The default mode network (DMN) consists of the deactivation of specific regions during the performance of cognitive tasks and activation during resting or mind wandering. Several pieces of evidence indicate the impairment of DMN in patients with mesial temporal lobe epilepsy (MTLE). However, most of these studies combined different underlying etiologies, failing to disentangle the influence of seizures and presence and side of hippocampal sclerosis (HS). We included 119 patients with MTLE divided into right-HS (n = 42), left-HS (n = 46), and magnetic resonance imaging (MRI)-negative MTLE (n = 31) and controls (n = 59). All underwent resting-state seed-based functional connectivity (FC), with a seed placed at the posterior cingulate cortex (PCC), an essential node for the DMN. To access group inferences, we used an SPM (Statistical Parametric Mapping) full-factorial model to compare patterns of activation using pairwise comparisons among all groups. Our results indicate a different pattern of DMN FC when controlling for side and presence of HS. The group with right-HS had increased FC in the left angular gyrus and the left middle occipital gyrus, when compared to controls, and increased FC of the left hippocampus when compared to the group with left-HS. The MRI-negative group had increased FC of the left hippocampus, left ventral diencephalon, and left fusiform gyrus as compared to left-HS, but did not show any areas of reduced FC compared to controls. By contrast, the group with left-HS did not show areas of increased FC compared to controls or the right-HS and had reduced FC in the left hippocampus compared to controls. Hence, the right-HS presented increased FC in areas related to the DMN in the left hemisphere; the MRI-negative group also showed increased FC in left-sided structures close to temporal lobe when compared to left-HS, probably indicating engagement in a compensatory system. In a subanalysis considering only the MRI-negative with left-sided EEG (electroencephalogram) subgroup, we found differences against controls, with left angular gyrus more connected in the first group, but no significant differences when compared to the group with left-HS. We conclude that the origin of seizures on the left hemisphere seems to engender a less prominent capacity of recruiting other neighbor areas related to DMN as compared to right-HS and controls. Considering recent studies that have revealed the importance of DMN for cognitive skills and memory, our findings may indicate that deficiencies exhibited by patients with left-HS temporal lobe epilepsy (TLE) in connecting to the DMN could be a surrogate marker of their known worse neuropsychological performance. Further studies with direct comparisons between cognitive tests and FC within the DMN are needed to validate these findings, especially for MRI-negative patients. This article is part of the Special Issue "NEWroscience 2018".

中文翻译：

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伴和不伴海马硬化的颞叶癫痫的默认模式网络模式

默认模式网络 (DMN) 由执行认知任务期间特定区域的停用和休息或走神期间的激活组成。几项证据表明内侧颞叶癫痫 (MTLE) 患者的 DMN 受损。然而，大多数这些研究结合了不同的潜在病因，未能解开癫痫发作和海马硬化症 (HS) 的存在和侧面的影响。我们纳入了 119 名 MTLE 患者，分为右侧 HS (n = 42)、左侧 HS (n = 46) 和磁共振成像 (MRI) 阴性 MTLE (n = 31) 和对照 (n = 59)。所有人都经历了基于静息状态种子的功能连接 (FC)，将种子放置在后扣带皮层 (PCC)，这是 DMN 的重要节点。要访问组推断，我们使用 SPM（统计参数映射）全因子模型在所有组之间使用成对比较来比较激活模式。我们的结果表明，在控制 HS 的侧面和存在时，DMN FC 的模式不同。与对照组相比，右侧 HS 组的左侧角回和左侧枕中回的 FC 增加，与左侧 HS 组相比，左侧海马的 FC 增加。与左侧 HS 相比，MRI 阴性组左海马、左腹侧间脑和左梭状回的 FC 增加，但与对照组相比未显示任何 FC 减少的区域。相比之下，与对照组或右侧 HS 相比，左侧 HS 组没有显示出 FC 增加的区域，并且与对照组相比，左侧海马中的 FC 减少。因此，右侧 HS 表现为左半球 DMN 相关区域的 FC 增加；与左侧 HS 相比，MRI 阴性组还显示靠近颞叶的左侧结构中 FC 增加，可能表明参与代偿系统。在仅考虑左侧脑电图（脑电图）MRI 阴性亚组的亚组分析中，我们发现与对照组的差异，第一组左侧角回连接更多，但与左侧 HS 组相比没有显着差异。我们得出结论，与右 HS 和对照相比，左半球癫痫发作的起源似乎导致招募与 DMN 相关的其他邻近区域的能力不那么突出。考虑到最近的研究揭示了 DMN 对认知技能和记忆的重要性，我们的研究结果可能表明，左 HS 颞叶癫痫 (TLE) 患者在连接到 DMN 方面表现出的缺陷可能是他们已知的更差的神经心理表现的替代标志。需要进一步研究直接比较 DMN 内的认知测试和 FC，以验证这些发现，尤其是对于 MRI 阴性患者。本文是特刊“NEWroscience 2018”的一部分。