Time-shift homotopic connectivity in mesial temporal lobe epilepsy

Abstract

Background and purpose: Voxel-mirrored intrinsic functional connectivity allows the depiction of interhemispheric homotopic connections in the human brain, whereas time-shift intrinsic functional connectivity allows the detection of the extent of brain injury by measuring hemodynamic properties. We combined time-shift voxel-mirrored homotopic connectivity analyses to investigate the alterations in homotopic connectivity in mesial temporal lobe epilepsy and assessed the value of applying this approach to epilepsy lateralization and the prediction of surgical outcomes in mesial temporal lobe epilepsy.

Materials and methods: Resting-state functional MR imaging data were acquired from patients with unilateral mesial temporal lobe epilepsy (n=62) (31 left- and 31 right-side) and healthy controls (n=33). Dynamic interhemispheric homotopic architecture seeding from each hemisphere was individually calculated by 0, 1, 2, and 3 repetition time time-shift voxel-mirrored homotopic connectivity. Voxel-mirrored homotopic connectivity maps were compared between the patient and control groups by using 1-way ANOVA for each time-shift condition, separately. Group comparisons were further performed on the laterality of voxel-mirrored homotopic connectivity in each time-shift condition. Finally, we correlated the interhemispheric homotopic connection to the surgical outcomes in a portion of the patients (n=20).

Results: The patients with mesial temporal lobe epilepsy showed decreased homotopic connectivity in the mesial temporal structures, temporal pole, and striatum. Alterations of the bihemispheric homotopic connectivity were lateralized along with delays in the time-shift in mesial temporal lobe epilepsy. The patients with unsuccessful surgical outcomes presented larger interhemispheric voxel-mirrored homotopic connectivity differences.

Conclusions: This study showed whole patterns of dynamic alterations of interhemispheric homotopic connectivity in mesial temporal lobe epilepsy, extending the knowledge of abnormalities in interhemispheric connectivity in this condition. Time-shift voxel-mirrored homotopic connectivity has the potential for lateralization of unilateral mesial temporal lobe epilepsy and may have the capability of predicting surgical outcomes in this condition.

Fig 1.

Workflow for time-shift voxel-mirrored homotopic connectivity calculation. A, Ts-VMHC of seeding from the left hemisphere. The left side was set as the seeding side; the right side, as the targeting side. The 0 TR, 1 TR, 2 TR, and 3 TR shifted time-courses of each voxel on the targeting side (blue line) were separately correlated with the time course of the mirrored voxel on the seeding side (red line), which generated 0 TR, 1 TR, 2 TR, and 3TR ts-VMHC hemispheric maps of the seeding (left) side. B, Similarly, 4 hemispheric ts-VMHC maps of the right side were also generated when taking the right hemisphere as the seeding side and the left hemisphere as the targeting side.

Fig 2.

Group comparisons of ts-VMHC maps between the patients and healthy controls. The left and right hemispheric ts-VMHC maps (0 TR, 1 TR, 2 TR, and 3 TR) of each patient group were compared with those of the HC by using 2-sample t tests (P < .05, AlphaSim corrected) under ANOVA. For a better visualization, we combined the comparison results of the left and right hemispheric ts-VMHC maps with a whole-brain map. The mesial temporal structures, limbic/paralimblic areas, and striatum areas show time-shift-dependent VMHC decreases.

Fig 3.

Laterality index analysis of ts-VMHC in mTLE. A, Group comparisons of voxelwise laterality maps of ts-VMHC. Along with the delay of time shifts, a more significant difference of VMHC laterality was found among the patient groups and healthy controls. B, Region of interest–based laterality analysis confirmed the above results. The region of interest was selected from the group comparing the result of voxelwise laterality map of ts-VMHC (white circle).

Fig 4.

Ts-VMHC and prediction of surgical outcomes of mTLE. The interhemispheric VMHC differences were compared by using 2-sample t tests between the patients with successful surgical outcomes and those with unsuccessful outcomes. The patients with unsuccessful surgical outcomes had larger differences than those with successful outcomes at each time-shift condition. Moreover, along with the time shifts, the interhemispheric VMHC differences increased in both the groups.