Editors' ChoiceNeurology

Lights Off—But Is Somebody Home?

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Science Translational Medicine  23 Nov 2011:
Vol. 3, Issue 110, pp. 110ec190
DOI: 10.1126/scitranslmed.3003457

Traumatic or hypoxic brain injury can be devastating, sometimes resulting in a persistent vegetative state. The clinical diagnosis of a vegetative state rests on the assumption that unresponsiveness is equivalent to unconsciousness. But does this assumption always hold true? Now, Cruse and colleagues show that some patients that meet clinical criteria for the vegetative state have electroencephalography (EEG) responses consistent with awareness. The investigators studied 16 patients who met the Coma Recovery Scale definition of vegetative state, as well as 12 healthy controls. Motor imagery (“Imagine that you are squeezing your right hand.”) is known to evoke EEG desynchronization and decreased voltage. Unexpectedly, when brain function was assessed with high-density EEG, 3 of 16 patients (19%) who had been diagnosed as in a vegetative state responded to the command of motor imagery. In these three patients, the neurophysiologic responses were located in the appropriate part of the brain for the specific motor imagery command (hand and toe) and were identical to the responses of conscious, healthy controls.

Detection of “covert consciousness” in vegetative-state patients has both clinical and ethical implications. The current study challenges the validity of conventional diagnosis of vegetative states through behavioral assessment alone. It also leads to the question whether end-of-life care decisions should be made on the basis of behavioral responsiveness. The study has translational potential because it was performed with EEG—a portable, practical, and relatively inexpensive device—in contrast to similar studies with functional magnetic resonance imaging. EEG protocols represent a potentially new diagnostic standard for pathologic states of unconsciousness. Traditionally, brain activity has been regarded as the source of behavioral responses in some other part of the body. In the future, specific brain activity itself may be considered a meaningful response, independent of any other behavior. Further research on the neurophysiologic basis of consciousness is required to prevent tragic instances in which the lights seem off when there is somebody home.

D. Cruse et al., Bedside detection of awareness in the vegetative state: A cohort study. Lancet 10 November 2011 (10.1016/S0140-6736(11)61224-5). [Abstract]

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