Cell Assemblies in Large Sparse Inhibitory Networks of Biologically Realistic Spiking Neurons

Cell assemblies exhibiting episodes of recurrent coherent activity have been observed in several brain regions including the striatum and hippocampus CA3. Here we address the question of how coherent dynamically switching assemblies appear in large networks of biologically realistic spiking neurons interacting deterministically. We show by numerical simulations of large asymmetric inhibitory networks with fixed external excitatory drive that if the network has intermediate to sparse connectivity, the individual cells are in the vicinity of a bifurcation between a quiescent and firing state and the network inhibition varies slowly on the spiking timescale, then cells form assemblies whose members show strong positive correlation, while members of different assemblies show strong negative correlation. We show that cells and assemblies switch between firing and quiescent states with time durations consistent with a power-law. Our results are in good qualitative agreement with the experimental studies. The deterministic dynamical behaviour is related to winner-less competition shown in small closed loop inhibitory networks with heteroclinic cycles connecting saddle-points.