Fear in the Brain

It can creep up on you when you’re walking down a dark street, or simply watching a movie. Fear is one of our basic emotions and is the basis of our ability to avoid danger.

Fear isn’t unique to humans – birds, amphibians, reptiles and mammals all release stress hormones and exhibit changes in heart rate when confronted with danger. Like most animals, humans are afraid of things that we perceive as threatening. But unlike most animals, we seem to have developed a penchant for fear – it forms the basis of our enjoyment of countless thrillers, horror movies, and violent games. What exactly is fear, and why are some of us hooked on it?

Like cornered rats, humans come with an inbuilt fear response that dictates how we respond to certain situations. Without it, we would be as useful as a bunch of base jumpers at staying out of danger. Fear keeps us alive, and allows us to recognise and respond to potentially dangerous events.

What is fear?

Psychologists describe fear as one of our basic emotions, along with happiness, sadness, anger, disgust, and (possibly) surprise.

Fear provokes a powerful physical response. When we are afraid our bodies respond by getting us ready to fight back or run away – known as the fight or flight response. Our heart rate increases, stress hormones are released; sweat forms on the brows and other parts of the body to help keep it cool, and muscles tighten.

Other parts of our body that deal with sensory input are also alerted. The hairs on the skin may be raised, and our pupils dilate to let in more light and ‘sharpen’ the senses to potential threats.

How does fear work?

All of this activity begins in the region of the brain called the thalamus, a paired symmetrical region in the central brain associated with regulating consciousness, arousal, and awareness. This region also acts as a translator for the brain’s cortex, the grey matter that deals with memory, language and ‘thinking’.

The thalamus alerts the cortex to a threat and provokes a response in the amygdala, an almond-shaped group of neurons situated deep in the temporal lobes, part of the limbic system, which is associated with emotions.

The amygdala is critical for fear. It co-ordinates our response to fear through signals to the hypothalamus and other parts of the brain. Changes within the amygdala record the emotional experience and this information is then stored in cortical areas, creating a permanent memory of the fear-provoking event.

In rodents the amygdala has been shown to connect a visual stimulus (like a light) to a physical stimulus (like an electric shock). On repeated applications, the light alone was enough to provoke fear in the rats of the expected shock.

Why are we afraid of snakes?

We are geared by evolution to respond to potential threats. A classic example is snakes. While we are not automatically afraid of snakes, our brain will kick-start a fear response when confronted with a snake, in the same way it would if we are confronted with a burglar breaking into our house.

If immediate family group members are indifferent to this threat, then children growing up around snakes will learn not to fear them. However there is evidence that humans and other primates learn to fear snakes more readily than other things that may be as unfamiliar (and potentially threatening). Psychologist Susan Mineka observed this phenomenon in the 80s in classic experiment that looked at the responses of monkeys reared in the wild or in a lab to snakes.

In the experiment, wild-reared monkeys showed fear in response to snakes but lab-reared monkeys didn’t. If a lab-reared monkey was present when a wild-reared monkey showed fear then the lab-reared monkey would also show fear. But this only happened if the lab-reared monkeys were not familiar with snakes: if they were familiar, then they didn’t learn to fear the snakes even though the wild-reared one showed the fear responses.

The results were the same when the lab-reared monkey was shown a video of the wild-reared monkey confronting the snake. Additional experiments fused a clip of a telephone and the fear reactions of the wild-reared monkey, but the lab-reared monkey did not learn to fear the phone.

To scientists, this indicates that we are predisposed to fear certain stimuli and whether we fear these or not depend on the people we are close to; if they show fear, then we learn to fear; if they are indifferent, then we don’t fear.

Fear and anxiety

Fear plays a part in our own evolution as individuals. It is part of our learning experience about the world around us, and reminds us to avoid painful or threatening situations.

Fear can also have adverse affects on our state of mind. We can experience fear where no threat is present, for example, we might experience an increase in heart rate while watching a threatening situation on a video. We become anxious about situations that are not directly threatening to us.

A phobia is a fear whose intensity is out of context with what is appropriate to the situation. For example, the anxiety disorder agoraphobia is the persistent fear of an embarrassing or difficult situation from which the sufferer cannot escape, particularly where the person is outside their familiar safe environment. Waiting in a queue, sitting in a car, and even crossing a bridge may become situations fraught with indescribable terror for people with this condition.

Panic disorder, characterised by frequent ‘attacks’ of extreme anxiety is another fear response that may happen when no physical threat is present.

Find out more about anxiety disorders and treatments in Fighting fear.

Whatever we feel about fear, it’s here to stay with us, along with happiness, anger and sadness. It makes us who we are – animals, like the rest of the kingdom.