Exploring The Aetiology of Functional Neurological Disorder (FND)

Functional Neurological Disorder (FND) stands as one of the most challenging and historically contentious conditions in neuropsychiatry. It's characterised by neurological symptoms that cannot be explained by conventional neurological disease. This has made FND a subject of significant academic and clinical debate for centuries. Our understanding of its underlying mechanisms, diagnostic methods, and treatment approaches has been constantly evolving (Carson et al., 2016).

The aetiology of FND has been particularly controversial, with explanatory models undergoing dramatic shifts over time. These shifts reflect broader changes in:

• Medical understanding
• Cultural contexts
• Scientific capabilities

This post will delve into the diverse aetiological theories of FND, tracing their historical development and analysing contemporary models. The understanding of FND has seen dramatic development in recent decades. Older conceptions are being replaced by more nuanced, integrative frameworks. These frameworks acknowledge the complex interplay of biological, psychological, and social factors.

While psychodynamic concepts of conversion once dominated traditional aetiological models, modern approaches recognise that no single explanatory framework can account for the heterogeneity of FND presentations.

This post will begin by:

1. Exploring historical perspectives on FND aetiology.
2. Moving from early supernatural explanations.
3. To the influential psychoanalytic theories of the early 20th century.

Historical Perspectives on FND Aetiology

Supernatural and Pre-Modern Explanations

The conceptualisation of what we now recognise as FND has undergone dramatic transformations throughout history. Early explanations for unexplained neurological symptoms often relied on supernatural frameworks. These explanations included demonic possession, divine punishment, or mystical influences (Kanaan, 2016). Such supernatural attributions represented attempts to make sense of perplexing neurological manifestations within the dominant cultural and religious paradigms of their time.

The historical trajectory of FND understanding can be traced through distinct epochs, each characterised by different explanatory models. As summarised in several historical analyses, the evolution progressed "from early supernatural explanations to modern cognitive and neurocircuitry-based models" (Kanaan, 2016). This transition reflects broader shifts in medical thinking, from mystical to mechanistic explanations of human suffering and disease.

FND and Reproductive Organs: The Wandering Womb

One of the earliest medical explanations for FND symptoms emerged in ancient Greek medicine with the concept of "hysteria" (from the Greek word for uterus). This theory proposed that symptoms were caused by the displacement of the uterus from its normal position - the so-called "wandering womb" theory. This gynaecological explanation persisted in various forms well into the 19th century, with FND being primarily conceptualised as a condition affecting women and directly linked to reproductive organs (Kanaan, 2016).

This gender-biased understanding had profound implications for how patients with FND symptoms were perceived and treated. It represented one of the earliest attempts to provide a physiological rather than supernatural explanation for functional neurological symptoms, albeit one that was deeply flawed and reflected the patriarchal medical perspectives of the time.

Charcot and Neurological Models

A significant shift in understanding FND occurred in the late 19th century through the work of Jean-Martin Charcot at the Salpêtrière Hospital in Paris. Charcot reconceptualised "hysteria" as a "nervous illness" rather than a gynaecological condition. His meticulous clinical observations led him to propose that FND had a neurological basis, suggesting that symptoms resulted from "dynamic lesions" in the brain, functional rather than structural abnormalities (Kanaan, 2016).

Charcot's approach represented a pivotal moment in FND history, as it legitimised these symptoms as genuine medical phenomena worthy of serious scientific investigation. His neurological framing of FND helped shift the condition from being viewed as a female reproductive disorder to being understood as a neurological condition that could affect both men and women. Although many of Charcot's specific theories were later challenged, his neurological conceptualisation laid important groundwork for future research.

Psychoanalytic Theory: Freud and Conversion

Perhaps the most influential historical theory of FND emerged from Sigmund Freud's psychoanalytic framework. Building partly on his early work with Charcot, Freud developed the concept of "conversion disorder," proposing that unconscious psychological conflicts, often related to traumatic experiences, were "converted" into physical symptoms as a defence mechanism. This conversion process supposedly protected the conscious mind from confronting distressing emotions or memories by channelling psychological distress into physical manifestations (Kanaan, 2016).

