Phase-dependent gating and primary/secondary (monophasic/biphasic) integration and differentiation mechanisms as exemplified by the carotid chemoreflex modulation of respiratory rhythm in rats. The chemoafferent input from the carotid sinus nerve (CSN) is habituated by a monophasic (input gated) differentiator in the nucleus tractus solitarius (NTS). The output from NTS is relayed by parallel pathways to I (inspiratory) or E (expiratory) neurons of the respiratory pattern generator or to I-PMN (inspiratory premotor neuron). Switches denote gating to either I or E phase. Each pathway is modulated by two biphasic integrators (∫L with fast or slow time constant) which either add or subtract to produce net short-term potentiation (STP) or depression (STD) effects. Adapted from .