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Freezing behavior

Freezing behavior, also known as the freeze response, is a defensive reaction characterized by a temporary cessation of voluntary movement and behavioral inhibition, typically in response to perceived threats or fear-inducing stimuli.^[1] This response is observed across a wide range of species, including rodents, nonhuman primates, and humans, and is defined operationally as the absence of visible skeletal muscle activity except for those necessary for respiration, often lasting at least one second and not attributable to physical disability.^[2]^[3] In animals, it manifests as a rigid posture that minimizes motion, accompanied by physiological changes such as parasympathetically mediated heart rate deceleration (bradycardia), distinguishing it from other fear responses like flight or fight.^[1] Evolutionarily, freezing serves as an adaptive survival mechanism by reducing an individual's detectability to predators, particularly in situations involving distal or ambiguous threats where immobility enhances camouflage or allows for better sensory assessment of danger before further action.^[1] This behavior is part of the broader defense cascade in the autonomic nervous system, activated at intermediate levels of threat imminence to prepare for potential escape or confrontation, and it has been conserved across vertebrates due to its role in threat avoidance and predator evasion.^[1] In rodents, for instance, freezing is elicited by both unconditioned stimuli (e.g., predator odors) and conditioned cues (e.g., tones paired with shocks), reflecting its utility in learned fear contexts.^[1] The response's evolutionary significance is further underscored by its prevalence in natural environments, where it balances the risks of detection against the costs of premature action.^[4] Neurobiologically, freezing is orchestrated by a network involving the amygdala, which processes threat signals and projects to the periaqueductal gray (PAG) in the brainstem; specifically, the ventrolateral PAG column mediates the immobility and bradycardia associated with freezing, while the dorsolateral PAG drives more active defenses like flight.^[1] This circuitry integrates sensory inputs with autonomic outputs, resulting in motor suppression via inhibition of the motor cortex and heightened vigilance through enhanced perceptual processing.^[1] In experimental settings, freezing is a reliable measure of fear in fear-conditioning paradigms, where animals exhibit increased freezing duration proportional to threat intensity, providing insights into anxiety disorders and trauma responses.^[2]^[5] In humans, freezing manifests similarly as reduced body sway, gaze fixation, or slowed reaction times during threat exposure, such as viewing aversive images, and is linked to the same amygdala-PAG pathway, though modulated by cognitive factors like attention and context.^[1] It plays a role in conditions like post-traumatic stress disorder (PTSD), where exaggerated freezing may reflect hypervigilance or dissociation, and is studied using paradigms like viewing fearful body postures that rapidly inhibit motor responses.^[1] Overall, freezing behavior exemplifies a fundamental adaptive strategy in threat processing, bridging ethology, neuroscience, and clinical psychology.^[1]

Definition and Behavioral Context

Definition and Characteristics

Freezing behavior is a defensive response observed primarily in prey animals, characterized by a state of attentive immobility or reduced voluntary movement triggered by perceived threats, such as the presence of a predator, to minimize detection and enhance sensory vigilance. This immobilization serves as an antipredator strategy, allowing the animal to blend into its environment while assessing the danger and preparing for potential escape or confrontation.^[1] Operationally, freezing is defined as the absence of all visible skeletal muscle activity except for those movements necessary for respiration, typically lasting at least one second and not attributable to physical disability.^[1] Key observable characteristics of freezing include the abrupt halt of ongoing activities, with the animal adopting a rigid posture due to sustained muscle tone, minimal respiration-related movements, and often a fixed gaze directed toward the stimulus. The duration of this response typically varies from a few seconds to several minutes, influenced by factors like threat proximity and the animal's prior experience, though it remains reversible and context-dependent.^[6]^[1] Unlike tonic immobility, which represents a more passive and profound state of collapse with reduced muscle tone employed as a last-ditch survival tactic when escape is impossible, freezing is an active, preparatory behavior that facilitates rapid shifts to other defenses like flight.^[1] This distinction underscores freezing's role as an intermediate response in the defensive cascade.^[7] The operational definition of freezing as a reliable index of fear was pioneered by Robert and Caroline Blanchard in 1969, building on earlier ethological observations of defensive immobility in the mid-20th century.^[8]^[9]

