Intrinsic voltage fluctuations reveal a form of phase-amplitude coupling in electrosensory pyramidal neurons.

The stochastic flickering of ion channels is known to cause ongoing membrane potential fluctuations in neurons. This channel noise is often considered negligible when compared with synaptic noise, yet it can shape the integrative properties of neurons. Here, in vitro recordings of electrosensory pyramidal neurons under synaptic blockade are characterized and shown to contain a nontrivial repertoire of dynamical features. Our analyses reveal an intrinsic noise structure that is much richer than what could be expected based on previous studies: we identify rapid, small-amplitude, shot noise-like events and we quantify how their rate and amplitude are modulated by slower, large-amplitude fluctuations. This cross-relation is evidence that, at the single-neuron level, membrane potential dynamics can exhibit a form of phase-amplitude coupling. We also investigate the appearance of fast, intermittent subthreshold oscillations and conclude that they are manifestation of stochastic linear dynamics, possibly with time-varying parameters. Our results, collectively, highlight that neurons can spontaneously display rich intrinsic behavior, which is likely to impact how they process synaptic input.NEW & NOTEWORTHY How do neurons behave in the absence of synaptic input? Can their intrinsic activity convey important information about how they function? Here, we provide evidence that the structure of intrinsic voltage noise in pyramidal neurons contains several nontrivial components, contrary to what is usually assumed. We show, for the first time, that a form of phase-amplitude coupling can exist in the spontaneous electrical activity of single neurons.