Figure 2.

LHb inactivation before memory test, after extinction, abolishes defensive responses. A₁, left, Schematic representation of rats training. Rats were trained to associate tones with foot-shocks (day 1; Cond, conditioning), which represents threat learning (red). One day later, rats were trained to associate the same tone with the absence of foot-shocks (day 2; Ext, extinction), which represents safety learning (green). Finally, the next day, rats were infused with SAL or M&B into LHb (gray arrow) before being presented with tones only (day 3, test), which involves the retrieval competition of coexisting threat (red) and safety (green) memories to control defensive responses. Right, Coronal drawings of rat brain atlas showing placements of the injector tips in LHb. A₂, LHb inactivation before retrieval test (day 3), after extinction (gray arrow and shaded area in graph), decreased defensive responses, as indicated by lower levels of tone-elicited percent freezing and lever-press suppression ratio [inset; late conditioning (last two-tone trial block), early extinction (first two-tone trial block), and test] in the experimental group as compared with the control groups (SAL, n = 7; miss M&B, n = 8; hit M&B, n = 9). Data are shown as ± SEM in blocks of two trials. LHb, lateral habenula. Inf, infusion. Supp. ratio, suppression ratio; x, baseline (pretone) freezing levels; *p < 0.05.