Occurrence Across Contexts

Freezing behavior manifests in various environmental and situational contexts, primarily as a response to immediate threats that demand immobility for survival. In natural settings, it is commonly elicited by predation threats, where animals adopt a state of attentive immobility at intermediate levels of danger to avoid detection by predators and to better assess the environment. This response is particularly prevalent in high-predator environments in the wild, as evidenced by greater defensive freezing in wild rats exposed to predator odors compared to their laboratory counterparts, which exhibit attenuated reactions due to reduced exposure to natural threats. Additionally, freezing occurs in reaction to novel or alarming stimuli, such as unfamiliar sounds or sudden movements, serving to minimize visibility while orienting toward potential dangers; unlike transient orienting responses, this immobility persists until the stimulus is evaluated as safe. Social dynamics also trigger freezing, especially in group-living animals experiencing subordination. During interactions with dominant conspecifics, subordinate individuals display freezing as part of submissive behaviors, including flight avoidance and postural yielding, to de-escalate aggression and maintain social hierarchy. This is observed in rodent models of social defeat, where repeated subordination leads to heightened freezing in aversive contexts associated with aggressors. In experimental research, freezing is systematically induced through conditioned fear paradigms, such as Pavlovian conditioning in rodents, where neutral cues like tones or lights are repeatedly paired with unconditioned aversive stimuli, typically footshocks of 0.5–1 mA intensity. This pairing results in reliable freezing upon re-exposure to the conditioned stimulus alone, with studies demonstrating high reproducibility in laboratory rodents, where freezing durations can exceed 50% of observation time post-conditioning. Such paradigms highlight the behavior's consistency in controlled settings, contrasting with its variable but frequent occurrence in wild populations under natural predation pressures. Developmentally, freezing emerges as an innate response in juveniles, with onset observable shortly after birth in many mammals; for instance, rat pups begin exhibiting freezing to adult male intruders around postnatal day 12, prior to weaning. This early manifestation underscores its hardwired nature, yet the response is modifiable by experience, as variations in maternal care or early social exposure can either dampen or intensify freezing thresholds in later life.

Evolutionary and Adaptive Role

Evolutionary Origins

Freezing behavior, characterized by immobility in response to perceived threats, has deep phylogenetic roots as an anti-predator strategy in invertebrates. In simple organisms such as arthropods and other invertebrates, this behavior manifested as thanatosis or death feigning, allowing prey to blend into their environment and evade detection by predators. For instance, stick insects employ prolonged stillness to mimic twigs or foliage, a tactic that enhances camouflage and survival against visual hunters. This ancient form of freezing likely evolved independently multiple times due to its simplicity, requiring no specialized anatomy, and is documented across diverse invertebrate taxa including crustaceans, spiders, and beetles.^[10] The behavior was conserved and elaborated in vertebrates, facilitating threat evasion across aquatic and terrestrial environments. This continuity reflects an adaptive progression from invertebrate immobility tactics to more nuanced vertebrate defenses, present across phyla as a fundamental survival mechanism.^[10] At the genetic level, freezing is linked to conserved pathways, particularly those involving serotonin, which modulate fear responses and immobility across species. Comparative genomics reveals homology in serotonin-related genes, such as those regulating neurotransmitter release in threat detection circuits, from insects to mammals. These shared elements underscore the evolutionary stability of freezing as an innate reaction, facilitating rapid inhibition of movement to assess risks. For example, in fruit flies, serotonin release drives the initial freeze response to startling stimuli.^[11] Seminal ethological studies, including Niko Tinbergen's and Konrad Lorenz's 1930s–1950s experiments on young birds, demonstrated this innateness; young turkeys instinctively exhibited fixating, alarm calling, and fleeing in response to hawk-like silhouettes, highlighting the behavior's hardwired origins without prior learning.^[12]^[13]

