Surreal illustration of a person frozen in stress with fragmented neural pathways.

Unlocking the Freeze: How Stress Impairs Movement in Functional Disorders

Kai Mendoza in Health & Wellness August 2025 • 4 min read.

"New research reveals the hidden link between stress, body movement, and functional movement disorders, offering insights into potential treatments and therapies."

Functional neurological disorders (FND), often misunderstood and characterized by symptoms like paralysis, tremors, or dystonia, have long puzzled medical professionals. These conditions, where neurological symptoms occur without visible lesions in the nervous system, affect a significant portion of the population, with up to 18% of neurological patients presenting such 'unexplained' symptoms. Understanding the intricate relationship between the brain, stress, and motor function is crucial for effective diagnosis and treatment.

Stress, a well-known trigger for various health issues, has been increasingly recognized as a key factor in FND. Psychological and physical stressors can initiate or exacerbate motor symptoms, highlighting the need to investigate how stress influences automatic motor behaviors. One such behavior is the 'freeze response,' a defensive mechanism characterized by decreased body movement and, sometimes, bradycardia (slowing of the heart rate) in response to perceived threats.

Recent studies employing advanced technologies like accelerometers and gyroscopes are providing new insights into postural behavior under stress. These tools allow researchers to analyze movement dynamics in detail, revealing subtle patterns that may be indicative of underlying neurological conditions. By examining how individuals with FND respond to stress-induced situations, scientists hope to unlock new therapeutic strategies and improve the lives of those affected.

What is the 'Freeze Response' and Why Is It Important?

Surreal illustration of a person frozen in stress with fragmented neural pathways.

The 'freeze response' is an automatic defensive mechanism deeply rooted in our evolutionary history. When faced with a threatening situation, our bodies instinctively reduce movement to assess the danger and prepare for action, whether it be fight or flight. This response is characterized by a decrease in body sway, often accompanied by a slowing of the heart rate. In healthy individuals, the freeze response is a temporary and adaptive reaction to stress.

However, in individuals with FMD, this response appears to be impaired. Research indicates that patients with FMD do not exhibit the same reduction in body sway under stress as healthy controls. This suggests that the neural circuits responsible for regulating the freeze response are disrupted in FMD, potentially contributing to the manifestation of motor symptoms.

Reduced Body Sway: Healthy controls show a decrease in body sway under stress, indicating a typical freeze response.
Lack of Freeze Response: FMD patients do not exhibit this reduction, suggesting an impaired defensive mechanism.
Lower Movement Complexity: FMD patients show a smoother, more regular movement pattern compared to controls, indicated by lower fractal dimension (HFD).
Cortisol Correlation: In healthy controls, changes in body sway correlate with changes in cortisol levels, but this correlation is absent in FMD patients.

These findings highlight the importance of the freeze response in understanding the pathophysiology of FMD. By further investigating the neural mechanisms underlying this response, researchers hope to identify potential targets for therapeutic intervention.

Moving Forward: Implications and Future Directions

This research sheds light on the critical role of stress and the freeze response in functional movement disorders. Recognizing the impaired defensive mechanisms in FMD patients opens new avenues for developing targeted therapies aimed at restoring normal motor control and improving patients' quality of life. Future studies should focus on further elucidating the neural circuits involved and exploring potential interventions, such as stress management techniques and rehabilitation programs, to help individuals with FMD regain control over their bodies and their lives.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.psyneuen.2018.11.020, Alternate LINK

Title: Abnormal Postural Behavior In Patients With Functional Movement Disorders During Exposure To Stress

Subject: Biological Psychiatry

Journal: Psychoneuroendocrinology

Publisher: Elsevier BV

Authors: Giuseppe Angelo Zito, Kallia Apazoglou, Anisoara Paraschiv-Ionescu, Kamiar Aminian, Selma Aybek

Published: 2019-03-01

Everything You Need To Know

What exactly is Functional Neurological Disorder (FND), and why is it so puzzling to medical professionals?

Functional Neurological Disorder or FND is a condition where patients experience neurological symptoms, such as tremors, paralysis, or dystonia, without structural lesions in their nervous system. It's considered an 'unexplained' symptom affecting a notable segment of the neurological patient population, up to 18%. The key is that these symptoms are not due to damage or disease that can be seen on standard neurological tests, which makes diagnosis and understanding challenging.

What is the 'freeze response', and what does its impairment suggest about Functional Movement Disorder (FMD)?

The 'freeze response' is an automatic defensive mechanism activated when facing a perceived threat. It's characterized by reduced body movement and sometimes a slowing of the heart rate or bradycardia. The purpose is to assess danger before deciding to either fight or flee. Research indicates that individuals with Functional Movement Disorder (FMD) do not exhibit this typical reduction in body sway under stress, suggesting disrupted neural circuits.

How does stress influence automatic motor behaviors in individuals with Functional Neurological Disorder (FND)?

Stress influences automatic motor behaviors in Functional Neurological Disorder (FND) because psychological and physical stressors can trigger or worsen motor symptoms. The freeze response, a defensive mechanism involving decreased body movement, is impaired in individuals with FMD. Studies using accelerometers and gyroscopes show that unlike healthy individuals, FMD patients don't exhibit the same reduction in body sway under stress, indicating that the neural circuits responsible for regulating this response are disrupted, contributing to motor symptoms.

How do advanced technologies like accelerometers and gyroscopes help us understand Functional Movement Disorder (FMD)?

Advanced technologies like accelerometers and gyroscopes contribute to understanding Functional Movement Disorder (FMD) by providing detailed analysis of movement dynamics. These tools can reveal subtle patterns in postural behavior that are indicative of underlying neurological conditions. For example, they have shown that individuals with FMD do not exhibit the typical reduction in body sway or freeze response under stress, unlike healthy controls. This kind of detailed movement analysis helps researchers identify disrupted neural mechanisms and develop targeted therapeutic strategies.

How do cortisol levels and movement complexity differ in individuals with Functional Movement Disorder (FMD) compared to healthy controls during stressful situations, and what does this imply?

Research indicates that in healthy controls, changes in body sway during a freeze response correlate with changes in cortisol levels, but this correlation is absent in patients with Functional Movement Disorder (FMD). In addition, FMD patients display lower movement complexity, indicated by a smoother, more regular movement pattern compared to controls, highlighted by lower fractal dimension (HFD). This suggests a disconnect between the physiological stress response (cortisol release) and motor control in FMD, which could be linked to impaired defensive mechanisms and altered neural processing.