GABA regulates resonance and spike rate encoding via a universal mechanism that underlies the modulation of action potential generation

Different mechanisms for action potential (AP) generation exist that shape neuronal coding and network dynamics. The neuro-transmitter GABA regulates neuronal activity but its role in modulating AP dynamics itself is unclear. Here we show that GABA indeed changes the AP mechanism: it causes regularly firing hippocampal CA3 neurons to bistably switch between spiking and quiescence, converts graded discharge-to-current relationships to have abrupt onsets, and induces resonance. Modeling reveals that A-currents enable these GABA-induced transitions. Mathematically, we prove that this transition sequence originates from a single universal principle that generically underlies the modulation of AP dynamics in any conductance-based neuron model. Conductance clamp experiments in hippocampal and brainstem neurons show the same transitions, confirming the universal theory. In simulated networks, synaptically controlled AP dynamics, permits dynamic gating of signals and targeted synchronization of neuronal sub-ensembles. These results advance the systematic understanding of AP modulation and its role in neuronal and network function.