Effect of extinction or ret+ext of a light CS after fear conditioning to the light on long-term memory (LTM) 24 h after extinction and spontaneous recovery (SR) tests 24 d after extinction. Both ret+ext (n = 12) and ext-only (n = 10) groups extinguish to the same levels, presented as the last four trials of extinction averaged together, and freeze at similar levels during LTM tests. Ret+ext does not show spontaneous recovery when tested 24 d after extinction compared to LTM (P = 0.193), but ext-only (n = 10) does show spontaneous recovery compared to LTM (P = 0.011) as evidenced by increased freezing during spontaneous recovery tests. Additionally, during SR tests ret+ext rats froze significantly less than ext-only rats. (*) P < 0.05.
