K. E. Moczulska, J. Tinter-Thiede, M. Peter, L. Ushakova, T. Wernle, B. Bathellier, S. Rumpel. Dynamics of dendritic spines in the mouse auditory cortex during memory formation and memory recall. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1312508110
Here is the abstract:
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.
In effect the researchers made microscopic ‘photos’ of the formation of memories and the weakening of the them plus the retrieval of the memories. The idea that ‘neurons that fire together wire together’ was clearly illustrated. The repeated conditioning increased the strength of the memory, while disrupting the conditioning decreased it, but did not destroy the memory. Retrieval of the memory did not change its strength. The notion that recall recapitulated the original memory formation was not supported.