Adaptive Functions

Freezing behavior provides key adaptive advantages in predation contexts by promoting survival through reduced visibility to predators. By remaining motionless, prey animals minimize movement cues that could attract visually oriented predators, such as birds or reptiles, thereby decreasing the likelihood of detection at a distance. This strategy is particularly effective when the threat is uncertain or distant, allowing the prey to blend into its environment via camouflage.^[14] Additionally, the attentive nature of freezing—characterized by heightened sensory vigilance—enables prey to monitor the predator's actions and evaluate escape opportunities without provoking further attention. Empirical field studies on camouflaged prey, such as frogs, demonstrate that immobility distracts predators' focus toward alternative prey items, enhancing individual survival in multi-prey scenarios.^[15] Beyond anti-predator roles, freezing conserves energy during extended threats, offering a low-metabolic-cost alternative to high-expenditure responses like flight. Unlike fleeing, which can demand rapid bursts of locomotion and deplete reserves quickly, freezing maintains baseline physiological activity while suspending unnecessary motion, preserving resources for potential later evasion or recovery. This is advantageous in scenarios where immediate escape is infeasible, such as when predators patrol a confined area over time. Studies on prey energetics confirm that anti-predator immobility incurs minimal additional cost compared to routine foraging or travel, supporting its utility in resource-limited environments.^[16] In social contexts, freezing functions as a submissive signal within group hierarchies, mitigating intra-specific aggression. Subordinate individuals often adopt immobility or freezing-like postures to signal non-threat to dominants, reducing the risk of escalated conflict and promoting group stability. For example, in primates like rhesus macaques, such displays during dominance interactions lower the probability of retaliatory attacks, fostering tolerance and resource access. This adaptive role extends freezing's utility beyond solitary predation avoidance to cooperative social dynamics.^[17] Despite these benefits, freezing has notable limitations, particularly against predators that rely on olfactory cues rather than vision. Mammalian hunters, such as foxes or cats, can detect prey scents regardless of motionlessness, rendering freezing ineffective and potentially delaying critical escape responses. This trade-off highlights the context-dependent nature of the behavior, where reliance on immobility may forfeit optimal flight opportunities against scent-driven threats. Field observations of mammalian predation confirm higher vulnerability of frozen prey to odor-guided attacks, underscoring the strategy's specificity to visual predation risks.^[18]

Neural Mechanisms

Brain Regions and Pathways

The amygdala serves as a central hub for threat detection in the initiation of freezing behavior, processing sensory information related to potential dangers and orchestrating downstream responses through its projections to brainstem structures. Specifically, the basolateral amygdala (BLA) evaluates contextual and sensory cues of threat, while the central nucleus of the amygdala (CeA) relays signals that promote immobility as a defensive strategy.^[14] The periaqueductal gray (PAG) in the midbrain plays a critical role in motor inhibition underlying freezing, with the ventrolateral PAG (vlPAG) particularly implicated in mediating immobility, bradycardia, and behavioral arrest during distal or ambiguous threats. The dorsolateral PAG (dlPAG), in contrast, is associated with active defenses such as flight or escape. Lesions in the vlPAG attenuate freezing, while dlPAG lesions can enhance it by reducing inhibition on passive responses.^[19] Key pathways linking these regions facilitate the rapid expression of freezing. Sensory inputs from the thalamus project directly to the amygdala, providing a fast conduit for unprocessed threat signals that bypass cortical evaluation, enabling immediate defensive responses like freezing during fear conditioning.^[20] Activation of the hypothalamic-pituitary-adrenal (HPA) axis, triggered by amygdalar signals to the hypothalamus, contributes to the modulation of fear responses, including sustaining aspects of freezing through stress hormone release, though primary motor inhibition is driven by direct CeA-vlPAG projections.^[14] Circuit dynamics within these structures have been elucidated through optogenetic studies since 2010, revealing how prefrontal-amygdala interactions regulate freezing. Inhibition of projections from the prelimbic prefrontal cortex to the amygdala disrupts the maintenance of fear memories, reducing freezing during recall by impairing the consolidation of threat associations.^[21] Imaging evidence from functional MRI (fMRI) supports heightened PAG activity during fear conditioning in both rodents and humans. In awake rodents, fMRI during conditioned fear tasks shows increased PAG activation correlating with freezing episodes, highlighting its role in threat expression.^[22] Similarly, in humans, fMRI reveals PAG engagement during imminent threat scenarios that elicit freezing-like immobility, underscoring conserved circuitry across species.

