Abstract
Abstract Recent findings indicate that the default mode resting state network (DMRSN) is closely associated with conscious awareness. Thus changes in consciousness level could be reflected in turn in the DMRSN functional state. One of the most important requirements for proper network function is connectivity within the network structural constituents. One of the measures of functional connectivity is analysis of the EEG coherences. In this study we have examined changes in the mean coherences in the gamma spectral band 30–45 Hz in the DMRSN during general anaesthesia (GA) in the open thorax surgery were investigated in twenty patients. They were compared with physiologic EEG findings in twenty alert subjects and the mathematical model of brain death. Results of this study indicate that the decrease in coherences in the physiologic EEG and the patients with one lung ventilation (OLV) groups was roughly proportional to the increasing distance between the electrodes. This created some kind of a structure in the DMRSN. In the OLV group the main finding was a decrease in the coherences in the gamma band. Ten of the anaesthetized subjects showed a clear burst suppression pattern. During this condition the coherences in the pairs connecting the posterior parts of the network decreased. Moreover, the differences between the connections of the anterior to posterior parts of the DMRSN and connections between the posterior parts of the DMRSN were almost lost. However, they showed still highly significant differences in all items when compared with the mathematical model of brain death. In summary the results suggest that the functional connectivity in the DMRSN assessed by mean coherences could be a reliable method for assessing the depth of GA and may be useful for understanding disorders of consciousness in general.
Highlights
The default mode resting state network (DMRSN) constitutes a set of brain areas which are active in conditions when the subject is at rest, typically with eyes closed
The flat EEG (Flat) group showed significantly more diffused slowing in the 2-25 Hz range compared to the one lung ventilation (OLV) group
The coherences showed a decrease with increasing distance. This decrease in the coherences in the control and the OLV groups was roughly proportional to the increasing distance between the electrodes
Summary
The default mode resting state network (DMRSN) constitutes a set of brain areas which are active in conditions when the subject is at rest, typically with eyes closed. In this condition the mental contents are delivered from internal sources, i.e. the subjects memory. They are subjected to the imaginary process. Attitudes are formed and future plans are created. The main areas that constitute this network are the following: the ventral medial prefrontal cortex, dorsal medial prefrontal cortex, posterior cingulate/retrosplenial cortex and the inferior parietal lobule (Buckner et al, 2008). The co-working between these spatially separated regions of the brain can be studied using methods which analyze the indices of connectivity in the EEG signals of spatially separated regions (Lehembre et al, 2012; Greenblatt et al, 2012; Sakkalis, 2011)
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