When Brain Injuryand Violence Collide

As the United States continues to grapple with mass shootings across schools, workplaces, and public spaces, researchers and public health experts are increasingly examining a difficult and often overlooked question: could traumatic brain injury (TBI) or degenerative brain disease play a contributing role in some acts of extreme violence?

Mass shootings are widely understood to be complex events with no single cause. Social isolation, untreated mental illness, access to firearms, ideological grievance, and trauma all intersect in ways that make prediction and prevention difficult. Yet emerging neurological research suggests that brain injury—particularly when undiagnosed or untreated—may increase vulnerability to emotional dysregulation, impaired judgment, and impulsive behavior in a small subset of individuals.

WHAT WE KNOW ABOUT TBI AND CTE
Chronic traumatic encephalopathy (CTE) is a degenerative brain disease associated with repetitive head impacts. It has been linked to symptoms such as impulsivity, aggression, depression, emotional instability, and suicidal thoughts. Similarly, TBIs—whether sustained through sports, military service, accidents, or assaults—can alter mood regulation, personality, and decision-making.
Neurologists are careful to emphasize that these conditions do not cause violence. However, they may lower an individual’s capacity to manage stress, control impulses, or regulate emotions—factors that can become significant when combined with other risks.

A CASE THAT INTENSIFIED THE NATIONAL CONVERSATION
This issue drew renewed attention following a July 2025 mass shooting in a Midtown Manhattan office building. The shooter, 27-year-old Shane Devon Tamura, killed four people before dying by suicide. In a note left behind, he wrote, “Study my brain please. I’m sorry,” attributing his actions to CTE linked to playing high school football.

A subsequent medical examination confirmed early-stage CTE—an unsettling finding given his age and nonprofessional athletic history. While CTE is most commonly associated with professional athletes, the case underscored that the disease can also affect younger, amateur players.

RISK FACTOR, NOT EXPLANATION
Experts strongly caution against viewing brain disease as a definitive explanation for violence. Mass shootings are never the result of a single variable, and most individuals with TBI or CTE are not violent. Still, the presence of brain injury raises urgent questions about prevention, monitoring, and early intervention.

Research across athletic, adolescent, and military populations shows that repeated head trauma can cause lasting structural brain changes, sometimes long after outward symptoms fade. Early identification, mental-health support, and ongoing monitoring may significantly reduce risk.

A BROADER PUBLIC HEALTH PERSPECTIVE
Public health experts emphasize that gun violence must be addressed as a layered societal issue. Biological vulnerability—when present—may intersect with mental illness, social isolation, grievance, trauma, or perceived injustice to produce catastrophic outcomes.
Ultimately, addressing mass shootings requires a holistic approach. Brain injury should neither be ignored nor overstated—but understood as one potential piece of a much larger puzzle. As researchers continue to investigate these connections, experts agree on one point: meaningful prevention depends on recognizing every risk factor, including those that remain invisible inside the brain.