Selective synaptic remodeling of amygdalocortical connections associated with fear memory

The authors uncovered a pathway from the lateral amygdala to the auditory cortex (ACx) of mice that is essential for auditory fear memory retrieval. Simultaneous imaging of pre- and postsynaptic structures in ACx in vivo revealed an increased rate of synapse formation in this pathway after auditory fear conditioning. Neural circuits underlying auditory fear conditioning have been extensively studied. Here we identified a previously unexplored pathway from the lateral amygdala (LA) to the auditory cortex (ACx) and found that selective silencing of this pathway using chemo- and optogenetic approaches impaired fear memory retrieval. Dual-color in vivo two-photon imaging of mouse ACx showed pathway-specific increases in the formation of LA axon boutons, dendritic spines of ACx layer 5 pyramidal cells, and putative LA–ACx synaptic pairs after auditory fear conditioning. Furthermore, joint imaging of pre- and postsynaptic structures showed that essentially all new synaptic contacts were made by adding new partners to existing synaptic elements. Together, these findings identify an amygdalocortical projection that is important to fear memory expression and is selectively modified by associative fear learning, and unravel a distinct architectural rule for synapse formation in the adult brain.