It is amazing that you can take out such a large part of the brain in children and see them recover function," said Assad. But, he adds, there are still questions left to be answered.

"There may be some differences between what's actually going on in terms of the brain—the brain's electrical communication—and what they're measuring."

It may also be that the changes to brain connectivity are a feature of the epilepsy itself, rather than evidence of the brain's plasticity in the face of major trauma, he explained.

It will require more research on larger sample sizes to find out what exactly is going on and how this can help patients with medical conditions and injuries affecting the brain in the future—something the researchers hope to look at in the future.

"As remarkable as it is that there are individuals who can live with half a brain, sometimes a very small brain lesion like a stroke or a traumatic brain injury like a bicycle accident or a tumor can have devastating effects," said Kliemann.

The article has been updated to include Dr. Wael Assad's affiliation to Brown University's Carney Institute for Brain Science. A previous version stated children's brains tend to be "more plastic or recoganizable."