Measuring the fading consciousness in the human brain.

PURPOSE OF REVIEW Recent neuroimaging studies have provided novel insights on residual brain function in patients with disorders of consciousness, but also raised a number of ethical issues concerning the clinical management of these patients. RECENT FINDINGS Clinical studies have rated the Coma Recovery Scale as the most appropriate scale to accurately differentiate patients in a vegetative state from patients in a minimally conscious state. At the population level, a number of neuroimaging studies have provided evidence for more preserved brain activity patterns and cerebral tissue integrity in minimally conscious as compared to vegetative-state patients. However, the use of neuroimaging techniques to diagnose consciousness at the single-patient level remains challenging. In particular, it has been shown that whereas command-following functional MRI paradigms may sometimes detect residual awareness in patients that are behaviorally unresponsive, they can also produce negative results in patients that are communicative at the bedside. SUMMARY There is an urgent need of validation of functional MRI active paradigms on larger patient populations before they can be used in clinical routine. Further research on neural correlates of consciousness should hopefully allow using passive paradigms to assess the patients' conscious state without requiring their active collaboration.