V5. Dynamic imaging of coherent sources in continues spikes and waves during slow sleep [Abstract]

The network of sources involved in the frequency oscillations of continuous spikes and waves during slow wave sleep and their causal architecture is still lacking in the current literature. In a couple of studies the network and causal connectivity was studied using fMRI by concentrating the analysis on the spikes and not on the background oscillations. In a number of studies the connectivity and the network of sources were studied during normal subjects sleep using fMRI. However, the earlier estimations do not directly relate to the background oscillations present during the interictal epileptiform patterns during sleep. In contrast the dynamic source coherence method is a tool to study the causality on the cortical and sub-cortical source level. In this study we measured the functional and directed connectivity with renormalized partial directed coherence during continuous spikes and waves during slow wave sleep EEG recordings from 12 patients. The network of sources involved was premotor cortex, posterior cingulate cortex, dorsolateral prefrontal cortex, middle temporal gyrus, medial thalamus and cerebellum. The cerebellum, thalamus and the posterior cingulate cortex showed significant bi-directional causality whereas all the other the sources showed uni-directional causality. Our results suggest that the mean source coherence could be an early biomarker for onset and severity of the disease. In addition we show the source network and the directed connectivity of the background frequency oscillations for continuous spikes and waves during slow wave sleep

Neuronal networks in West syndrome as revealed by source analysis and renormalized partial directed coherence

West syndrome is a severe epileptic encephalopathy of infancy with a poor developmental outcome. This syndrome is associated with the pathognomonic EEG feature of hypsarrhythmia. The aim of the study was to describe neuronal networks underlying hypsarrhythmia using the source analysis method (dynamic imaging of coherent sources or DICS) which represents an inverse solution algorithm in the frequency domain. In order to investigate the interaction within the detected network, a renormalized partial directed coherence (RPDC) method was also applied as a measure of the directionality of information flow between the source signals. Both DICS and RPDC were performed for EEG delta activity (1–4 Hz) in eight patients with West syndrome and in eight patients with partial epilepsies (control group). The brain area with the strongest power in the given frequency range was defined as the reference region. The coherence between this reference region and the entire brain was computed using DICS. After that, the RPDC was applied to the source signals estimated by DICS. The results of electrical source imaging were compared to results of a previous EEG-fMRI study which had been carried out using the same cohort of patients. As revealed by DICS, delta activity in hypsarrhythmia was associated with coherent sources in the occipital cortex (main source) as well as the parietal cortex, putamen, caudate nucleus and brainstem. In patients with partial epilepsies, delta activity could be attributed to sources in the occipital, parietal and sensory-motor cortex. In West syndrome, RPDC showed the strongest and most significant direction of ascending information flow from the brainstem towards the putamen and cerebral cortex. The neuronal network underlying hypsarrhythmia in this study resembles the network which was described in previous EEG-fMRI and PET studies with involvement of the brainstem, putamen and cortical regions in the generation of hypsarrhythmia. The RPDC suggests that brainstem could have a key role in the pathogenesis of West syndrome. This study supports the theory that hypsarrhythmia results from ascending brainstem pathways that project widely to basal ganglia and cerebral cortex