Figure 4.

Optogenetic inhibition of dHPC-to-LS pathway during memory retrieval. (A) Schematic drawing (left) of bilateral injections of AAV viruses that encode either halorhodopsin (Halo) or YFP (Ctrl) into the dHPC and an optical fiber implant into the LS. Contextual fear conditioning procedure (right). Mice were trained during acquisition of memory on day 0, receiving no laser stimulation. Then, mice received optogenetic inhibition of the dHPC-to-LS neuronal terminals during both recent (day 1) and remote (day 31) memory tests. (B) Percentage of freezing (mean of 5 min) during the recent memory test (day 1) and remote memory test (day 31). (**) P = 0.004; repeated measures ANOVA between groups. (C) Minute-by-minute percentage of freezing from B of recent (left) and remote (right) memory tests. Both left and right, P < 0.05; Bonferroni post-hoc of the means between Halo/Ctrl. All error bars indicate SEM. (D) Optical fiber placements of the Halo group were confirmed mostly dorsal to the LS, arranged anterior (top) to posterior (bottom).