We’ve all experienced the stomach dropping, paralysing feeling of fear, but how many of you have stopped to wonder what it is that makes us feel this way? Many fears are learned during our lifetime, some of which remain with us forever, others fade with time. Yet more fears appear to be more deep-seated and instinctive.
Fear to stimuli can be ‘taught’ in a lab by applying a neutral stimulus (known as the conditioned stimulus) to an animal, alongside something to cause aversion, such as a foot shock (known as the unconditioned stimulus). After multiple trials, the non-scary stimulus will stimulate a fear response without the foot shock. This process is known as fear conditioning.
Fear learning is a very unique neurological process, as it only requires one experience to be ingrained long-term in the brain, and is easily retrieved upon exposure to the same stimulus. The basis of the fear conditioning procedure relies on us having innate fears for the unconditioned stimulus, and the ability to learn new fears via the conditioned stimulus.
As a natural part of human functioning, many of our memories are ‘unlearned’ to prevent an overload on the brain. Contextual fears are associated with memories, so can be lost throughout our lifetime, often overlaid by new memories in the presence of the fear-provoking stimulus in a different environment. These kind of fears are often not completely forgotten, so can produce a response in an environment associated with the fear-stimulus, even without the existence of the stimulus itself.
Memories are thought to be stored in an area of the brain known as the hippocampus. Studies have taken place to assess the importance of this region in the storage of contextual fears, and have found that removal of the hippocampus led to a normal fear response during conditioning, but none caused by the environment. This illustrates how closely related the memory and fear systems are.
Another region of the brain involved in fear learning is the amygdala. Damage to an area of this, known as the basolateral nucleus, results in a disruption to the development of fear associated with a particular stimulus.
Contemporary and ancient threats
A puzzling field of fear research is the distinction between innate fears that appear to pass from generation to generation and the fears developed by an individual’s experience. An example of an intrinsic fear is falling from a height; no one has told you to be afraid of this, and if you’re reading this it probably isn’t a fear you’ve learnt yourself, yet something is causing you to avoid jumping from tall buildings.
This kind of instinctive fear has been found to be more difficult to “switch off” compared to contemporary fears learned through conditioning. In one study, people were conditioned to produce a fear response to images of weapons, such as guns and knives, and predators, such as spiders and snakes. Although fear conditioning was similar in both types of image, it was found that fear extinction, aka the loss of fear response to the stimulus, took much longer for the predator images (Fox, E., 2012). This suggests that this kind of ancient threat forms stronger connections within the brain.
An interesting twist on intrinsic fear is a phenomenon known as illusory correlation. Here, volunteers in trials describe a slanted likelihood of an event having taken place during the study. For example, in a study by Sue Mineka, Michael Cook and Andrew Tomarken at Vanderbilt University, volunteers were shown a variety of threatening and non-threatening images, each with an equal likelihood of being accompanied by an electric shock, a loud tone or nothing. Despite this, the volunteers all said that there was a link between seeing a threatening image and getting shocked.
Another study by Richard Viken at Indiana University showed female volunteers images of underweight, normal and overweight women, all equally likely to look happy or sad. The volunteers however thought that the thinner women looked happier. Remarkably, this correlation was particularly pronounced in women with a history of eating disorders. This illusory correlation may play a role in the understanding of our instinctive fears.
The science behind fear
As fear conditioning involves the association of a particular stimulus with one that produces a fear response, it requires the integration of multiple senses. Auditory and somatosensory stimuli are thought to converge in the lateral amygdala, which indirectly sends projections to the brainstem and the hypothalamus. The hypothalamus is a brain region important in expressing defensive behaviour and autonomic response. (Sigurdsson, T. et al., 2007)
Two vital areas of the brain involved in the fear response are the previously mentioned amygdala, and the dorsal medial prefrontal cortex. Rhythmic activity at a specific frequency along the neuronal connections between these regions has been connected to the ‘freezing’ response in laboratory rats exposed to aversive stimuli. This recent discovery may provide a target for therapeutically treating anxiety disorders, by reducing the physiological symptom expression of fear. (Anon., 2016)
Fear is something that affects most of us daily, whether it’s nerves for a presentation, shying away from a loud noise or being unable to take a shower because of that large spider lurking in the corner. These can be categorised into innate fears, that we’re born with, and conditioned fears that we learn as we experience life. Fear conditioning in the lab has provided us with information about the pathways within the brain, and the way that responses to different types of fear can change over time.
[Sigurdsson, T. et al, 2007]
Anon, 2016. Study unravels physiological signature of fear memory within prefrontal-amygdala networks. News Medical. Available at: http://www.news-medical.net/news/20160223/Study-unravels-physiological-signature-of-fear-memory-within-prefrontalc2adamygdala-networks.aspx [Accessed February 23, 2016].
Fox, E., 2012. Rainy Brain, Sunny Brain, London: Arrow Books.
Sigurdsson, T. et al., 2007. Long-term potentiation in the amygdala: A cellular mechanism of fear learning and memory. Neuropharmacology, 52, pp.215–227.
Article Author: Ellie Sanderson
Editor: Molly Campbell