Neurotransmitter Roles

GABA, the primary inhibitory neurotransmitter in the central nervous system, plays a crucial role in promoting the motor suppression characteristic of freezing behavior. Within the periaqueductal gray (PAG), GABAergic neurons facilitate the immobility response during threat detection by inhibiting motor output pathways, thereby enforcing a state of defensive stillness.^[23] Chemogenetic inhibition of these GABA neurons in the ventral PAG has been shown to impair contextual fear responses, underscoring their necessity for sustaining freezing as an adaptive reaction to conditioned threats.^[24] In contrast, glutamate serves as the main excitatory neurotransmitter, amplifying threat processing in key brain regions such as the amygdala. Glutamatergic signaling enhances synaptic transmission in amygdaloid circuits, facilitating the rapid encoding and expression of fear memories that trigger freezing.^[25] Activation of metabotropic glutamate receptors (mGluR5) in the amygdala, for instance, directly contributes to the initiation of freezing by heightening neuronal excitability in response to aversive stimuli.^[26] Serotonin modulates freezing through its action on 5-HT1A receptors, where reduced serotonergic activity prolongs the duration of this behavior. Low serotonin levels, as observed in deficiency models, intensify contextual fear responses, leading to heightened and persistent freezing episodes.^[27] Conversely, enhancing serotonin transmission via 5-HT1A agonists attenuates freezing, indicating its role in dampening excessive fear expression.^[28] Norepinephrine, released from the locus coeruleus, heightens overall arousal during stress but promotes a shift toward freezing at elevated concentrations. Phasic activation of locus coeruleus noradrenergic neurons reinstates fear memories, eliciting robust freezing behaviors in response to previously extinguished cues.^[29] This effect is particularly pronounced under acute stress, where norepinephrine facilitates the transition from exploratory activity to immobility as a defensive strategy.^[30] Pharmacological interventions targeting these neurotransmitters provide evidence for their mechanistic roles. Benzodiazepines, as GABA_A receptor agonists, reliably reduce freezing in animal models of conditioned fear, confirming GABA's inhibitory promotion of the behavior.^[31] Selective serotonin reuptake inhibitors (SSRIs), while acutely increasing fear expression, alter freezing responses under chronic stress conditions by normalizing serotonergic tone and mitigating prolonged immobility.^[32]

Physiological and Hormonal Responses

Autonomic Nervous System Involvement

Freezing behavior involves coordinated activation of the autonomic nervous system, with parasympathetic dominance resulting in bradycardia—a deceleration of heart rate—that aids energy conservation and reduces detectability by predators. Sympathetic activity provides background arousal and maintains muscle readiness while parasympathetic input promotes immobility.^[14]^[33]^[1] Respiratory adjustments during freezing further support concealment, featuring shallow and slowed breathing patterns that minimize audible noise and visible chest movement. These changes reduce the risk of detection in natural environments, aligning with the adaptive goal of predator avoidance. Studies in rodents and humans confirm this respiratory suppression as a hallmark of the response, often coupled with overall metabolic slowing.^[1] Muscular effects in freezing manifest as hypertonia, characterized by sustained muscle tension without tremor or phasic contractions, ensuring rigid immobility. This state is mediated by tonic activation of alpha-motor neurons, which sustain postural readiness without overt motion. Unlike trembling responses in other stress states, the absence of tremor preserves the stillness critical for survival.^[14] Autonomic involvement is commonly assessed through heart rate variability (HRV) analyses, which indicate reduced variability during freezing due to sympathetic-parasympathetic interplay, followed by a parasympathetic rebound post-threat that restores baseline HRV. This rebound signifies autonomic recovery and is evident in both animal models and human analogs of fear. Seminal 1960s research on cats exposed to conditioned fear stimuli, including work examining amygdala functions, highlighted these cardiovascular and respiratory correlates, establishing early evidence for peripheral autonomic patterning in defensive behaviors.^[34]^[35]

