Imaging collective synaptic dynamics in the mouse auditory cortex during learning

There is strong evidence that alterations in the structural and functional properties of synaptic connections during learning are underlying the formation of long-term memories. However, what specific changes in the architecture of the neuronal network are mediated by learning-induced plasticity is still poorly understood. A major limiting factor of current in vivo imaging studies of synaptic dynamics is that typically only at a small number of synapses are assessed in a given animal, typically tens to hundreds. Here, we started to apply longitudinal in vivo two-photon imaging of more than a million synapses in layers 1-3 of the auditory cortex of an individual mouse. We label endogenous PSD-95, a major postsynaptic scaffolding protein of excitatory synapses in the cortex, using AAV-mediated expression of FINGR constructs and re-image the same volumes of neuropil in 12 imaging sessions over an 11-day period in control groups during environmentally and behaviorally stable conditions. Using the same imaging schedule, we also image synaptic dynamics in mice that undergo classical conditioning using auditory cues in a single session, a paradigm we have previously shown to induce a transient disbalance in the ongoing formation and elimination of dendritic spines in the auditory cortex. In parallel, we are developing an automated detection and tracking methodology for PSD-95 puncta to quantitatively analyze synaptic changes. With this dataset, we hope to provide an entry point for the study of the collective dynamics of synapses during learning, but also basal conditions.