Fear is a complex sensation elicited by a perceived risk or danger that can directly produce a number of behavioural modifications. Fear can be conscious, subconscious, both, and can be acute or learned. This complexity explains why there is so much variety in how people perceive and respond to threatening cues. Some fears may have an evolutionary basis; ie. fear of poisonous snakes; while other fears may be the result of conditioning from a bad experience, and some fears have no rational basis (phobias). Responses range from freezing at the sight of a clown, to instinctively punching the actor in the haunted house as there are many factors that control our response to fears.
To fully understand how we perceive and respond to fear we need to look at the brain:
Rethinking the Amygdala:
The amygdala refers to two almond shaped clusters of neurons deep within the brain's medial temporal lobes that are part of the limbic system. This system is activated in many of those primal reflexes such as aggression, fear or threat detection and responses, pleasure and more. While the amygdala was traditionally thought of as the fear centre of the brain, and it certainly does regulate the nonconscious response to fear, it is one piece of a complex “fear” circuit. The amygdala detects threats and initiates a response that would help us cope, from neurotransmitter or hormone release to initiate fleeing or fighting.
As more information regarding fear perception and responses comes to light, researchers understand the concept of the “extended amygdala” for the assembly of fear and anxiety states in response to a broad spectrum of learned and unlearned threats. Researchers have been able to identify which portions of this extended amygdala are related to immediate vs long lasting responses, and how these regions communicate with each other. It is also important to note that there is a conscious perception of fear that overlaps with and alters responses from the amygdala. The hippocampus is involved in evaluating the context of the fear and also creates a memory of the experience which serves as its own stimuli (so you can get scared just thinking about something scary).
When Fear Takes Over:
While fear can be protective there are times when it can become pathological. Many anxiety disorders and phobias are rooted in inaccurate perception of a fearful stimulus, hyperexcitable fear pathways, inappropriate fear extinction. As mentioned earlier, fear can be acquired through conditioning, pairing a specific stimulus (eg. a threatening face, loud noises) with a painful stimulus which elicits some sort of response (profuse sweating, dilated pupils etc.) Over time exposure to the stimulus alone can induce the response. While the exact physiology of the disordered functioning is murky there is a strong link with neurotransmitter dysfunction ie. serotonin, dopamine, and gammaaminobutyric acid (GABA.) A deficiency in any of these could cause inappropriate fear responses.
Fortunately, “fear extinction” is also possible, whereby exposure to a previously fearful stimulus no longer elicits any response. It involves some inhibition of the neurons in the extended amygdala, and is related to repeated exposure to a stimulus without the adverse event that they expect. Individuals must learn that the outcome they predict from a fearful stimulus is different from the outcome that actually occurs. This process may not occur in individuals with severe, maladaptive fear responses such as PTSD and is inhibited by chronic stress and possibly even GABA deficiency. The “fear extinction pathway” presents a sustainable therapeutic approach for these individuals and is a growing field.