Classical conditioning | What is fear conditioning | “Little Albert” experiment | Trace and delay fear conditioning | Cued and contextual fear conditioning | Extinction vs conditioning | Examples | Fear and the brain
What Is Fear Conditioning
Fear conditioning refers to learning a certain environmental stimulus (conditioned stimulus) can predict the occurrence of an aversive stimulus (neutral stimulus)2. The fear results from this association is a conditioned response.
Fear conditioning is a form of classical conditioning. It is the mechanism we learn to fear people, objects, places, and events that are aversive such as an electric shock. In evolution, this form of associative fear learning plays a critical role in our survival from future threats3.
Although meant to be a survival mechanism, unchecked conditioned fear may contribute to disorders of fear and anxiety in humans, resulting in panic disorder, phobias, or post-traumatic stress disorder (PTSD)4. Conditional fear can be powerful and long-lasting for some individuals.
Classical conditioning, also known as Pavlovian conditioning, is learning through the association of a neutral stimulus with a biologically potent stimulus1.
Russian psychologist, I.P. Pavlov, stumbled upon classical conditioning by accident. In his research on the digestive systems of dogs, he noticed a subtle change in the dogs’ responses to food over time. Initially, the dogs would only salivate when food was presented. Over time, they began salivating slightly before the food arrived, when they heard the sound of approaching food carts. Pavlov then conducted an experiment. He rang a bell shortly before presenting food to the dogs. In the beginning, the dogs did not react to the bells. Eventually, though, just hearing the bell caused the dogs to salivate. The dogs associated the bells with being fed.
Before conditioning, the bell was a neutral stimulus (NS) that did not trigger a response in the dogs. However, after repeatedly ringing the bell before bringing food, an unconditioned stimulus (US), hearing the bell became a conditioned stimulus (CS). The conditional stimulus could then trigger the dogs to salivate involuntarily. This reaction to the conditioned stimulus is a conditioned response (CR).
In humans, learning the associations between aversive events and the environmental stimuli that predict such events is an essential survival skill. The fear conditioning paradigm is the epitome of this form of associative learning.
The “Little Albert” Experiment
In the 1920s, psychologists John Watson and Rosalie Rayner devised one of the most documented fear-conditioning experiments5. The goal was to condition a baby, named “Little Albert”, with fear of a white rat.
At first, Little Albert was not afraid of rats. In the experiment, after Watson presented the rat, he made a loud, aversive noise by striking a hammer on a suspended steel bar to generate a fear response in Little Albert. The baby was startled violently and broke into a sudden crying fit. After repeating this procedure several times in the conditioning session, little Albert came to fear the rat itself.
Later on, when the rat was presented without the aversive sound, Little Albert had involuntary fear responses, such as falling over, crying, and crawling away from the rat.
Note: This cruel experiment would certainly not be acceptable by current ethical standards.
Little Albert had learned that the presentation of the conditioned stimulus (CS, the white rat) predicted the occurrence of the aversive unconditioned stimulus (US, the loud noise) which would trigger a conditioned response (CR, crying). This experiment exemplifies the emergence of fear conditioning in children.
Trace and Delay Fear Conditioning
Trace conditioning and delay conditioning are two Pavlovian learning procedures that differ in their temporal relationship between the CS and UCS.
In the classical Pavlovian fear conditioning, the CS comes before the UCS. But when CS is delayed, then a delay conditioning results.
In delay conditioning, the appearances of CS and UCS overlap and end at the same time.
In trace conditioning, after CS appears, there is a temporal gap (i.e., the trace interval) before the onset of UCS6.
Cued and Contextual Fear Conditioning
A context is the set of circumstances around an event. They are typically places or environments. Other different contexts include relationships between spatial, temporal (time), interoceptive (e.g. hunger, stress), cognitive (how info is encoded and retrieved), social, and cultural7.
When a CS is a static context of the environment, such as a room, the result is called contextual fear conditioning. The conditioned fear in this case is associated with the context. When the conditioned person is returned to the same context, CR is triggered.
Cued fear conditioning is similar to contextual conditioning, except that the CS is added to the context. This CS is a discrete cue such as an auditory cue like a brief signal or a loud sound. In this case, the conditioned fear is paired with a cue.
Fear Extinction vs Fear Conditioning
When a conditioned person is repeatedly exposed to the fear-eliciting CS in the absence of the aversive US, the conditioned fear response will decline and eventually become extinct. This procedure is called fear extinction, in which the predictive value of the CS as to the occurrence of the US is reduced.
Extinction is not the same as unlearning or forgetting. Rather, it’s new associated learning of fear inhibition8.
Human studies have found that fear memories can last for years with little forgetting. So extinction does not remove the fear memory. But it creates a new memory that pairs the CS with the absence of the US.
Fear Conditioning Examples
To study human fear conditioning, behavioral neuroscience researchers use rats extensively.
In typical fear conditioning studies, a rat or rodent is not presented with the aversive stimulus in the home cage. The animal is then placed in a novel environment, provided aversive stimuli, e.g. mild electrical shock in the foot, and subsequently removed.
When it is returned to the same “novel” environment, it generally will demonstrate a freezing response or changes in heart rate if it becomes fear-conditioned9.
Fear and the Human Brain
Being able to use neutral cues to predict threats is crucial in survival. However, when this type of conditioned fear fails to extinguish when it’s no longer a threat, anxiety disorders such as posttraumatic stress disorder (PTSD) result. In those who suffer from PTSD, the conditioning memory of traumatic events can cause debilitating conditioned fear responses for decades after the danger has passed.
Not everyone who is exposed to the conditioning experiences will develop disorders. Lesion studies have found that the neural circuitry involved in fear acquisition and extinction include the brain regions in the central amygdala, hippocampus, and medial prefrontal cortex. Dysfunction in these networks can cause individuals to develop fear10.
Pharmacological studies and synaptic studies in amygdala lesions also support the crucial role of the amygdala in fear conditioning. Damages in the basolateral amygdala can prevent the learning and expression of fear responses.
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