An autorhythmic population of excitatory neurons in the brainstem pre-Bötzinger complex is a critical component of the mammalian respiratory oscillator. Two intrinsic neuronal biophysical mechanisms—a persistent sodium current () and a calcium-activated non-selective cationic current ()—were proposed to individually or in combination generate cellular- and circuit-level oscillations, but their roles are debated without resolution. We re-examined these roles in a model of a synaptically connected population of excitatory neurons with and . This model robustly reproduces experimental data showing that rhythm generation can be independent of activation, which determines population activity amplitude. This occurs when is primarily activated by neuronal calcium fluxes driven by synaptic mechanisms. Rhythm depends critically on in a subpopulation forming the rhythmogenic kernel. The model explains how the rhythm and amplitude of respiratory oscillations involve distinct biophysical mechanisms.
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