Freud's conversion model dominated understanding of FND throughout much of the 20th century. The theory suggested that "trauma being relevant to such symptoms was present prior" to Freud's work, but his systematic formulation gave it scientific credibility and clinical application. The psychoanalytic framework positioned FND as fundamentally psychological in origin, with physical symptoms serving as symbolic representations of repressed psychological material.

World War I and Shell Shock

The concept of "shell shock" that emerged during World War I represented another significant development in FND understanding. The large numbers of soldiers presenting with neurological symptoms following combat experience challenged purely psychological explanations and highlighted the potential role of physical trauma, stress, and environmental factors in symptom development. This period saw "the re-emergence of neurobiological theories of FND" as clinicians observed that extreme stress and physical trauma could precipitate functional neurological symptoms in individuals with no prior psychiatric history (Kanaan, 2016).

The shell shock phenomenon demonstrated that FND could affect otherwise psychologically healthy individuals when exposed to extreme circumstances, challenging simplistic psychological formulations. It also highlighted the complex interplay between physical experiences, psychological processing, and symptom manifestation - pointing toward more integrative models that would later emerge.

The Shift Toward Neurobiological Models

Neuroimaging Findings and Renewed Interest

After decades of dominance by psychoanalytic explanations, interest in neurobiological approaches to FND began to reemerge in the late 20th century. A critical turning point came approximately 30 years ago with "the findings of distinct regional cerebral metabolic changes in physiological brain imaging studies in persons with FND, not found in neurologically healthy individuals" (Perez et al., 2021). These early neuroimaging studies "invigorated neuroscientific investigations in FND" and challenged purely psychological explanations.

The advent of functional neuroimaging techniques allowed researchers to observe brain activity patterns in FND patients, revealing abnormalities that could not be explained by conscious simulation or purely psychological mechanisms. This research has "continue[d] at an accelerating pace," as evidenced by the exponential growth in FND publications indexed in PubMed in recent decades. These studies increasingly "suggest, instead, that FND has a biological basis" (Perez et al., 2021).

Neural Circuit Models

Contemporary neurobiological theories of FND focus on dysfunctional neural circuits rather than localised structural abnormalities. Research has found that "while no specific brain lesion or abnormality can explain FND, differences in activation and connectivity in specific" brain networks appear to be associated with functional neurological symptoms (Edwards, 2016). These findings have led to the development of neural circuit models that attempt to explain how alterations in brain connectivity and information processing might generate FND symptoms.

Key neural networks implicated in FND include attention networks, sensorimotor integration circuits, and systems involved in self-agency and emotional processing. Some models propose that FND involves "a combination of dysfunction in several of these networks and related processes" (Ludwig et al., 2018). These neurobiological approaches do not necessarily contradict psychological factors but rather provide mechanisms through which psychological processes might manifest as neurological symptoms.

Predictive Processing and Agency

Among the most promising neurobiological frameworks for understanding FND are theories based on predictive processing and sense of agency. These models suggest that FND symptoms may arise from disruptions in the brain's predictive mechanisms, which normally allow us to distinguish between externally caused sensations and those resulting from our own actions. In FND, this distinction becomes blurred, leading to alterations in the sense of agency over bodily functions (Edwards, 2016).

The predictive processing model proposes that the brain continuously generates predictions about sensory input based on prior beliefs and experiences. In FND, abnormally strong prior beliefs or expectations may override normal sensory processing, generating symptoms that align with these expectations rather than with actual physiological states. This framework helps explain how psychological factors such as attention, expectation, and belief can influence neurological functioning without requiring conscious simulation of symptoms.

Contemporary Biopsychosocial Network Models

Integration of Multiple Factors

Current understanding of FND has largely moved beyond single-factor explanations toward comprehensive biopsychosocial network models. These contemporary aetiological frameworks "adopt a biopsychosocial network (systems) perspective" and "propose that FND involves complex interactions between biological, psychological, and social factors" (Carson et al., 2016). Rather than seeking a single cause, these models recognise FND as emerging from the dynamic interplay of multiple factors operating across different levels of analysis.

The biopsychosocial approach acknowledges that "FND cannot be assigned to a simple psychological or physical category" because "our brain is a complex organ, responsible for emotions, attention, movement, sensations and predictions about the world. All of these aspects exert influence on each other" (Stone et al., 2020). This perspective helps resolve the artificial dichotomy between "psychological" and "neurological" explanations that has historically complicated FND understanding.

