Abstract
ObjectiveEpilepsy is a chronic brain disease, which is prone to relapse and affects individuals of all ages worldwide, particularly the very young and elderly. Up to one-third of these patients are medically intractable and require resection surgery. However, the outcomes of epilepsy surgery rely upon the clear identification of epileptogenic zone (EZ). The combination of cortico-cortical evoked potential (CCEP) and electrocorticography (ECoG) provides an opportunity to observe the connectivity of human brain network and more comprehensive information that may help the clinicians localize the epileptogenic focus more precisely. However, there is no standard analysis method in the clinical application of CCEPs, especially for the quantitative analysis of abnormal connectivity of epileptic networks. The aim of this paper was to present an approach on the batch processing of CCEPs and provide information relating to the localization of EZ for clinical study.MethodsEight medically intractable epilepsy patients were included in this study. Each patient was implanted with subdural grid electrodes and electrical stimulations were applied directly to their cortex to induce CCEPs. After signal preprocessing, we constructed three effective brain networks at different spatial scales for each patient, regarding the amplitudes of CCEPs as the connection weights. Graph theory was then applied to analyze the brain network topology of epileptic patients, and the topological metrics of EZ and non-EZ (NEZ) were compared.ResultsThe effective connectivity network reconstructed from CCEPs was asymmetric, both the number and the amplitudes of effective CCEPs decreased with increasing distance between stimulating and recording sites. Besides, the distribution of CCEP responses was associated with the locations of EZ which tended to have higher degree centrality (DC) and nodal shortest path length (NLP) than NEZ.ConclusionOur results indicated that the brain networks of epileptics were asymmetric and mainly composed of short-distance connections. The DC and NLP were highly consistent to the distribution of the EZ, and these topological parameters have great potential to be readily applied to the clinical localization of the EZ.
Highlights
Epilepsy is one of the most common and chronic neurological disorders and is usually caused by excessive and abnormal firing of neurons in the brain cortex
This study investigated the effective connectivity derived from direct electrophysiological recordings of cortical evoked potential (CCEP) in eight medically intractable epilepsy patients, three different connectivity networks over different spatial scales were constructed for each patient
We confirmed that connectivity networks reconstructed with CCEP amplitudes can indicate the effective connectivity of brain networks both at the electrode-pair-level and at the region-level
Summary
Epilepsy is one of the most common and chronic neurological disorders and is usually caused by excessive and abnormal firing of neurons in the brain cortex. In China, 9 million people suffer from epilepsy, a condition which is usually treated with anti-epileptic drugs (AEDs). While the effects of AEDs are not satisfactory, one possible option is resective surgery of the epileptogenic zone (EZ), a procedure which can benefit patients by reducing or eliminating seizure activity (Vos et al, 2016; Yue et al, 2017). Incomplete resection of the focus, or damage incurred by normal brain regions during surgery may fail to achieve an effect, or may even aggravate the condition (van Mierlo et al, 2014). Precise delineation of the EZ is the key to epilepsy surgery; abnormal connectivity of epileptic networks makes it difficult for the clinicians to delineate the epileptogenic focus unambiguously
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