Distinctive Structural and Effective Connectivity Changes of Semantic Cognition Network across Left and Right Mesial Temporal Lobe Epilepsy Patients

Yi Shan,Xiaocui Wang,Guoguang Zhao,Jie Lu,Kun Shang,Peipei Wang,Xiaotong Fan,Hao Yan,Yongzhi Shan

doi:10.1155/2016/8583420

Abstract

Occurrence of language impairment in mesial temporal lobe epilepsy (mTLE) patients is common and left mTLE patients always exhibit a primary problem with access to names. To explore different neuropsychological profiles between left and right mTLE patients, the study investigated both structural and effective functional connectivity changes within the semantic cognition network between these two groups and those from normal controls. We found that gray matter atrophy of left mTLE patients was more severe than that of right mTLE patients in the whole brain and especially within the semantic cognition network in their contralateral hemisphere. It suggested that seizure attacks were rather targeted than random for patients with hippocampal sclerosis (HS) in the dominant hemisphere. Functional connectivity analysis during resting state fMRI revealed that subregions of the anterior temporal lobe (ATL) in the left HS patients were no longer effectively connected. Further, we found that, unlike in right HS patients, increased causal linking between ipsilateral regions in the left HS epilepsy patients cannot make up for their decreased contralateral interaction. It suggested that weakened contralateral connection and disrupted effective interaction between subregions of the unitary, transmodal hub of the ATL may be the primary cause of anomia in the left HS patients.

Highlights

Temporal lobe epilepsy (TLE) is the most common drug resistant epilepsy in adults
The majority of seizures in TLE are associated with hippocampal sclerosis (HS) or other temporal lobe abnormalities [1], which can reliably be detected in vivo by MRI [2, 3]
In the left HS subgroup, gray matter volume (GMV) loss was found in 12 ipsilateral Regions of Interest (ROIs) and 7 contralateral ROIs (Figure 1, left column); in the right HS subgroup, GMV loss was in 2 ipsilateral ROIs and 1 contralateral ROI (Figure 1, right column)

Summary

Introduction

Temporal lobe epilepsy (TLE) is the most common drug resistant epilepsy in adults. The majority of seizures in TLE are associated with hippocampal sclerosis (HS) or other temporal lobe abnormalities [1], which can reliably be detected in vivo by MRI [2, 3]. Patients with resection for TLE generally do not report comprehension difficulties through either clinical reports or formal testing [4] but complain of significant amnesia and anomia which reflect a semantic weakness [5,6,7]. A systematic review calculating pooled estimates of neuropsychological outcomes reported a 44% risk of decline in verbal memory and 34% risk of decline in naming after left-sided surgery [8]. There are no reports of naming decline following nondominant hemisphere resection [9]. It reflects that left and right HS patients may experience distinctive functional reorganization in the nonepileptic temporal lobe under distinctive compensatory mechanisms to sustain key cognitive functions, such as language

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