Figure 4: Fear conditioning to a discrete clicker.

Rats were reactivated and extinguished 1 h later (filled columns/symbols, N=8) or given extinction alone (open columns/symbols, N=8). (a) Freezing to the clicker at reactivation/start of extinction (R/E) and at the post-extinction test. Reactivation and extinction impaired the decrement in memory expression compared with extinction alone. (b) Freezing during the extinction session. The final ten presentations of the CS (that is, excluding the initial presentation of extinction or the prior reactivation presentation) are presented. The reduction in freezing levels across CS presentations was retarded in the reactivation+extinction condition, compared with the extinction alone condition (mixed ANOVA; presentation×condition: F(4.6,64.3)=3.025, P=0.019; condition: F(1,14)=1.228, P=0.286). Analysis of simple effects (P<0.05) revealed that both conditions reduced their freezing levels across the session, and there was no absolute difference between the conditions at any of the CS presentations. Data presented as mean±s.e.m.