Recent studies in patients with disorders of consciousness (DOC) tend to support 
the view that awareness is not related to activity in a single brain region but 
to thalamo-cortical connectivity in the frontoparietal network. Functional 
neuroimaging studies have shown preserved albeit disconnected low-level cortical 
activation in response to external stimulation in patients in a "vegetative 
state" or unresponsive wakefulness syndrome. While activation of these "primary" 
sensory cortices does not necessarily reflect conscious awareness, activation in 
higher-order associative cortices in minimally conscious state patients seems to 
herald some residual perceptual awareness. PET studies have identified a 
metabolic dysfunction in a widespread frontoparietal "global neuronal workspace" 
in DOC patients including the midline default mode network ("intrinsic" system) 
and the lateral frontoparietal cortices or "extrinsic system." Recent studies 
have investigated the relation of awareness to the functional connectivity 
within intrinsic and extrinsic networks, and with the thalami in both 
pathological and pharmacological coma. In brain damaged patients, connectivity 
in all default network areas was found to be non-linearly correlated with the 
degree of clinical consciousness impairment, ranging from healthy controls and 
locked-in syndrome to minimally conscious, vegetative, coma, and brain dead 
patients. Anesthesia-induced loss of consciousness was also shown to correlate 
with a global decrease in cortico-cortical and thalamo-cortical connectivity in 
both intrinsic and extrinsic networks, but not in auditory, or visual networks. 
In anesthesia, unconsciousness was also associated with a loss of cross-modal 
interactions between networks. These results suggest that conscious awareness 
critically depends on the functional integrity of thalamo-cortical and 
cortico-cortical frontoparietal connectivity within and between "intrinsic" and 
"extrinsic" brain networks.