Figure 1.

Fear conditioning and conditioned inhibition of fear are based upon associative learning process involving the conditioned stimulus (CS), the unconditioned stimulus, and conditioning context. (a) Classical conditioning paradigms based on associative learning involve the conditioning chamber where the training procedures are carried out which constitutes the conditioning context. During training, the unconditioned stimulus (US), which has an intrinsic valence (here, aversive such as a mild electric footshock) becomes associated with the CS (such as an auditory signal) that is a priori neutral. (b) During fear conditioning, the temporal pairing of the US and the CS induces a transfer of the fear-inducing properties from the US to the CS. Consecutively, the previously neutral stimulus CS and the conditioning context elicit the physiological and behavioral responses (such as freezing) inherent to the US. Conditioned inhibition of fear (or learned safety) is mediated by the temporal dissociations of the US and the CS, in a way that the two stimuli never coincide. Consequently, the presence of the conditioned inhibitor leads to a reduction of the fear response induced by the conditioning context.