Understanding the Acute Stress Response (aka "Fight or Flight")

What is the Acute Stress Response?

The acute stress response is an automatic physiological reaction to an event perceived as threatening or dangerous. It is sometimes called the "Fight or Flight" response in reference to the instinct to either fight back or flee from the danger in order to maintain safety. The acute stress response can include any combination of the physiological sensations below. Each of these sensations is an adaptive response to increase our chances of survival. An increased heart rate, for example, allows for increased blood flow to our muscles (to fight or flee).

Each person has their own “constellation” of symptoms that make up their individual acute stress response. Take a look at the list below and notice which sensations are most common for you when you are experiencing “fight or flight.”

Fight Or Flight Sensations

• Rapid heart beat

• Tingling

• Trembling

• Shallow breathing

• Hyperventilation

• Chest tightness

• Racing thoughts

• Dissociation

• Dry mouth

• Lump in throat

• Bladder urgency

• Vision changes

• Muscle tension

• Sweaty hands

• Clammy hands

• Feeling warm

• Nausea

• “Butterflies” feeling

• Weak feeling in legs

• Lightheadedness

• Dizziness

What Happens When the Acute Stress Response is Triggered?

"When the brain receives a sensory stimulus indicating danger, it is routed first to the thalamus. From there, the information is sent out over two parallel pathways: the thalamo-amygdala pathway (the 'short route') and the thalamo-cortico-amygdala pathway (the 'long route').

The short route conveys a fast, rough impression of the situation, because it is a sub-cortical pathway in which no thinking is involved” (McGill University, Two Pathways). This pathway activates the amygdala which generates the acute stress response before the brain has even fully integrated what it is perceiving. This process is called First Fear (aka "fight or flight") and you do not have control over it, it is automatic (Winston, 2017). "Subsequently, the information that has travelled via the long route and been processed in the frontal cortex reaches the amygdala and tells it whether or not the stimulus represents a real threat” (McGill University, Two Pathways).

In the case of a normally functioning acute stress response, when the information from the thalamo-cortico-amygdala pathway (the “long route”) arrives, you are able to recognize that the situation is safe. The acute stress response begins to wind down. It might take a few minutes but your body will return to its formerly calm state.

In the case of a phobia, when the information from the thalamo-cortico-amygdala pathway (the “long route”) arrives, either your thoughts are distorted ("all snakes are dangerous”), you are frightened by your physiological sensations ("I feel like I can't breathe") or you are overwhelmed due to memories of past experiences with snakes. Your fear of First Fear actually re-triggers the acute stress response. This re-triggering is called Second Fear It can be thought of as a "fear of fear." When Second Fear happens repeatedly, a phobia develops.

How Does Exposure Therapy Affect the Acute Stress Response?

In-Vivo (in real life) Exposure Therapy allows you to gradually increase your contact with the feared situation so that two important changes happen: 1) your Second Fear reaction shifts, allowing your acute stress response to diminish and 2) you learn that you can tolerate the physiological arousal brought on by First Fear and still be okay.

Sources:

1. Winston, S., Seif, M. (2017) , F. M. (Year of Publication). Overcoming Unwanted Intrusive Thoughts. New Harbinger Publications.

2. McGill University. (n.d.). Two Pathways of Fear. The Brain From Top to Bottom. https://thebrain.mcgill.ca/flash/a/a_04/a_04_cr/a_04_cr_peu/a_04_cr_peu.html#2