Last week’s brief report in Science describing the first demonstration that a woman previously determined to be in a “PersistentVegetative State” (PVS) had specific, localized changes in brain activity in response to external commands that she “imagine” herself playing tennis or walking through her home. These responses were documented by Functional Magnetic Resonance Imaging (fMRI) studies obtained from both the patient and healthy volunteers.
This report, if its results can be reproduced by other research centers, will undoubtedly lead to a serious reconsideration of what actually “creates” or “defines” consciousness.
Much of our understanding concerning the mechanisms that are responsible for the development of coma has been acquired only over the past three decades and there remains some debate within the medical community as to the “proper” term that should be used when describing the different clinical manifestations of “coma” vs. “persistent vegetative sate” or even “minimally conscious state (MCS).”
We can, however, state what PVS / MCS is not:
1) PVS is not the same medical condition as a coma.A coma is a state in which the subject does not respond in any way to external stimulation. A comatose subject does not open his/her eyes. The subject that has entered PVS will sometimes open their eyes and respond to specific commands. However, these responses are very rarely (if ever) reproducible.
2) PVS is not a stage in the emergence from a coma.The current state of knowledge regarding the “natural history” of coma is based on case studies involving subjects that became comatose due to a wide variety of causes. Therefore, it is very difficult to predict what will happen in one particular case based on what happened in another case. As noted elsewhere, the continuum of conscious is still poorly understood.
3) PVS is not the state of being “brain dead.”Brain death refers to either the complete absence of electrical signals that arise from the brain or the presence of only chaotic and random activity. Those that have been declared brain dead require constant life support measures in order to survive.
4) PVS is not the same thing as a “near-death experience.”
The “light and tunnel” or similar phenomena that have been reported by the thousands of people that have survived an incident in which they were either “clinically dead” or very near death do not generally suffer the extreme metabolic insult to the brain required to induce PVS.
As mentioned earlier, the report by Owen and colleagues may one day be viewed as a “watershed event” in fields as intellectually diverse as neuropsychology, neurology, and even biomedical ethics simply because the current definition of consciousness has been challenged by direct evidence that something had survived the initial trauma to the subject’s brain. What was it that survived? Was it merely some primitive auditory pathway that evolved as a protective measure that allowed our ancestors to maintain some form of vigilance while sleeping? Were the subject’s responses specific to the activity that was “suggested” by the investigators?
In my opinion, we (meaning both society and the medical community) may be only a few steps away from a new definition of “consciousness.” If “self-awareness” is eventually proven to be a critical component of “consciousness,” what will we assign as the definition of “self-aware?”
I’ll return to these topics, and others, in future articles.
Boly, M et al. Auditory Processing in Severely Brain Injured Patients: Differences between the Minimally Conscious State and the Persistent Vegetative State. Arch. Neurol. 2004; 61:233-238.
Giacino, J.T et al. The minimally conscious state: Definition and diagnostic criteria. Neurology 2002; 58:349-353.
Jennet, B. and Plum, F: Persistent Vegetative State after Brain Damage; a Syndrome in Search of a Name.
Lancet 1972; 734-737.
Owen A.M. et al, Detecting Awareness in the VegetativeState, Science 2006; 313:1402.
Schenk, Mark; Sugeng, Andi; Gunasekaran, Mirunalini; and Wei, Qiang: Introduction to MRI (2006). Available online at Accessed Septenber 15, 2006.