The Science of Anxiety: How the Brain’s Fight-or-Flight Response Works
Stress is often viewed as a negative part of life, but it evolved as an important survival mechanism. For our ancestors, the ability to respond rapidly to threats increased their chances of survival. Although modern stressors are often deadlines, exams, and financial concerns rather than predators, the body still reacts using the same biological systems (Lupien et al., 2009).
To better understand how stress affects the brain and body, watch this introductory video explaining how emotions and stress responses can sometimes overwhelm our thinking brain:
For kids:
● https://youtu.be/3bKuoH8CkFc?feature=shared
For adults:
● https://youtu.be/qFTljLo1bK8
According to Hans Selye's General Adaptation Syndrome, the stress response occurs in three stages: alarm, resistance, and exhaustion (Selye, 1950).
● The alarm stage is the body's immediate reaction to a stressor. ○ During this phase, the fight-or-flight response is activated, releasing hormones that increase heart rate, blood pressure, and energy availability. These changes prepare the body to respond quickly to a challenge or threat.
● If the stressor persists, the body enters the resistance stage. ○ During this period, the body attempts to adapt to the ongoing challenge while remaining in a heightened state of alertness. Although individuals may appear to be functioning normally, physiological resources continue to be used at an elevated rate as the body works to maintain stability (McEwen, 2007).
● When stress becomes chronic and recovery is limited, the body may enter the exhaustion stage. ○ At this point, energy reserves become depleted, and the prolonged activation of the stress response can begin to negatively affect physical and mental health. Individuals may experience fatigue, burnout, weakened immune functioning, and an increased risk of illness (McEwen, 2007).
Understanding these stages helps explain why stress is neither inherently good nor bad. Although challenges are a normal part of life, navigating them successfully often requires support. Healthy coping strategies, strong social connections, and access to professional help when needed can buffer the effects of stress, promote resilience, and prevent temporary difficulties from developing into more serious long-term concerns.
References
McEwen, B. S. (2007). Physiology and neurobiology of stress and adaptation: Central role of the brain. Physiological Reviews, 87(3), 873–904. https://doi.org/10.1152/physrev.00041.2006
Selye, H. (1950). Stress and the general adaptation syndrome. British Medical Journal, 1(4667), 1383–1392. https://doi.org/10.1136/bmj.1.4667.1383
Lupien, S. J., McEwen, B. S., Gunnar, M. R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behaviour and cognition. Nature Reviews Neuroscience, 10(6), 434–445. https://doi.org/10.1038/nrn2639
— Noah D. Gubert