Covert brain complexity in the intensive care unit

Early detection of consciousness in critically ill patients with severe brain injuries can profoundly impact prognostication and clinical care decisions. Advanced multimodal protocols to detect signs of consciousness include standardized behavioral assessments, task-based functional magnetic resonance imaging (fMRI), and task-based electroencephalography (EEG). However, these approaches have limited diagnostic sensitivity because patients may lack auditory function, attention, language, or other cognitive capacities required to perform a task or process a sensory stimulus, even if they are conscious. Transcranial magnetic stimulation EEG (TMS-EEG) has the potential to overcome these limitations by directly engaging corticothalamic circuits to compute the perturbational complexity index (PCI), an emerging indicator of consciousness. To date, TMS-EEG studies have focused on patients in the subacute or chronic stage of recovery from severe brain injury. Here, we report the proof-of-concept application of TMS-EEG for a critically ill patient in the acute stage of brain injury, in which multimodal assessments suggested a vegetative state/unresponsive wakefulness syndrome. We demonstrate that TMS-EEG may detect signs of consciousness that elude current advanced evaluations, showing the feasibility of TMS-EEG as part of a multimodal protocol for assessing consciousness in the intensive care unit.