Assessing the Role of Sleep in Shaping Hippocampal Engram Connectivity in CA3-CA1

Memories are stored in engrams. Crucial to the formation of engrams is the enhancement of synaptic strength between the neurons co-active during learning. Sleep has been hypothesized as a state which drives the ‘offline’ synaptic modification. Recent studies now corroborate this account, uncovering sleep-dependent changes at the synaptic scale. However, the interaction between sleep and the strengthening of engram synapses had not been experimentally reported. We hypothesized that sleep supports the enhancement of engram-engram (E-E) connectivity that occurs during learning. We leveraged dual-eGRASP, a viral labeling strategy which tags converging inputs from engram and non-engram presynaptic populations onto postsynaptic engram and non-engram dendrites, to assess the synaptic connectivity patterns of mice that were sleep deprived after contextual fear conditioning. Our results showed no effect of learning or sleep deprivation on the E-E connectivity in CA3-CA1. Additional experiments are needed to validate this result.M.Sc