Predisposing, Precipitating, and Perpetuating Factors

A key feature of contemporary FND models is the recognition of different types of causal factors that may contribute to symptom development and maintenance. These are typically categorised as predisposing, precipitating, and perpetuating factors:

• Predisposing factors increase vulnerability to FND and may include genetic predispositions, early life experiences, personality traits, and pre-existing medical conditions. Although research on genetic risks for FND is limited, with "to date no evidence for genetic risks of FND with only one study reporting" preliminary findings, the possibility of "gene-environment interaction is plausible, as it could theoretically integrate life stressors as precipitating factors in a subset of susceptible individuals" (Nicholson et al., 2020).
• Precipitating factors trigger the onset of symptoms and may include psychological stressors, physical events, or medical procedures. Research indicates that both psychological and physical precipitants are common, with many patients reporting "preceding medical events, such as illness or surgery, suggesting a biopsychosocial aetiology" (Stone et al., 2020). Specifically, potential precipitating factors include "physical injury (e.g., fractures, or a hit on the head), and medical procedures (e.g., surgery, imaging procedures, and vaccinations)" (Carson et al., 2016).
• Perpetuating factors maintain symptoms once established and may include attentional processes, illness beliefs, avoidance behaviours, and social responses to symptoms. These factors help explain why FND symptoms often persist long after the initial precipitating event has resolved.

This framework allows for significant heterogeneity in FND presentations and recognises that different factors may be more relevant for different individuals. As noted in contemporary research, "Recent etiological models acknowledge the significant heterogeneity in the" presentation and underlying mechanisms of FND (Ludwig et al., 2018).

The Role of Trauma and Adverse Life Events

The relationship between trauma, adverse life experiences, and FND has been a particular focus of research and debate. While traditional psychoanalytic models positioned trauma as the central causal factor in FND, contemporary perspectives offer a more nuanced view. Research confirms that "maltreatment was substantially more common in people with FND than in healthy controls and patient controls" (Ludwig et al., 2018), suggesting trauma plays an important role for many patients.

However, modern understanding recognises that "while the traditional model of FND sees it as a reaction to stressful life events of certain types, these are not always detected in FND" (Stone et al., 2020). Indeed, "questions remain regarding how to contextualise the role of ALEs [adverse life events] in our modern-day conceptualisation of FND" (Perez et al., 2021) since "not all patients endorse ALEs" (Perez et al., 2021).

Current models therefore "use a biopsychosocial etiological explanation that can account for mood and trauma as risk factors for FND without explaining them as the direct cause of FND symptom onset or requiring them to be present in every individual with FND" (Ludwig et al., 2018). This allows for integration of trauma-related factors when relevant, while acknowledging the diversity of FND presentations and potential aetiological pathways.

Cognitive and Attentional Mechanisms

Cognitive and attentional processes play a central role in contemporary FND models. Rather than focusing exclusively on historical events or unconscious conflicts, these approaches examine how current cognitive processes may generate and maintain functional neurological symptoms. Key cognitive mechanisms implicated in FND include:

• Attentional focus: Heightened attention to bodily sensations and functions may disrupt automatic processes that normally operate outside conscious awareness. Research suggests that "links between the attentional system, illness beliefs, and FND symptoms" (Ludwig et al., 2018) may be particularly important in symptom generation and maintenance.
• Expectation and prediction: Strong expectations about symptoms may generate prediction errors that the brain resolves by producing symptoms that match these expectations. This aligns with predictive processing models discussed earlier.
• Belief systems: Patients' understanding of their symptoms, often referred to as "illness beliefs" or "illness representations," may influence symptom expression and persistence. Some models highlight how "schemas or frames of understanding that underpin FND and result in symptoms being activated" (Ludwig et al., 2018) may shape the clinical presentation.

These cognitive mechanisms help explain how psychological factors can influence neurological functioning without implying conscious symptom production or simulation. They also offer targets for psychological interventions aimed at modifying these processes.

