n the traditional model of neurons, excitatory inputs to dendrites cause depolarization that spreads across the soma to the axon initial segment, where, if a threshold is surpassed, an action potential is generated. There are many exceptions to this general rule, however. Some neurons exhibit rebound spiking when freed from inhibition and others produce spike trains without additional synaptic input when depolarized above a plateau potential. In addition, recent studies revealed that some neurons enter a persistent firing mode after receiving prolonged, high-frequency stimulation. For example, repeated stimulation of interneurons in hippocampal CA1 led to persistent firing in which action potentials were generated in the distal axon (Sheffield et al., 2010, Nat Neurosci 14:200).