Abstract
How does a stimulus never associated with danger become frightening? The present study addressed this question using a sensory preconditioning task with rats. In this task, rats integrate a sound-light memory formed in stage 1 with a light-danger memory formed in stage 2, as they show fear when tested with the sound in stage 3. Here we show that this integration occurs 'online' during stage 2: when activity in the region that consolidated the sound-light memory (perirhinal cortex) was inhibited during formation of the light-danger memory, rats no longer showed fear when tested with the sound but continued to fear the light. Thus, fear that accrues to a stimulus paired with danger simultaneously spreads to its past associates, thereby roping those associates into a fear memory network.
Highlights
Memory is the means by which the past connects with the present to guide our future interactions with the environment
Previous work had shown that formation of the sound-light memory requires activation of NMDAr in the perirhinal cortex (PRh) (Holmes et al, 2013), and that the consolidation of this memory requires ERK/MAPK signaling in the PRh (Holmes et al, 2018)
The present work shows that this consolidation requires de novo protein synthesis in the PRh (Experiment 2)
Summary
Memory is the means by which the past connects with the present to guide our future interactions with the environment. When again hiking through the rainforest you hear the booming sound and feel apprehensive, even frightened. This hypothetical scenario illustrates how the sound-animal memory formed at one point in time and the animal-danger memory formed at a second point were integrated via their common, animal, element to generate defensive/fear reactions to the sound. This type of integration could occur in two ways (Shohamy and Daw, 2015; Schlichting and Preston, 2015). The second is through retrieval and chaining of memories at choice points (Rizley and Rescorla, 1972; Sadacca et al, 2018; Sharpe et al, 2017): that is re-exposure to the sound activates the sound-animal memory, which in turn, activates the animal-danger memory, resulting in expression of defensive/fear reactions to the sound (‘memory-chaining’)
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