Cognitive Decline Linked to Severity of Chronic Traumatic Encephalopathy

Researchers have found a strong association between the severity of chronic traumatic encephalopathy (CTE) and the presence of dementia and cognitive impairment. The study, published in Alzheimer’s & Dementia on January 26, 2026, provides some of the clearest evidence to date regarding the long-term impact of repetitive head injuries on brain health.¹

Repetitive head impacts are common among athletes in contact sports, military personnel and individuals experiencing physical violence. These impacts can lead to CTE, a progressive brain disorder that is currently difficult to diagnose during life and is definitively confirmed only through post-mortem brain examination. CTE can often be misdiagnosed as other neurodegenerative diseases, such as Alzheimer’s disease or other forms of dementia.

Study Details and Findings

Researchers at Boston University, led by Dr. Michael Alosco, examined brain tissue from 614 donors with a history of repetitive head impacts.¹ None of the donors had been diagnosed with neurodegenerative diseases other than CTE. The research team accounted for factors such as vascular injury, substance use, and age. They also gathered information about the donors’ mood, behavior, and cognitive abilities.

The brains were categorized into those with CTE (366) and those without (248). The study revealed that individuals with more severe stages of CTE (stages III and IV) exhibited worse cognitive and functional symptoms. Specifically, those with stage IV CTE were 4.5 times more likely to have received a dementia diagnosis compared to those without CTE.¹

Interestingly, milder forms of CTE (stages I and II) were not associated with dementia, cognitive symptoms, or functional impairment.

While mood and behavioral symptoms are frequently reported by individuals with a history of repetitive head impacts, the study found these symptoms were not directly linked to any stage of CTE. Researchers suggest these symptoms may be caused by other types of brain damage resulting from repetitive head impacts, rather than CTE itself.

Implications for Diagnosis and Research

“By examining hundreds of brains and ruling out other common neurodegenerative diseases, the team could look at CTE alone and linked it to symptoms reported during life,” explained Dr. Amy Bany Adams, acting director of NIH’s National Institute of Neurological Disorders and Stroke, which funded the research.¹

Dr. Alosco added, “Establishing that cognitive symptoms and dementia are outcomes of CTE moves us closer to being able to accurately detect and diagnose CTE during life, which is urgently needed.”¹

Understanding CTE

Chronic traumatic encephalopathy (CTE) is a progressive and fatal brain disease associated with repeated traumatic brain injuries (TBIs), including concussions and repeated blows to the head.² It is also linked to the development of dementia. People who experience TBIs in early to midlife are two to four times more at risk of developing dementia later in life.³

Those at greatest risk for CTE include athletes participating in contact sports (such as boxing, football, and ice hockey) and military veterans.² As of 2026, a definitive diagnosis of CTE can only be made after death through autopsy.¹

Key Takeaways

• More severe stages of CTE (III and IV) are strongly associated with cognitive decline and dementia.
• Milder stages of CTE (I and II) do not appear to be directly linked to these outcomes.
• Mood and behavioral symptoms may be caused by other types of brain damage related to repetitive head impacts, not CTE itself.
• Research is ongoing to develop methods for diagnosing CTE during life.

References

1. Layden RM, Groh JR, Miner AE, et al. CTE Neuropathology Alone Associated with Dementia and Cognitive Symptoms. Alzheimer’s & Dementia. 2026. 22(1):e71032. Doi: 10.1002/alz.71032
2. Mayo Clinic. Chronic traumatic encephalopathy. https://www.mayoclinic.org/diseases-conditions/chronic-traumatic-encephalopathy/symptoms-causes/syc-20370921 Accessed February 24, 2026.
3. Alzheimer’s Association. Chronic Traumatic Encephalopathy. https://www.alz.org/alzheimers-dementia/what-is-dementia/related_conditions/chronic-traumatic-encephalopathy Accessed February 24, 2026.