Hormonal Influences

Freezing behavior is significantly influenced by the activation of the hypothalamic-pituitary-adrenal (HPA) axis, which leads to the release of cortisol, a glucocorticoid hormone that sustains the response over longer periods. In rodents and primates, stress-induced cortisol elevations are positively associated with increased freezing duration, promoting vigilance and immobility to evade detection by predators. Cortisol levels typically peak 10-30 minutes following threat exposure, helping to maintain heightened arousal and metabolic support for prolonged defensive states without immediate escape.^[14]^[36]^[37] Adrenaline (epinephrine), released rapidly from the adrenal medulla within seconds of threat detection, contributes to the freezing response as part of the sympathetic activation, preparing the body for potential shifts to active defense like flight if the stimulus persists. This catecholamine enhances sensory processing and cardiovascular adjustments to support immobility, but its quick onset allows for flexible behavioral transitions based on threat assessment. In animal models, epinephrine facilitates the consolidation of fear memories underlying freezing, contributing to its persistence in traumatic contexts.^[38]^[39] Oxytocin, a neuropeptide hormone, modulates freezing in social settings by inhibiting the response, thereby favoring affiliation and protective behaviors over isolation. In maternal rats exposed to threats near offspring, central oxytocin release suppresses freezing in the amygdala, enabling alternate defenses such as retrieval of pups and promoting social bonding to buffer stress. This inhibition highlights oxytocin's role in context-dependent fear regulation, reducing immobility when social cues signal safety or collective protection.^[40]^[41] Negative feedback mechanisms involving glucocorticoid receptors in the hippocampus limit excessive cortisol release, preventing exhaustion from sustained freezing. These receptors detect elevated glucocorticoids and signal the HPA axis to dampen further hormone production, restoring homeostasis after the threat subsides. Disruptions in this feedback can prolong defensive responses, underscoring the hippocampus's role in balancing stress adaptation.^[42]

Variations Across Species

In Non-Mammalian Animals

In non-mammalian animals, freezing behavior manifests as a primitive anti-predator strategy, often involving immobility to evade detection or facilitate camouflage, with mechanisms rooted in basic sensory processing rather than higher cognitive integration. In invertebrates, cephalopods such as the cuttlefish Sepia officinalis employ a freezing response that combines behavioral immobility with rapid changes in skin color and texture to achieve visual and bioelectric crypsis against predators like sharks. This freeze reduces the animal's self-generated electric field, making it harder for electroreceptive predators to locate it, as demonstrated in controlled predation simulations. In insects, escape-related immobility, known as tonic immobility or thanatosis, occurs when individuals are restrained or threatened, causing them to adopt a rigid, death-feigning posture to deter predators that prefer live prey; for instance, in weevils like Eucryptorrhynchus brandti, this response suppresses metabolic activity and movement for extended periods until the threat subsides. Among fish and amphibians, visual and auditory cues trigger whole-body freezing as an initial defensive halt before potential escape. In larval zebrafish (Danio rerio), visual threats such as looming stimuli or conspecific alarm cues induce freezing via segregated visuomotor pathways in the optic tectum, where anterior neurons process hunting cues, middle ones mediate freezing, and posterior ones drive escape, allowing rapid assessment of predation risk. Auditory stimuli in frogs, such as biologically relevant calls mimicking threats, elicit stasis or freezing responses through activation of the lateral amygdala homologue, promoting immobility to avoid detection by acoustic predators, as observed in species like Physalaemus pustulosus. These responses highlight the role of sensory-specific circuits in coordinating brief immobility for survival. Reptiles exhibit extended forms of freezing, particularly thanatosis, where lizards simulate death by remaining limp and motionless in response to tactile threats like handling or predation attempts. In species such as Liolaemus occipitalis and Leposoma scincoides, this behavior is triggered by physical contact, causing the animal to flatten and cease voluntary movement, often lasting minutes until the predator loses interest and departs, thereby increasing escape probability without active flight. The neural basis of freezing in these taxa is simpler than in more advanced vertebrates, lacking a complex amygdala and instead relying on spinal reflexes for rapid immobility and basic ganglia for sensory integration. For example, in insects and amphibians, tonic immobility is mediated by direct mechanosensory inputs to spinal circuits, bypassing higher brain centers to ensure instantaneous suppression of locomotion. Comparative studies from the 2010s have identified conserved periaqueductal gray (PAG)-like structures, such as the griseum centrale in zebrafish, which orchestrate defensive freezing through midbrain pathways homologous to those in tetrapods, underscoring broad evolutionary conservation across vertebrates.

