Hippocampal dysfunction is associated with memory impairment in multiple sclerosis: A volumetric and functional connectivity study

BACKGROUND: Previous studies have suggested a relationship between neuroanatomical and neurofunctional hippocampal alterations and episodic memory impairments in multiple sclerosis (MS) patients OBJECTIVE: We examined hippocampus volume and functional connectivity (FC) changes in MS patients with different episodic memory capabilities. METHODS: hippocampal subfield volume and FC changes were compared in two subgroups of MS patients with and without episodic memory impairment (MSi and MSp, respectively) and healthy controls. A discriminant function (DF) analysis was used to identify which of these neuroanatomical and neurofunctional parameters were the most relevant components of the mnemonic profiles of HC, MSp and MSi. RESULTS: MSi showed reduced volume in several hippocampal subfields compared to MSp and HC. Ordinal gradation (MSi>MSp>HC) was also observed for FC between the posterior hippocampus and several cortical areas. DF-based analyses revealed that reduced right fimbria volume and enhanced FC at the right posterior hippocampus were the main neural signatures of the episodic memory impairments observed in the MSi group. CONCLUSIONS: Before any sign of episodic memory alterations (MSp), FC increased on several pathways that connect the hippocampus with cortical areas. These changes further increased when the several hippocampal volumes reduced and memory deficits appeared (MSi).This study was sponsored by grants P1-1B2014-15 awarded by Universitat Jaume I and PSI2015-67285-R awarded by MINECO to Dr. Cristina For