Period-Adding Bifurcation with Chaos in the Interspike Intervals Generated by an Experimental Neural Pacemaker

The dynamics of the generation of the various spike trains in neural pacemakers is of fundamental importance to the understanding of neural coding. Recent studies have demonstrated, theoretically and experimentally, that neural pacemakers produce chaotic oscillations. Deeper analyses in several neuronal models have revealed many nonlinear phenomena including period-adding bifurcations whose existence has not been experimentally confirmed. In this letter, we reported that the period-adding bifurcation with chaos was observed in the interspike interval (ISI) series generated by an experimental neural pacemaker when the extracellular calcium concentration was changed or a potassium channel blocker was administered at the site of the pacemaker. We also simulated our experimental discoveries by computing a generalized model of excitable cells. The chaotic phenomenon in the experiment and that in the model were demonstrated and compared using the nonlinear forecasting and surrogate data methods.