For nearly a decade, much of the groundbreaking work in the study of head trauma and its impact on athletes has been done at the Center for the Study of Traumatic Encephalopathy at the Boston University School of Medicine. The decision by Seau’s family to donate his brain to the N.I.H. was an acknowledgment that the study of head trauma had grown well beyond the province of a handful of pathologists, and become a public health issue of national importance. Financing for the research has expanded, too; the N.F.L. donated $30 million to the N.I.H. as part of its battle to address head trauma and the long-term health issues that stem from it. The prominence of soldiers returning from battlefields with head trauma has also prompted the Defense Department to play a larger role.

“What’s been coming out has raised a lot of questions about public health,” said Dr. Walter J. Koroshetz, the deputy director of the National Institute of Neurological Disorders and Stroke, which is part of the N.I.H. and finances traumatic brain injury research. “What we have now is a tip of the iceberg, and we don’t know what’s below.”

The N.I.H. is not the only government organization studying head trauma. In September, the National Institute of Occupational Safety and Health, which is part of the Centers for Disease Control and Prevention, released a study that showed that a disproportionate number of men who played at least five seasons in the N.F.L. from 1959 to 1988 developed Alzheimer’s disease or Lou Gehrig’s disease. Players in “speed” positions more prone to high-speed collisions were three times more likely to have died as a result of a neurodegenerative disease, according to the study. The Institute of Medicine, which is part of the National Academies of Science, has also undertaken a 15-month investigation into sports-related concussions sustained by young athletes.

Researchers and advocates for retired players who now have degenerative brain diseases welcome the government’s greater role, in part because of its deep pockets and ability to shine a brighter light on a complicated topic. Already, the increased attention on the issue has made it easier to get athletes and soldiers to commit to donating their brains to science.

“That’s what the C.T.E. field needs, funding and attention of the country’s top scientists,” said Chris Nowinski, the executive director of the Sports Legacy Institute and the co-director of the Center for the Study of Traumatic Encephalopathy at the Boston University School of Medicine. “Our researchers are great, but there’s more work that needs to be done.”

Seau’s suicide was one of several by former N.F.L. players, including Waters, raising concern about head injuries in the sport. In February 2011, Dave Duerson, a former Chicago Bears player, shot himself in the chest, saying in a note that he wanted his brain donated for research. Doctors determined that Duerson had C.T.E.

Duerson’s son, Tregg, is suing the N.F.L., claiming the league did not meaningfully warn players about the potential risks of concussions.