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You Gave Me A Fright: The Science of Fear

October 30, 2018

Happy Halloween Folks! The day of the dead is upon us; an occasion to celebrate all things spooky, ghoulie and macabre. The Halloween holiday is best known for fuzzy teeth, dunking your head in the washing up bowl and scaring yourself for fun. And while now it may be the one time of year you can wear whatever you want and get away with it, the reason Halloween exists is all down to human fear. The festival of Halloween dates back over a thousand years and while you would not have found a Harley Quinn or dead Batman back in the 8th Century, costume-wearing people would gather together to light bonfires on the night they believed the living and dead worlds collided. These rituals were spurred on by fear ghosts were responsible for the long, harsh winters which would kill many crops and people. Centuries on, fear is still a driver of human behaviour and on the holiday when you go out seeking a scare, certain brain regions will be firing out for you to run and hide.  

 

The Root of Fear: Why do we get scared?

The spectrum of things we humans fear is endless; spiders, heights, buttons, the unknown. Some of these fears exist to protect your life while others are more of a burden than a benefit. A fear of heights will stop you from tightrope-walking across a telephone wire from one building to another and protect your well-being. Whereas being afraid of clowns doesn't do much in the way of protecting your body or dignity; leaving you screaming in a corner at your cousin’s 4th birthday party. Unless the clown is running towards you with a carving knife, having a fear of an adult man wearing makeup and big shoes making balloon animals holds little advantage. However odd some phobias seem, the raw emotion and reaction to a fearful stimulus is an evolutionary advantage found accross many species.

 

Fear is an emotion. And when you break down what an emotion is, it is basically a response to a stimulus. Even the simplest of organisms like bacteria are able to respond to a threatening situation to improve their chances of survival. From these single celled organisms, vertebrates and invertebrates (animals with and without backbones) evolved and while invertebrates, such as spiders and squid, maintained an emotional response similar to their bacterial ancestors, vertebrates went on to develop a more complex range of expressions. Of these responses, fear became one vital for survival. Fear granted vertebrates not only with the option to escape a threatening situation but also gave them the choice to battle through their phobias to advance the survival of their species. In many vertebrates, fear is a rapid, impulsive response that propels the body into a highly-alert, ‘survival-mode’ state and us humans are no different. However, a key alteration between the human response to fear and our other ancestors is that we have sacrificed the size of brain regions associated with activating fear to gain areas which provide control over our response. Think back to a time you were given a fright; your impulsive reaction may have let out a scream but your brain then assesses the situation before you make your next move. It would be pretty bad if your mate jumped out on you in the supermarket and following your initial yelp, you proceeded to run screaming down the aisles and out of the building. Human control over the fear response has provided us with evolutionary advantage as we can detect real and fake threats before spending valuable energy escaping.

 

It’s all in your head: The Amygdala

In humans and other vertebrates, a brain region called the limbic system was thought to be the centre of emotional responses. Despite evidence for the limbic system mediating all emotion falling short, it’s role in the fear response has been confirmed. The limbic area responsible for fear is called the amygdala, which sits deep in the temporal lobes of both hemispheres. The removal of this general brain region from monkeys (back in the early 20th century when animal ethics were non-existent) made the animals lose their fear towards objects they normally would not go near, like snakes and humans. These experiments lead to the prediction that humans without an amygdala would also be fearless. 

 

As well as the amygdala’s role in directing a person’s feeling of fear, it is also vital in the role of fear memory. Research in the mid-20th century showed that the amygdala is activated in fear conditioning experiments. These tests involve presenting a subject with a normal stimulus (not harmful) or an unconditioned stimulus (harmful). For example, you could use two sounds with different stimuli associated with them; one noise with no stimulus and the other with an electric shock. If you give these to an individual at random intervals during the experiment, the second noise will eventually elicit the fear response; even without the electric shock happening. This is because the amygdala is activated in by the unconditioned stimulus; leading its neurons to form strong connections with other brain regions to make a memory of the 'scary' noise. It has been shown that damage to the amygdala in humans inhibits fear conditioning. Think about not being able to remember something which causes you pain – like touching a hot pan. You would continually pick up the pan and burn yourself until you caused permeant damage to your hand. The role of amygdala in fear memory is another vital component of human survival.

 

The 3 F's of Fear: Fight, Flight or Freeze

Once the amygdala has been activated by a fearful stimulus, it then alerts the rest of your brain and body to the potential danger. The amygdala signals to motor areas to have them on stand-by for rapid movement and also activates a response similar to the stress pathway By signalling to the hypothalamus, the amygdala can stimulate the release of hormones needed to increase heart rate, dilate pupils, quicken breathing and make you sweat. This enables the body for ‘fight or flight’; to stay and fight the fear out or to run as fast as possible out of danger. This response is also activated in face recognition when the person you are looking at looks afraid or angry. Even though a facial expression is not an active threat, your body gets prepped from this cue in anticipation of having to leg it.

 

Another response associated with fear is ‘freezing’; when you feel stuck to the spot unable to move or speak. This behaviour is similar that seen in prey animals and normally occurs before fight or flight. The freezing period is activated by a sensory stimulus, such as a rustle in the bushes, and its purpose is to heighten the prey’s senses to detect where the potential threat is coming from. The amygdala is activated by the sensory stimulus and triggers the freezing response in another brain region called the periaqueductal grey (PAG); the brain region in the cerebellum associated with tension and relaxation. Activation of the PAG leads to a tense state; heightening senses and alertness. The amygdala also stimulates the fight or flight response during the freezing period so once the threat makes itself known, activation of the PAG is inhibited and the prey can take action on the danger.

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Fear is fundamental to human survival but can be inhibiting for some. Fears of ‘non-scary’ stimuli can be debilitating and make everyday life hard. These phobias may develop following trauma or during your childhood when your amygdala is more plastic. So, when you walked into your best friend’s party and saw these huge man wearing face paint and a red wig, your amygdala may have triggered the formation of a fear memory, leading your adult self to still freeze with fear when you see a clown. Some people also love getting scared as it caused the release of adrenaline; the hormone associated with ‘living on the edge’. For those thrill seeking who will stay up late this Halloween to watch that scary film that you definitely shouldn’t watch (or the Haunting of Hill House because you might actually want to sleep again in 2018), it is your amygdala that will be on a mad one; triggering your heart to thump, senses to be heightened and create those fear memories which will haunt you all night long. Enjoy!

 

For more info on fear and the amygdala, check out this article:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3600914/

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