Abstract :
[en] 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.
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