Interhemispheric functional and structural alterations and their relationships with alertness in unilateral temporal...

Many neuroimaging studies have shown that temporal lobe epilepsy (TLE) is associated with functional and structural abnormalities at specific brain areas. Unfortunately, relatively limited information has been presented about the alterations of interhemispheric functional and anatomic connectivity in patients with unilateral TLE. In the present study, we investigated interhemispheric functional connectivity using a voxel-mirrored homotopic connectivity (VMHC) method. We further revealed fractional anisotropy (FA) changes in the areas with abnormal VMHC values in TLE patients by diffusion tensor imaging (DTI). Moreover, their relationships with alertness in patients with drug-naïve unilateral TLE were also investigated.

Forty-three patients with unilateral TLE (21 left TLE and 22 right TLE) and 20 normal controls (NC) were recruited for case-control study. All of the subjects underwent acquisition of resting-state functional magnetic resonance images, Mini-Mental State Examination (MMSE) and the attention network test. DTI images were collected in 26 patients with unilateral TLE (10 left TLE and 16 right TLE) and 20 NCs. Functional connectivity between bilateral homotopic voxels was calculated. Homotopic regions showing abnormal functional connectivity in patients were adopted as regions of interest for the analysis of DTI. The FA values, MMSE scores, and alertness were compared between groups. Correlation analyses were employed to examine the relationships between each radiographic parameter (VMHC and FA) and each clinical and neuropsychological parameter in patients with drug-naïve unilateral TLE.

Compared with NC, patients with left TLE exhibited significantly higher VMHC values in the bilateral angular gyrus, inferior occipital gyrus and superior parietal gyrus and lower VMHC values in the bilateral supplementary motor area, inferior parietal lobule, middle temporal gyrus, and medial superior frontal gyrus. In patients with right TLE, higher VMHC values were found in the bilateral inferior occipital gyrus, parahippocampal gyrus and cerebellum; lower VMHC values were observed in the bilateral middle temporal gyrus and precentral gyrus/inferior frontal gyrus. FA values of the commissural fiber bundles connecting the bilateral parahippocampal gyrus were smaller in the right TLE than those in the NC group. Meanwhile, the alerting effect of patients was determined to be impaired and positively correlated with FA values of the commissural fiber bundles connecting the bilateral parahippocampal gyrus in right TLE patients.

Our findings indicate that the bilateral parahippocampal gyrus may be important to the pathophysiology of patients with drug-naïve unilateral TLE. The significant correlation between the FA values and alertness indicates that structural changes are involved in the alterations in the alertness network in unilateral right TLE patients.