title: Brain connectivity in pathological and pharmacological coma.
abstract: 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.
authors.affiliation: Coma Science Group, Cyclotron Research Centre and Neurology Department, University and University Hospital of Liège Liège, Belgium.
authors.forename: Quentin
authors.initials: Q
authors.lastname: Noirhomme
authors.forename: Andrea
authors.initials: A
authors.lastname: Soddu
authors.forename: Rémy
authors.initials: R
authors.lastname: Lehembre
authors.forename: Audrey
authors.initials: A
authors.lastname: Vanhaudenhuyse
authors.forename: Pierre
authors.initials: P
authors.lastname: Boveroux
authors.forename: Mélanie
authors.initials: M
authors.lastname: Boly
authors.forename: Steven
authors.initials: S
authors.lastname: Laureys