A positive feedback at the cellular level promotes robustness and modulation at the circuit level

Area of Science:

• Neuroscience
• Computational Neuroscience
• Cellular Electrophysiology

Background:

• Rhythmic activities in neural circuits are fundamental to many brain functions.
• Half-center oscillators, composed of reciprocally inhibitory neuronal populations, are simple models for studying rhythmic circuits.
• Postinhibitory rebound, a cellular property, plays a role in generating rhythmic outputs.

Purpose of the Study:

• To investigate the role of cellular-level positive feedback mechanisms in the robustness and modulation of network-level rhythmic activity.
• To identify specific ionic currents responsible for essential cellular properties contributing to network dynamics.
• To determine the necessity of slow positive feedback for physiological modulation and robustness in rhythmic circuits.

Main Methods:

• Modeling of half-center oscillators with different ionic current properties.
• Analysis of cellular excitability, focusing on postinhibitory rebound.
• Comparison of rhythms generated by hyperpolarization-activated cation currents versus T-type calcium currents.

Main Results:

• A slow positive feedback mechanism, specifically from the T-type calcium current's slow activation, is essential for network rhythm robustness.
• This slow positive feedback enables physiological modulation of rhythmic activity at the circuit level.
• Hyperpolarization-activated cation currents, lacking slow activation, do not support these robust and modulated rhythmic properties.

Conclusions:

• The T-type calcium current's slow activation provides a critical cellular-level positive feedback essential for network rhythm robustness and modulation.
• Modeling network robustness and modulation requires retaining this specific cellular property at the network level.
• This study identifies a key cellular mechanism underlying the functional properties of neural rhythmic circuits.