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Dynamics of dendritic spines in the mouse auditory cortex during memory formation and memory recall

Significance Memories are believed to be stored as long-lasting structural changes in synapses. We tested the hypothesis that formation of a tone-shock association induces changes in the mouse auditory cortex by combining chronic in vivo imaging of dendritic spines with auditory fear conditioning. We find that memory formation is correlated with a transient increase in spine formation that leaves a long-lasting trace in the network. Memory recall does not lead to a recapitulation of structural remodeling as observed during initial memory formation. Our findings provide a potential synaptic mechanism underlying previously reported functional changes in auditory cortex following fear conditioning and challenge models in which memory traces are modified upon memory retrieval. Long-lasting changes in synaptic connections induced by relevant experiences are believed to represent the physical correlate of memories. Here, we combined chronic in vivo two-photon imaging of dendritic spines with auditory-cued classical conditioning to test if the formation of a fear memory is associated with structural changes of synapses in the mouse auditory cortex. We find that paired conditioning and unpaired conditioning induce a transient increase in spine formation or spine elimination, respectively. A fraction of spines formed during paired conditioning persists and leaves a long-lasting trace in the network. Memory recall triggered by the reexposure of mice to the sound cue did not lead to changes in spine dynamics. Our findings provide a synaptic mechanism for plasticity in sound responses of auditory cortex neurons induced by auditory-cued fear conditioning; they also show that retrieval of an auditory fear memory does not lead to a recapitulation of structural plasticity in the auditory cortex as observed during initial memory consolidation.