Pasadena Neurologist Explains How Repeated Head Hits Damage the Brain

Picture a bundle of copper wires. Now imagine twisting them and striking them against a hard surface, over and over. Eventually the wires fray, and the current stops.

That, a Pasadena neurologist told public-radio listeners on Aug. 25, is close to what repeated blows do to the brain — and it is at the center of a new study of former NFL players.

The study, published Aug. 25 in The BMJ, estimated that at least about one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, or CTE, at death. Dr. Yafa Minazad, a Huntington Hospital–affiliated neurologist who practices at Southern California Neurology Consultants on South Fair Oaks Avenue in Pasadena, appeared on LAist’s AirTalk the same day — alongside Dr. William P. Flavin, an assistant professor of neurology at UCLA who played college football at Notre Dame — to explain, in plain terms, how the disease takes hold.

The brain runs on roughly 86 billion neurons, Minazad said — tiny wires that carry the electrical signals behind speech, memory and thought. Repeated impacts cause microscopic injuries to those wires that accumulate over years. And the damage does not require a headline-grabbing concussion.

“The repetitive impact on the brain without giving it time to heal adds up over time and causes the symptoms that causes disability in these patients,” she said.

The symptoms she described range from memory loss, brain fog and trouble learning to severe mood disorders. In advanced cases, she said, patients can experience violent behavior, suicidal thoughts and significant disability. Why one person’s symptoms differ from another’s comes down to where the injury lands.

“The brain is like real estate,” she said. “It’s location, location, location.” Damage to the frontal lobe can bring personality changes and poor judgment, she said, while injury to the temporal lobe is tied more to memory, mood and anxiety.

The researchers — from Mass General Brigham, Boston University and the Concussion & CTE Foundation — built their estimate by starting with every man who had played in at least one NFL game since 1949, then focusing on the years when brain donations were most common. Among the brains actually donated and examined from 2008 to 2021, 93% showed CTE. That figure, the authors caution, reflects families who chose to donate, often because a relative had struggled, and is not the rate for all players. Earlier research had already found CTE in nearly all NFL brains examined — 110 of 111 in a widely cited 2017 study — but those samples, too, came only from families who chose to donate. The population estimate for 2016–2021 ran from a floor of 24.5% to as high as 97.7%; the lead author, Dr. Daniel Daneshvar, has said the true number sits somewhere in between and called the 25% figure the “low end.” Among the donated brains, those with the most advanced form of the disease, stage IV, were more likely to have shown signs of dementia before death — a 44% higher prevalence of clinician-diagnosed dementia, the study reported.

CTE still cannot be diagnosed in a living person. The damage is too small to show up on standard scans, can be confirmed only by examining brain tissue after death, and, once it takes hold, is irreversible. Even so, Minazad said early evaluation and monitoring matter, and that prevention is the priority.

The findings also drew renewed attention to a long-running policy question. In a separate report, The New York Times asked why federal workplace regulators have not stepped in; one former head of the Occupational Safety and Health Administration, Doug Parker, told the paper, “I don’t think that this would be abided in any industry.” OSHA, in a statement to the Times, said it “does not take enforcement action with regard to professional athletes” in most cases. The NFL, in its own statement, said it “continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts.” The NFL Players Association, in its own statement, called the study “a sobering reminder that football carries real risks, and those risks can have lasting consequences for players and their families.”

For now, the science outpaces the tools to act on it. The wires fray silently and invisibly — unseen until it is too late to look.