About three years ago, a six-year-old boy in Pittsburgh underwent surgery to remove a large part of the right side of his brain. Identified publicly as “U.D.” by doctors, the boy suffered from epilepsy, and drugs were not helping to control his seizures. His doctors and his parents decided that taking out U.D.’s right occipital and posterior temporal lobes would be the best way to improve his quality of life. But the medical team was not certain how the surgery would affect the boy’s ability to recognize visual images and printed words, which are normally processed by regions within these parts of the brain.
This uncertainty stemmed from neuro-scientists not having a clear understanding of how the brain’s visual system reorganizes itself after trauma caused by disease, injury, or surgery. “There is a general and ubiquitous question that people who are interested in brain function need to grapple with,” says Marlene Behrmann, a psychologist at Carnegie Mellon University in Pittsburgh. “It has to do with the extent to which brain function and even brain structure is concretized or potentially more malleable.” U.D.’s surgery and recovery marked an opportunity for Behrmann and her colleagues to address “one small nugget in this much, much larger question,” she says.
U.D. is one patient out of many whom Behrmann and her colleagues are now studying to assess the brain’s visual system’s plasticity—its ability to change—after undergoing a similar surgery. Unlike memory or language processing, which have been explored by many studies of brain recovery following surgery, “there’s been really very little work that’s looked at reorganization or compensation in the visual system of the brain,” she says.
In particular, Behrmann’s team is interested in these patients’ ability to recognize written words or faces because they are among the most complex stimuli for the visual system to process. To ease the burden on the visual system, a normal brain typically splits responsibility for processing words and faces across the occipital and posterior temporal lobes, with the left-hemisphere sides of those regions recognizing words, and the right-hemisphere sides recognizing faces. “It’s not exactly cut-and-dried like that, but one or the other hemisphere bears the burden, to some degree, in each task,” Behrmann says. Given this division of labor, she and her colleagues wanted to know what would happen to U.D.’s ability to process images on removal, or resection, of a large portion of the right side of his brain—and more importantly, how his brain might compensate for that loss.
How did the brain organize itself so that both tasks could be taken on in only one hemisphere?–Marlene Behrmann, Carnegie Mellon University
In a paper published in July, the team describes the neurological and cognitive development of the boy during the four years following his lobectomy (Cell Rep, 24:1113–22.e6). “We decided to publish that single case ahead of the comprehensive group data because it is the first study that has monitored the change over time in an individual following a resection,” Behrmann says. Usually, studies that assess patients’ ability to recover cognitive abilities are started many years after surgery rather than just one year afterwards, as this study was.
When the researchers examined U.D. 13 months after the operation, they found that the seven-year-old exhibited cognitive skills that were on a par with other kids his age. “We were really surprised that this young child learned to read very well and showed absolutely normal face recognition,” says Behrmann. Consequently, “we wanted to know: How did the brain organize itself so that both tasks could be taken on in only one hemisphere?”
Sifting through neuroimaging data collected on several occasions over the three-year period following that first examination, when Berhmann and her colleagues would ask U.D. to identify words or faces, the researchers detected activity in a tiny region of the left hemisphere of his brain during face recognition tasks. This unidentified region sat right next to a different, known region, the visual word form area, that showed activation during word recognition tasks. Although word recognition is normally associated with the visual word form area, face recognition usually is not processed in this part of the brain. “It was as if these two little brain regions were jockeying for position, pushing each other apart,” Behrmann says. They were abutting, and only partially overlapping, but allowed for word and face recognition in the single left hemisphere, the researchers concluded.
U.D. hadn’t regained all visual functions of the right hemisphere, however. He still was unable to see his left visual field as a result of the surgery, suggesting his brain did not have the plasticity to remap the region in the right hemisphere that processes visual stimuli from the opposite-side visual field. Instead, Behrmann says, he had to move his eyes or head to bring an object into his right visual field, where it would be processed by the left hemisphere.
“The study is very carefully done and took advantage of a very unique opportunity,” writes Isabel Gauthier, a cognitive neuroscientist at Vanderbilt University who studies object perception and was not involved in the work, in an email to The Scientist. “The authors certainly got a lot of information out of this one patient, and studies that follow patients over time like this are pretty rare.” However, she notes, the data indicate that although U.D. had regained normal face recognition abilities a year after surgery, brain activity in the left hemisphere associated with recognizing faces didn’t appear until about a year and seven months after surgery. Based on this observation, “it’s unclear what part of his brain he was using for face recognition before the resection,” Gauthier says. That resection had no effect on his ability to recognize faces, she adds, might mean that face recognition was in fact being processed, both before and after surgery, in an area outside of the large part that was removed.
If U.D.’s brain had rewired itself even prior to the surgery, Gauthier notes that it may not have been the procedure but the epilepsy itself that drove this neuronal plasticity—a form of reorganization that Behrmann and colleagues have explored before. “This is consistent with the idea that when something abnormal—the epilepsy here, not so much the surgery—happens early enough, the brain is better able to reorganize,” Gauthier says, noting such plasticity is much more difficult for adult brains.
Behrmann says she and her colleagues did not have presurgical scans of U.D.’s brain to compare with postsurgical ones. However, in subsequent studies of other patients in which they tracked organization and activity both before and after surgery, they found significant differences in the pre- and postsurgical scans, “so we know that the surgery has played a role in bringing about change over and above any that might have come about presurgically because of the epilepsy itself,” she says.
“It is really important to understand how the brain is organized around epileptic tissue and how the brain reorganizes itself after surgery,” says Taylor Abel, a pediatric neurosurgeon at Children’s Hospital of Pittsburgh of the University of Pittsburgh Medical Center. Abel, who was not involved in the study or treatment of U.D., specializes in operating on epileptic patients, and is planning to start working with Behrmann soon. The results of the current study are important, he adds, because if paired with future findings from patients similar to U.D., they could help clinicians counsel parents on how their children will respond to surgery, not only for epilepsy, but other types of neurological disorders, too.