- Shades of Gray:New Insights into the Vegetative State
They say a picture is worth a thousand words. Herewith, just under that to explain several images in a recent Science paper by Adrian Owen and colleagues that demonstrated a clear response to environmental stimuli in the persistent vegetative state. A New York Times account described them as showing that "a brain thought to be all but dark flared with conscious activity."
The subject was a twenty-three-year-old woman who was studied five months after a traumatic brain injury. Clinically, she had an exam consistent with being in a vegetative state save for visual fixation, which is considered a sign of evolving recovery in some diagnostic frameworks. She exhibited sleep-wake cycles and what Jennett and Plum first described as a state of "wakeful unresponsiveness" in their classic description of the vegetative state in 1972. When her eyes were open she did not respond to stimuli or to her environment and did not initiate spontaneous behaviors.
That was her behavioral status, but imaging of her brain demonstrated quite a bit more. Using functional MRI (fMRI), investigators found that she was able to activate very specific brain regions in response to commands. For example, when asked to imagine playing tennis she exhibited elevated brain activity in the supplementary motor areas. When asked to imagine walking through the rooms of her house, activation was seen in the parahippocampal gyrus, posterior parietal cortex, and the lateral premotor cortex. Likewise, when she was presented with linguistically ambiguous sentences that required her to demonstrate "semantic processes critical for speech comprehension," she activated the middle and superior temporal gyrus bilaterally, as well as the left inferior frontal region. All of these circuit responses were "indistinguishable" from normal controls.
What do these remarkable findings mean for our common understanding of the vegetative state? Here the answer requires an appreciation of our growing comprehension of how the severely injured brain recovers. A vegetative state after traumatic injury may give way to further recovery after intervals of six to twelve months in existing prognostic frameworks. How these late transitions occur is unknown, but the usual progression begins with the appearance of nonreflexive signs such as visual fixation (noted at the time of the imaging studies) and visual tracking (observed six months later).
These signs are considered transitional and suggest a patient evolving into the minimally conscious state (MCS), a condition characterized by behavioral response to environmental stimuli and the ability to follow commands, but one in which the patient does not exhibit a capacity for consistent communication. Following commands and the subsequent fMRI activations indicate that the subject had recovered to at least the level of MCS, even though behavioral evidence was lacking.
That is where our understanding ends and ignorance begins. The investigators did not provide a method for the the subject to make an effort at communication, so we cannot draw conclusions about her level of awareness. Thus the dramatic assertion in an accompanying Science commentary by Lionel Naccache—that "the fMRI findings indicate the existence of a rich mental life"—is simply unjustifiable. The data do not show this. She may possess a rich mental life, but the more likely scenario is that, like many patients in MCS, this woman can follow commands yet remains unable to communicate and carry out goal-directed and intentional behaviors because of generalized cognitive impairment.
Entertaining the possibility of a vegetative patient's rich mental life is especially alarming when one considers famous right-to-die cases featuring patients in that state (witness Quinlan, Cruzan, and Schiavo). But the alarm depends partly on a false dichotomy: it is not true that the patient is either in an immutable state of permanent unconsciousness or has a heartwrenchingly normal inner life. In fact, what we must confront is a scale of important gradations—most of which are yet to be discovered and described. Viewing the emerging complexity of these brain states as a simple dichotomy only feeds the polemicists who see these scientific findings through an ideological prism. It also discourages recognition of incremental developments in neuroscience that are coalescing into a theory of...