Abstract
PurposePharmaco-resistant temporal lobe epilepsy (TLE) is often treated with surgical intervention at some point. As epilepsy surgery is considered a last resort by most physicians, a long history of epileptic seizures prior to surgery is not uncommon. Little is known about the effects of ongoing TLE on neural functioning. A better understanding of these effects might influence the moment of surgical intervention. Functional connectivity (interaction between spatially distributed brain areas) and network structure (integration and segregation of information processing) are thought to be essential for optimal brain functioning. We report on the impact of TLE duration on temporal lobe functional connectivity and network characteristics.MethodsFunctional connectivity of the temporal lobe at the time of surgery was assessed by means of interictal electrocorticography (ECoG) recordings of 27 TLE patients by using the phase lag index (PLI). Graphs (abstract network representations) were reconstructed from the PLI matrix and characterized by the clustering coefficient C (local clustering), the path length L (overall network interconnectedness), and the “small world index” S (network configuration).ResultsFunctional connectivity (average PLI), clustering coefficients, and the small world index were negatively correlated with TLE duration in the broad frequency band (0.5–48 Hz).DiscussionTemporal lobe functional connectivity is lower in patients with longer TLE history, and longer TLE duration is correlated with more random network configuration. Our findings suggest that the neural networks of TLE patients become more pathological over time, possibly due to temporal lobe changes associated with long-standing lesional epilepsy.
Highlights
Epilepsy surgery is often a more effective way to treat temporal lobe epilepsy (TLE) than anti-epileptic drugs (AEDs) [1,2], but it is considered a last resort by many physicians
Functional connectivity, clustering coefficients, and the small world index were negatively correlated with TLE duration in the broad frequency band (0.5–48 Hz)
Our findings suggest that the neural networks of TLE patients become more pathological over time, possibly due to temporal lobe changes associated with long-standing lesional epilepsy
Summary
Epilepsy surgery is often a more effective way to treat temporal lobe epilepsy (TLE) than anti-epileptic drugs (AEDs) [1,2], but it is considered a last resort by many physicians This reluctance can be explained by a failure of the surgical procedure to alleviate epileptic seizures in a considerable number of cases and by the risk of postoperative cognitive and visual deficits. A correlation between the number of brain structures with epileptogenic characteristics and epilepsy duration has been described in TLE patients [7] It is not known how functional neural networks change during disease progression, and what the impact of changes is on seizure initiation and propagation. A contralateral increase of functional connectivity for TLE patients has been described [8]
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