question: Why do some freeze in terror when presented with danger rather than fight/flight?
comment: I'll note the psychology on this is somewhat speculative. There is an evolutionary basis for this. Not all threats are able to be fought or fled from. A young rabbit may not be able outrun a grown fox and certainly cannot fight it, but it can perhaps avoid being found by holding perfectly still. Other animals will go limp and "play dead" around predators to appear less appetizing.
passages: Section::::Other animals.:Varieties of responses.
  
  Animals respond to threats in many complex ways. Rats, for instance, try to escape when threatened, but will fight when cornered. Some animals stand perfectly still so that predators will not see them. Many animals freeze or play dead when touched in the hope that the predator will lose interest.
   An evolutionary psychology explanation is that early animals had to react to threatening stimuli quickly and did not have time to psychologically and physically prepare themselves. The fight or flight response provided them with the mechanisms to rapidly respond to threats against survival.
  
  Section::::Other animals.:Examples.
   The fight or flight actions also have polarity – the individual can either fight or flee against something that is threatening, such as a hungry lion, or fight for or fly towards something that is needed, such as the safety of the shore from a raging river.
   In vertebrates, the avoidance behaviour appears to be processed in the telencephalon. This has been shown repeatedly in goldfish, as individuals with ablated telencephalons were significantly impaired in acquiring avoidance behaviour. As a result, some researchers conclude that damage to the telencephalon can interfere with the emotion internal fear to produce an avoidance response.
  
  Researchers will often evoke an escape response to test the potency of hormones and/or medication and their relationship to stress. As such, the escape response is fundamental to anatomical and pharmacological research
  
  Section::::The role of learning in the escape response.
   The perception of a "threat" may also trigger an associated ‘feeling of distress’.
  
  Physiological reactions triggered by mind cannot differentiate both the physical or mental threat separately, Hence the "fight-or-flight" response of mind for the both reactions will be same.
  
  Section::::Duration of threat and its different physiological effects on the nervous system..
   Other animals have alternative self-protection methods. Some species of cold-blooded animals change color swiftly, to camouflage themselves. These responses are triggered by the sympathetic nervous system, but, in order to fit the model of fight or flight, the idea of flight must be broadened to include escaping capture either in a physical or sensory way. Thus, flight can be disappearing to another location or just disappearing in place. And often both fight and flight are combined in a given situation.
   Post-encounter defensive behaviours are avoidance behaviours performed when a predator is present and has been detected. When this stage of threat has been reached, behaviours are limited to species-specific defence reactions. These behaviours are commonly freezing, fleeing or threatening. The goal of a post-encounter defensive behaviour is to prevent the predatory imminence from further increasing. The dominant post-encounter defensive behaviour can depend on whether the predator has also detected the prey and how far away the two animals are from one another. Varying levels of predatory imminence, even in post-encounter situations, can affect the expressed defensive behaviour. If the prey has yet to be detected, the goal of the post-encounter behaviour will be to prevent the predator from detecting the prey. If both the predator and prey have detected each other, the goal will be to avoid making contact with the predator. Freezing behaviour in rats is an example of a post-encounter defensive behaviour which has been well studied. Freezing in rats is characterized by sudden, extended immobility, followed by a decreased heart rate and an increased respiration rate. This behaviour is often the dominant post-encounter defence behaviour in rats. In the laboratory setting, post-encounter defensive behaviours can be elicited by pairing a neutral stimulus, such as a light, with an aversive stimulus, such as a shock. The rat will engage in its post-encounter defensive behaviour when it becomes aware of the neutral stimulus, as the stimulus is acting as a predictor for the shock. Since the freezing behaviour is dominant in these situations, it can be assumed that it serves an adaptive function by preventing an additional increase in predatory imminence. Freezing is the dominant post-encounter behaviour because even when there are alternative defensive reactions available, freezing has been observed to be the rat's response the majority of the time. Even when a clear method of escape was made available, rats would freeze instead of fleeing. Freezing can prevent the perceived level of threat from increasing in several ways. If a rat becomes aware of a predator before the predator is aware of the prey, freezing can reduce the likelihood that the prey will be detected. As well, since many predators rely on motion to keep track of their prey, freezing may cause the predator to either lose site of their prey or shift their attention to a more active object.
   Section::::Neurobiology of FPS.
   Section::::Evolutionary importance.
  
