Relationship Between EEG Electrode and Functional Cortex in the International 10 to 20 System

Area of Science:

• Neuroscience
• Medical Imaging
• Electrophysiology

Background:

• Understanding the precise relationship between scalp electroencephalography (EEG) electrodes and underlying cortical function is crucial.
• Variability in this anatomical relationship can affect the accuracy of EEG interpretations.

Purpose of the Study:

• To quantify the anatomical variability between scalp EEG electrode positions and functionally defined eloquent cortical areas using functional magnetic resonance imaging (fMRI).

Main Methods:

• MRI-compatible fiducial markers were placed at standard EEG electrode locations (Cz, C3/C4, T3/T4, F7/F8) in 10 healthy subjects.
• fMRI was used to identify BOLD signal changes in primary motor and language cortices during specific activation paradigms.
• Distances between fiducial markers and activated brain regions were measured.

Main Results:

• Distances between EEG electrode locations and the BOLD signal in motor and language cortices ranged from 16 to 42 mm.
• The distance from the skin to the underlying cortex accounted for 11 to 21 mm of this measurement.
• Significant variability was observed in the electrode-to-cortex distances.

Conclusions:

• Considerable anatomical variation exists between scalp EEG electrode positions and fMRI-defined eloquent cortex.
• This variability may be underestimated in patient populations with neurological disorders like epilepsy.
• The findings highlight the potential clinical and surgical importance of electrode placement variability in relation to cortical function.