Cellular Mechanisms of Phase Maintenance in a Pyloric Motif of a Central Pattern Generator

TL;DR

This study explores how neuromodulation maintains phase relationships in a crustacean pyloric CPG across different periods by modeling cellular mechanisms and bifurcations.

Contribution

It introduces a biophysical model revealing three distinct mechanisms for phase maintenance based on bifurcation theory in a pyloric network.

Findings

Three mechanisms control burst and interburst durations.

Phase maintenance involves bifurcations like blue-sky and saddle-node.

Quantitative growth follows an inverse-square-root law.

Abstract

In many neural networks, patterns controlling rhythmic behaviors are maintained across a wide range of periods. In the crustacean pyloric central pattern generator (CPG), a constant bursting pattern is preserved over a three-to-fivefold range of periods. We idescribe how neuromodulation could adjust neuronal properties to preserve phase relations as the period changes. We developed a biophysical model implementing a reduced pyloric network motif, which has a bursting neuron and two follower neurons interconnected through inhibitory synaptic coupling. We described cellular mechanisms supporting phase maintenance and investigated possible coordination between these mechanisms in four dynamically distinct ensembles of a pyloric CPG producing a triphasic pattern. The coordinated variation of the voltages of half-activation for potassium (VK2) and hyperpolarization-activated (Vh) currents provides a family of three mechanisms for control of burst duration, interburst interval, and latency to spiking. The mechanisms are determined by the Cornerstone bifurcation, one of the Shilnikov blue sky catastrophe scenarios. In Mechanism 1, in a bursting neuron, the burst duration increases as VK2 nears a blue-sky catastrophe bifurcation, while the interburst interval grows as Vh approaches a saddle-node on an invariant circle bifurcation. In Mechanism 2, a silent neuron responds with a single burst to short input; the burst duration grows as VK2 approaches a saddle-node bifurcation for periodic orbits. In Mechanism 3, a spiking neuron responds with a pause to short input; the pause duration grows as Vh nears a saddle-node bifurcation for stationary states. In all three mechanisms, the measured quantities grow without bound as the bifurcation parameter nears its critical value, consistent with an inverse-square-root law.