Abstract
Objectives: Accurate localization of epileptogenic zones (EZs) is essential for successful surgical treatment of refractory focal epilepsy. The aim of the present study is to investigate whether a dynamic network connectivity analysis based on stereo-electroencephalography (SEEG) signals is effective in localizing EZs.Methods: SEEG data were recorded from seven patients who underwent presurgical evaluation for the treatment of refractory focal epilepsy and for whom the subsequent resective surgery gave a good outcome. A time-variant multivariate autoregressive model was constructed using a Kalman filter, and the time-variant partial directed coherence was computed. This was then used to construct a dynamic directed network model of the epileptic brain. Three graph measures (in-degree, out-degree, and betweenness centrality) were used to analyze the characteristics of the dynamic network and to find the important nodes in it.Results: In all seven patients, the indicative EZs localized by the in-degree and the betweenness centrality were highly consistent with the clinically diagnosed EZs. However, the out-degree did not indicate any significant differences between nodes in the network.Conclusions: In this work, a method based on ictal SEEG signals and effective connectivity analysis localized EZs accurately. The results suggest that the in-degree and betweenness centrality may be better network characteristics to localize EZs than the out-degree.
Highlights
Focal epilepsy, in which the origin of epileptic seizures is limited to one hemisphere (Berg et al, 2010), is common and comprising more than 50% of patients with epilepsy (Hauser et al, 1996)
epileptogenic zones (EZs) can sometimes be adequately identified by a combination of non-invasive techniques, such as analysis of ictal symptomatology, neurological examination, electroencephalography (EEG), magnetoencephalography (MEG), and magnetic resonance imaging (MRI) (Rosenow and Luders, 2001)
We examined the applicability of a method based on time-variant effective connectivity and graph analysis to identify EZs based on SEEG signals of patients with focal refractory epilepsy
Summary
In which the origin of epileptic seizures is limited to one hemisphere (Berg et al, 2010), is common and comprising more than 50% of patients with epilepsy (Hauser et al, 1996). Despite great developments in pharmacological treatment, about 30–50% of patients with focal epilepsy cannot be sufficiently controlled with antiepileptic drugs (Beleza, 2009). For these patients, surgical resection of the epileptogenic zones (EZs), the brain areas that are essential for the generation of epileptic seizures (Rosenow and Luders, 2001), may be the only way to suppress or reduce seizures. When the EZs cannot be precisely identified, invasive intracranial EEG recordings are required. Stereo-EEG (SEEG) can record neural activities by stereotactic placement of intracranial electrodes within different brain regions, especially in deep areas (Bancaud and Talairach, 1973). SEEG is a relatively safe tool and has been considered the gold standard for EZ identification (Cossu et al, 2005)
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