Scalp EEG Signals: Generators and Dipoles

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Scalp electroencephalogram (EEG) interpretation traditionally focuses on negative phase reversals.
• This method oversimplifies the complex biophysical principles of cortical current generation.
• EEG signals originate from extracellular currents of postsynaptic potentials in pyramidal neurons.

Purpose of the Study:

• To highlight the importance of understanding dipole orientation in EEG signal generation.
• To advocate for a topographic approach in EEG interpretation, considering both positive and negative poles.
• To improve diagnostic accuracy by aligning EEG interpretation with neurophysiologic principles.

Main Methods:

• Review of biophysical principles of EEG generation.
• Analysis of scalp voltage topography influenced by dipole orientation (radial, tangential, oblique).
• Discussion of electrode placement, montage selection, and digital filtering effects.
• Validation using simultaneous MEG-EEG recordings.

Main Results:

• Dipole orientation significantly influences scalp voltage distribution.
• Both positive and negative scalp poles offer valuable insights into source localization.
• Simultaneous MEG-EEG confirms the physiologic significance of scalp positivities.

Conclusions:

• A comprehensive interpretation of EEG signals requires considering both positive and negative polarities.
• Shifting from solely relying on negativity to a topographic approach enhances diagnostic accuracy.
• This approach aligns EEG interpretation with a more complete understanding of neurophysiology.