Dynamical origin of independent spiking and bursting activity in neural microcircuits

The relationship between spiking and bursting dynamics is a key question in neuroscience, particularly in understanding the origins of different neural coding strategies, the mechanisms of motor command generation, and the process of neural circuit coordination. Experiments indicate that spiking and bursting dynamics can often be independent. We hypothesize that different mechanisms for spike and burst generation are the origin of this independence. If bursts result from a modulation instability of the network while spikes are produced by individual neurons, the bursting dynamics are independent of the details of the spiking activity. We tested this hypothesis in a detailed dynamical analysis of a minimal inhibitory neural microcircuit (motif) consisting of three reciprocally connected Hodgkin-Huxley neurons. We show that this high-dimensional system can be reduced to a time-averaged rate model and demonstrate that the H-H neural network and the rate model have identical bifurcations on the way from tonic spiking to burst generation. Burst generation in this system consequently does not depend on the details of spiking activity.