Figure 1.

Experimental design. Acquisition, Extinction, and Reinstatement testing occurred on three consecutive days. On day 1, subject were fear conditioned to two different CSs (CS + r, CS + nr) that were followed by an electrical shock on 50% of the presentations whereas a control stimulus (CS−) was never followed by the shock (Acquisition). On day 2, subjects received one single reminder trial of the CS + r (Reactivation). This was followed by a 10 min pause after which subjects were exposed to repeated non-reinforced presentations of each CS (Extinction). On day 3, subjects received four unsignaled presentations of the US (Reinstatement). This was followed by a 10 min pause after which subjects again were exposed to repeated non-reinforced presentations of each CS (Re-Extinction).