Alterations in Hippocampal Functional Connectivity in patients with Mesial Temporal Sclerosis

Introduction: Medial temporal sclerosis (MTS) is a form of mesial temporal lobe epilepsy (mTLE). It is typically characterized by structural alterations in hippocampus (HC) and related mesial temporal lobe (MTL) network. Resting state functional connectivity (RSFC) is considered an ideal technique in quantifying the dysfunction and maladaptation in MTL network. It is well- demonstrated that the seizure effects go beyond epileptogenic zones and alterations in connectivity are fairly widespread across cortical and subcortical regions. This study aims to assess the alterations in RSFC in hippocampus in patients with MTS. Materials and Methods: Resting state Functional magnetic resonance imaging was performed during interictal activity on 18 patients with MTS (7 patients with right and 11 patients with left MTS). Preprocessing included removing the first 10 time points, slice timing, head motion correction, normalization and removing the linear fMRI signal trend. Processing and statistical analysis were conducted using DPARSF and MATLAB, respectively. For all patients, the RSFC for both right and left hippocampi to 116 regions of interest (ROIs) were calculated and statistically analyzed. Connectivity of left and right hippocampi were compared between left and right MTS cohorts using paired t-student test. Results: Statistically significant differences between left and right hippocampi were observed in 1 and 15 ROIs for right and left MTS cohorts, respectively. Left paraHippocampus was the only ROI with significant difference in RSFC with right and left hippocampi in right MTS patients. Left Amygdala, Right Rolandic_Ope, Cingulum_posterior, paraHippocampus, Occipital_Inf, Fusiform, Parietal_Inf, Supra Marginal, Angular, Heschl, Temporal_Sup, Temporal_Mid, Temporal_Pole_Mid, Temporal_Inf gyri, and Cerebelum_4_5 showed significant difference between their connectivity with respect to left and right hippocampi in patients with left MTS. Conclusion: Left MTS may be associated with more extensive network impairment compared to right MTS. This result is in agreement with previous studies (Pereira et al and Doucet et al). Our findings also show that the behaviour of left paraHippocampus in the alteration in RSFC can be used as an indication for Right MTS.