Specific Aetiological Factors and Their Evidence Base

Biological Factors

Genetic and Familial Factors

Research on genetic contributions to FND remains limited. As noted earlier, there is "to date no evidence for genetic risks of FND with only one study reporting" preliminary findings (Nicholson et al., 2020). However, the possibility of genetic influences on vulnerability to FND, perhaps operating through temperamental traits or stress responsivity, remains an area of interest for future research.

The concept of a "gene-environment interaction is plausible" (Nicholson et al., 2020), potentially explaining why some individuals develop FND in response to particular stressors while others exposed to similar circumstances do not. This aligns with a broader understanding of complex neuropsychiatric conditions, where genetic factors may confer vulnerability rather than directly causing the disorder.

Neurobiological Abnormalities

Neuroimaging studies have identified several potential biological markers associated with FND. These include:

• Altered neural connectivity: Functional connectivity studies have found differences in how brain networks communicate in FND patients compared to healthy controls.
• Abnormal attention and motor control networks: Disruptions in networks governing attention allocation and motor planning/execution appear relevant to FND symptoms.
• Altered emotion processing: Some studies suggest abnormalities in how emotional information is processed and integrated with sensorimotor systems in FND.

Research continues to investigate "pathophysiological mechanisms underlying FND symptoms, with the goal of identifying disease biomarkers and novel therapeutic alternatives" (Perez et al., 2021). These efforts aim to develop "a more complete mechanistic understanding of FND" (Perez et al., 2021) that can inform both diagnosis and treatment.

Neuroendocrine and Autonomic Factors

Emerging research is examining the role of neuroendocrine and autonomic nervous system dysfunction in FND. These biological systems govern stress responses and may provide a link between psychological stressors and physical symptoms. As noted in recent work, "there is a need to contextualise autonomic, endocrine, and inflammation findings for a more complete mechanistic understanding of FND" (Perez et al., 2021).

Investigation of these systems may help explain how stress and trauma can "get under the skin" to affect neurological functioning. This research represents an important bridge between psychological and biological levels of explanation, consistent with the integrated biopsychosocial approach.

Psychological Factors

Trauma and Adverse Life Events

As discussed earlier, trauma and adverse life experiences represent significant risk factors for many FND patients, though not all. A "recent systematic review and meta-analysis found maltreatment was substantially more common in people with FND than in healthy controls and patient controls" (Ludwig et al., 2018). This suggests that traumatic experiences may create vulnerability to FND through various potential mechanisms, including alterations in stress response systems, changes in cognitive processing, or disruption of normal developmental processes.

The relationship between trauma and FND appears complex, with different types of adverse experiences potentially contributing in different ways. Some research suggests that "acute stressors and trauma" (Kanaan, 2016) may be particularly relevant, while other work points to the potential importance of cumulative adversity or specific forms of maltreatment.

Psychiatric Comorbidities and Their Causal Relationship

Psychiatric conditions frequently co-occur with FND, raising questions about their aetiological significance. However, "it is unclear whether their psychiatric diagnosis relates to the aetiology of their FND, and if yes, how" (Ludwig et al., 2018). The relationship between psychiatric comorbidities and FND may be complex and bidirectional, with several possible patterns:

• Psychiatric conditions as predisposing factors: Some psychiatric disorders may increase vulnerability to FND through shared neurobiological mechanisms, altered stress responses, or cognitive patterns.
• Psychiatric conditions as consequences: "Additionally, psychiatric comorbidities may be the result of living with FND" (Ludwig et al., 2018). The distress, disability, and social consequences of FND may contribute to the development of depression, anxiety, or other psychiatric conditions.
• Shared risk factors: Both FND and psychiatric comorbidities may arise from common underlying vulnerabilities, such as trauma history, genetic factors, or neurobiological abnormalities.

This complex relationship highlights the importance of comprehensive assessment and integrated treatment approaches that address both neurological symptoms and psychiatric comorbidities. The high prevalence of psychiatric conditions in FND patients suggests they may be clinically relevant even if their causal relationship remains uncertain.

