Synaptic correlates of associative fear memory in the lateral amygdala

Successful adaptation to the environment requires accurate responding to external threats by recalling specific memories. However, elucidating underlying neural substrates of associative fear memory was limited due to the difficulties in direct examination of extinction-induced changes of specific synapses that encode an auditory fear memory. Using dual-eGRASP (enhanced Green Fluorescent Protein Reconstitution Across Synaptic Partners), we found that synapses between engram cells or synaptic engram showed a significantly larger spine morphology at auditory cortex (AC) to lateral amygdala (LA) projections after auditory fear conditioning. Fear extinction reversed the enhanced synaptic engram spines while re-conditioning with the same tone and shock restored the size of the synaptic engram. Taken together, we suggest that the synaptic engram may represent a different state of fear memory. One Sentence Summary Associative fear memory enlarged the spine morphology of synapses between engram neurons in the amygdala, which was diminished by memory extinction and restored by re-conditioning, suggesting that connections between engram cells represent a different state of fear memory.