Abstract
The default-mode network (DMN) is a major resting-state network. It can be divided in two distinct networks: one is composed of dorsal and anterior regions [referred to as the dorsal DMN (dDMN)], while the other involves the more posterior regions [referred to as the ventral DMN (vDMN)]. To date, no studies have investigated the potentially distinct impact of temporal lobe epilepsy (TLE) on these networks. In this context, we explored the effect of TLE and anterior temporal lobectomy (ATL) on the dDMN and vDMN. We utilized two resting-state fMRI sessions from left, right TLE patients (pre-/post-surgery) and normal controls (sessions 1/2). Using independent component analysis, we identified the two networks. We then evaluated for differences in spatial extent for each network between the groups, and across the scanning sessions. The results revealed that, pre-surgery, the dDMN showed larger differences between the three groups than the vDMN, and more particularly between right and left TLE than between the TLE patients and controls. In terms of change post-surgery, in both TLE groups, the dDMN also demonstrated larger changes than the vDMN. For the vDMN, the only changes involved the resected temporal lobe for each ATL group. For the dDMN, the left ATL group showed post-surgical increases in several regions outside the ictal temporal lobe. In contrast, the right ATL group displayed a large reduction in the frontal cortex. The results highlight that the two DMNs are not impacted by TLE and ATL in an equivalent fashion. Importantly, the dDMN was the more affected, with right ATL having a more deleterious effects than left ATL. We are the first to highlight that the dDMN more strongly bears the negative impact of TLE than the vDMN, suggesting there is an interaction between the side of pathology and DM sub-network activity. Our findings have implications for understanding the impact TLE and subsequent ATL on the functions implemented by the distinct DMNs.
Highlights
The default-mode network (DMN) has been identified as one of the most robust and consistent resting-state network [see review of Ref. [1, 2]]
LTLE groups did not differ by age of seizure onset, illness duration, number of anti-epileptic drugs, presence/absence of unilateral mesial temporal sclerosis (MTS), nor the time interval between the fMRI scans and surgery (Table 1)
We demonstrate that the subdivisions of the well-known defaultmode resting-state network are effected differently by both the original temporal lobe epilepsy (TLE) pathology, and subsequent anterior temporal lobectomy (ATL) procedure
Summary
The default-mode network (DMN) has been identified as one of the most robust and consistent resting-state network [see review of Ref. [1, 2]]. While much about its function remains unclear, research has suggested it is engaged in the maintenance of “tonic” or baseline cognitive processing related to self-awareness, episodic memory, or the modulation of internal (mental) versus external tasks. Others have linked it to anticipatory cognitive processes, the strength of cognitive reserve, or consciousness [see review of Ref. There has been new evidence that this network is modulated by the nature of the spontaneous thoughts during a conscious resting-state [3, 4] It primarily consists of posterior cingulate cortex (PCC)/precuneus, ventral anterior cingulate cortex (ACC)/mesial prefrontal cortex, angular gyri, lateral temporal cortex, and mesial temporal lobes. The second division involves posterior and mesial temporal regions [referred to as the ventral DMN (vDMN)], and engages during decision-making related to constructing a mental scene, a scene called up from episodic or semantic memory
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