Abstracts

Rationale: The thalamus is considered to play a crucial role in determining surgical outcome following anterior temporal lobectomy (ATL) in temporal lobe epilepsy (TLE)1. Before successfully quantifying the impact of the thalamus on ATL outcomes, this structure’s own intrinsic connectivity must be understood. Accordingly, we characterize the thalamic intrinsic connectivity through resting-state fMRI (rsfMRI) longitudinally, exploring its change pre- to post-surgery. Methods: Twenty-six TLE patients (L/R=14/12) underwent two 5-min rsfMRI scans prior and ~1 year following their ATLs. All patients were seizure free at the time of second scan. A 5-min rsfMRI scan was collected from 28 matched healthy controls (HC). After standard post-processing, voxel-wise amplitude of low frequency fluctuations (ALFF, power of low frequency oscillation) and intrinsic connectivity contrasts (ICC, mean square root of all connections) were calculated for the bilateral thalami. The ICC was calculated within the ipsilateral thalamus (intra) and contralateral thalamus (inter) respectively, and the analyses was focused on their contrast, ICC(intra-inter). Mean values of ALFF and ICC were extracted from thalamic subdivisions (8 each side), using a multimodal connectome based atlas2 (Fig1A). Deviation scores (Z) were then calculated based on the data from HC’s. Lastly, data of the RTLEs were flipped right-to-left to maintain access to ictal versus nonictal thalamus. Results: In TLE, repeated measures ANOVAs revealed significant session (pre/post), by side (ictal/ nonictal), by thalamic subdivision interactions for both measures (ALFF: F=5.1, p < 0.001; ICC: F=9.1, p < 0.001. Fig1B, C). Most thalamic subdivisions showed stronger ALFF preoperatively comparing to HC’s, and a significant increase in ALFF after surgery, specifically involving ictal subdivisions (medial prefrontal, rostral temporal). No significant postoperative change was observed in the nonictal thalamus. In contrast, no TLE/HC difference in ICC was observed preoperatively. Post-surgery, ICC(intra-inter) were increased in ictal subdivisions (occipital, rostral and caudal temporal), and decreased in the homologous nonictal subdivisions. Conclusions: These results show broad intrinsic thalamic organization abnormalities in TLE prior to surgery in connectivity measures of power (ALFF) but not strength (ICC). ATL produces a consistent pattern of increases both in power and intra-thalamic strength, but only for the ictal thalamus. The nonictal thalamus behaved very differently in response to ATL, showing only increase in inter-thalamic strength. The subdivisions involved are mainly connected to the temporal lobe. These findings provided the first evidence of adaptive changes in the thalamus for TLE following ATL, which should be explored further as potential catalysts of seizure freedom.References:1              He, X. et al. (2017) Presurgical thalamic "hubness" predicts surgical outcome in temporal lobe epilepsy. Neurology 88, 2285-2293.2              Fan, L. et al. (2016) The Human Brainnetome Atlas: A New Brain Atlas Based on Connectional Architecture. Cereb Cortex 26, 3508-3526. Funding: None.