Electrical Source Imaging in Stereoelectroencephalography: A Proof-of-Concept Study

Electrical source imaging (ESI) estimates the intracerebral generators of EEG signals. Although traditionally applied to scalp EEG sensors, recent studies suggested its potential applicability to intracerebral recordings. We systematically evaluated the localization accuracy of ESI applied to SEEG data rather than scalp EEG.

We compared three different inverse solution methods (standardized low-resolution electromagnetic tomography [sLORETA], minimum norm estimate, and dynamic statistical parametric mapping) in localizing the stimulation artifact in 12 subjects undergoing SEEG. Localization accuracy was defined as the Euclidean distance between the stimulation site and the peak of the estimated source.

Standardized low-resolution electromagnetic tomography showed the highest accuracy. For single stimuli, the mean localization error was 11.65 mm, improving to 9.28 mm when averaging 10 stimuli. Subcentimeter accuracy was achieved in 77.5% of averaged trials. Although localization based on the maximum amplitude artifact increased linearly with the distance from the nearest SEEG contact, sLORETA maintained higher accuracy, typically within ∼1 cm. The weak association between sLORETA error and sensor distance disappeared when excluding stimulations at the outermost boundaries of the explored region.

These results support the application of ESI to SEEG data for accurate source localization. Among tested methods, sLORETA was the most effective and may improve spatial interpretability in challenging epilepsy cases, including those with suboptimal spatial sampling.