Kliemann D, Adolphs R, Tyszka JM, Fischl B, Yeo BTT, Nair R,
Dubois J, Paul LK. Intrinsic Functional Connectivity of the Brain in Adults
with a Single Cerebral Hemisphere. Cell Rep. 2019 Nov 19;29(8):2398-2407
Abstract
A reliable set of functional brain networks is found in
healthy people and thought to underlie our cognition, emotion, and behavior.
Here, we investigated these networks by quantifying intrinsic functional
connectivity in six individuals who had undergone surgical removal of one
hemisphere. Hemispherectomy subjects and healthy controls were scanned with
identical parameters on the same scanner and compared to a large normative
sample (n = 1,482). Surprisingly, hemispherectomy subjects and controls all
showed strong and equivalent intrahemispheric connectivity between brain
regions typically assigned to the same functional network. Connectivity between
parts of different networks, however, was markedly increased for almost all
hemispherectomy participants and across all networks. These results support the
hypothesis of a shared set of functional networks that underlie cognition and
suggest that between-network interactions may characterize functional
reorganization in hemispherectomy.
Many people think of their brain as an overstuffed attic.
Every square-inch is either crammed with information or working overtime to
help the body function properly. So is it even conceivable that a person be
normal with just half a brain?
Yes, apparently it is, according to a new analysis that
assessed brain health among six adults who had undergone a hemispherectomy as
children. The highly invasive surgery, which entails removal or severing of
half the brain, had been part of a pediatric epilepsy treatment to reduce
seizure risk.
"The people with hemispherectomies that we studied were
remarkably high-functioning," study author Dorit Kliemann said in a
statement. "They have intact language skills. When I put them in the
[brain] scanner, we made small talk, just like the hundreds of other individuals
I have scanned," she explained.
"You can almost forget their condition when you meet
them for the first time," added Kliemann, who is a post-doctoral scholar
in cognitive neuroscience at the California Institute of Technology, in
Pasadena.
Kliemann and her team noted that the six patients in the
study had all struggled with relentless epileptic seizures from a very early
age, with one patient initially struck by seizures just minutes after birth.
Hemispherectomies are typically performed as a means to
bring such "intractable" epilepsy under control, the team explained.
The aim is to isolate whichever half (or hemisphere) of the brain is affected
by the disease. That can mean either actual removal of the problematic half of
the brain or a cutting off of all physical connections between the two halves.
All of the patients had undergone full removal of half their
brain. The youngest patient was just 3 months old at the time of surgery, while
the oldest had been 11. Four involved excision of the right side of the brain,
while two had the left side removed.
Now in their 20s and 30s, the six patients agreed to undergo
functional MRI brain scans while awake at the Caltech Brain Imaging Center.
Brain activity was tracked in areas tasked with regulating
vision, movement, emotion and thought processes.
Results were then stacked up against those of six healthy
adults who also underwent scans, and with data previously collected on nearly
1,500 healthy adults (average age of 22).
Because brain networks devoted to a single regulatory
function often span both hemispheres of the brain, the team expected to see
weaker neural activity among the hemispherectomy patients. That was not the
case.
In fact, scans revealed normal in-network communication and
activity function. And communication running between different regulatory
networks was actually found to be stronger than normal among hemispherectomy
patients.
Dr. Joseph Sirven, a professor of neurology with the Mayo
Clinic in Florida and editor-in-chief of Epilepsy.com, said the findings did
not strike him as entirely surprising. He said he often sees patients
functioning at a very high level post-hemispherectomy.
"But what surprises me is the degree of compensation
that was noted," added Sirven, who was not part of the study team.
"And if we could figure out the way that the brain compensates
in this dramatic setting, and harness this compensatory mechanism for patients
affected by stroke, traumatic brain injury or other conditions, that would be a
very big deal," Sirven noted.
That thought was echoed by Kliemann. "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 or a tumor
-- can have devastating effects," she noted.
That is why it's so important to get a better understanding
of exactly how the brains of hemispherectomy patients managed to reorganize and
compensate for the loss of half a brain, Kliemann said. Because doing so could
eventually lead to new "targeted intervention strategies" to help
other types of patients struggling with the debilitating effects of a variety
of brain injuries, she theorized.
https://www.webmd.com/brain/news/20191119/they-had-half-their-brains-removed-heres-what-happened-after#2
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