What Causes FND

Functional Neurological Disorder does not have a single confirmed cause, and that is not a gap in the research so much as an accurate reflection of how the condition works. FND arises from a combination of neurological, biological, and psychosocial factors that interact differently in each person. What the research does confirm is that FND involves measurable changes in how the brain's networks function, and that those changes produce symptoms that are real, disabling, and not under the person's voluntary control.

Understanding what causes FND matters because it shapes how families and caregivers interpret what they are seeing, and how medical teams approach treatment. The old framing of FND as a psychological response to stress has been replaced by a more accurate neurobiological model, though psychosocial factors still play a documented role for many patients.

FND Is a Disorder of Brain Network Function

The clearest way current research describes FND is as a condition in which the brain's networks are not communicating correctly, even when the brain's physical structure looks normal on imaging. A landmark 2022 paper in Lancet Neurology by Hallett, Dworetzky, Stone, and colleagues describes FND as a condition in which "the primary pathophysiological processes are alterations in functioning of brain networks rather than abnormalities of brain structures."

This is why MRI scans and standard neurological tests often return normal results. The hardware is intact. The problem is in how the system is running, not in any structural damage that imaging can detect.

The Predictive Coding Framework

One of the leading current models for explaining how FND symptoms develop involves the concept of predictive coding, which refers to the brain's continuous process of generating predictions about the body and updating those predictions based on incoming sensory information.

In healthy brain function, the motor cortex generates a movement, and the brain compares what it predicted would happen with what actually happened. When those signals match, the movement feels voluntary and under control. According to the Hallett et al. Lancet Neurology analysis, in FND this comparison process breaks down. Prediction errors are not accurately updated, which means the brain continues operating from faulty predictions about how the body should be moving, sensing, or functioning. The result is symptoms that the person experiences as real and involuntary, because neurologically they are.

The limbic system, which processes emotion, also plays a documented role. The same Lancet Neurology paper identifies overactivity of the limbic system as part of FND pathophysiology, which helps explain why emotional stress can trigger or worsen symptoms without those symptoms being "psychological" in origin. Emotion affects brain network function, and brain network dysfunction produces neurological symptoms.

Predisposing, Precipitating, and Perpetuating Factors

Researchers use a three-category framework to describe the factors involved in FND development. This framework is not unique to FND, but it is particularly useful here because no single factor causes FND in everyone.

Predisposing Factors

These are characteristics that may increase a person's vulnerability to developing FND. A 2025 systematic review published in Brain Sciences identified predisposing factors across FND subtypes including prior neurological conditions, anxiety and mood disorders, history of physical illness, and in some subtypes, adverse childhood experiences. Importantly, not all people with FND have a trauma history, and having a trauma history does not make symptoms any less neurological.

The National Institute of Neurological Disorders and Stroke (NINDS) notes that while psychological stressors and childhood adversity are documented risk factors in adults, they are not present in all people with FND. Biology, prior neurological injury, and genetic factors are also under active investigation.

Precipitating Factors

These are events or circumstances that appear to trigger symptom onset. Physical injury, illness, surgical procedures, and psychologically significant events have all been documented as precipitating factors across different FND subtypes. In veterans and people with prior traumatic brain injury, the overlap between neurological injury and FND onset is particularly well documented, and this is explored further in our article on FND and brain injury overlap.

The relationship between a precipitating event and symptom onset is not always immediate or straightforward. Symptoms sometimes develop weeks or months after the triggering event, which can make the connection difficult to identify during a clinical evaluation.

Perpetuating Factors

These are factors that maintain symptoms once they have developed. Attention to symptoms, learned movement patterns, ongoing stress, lack of accurate diagnosis, and insufficient treatment all contribute to symptom persistence. The brain's predictive coding system can become locked into a pattern that reinforces dysfunction, which is part of why early, accurate diagnosis matters for outcomes.

What FND Is Not Caused By

FND is not caused by the person choosing to have symptoms, exaggerating, or faking. A 2023 paper in Nature Reviews Neurology by Edwards, Yogarajah, and Stone addresses this directly, examining why FND is neurologically distinct from feigning or malingering. The mechanisms that produce FND symptoms are measurable, involve documented changes in brain network activity, and operate outside conscious control.

FND is also not diagnosed by exclusion alone. The current diagnostic standard requires positive clinical signs, such as the Hoover's sign for functional leg weakness, which reflect the specific inconsistencies in voluntary movement control that characterize FND. A diagnosis based only on "we couldn't find anything else" is not a complete FND diagnosis.

Why the Cause Matters for Caregivers

Families supporting someone with FND often encounter skepticism from other people, and sometimes from clinicians who are unfamiliar with the current research. Understanding that FND has a documented neurobiological basis, that symptoms are real and not deliberate, and that the condition arises from measurable brain network dysfunction rather than weakness of character gives caregivers accurate language to use when advocating for their person.

It also reframes the caregiving task. FND is not a condition that responds to pressure, disbelief, or being told to push through. Treatment that works targets the underlying brain network dysfunction through approaches like FND-specific physiotherapy, which retrains movement patterns, and appropriate psychological support that addresses perpetuating factors without dismissing the neurological reality of symptoms.

For a full overview of how FND affects brain function at the network level, see our page on how FND affects the nervous system. For a plain-language introduction to the diagnosis itself, start with Functional Neurological Disorder Explained.

Educational content only. Robbins Nest Alliance does not provide medical diagnosis or treatment advice. Seek qualified neurological care for new or worsening symptoms. Content references peer-reviewed research including Lancet Neurology, Nature Reviews Neurology, Brain Sciences, and NINDS publications.