How well does electrical source imaging reconstruct neural time series? Evidence from simultaneous scalp and intracranial EEG recordings

Electrical source imaging of spontaneous activity in 34 patients with drug-resistant focal epilepsy reconstructs virtual intracranial EEG time series only weakly, with a highest estimated correlation of 0.126.

• Why it matters: It is unclear whether scalp EEG–based electrical source imaging preserves the temporal dynamics of spontaneous brain activity beyond estimating source locations.
• What they did: Using simultaneous high-density EEG and intracranial EEG in 34 patients, four ESI approaches (three distributed source models and one beamformer) generated virtual iEEG signals at iEEG electrode locations, compared via Pearson correlations plus peak localization error and spatial deviation.
• The result: Temporal reconstruction is limited (max correlation 0.126), with localization errors of ~3 cm and substantial spatial leakage; quality decreases with electrode depth and higher frequency, but improves with higher epileptic spike rates, and beamforming shows the weakest temporal reconstruction.