A Novel Phase Portrait to Understand Neuronal Excitability

TL;DR

This paper revises the classic Fitzugh-Nagumo phase portrait by incorporating calcium channels into Hodgkin-Huxley models, significantly enhancing the understanding of neuronal excitability and firing modes.

Contribution

It introduces a modified phase portrait that includes calcium currents, expanding the modeling capabilities of neuronal excitability and capturing key electrophysiological signatures.

Findings

Revised phase portrait with calcium channels alters traditional models.

Model captures firing mode control by calcium conductance.

Highlights a core dynamical mechanism in thalamocortical neurons.

Abstract

Fifty years ago, Fitzugh introduced a phase portrait that became famous for a twofold reason: it captured in a physiological way the qualitative behavior of Hodgkin-Huxley model and it revealed the power of simple dynamical models to unfold complex firing patterns. To date, in spite of the enormous progresses in qualitative and quantitative neural modeling, this phase portrait has remained the core picture of neuronal excitability. Yet, a major difference between the neurophysiology of 1961 and of 2011 is the recognition of the prominent role of calcium channels in firing mechanisms. We show that including this extra current in Hodgkin-Huxley dynamics leads to a revision of Fitzugh-Nagumo phase portrait that affects in a fundamental way the reduced modeling of neural excitability. The revisited model considerably enlarges the modeling power of the original one. In particular, it captures essential electrophysiological signatures that otherwise require non-physiological alteration or considerable complexication of the classical model. As a basic illustration, the new model is shown to highlight a core dynamical mechanism by which the calcium conductance controls the two distinct firing modes of thalamocortical neurons.