Current dipole orientation and distribution of epileptiform activity correlates with cortical thinning in left mesiotemporal epilepsy

Abstract

To evaluate cortical architecture in mesial temporal lobe epilepsy (MTLE) with respect to electrophysiology, we analyze both magnetic resonance imaging (MRI) and magnetoencephalography (MEG) in 19 patients with left MTLE. We divide the patients into two groups: 9 patients (Group A) have vertically oriented antero-medial equivalent current dipoles (ECDs). 10 patients (Group B) have ECDs that are diversely oriented and widely distributed. Group analysis of MRI data shows widespread cortical thinning in Group B compared with Group A, in the left hemisphere involving the cingulate, supramarginal, occipitotemporal and parahippocampal gyri, precuneus and parietal lobule, and in the right hemisphere involving the fronto-medial, -central and -basal gyri and the precuneus. These results suggest that regardless of the presence of hippocampal sclerosis, in a subgroup of patients with MTLE a large cortical network is affected. This finding may, in part, explain the unfavorable outcome in some MTLE patients after epilepsy surgery.

Fig. 1

Typical patterns of ECD distribution and orientation in Group A and B. A. Group A: ECDs are distributed in the anterior medial temporal lobe with vertical orientation. B. Group B: ECDs are distributed in the lateral temporal and frontal lobes with variable orientation. Note that in Group A the dipole orientation is consistent across the ECD locations, whereas Group B has variable dipole orientations.

Fig. 2

(Top) Statistical cortical thickness difference maps from the comparison of Group A and B. Yellow and red colors indicate thicker cortices in Group A, blue and turquoise colors indicate thicker cortices in Group B. All colored areas have the statistical difference of p < 0.05 (corrected for age and duration of epilepsy). Mean cortical thickness of each patient, obtained from the circled subregions of a) and b) is shown at the bottom of the figure, plotted versus age and duration of epilepsy.