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

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.

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.

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.

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.

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.