How does the brain function when half is removed? Scientists have found it performs remarkably well.
A small study involving those who have had one of their brain hemispheres removed since childhood has shown that the remaining half performs significantly better than once thought. The research, published to Cell Reports by a team from the California Institute of Technology (Caltech), looked at six adults who had hemispherectomies to reduce epileptic seizures and six control subjects.
They were instructed to lay down in an fMRI machine, relax and try not to fall asleep while the researchers tracked spontaneous brain activity at rest. The team then looked at networks known to control things such as vision, movement, emotion and cognition, which were then compared with a database of 1,500 typical brains.
This revealed that in those with a hemisphere removed, their remaining half formed unusually strong connections between different functional networks, potentially helping the body to function as if the brain were fully intact.
Future treatment for brain injuries
“The people with hemispherectomies that we studied were remarkably high functioning,” said the study’s first author, Dorit Kliemann.
“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.”
The team said it was expecting to find weaker connections within particular networks given that many of them usually involve both hemispheres. Instead, it found surprisingly normal global connectivity, and stronger connections than the study’s controls between different networks.
Those taking part in the study were in their 20s and 30s, but had received their hemispherectomies at ages ranging from three months to 11. This, the team said, can help it figure out how the organ reorganises itself when injured.
“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 tumour can have devastating effects,” Kliemann said.
“We’re trying to understand the principles of brain reorganisation that can lead to compensation. Maybe down the line, that work can inform targeted intervention strategies and different outcome scenarios to help more people with brain injuries.”