From earthquakes to stage fright. This is how our brain handles danger, real or imagined

Imagine that you are crossing the road (at a crosswalk, of course) on your way to visit a friend. Suddenly, you hear screeching brakes and see a car speeding toward you, and you’re not sure if you’ll be able to move before it hits you. Your body responds, your senses sharpen, and in a burst of energy, you manage to leap to the side just before the car arrives. You’re safe! You are still in one piece, but dripping with cold sweat and shaking like a leaf blowing in the wind. Only then, as your heart still beats wildly, do you begin to realize what happened.

The response you’ve just experienced is called “fight or flight,” and as the name suggests, it’s triggered in response to a significant threat that requires an immediate response. The response can be confrontation (fight) or avoidance (flight). This mechanism exists in many diverse species and is activated in response to danger, such as an encounter with a dangerous predator. 

The term “fight or flight” was coined by the doctor and physiologist Walter Cannon in 1915. Cannon noticed that the muscles of the digestive system change their activity in states of fear. Later, he found that high levels of arousal affect the allocation of energy to each of the body’s organs in a way that allows us to respond quickly and effectively in dangerous situations.

אדם עומד על דרך מושלגת מול מכונית נוסעת | Shutterstock, Realstock

Suddenly you hear screeching breaks and see a car speeding towards you. What is happening inside your body? A man standing on a snowy road in front of a moving vehicle | Shutterstock, Realstock


Caution, Danger Ahead

In order to respond effectively to a potential threat, we must first recognize it. The information we perceive from the environment by our senses of sight and hearing is transmitted to a critical brain region called the amygdala, which has an important role in the processing and generation of emotions, particularly fear. When confronted with danger, the amygdala sends an alarm signal to another part of the brain, the hypothalamus. The hypothalamus acts as a central control hub that regulates the body’s activity to maintain a stable and relatively constant physiological state. It affects various physiological parameters, such as body temperature and blood pressure, as well as feelings of thirst and hunger.

After receiving a message from the amygdala, the hypothalamus activates the sympathetic nervous system, which forms part of our autonomic nervous system. It is responsible for nervous responses over which we have no voluntary control. This system includes nerve cell extensions that run from from the brain to the rest of the body’s organs, with the help of which it instructs our internal organs to produce the physiological response that characterizes states of alertness. This response includes, among other things, accelerating of the heart rate to supply more oxygenated blood to the body’s organs, expanding blood vessels in the muscles to allow for more oxygen during increased muscle activity, and dilating the pupils to allow for clearer vision.


אילוסטרציה של קורטיזול בבלוטת יותרת-הכליה | Shutterstock, Kateryna Kon

In addition to its direct effect on the nervous system, it also triggers the release of hormones such as adrenaline and cortisol, which alter the activity of various organs. Illustration of cortisol in the adrenal gland | Shutterstock, Kateryna Kon


In addition to its direct effects on the internal organs, the sympathetic nervous system also affects the body indirectly by signaling to the adrenal gland to secrete the hormone adrenaline into the bloodstream, which fundamentally alters the body’s activity. Adrenaline travels in the bloodstream and affects the function of the organs it reaches. Its effects include an increase in heart rate, accelerated breathing, as well as the breakdown of the polysaccharide glycogen in the liver into the monosaccharide glucose, which serves as a quick and available source of energy for the body’s organs.

Another hormone, cortisol, which is also secreted from the adrenal gland, boosts the availability of glucose to the body’s cells, allowing them to extract energy. In the meantime, this hormone also reduces blood flow to organs that aren’t required for the immediate response to danger, leading to a decrease in their activity. For instance, the activity of the digestive system temporarily slows down in such situations. 

After the threat has subsided, the body’s equilibrium must be restored in order for it to function properly. The parasympathetic nervous system comes into play at this stage, counterbalancing the sympathetic nervous system. With the help of the parasympathetic system, we regain a state of calmness and conserve energy to facilitate routine body processes such as digestion and urine production. To draw a comparison, if we liken our body to a car, the complementary activity of the two systems can be likened to the activity of the accelerator pedal and brakes: alternating their use allows us to respond to a threat, and then to relax after dealing with it.


תגובת "הילחם או ברח" מתרחשת לעיתים גם כשהאיום אינו מוחשי אלא מנטלי - כמו האישה בציור, שחווה לחץ כאשר היא מדברת מול קהל | Shutterstock, Drawlab19

The “fight or flight” response sometimes occurs even when the threat isn’t tangible but mental - like the woman in the illustration, who experiences stage fright when speaking in front of an audience | Shutterstock, Drawlab19


The Tiger In Our Minds

In humans, the “fight or flight” response can be triggered even when the threat isn’t tangible but rather mental - such as when we’re required to speak in front of a large audience. Therefore, everyday stressors can cause an overactivation of the “fight or flight” response. Researchers have found a link between such chronic stress and harm to both physical and mental health, and doctors recommend avoiding it whenever possible. 

We can reduce stress by maintaining a healthy lifestyle, inclusing proper nutrition and adequate sleep. It is also essential to remember that stress is a common problem and that we can and should ask for help in case of need. For instance, during the COVID-19 pandemic in 2021, an American study found that one-third of people occasionally experience stress levels so high that they struggle with making simple daily decisions, such as what clothes to wear. 

In recent decades, it has become increasingly evident that the “fight or flight” concept is inaccurate and ignores a well-documented third reaction: “freeze”, a state in which the heart rate actually slows, muscles tense up, and the individual or animal becomes motionless.A classic example of the “freeze” response is embodied by the English expression “like a deer in the headlights”, which describes a situation in which a deer notices a car coming towards it and freezes in its place. While “fight” and “flight” have clear advantages, it is harder to explain the evolutionary benefits of the “freeze” response. Some researchers believe that it may help in camouflaging from a predator that is lurking nearby and hasn’t noticed us yet. Another hypothesis is that the “freeze” helps us detach from the situation and protects us from potential future trauma.   

Stressful situations, and their resulting “fight or flight” responses, occur frequently in our lives. Therefore, a thorough understanding of the body’s response to such situations may come in handy. The cumulative findings on the subject can enhance our self-awareness and our understanding of others, improve our lifestyle and prompt the development of potential treatments for stress and anxiety.