The Hidden Impact: Understanding Traumatic Encephalopathy Syndrome (TES)
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New to TES? Start with the plain-language introduction first.
Brain Injury 101: Traumatic Encephalopathy Syndrome, the living face of CTE →A soldier absorbs another blast wave. A football player shrugs off another hit. A boxer takes one more round. None of them lose consciousness. None of them call it a concussion. Over months and years, something changes. Headaches become memory gaps. Restlessness becomes rage. Words slip away mid-sentence.
This is the clinical reality of Traumatic Encephalopathy Syndrome, known as TES. It is the term researchers use to describe the measurable neurological symptoms that appear during life in people with a history of repetitive head impacts. Its better-known counterpart, Chronic Traumatic Encephalopathy (CTE), can only be confirmed by examining brain tissue after death. TES describes what we can observe, document, and work with while someone is still alive.
TES explained: what it is, how it develops, and what caregivers see at home
What TES is and how it develops
TES develops from repetitive head impacts, including sub-concussive blows that never produce a diagnosed concussion and are often not remembered by the person who experienced them. The cumulative effect of those impacts causes axonal shearing, chronic neuroinflammation, and a progressive buildup of tau protein inside neurons.
Tau is a structural protein that normally stabilizes neurons. Under repeated mechanical stress, it misfolds and aggregates into toxic tangles that disrupt intracellular communication. Over time, this process spreads and damages the brain's functional networks, particularly in the frontal and temporal lobes, which govern judgment, emotional regulation, impulse control, and memory.
In 2021, Dr. Ann McKee and colleagues at the Boston University CTE Center published formal diagnostic criteria for TES, establishing a framework that clinicians can apply during life rather than waiting for post-mortem confirmation. The criteria define TES based on exposure history, core cognitive and behavioral features, and supportive biomarker findings.
McKee AC, et al. (2021). Traumatic encephalopathy syndrome: application of formalized criteria. Nature Reviews Neurology.
An important finding from McKee's research is that the risk of TES does not correlate with the number of diagnosed concussions. It correlates with cumulative exposure to head impacts over time. As her team noted, it is the exposure load, not the concussion count, that drives the pathological process. This is why athletes and veterans who never received a formal concussion diagnosis can still develop TES.
The symptom profile: what TES looks like in practice
TES symptoms cluster into three primary domains, though individual presentations vary considerably depending on exposure history, age at first exposure, and other biological factors.
Behavioral and mood changes
- Impulsivity and disinhibition
- Explosive anger or aggression that seems disproportionate to the trigger
- Depression, apathy, or emotional flatness
- Withdrawal from relationships and activities
- Irritability and low frustration tolerance
Cognitive changes
- Memory loss, particularly for recent events
- Slowed processing speed
- Word-finding difficulty mid-conversation
- Reduced executive function, including planning, sequencing, and decision-making
- Difficulty sustaining attention
Motor and physical changes
- Balance problems and coordination difficulties
- Parkinsonism features in some cases, including tremor and rigidity
- Headaches
Caregivers are frequently the first to recognize TES, often describing a gradual but unmistakable shift: "He just is not the same person." These changes can be misread as depression, personality disorder, or willful behavior. Understanding their neurological origin changes how families and providers respond.
TES and PTSD: different causes, overlapping neurobiology
TES and PTSD originate through different mechanisms. TES results from the physical mechanics of repetitive head impacts. PTSD results from psychological trauma and the neurobiological stress response it triggers. Despite those different origins, the two conditions produce overlapping changes in brain structure and function that make them difficult to distinguish clinically and frequently cause them to co-occur.
Both conditions produce measurable changes in three key regions. The amygdala, which processes threat and generates emotional responses, becomes hyperreactive. The prefrontal cortex, which regulates emotional responses and supports executive function, shows reduced activation. The hippocampus, which is central to memory formation and distinguishing past threats from present safety, shows structural atrophy under chronic stress.
This neurobiological overlap explains why veterans and first responders in particular are so often misdiagnosed or receive only a partial diagnosis. A person experiencing volatile anger, hypervigilance, memory gaps, and emotional withdrawal may be presenting with TES, PTSD, or both simultaneously, each reinforcing the other's symptom profile.
Where the research is heading
There is currently no cure for TES and no treatment that reverses tau accumulation once it has begun. Research is advancing in several directions.
Advanced imaging methods, including tau-specific PET scanning, are being used to visualize tau burden in living patients. Blood biomarkers, particularly phosphorylated tau proteins, are being studied as potential early detection tools that could identify at-risk individuals before symptoms become severe. AI-based diagnostic approaches are being developed to integrate imaging, biomarker, and clinical data into more precise diagnostic frameworks.
On the clinical side, supportive interventions targeting inflammation, sleep, and cognitive reserve are being studied as strategies to slow symptom progression. The evidence base for these approaches is still developing, and none has been established as a standard of care specific to TES. Anti-inflammatory nutrition, structured exercise that promotes brain-derived neurotrophic factor production, and sleep optimization are areas of active investigation cited in the peer-reviewed literature, though individual responses vary and these should be discussed with a treating clinician.
What this means for caregivers
Caregivers of people with TES carry a significant secondary burden. Sustained vigilance, emotional strain, and repeated exposure to dysregulated behavior produce their own physiological stress response over time. Understanding that a loved one's volatility or cognitive changes have a measurable neurological basis does not make caregiving easier in practical terms, but it does change the framework. It shifts the interpretation of behavior from character to circuitry, which changes how caregivers respond, what they ask for from providers, and how they talk about what is happening in their household.
Robbins Nest Alliance exists specifically to close the gap between what the research shows and what families are actually told. TES is one of the clearest examples of that gap. The science is years ahead of what most caregivers are hearing at appointments.
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Subscribe free →Educational use only. This article is for education and does not constitute medical advice, diagnosis, or treatment. TES research is still developing and diagnostic criteria continue to evolve. Do not make clinical or treatment decisions based on this article. Consult a neurologist or other licensed clinician familiar with TBI and CTE for evaluation and care specific to your situation.