Abstracts

Coherence is a measure of synchronization between brain regions. Focal regions that sporadically drive the neural network will exhibit high coherence with all other regions. This study was completed to determine if MEG images of brain coherence are concordant with the epileptogenic zone., A retrospective analysis of MEG data acquired in the presurgical evaluation of patients with refractory partial epilepsy was completed. MEG data was imaged using MR-FOCUSS (Moran JE, Bowyer SM, Tepley N. Multi-Resolution FOCUSS: A Source Imaging Technique Applied to MEG Data. Brain Topography 18:1:1-17, 2005) and ICA source separation techniques. For active brain sources, average coherence with all other active sites was calculated. Brain maps showing high coherence were compared to ictal maps from previous intracranial ictal recordings and post-operative MRI studies, showing the area of resection. Thirty second epochs in no specific state (awake, drowsy and sleep) were analyzed. Total analysis included 600-900 seconds of data per patient. Additionally, some samples specifically examined coherence during spike activity (n=2), or in the preictal state (n=1). Filtering of data to exclude major artifacts (ECG) was done in selected cases., Seven patients were identified who were seizure-free with at least two years post-operative follow-up. 5/7 were temporal lobe resections, and the remaining 2/7 were frontal resections. MRI was normal in 4/7 patients, with the remaining patients showing either cortical dysplasia, cystic encephalomalacia, or mesial temporal sclerosis. 2/5 temporal lobe cases showed increased coherence over the epileptogenic zone in the interictal state, 1/5 showed bitemporal changes, but correctly localized during interictal spike activity, while the remaining 2/5 showed bitemporal coherence changes with variation over the anterior and mesial temporal regions. One frontal case showed increased coherence over the epileptogenic region, while the remaining case showed bilateral frontoparietal changes, but appeared more prominent contralateral to the epileptogenic zone in the interictal and preictal states., Retrospective analysis of MEG coherence maps in patients with refractory partial epilepsy suggests that valuable localizing data may be obtained with this technique. Imaging high coherence between brain regions can be used to identify zones of epileptic activity characterized by abnormally synchronized neuronal activity within a distributed network. MEG coherence imaging is computationally fast and easily automated. Further analysis of coherence in the interictal, preictal, and ictal states in a larger sample size (including awake, drowsy, and sleep states) will help determine its role in identifying the epileptogenic zone., (Supported by NIH/NINDS Grant R01-NS30914.)