Fleury, Marine Nadine; (2025) Longitudinal Changes in the Episodic Memory Network Following Anterior Temporal Lobe Resection. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Anterior temporal lobe resection (ATLR) is an effective treatment for medicationresistant TLE but carries a 40% risk of significant episodic memory decline. Evidence indicates that TLE is a network disorder extending beyond the seizure-onset zone. Postoperative memory reorganisation has been explored using task-based and resting-state functional MRI within two years post-ATLR. This thesis investigates episodic memory network changes over 10 years after ATLR and their relationship to memory function. Preoperatively, there were functional connectivity changes in the episodic memory network associated with TLE. I delineated for the first time an efficient network in unilateral TLE compared to controls, disrupted with greater disease burden. The medial temporal lobe engaged widespread regions during memory encoding. Postoperatively, functional and structural connectivity changes persisted over 10 years. Presurgical clinical and cognitive factors influenced postoperative memory outcomes. I defined lasting network changes supporting memory function 10 years post-surgery. Longitudinal analysis of functional connectivity changes in memory encoding networks from short-term (3-12 months) to long-term (10 years) after unilateral ATLR revealed ongoing plasticity and identified efficient long-term plasticity patterns for continuing recovery of memory function. Using diffusion-weighted MRI, I explored long-term functional plasticity in the episodic memory network in relation to structural network changes. The microstructural integrity of medial temporal fibre bundles was assessed using diffusion tensor imaging and neurite orientation dispersion and density imaging (NODDI). I revealed that neural information transfer in parahippocampal pathways may facilitate long-term memory recovery. Contralateral fronto-temporal connectivity supported verbal memory after left ATLR and visual memory regardless of surgical laterality. Lastly, memory outcomes were related to differences in NODDI-weighted connectivity in regions associated with long-term functional plasticity. There were long-term changes in structural connectivity supporting memory function 10 years post-ATLR. The neurite orientation dispersion index emerged as a potential neuroimaging marker for new structural connectivity underlying long-term postoperative function.

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