Synchronization analysis of intraoperative electrocorticographic data: Inhomogeneous patterns of interictal activity in mesial temporal lobe epilepsy

J. PASTOR, L. MENENDEZ DE LA PRIDA, R.G. SOLA Y GUILLERMO J. ORTEGA

Edinburgh

Congreso; 28th International Congress of Clinical Neurophysiology; 2006

International Federation of Clinical Neurophysiology

Background. Localization of the epileptogenic zone is an important issue in epileptology. Several diagnostic tools exist (SPECT, MRI, Video-EEG, etc.) aimed to lateralize/localize different areas involved in the generation of the clinical seizures. Objectives. The main objective of the present study is to characterize cortical activity in temporal lobe epileptic patients by using intraoperative ECoG data. Linear and nonlinear multivariate methods were applied to identify cortical regions producing synchronous activity. Patients and methods. Intraoperative ECoG from 32 patients suffering mesial temporal lobe epilepsy (MTLE) were analysed. Recordings were obtained using a grid of 20 electrodes (5x4) covering regions T1, T2 and T3 of the lateral temporal lobe. Linear correlation, coherency, mutual information and phase correlation has been used to quantify intra-cortical synchronization. Multivariate stochastic and surrogate data files have been generated in order to validate statistically the results. Results. By distributing local and global interactions among electrodes, we characterized the spatial patterns of activity. In most patients (81%), synchronized activity distributes homogenously at specific areas of the temporal cortex; whereas in others it derives from multiple areas. We found that in patients exhibiting a homogenous distribution synchronous activity mainly derives from anterior regions at T2-T3, indicating specific patterns of functional connectivity among the temporal regions. In patients exhibiting an inhomogeneous distribution no clear pattern were detected, although activity tended to originates from the anterior areas of the temporal lobe. Discussion. Our results show significant patterns of inhomogeneous cortical activity in MTLE patients. These findings suggest that synchronous interictal activity emerges from specific cortical areas which are highly differentiated from the rest of the temporal cortex. We propose that synchronization analysis could be used to functionally zoom into the temporal cortex of MTLE patients and eventually to guide further histophatological characterization.