Question: How functional connectivity of the default mode network changes in patients with disorders of consciousness?

Context:
Functional connectivity in the default mode network (DMN) is known to be reduced in patients with disorders of consciousness, to a different extent depending on their clinical severity.
Patients showed significant impairments in all of the pathways connecting cortical regions within this network, as well as the pathway connecting the posterior cingulate cortex/precuneus with the thalamus, relative to the healthy volunteers.
Moreover, the structural integrity of this pathway, as well as that of those connecting the posterior areas of the network, was correlated with the patients' behavioral signs for awareness, being higher in EMCS patients than those in the upper and lower ranges of the MCS patients, and lowest in VS patients.
These results provide a possible neural substrate for the functional disconnection previously described in these patients, and reinforce the importance of the DMN in the genesis of awareness and the neural bases of its disorders.
Although the functional significance of the default-mode network remains a matter of debate, it has been suggested to be a candidate for the network subserving basic functions related to consciousness.
Despite resolution of corpus callosum lesion on magnetic resonance imaging (MRI) within 1 week, the patient persistently presented disturbance of consciousness. Resting-state functional MRI revealed that the posterior cingulate cortex/precuneus was functionally disconnected from other brain regions within the default-mode network.
Our case report suggests that assessment of the functional connectivity in the resting-state default-mode network could be a useful marker of consciousness disturbance even in the presence of a reversible brain lesion.
A present and intact DMN was observed in controls and those patients who subsequently regained consciousness, but was disrupted in all patients who failed to regain consciousness.
The results suggest that the DMN is necessary but not sufficient to support consciousness.
Clinically, DMN connectivity may serve as an indicator of the extent of cortical disruption and predict reversible impairments in consciousness.
Recent studies on resting state activity in DOC, measured with functional magnetic resonance imaging (fMRI) techniques, show that functional connectivity is disrupted in the task-negative or the default mode network.
This report shows for the first time, in three patients, that the persistent vegetative state (PVS) is marked by a dysfunctional default mode network, with decreased connectivity in several brain regions, including the dorsolateral prefrontal cortex and anterior cingulated cortex, especially in the right hemisphere.

Answer: Functional connectivity in the default mode network (DMN) is reduced in patients with different disorders of consciousness, and correlates with the level of consciousness. 
Specifically, functional connectivity in the default mode network was shown to be absent in brain death patients, extremely low in vegetative state patients and slightly decreased in minimally conscious state patients when compared to healthy subjects. Therefore, functional connectivity in the default mode network was suggested to be valuable in differentiating patients with different disorders of consciousness. Clinically, functional connectivity in the default mode network was also shown to be an indicator of the extent of cortical disruption and predict reversible impairments in consciousness.