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Causal characterization of functional connectivity through the spread of electrically induced oscillations in the epileptic human brain
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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.
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Palavras-chave
Brain Connectivity Epilepsy Stimulation iEEG