To understand what fear conditioning is, we must first understand what the term conditioning means. Classical conditioning is a type of learning, in which a neutral stimulus, which initially elicits no response in a subject (conditioned stimulus), is paired with a stimulus that provokes a strong response (unconditioned stimulus). If the conditioned and unconditioned stimuli are presented consecutively and repeatedly, the subject will associate the first stimulus with the second, and will react to the first stimulus alone. Fear conditioning is simply classical conditioning where the unconditioned stimulus evokes fear and thus a fear response is elicited on presentation of the conditioned stimulus. It is one of the mechanisms of survival, so that dangerous situations can be avoided after learning that they have unpleasant effects.
Pavlov’s experiment in 1901 with dogs is perhaps the most famous of classical conditioning experiments. He found that when dogs were presented with food, the dog salivates. The sound of a bell evoked no similar response. However, after the bell is paired with the food on several trials, the bell alone will generate salivation. The bell is now a conditioned stimulus, and salivation to it is a conditioned response. The dog had been conditioned to respond to the bell.
To be able to measure whether the subject is responding fearfully, changes in the autonomic nervous system and patterns of movement are usually examined. LeDoux in 1994 demonstrated fear conditioning by pairing a sound, with an electrical shock to the foot of a rat. The blood pressure of the rat and change in movement patterns was monitored and a rise in blood pressure and cessation or reduction in movement was taken to be a response to fear. Initially, the rat heard the sound alone. This had little effect on the blood pressure of the rat, or its movement patterns. The next set of trials involved playing the sound to the rat, and immediately afterwards giving the rat an...