How the brain reorganizes after one half of it is removed?

Removing one half of the brain in children, a procedure performed to treat neurological disorders like epilepsy, may cause the remaining parts to gradually form strong nerve connections within the existing hemisphere, according to a study.

The researchers, including those from California Institute of Technology in the US, said this rewiring potentially helps the body to function as if the brain were intact. The study, published in the journal Cell, assessed brain function in six individuals - in their 20s to early 30s - who had undergone a procedure to remove one half of the brain called hemispherectomy. The individuals ranged from three months to 11 years of age at the time of their hemispherectomies, the study noted.

The six participants along with six controls were instructed to lay down in a brain scanning device called a functional Magnetic Resonance Imaging (fMRI) machine. The were asked to relax, and try not to fall asleep while the researchers tracked their spontaneous brain activity at rest. The researchers looked at networks of brain regions known to play a part in processes like vision, movement, emotion, and cognition.

They also compared the data collected at the university's Brain Imaging Center against a database of about 1,500 normal brains without the surgery. The researchers hoped to find weaker connections within particular brain networks in the participants with only one hemisphere - since many of those networks function with both hemispheres in those with typical brains. However, they found normal connectivity, and stronger connections in the participants who had undergone hemispherectomy than the people with both halves intact.

"The people with hemispherectomies that we studied were remarkably high functioning. They have intact language skills; when I put them in the scanner we made small talk, just like the hundreds of other individuals I have scanned," said study first author Dorit Kliemann from the California Institute of Technology. "You can almost forget their condition when you meet them for the first time. 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," Kliemann said. The researchers said the wide range of ages at which the participants had their surgeries allowed them to see how the brain reorganised itself when injured. "It can help us examine how brain organization is possible in very different cases of hemispherectomy patients, which will allow us to better understand general brain mechanisms," said Kliemann.