On the origin of the extracellular action potential waveform: A modeling study

Area of Science:

• Neuroscience
• Computational Biology
• Electrophysiology

Background:

• Extracellular unit recording typically detects spike occurrences.
• Theoretical potential exists for extracellular recordings to reveal intracellular action potential features.

Purpose of the Study:

• To develop a model system for extracellular action potentials (EAPs) capturing features of simultaneous intracellular and extracellular recordings.
• To investigate how EAP waveforms relate to intracellular events and neuronal properties.

Main Methods:

• Utilized the line source approximation method (Holt and Koch) to model EAP voltage.
• Developed a model system based on simultaneous intracellular and extracellular recordings of CA1 pyramidal neurons in vivo.
• Compared model predictions with compartmental models of reconstructed neurons.

Main Results:

• The model accurately reproduced EAP waveform and amplitude.
• Achieving simultaneous good matches for both intracellular and extracellular waveforms proved challenging.
• EAP waveform variations were explained by electrode position relative to the neuron.
• Dendritic morphology had minimal impact on the EAP waveform.
• Varied ionic current compositions in different cells were reflected in EAP features.

Conclusions:

• Extracellular action potential waveforms provide constraints on neuronal models.
• EAP waveform analysis can reveal information about intracellular ionic currents.
• Electrode proximity is a key determinant of EAP waveform characteristics.