Covert consciousness in behavioral coma

Approximately 25% of patients with severe brain injuries who appear unresponsive on the bedside behavioral examination are covertly conscious-able to volitionally modulate their brain activity using task-based functional MRI or task-based EEG. Since the first description of covert consciousness in 2006, nearly all reports of covert consciousness have been in patients who were behaviorally awake, with their eyes open. These observations led to a widespread assumption that cortical activation associated with consciousness required a foundation of subcortical connections to produce wakefulness. We report the case of an 80-year-old woman with acute severe traumatic brain injury, whose level of consciousness was evaluated in the intensive care unit with a multimodal diagnostic protocol integrating behavioral, task-based fMRI, and task-based EEG assessments. Despite behavioral evidence of coma on every behavioral examination, the task-based fMRI and task-based EEG assessments both indicated the presence of covert consciousness. These observations suggest an unexpected phenomenon whereby awareness (i.e., volitional brain activity) can be dissociated from wakefulness (i.e., eye opening) in the human brain. The possibility that individuals who outwardly appear comatose may harbor covert consciousness carries both clinical and ethical weight, and unsettles long-held assumptions, embedded in the very term coma, that patients diagnosed as such are uniformly unaware and insensate.