The fight-or-flight or fight-flight-or-freeze response, also termed hyperarousal or acute stress response, represents a physiological reaction triggered by a perceived harmful event, attack, or threat to survival. Walter Bradford Cannon first described this phenomenon in 1914, referring to it as "the necessities of fighting or flight" in 1915. His theory posits that animals respond to threats through a generalized activation of the sympathetic nervous system, thereby preparing the organism for either confrontation or evasion. Specifically, the adrenal medulla initiates a hormonal cascade, leading to the secretion of catecholamines, particularly norepinephrine and epinephrine. Additionally, hormones such as estrogen, testosterone, and cortisol, alongside neurotransmitters like dopamine and serotonin, influence an organism's stress response. The hormone osteocalcin may also contribute to this process.
This response is identified as the initial stage of the general adaptation syndrome, which governs stress reactions across vertebrates and other organisms.
Nomenclature
Initially conceptualized as the "fight-or-flight" response within Cannon's research, the state of hyperarousal encompasses several reactions beyond mere combat or escape. This broader understanding has prompted the adoption of terms such as "fight, flight, freeze," "fight-flight-freeze-fawn," or "fight-flight-faint-or-freeze," among other variations.
The expanded spectrum of responses, including freezing, flopping, fainting, fleeing, and fright, has led researchers to employ more neutral or inclusive terminology, such as "hyperarousal" or "acute stress response."
Physiology
Autonomic Nervous System
The autonomic nervous system (ANS) is a control system that largely operates unconsciously, regulating vital functions including heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system serves as the primary mechanism governing the fight-or-flight response, with its function mediated by two distinct components: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The acute stress response, an inherent survival mechanism, activates involuntarily, preparing an individual to either confront danger or escape it. This response is controlled by the ANS, which comprises the SNS, responsible for activating the fight-or-flight reaction, and the PNS, which facilitates recovery and calming once the threat subsates.
Sympathetic Nervous System
Originating in the spinal cord, the sympathetic nervous system's primary role is to activate the arousal responses characteristic of the fight-or-flight reaction. It transmits signals from the dorsal hypothalamus, which subsequently stimulates cardiac activity, increases vascular resistance, and enhances blood flow, particularly to muscle, heart, and brain tissues. The SNS also activates the adrenal medulla, leading to the release of catecholamines that amplify the sympathetic response. Furthermore, this component of the autonomic nervous system facilitates the release of norepinephrine from the adrenal glands during the reaction.
Parasympathetic Nervous System
The parasympathetic nervous system (PNS) originates in the sacral spinal cord and medulla, anatomically adjacent to the sympathetic nervous system's origin, and operates in conjunction with it. It is recognized as the restorative component of the autonomic nervous system. While the sympathetic nervous system is active, the parasympathetic nervous system attenuates its response. Efferent vagal fibers from the nucleus ambiguous fire in parallel with the respiratory system, thereby decreasing vagal cardiac parasympathetic tone. Following the fight-or-flight response, the primary function of the parasympathetic system is to initiate the "rest and digest" response, restoring the body to homeostasis. This system mediates the release of the neurotransmitter acetylcholine.
Reaction
The physiological response initiates in the amygdala, which subsequently activates a neural pathway to the hypothalamus. This initial activation is succeeded by the stimulation of the pituitary gland and the release of sex ACTH. Concurrently, the sympathetic nervous system triggers the adrenal gland, prompting the secretion of epinephrine. The cumulative effect of these chemical messengers culminates in the production of cortisol, a hormone that elevates blood pressure and blood sugar levels while suppressing the immune system.
Both the initial and subsequent physiological reactions are instigated to generate a rapid surge of energy. This energy surge is facilitated by epinephrine's binding to liver cells, which then stimulates glucose production. Furthermore, circulating cortisol converts fatty acids into readily available energy, thereby priming the body's musculature for immediate action.
Catecholamine hormones, including adrenaline (epinephrine) and noradrenaline (norepinephrine), mediate immediate physical responses that prepare the organism for intense muscular exertion.
