The brains of children reorganize after epilepsy surgery to maintain their visual perception

Press release

Tuesday, June 4, 2019

An NIH-funded study shows that in children, the brain can compensate for missing areas of the visual cortex.

According to a study funded by the National Eye Institute (NEI), part of the National Institutes of Health, children can maintain a total visual perception – the ability to process and understand visual information – after brain surgery for severe epilepsy . Although brain surgery can put an end to seizures, it carries significant risks, including impaired visual perception. However, a new report by Carnegie Mellon University in Pittsburgh from a study of children with epilepsy suggests that lasting effects on visual perception may be minimal, even in children who have lost tissue in the visual centers of the brain.

Normal visual function requires not only information sent by the eyes (view), but also a treatment in the brain that allows us to understand and act on this information (perception). Eye signals are first treated in the early visual cortex, a region located at the back of the brain necessary for sight. They then travel through other parts of the cerebral cortex, allowing the recognition of patterns, faces, objects, scenes and written words. In adults, even if their eyesight is still present, an injury or removal of a small portion of the brain vision treatment centers can result in a dramatic and permanent loss of perception, preventing them from recognizing faces, locations or read, for example. But in children, who are still developing, this part of the brain seems able to rewire itself, a process known as plasticity.

"Although studies have been done on the memory and functioning of language in children in whom part of the brain was surgically removed for the treatment of epilepsy, few studies have been devoted to Impact of surgery on the visual system of the brain and the consequences that result. Perceptual behavior, "said Marlene Behrmann, Ph.D., lead author of the study." Our goal was to close that gap. "

Behrmann and his colleagues recruited 10 children operated on for severe epilepsy – caused in most cases by an injury such as a stroke during infancy or by a tumor – and 10 children in good health part of the control group. Of the children operated on, three had lost parts of the visual cortex on the right, three on the left, and the other four had lost other parts of the brain not involved in perception, thus constituting a second type of control group. Of the six children whose visual cortex areas were removed, four presented a permanent reduction in peripheral vision from one side due to early visual cortex loss. Epilepsy was resolved or significantly improved in all children after surgery. The children were aged 6 to 17 at the time of the surgery and most of them joined the study a few years later.

The researchers tested children's perception abilities, including facial recognition, ability to classify objects, reading and pattern recognition. Although in some cases one side of the visual cortex is totally lacking, almost all children have been able to carry out these behavioral tasks and to be within normal limits even for perception activities. and complex memory.

To better understand how children were able to compensate after surgery, the team imaged the brain of these children using functional magnetic resonance imaging (fMRI), while the children performed perception tasks. The fMRI allows researchers to visualize which regions of the brain are activated during specific activities. The team was able to map specific locations in the brain needed for individual perception tasks in both control and operated children. These areas included the early visual cortex, fusiform facial area (necessary for facial recognition), parahippocampal area (required for treatment of scenes and locations), lateral occipital complex (required for object recognition) and the area of ​​visual form (necessary for reading).

Most areas of visual perception exist bilaterally, that is, both sides of the brain are involved in these tasks. The exceptions, however, relate to facial recognition (fusiform facial area), which tends to be more dominant in the right hemisphere, and the area of ​​visual verbal form.

"We believe there is some competition between facial and verbal representation," said Erez Freud, Ph.D., lead author of the study, who is now an assistant professor at York University in Toronto. "When we learn to read, a specific area for reading appears on the left, which causes face recognition to move to the right hemisphere."

Curiously, for a participant whose operation had eliminated most of the visual cortex of the left hemisphere, this region of visual-specific visual word form was mapped to the right hemisphere, in sharing a space next to the facial recognition area on that side. But even for participants who had not shown such clear remapping, the remaining hemisphere was still able to compensate for missing regions in a way that was not usually seen in adults.

Compensation has not been determined yet, but researchers believe it can begin well before surgery, in response to the damage that caused epilepsy.

"It is possible that early surgical treatment for children with epilepsy may allow this new mapping," but further research is needed to understand what governs this type of brain plasticity, "Freud said.

"It turns out that the residual cortex can actually support most of the visual functions we are looking at," said Tina Liu, Ph.D., lead author of the study. "These visual functions – recognizing patterns, facial recognition, and object recognition – are really important to support daily interactions."

NEI directs federal government research on the visual system and eye diseases. NEI supports basic and clinical science programs aimed at developing eye-saving treatments and meeting the special needs of the visually impaired. For more information, visit https://www.nei.nih.gov.

About the National Institutes of Health (NIH):
The NIH, the country's medical research agency, has 27 institutes and centers and is part of the US Department of Health and Human Services. NIH is the lead federal agency that leads and supports basic, clinical and translational medical research. She studies causes, treatments and cures for common and rare diseases. For more information on NIH and its programs, visit www.nih.gov.

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