Post-extinction selective persistence of large dendritic spines in fear remodeled circuits may serve to reactivate fear.

Memory formation associates with changes in strength and efficacy of existing synapses and with the formation of new synapses. Dendritic spines, the membranous protrusions from neuron dendrites that host the majority of excitatory synapses, are the anatomical sites where neuronal activity reshapes brain networks in response to stimuli. Mounting evidence indicates that structural changes in fear-remodeled circuits undergo partially erasure following extinction, suggesting that the changes that persist may serve to reactivate memory. Here we review data showing how brain circuits are remodeled at the time fear memory is formed and extinguished, with a special focus put on the post-extinction persistence of spine enlargement in relation to memory reactivation