Abstract
Focal epilepsy is a network pathology, where the brain connectivity of the epileptic focus (EF) influences seizure frequency and cortical dysfunction. Growing evidence supports a clinical efficacy of cathodal transcranial direct current stimulation (ctDCS) in drug-resistant epilepsy (DRE). ctDCS effects can be merely attributed to the inhibition of cortical excitability, which is abnormally increased in epilepsy, but its effect on brain network of DRE patients has never been reported. We aimed at exploring the hypothesis that functional connectivity (FC) changes may explain part of ctDCS clinical effects in DRE patients. We assessed the ctDCS-induced changes of electroencephalography-derived brain FC of a group of six temporal lobe DRE patients receiving a seizure reduction after ctDCS. By a single-subject eLORETA analysis, we compared the FC among the EF region and other nine bilateral macro-regions, before and after Real and Sham ctDCS in a double-blind Sham-controlled crossover design. FC changed after Real ctDCS in all patients despite no appreciable changes occurred after Sham. Most of FC changes (73%) involved the EF region. The epileptic seizure reduction correlated with the increase of the EF FC, in the whole frequency band and in the theta band. This small-sample analysis clearly revealed that ctDCS induced FC changes in the brain network of temporal lobe DRE patients. Our data support the hypothesis that FC changes may contribute to explain the effects of ctDCS in epilepsy, offering a new scenario in the personalization of neuromodulation interventions in epileptic people.
Highlights
The brain is a network in nature, the understanding of neurological disorders requires to go beyond the selective study of the structural alterations and to deal with its short- and long-range connections
Brain functional connectivity (FC) changes induced by cathodal transcranial direct current stimulation (ctDCS) were studied in six patients affected by temporal lobe drug-resistant epilepsy (tDRE), who are part of the sample treated by Assenza et al (2017a) in a randomized double-blind sham-controlled crossover trial demonstrating the clinical efficacy of ctDCS in tDRE
FC changes induced by ctDCS involved the epileptic focus (EF) region, which was one node in the 73 ± 24% of changed connections across patients (Table 2)
Summary
The brain is a network in nature, the understanding of neurological disorders requires to go beyond the selective study of the structural alterations and to deal with its short- and long-range connections. Epileptic activity drives a certain degree of plastic reorganization of brain networks (Englot et al, 2015; Gleichgerrcht et al, 2015). This reorganization can be clinically relevant, as it can improve the accuracy of the diagnosis (Douw et al, 2010), helps the presurgical planning (Van Dellen et al, 2014), and represents a marker of the efficacy of surgical therapies (Douw et al, 2008). A recent study suggests a clinical efficacy of ctDCS applied over the EF in reducing seizure frequency in focal temporal lobe drug-resistant epilepsy (tDRE) (Assenza et al, 2017a)
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