We are all afraid from time to time. Some cannot stand horror films, others are afraid of spiders, and yet others get weak in the knees from high altitudes. But why do we experience fear in the first place? And how does that work in the brain?
Experiencing some degree of fear is very useful. In the past, it ensured that our ancestors did not get too close to a deep cliff or an angry bear. Therefore they had a better chance of survival and thus passing on their genes to the next generation. So, a certain degree of fear was evolutionarily very beneficial. This answers the question why we experience fear. But how does fear actually arise?
Information from the environment always passes the thalamus (the brain's gatekeeper, as explained in the Brain Basics article). When this is threatening information, the thalamus transmits it directly to the amygdala. The amygdala, also known as the “fearcenter” of the brain, is a small almond-shaped cluster of neurons in both medial temporal lobes. When we perceive a fear stimulus (something scary), the amygdala becomes active. It then sends a signal to the hypothalamus, an area that makes sure the body is in balance. The hypothalamus triggers a "fight, flight, or freeze" response in the body via the stress hormones cortisol and adrenaline. Your heart starts beating faster in preparation to run. Your pupils enlarge so you can see better. Even your pain sensation may temporarily diminish during a fear response. When the fear stimulus is gone, your body returns to its original state.
This fear-invoking event is stored in the hippocampus, an area responsible for memories. To make sure we don't forget this fearful event, the amygdala puts a kind of stamp on the memory with "DON'T FORGET, IMPORTANT!". The more intense the experience, the bigger the stamp, and the better we remember it. This is why we often remember scary events from the past (losing your mother in town as a child), while we quickly forget mundane emotionless events (what you had for breakfast last week). This is useful. By remembering the unpleasant experience you can, hopefully, avoid similar situations from happening in the future.
The interaction between the amygdala and the hippocampus also goes the other way around. For example, you may be very startled by something at first, such as a barking dog. The amygdala then immediately jumps into action. Once the information is also processed by the hippocampus and the frontal cortex, they have the ability to suppress the activation of the amygdala. For example, when you realize the barking came from your neighbour's sweet dog. The hippocampus does this with positive memories (e.g. every time you pet the dog), and the frontal cortex throws logic into the fray (e.g. that the dog is behind a fence and is therefore harmless). Because of these two brain areas, you realize that the initial fear reaction was unjustified, and there is nothing to be afraid of.
To sum up: Although the amygdala is known as the "fear-center" of the brain, this is oversimplified. Fear is caused by a complex interaction between a fast pathway via the amygdala, which triggers the initial fear response, and a slow pathway via the hippocampus and frontal cortex, which analyses the situation with more nuance. The collaboration between the amygdala and the hippocampus causes us to remember scary things better. So, if sometimes you are still plagued by a memory of when you were stuck in the toilet stall as a child, know that your brain is not holding on to this memory to harass you, but to help you not make the same mistake again.
Author: Pauline van Gils
Illustrations: Pauline van Gils