Strength and Topography of Synchronization of EEG Dynamics during Sleep in Patients with Epilepsy

Balu Krishnan, Gatha Nair, Aaron Faith, Austin Roth, Efstathios Kondylis, Korwyn Williams, Lisa Tapsell, Joseph Sirven, and Leonidas Iasemidis


Sleep, Epilepsy, Electroencephalography, Signal Processing, Spatio-Temporal Brain Dynamics, Synchronization


The occurrence of epileptic seizures and interictal epileptiform discharges (e.g., spikes, sharp waves) are common during sleep. In this study, we investigated the changes in brain dynamics during sleep and wakefulness states in two patients with focal epilepsy. The electroencephalographic (EEG) activity was recorded from scalp electrodes continuously over several days. Three different measures of dynamics were employed: the measures of Energy, maximum Short-Term Lyapunov exponents (STLmax) and maximum Phase. On the basis of these measures we then estimated the degree of entrainment (synchronization) of dynamics between brain sites. There is a significant (p<0.001) increase in dynamical entrainment during sleep compared to wakefulness, which is indicative of a higher level of synchronization during sleep versus awake. The nonlinear dynamical measure of STLmax is more sensitive in capturing this entrainment than the classical energy or phase measures. The topography of the observed dynamical entrainment, indicates that the spatial extent of the dynamical entrainment between different brain sites during sleep is larger compared to wakefulness. These spatiotemporal findings provide new insights into brain dynamics and the topography of their synchronization during sleep,and may lead to a better understanding of seizure onset and treatments.

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