Fig. 1. Schematic representation electrode location distance issue in Euclidean space.

The left image shows a hypothetical SEEG trajectory passing through the folded cortex. SEEG recording electrodes are equally spaced along the trajectory. However, if the cortical grey matter is stretched out (as it would be in an inflated representation), the distances between the recording locations change. For example, the distance between electrodes 2 and 3 increases since the sulcus separates them. Note that the trajectory crosses a sulcus to demonstrate how sulci and gryi are represented on the inflated brain, not as a realistic trajectory.