A recent MRI study shows how some people work with half a brain. It reveals how human brain’s remarkable ability to multitask when parts of it are literally absent.
Incredible stories of people living relatively normal lives with damaged or missing giant chunks of their brains often seem to contradict reason. Yet, given the chance, the capacity of our brains to shape their abilities around the missing bits is incredible.
A recent study of people losing entire brain halves has given insights into how this can be achieved, exposing the remarkable ability of the human brain to multitask while portions of it are simply absent.
“You can almost forget their condition when you first meet them,” said the California Institute of Technology neuroscientist Dorit Kliemann.
“When I sit in front of the computer and see these MRI pictures showing only half a brain, I still marvel that the images come from the same person I just saw talking and walking and who chose to devote his or her time to research.”
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Six of the participants in the study had undergone the frightening drastic procedure of removing one of their brain hemispheres during childhood to treat a rare and severe form of epilepsy. The technique is called hemispherectomy and will only be used if the seizures are “catastrophic” or if medications fail.
“What these patients can do is truly amazing. Sure, they have problems, but their cognitive abilities are still remarkably high, when half of the brain tissue is missing,” Kliemann said.
By comparing these participants MRI scans with six controls that had no brain parts removed, together with a database of 1,482 brains scanned for the Brain Genomics Superstructure Project, Kliemann and colleagues found that the pattern of resting-state brain activity in participants with only half of their brain is remarkably similar to those who have all of their brain matter.
But the team also noticed a difference: there was a lot more interaction between brain networks among participants who had hemispherectomies.
These networks control activities such as attention, sensory, and limbic (emotion and memory), often involving both brain hemispheres. Studies suggest that network activity links to capabilities such as motor control, while network connections are essential to executive capabilities such as working memory.
The rise in connections across the six non-control participants and across all the different networks was consistent-so, for instance, the focus network had more visual network connections than normal. The patterns of network connectivity remained the same as the controls, they just did more.
“Their brain networks seem to be multitasking,” Carnegie Mellon University neuroscientist Marlene Behrmanntold told The New York Times, who did not participate in the study.
This increase in network connection reflects how the remaining brain compensates for the loss of available brain hardware, the researchers explain in their paper to maintain cognitive function and awareness.
They point out that they were unable to create connections between the differences in brain activity and actual behaviors or intelligence such as IQ due to the very small sample size.
For future research, the team is now interested in learning how these brain networks work together in order to compensate for damaged or absent brain parts during specific tasks-as opposed to resting-state tested here.
And understanding how our various brain networks can multi-task through increased connections could help scientists to uncover other brain injuries treatments.
“As remarkable as there are people who can survive with half a brain, sometimes a very small brain injury such as a stroke or a traumatic brain injury such as a bicycle accident or a tumor can have devastating effects,” Kliemann said.
Full paper is published in Cell Reports.