Physiological Adaptations and Their Functions
The physiological alterations observed during the fight-or-flight response are initiated to augment the body's strength and speed, preparing it for either confrontation or evasion. Key physiological changes and their respective functions encompass:
- Blood flow is redirected from other bodily systems to the muscles and brain, thereby facilitating rapid action. This diversion concurrently diminishes blood flow to the digestive system, resulting in reduced appetite and impaired digestive function.
- Elevated blood pressure and heart rate augment cardiac output, ensuring an increased supply of energy to the body.
- The liver releases elevated quantities of glucose (via adrenaline-induced glycogenolysis) and fats into the bloodstream, furnishing the body with essential fuel to satisfy heightened energy requirements.
- Respiratory rate accelerates to provide the requisite oxygen for metabolizing the additional glucose.
- The body's blood clotting mechanism accelerates, aiming to minimize hemorrhage and prevent excessive blood loss should an injury occur during the response.
- Elevated muscle tension confers enhanced speed and power upon the body, a state that may manifest as trembling or shaking until the tension is alleviated.
- Pupillary dilation occurs to maximize light intake, thereby enhancing visual acuity and environmental awareness.
Emotional Dimensions
Affective Regulation
Within the framework of the fight-or-flight response, emotional regulation is proactively employed to mitigate perceived stressors or to manage the degree of emotional activation. Emotional socialization can foster an individual's capacity for successful emotional regulation. When confronted with a perceived threat in a fight-or-flight scenario, individuals who experienced supportive parental behaviors during development demonstrate a significantly greater propensity for effective self-regulation of their emotions.
Affective Reactivity
The intensity of emotion elicited by a stimulus during the fight-or-flight response significantly influences the character and magnitude of the subsequent behavioral reaction. For instance, a 2019 experiment by Clayton, Lang, Leshner, and Quick observed the responses of 49 participants to antitobacco messages. After viewing messages depicting individual smokers and their impact on others, participants exhibited two distinct patterns of reaction. Those with higher defense mechanisms chose to disregard the messages, whereas participants with lower defense mechanisms displayed argumentative and frustrated behaviors. Individuals exhibiting elevated levels of emotional reactivity (e.g., an anxiety disorder) may be predisposed to heightened anxiety and aggression, thereby underscoring the significance of adaptive emotional responses within the fight-or-flight paradigm.
Cognitive Dimensions
Specificity of Cognitive Content
The cognitive components specific to the fight-or-flight response are predominantly negative. These negative cognitions are often characterized by: an attentional bias towards negative stimuli, the interpretation of ambiguous situations as adverse, and the recurrent recall of negative terminology. Furthermore, distinct negative thoughts may be associated with emotions frequently observed during this response.
Perceived Locus of Control
Perceived control refers to an individual's cognitive assessment of their influence over circumstances and occurrences. This construct must be distinguished from actual control, as an individual's convictions regarding their capabilities may not correspond with their objective proficiencies. Consequently, either an overestimation or underestimation of perceived control can precipitate states of anxiety and aggressive behaviors.
Social Information Processing
The social information processing model posits numerous determinants of behavior within social contexts and influenced by pre-existing cognitions. Specifically, the attribution of hostility, particularly in ambiguous scenarios, appears to be a critical cognitive factor linked to the fight-or-flight response due to its direct implications for aggressive conduct.
Other Animal Species
Evolutionary Perspective
From an evolutionary psychology standpoint, ancestral organisms were compelled to react instantaneously to threatening stimuli, lacking the temporal luxury for extensive psychological or physiological preparation. The fight-or-flight response thus furnished the requisite mechanisms for a swift reaction to existential threats.