Cognitive and Attentional Factors

Cognitive and attentional processes have gained increasing prominence in contemporary FND models. These approaches focus on how current information processing patterns, rather than historical events, may generate and maintain functional neurological symptoms. Key cognitive mechanisms include:

• Attentional dysregulation: Heightened self-focused attention may disrupt normally automatic bodily processes. Research highlights "links between the attentional system, illness beliefs, and FND symptoms" (Ludwig et al., 2018), suggesting that attention allocation may be particularly important in symptom generation and maintenance.
• Expectancy effects: Expectations about symptoms may generate prediction errors that the brain resolves by producing symptoms that match these expectations. This aligns with predictive processing models discussed earlier.
• Cognitive schemas: "Cognitive explanations highlight schemas or frames of understanding that underpin FND and result in symptoms being activated" (Ludwig et al., 2018). These mental frameworks may shape how bodily sensations are interpreted and experienced.

Personality Factors

Personality traits have historically been considered in FND aetiology, though their significance has been reframed in contemporary models. Rather than viewing specific personality types as causes of FND, current approaches consider how personalitydimensions might influence vulnerability, symptom expression, and treatment response. Relevant personality factors may include:

• Alexithymia: Difficulty identifying and describing emotions may contribute to somatisation, whereby emotional distress is experienced and expressed physically rather than psychologically.
• Suggestibility: Heightened responsiveness to suggestion might influence symptom development in some cases, particularly in response to iatrogenic factors such as clinician communication or medicalprocedures.
• Perfectionism and stress sensitivity: Traits associated with heightened stress responses may increase vulnerability to FND through their impact on physiological arousal and cognitive processing.

While personality factors may contribute to FND vulnerability, contemporary models avoid stigmatising characterisations that have historically been applied to these patients. Instead, personality dimensions are considered as one of many potential contributing factors within a complex biopsychosocial framework.

Social and Environmental Factors

Iatrogenic Factors

Medical encounters and healthcare interactions may play an important role in the development and maintenance of FND. Iatrogenic factors—those inadvertently caused by medical examination, communication, or treatment—have received increasing attention in contemporary FND models. These may include:

• Diagnostic uncertainty and miscommunication: "FND is a challenging diagnosis to communicate because of aetiological complexity and limited awareness in clinicians and wider society" (Stone et al., 2020). Unclear or contradictory explanations from healthcare providers may reinforce illness beliefs and anxiety.
• Medical procedures as precipitants: Research indicates that medical procedures, including "surgery, imaging procedures, and vaccinations" (Carson et al., 2016), may trigger FND symptoms in vulnerable individuals, possibly through expectancy effects, stress responses, or attentional mechanisms.
• Inadvertent reinforcement: Medical attention focused on symptoms may inadvertently reinforce symptom-focused attention and illness behaviours, potentially contributing to symptom persistence.

Understanding these iatrogenic influences has important implications for clinical practice, highlighting the need for clear communication, consistent explanations, and cautious medical investigations once FND has been diagnosed.

Cultural and Societal Influences

Cultural factors shape how symptoms are experienced, expressed, and interpreted, potentially influencing FND manifestation and course. These sociocultural dimensions include:

• Cultural illness models: Different cultural contexts provide varying frameworks for understanding unexplained symptoms, influencing how individuals interpret and respond to their experiences.
• Media representations and social learning: Exposure to portrayals of neurological symptoms (in media, social networks, or clinical settings) may shape symptom expectations and expressions through social learning mechanisms.
• Stigma and legitimacy concerns: "These old-fashioned but ever-present and stigmatising attitudes are further fuelled by misunderstanding around the aetiology and presentation of FND" (Stone et al., 2020). Societal stigma surrounding unexplained symptoms may influence illness behaviour and healthcare interactions.

The historical evolution of FND conceptualisation itself reflects changing cultural attitudes toward mind-body relationships, gender, and psychological distress. Contemporary models acknowledge these sociocultural dimensions as important contextual factors in understanding FND development and expression.

Family Systems and Interpersonal Factors

Family and interpersonal dynamics may contribute to FND development and maintenance through various mechanisms. Research suggests that "systemic and family-based aspects are of importance with respect to aetiological and disorder maintaining factors as well as treatment-related themes" (Stone et al., 2020). Relevant family factors include:

• Family illness models and responses: "Family members of patients with FND attributed more often psychological explanations and a greater emotional impact than patients themselves" (Stone et al., 2020). These differing understandings may create tensions that influence symptom course.
• Relationship patterns: Interpersonal dynamics characterised by high expressed emotion, overprotection, or conflict may contribute to symptom maintenance through their impact on stress, attention, and behaviour.
• Social reinforcement: Family responses to symptoms (such as attention, assistance, or relief from responsibilities) may inadvertently reinforce illness behaviours through operant conditioning mechanisms.

