Fig. 4.

Long-term retention of strong appetitive spatial memory. (A) Behavioral procedures for long-term probe tests. Rats received strong encoding (filled circle). Twenty-four hours later, they were tested in a probe trial with 5 nonrewarded sandwells (open circles). Exploration in a novel box (gray square) was conducted or omitted 30–40 minutes after encoding. (B) In young rats, the percentage of correct digging was significantly higher than chance (dashed line). (C) In middle-aged rats, the percentage of correct digging was not different from chance. (D) Within-subject comparison between young (B) and middle-aged rats (C). (E) Middle-aged rats received strong encoding, and 3 different memory-modulating events took place 30–40 minutes later. Twenty-four hours after encoding, they were tested in a probe trial with 5 nonrewarded sandwells (open circles). (F) Novelty after encoding did not improve the percentage of correct digging, which was not different from chance. (G) Exploration in the encoded zone after encoding increased the percentage of correct digging, which was significantly higher than chance. (H) With a second strong encoding trial, the percentage of correct digging was significantly higher than chance. Data are presented as mean ± SEM. * p < 0.05, ** p < 0.005.