  The escape response, a particular type of anti-predator behaviour, is vital to the survival of species. Individuals that are able to execute an escape response quickly are more likely to flee from predators and avoid predation.
   Section::::Fear circuitry.:Conditioned stimuli.
  
  There has been a substantial amount of research done on conditioned stimuli, where a neutral stimulus, such as a flash of light, is paired with a shock is given to a rat. The result of this conditioned stimulus is to provoke the unconditioned response, fear. The once neutral stimulus is given again to see if the rat would show the responses of fear. However, because fear responses involve many behaviors, it is important to see which behaviors are exhibited when the conditioned stimulus is given.
  
  Section::::Fear circuitry.:Visual and auditory stimuli.
   Section::::Measuring the startle response and utilization of FPS data.
   Robert C. Bolles (1970), a researcher at University of Washington, wanted to understand species-specific defense reactions and avoidance learning among animals, but found that the theories of avoidance learning and the tools that were used to measure this tendency were out of touch with the natural world. He theorized the species-specific defense reaction (SSDR). There are three forms of SSDRs: flight, fight (pseudo-aggression), or freeze. Even domesticated animals have SSDRs, and in those moments it is seen that animals revert to atavistic standards and become "wild" again. Dr. Bolles states that responses are often dependent on the reinforcement of a safety signal, and not the aversive conditioned stimuli. This safety signal can be a source of feedback or even stimulus change. Intrinsic feedback or information coming from within, muscle twitches, increased heart rate, are seen to be more important in SSDRs than extrinsic feedback, stimuli that comes from the external environment. Dr. Bolles found that most creatures have some intrinsic set of fears, to help assure survival of the species. Rats will run away from any shocking event, and pigeons will flap their wings harder when threatened. The wing flapping in pigeons and the scattered running of rats are considered species-specific defense reactions or behaviors. Bolles believed that SSDRs are conditioned through Pavlovian conditioning, and not operant conditioning; SSDRs arise from the association between the environmental stimuli and adverse events. Michael S. Fanselow conducted an experiment, to test some specific defense reactions, he observed that rats in two different shock situations responded differently, based on instinct or defensive topography, rather than contextual information.
   During the reaction, the intensity of emotion that is brought on by the stimulus will also determine the nature and intensity of the behavioral response. Individuals with higher levels of emotional reactivity may be prone to anxiety and aggression, which illustrates the implications of appropriate emotional reaction in the fight or flight response.
  
  Section::::Cognitive components.
  
  Section::::Cognitive components.:Content specificity.
   Arjun et al. (2017) found that it is not necessarily the speed of the response itself, but the greater distance between the targeted individual and the predator when the response is executed. In addition, the escape response of an individual is directly related to the threat of the predator. Predators that pose the biggest risk to the population will evoke the greatest escape response. Therefore, it may be an adaptive trait selected for by natural selection.
   In one study, Stankowich & Coss (2007) studied the flight initiation distance of Columbian black-tailed deer. According to the authors, the flight initiation distance is the distance between prey and predator when the prey attempts an escape response. They found that the angle, distance, and speed that the deer escaped was related to the distance between the deer and its predator, a human male in this experiment
  
  Section::::Examples.:Other examples.
   In animal behaviour, escape response, escape reaction, or escape behaviour is a rapid series of movements performed by an animal in response to possible predation. Some types of escape response may include camouflage, freezing behaviour, and fleeing, among others It is an anti-predator behaviour that varies from species to species. In fact, variation between individuals is linked to increased survival. In addition, it is not merely increased speed that contributes to the success of the escape response; other factors, including reaction time and the individual's context can play a role. The individual escape response of a particular animal can vary based on an animal's previous experience and current state
   Section::::Regine.
   The specific components of cognitions in the fight or flight response seem to be largely negative. These negative cognitions may be characterised by: attention to negative stimuli, the perception of ambiguous situations as negative, and the recurrence of recalling negative words. There also may be specific negative thoughts associated with emotions commonly seen in the reaction.
  