In Mammals and Humans

In mammals, freezing behavior serves as a key defensive response to predators and social threats, often elicited instinctively to avoid detection. In rodent models, such as rats, exposure to predator odors like trimethylthiazoline (TMT), a component of fox feces, reliably induces freezing as an unconditioned fear response, characterized by immobility and reduced locomotion in open environments.^[43] This response is modulated by the olfactory bulb and amygdala, highlighting its role in innate threat detection.^[44] Primate studies further illustrate social modulations of freezing within dominance hierarchies, where subordinate individuals exhibit freezing upon approach by dominants as a submissive behavior to signal non-aggression and reduce conflict. In rhesus macaques, for instance, submissive displays including freezing or turning away occur in response to dominant aggression, helping maintain social stability in despotic groups.^[45] These behaviors are context-dependent, integrating sensory cues from the dominant's posture and vocalizations to calibrate the intensity of immobility.^[46] In humans, freezing manifests more subtly than in other mammals, often as "attentional freezing" during anxiety-provoking situations, involving prolonged gaze fixation on threats without full bodily immobility. This response aids threat monitoring but can impair action preparation, as seen in studies where participants under threat imminence show reduced saccades and stabilized gaze toward potential dangers.^[47] Among trauma survivors, freezing episodes are common during reminders of past events, reflecting a hypervigilant pause that may underlie persistent fear responses in conditions like PTSD.^[48] Cognitive influences in humans allow greater voluntary control over freezing compared to more instinctive expressions in other mammals, primarily through prefrontal cortex (PFC) mechanisms that override amygdala-driven immobility. The dorsomedial PFC, in particular, facilitates suppression of freezing by integrating contextual safety signals, enabling shifts to active coping strategies like avoidance.^[1] This top-down regulation is evident in fear extinction tasks, where PFC activation reduces persistent freezing to conditioned threats.^[49] Measurement of subtle freezing in humans relies on physiological indicators such as skin conductance response (SCR) for autonomic arousal and electromyography (EMG) for postural muscle tension, capturing immobility without relying on overt observation. In fear conditioning paradigms, SCR increases during freezing-like states, correlating with threat anticipation, while EMG detects micro-movements in the neck or limbs.^[50] Recent EEG studies from the 2020s link freezing to elevated theta wave activity (4-8 Hz) in prefrontal regions, reflecting heightened emotional processing and conflict monitoring during threat exposure.^[51]

Clinical and Applied Implications

Association with Anxiety Disorders

Freezing behavior, characterized by immobility and reduced responsiveness, manifests prominently in posttraumatic stress disorder (PTSD), where individuals exhibit persistent freezing in response to trauma-related cues, reflecting an exaggerated defensive reaction that impairs daily functioning.^[48] This response aligns with PTSD's core symptoms of re-experiencing trauma through hyperarousal and avoidance, as freezing serves to minimize perceived threat but becomes maladaptive when triggered by neutral or ambiguous reminders.^[52] In generalized anxiety disorder (GAD), freezing appears as anticipatory immobility, where chronic worry leads to prolonged states of postural stillness and cognitive disengagement during perceived ongoing threats, mirroring patterns observed in animal models of contextual anxiety.^[53] Symptomatically, hypervigilance in specific phobias induces freezing as individuals fixate on the phobic stimulus, resulting in a temporary shutdown of motor activity to avoid escalating the threat, which exacerbates avoidance behaviors central to the disorder.^[54] Similarly, in panic disorder, episodes of dissociation during attacks can involve motor inhibition and a sense of detachment. These features highlight freezing's role in the diagnostic criteria of anxiety disorders, contributing to the persistence of symptoms beyond acute threat. In a study of 23 PTSD patients who were victims of urban violence, 43% reported peritraumatic tonic immobility—a freeze-like state during trauma—which correlated with more severe and treatment-resistant symptoms under DSM-5 criteria; prevalence varies across populations and trauma types.^[55] Neuroimaging studies reveal overactive connectivity in the amygdala-periaqueductal gray (PAG) circuit among individuals with anxiety disorders, as shown in fMRI scans where heightened amygdala-PAG interactions predict elevated trait anxiety and defensive immobility.^[56]

