Although functional connectivity (FC) studies in temporal lobe epilepsy (TLE) have revealed alterations in brain resting state (RS) networks (mainly in the Default Mode Network (DMN)), fewer studies have investigated the impact of unilateral and bilateral hippocampal sclerosis (HS) on FC.

Compare patterns of connectivity dysfunction in patients without HS (NEG-TLE), right (RTLE) and left HS (LTLE), and bilateral HS (BIL-TLE).

Resting-state fMRI (and 3D T1weighted) were acquired on 3T-PHILIPS from 145 patients (80 women, median age 52) and 153 controls (82 women, median age 52), balanced for age (p=0.19) and gender (p=0.44).  Patients were separated in 45 LTLE, 43 RTLE, 22 BIL-TLE, 35 NEG-TLE. We used a seed-based approach running on UF2C/SPM12/MATLAB2017 (https://www.lniunicamp.com/uf2c) (https://www.fil.ion.ucl.ac.uk/spm/) to extract FC maps from DMN (0,-51,21), right  hippocampus (29,-11,-19) and left hippocampus (-29,-11,-19) based on BOLD time-series. Statistical comparisons of maps between patients and controls were performed with SPM12 (minimum T-statistic of 3). Clinical data were analyzed with SPSS2.0. 

While NEG-TLE group presented few areas of abnormal FC, there was a widespread pattern of altered FC, mainly on BIL-TLE and LTLE groups (mostly on connectivity derived from left hippocampus and right hippocampus). RTLE group presented alterations of DMN maps and abnormal FC associated with seed in the right hippocampus. On the contrary, LTLE group showed extensive dysfunction for seeds in ipsilateral and contralateral hippocampi, and restricted alteration of DMN.

BIL-TLE and LTLE groups present a similar pattern with severe damage, compromising not only the ipsilateral but also the contralateral networks.  As NEG-TLE showed limited areas of dysfunction and RTLE a more ipsilateral pattern of abnormalities (associated with seed in the ipsilateral hippocampus), we hypothesize that left hippocampal atrophy related to higher number of unidirectional connections yielding a severe pattern of WM deterioration.