Illustrative Cases
A quintessential illustration of the stress response involves a grazing zebra. Upon perceiving an approaching lion, the stress response is initiated, facilitating an escape from the predator. This evasive action necessitates considerable muscular exertion, supported by the organism's integrated physiological systems. The activation of the sympathetic nervous system specifically addresses these demands. Analogously, a cat facing an imminent dog attack exemplifies the fight response, exhibiting an accelerated heart rate, piloerection (erection of hairs), and pupillary dilation, all indicative of sympathetic arousal. It is noteworthy that both the zebra and the cat sustain homeostatic balance across these various states.
In July 1992, Behavioral Ecology featured experimental research by biologist Lee A. Dugatkin, in which guppies were categorized into "bold," "ordinary," and "timid" cohorts based on their responses to a smallmouth bass (e.g., predator inspection, concealment, or evasion). Subsequently, these guppies were housed with the bass in a controlled environment. After 60 hours, survival rates indicated that 40 percent of the timid guppies and 15 percent of the ordinary guppies persisted, whereas none of the bold guppies survived.
Diverse Response Modalities
Animals exhibit a multitude of intricate responses to perceived threats. For example, rats typically attempt to escape when menaced but will engage in combat when cornered. Certain species employ immobility as a cryptic strategy to avoid predator detection. Furthermore, numerous animals adopt a freezing posture or feign death upon physical contact, anticipating that the predator will consequently disengage.
Additional species possess alternative self-protective mechanisms. For instance, certain cold-blooded animals rapidly alter their coloration for camouflage. While these responses are mediated by the sympathetic nervous system, integrating them into the fight-or-flight paradigm necessitates expanding the concept of flight to encompass evasion of capture through either physical displacement or sensory concealment. Therefore, flight can manifest as relocation to a different environment or remaining in situ while becoming imperceptible, and the fight and flight responses frequently co-occur in specific contexts.
The fight-or-flight actions also exhibit a dualistic nature, characterized by polarity. An individual may either confront or evade a threatening entity, such as a predatory lion, or alternatively, strive for or move towards a desired outcome, like seeking the safety of a riverbank from turbulent waters.
An inter-animal threat does not invariably culminate in an immediate fight-or-flight response. Instead, a phase of heightened vigilance may precede, during which each animal deciphers the behavioral cues of the other. Indicators such as pallor, piloerection, immobility, vocalizations, and body posture convey the respective status and intentions of the animals. A form of negotiation may transpire, potentially leading to fight or flight, but also possibly resulting in play, mating, or no further interaction. Kittens engaging in play serve as an illustrative example: despite exhibiting signs of sympathetic arousal, they refrain from inflicting actual harm.
In Criminal Jurisprudence
The acute stress response frequently constitutes a pertinent factor in criminal cases involving self-defense. Expert testimony is typically necessitated when the culpability of the defendant becomes the central evidentiary concern.
References
References
Sapolsky, Robert M., 1994. *Why Zebras Don't Get Ulcers*. W.H. Freeman and Company.
- Sapolsky, Robert M., 1994. Why Zebras Don't Get Ulcers. W.H. Freeman and Company.
- This article integrates public domain content originating from the United States government.
- Arun, C. P. (2004). Fight or flight, forbearance and fortitude: The spectrum of actions of the catecholamines and their cousins. Annals of the New York Academy of Sciences, 1018(1), 137-140.
- Seng, J., & Group, C. (2019). From fight or flight, freeze or faint, to "flow": Identifying a concept to express a positive embodied outcome of trauma recovery. Journal of the American Psychiatric Nurses Association, 25(3), 200-207.
- Katz, C., Tsur, N., Talmon, A., & Nicolet, R. (2021). Beyond fight, flight, and freeze: Towards a new conceptualization of peritraumatic responses to child sexual abuse based on retrospective accounts of adult survivors. Child Abuse and Neglect, 112(1), 1-12.
- O'Dea, C., Castro Bueno, A. M., & Saucier, D. A. (2017). Fight or flight: Perceptions of men who confront versus ignore threats to themselves and others. Personality and Individual Differences, 104(1), 345-351.
- Media related to Fight-or-Flight Response at Wikimedia Commons