Fig. 7. Fear conditioning. Freezing (absence of motion except respiration) was assessed before (A ) and immediately after (B ) three pairings of a conditioned stimulus (tone) and an unconditioned stimulus (shock). On the following day the association between the shock and the tone was tested in a completely different context. Freezing was assessed before (C ) and after (D ) reexposure to the tone. Then, rats were returned to the original context, in the absence of tone or shock, and freezing was assessed once again (E ). *P < 0.05, **P < 0.01, Kruskall-Wallis test with Dunn's multiple comparisons test (one or more groups did not pass normality test). P < 0.05, one-way ANOVA, Bonferroni post hoc corrections. EE = enriched environment; NH = normal housing; Sevo = sevoflurane.