Ideal current dipoles are appropriate source representations for simulating neurons for intracranial recordings

Abstract

Objective: To determine whether dipoles are an appropriate simplified representation of neural sources for stereo-EEG (sEEG).

Methods: We compared the distributions of voltages generated by a dipole, biophysically realistic cortical neuron models, and extended regions of cortex to determine how well a dipole represented neural sources at different spatial scales and at electrode to neuron distances relevant for sEEG. We also quantified errors introduced by the dipole approximation of neural sources in sEEG source localization using standardized low-resolution electrotomography (sLORETA).

Results: For pyramidal neurons, the coefficient of correlation between voltages generated by a dipole and neuron model were > 0.9 for distances > 1 mm. For small regions of cortex (∼0.1 cm²), the error in voltages between a dipole and region was < 100 µV for all distances. However, larger regions of active cortex (>5 cm²) yielded > 50 µV errors within 1.5 cm of an electrode when compared to single dipoles. Finally, source localization errors were < 5 mm when using dipoles to represent realistic neural sources.

Conclusions: Single dipoles are an appropriate source model to represent both single neurons and small regions of active cortex, while multiple dipoles are required to represent large regions of cortex.

Significance: Dipoles are computationally tractable and valid source models for sEEG.

Keywords: Computational modeling; Dipole; Intracranial EEG; Inverse problem; Source localization.