Verbal Memory Dysfunction And Papez Circuit Impairment In Mesial Temporal Lobe Epilepsy:A Diffusion Tensor Imaging Study

Objective:Memory dysfunction is a common comorbidity in mesial temporal lobe epilepsy with hippocampal sclerosis(mTLE-HS).However,its mechanism is not well elucidated We observed the white matter damage underlying verbal memory deficit and further investigated the role of Papez circuit impairment in a cohort of mTLE-HSMethods:We recruited 58 unilateral mTLE-HS patients(27 right and 31 left)and 25 control subjects.Verbal memory scores and quotient was derived from Wechsler Memory Scale Revised,Chinese version(WMS-RC).The volume of hippocampus was measured by Freesurfer software.Fractional anisotropy(FA)and mean diffusivity(MD)values were compared between mTLE-HS patients and controls by Tract-Based Spatial Statistics(TBSS).Probabilistic diffusion tensor tractography(DTT)was used to reconstruct the fornix and parahippocampal cingulum(PHC).The relationship between diffusion tensor imaging(DTI)metrics and verbal memory scores was investigatedResults:Only left mTLE-HS patients had significant verbal memory dysfunction when compared with control subjects.More impaired verbal memory,more bigger volume of fimbria in right mTLE-HS.Widespread decreased FA was observed in both left and right mTLE-HS groups compared to controls.A diffuse increase of MD was observed in the bilateral hemisphere in right mTLE-HS group;while it is mainly limited in the left hemisphere and right frontal lobe in left mTLE-HS group.Compared with control subjects,abnormal DTI metrics of bilateral fornix and ipsilateral PHC was found in left mTLE-HS while only ipsilateral fornix showed DTI abnormalities in right mTLE-HS No difference was demonstrated by TBSS between moderate verbal memory group and worse verbal memory group in either left or right mTLE-HS group.No relation between volumes of hippocampus and verbal memory scores was found in each subgroup after correction of age.The MD value of left fornix was negatively correlated with verbal memory score only in left TLE-HS group,but not in right mTLE-HS or control subjectsSignificance:The left and right mTLE-HS displayed different verbal memory function as well as different patterns of Papez circuit impairment.The association between fornix and verbal memory could existed from the level of entire fibers by using tract-based approach even if a voxel-wise comparison was negative in regional white matter integrity.