Causal characterization of functional connectivity through the spread of electrically induced oscillations in the epileptic human brain

• Autor(a) principal: Duarte, Miguel Fernandes
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/42528
• topic: Brain; Connectivity; Epilepsy; Stimulation; iEEG; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Little is known about the rules governing the spread of local entrainment within synchronized networks distributed across the brain. The assessment of the causal influences impacting information flow between two brain regions have mainly relied on confirmatory model-driven approaches (such as dynamic causal modeling and structural equation modeling) and exploratory data driven approaches (such as Granger Causality analysis). However, stimulation-driven approaches offer a unique opportunity to impact ongoing brain activity and describe the causal consequences of such manipulations, performed on a specific node of a complex cerebral network. In this project, we characterize causal functional interactions between brain regions by assessing how frequency-tuned electrical currents delivered intracranially in awaken epileptic patients enhance inter-regional synchrony between pairs of areas. To achieve this goal, we worked with an existing iEEG database from 18 medication-resistant epilepsy patients undergoing Intracortical Stimulation Mapping Procedures (ISMP) performed to causally identify and localize the epileptogenic foci, prior to neurosurgical removal. Patients are implanted with series of multi-electrodes in well-known brain regions under MRI guidance. Intracranial EEG contacts allow continuous recordings and the delivery through pairs of adjacent contacts of biphasic pulses of rhythmic Direct Electric Stimulations (DES) at a 50Hz frequency coupled to electrophysiological recordings. Measuring significant increases in gamma power ( 50Hz) observed during the stimulation period (vs. prior the stimulation), and significant increases of Phase-Locking Value (PLV) between signals recorded in the electrically stimulated regions and activity evoked in the rest of implanted regions during stimulation (vs. prior simulation), we characterize the spread of oscillatory entrainment from the stimulated region to the remaining regions, thus establishing a network of functional connectivity in the brain. By comparing this network with the one shown during resting-state, we assess how entrainment to frequency-tuned electrical currents delivered intracranially is predicted by the resting-state functional connectivity network.