Neuronal networks of burst suppression EEG as revealed by source analysis and renormalized partial directed coherence
Burst-suppression (BS) is an electroencephalography (EEG) pattern consist-ing of alternative periods of slow waves of high amplitude (the burst) and periods of so called flat EEG (the suppression). It is generally associated with the reduced level of consciousness. The aim of this study was to reveal the neuronal network underlying both burst and suppression phases using a source analysis method: dynamic imaging of coherent sources (DICS) and to describe the effective connectivity between the identified sources using renormalized partial directed coherence (RPDC). DICS was applied separately to the EEG segments of 13 neonates with burst and suppression EEG pattern. Power spectrum analyses were performed to identify the predominant frequencies. The brain area with the strongest power in the analyzed frequency (1-4 Hz) range was defined as the reference region. DICS was used to compute the coher-ence between this reference region and the entire brain. RPDC was used to describe the in-formational flow between the described sources. Delta activity during burst phases was associated with sources in the thalamus and brainstem as well as bilateral sources in the cortical regions mainly frontal and parietal, whereas suppression phases were associated with coherent sources only in the cor-tical regions. Results of the RPDC analyses showed an ascending informational flow from the brainstem towards the thalamus and from the thalamus to cortical regions, which was absent during suppression phases. Especially those brain regions were affected, that are im-portant for cognitive processing. The results of this study strengthen the assumption that there is a specific periodicity of neural activity and that thalamocortical deafferentiation is an essential feature of BS. Thus a burst can be understood as short, repetitive recovery of cortical neural dynamics. The described deafferentation may play a role in the poor neuro-logical outcome in these encephalopathies.