Figure 3.

Fear conditioning and extinction. In a typical fear-conditioning paradigm, a neutral event such as a blue light (the CS), which normally does not elicit a fear response, is paired with an aversive event, such as a shock (the US), which normally does elicit a fear response (the UR). After several pairings of the blue light and shock (conditioning phase), the presentation of the blue light itself leads to a fear response (the CR). Extinction occurs when a CS is presented alone, without the US, for a number of trials and eventually the CR is diminished or eliminated. The recall of extinction can be assessed with re-exposure to the CS after a subsequent delay.