Fig. 2. Time between learning sessions has a critical impact on memory.

a Experimental design. The groups differed by the interval between the two enrichment periods: 4, 14, 24 or 34 days separating the two enrichments. b, c Behavioral results. b Discrimination between +lim/−lim. Groups T1 and T3′ discriminate. No discrimination is observed for the other groups (T2′, T4′, T5′) (T1 n = 11; T2’ n = 11; T3′ n = 11; T4′ n = 6; T5′ n = 7) t-test, **p < 0.005; ***p < 0.001. c Dec is discriminated from dodec in Group T2′ to T5′ (T1 n = 10; T2′ n = 11; T3′ n = 11; T4′ n = 10; T5′ n = 11) t-test **p < 0.005; ***p < 0.001. d Adult-born neuron density. Higher density of adult-born neurons is observed in groups that are able to discriminate +lim from −lim (T1 and T3′) (n = 6–7/group), Tukey corrected t-tests *p < 0.05; ***p < 0.001. e Density of activated adult-born neurons (BrdU+/Zif268+ cells) in response to +lim (T1 n = 4; T2′ n = 6; T3′ n = 4; T4′ n = 6; T5′ n = 6) or dec (T1 n = 4; T2′ n = 6; T3′ n = 4; T4′ n = 6; T5′ n = 6) after successive enrichments. Density of double-labeled cells is higher in response to +lim at T1 and T3′ compared to T2′, T4′, and T5′. In response to dec, the density of BrdU/Zif268 cells is higher at T3′ compared to the other groups. T-test *p < 0.05 for enriched animals responding to +lim at T1 and T3′ different from all other groups. Data are represented as data points and mean ± sem. Source data are provided as a Source Data file.