Contribution of the Axon Initial Segment to Action Potentials Recorded Extracellularly

Area of Science:

• Neuroscience
• Computational Biology
• Electrophysiology

Background:

• Action potentials (APs) are fundamental electrical signals in neurons, critical for neural communication.
• Extracellular recordings capture these APs, but their precise origin and interpretation, especially concerning the dipole formation, remain areas of active research.
• The axon initial segment (AIS) is the primary site for AP initiation.

Purpose of the Study:

• To investigate the dipole formation at the onset of an action potential (AP) involving the soma and the axon initial segment (AIS).
• To characterize the extracellular AP (EAP) signature generated by this dipole.
• To contrast EAP waveforms and spatial dependence in models with axonal versus somatic AP initiation.

Main Methods:

• Detailed morphological modeling of a reconstructed pyramidal neuron.
• Simulations to demonstrate dipole formation and its extracellular signature.
• Comparative analysis of EAP waveforms in models with axonal and somatic AP initiation.

Main Results:

• Demonstrated dipole formation between somatodendritic compartments and the AIS during axonal AP initiation.
• Observed distinct EAP waveforms and spatial dependencies based on AP initiation site (axonal vs. somatic).
• Confirmed that the classical soma-dendrites dipole is specific to somatic AP initiation.

Conclusions:

• The study clarifies the origin of extracellular APs (EAPs), attributing specific signatures to axonal AP initiation involving the AIS.
• Findings impact the interpretation of extracellular recordings for single-neuron activity and electrophysiological typing.
• Provides insights into the generation of macroscopic extracellular potentials in the brain.