Conditions for replay of neuronal assemblies

From cortical synfire chains to hippocampal replay, the idea that neural populations can be activated sequentially with precise spike timing is thought to be essential for several brain functions. It has been shown that neuronal sequences with weak feedforward connectivity can be replayed due to amplification via intra-assembly recurrent connections. However, this phenomenon was thought to depend on inhibitory feedback, but its mechanisms were still unclear. Here, we arrive at a minimal spiking model that shows that feedback inhibition is not needed for this amplification to occur. We then introduce a population model of membrane-potential distributions that explains the spiking network behavior, and we analytically describe how different connectivity structures determine replay speed, with weaker feedforward connectivity generating slower pulses that can be sustained by recurrent connections. These pulses can only propagate if neuronal leak currents are slow enough with respect to the pulse speed. Together, our simulations and analytical results predict the conditions for replay of neuronal assemblies.