Abstracts

Surgical remove the epileptogenic zone is the preferred treatment option for medically refractory epilepsy. Unfortunately, The epileptogenic zone is a theoretical concepts, so far there are no any techniques can accurately locate epileptogenic zone. A large number of studies have shown that the blood oxygenation level dependent (BOLD) effect caused by epileptiform discharges are closely related to the seizure onset zone, epileptogenic zone, and epileptic network. However, the relationship between ictal-related BOLD signal activation and the seizure onset zone and epileptogenic zone is still uncertain. In this study, we used EEG-fMRI synchronously record technique to record the seizures in the rat acute focal epilepsy mode induced by 4-aminopyridine, to study the correlation between BOLD signal activation and seizure onset, and to explore the possibility of EEG-fMRI synchronously record technique as a non-invasive technique to locate epileptogenic zone or seizure onset zone.

Adult male Sprague Dawley rats weighing 250-350g were used in the experiments.Two pair of MRI-compatible tungsten electrodes (50μm diameter) were stereotaxically implanted symmetrically into bilateral hemisphere respectively and differentially recorded the EEG between the two hemisphere. For experimental group, acute focal epileptic seizures were induced by injection of 4-aminopyridine (25 mM, 1.0 uL) into M1 area of the right motor cortex, while saline (0.9%, 1.0 uL) was injected into same area for control group. After the operation, EEG-fMRI was synchronously recorded for about one hour in all rats. Then all data were analyzed offline. We use Analyzer software to denoise EEG signals, and SPM12 software package based on MATLAB to pretreat and analyze the magnetic resonance data. We compared the temporal and spatial correlation between seizures recorded by EEG and BOLD signals activation during seizures.

The activation regions of BOLD signal in the experimental group (n=6) were all located near the 4-AP injection site in the initial few seizures, Then it gradually spread to other brain regions. We extracted the percentage of BOLD signal changes during each seizures in all rats. The results after statistical calculation showed that the percentage of BOLD signal changes on the 4-AP injection side cortex was statistically higher than the contralateral side and the control group. However, there is no statistically different among the contralateral injection sides and same brain areas in control group. We also analyzed the BOLD signal-activated cluster size corresponding to each seizure in all rat and performed regression analysis. Our results showed that R2 = 0.421, suggesting that the spatial range of BOLD signal activation gradually increased with the increase of seizures.

Our study shows that EEG-fMRI synchronous recording technique can locate the seizure onset zone accurately and noninvasively in an acute focal seizure animal model and this technique also can map dynamic epileptic network.