Figure 8. Amygdala inactivation facilitates extinction of duration memories.
(a) Schematic explaining experimental design in control saline and experimental lidocaine shift groups. Saline and lidocaine groups underwent an aversive conditioning protocol with a CS–US interval of 30 s until they were shifted to 10 s; saline or lidocaine was infused in the basolateral amygdala (20 μg μl−1; 0.5 μl) just before the shift session. Rats were perfused and brains harvested 90 min after the shift session and processed for Arc immunohistochemistry (saline n=6; lidocaine n=5). (b–c) Immunostaining for Arc in DMS and DLS revealed that inactivating the amygdala prevents the reduction of Arc up-regulation in the DMS, but not in the DLS (ANOVA, *P=0.02). Scale bar, 200 μm. These data indicate that blocking neuronal activity in the amygdala prevents the change in striatal plasticity processing occurring during learning of a new duration. Furthermore, control rats (n=5) not exposed to the CS showed markedly low levels of Arc in both DMS and DLS. (d) For a behavioural assessment of the effect of amygdala blockade, additional rats were infused with saline (n=10) or lidocaine (n=9) before the first two shift sessions. Upper panels show behavioural patterns of suppression for both groups before the shift (US@30 s) and after 10 sessions of learning the new duration (US@10 s). In the lower panels analyses of the suppression curves by blocks of 2 sessions after the drug-infused sessions indicate that the lidocaine group continues to increase up to block 5, whilst in the control saline group no significant evolution of the peak amplitude could be detected. (e) Peakfit analyses revealed that acquisition of the peak time is very rapid as it occurred within the first block in both groups (upper panel). Strikingly, analysis of the width (red arrow in d), reflecting processes related to extinction of the old duration, shows non-immediate adaptation in controls whilst in the lidocaine group such process is immediate (post hoc Bonferroni, *P<0.05).