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When We Perceive Danger, What Happens in the Brain?

Updated: Jan 19

angry car driver cursing

You're hurrying through drizzle along the high street on your way to the supermarket, mentally going through your kitchen cupboards, recalling what you need to stock up on, and you step out to cross the busy road, and suddenly see an oncoming car. What happens? Well, before you know it, you're back on the pavement, catching your breath and sheepishly avoiding eye contact with the driver who you just know is scowling as they speed on by.

Just how did your amazing brain pull you instantly out of harm's way before you could even think about it? This article is about the split-second process that took place in your brain to ensure your survival—and how understanding this goes a long way to explaining why it is often so difficult to change our unhelpful, or unhealthy, behaviours.

When a person perceives a threat, several processes occur in the brain to activate the body's "fight or flight" response, which readies the body to either confront or flee from the danger. This involves a number of brain structures, neurotransmitters, and hormones:

Threat Recognition

The process starts with the perception of a potential threat, which might come in through any of the senses—sight, sound, smell, touch, or taste. The sensory information travels to the thalamus, the brain's relay station, which sends the information to the appropriate areas for further processing.

Fear Response

From the thalamus, the information about the potential threat is sent to the amygdala, a key structure involved in processing emotions, particularly fear and anxiety. If the amygdala interprets the sensory information as indicating a threat, it sends a distress signal to the hypothalamus.

Activation of the Autonomic Nervous System

The hypothalamus acts as the command center for the autonomic nervous system, which controls involuntary body functions. In response to the distress signal from the amygdala, the hypothalamus activates the sympathetic nervous system, initiating the body's "fight or flight" response. This leads to various physiological changes, such as an increased heart rate, faster breathing, dilated pupils, and a release of glucose for energy.

Release of Stress Hormones

The hypothalamus also stimulates the adrenal glands to release stress hormones like adrenaline (also known as epinephrine) and cortisol. Adrenaline boosts the body's energy supply, while cortisol suppresses non-emergency bodily functions like the immune response and digestion, curbs functions that would be nonessential in a fight or flight situation and enhances the body's ability to repair tissues.

Higher Brain Processing

The threat information is also sent to the prefrontal cortex, the area of the brain responsible for higher cognitive functions. Here, the situation is analysed in depth, taking into account additional factors like past experiences and learned information. The prefrontal cortex then communicates with the amygdala to adjust the fear response based on this more nuanced understanding of the situation.

Return to Homeostasis

After the threat has passed, the parasympathetic nervous system, which acts as a counterbalance to the sympathetic nervous system, helps the body return to its normal, non-emergency state.

This entire process happens incredibly quickly, often before the person consciously realises what's happening. This rapid response to threats is a survival mechanism that has evolved to help us react quickly to dangerous situations. However, in cases of chronic stress or anxiety disorders, these processes can be activated too frequently or intensely, leading to a range of physical and psychological health problems.

So, as you stood on that rain-dampened high street, staring at the receding taillights of the car you narrowly missed, it wasn’t just a simple fluke that pulled you back to safety—it was a finely tuned, ancient mechanism within your brain working tirelessly to ensure your well-being. This neural dance, remarkable as it is, offers a clear window into the complex interplay of systems at work when our bodies detect danger. But it also underscores the challenges we face when trying to address and amend deep-rooted behaviours.

After all, the same processes that save us from the oncoming car are the same ones that can hold us captive to patterns of behaviour that no longer serve us. Through understanding this, we can appreciate our brain's incredible abilities and at the same time, seek to better navigate the obstacles that arise from its protective mechanisms. Knowledge, as they say, is power—and understanding our brain's instinctive reactions gives us the potential power to harness them for our benefit.

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