Brain scan illustration showing the connection between head injury and functional neurological disorder symptoms

How Head Injuries and Concussions Can Trigger Functional Neurological Disorder

You watched someone survive a concussion. The scans looked okay. The doctors said to rest and give it time. But weeks or months later, the symptoms didn't go away — or new ones appeared that didn't fit what anyone expected. If that sounds familiar, you may be dealing with something that doesn't get talked about enough: the connection between head injuries and Functional Neurological Disorder.

What the research actually says

The connection between concussion, traumatic brain injury, and FND is documented and growing in the research literature — even though most families never hear about it.

A retrospective case series published in the Journal of Neuropsychiatry and Clinical Neurosciences examined 50 patients with a confirmed FND diagnosis whose functional neurological symptoms began after a concussion. The study found that functional neurological symptoms can arise after a concussion, presenting either abruptly or developing gradually over time. Symptoms included gait changes, seizure-like episodes, speech and language dysfunction, weakness, sensory symptoms, and tremors. The authors concluded that FND should be considered in the differential diagnosis of anyone presenting with neurological symptoms that begin after a concussion. (Polich et al., Journal of Neuropsychiatry and Clinical Neurosciences, 2024)

A separate study published in the Journal of Psychosomatic Research found a significant association between FND and persistent post-concussion symptoms, as well as an association between FND and symptoms of depression and anxiety in that population — concluding that patients with persistent post-concussion symptoms should be routinely screened for FND. (PubMed, 2023)

And a 2025 review published in Brain Sciences introduced what researchers called the Functional Overlay Model — a framework describing how FND symptoms can coexist with or develop alongside the initial effects of a head injury, particularly in patients showing symptoms that don't match standard post-concussion patterns. (Brain Sciences, 2025)

Why this happens — the mechanism families need to understand

FND is not caused by brain damage in the way a stroke or hemorrhage is. It is caused by disruption in how the brain sends and interprets signals — a problem of function rather than structure. Standard MRI and CT scans can look completely normal even when FND is significantly disabling.

Head injuries create the conditions in which FND can develop in several ways:

The initial trauma disrupts normal nervous system function. Even a mild concussion temporarily alters how brain networks communicate. For most people this resolves. For some, the disruption becomes self-perpetuating.

Persistent symptoms create fear-avoidance patterns. Research shows that fear avoidance behavior — avoiding activities out of fear of worsening symptoms — is one of the strongest predictors of unexpected neurological symptoms after concussion. The brain learns to protect itself in ways that can entrench functional symptoms.

The injury becomes a trigger, not the full explanation. The 2024 research from Harvard's Massachusetts General Hospital found that while concussion can trigger FND, the concussion itself does not fully explain the functional symptoms. Other factors — including how the injury was explained, what beliefs formed about the injured brain, and psychological responses — all contribute to whether FND develops.

This is important for families to hear: if your person developed FND after a head injury, it does not mean the injury was minor or that symptoms are exaggerated. It means the nervous system responded in a documented, recognized way that requires its own understanding and its own treatment approach.

Why this gets missed so often

The overlap between post-concussion symptoms and FND symptoms is significant. Both can involve headache, cognitive slowing, fatigue, dizziness, emotional dysregulation, and sleep disruption. That overlap creates diagnostic confusion.

The problem is that post-concussion rehabilitation and FND rehabilitation are not the same thing. Treating FND with standard concussion protocols can actually reinforce the functional symptoms rather than resolve them. Early recognition matters — research has shown that delay in FND diagnosis is associated with worse outcomes.

What families often experience is a cycle: the symptoms don't fit a clean concussion picture, doctors become uncertain, families get dismissed or told it's anxiety, and the real condition goes unaddressed while the person continues to decline.

If your person has persistent neurological symptoms after a head injury that aren't responding to standard treatment — or that look different from what the doctors expected — FND is worth raising specifically with a neurologist who has experience with functional disorders.

What to ask and what to document

If you suspect FND following a head injury, here are the questions worth raising with a neurologist:

  • Could these symptoms reflect a functional neurological disorder rather than or in addition to post-concussion syndrome?
  • Have you evaluated for FND specifically, not just ruled out structural damage?
  • What positive clinical signs are present that help distinguish what's happening?
  • Is this person a candidate for FND-specific rehabilitation rather than standard concussion protocols?

Document symptom patterns carefully. Note what makes symptoms better or worse, what time of day they're worst, what activities trigger them, and how they've changed since the injury. This information is essential for a proper FND evaluation.

For veteran families specifically

The connection between blast exposure, repeated concussions, PTSD, and FND is particularly complex in veteran populations. Research has shown that military-related trauma — both physical and psychological — creates conditions in which FND can develop and may be missed or misattributed to PTSD or TBI alone.

If your veteran has neurological symptoms that don't fit cleanly into a TBI or PTSD diagnosis, FND is worth investigating. The VA's Polytrauma system of care includes specialists equipped to evaluate for functional neurological symptoms in veterans — ask specifically for a referral.

Related reading

Resources cited in this article

Robbins Nest Alliance is a 501(c)(3) educational nonprofit focused on brain injury, dementia, Parkinson's, PTSD, FND, and CTE. We publish free, medically-cited resources for patients, caregivers, and families — because the best information shouldn't be behind a paywall.

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