Instead, researchers found that while the type of connections remained the same in the individuals with just one hemisphere, different regions responsible for processing sensorimotor information, vision, attention and social cues strengthened existing connections, communicating more frequently with each other compared with ordinary brains.

It was almost as if parts of the brain that may have normally been specialized, say, as trumpet players, had talked to the rest of the band and taken additional responsibilities to play percussion instruments as well, Dr. Behrmann said. “Their brain networks seem to be multitasking.”

The results are encouraging for researchers and families trying to understand how the brain adapts and functions after a hemispherectomy.

“I think there’s more and more evidence to suggest that brain plasticity is a really long-lasting phenomena,” said Dr. Ajay Gupta, a pediatric neurologist at the Cleveland Clinic, who has followed nearly 200 children after the surgery.

Until recently, the scientific consensus has been that hemispherectomy surgery is best performed at a very young age, before a child reaches the age of 4 or 5. That way, they can regain normal function as they grow older. While neuroplasticity is stronger in early childhood, the new study suggests that surgery should not be withheld after an arbitrary end date, Dr. Gupta said. Adults in the study had undergone hemispherectomy surgery at ages ranging from 3 months to 11 years old.

A factor that may play a more important role in patient outcomes is the age at which seizures begin to occur. The surgery is still considered a last resort after medical treatment. But if the duration of seizures and resulting brain damage can be limited, patients may recover more function.

“The other hemisphere is already having to handle extra responsibilities before patients get treated,” said Lynn K. Paul, a neuroscientist at California Institute of Technology and a co-author of the study. “It continues to do so when you take out the damaged hemisphere. So what we really want is to protect the hemisphere that’s working.”