The location of electrode contacts was ascertained by MRI in each patient. MRI scans were acquired in sagittal, adjusted coronal (perpendicular to the longitudinal axis of the hippocampus), and axial (parallel to this axis) planes, typically in 2 mm sliced T1- and T2-weighted sequences as well as 3 mm sliced FLAIR sequences. Anatomical boundaries were ascertained according to Insausti et al. (1998). Among others, we used the collateral sulcus, hippocampal fissure, and sulcus semiannularis as landmarks to delineate the entorhinal cortex from neighboring structures. As detailed above, only patients with at least two clearly entorhinal contacts adjacent to at least two clearly hippocampal contacts were included in the study.