These interpersonal dimensions highlight the importance of including family members in both assessment and treatment, addressing family understanding of the condition, and modifying unhelpful interaction patterns that may maintain symptoms.

Integrative Models and Future Directions

The Bayesian Predictive Processing Framework

One of the most promising integrative frameworks for understanding FND is the Bayesian predictive processing model. This approach conceptualises FND symptoms as arising from abnormalities in how the brain generates predictions about sensory input and bodily states. According to this model, symptoms emerge when abnormally strong prior beliefs or expectations override normal sensory processing, generating experiences that align with these expectations rather than with actual physiological states.

The predictive processing framework offers several advantages as an explanatory model for FND:

• Integration of multiple factors: The model can accommodate biological, psychological, and social influences, as all may shape the prior beliefs and prediction errors that drive symptom generation.
• Mechanistic explanation: It provides a neurobiologically plausible mechanism for how psychological factors might influence neurological functioning without requiring conscious symptom production.
• Continuity with normal functioning: The model positions FND on a continuum with normal perceptual and motor processes, which all involve predictive mechanisms, rather than as a categorically distinct phenomenon.

This framework helps explain puzzling aspects of FND, such as the genuine nature of symptoms despite the absence of conventional neurological damage, the influence of attention and expectation on symptom expression, and the potential role of suggestion in both symptom generation and therapeutic interventions.

Challenges in FND Research

Despite significant advances in understanding FND aetiology, important challenges remain in researching this complex condition:

• Heterogeneity: "Recent etiological models acknowledge the significant heterogeneity in the presentation and underlying mechanisms of FND" (Ludwig et al., 2018). This diversity complicates research efforts, as findings from one subgroup may not generalise to others.
• Measurement limitations: The subjective nature of many FND symptoms poses challenges for objective measurement, though advances in neuroimaging and physiological monitoring offer promising approaches.
• Stigma and funding barriers: Historical stigma surrounding FND has contributed to research neglect, with limited funding compared to other neurological and psychiatric conditions of similar prevalence and impact.
• Interdisciplinary divides: The position of FND at the intersection of neurology, psychiatry, and psychology has created challenges for coordinated research efforts, though this is improving with greater interdisciplinary collaboration.

Addressing these challenges requires continued interdisciplinary collaboration, methodological innovation, and increased research funding for this historically neglected condition.

Implications for Clinical Practice

Contemporary aetiological models have important implications for clinical practice across multiple domains:

• Diagnosis and explanation: Understanding the complex, multifactorial nature of FND informs how clinicians communicate the diagnosis to patients. As noted, "FND is a challenging diagnosis to communicate because of aetiological complexity" (Stone et al., 2020), requiring careful, individualised explanations that avoid both oversimplification and stigmatisation.
• Assessment approach: Comprehensive assessment should evaluate potential predisposing, precipitating, and perpetuating factors across biological, psychological, and social domains, recognising that different factors may be relevant for different individuals.
• Treatment planning: Aetiological understanding guides treatment selection, with interventions ideally targeting the specific mechanisms maintaining symptoms for each individual. As research has noted, "contemporary FND models posit a mix of factors in symptom maintenance, requiring multidisciplinary treatment aligned with biopsychosocial principles" (Stone ett al., 2020).
• Prognosis and expectations: Understanding the factors that maintain FND symptoms helps in providing realistic prognostic information and setting appropriate treatment goals.

The evolution from simplistic, single-factor explanations to nuanced biopsychosocial models has supported more effective, non-stigmatising approaches to clinical management.

