Auditory sensitivity may require dynamically unstable spike generators: evidence from a model of electrical...

Area of Science:

• Neuroscience
• Computational Biology
• Auditory System Research

Background:

• The auditory nerve exhibits extreme sensitivity to minute electrical stimulation (<0.5% modulation).
• Understanding the biophysical mechanisms underlying this high sensitivity is critical for auditory prosthetics and neuroscience.

Purpose of the Study:

• To investigate the role of dynamical instability in auditory nerve sensitivity to electrical stimulation.
• To model spike generation using a modified FitzHugh-Nagumo model and assess the impact of noise.

Main Methods:

• Utilized a modified FitzHugh-Nagumo model to simulate neuronal spike generation.
• Analyzed the system's dynamics, specifically focusing on Lyapunov exponents to identify instability.
• Investigated the influence of varying input noise levels on model sensitivity.

Main Results:

• Dynamical instability, characterized by a positive Lyapunov exponent, successfully accounts for the auditory nerve's high sensitivity.
• This sensitivity is maintained provided that the input noise amplitude remains below a critical threshold.
• The model suggests that physiological noise, like that from sodium channels, has a small amplitude.

Conclusions:

• Spike generator instability is a necessary mechanism to explain the high sensitivity of the auditory nerve to electrical stimuli.
• The findings support the hypothesis that low physiological noise levels are compatible with high sensitivity.
• Dynamical instability may also explain the cross-fiber independence observed during acoustic stimulation.