The freeze response, also known as freezing behavior, or tonic immobility, is a survival mechanism triggered by the brain in response to perceived threat, involving a sophisticated interplay between psychological and physiological factors.
It stands alongside the well-documented fight or flight responses as a fundamental mode of stress reaction, although the phenomenon, while well-researched in animals, has still not been studied much as a human response.
The term describes a state of immobility that an organism may enter when faced with a threat. In this state, individuals may find themselves unable to move or act against the danger. Historically, this response was advantageous for survival, as predators are less likely to notice prey that remains still. In modern humans, the freeze response can occur during intense stress or fear, manifesting as a temporary inability to react.
The freeze response is a distinct component of the larger fight, flight, or freeze response, which is the human body’s primitive, automatic, inborn stress response that prepares the body to “fight” or “flee” from perceived attack, harm, or threat to our survival. Whereas flight represents escape, fight denotes confrontation.
Triggers and Responses
Trigger events are specific incidents that evoke intense emotional reactions, such as trauma. They can range from sudden and unexpected occurrences to specific reminders of past traumatic experiences.
For instance, individuals with post-traumatic stress disorder (PTSD) may experience a freeze response when exposed to emotional information that resembles their traumatic past. This reaction can be both a psychological and physiological state of paralysis as the body’s natural defence mechanism takes hold.
Threat-induced freezing reflexes in people have typically been studied with a focus on inducing fear bradycardia (slow heart rate) through aversive picture viewing and the threat of mild electric shock. Among the intriguing findings in these studies is that freezing is connected to altered perceptual sensitivity and action preparation.
Anxiety disorders frequently involve the freeze response as a core feature of the symptomatology. For those with anxiety disorders, perceived threats — whether real or imagined — can trigger this overwhelming sense of immobility. In the context of anxiety, the freeze response is not simply a physical state but also an acute psychological experience, often linked with a heightened state of fear.
Signs of a Freeze Response
Initially, heart rate may spike as part of the acute stress response, but during a freeze, it can slow down markedly. This counterintuitive shift is part of the body’s effort to conserve energy and avoid detection by a perceived threat.
As the sympathetic nervous system activates the body’s ‘fight or flight’ mechanism, individuals might experience a redirection of blood flow to essential areas, leaving the skin feeling cold or clammy.
The redirection of blood flow can also lead to notable paleness or a sensation of numbness in the skin, which are observable indicators of the freeze response.
There might be a dilation of pupils as the eyes prepare to take in as much visual information as possible. The ears might also become attuned to specific sounds, heightening auditory perception to detect potential dangers.
Behavioral Indicators
- Immobility: A primary indicator is an abrupt cessation of movement. An individual might become still, seemingly paralyzed, as the body conserves energy and assesses the threat.
- Facial Expressions: There can be an absence of expressive facial movements. The individual might have a fixed gaze or a blank expression, which is part of the attentive immobility that allows for a heightened sensory scan of the environment.
- Quietness: A person might become silent if they are in a freeze state, reducing noise that could attract attention from a threat.
Mental Health Issues
The freeze response can leave lasting effects on one’s mental health. During the freeze response, individuals may experience a temporary immobilization, but the aftermath can manifest in various forms of psychological distress. Prolonged stress reactions may evolve into anxiety disorders, affecting an individual’s daily functioning and overall quality of life.
Researchers have observed that individuals who experience freeze responses frequently may display heightened sensitivity to stress and face difficulty returning to pre-stressor mental states. The link between chronic exposure to the stress response and anxiety disorders is well-established, often rooted in persistent fear and worry.
In the context of traumatic stress, the freeze response can be an indicative precursor to PTSD if the individual finds themselves repeatedly reliving the traumatic event and exhibiting avoidance behaviors, hyperarousal, and negative alterations in cognition and mood.
- Hyperarousal: Symptoms include being easily startled, feeling tense, difficulty sleeping, and constant vigilance.
- Avoidance Behaviors: This includes steering clear of reminders of the trauma, distancing from social interactions, and emotional numbing.
Biological Basis
Research indicates that some brain regions are known to either induce or prevent (in the case of lesions) freezing behavior in humans. The hippocampus and basolateral amygdala are two of these areas.
In 2002, Ann E. Power and colleagues carried out a study to look at the consequences of basolateral amygdala lesions. Cat hair was put in a chamber with rats. Rats in two groups — rats with basolateral amygdala lesions and rats in the control group — were evaluated.
At first touch, every rat froze for a little while before retreating away from the stimulus. The results revealed that, in comparison to the rats in the control group, the rats with lesions froze to the cat fur far less. These results imply that freezing behavior and the basolateral amygdala are related. It was also found that muscarinic cholinergic activation plays a role in the behavior.
Hashimoto et al. investigated the effects of conditioned fear on serotonin and freezing behavior in rats. Through in vivo microdialysis, certain concentrations of extracellular serotonin in the rat brain were able to be measured.
It was found that conditioned fear stress increased the levels of the serotonin in the medial prefrontal cortex. This increase was correlated with an increased freezing behavior that was observed.
The rats were then given an inhibitor for the extracellular serotonin, which resulted in a reduced freezing behavior. It can be suggested from these results that inhibition of serotonin can decrease freezing behavior and, also, anxiety.
References:
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- Crosby, G. (2008). Fight Flight Freeze. United States: AEG Literary Publishing Services, Incorporated
- Gladwin TE, Hashemi MM, van Ast V, Roelofs K. (2016) Ready and waiting: freezing as active action preparation under threat. Neurosci. Lett. 619, 182–188
- Hashimoto S, Inoue T, Koyama T (1999). Effects of conditioned fear stress on serotonin neurotransmission and freezing behavior in rats. European Journal of Pharmacology. 378 (1): 23–30. doi: 10.1016/S0014-2999(99)00441-0
- Karin, Roelofs. (2017). Freeze for action: Neurobiological mechanisms in animal and human freezing. Philosophical Transactions of the Royal Society B, doi: 10.1098/RSTB.2016.0206
- Karin, Roelofs., Peter, Dayan. (2022). Freezing revisited: coordinated autonomic and central optimization of threat coping. Nature Reviews Neuroscience, doi: 10.1038/s41583-022-00608-2
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