Future Research Directions

Several promising directions for future research may further advance understanding of FND aetiology:

• Subtyping and personalised approaches: Further research into potential FND subtypes with distinct aetiological pathways may support more targeted interventions. As noted, "Recent etiological models acknowledge the significant heterogeneity in the presentation and underlying mechanisms of FND" (Ludwig et al., 2018).
• Longitudinal studies: Prospective research tracking individuals from vulnerability through symptom development and resolution could clarify causal relationships and developmental trajectories.
• Advanced neuroimaging and physiological monitoring: Continued development of neuroimaging methods and physiological measures may identify more specific biomarkers and mechanisms underlying FND symptoms.
• Integration with other functional disorders: Exploring overlaps between FND and other functional somatic syndromes (such as fibromyalgia, irritable bowel syndrome, and chronic fatigue syndrome) may identify common mechanisms and inform integrated treatment approaches.
• Neuromodulation approaches: Research into targeted neuromodulation techniques based on identified neural circuit abnormalities represents a promising bridge between neurobiological understanding and novel interventions.

These research directions reflect the field's movement toward increasingly sophisticated, integrative models that acknowledge the complex, multifactorial nature of FND.

Conclusion

The understanding of FND aetiology has evolved dramatically over time, from early supernatural explanations and the "wandering womb" theory to contemporary biopsychosocial network models that integrate biological, psychological, and social factors. This evolution reflects broader shifts in medical thinking, scientific capabilities, and cultural attitudes toward mind-body relationships.

Contemporary aetiological models recognise FND as emerging from complex interactions between multiple factors operating across different levels of analysis. These include predisposing vulnerabilities (such as trauma history or temperamental traits), precipitating triggers (including both psychological stressors and physical events), and perpetuating mechanisms (such as attentional processes, illness beliefs, and social responses). This framework accommodates the significant heterogeneity observed in FND presentations and acknowledges that different factors may be more relevant for different individuals.

Neurobiological research has identified abnormalities in brain networks governing attention, sensorimotor integration, emotional processing, and sense of agency, providing potential mechanisms through which psychological factors might influence neurological functioning. These findings have helped bridge the artificial divide between "psychological" and "neurological" explanations that has historically complicated FND understanding.

The predictive processing framework offers a particularly promising integrative model, conceptualising FND symptoms as arising from abnormalities in how the brain generates and updates predictions about bodily states. This approach provides a neurobiologically plausible mechanism for symptom generation that can accommodate multiple influencing factors.

Despite significant advances, important challenges remain in FND research, including the condition's heterogeneity, measurement limitations, and historical research neglect. Addressing these challenges requires continued interdisciplinary collaboration, methodological innovation, and increased research funding.

The evolution of aetiological understanding has important implications for clinical practice, informing diagnosis, communication, assessment approaches, treatment planning, and prognostic expectations. Contemporary models support more effective, non-stigmatising approaches to clinical management that recognise the legitimacy of patients' experiences while offering pathways to symptom improvement.

Future research directions include subtyping approaches, longitudinal studies, advanced neuroimaging methods, integration with other functional disorders, and novel neuromodulation techniques. These efforts promise to further refine understanding of FND aetiology and support more targeted, effective interventions.

In conclusion, the aetiology of FND is best understood through a complex, integrative lens that acknowledges multiple contributing factors and mechanisms. This nuanced understanding represents a significant advance from historical single-factor explanations and provides a foundation for continued research and clinical innovation in this challenging but increasingly well-understood condition.

References

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• Edwards, M. J. (2016). How and why do functional symptoms occur? Journal of Neurology, Neurosurgery & Psychiatry, 87(3), 233-240.

• Kanaan, R. A. A. (2016). The aetiology of functional neurological symptoms: From the supernatural to the sophisticated. World neurology, 12, 26-31.

• Ludwig, L., Pasman, J. A., Nicholson, T. R., Aybek, S., & David, A. S. (2018). What is the role of adverse life events in functional neurological disorders? Journal of Neurology, Neurosurgery & Psychiatry, 89(6), 666-675.

• Nicholson, T. R., Stone, J., & Selvaraj, M. D. (2020). Functional neurological disorder. Practical Neurology, 20(2), 101-111.

• Perez, D. L., Aybek, S., Price, M., & Nicholson, T. R. (2021). Aetiology of functional neurological disorder: An update and synthesis. Journal of Neurology, 268(Suppl 1), 33-47.

• Stone, J., Reuber, M., & Carson, A. J. (2020). Functional neurological disorder. Continuum (Minneap Minn), 26(1), 58-85.