Pitfalls in the dipolar model for the neocortical EEG sources

Area of Science:

• Neuroscience
• Biophysics

Background:

• The electroencephalogram (EEG) is a key tool for studying brain activity.
• For decades, EEG current sources have been modeled as dipolar.
• This model's biophysical accuracy requires re-evaluation.

Purpose of the Study:

• To revise the biophysical foundations of the EEG dipolar model.
• To investigate the nature of intracortical current sources.
• To assess the contribution of monopolar components to EEG signals.

Main Methods:

• Electrophysiological recordings in anesthetized Wistar rats.
• Three-dimensional extracellular potential recordings in the barrel field.
• Estimation of intracortical multipolar moments from single neurons and neuronal populations.
• Concurrent high-resolution skull EEG and laminar local field potential recordings.
• EEG inverse solutions (multiple dipole fitting, distributed) to estimate equivalent dipoles.

Main Results:

• Backpropagating spikes in pyramidal cells generated significant dipolar components.
• Spiny stellate cells exhibited negligible dipolar moments.
• Detectable monopolar field components were found at single-unit and mesoscopic levels.
• Mesoscopic multipolar components were absorbed by equivalent dipoles in EEG inverse solutions.

Conclusions:

• The single equivalent dipole model is insufficient for precisely representing rodent neocortical EEG sources.
• Monopolar components are significant at the mesoscopic level and must be considered.
• A revised biophysical model of EEG generation is needed.