Abstract: Recent neuroimaging and electrophysiology studies are illuminating the relationships between awareness and: (i) global brain function; (ii) regional brain function; (iii) changes in functional connectivity; and (iv) primary vs associative cortical activation in response to external stimulation. Is awareness lost when overall cortical activity falls below a certain threshold? In the vegetative state, global metabolic activity decreases to about 50% of normal levels—similar to what is observed in sleep, anaesthesia and coma. However, it seems that some areas in the brain are more important than others for consciousness. Voxel-based statistical analyses have identified a dysfunction in a wide frontoparietal network encompassing the polymodal associative cortices. Consciousness seems not exclusively related to the activity in the frontoparietal network but, as importantly, to the functional connectivity within this network and with the thalami. In addition to measuring resting brain function and connectivity, neuroimaging studies have identified which brain areas still “activate” during external stimulation in vegetative patients. Studies using external (noxious or auditory) stimulation showed robust activation in subcortical and primary sensory cortex which was however isolated and dissociated from the frontoparietal cortical network. Of clinical importance, this knowledge now permits to improve the diagnosis of patients with disorders of consciousness, which remains very challenging at the bedside. Current technology now also permits to show command-specific changes in EEG or fMRI signals providing motor-independent evidence of conscious thoughts. Such brain computer interfaces now permit communication via voluntary EEG or fMRI control, enabling locked-in patients to control their surroundings and giving a voice to minimally conscious state patients. http://www.comascience.org with state-of-the-art multimodal imaging combining the information from positron emission tomography (PET), functional MRI, structural MRI, electroencephalography (EEG), event related potential (ERP) and transcranial magnetic stimulation (TMS) data.
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