Abstract
The default mode network (DMN) has been consistently activated across a wide variety of self-related tasks, leading to a proposal of the DMN’s role in self-related processing. Indeed, there is limited fMRI evidence that the functional connectivity within the DMN may underlie a phenomenon referred to as self-awareness. At the same time, none of the known studies have explicitly investigated neuronal functional interactions among brain areas that comprise the DMN as a function of self-consciousness loss. To fill this gap, EEG operational synchrony analysis [1, 2] was performed in patients with severe brain injuries in vegetative and minimally conscious states to study the strength of DMN operational synchrony as a function of self-consciousness expression. We demonstrated that the strength of DMN EEG operational synchrony was smallest or even absent in patients in vegetative state, intermediate in patients in minimally conscious state and highest in healthy fully self-conscious subjects. At the same time the process of ecoupling of operations performed by neuronal assemblies that comprise the DMN was highest in patients in vegetative state, intermediate in patients in minimally conscious state and minimal in healthy fully self-conscious subjects. The DMN’s frontal EEG operational module had the strongest decrease in operational synchrony strength as a function of selfconsciousness loss, when compared with the DMN’s posterior modules. Based on these results it is suggested that the strength of DMN functional connectivity could mediate the strength of self-consciousness expression. The observed alterations similarly occurred across EEG alpha, beta1 and beta2 frequency oscillations. Presented results suggest that the EEG operational synchrony within DMN may provide an objective and accurate measure for the assessment of signs of self-(un)consciousness in these challenging patient populations. This method therefore, may complement the current diagnostic procedures for patients with severe brain injuries and, hence, the planning of a rational rehabilitation intervention.
Highlights
The brain ‘default mode network’ (DMN) is commonly defined as a set of cortex areas, encompassing mostly left and right middle frontal gyruses, bilateral frontal medial areas, left and right middle temporal and occipital gyruses, and left and right precuneus, that are more active when the subjects are at rest than when they are engaged in attentiondemanding tasks [3,4,5]
Because there were no significant differences between the minimally conscious state (MCS) and vegetative state (VS) groups in terms of age and time post brain injury, distribution of TBI and non-TBI etiologies, left- and right-side lesions, and distribution of medicated vs nonmedicated patients, all these factors could not be responsible for the differences in EEG parameters found between MCS and VS groups
Considering that DMN has been shown to be involved in self-referential processing [12, 1416, 20-22], these results suggest that the strength of EEG DMN operational synchrony could be a potential indicator of a patient’s expression of self-consciousness
Summary
The brain ‘default mode network’ (DMN) is commonly defined as a set of cortex areas, encompassing mostly left and right middle frontal gyruses, bilateral frontal medial areas, left and right middle temporal and occipital gyruses, and left and right precuneus, that are more active when the subjects are at rest than when they are engaged in attentiondemanding tasks [3,4,5]. The activity of these areas is usually measured indirectly using metabolically/hemodynamically based methods (PET and fMRI) by evaluating the local metabolic or hemodynamic activity. The DMN has been consistently activated across a wide variety of self-related tasks [6,7,8,9,10,11], leading to the proposal (even though interpretations vary) of DMN’s role in
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