Interventions and Management

Pharmacological interventions target neurochemical imbalances underlying maladaptive freezing responses. Selective serotonin reuptake inhibitors (SSRIs), such as citalopram and fluvoxamine, have been shown to reduce the duration of conditioned fear-induced freezing in animal models by normalizing serotonin levels, with acute doses of 1-30 mg/kg demonstrating anxiolytic effects.^[32] Beta-blockers like propranolol dampen autonomic arousal associated with freezing by blocking noradrenergic activity in the basolateral amygdala, leading to decreased fear expression and lower freezing levels during memory reactivation in rodents.^[57] These agents are often prescribed off-label for anxiety disorders where freezing manifests as immobility during threats.^[58] Behavioral therapies emphasize habituation and cognitive restructuring to replace freezing with adaptive coping. In cognitive behavioral therapy (CBT), exposure therapy involves gradual confrontation with fear cues to extinguish conditioned responses, reducing PTSD-related freezing by promoting emotional processing and distinguishing past threats from present safety.^[59] Eye movement desensitization and reprocessing (EMDR) uses bilateral stimulation to reprocess trauma memories, decreasing physiological arousal and freeze-like dissociation in PTSD patients by enhancing prefrontal control over limbic hyperactivity.^[60] In veterinary practice, desensitization training addresses freezing in companion animals during handling or clinical procedures. Systematic desensitization paired with counterconditioning exposes pets to low-intensity stimuli (e.g., veterinary environments) while providing positive reinforcements, resulting in lower fear scores and reduced submissive postures in dogs after a four-week program, though effects are mild and compliance-dependent.^[61] Emerging neuromodulation techniques in the 2020s offer non-invasive options to modulate brain circuits driving freezing. Transcranial direct current stimulation (tDCS) applied to the dorsolateral prefrontal cortex inhibits amygdala-driven fear retrieval, increasing latency to freezing and reducing its duration in animal models with medium effect sizes (Hedges' g = -0.50 to -0.63).^[62] Cathodal tDCS over the prefrontal area similarly enhances fear extinction by downregulating threat processing.^[63] As of 2025, virtual reality (VR)-assisted exposure therapies have shown promise in reducing freezing responses in PTSD by simulating safe threat environments, with ongoing clinical trials reporting improved outcomes in hypervigilance.^[64] Randomized controlled trials of these interventions demonstrate substantial efficacy in reducing freeze responses, with behavioral therapies like prolonged exposure achieving 60-76% rates of clinically significant symptom improvement in PTSD cohorts, including diminished fear immobility.^[65] Pharmacological and neuromodulation approaches show comparable reductions in animal fear paradigms, supporting their translation to human anxiety management where freezing links to disorders like PTSD.^[59]

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The evidence shows that the amygdala is very important in the regulation of drives, especially fear, but is not itself essential for their elaboration.
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High glucocorticoid stress-responses are associated with prolonged freezing reactions and decreased active approach and avoidance behavior in animals.
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Single prolonged stress increases contextual freezing and the ...
Rats subjected to single prolonged stress (SPS) show enhanced HPA negative feedback, exaggerated acoustic startle response, and enhanced contextual freezing ...
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E2 is Associated with Increased PTSD Severity and Alterations in Salivary Cortisol Concentrations in Combat Veterans. We next assessed the effects of E2 on PTSD ...
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including humans — to flee or freeze in the face of a perceived threat. But if these behaviors persist ...<|separator|>
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Theta-Range Oscillations in the HPC-PFC-Amy Circuit Related to Emotional Behavior. Dysregulation of emotions and increased anxiety are crucial hallmarks of ...
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Review Different patterns of freezing behavior organized in the ...
The understanding of how the periaqueductal gray generates and elaborates different types of freezing is of relevance for our better knowledge of distinct types ...
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Freezing in response to social threat: a replication - PMC
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Propranolol decreases fear expression by modulating fear memory ...
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May 2, 2017 · Rats that received intra-BLA propranolol immediately after fear conditioning exhibited lower levels of freezing than those receiving mPFC ...
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[PDF] Prolonged exposure therapy for the treatment of posttraumatic stress ...
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How Does Eye Movement Desensitization and Reprocessing ...
Eye movement desensitization and reprocessing [EMDR] is an innovative, evidence-based and effective psychotherapy for post-traumatic stress disorder [PTSD].
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Trauma-focused Exposure Therapy for Chronic Posttraumatic Stress ...
In regard to clinically significant improvement in trauma symptoms, 75.8 % of the mPE participants, 60.0% of the mPE+MET-PTSD participants, and 44.4% of the HLS ...