What Happens in the Brain When We Feel Fear

October 30, 2017

Fear may be as old as life on Earth. It is a fundamental, deeply wired reaction, evolved over the history of biology, to protect organisms against perceived threat to their integrity or existence. Fear may be as simple as a cringe of an antenna in a snail that is touched, or as complex as existential anxiety in a human.

Whether we love or hate to experience fear, it’s hard to deny that we certainly revere it – devoting an entire holiday to the celebration of fear.

Thinking about the circuitry of the brain and human psychology, some of the main chemicals that contribute to the “fight or flight” response are also involved in other positive emotional states, such as happiness and excitement. So, it makes sense that the high arousal state we experience during a scare may also be experienced in a more positive light. But what makes the difference between getting a “rush” and feeling completely terrorized?

We are psychiatrists who treat fear and study its neurobiology. Our studies and clinical interactions, as well as those of others, suggest that a major factor in how we experience fear has to do with the context. When our “thinking” brain gives feedback to our “emotional” brain and we perceive ourselves as being in a safe space, we can then quickly shift the way we experience that high arousal state, going from one of fear to one of enjoyment or excitement.

When you enter a haunted house during Halloween season, for example, anticipating a ghoul jumping out at you and knowing it isn’t really a threat, you are able to quickly relabel the experience. In contrast, if you were walking in a dark alley at night and a stranger began chasing you, both your emotional and thinking areas of the brain would be in agreement that the situation is dangerous, and it’s time to flee!

But how does your brain do this?

Fear reaction starts in the brain and spreads through the body to make adjustments for the best defense, or flight reaction. The fear response starts in a region of the brain called the amygdala. This almond-shaped set of nuclei in the temporal lobe of the brain is dedicated to detecting the emotional salience of the stimuli – how much something stands out to us.

For example, the amygdala activates whenever we see a human face with an emotion. This reaction is more pronounced with anger and fear. A threat stimulus, such as the sight of a predator, triggers a fear response in the amygdala, which activates areas involved in preparation for motor functions involved in fight or flight. It also triggers release of stress hormones and sympathetic nervous system.

This leads to bodily changes that prepare us to be more efficient in a danger: The brain becomes hyperalert, pupils dilate, the bronchi dilate and breathing accelerates. Heart rate and blood pressure rise. Blood flow and stream of glucose to the skeletal muscles increase. Organs not vital in survival such as the gastrointestinal system slow down.

A part of the brain called the hippocampus is closely connected with the amygdala. The hippocampus and prefrontal cortex help the brain interpret the perceived threat. They are involved in a higher-level processing of context, which helps a person know whether a perceived threat is real.

For instance, seeing a lion in the wild can trigger a strong fear reaction, but the response to a view of the same lion at a zoo is more of curiosity and thinking that the lion is cute. This is because the hippocampus and the frontal cortex process contextual information, and inhibitory pathways dampen the amygdala fear response and its downstream results. Basically, our “thinking” circuitry of brain reassures our “emotional” areas that we are, in fact, OK.

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