Figure 2.

Acquisition, extinction, retrieval, and renewal. A, Day 1 acquisition. There were no genotype differences within the young adult or middle-aged groups. Within the older-aged group, there was a significant main effect of genotype and a significant genotype × trial interaction such that WT showed greater %time freezing relative to TgAD. With the exception of older-aged TgAD rats, all groups acquired fear memory during day 1. The x-axis represents BL, CS–US paring trials (1–4), and PPs. B, Days 2–4 extinction, retrieval, and renewal. Within the young adults, there was a main effect of genotype such that TgAD rats showed greater %time freezing relative to WT. While young adult WT rats showed successful fear extinction and retrieval, young adult TgAD rats did not. Within the middle-aged group, there was a significant genotype × trial interaction. Middle-aged TgAD rats showed intact acute fear extinction but not retrieval, whereas the WT middle-aged rats did not show either. There were no genotypic differences within the older-aged group. Older-aged WT rats showed intact acute fear extinction but not retrieval, whereas there was no extinction or retrieval in the older-aged TgAD rats. The x-axis represents the memory probe trial (Mem), extinction (Ext), retrieval (Ret), and renewal (Ren). Data are plotted as the mean with SEM. ***p < 0.001 for main effects of genotype; ××p < 0.01, ×××p < 0.001 for genotype × intensity interactions; ++p < 0.01, +++p < 0.001 for significant differences between Ext or retrieval and Mem within groups (blue for WT and red for TgAD); ##p < 0.01, ###p < 0.001 for significant differences between BL and PP during acquisition within groups (WT, blue; TgAD, red). Dotted black line represents mean of YA-WT PP in A and mean of YA-WT Ext in B.