A new study reveals how word and face recognition can be supported with only half the brain

Researchers conclude that one hemisphere of the brain can adequately function as if it were doing so for two hemispheres.
Brittney Grimes
Left and right human brain hemispheres.
Left and right human brain hemispheres.

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People who underwent surgery as children to remove half of their brain were still able to accurately recognize differences between pairs of words or faces, a press release reveals.

The research was done to study brain plasticity and perception. Plasticity is when the brain can be molded to reorganize itself in the hemispheric region not injured, or in this case, the only hemispheric region that is there. The participants were able to correctly identify differences between words or faces with more than 80% accuracy.

The study was published in the Proceedings of the National Academy of Sciences.

The brain’s ability to rewire itself

The large volume of brain tissue removed allowed researchers to discover the brain’s ability to restructure itself and adapt to damage or surgical procedures. The study attempts to discover the neuroplasticity in the human brain and comprehend if one side of the brain can perform functions usually split between the two hemispheres. Neuroplasticity is the brain’s ability to change and rewire itself following injury.

“Working with hemispherectomy patients allowed us to study the upper bounds of functional capacity of a single brain hemisphere. With the results from this study, we now have a foot in the door of human neuroplasticity and can finally begin examining the capabilities of brain reorganization,” said Dr. Marlene Behrmann, senior author of the study and professor of ophthalmology and psychology at the University of Pittsburgh and Carnegie Mellon University.

The research

The study explores what happens to the brain when it is still “highly plastic” and forced to make changes. Researchers looked at people who, as children, underwent a complete hemispherectomy, or the surgical removal of one hemisphere of the brain to control seizures. The study had 40 participants.

Researchers gave the participants pairs of words, each differing by one letter, to evaluate word recognition abilities. For example, words such as “soup” and “soap” were given to each participant. To assess how well they could recognize faces, each person was shown a pair of people in images on a screen. The images or words were only shown on the screen for a fraction of a second. Then, the participants had to determine if the pair of faces or words were the identical or distinct in any way.

Outcome

The research team noticed that the one hemisphere of the brain supported both of those functions precisely. They noted that the capacity for word and facial differed by less than 10% and the accuracy was greater than 80%. The precision was comparable regardless of whether the left or right hemisphere was removed. “Reassuringly, losing half of the brain does not equate to losing half of its functionality,” said Dr. Michael Granovetter, first author of the study and a student in the Medical Scientist Training Program at Pitt’s School of Medicine.

The study provides a positive outlook for patients that need to get a hemispherectomy due to epileptic seizures. “While we can’t definitively predict how any given child might be affected by a hemispherectomy, the performance that we see in these patients is encouraging. The more we can understand plasticity after surgery, the more information, and perhaps added comfort, we can provide to parents who are making difficult decisions about their child’s treatment plan,” Granovetter continued.

The study allows researchers to understand the functionality of the human brain and realize its ability to reorganize under certain circumstances.

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