What is CTE, and did it factor into the NYC deadly shooting?

The man who police say fatally shot four people in Manhattan and who New York City Mayor Eric Adams said Tuesday was targeting the offices of the National Football League claimed he suffered from a degenerative brain injury caused by repeated brain injuries and trauma.

Police say that gunman Shane Tamura, 27, had a three-page note in his wallet saying he suffered from a brain disease and was requesting that the league study his brain. Although repeated brain trauma can lead to CTE, the disease can only be definitively diagnosed after death.

Experts do not believe CTE is linked to one single brain injury, according to the Mayo Clinic. However, in many cases, it is related to repeated head injuries, like concussions, which may be linked to contact sports such as football or to military combat.

Tamura played high school football outside of Los Angeles, according to the Los Angeles Times, but did not play beyond that level.

Police said Tamura shot himself in the chest rather than in the head, according to The New York Times.

“Study my brain, please,” his note read. “I’m sorry.”

A request seeking comment from the NFL was not immediately returned to NewsNation on Tuesday.

Despite Tamura’s belief that he suffered from CTE, Dr. Robert Cantu, the co-founder and medical director at the Concussion Legacy Foundation, told NewsNation that, in all likelihood, he did not.

“It’s a tragedy beyond belief that he did what he did,” Cantu said Tuesday. “But it’s also a tragedy that he thought he had CTE, and the next thing he’s going to do is give up hope and probably lose his own life as well as others.”

Traumatic brain injuries experienced by young athletes

A 2023 study conducted by the Boston University Chronic Traumatic Encephalopathy Center shows that the disease is common among youth sports, NewsNation previously reported.

The study found that more than 40 percent of young athletes who died before the age of 30 suffered from CTE, which has been reported in patients as early as the age of 17.

Recent brain scans of NFL Hall of Famer Joe DeLamielleure, who was diagnosed with CTE, the brain injury that is affecting so many former football players. (Jeff Siner/Charlotte Observer/MCT)

The study analyzed the brains of 152 donors, all of whom played contact sports and were younger than 30 when they died. Research found that 63 of the 152 patients had CTE based on criteria, although most of the cases were considered mild. Most of the donors, including 70 percent of those found to have the condition, only played amateur sports, the study found.

Cantu, citing the study, said that young people who were found to have Stage 1 or Stage 2 CTE suffered the same symptoms as people who were not diagnosed with the disease after their death. Most of the brains that were examined as part of the study experienced primarily psychiatric symptoms of anxiety, depression or behavioral issues such as being easily angered.

Most troubling to researchers, Cantu said, is that those who were diagnosed as having CTE were not distinguishable from those who did not, based on the symptoms alone. He said that it was caused by repetitive head trauma, which can produce psychiatric, behavioral and cognitive symptoms even without the condition being present.

What are the symptoms of CTE?

Experts at the Mayo Clinic report that there are no specific symptoms that are linked directly to CTE. However, some of those who have been diagnosed with degenerative brain injury have experienced cognitive, behavioral and mood changes.

Robert Cantu, chief of neurosurgery service and director of sports medicine at Emerson Hospital in Concord, Mass., during the House Judiciary hearing on head injuries among NFL players. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)

Among those behavioral changes listed by the Minnesota-based clinic are impulsive behavior and aggression, while medical experts have also found that those who experience brain trauma-related symptoms often experience depression or apathy.

Those who are believed to suffer from CTE often experience symptoms in two ways. Those in their 20s or 30s often deal with depression, anxiety, impulsive behavior or aggression, researchers at the Mayo Clinic found. The second form of the disease is known to cause symptoms including memory loss and difficulties thinking, which often affects older patients around age 60.

Cantu said that given the severity of CTE, the disease tends to create hysteria. However, he noted that statistically, more than four years of high school football are needed to produce the level of trauma needed to place a person at significant risk of CTE.

In most cases, Cantu said the average person who is diagnosed with the condition would need to play at least five years of football, including two at the high school level.

However, there are limited cases of patients who did not play football beyond high school who are later diagnosed with the disease, he said. Cantu warned, however, that the 2023 study only represents a limited sample size and said that CTE is diagnosed in more boxers than those who played football.

In many cases, repeated blows to the head can cause traumatic brain injury, Cantu said. But generally, one would need to sustain thousands of blows to the head to lead to CTE, which involves a progressive, relentless downhill course in brain health, he added.

Warning signs for patients experiencing brain trauma include mood changes, the onset of anxiety or depression or reacting to circumstances in ways one normally would not, the doctor said. Anyone experiencing such feelings should seek professional help to be treated before feelings of hopelessness can contribute to events like Monday’s deadly shooting.

“Something awful was done because a person thought they had CTE,” Cantu told NewsNation. “And what someone needs to understand is that if they think they have CTE, you go to a health professional and get work done and get appropriate therapy because there are therapies that can help you.”