Abstracts

Rationale: Refractory temporal lobe epilepsy (TLE) can be treated by resection of the affected temporal lobe including the hippocampus. Functional MRI can be used as a diagnostic tool to assess hippocampal functional connections non-invasively. In a previous resting-state EEG-fMRI study [1] it was shown that spike-correlated increases in BOLD activity in the hippocampus of the affected temporal lobe are typically associated with decreased BOLD signal in the precuneus. Here using fMRI data only we investigated whether the functional connectivity (FC) between the hippocampus and the precuneus was different in patients with TLE compared to healthy volunteers and thus may serve to identify abnormal temporal lobe activity.Methods: Eighteen TLE patients and nine healthy controls were studied. Resting-state T2*-sensitive echo planar images were acquired at 3T (GE Signa Excite HDX) and 1.5 T (GE Signa Horizon Echospeed). Using SPM5, images were realigned and normalized (http://www.fil.ion.ucl.ac.uk/). The following ROI’s were defined for each subject: (1) individually segmented hippocampi using high resolution T1 images [2], (2) precuneus defined as a ROI according to the WFU PickAtlas (http://www.ansir.wfubmc.edu). Following regression of head motion and cardiac-related effects, and of signal changes from the CSF and white matter, BOLD signal time courses were extracted by averaging across each ROI using MarsBar (http://marsbar.sourceforge.net). Correlation coefficients were calculated as a measure of FC. Non-parametric statistical tests (Wilcoxon rank sum criterion and t-test) were performed to test whether hippocampal-precuneal (Hc-PC) FC differ (i.e. towards anti-correlation) in patients than in controls (one sided t-test).Results: FC was significantly (p<0.01) different for patients compared to controls (see Table). Specifically, correlation coefficients in patients were significantly lower than those in the control group reflecting a tendency towards anti-correlation in the former. There was no significant difference in Hc-PC FC between patients scanned at 1.5T vs 3T (p>0.2).Conclusions: We demonstrated that resting state fMRI Hc-PC functional connectivity in a group of TLE patients was significantly different from that in healthy subjects. This result can be seen as generalisation of previous findings based on EEG-correlated fMRI and motivates further studies testing whether the proposed approach can provide a reliable marker of TLE and possibly focus lateralisation. (This work is supported by Medical Research Council grant #G0301067) References 1. Laufs H., et. al., Hum Brain Map, 2006 Nov 28; [Epub ahead of print] 2. Chupin M., et al., Neuroimage, 2007, 34(3):996-1019.