Altered EEG resting-state effective connectivity in drug-naïve childhood absence epilepsy

Objective: We investigated interictal EEG activity in patients with childhood absence seizures with the aim of detecting markers of network defects generating "idiopathic" hyperexcitability in this form of epilepsy. Methods: We included 11 drug-naïve patients with childhood absence epilepsy (CAE), and 11 age matched controls (CTRL). We analyzed interictal EEG using partial directed coherence (PDC), a connectivity estimator in frequency domain based on autoregressive multivariate (MVAR) modeling giving the advantage of indicating the direction and strength of the interactions between multiple variables. Results: Our results revealed the presence of an abnormal cortico-cortical network occurring in the interictal condition in CAE and involving a large span of frequencies, with prominence in the alpha band; the most evident finding was a highly significant increase of out-going connectivity involving frontal and central cortical areas in CAE patients compared to CTRL subjects. Conclusions: Our observation indicates that, in interictal conditions, a distorted network characterizes CAE, and a hyperconnected network is already detectable under resting conditions in the delta, theta and alpha bands. Significance: The increased interictal EEG connectivity demonstrated here provides support for a persistent abnormal relationship between the thalamus and a hyperexcitable cortex outside the ictal phase.