Evidence for "type I" excitability in molluscan neurons

The transition between silent and oscillatory activity as a function of a change in parameters is known as a bifurcation in nonlinear dynamical systems theory. The role of the saddle-node and Hopf bifurcations in such transitions have become ubiquitous in computational models and underly a classification scheme of spiking mechanisms: type I (saddle-node) and type II (Hopf). Here we present experimental evidence from molluscan neurons of bifurcation diagrams that are similar in structure to those from type I neuron models. These results mark one of the first attempts at validating such bifurcation mechanisms in single neurons.