The most common and understandable question following a diagnosis of Functional Neurological Disorder (FND) is: What causes FND? People are often looking for a clear, single cause – something that explains the onset of symptoms in a direct and definitive way. However, in most cases, FND doesn’t arise from a single factor. Rather, it develops from the interaction of a multiple influences over time.

In clinical practice, FND is best understood using a biopsychosocial framework. This approach considers how biological, psychological, and social factors combine to shape the way an individual’s nervous system functions. This framework allows for a more individualised understanding of FND, and avoids the limitation of focussing too narrowly on either physical and psychological causes alone.

Biological factors underlying FND can include a person’s neurological sensitivity, patterns of arousal within the nervous system and general health. Some individuals can have heightened responsiveness to stress or physical change, which may influence how symptoms emerge. There may also be a history of other health conditions, fatigue, or periods of physical illness that place additional strain on the system. These factors do not cause FND in isolation, but they can increase a person’s vulnerability to developing FND.

Psychological processes often play a role, particularly in how FND symptoms are triggered and maintained. This does not mean an individual with FND has a psychological disorder, nor that symptoms are intentional. Rather, it reflects the way in which the brain integrates emotional, cognitive, and physical information. For example, sustained stress, difficulties with emotional processing, or patterns of heightened self-monitoring can influence how bodily sensation are experienced and interpreted. In some cases, individuals may have learned to manage distress through emotional repression which can inadvertently manifest as physical symptoms. Alternatively, chronic worry that the body is broken or will become sick can ultimately become a self-fulfilling prophecy resulting in real FND symptoms (predictive coding model).

Social and environmental factors can influence the development of FND. These factors may include chronic life stressors, workplace pressure, family responsibilities, or a lack of available support compared to the individual’s capacity to cope with demand. The experience of navigating the healthcare system can also have an impact. For some, repeated investigations and prolonged uncertainty around diagnosis can increase health anxiety, reinforce a focus on symptoms and delay access to treatment, thereby making recovery more difficult.

Lived experiences are also relevant in the development of FND. Many, although not all, individuals with FND report periods of significant stress, adversity, or trauma at some point in their lives. These experiences can shape how the nervous system responds to threat and how easily or quickly it becomes dysregulated. It is important to emphasise, however, that there is no single biopsychosocial profile that explains FND. Some individuals have clear histories of adversity, while others do not. FND is a heterogenous condition, and explanations around what may cause it, and how to treat it, need to be tailored to the individual.

When considering what causes FND, it is often helpful to think in terms of three broad categories:

Factors that may have increased the person’s vulnerability over their lifespan
Factors that triggered the initial onset of symptoms
Factors that contribute to the persistence or maintenance of symptoms now as FND symptoms can change over time

A person may, for example, have a longstanding tendency toward heightened physiological arousal from, for example, undiagnosed neurodiversity, or they may have experienced a period of overexertion, illness, or stress that precipitates symptoms, or they may be holding onto a depth of sadness from grief and loss of a loved one. Overall, FND symptoms can be triggered and maintained by changes in attention, behaviour, and emotional response. A key mechanism in this process appears to involve the way attention is directed within the body. Under typical circumstances, many aspects of movement and sensation occur automatically, without conscious awareness. With FND, internal processes become more consciously monitored, which can interfere with smooth execution of movement. The more effort that is applied to controlling a movement that is usually automatic, the less coordinated it becomes. This is not a deliberate process, but rather a consequence of how attention interacts with motor control.

Similarly, expectations about FND symptoms can influence how they are experienced. If the brain comes to anticipate a particular difficulty – such as limb weakness or the onset of seizures – this expectation can shape neural processing in a way that makes the symptoms more likely to occur. This is not unique to FND; it reflects broader principles of brain function, where perception and expectation are closely linked. in FND, however, these processes appear to become amplified or less flexible.

Understanding these mechanism can be helpful not only in explaining the condition, but also in guiding treatment. When individuals are able to notice how symptoms arise from understandable processes within the nervous system, rather than from damage or disease, it can reduce fear and uncertainty. It also provides a rationale for therapeutic approaches that focus on retraining attention, behaviour, and emotion regulation skills.

Importantly, a biopsychosocial explanation is not about attributing blame. It is not suggesting the individual caused their own FND symptoms, nor that they can simply choose to stop them. Rather, it offers a framework for understanding how a complex system has become dysregulated, often in the context of multiple interacting pressures. This perspective tends to be more acceptable and more useful than explanations that imply either purely physical disease or purely psychological causation.

In clinical work, I have found individuals are often able to identify aspects of this model that resonates with their experience, even if not every element applies to them. The aim is not to fit a person into a predefined explanation, but to develop a shared understanding that helps the individual make sense of their experience and develop a foundation for treatment that works for the individual.

In summary, FND arises from the interaction of biological sensitivities, psychological processes, and social contexts across the lifespan. It is not caused by a single factor, but develops through patterns that can, over time, become established in a more vulnerable nervous system. A biopsychosocial framework provides a coherent way of understanding these patterns and supports a more targeted, collaborative, and effective approach to treatment.

** April is FND Awareness Month. Visit FND Hope to show your support and donate – www.fndhope.org/fndaware