Multi-Parameter Asymmetric Regulation of Bursting Dynamics in Mesencephalic Trigeminal Neurons: Insights from Bifurcation Analysis

Bursting is fundamental to neural information encoding and plays critical roles in rhythm generation, sensory processing, and motor control. However, the dynamical mechanisms by which multiple parameters coordinately regulate bursting properties in mesencephalic trigeminal neurons remain unclear. Here, using fast–slow decomposition we reveal three distinct asymmetries in the regulation of bursting dynamics by four key parameters, gNaR, gNaP, Iapp, and kb. First, asymmetric shifts in the SNLC and subH bifurcation curves in the two-parameter plane, rather than symmetric displacements, underlie the expansion or compression of the subH–SNLC window, directly modulating bursting duration (BD) and inter-burst interval (IBI). Second, gNaP produces a paradoxical asymmetry: although it narrows the subH–SNLC window, it simultaneously reduces the per-spike consumption of the slow variable hp via sustained depolarization, thereby prolonging BD while shortening IBI, a dissociation that cannot be predicted from the bifurcation window alone. Third, Iapp induces an opposing asymmetry: it widens the subH–SNLC window while shortening IBI, revealing that bifurcation expansion and the silent phase duration are not monotonically coupled. All four parameters increase spike count per burst (SCPB) and BD, yet their effects on IBI diverge, with gNaR and kb extending it whereas gNaP and Iapp shorten it, establishing that active and silent phases are asymmetrically regulated. Our findings demonstrate that bursting characteristics emerge from the cooperative interplay of bifurcation positions, membrane potential, slow-variable dynamics, and hysteresis. These results provide dynamical insights into the asymmetric regulation of bursting rhythms by ion channel parameters, and may offer theoretical guidance for neuromodulation strategies targeting channel-related disorders.