Correlation between intra- and extracranial background EEG.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Scalp electroencephalography (EEG) is a primary tool for brain activity recording.
• Volume conduction through tissues like brain, CSF, skull, and scalp degrades EEG spatial resolution and amplitude.
• Previous research on volume conduction relied on head models or interictal spike analysis.

Purpose of the Study:

• To compare information content between intracranial EEG (iEEG) and scalp EEG.
• To investigate the extent of volume conduction effects on EEG signals.
• To determine the cortical area influencing scalp EEG.

Main Methods:

• A novel experimental setup enabling simultaneous intra- and extracranial EEG recording.
• Analysis of signal correlation between closely spaced iEEG channels.
• Comparison of correlated patterns between iEEG and scalp EEG channels at varying distances.
• Estimation of the cortical area influencing scalp EEG signals.

Main Results:

• Intracranial EEG channels showed correlated patterns within 30 mm.
• Intra- and extracranial EEG channels exhibited partial correlation within 40 mm.
• Extracranial EEG channels likely correlated over greater distances.
• The estimated cortical area influencing scalp EEG was up to 45 cm², exceeding previous reports.

Conclusions:

• The study provides a more realistic assessment of EEG volume conduction effects.
• Scalp EEG spatial resolution is limited, but the influencing cortical area is substantial.
• Findings enhance the understanding of EEG signal propagation and interpretation.