  Section::::Cognitive components.:Perception of control.
   Another study, conducted by Gisquet-Verrier et al., tested the effects of the hippocampus, in three experiments, on both the freezing behavior and avoidance. The rats were lesioned with ibotenic acid, and were tested against a control group. They first investigated changes from conditioned fear, and results showed that lesions to the hippocampus did not alter freezing behavior and marginally affected avoidance. Next, they tested single conditioning sessions, and it was found that freezing behavior remained unchanged while avoidance was disrupted. Finally, they tested conditioning with a larger stimulus (footshock intensity). It was found that avoidance was unaltered while freezing behavior decreased. Not only did these investigations show that the hippocampus is involved with freezing behavior, but avoidance and freezing behavior do not seem to have similar ways of being quantified when it comes to fear conditioning.
   Section::::Behavioral basis.
   The extended parallel process model concludes that cognitions (attitudes, intentions, and behavior changes) result in fear appeal success via the danger control process. It also concludes that fear appeals fail when the fear emotion is reduced via the fear control process.
  
  Defensive avoidance is an example of a fear control response that leads to the failure of fear appeals.
  
  Section::::Models.:Drive theory.
   The central brain structure through which fear-associated responses are mediated has been determined to be the amygdala, which is located in the brain's temporal lobe. When the central nucleus of the amygdala is stimulated - what is popularly referred to as the "fight-or-flight" response is activated - the organism in question reacts passively (is rendered frozen in its tracks, becomes hyper-vigilantly attentive, etc.), or displays a physiological reaction geared toward facilitating an aggressive reaction (e.g., increased heart-rate/pulse, rapid breathing). These fear-induced reactions result from communication between the amygdala and a variety of other brain regions (such as the brain stem and hypothalamus), resulting in a variety of physiological responses in the organism. For instance, communication between an activated amygdala and the lateral hypothalamus results in increased blood pressure and dilation of the pupils; the initiation of the central grey via communication from the amygdala results in the organism's becoming frozen in its tracks; communication between the activated amygdala and the paraventricular nucleus of the hypothalamus releases hormones associated with stress.
   Animals have many different tactics for defending themselves, depending on the severity of the threat they are encountering. Stages of threat vary along a spectrum referred to as the "predatory imminence continuum," spanning from low-risk (pre-encounter) to high-risk (interaction) threats. The main assumption of the predatory imminence continuum is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a predator is nearby, the animal may begin to express species specific defense reactions such as freezing in an attempt to avoid detection by the predator. However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival. At this point, the animal enters the circa-strike phase, where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.
   Heightened FPS response has also been implicated in the following disorders, falling under the current DSM-IV-TR classification of anxiety disorders: phobia (social and specific) and obsessive-compulsive disorder. On the converse, mood disorders such as depression have been shown to cause weakened FPS responses in diagnosed individuals.
  
  Section::::Treatment options.
   Individuals with PTSD have been shown to have an increased FPS response, and data have also suggested that this response becomes further exaggerated when these individuals experience stress. People having been diagnosed with PTSD display similar FPS response to threatening and neutral stimuli, indicating that (unlike those not suffering from PTSD) these individuals have difficulty distinguishing a stimulus as posing a threat or being benign. Additionally, data has displayed a significantly reduced ability for the extinction of conditioned fear responses in combat Veterans with severe, chronic PTSD The reduced ability for fear extinction over longer periods of time in combat veterans, as a result of the pathology associated with PTSD, has also been asserted.
  