- The brain surgery that ended boy's epileptic seizures also removed parts of the right hemisphere
- His brain rewired itself so that the left hemisphere now performs work normally done by the right
(CNN)What does a child's brain, which repaired itself after a full third of the right hemisphere was surgically removed, teach us about all brains?
Our developing brains find unique ways to rewire themselves as necessary, suggests a new case study of a nearly 11-year old boy referred to only as "UD" (his privacy is respected by never revealing his true name).
The operation when he was 6 years 10 months old eliminated UD's entire occipital lobe, home of the brain's vision processing center, and most of his temporal lobe, where both visual and auditory signals land and then get sorted. Yet, UD's left hemisphere compensated for any losses on the right side of his brain by assuming the roles of both hemispheres. As a result, both his cognitive and visual function are now intact.
"UD's case [has] essentially shown us that one hemisphere is enough for normal visual function," said Marlene Behrmann, senior author of the study and a neuroscientist at Carnegie Mellon's Department of Psychology and Center for the Neural Basis of Cognition.
This is the "key finding" of the new case study published Tuesday in the journal Cell Reports, said Behrmann, though she added that UD's vision remains partially impaired by the surgery. Seemingly, a small price paid to be cured of a life-threatening disorder.
At age 4, when most children have begun to somersault, to dress themselves and to name the many colors they see, UD suffered his first epileptic seizure. Soon, his seizures became frequent and severe.
Over the next couple of years, his doctors made many attempts to try and control UD's seizures, mostly through medication, explained Behrmann. Though some drugs reduced his seizures, none stopped them.
"As a last resort, the decision was made for him to undergo lobectomy," said Behrmann, who explained that this procedure requires a surgical plan to remove the focal point of epilepsy without affecting other regions of the brain.
"The surgery eliminates, completely, the seizures in roughly 60% to 70% of the children [who undergo the operation], so it's really highly effective," said Behrmann, who took no part in the surgery, which is performed on about 4% to 6% of all patients with uncontrollable epilepsy.
In UD's case, a localized tumor in his right hemisphere was the cause of his epilepsy. The surgery, which took place when he was age 6 years and 9 months old, removed the tumor along with most of two of his four lobes situated within the right hemisphere.
"We saw him almost a year later, when he was fully stable and no longer on medication and ready to participate," said Behrmann. Prior to the surgery, he had undergone extensive behavioral and visual testing, which was necessary "because they were going to remove part of the visual system," she explained.
Over the next three years, Behrmann and her team studied UD's post-surgical progress using high tech scans to measure his brain activity at five separate timepoints.
Essentially, then, she and her colleagues watched how UD's brain rewired itself after the surgery.
What they witnessed was the left hemisphere assuming the functions usually performed by the missing regions of his brain. His left hemisphere, then, did its usual work of word recognition yet also took on the role of recognizing faces, usually the responsibility of the right hemisphere.
"So as word recognition was emerging, we could see a kind of jostling for position between word recognition and face recognition in the same left hemisphere," said Behrmann. "They kind of like pushed each other around a little bit and then settled down."
"And now [UD's] face and word recognition skills are entirely normal," she said, noting that the two skills "sort of settled down in neighboring and abutting regions" of his brain in the left hemisphere.
Both word and face recognition is thought of as "a complex pattern recognition problem," explained Behrmann. The reason is that words are all "visually very similar" to each other just as faces are.
Even in typically-developing children, the brain takes a long time to acquire these separate recognition abilities, said Behrman, probably because of how "fine-grained the mechanism needs to be" to tease apart similar appearing words and similar appearing faces.
Not only did she and her colleagues compare UD's abilities to his peers, they also tested him with "the most challenging tests that we could do," she said. "We really drilled down to understand whether or not there was any loss or alteration of function. And we weren't able to see any."