Head injuries have left more than five million Americans permanently disabled. They have difficulty concentrating on even simple tasks and often have to quit their jobs or drop out of school.

A published study On Monday, you offered them a glimmer of hope. Five people with moderate to severe brain injuries had electrodes implanted in their heads. As the electrodes stimulated their brains, their performance on cognitive tests improved.

If the results are confirmed in larger clinical trials, the implants could become the first effective treatment for chronic brain damage, the researchers said.

“This is the first evidence that we can make a difference to this problem,” said Dr. Nicholas Schiff, a neurologist at Weill Cornell Medicine in New York, who led the study.

Gina Arata, one of the volunteers who received the implant, was 22 when a car accident left her with fatigue, memory problems and uncontrollable emotions. She abandoned her plans to study law and lived with her parents in Modesto, California, unable to hold down a job.

In 2018, 18 years after the accident, Ms. Arata received the implant. Her life has changed profoundly, she says. “I can be a normal human being and have a conversation,” she said. “It’s pretty amazing how much I’ve seen myself improve.”

Dr. Schiff and his colleagues designed this trial based on years of research into brain structure. These studies suggest that our ability to focus on tasks depends on a network of brain regions connected to each other by long branches of neurons. The regions send signals to each other, creating a feedback loop that keeps the entire network active.

Sudden jolts of the brain – during a car accident or fall, for example – can sever some of the network’s long-distance connections and lead people to fall into a coma, Dr. Schiff hypothesized and of his colleagues. During recovery, the network may be able to power itself back on. But if the brain is severely damaged, it may not fully rebound.

Dr. Schiff and his colleagues identified a structure deep inside the brain as a crucial hub of the network. Known as the central lateral nucleus, it is a thin layer of neurons about the size and shape of an almond shell.

The human brain has two of these structures, one in each hemisphere. They appear to help the brain calm down at night for sleep and wake it up in the morning. Stimulate neurons in these regions can wake a sleeping ratDr. Schiff’s research showed.

These studies raised the possibility that stimulation of the central lateral nuclei could help people with head injuries regain focus and attention.

Surgeons routinely implant electrodes in patients with Parkinson’s disease. Small electrical impulsesreleased by the implants hundreds of times per second, induce neighboring neurons to emit their own signals, thus restoring certain brain functions.

In 2018, Dr. Schiff and his colleagues began recruiting volunteers, like Ms. Arata, who suffered from chronic problems for years after their accidents. Before inserting the electrodes, the researchers gave the volunteers a battery of tests to judge their ability to concentrate and switch tasks. In one exam, for example, volunteers were each given a sheet of paper covered in letters and numbers and asked to draw a line that connected them in order as quickly as possible.

Before the operation, the researchers scanned each volunteer’s brain to make a precise map. Dr. Jaimie Henderson, a neurosurgeon at Stanford University, guided the electrode through the brain, to the central lateral nucleus.

Dr. Henderson implanted the electrodes in six volunteers, but one had to drop out of the study after developing a scalp infection. One month after the operation, the five remaining volunteers underwent follow-up tests. On the exam with letters and numbers, their scores jumped from 15 to 52 percent.

To better understand the volunteers’ experiences, Dr. Joseph Fins, medical ethicist at Weill Cornell Medicine, conducted a interview series with them and their family members. Most volunteers, like Ms. Arata, said the implant made them more like themselves.

In contrast, the volunteer who saw the greatest improvement on cognitive tests had a lukewarm reaction. “I don’t think it hurts,” he said. “I just don’t know if it helped much.”

And yet, in this patient, we observe significant changes, particularly in his father’s self-awareness. “It’s day and night,” said the son.

Dr. Steven Laureys, a neurologist at the University of Liège in Belgium who was not involved in the study, said the findings support the theory that attention and other forms of thinking depend on the brain’s network. “There is enough reason to believe that this is worth pursuing,” he said of the research.

Dr. Schiff and his colleagues are planning a much larger study of brain implants. “We need to see how the data evolves,” he said.

The central lateral nuclei are not the only regions showing promise as brain network hubs, said Dr. Alex Green, a neurosurgeon at the University of Oxford who was not involved in the study.

“We don’t really know yet the best place to stimulate,” Dr. Green said. He and his colleagues are preparing their own brain injury trial to try electrodes in a region called the pedunculopontine nucleus.

Dr Laureys acknowledged that implant surgeries would be expensive, but argued that society should recognize the millions of people who suffer from head injuries. “This is a silent epidemic,” he said.

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