EMOTIONAL VALUE OF THE INITIAL ENCODING CONTEXT MODULATES THE NEURAL SUBSTRATES OF MEMORY INTEGRATION IN SENSORY PRECONDITIONING

In a standard sensory preconditioning protocol, rats integrate a tone-light association formed in stage 1 with a light-shock association formed in stage 2 to generate fear responses (e.g., freezing) to the tone in stage 3. Here, we examined whether the emotional value of the context in stage 1 (frightening or not) influences how the tone-light and light-shock associations are integrated in the perirhinal cortex (PRh) and basolateral amygdala complex (BLA). Specifically, we manipulated the value of the context at the time of the tone-light pairings in stage 1, injected the NMDA receptor antagonist DAP5 into either region immediately prior to the session of light-shock pairings in stage 2 (as this is when the integration occurs), and assessed the impact of this injection on freezing to the tone in stage 3. The results showed that: 1) when the initial encoding context was neutral, freezing to the tone was disrupted by a DAP5 infusion into the PRh, not the BLA; 2) when the initial encoding context was frightening, freezing to the tone was disrupted by a DAP5 infusion into the BLA, not the PRh; and 3) when the initial encoding context ceased to be frightening (achieved through extinction), freezing to the tone was again disrupted by a DAP5 infusion into the PRh and not the BLA. Thus, the value of the initial encoding context regulates the substrates of memory integration in the PRh and BLA. The findings are discussed with respect to theories of memory integration in the medial temporal lobe.