A new study challenges the common belief that chronic traumatic encephalopathy (CTE) causes aggressive behavior, instead finding evidence that the brain disease may be linked to cognitive decline and dementia. Researchers at Boston University's CTE Center analyzed 248 donated brains with CTE pathology and 366 without, publishing their findings in the journal Alzheimer's & Dementia. The study found no connection between CTE and mood or behavioral changes like aggression, which are often emphasized in media coverage, but did identify an increased risk for dementia in advanced stages of the disease .

What Does This Study Actually Show About CTE and Dementia?

The research team, led by Michael Alosco, co-director of Boston University's CTE Center, staged each brain from zero to four based on abnormal tau protein levels. Early stages of CTE showed no link to cognitive symptoms or dementia diagnosis, but participants in stage three or four had a higher likelihood of reporting memory and thinking problems or receiving a dementia diagnosis . The strength of this association was comparable to the link between Alzheimer's-related proteins and symptoms, according to Alosco.

However, experts caution that the findings come with important limitations. Dr. Rebecca Folkerth, a neuropathologist at the Icahn School of Medicine at Mount Sinai who was not involved in the study, noted that the research doesn't make a clear-cut case that CTE alone causes dementia. The study excluded people with Alzheimer's and other major neurodegenerative conditions to isolate CTE's effects, but it did not exclude participants with TDP-43 protein aggregates or vascular problems that could contribute to cognitive decline .

"It really emphasizes the need for clinicians to assess and consider exposure to head trauma when they're making diagnoses and managing care," said Michael Alosco, co-director of Boston University's CTE Center.

Michael Alosco, Co-Director, Boston University CTE Center

Why Are Researchers Concerned About Misdiagnosis?

One striking finding from the study was the rate of misdiagnosis among participants. Nearly 40 percent of study participants were incorrectly diagnosed with Alzheimer's disease, even though they actually had CTE . This discovery underscores a critical gap in clinical practice: many doctors may not be considering repetitive head trauma when evaluating patients with memory loss and cognitive decline. The oversight could lead to patients receiving inappropriate treatment or missing opportunities for proper management of their condition.

The study population itself had notable characteristics that may limit how broadly the findings apply. Almost 97 percent of participants were men, more than 80 percent were white, and many were football players . This demographic skew means the results may not reflect how CTE affects women, people of color, or those with head trauma from other causes like military service or accidents.

What Should People With Head Injuries Know About CTE Risk?

Even though repetitive head trauma may be a risk factor for dementia, experts emphasize that developing CTE is not inevitable. The disease progression remains poorly understood, and researchers are still grappling with fundamental questions about what triggers symptoms . One critical unknown is the "tipping point" where tau buildup in CTE causes cognitive problems to emerge.

• Get Evaluated Early: If you're noticing thinking and memory problems, seek evaluation at a neurology clinic to get a proper diagnosis and rule out treatable causes.
• Report Your Head Injury History: When seeing a doctor for cognitive concerns, inform them about any history of head injuries, concussions, or repetitive trauma, as this information is essential for accurate diagnosis.
• Avoid Catastrophizing: Having multiple head injuries does not guarantee you will develop CTE or dementia, so avoid assuming you're destined for a progressive disorder without medical evaluation.

The case of the Manhattan shooter who opened fire at an office building in 2024 illustrates how quickly people can jump to conclusions about CTE and behavior. Neuropathologists later found that the shooter had early-stage CTE, but this study adds evidence that mood and behavioral symptoms may not be direct consequences of the disease . As Dr. Folkerth observed, the focus on CTE as an explanation for his actions may have diverted attention from other treatable causes of behavioral changes.

"People were so quick to ascribe his behavior to the fact that he had stage two CTE that they stopped looking at other treatable causes," noted Dr. Rebecca Folkerth, neuropathologist at the Icahn School of Medicine at Mount Sinai.

Dr. Rebecca Folkerth, Neuropathologist, Icahn School of Medicine at Mount Sinai

What Questions Remain About CTE?

The study raises as many questions as it answers. The CTE staging system used by Boston University researchers has not been externally validated by any group outside the institution, according to Dr. Folkerth . Additionally, participants in later stages of CTE identified in the study were also older, which could independently contribute to cognitive symptoms rather than CTE being the sole cause.

Dr. Folkerth

Currently, CTE cannot be diagnosed in living people; it can only be confirmed through brain autopsy after death. This limitation means researchers must rely on donated brains to study the disease, which introduces selection bias and makes it difficult to understand how CTE progresses in the general population. Despite these challenges, the Boston University research represents one of the most comprehensive efforts to understand CTE's relationship to cognitive decline and dementia, offering important insights for clinicians evaluating patients with head injury histories .