**Figure 5.** **Memory retention after strong encoding and non-rewarded reactivation in aging.** (**A**) Rats received a strong encoding trial (3 rewards, filled circle), a reactivation trial with a non-rewarded sandwell (open circle) at 6 hours later, and a non-rewarded probe trial at another 18 hours later. Exploration in a novel box was introduced or omitted at 30 min after reactivation. (**B**) In rats without prior training, the percentage of correct digging was not different from chance (dashed line) without novelty (one-sample *t*-test, t_{9} = 0.41, *p* = 0.69, attrition of 2 rats) and was significantly above chance with novelty (one-sample *t*-test, t_{9} = 3.21, *p* = 0.01). No difference was observed between the conditions (paired *t*-test, t_{9} = 1.91, *p* = 0.09; Bonferroni’s multiple comparison test *p* = 0.18). (**C**) In rats with prior training, the percentage of correct digging was not different from chance (dashed line) without novelty (one-sample *t*-test, t_{12} = 0.18, *p* = 0.86) and was significantly above chance with novelty (one-sample *t*-test, t_{11} = 6.01, *p* < 0.001). The condition difference was significant (paired *t*-test, t_{11} = 2.84, *p* = 0.02; Bonferroni’s multiple comparison test *p* = 0.014). (**D**) Rats received a strong encoding trial (filled circle), exploration in a novel box at 6.5 hours later, and a non-rewarded probe trial at another 17.5 hours later. (**E**) The percentage of correct digging was not above chance in either group (No prior training: one-sample *t*-test, t_{9} = 0.09, *p* = 0.93; Priorly trained: one-sample *t*-test, t_{11} = 0.31, *p* = 0.76). Data are presented as mean ± SD. ^{*}*p* < 0.05, ^{***}*p* < 0.005.