For many, the term “vegetative state” brings to mind the American case of Terri Schiavo and her decade long legal battle (1992-2002) surrounding the “right-to-die”. Terri sustained serious brain damage in 1990 following a cardiac arrest, which led to an eventual diagnosis of a persistent vegetative state. Terri's husband fought for the right to remove her feeding tube while her parents were desperate to keep her alive, believing she was conscious. Ultimately, Terri's artificial life support was withdrawn in 2005, stirring an ongoing debate on the difficult ethical and legal implications in similar cases. Progress in neuroscience gives us hope in being able to answer key questions about brain and behaviour with direct relevance for the legislature and the courtroom.
Disorders of Consciousness
Vegetative state can be defined as “wakefulness without awareness”, in which patients show normal sleep-wake cycles (unlike a coma which is analogous to a deep sleep) but without any evidence of purposeful behaviour connected to awareness of the self or the environment. While wakefulness is straightforward to detect based on sustained eye opening and specific electroencephalogram (EEG) activity, the existence of awareness poses a much more complicated question.
In order to measure consciousness or awareness, we rely on behavioural evidence of “command following” as a proxy to make inferences about mental states. For example, locked-in syndrome patients have lost almost all ability to make voluntary movements but retain the ability to respond to “yes” or “no” questions by moving their eyes or eyelids in a consistent manner. This residual ability to form purposeful behaviour leaves no question that the patient is indeed conscious.
Unfortunately, the difficulty with vegetative state patients is that they do not show any such meaningful behaviour or evidence of language comprehension. These patients will stare into space, move their eyes in an inconsistent manner and may even burst out into laugher or tears; however, none of these behaviours are linked to environmental stimuli.
For a long time, it was believed that such patients were completely unconscious. However, in the last decade this orthodox notion has faced serious scrutiny, regarding at least some of these patients, due in large part to the work of Canadian neuroscientist Dr. Adrian Owen from the University of Western Ontario.
Neural Activity as A Proxy for Behaviour
Dr. Owen's research method allows certain patients who are labelled as vegetative to communicate solely by modulating their brain activity, recoded using functional magnetic resonance imaging (fMRI). fMRI makes inferences about brain activity indirectly by measuring blood flow, which is temporally linked to neural activity in that recently active cells require a fresh supply of oxygenated blood. This allows scientists to gauge which parts of the brain are involved in various cognitive tasks with high spatial resolution.
In a notable study, Dr. Owen's team asked “vegetative state” patients in the fMRI scanner to imagine playing tennis or to imagine walking around their house from room to room. When healthy patients are asked to perform this same task, imagining playing tennis shows activation in a part of the brain called the supplementary motor area (SMA) while walking around the house activates parahippocampal corticies (PPA) which are involved in real and imaginary spatial navigation.
Remarkably, a portion of vegetative state patients (17%), diagnosed based on internationally recognized behavioural standards, show consistent SMA activity when instructed to imagine playing tennis and PPA activity in the case of walking around the house. Even more remarkably, they were then able to use imagining playing tennis or imagining walking around the house to respond “yes” or “no” to questions – with 100 percent accuracy. Using their imagination, this select group of vegetative state patients responded correctly to questions about their own name, their parents' names, the current year, and so forth.
These findings make legal characterizations pertaining to the decision to withdraw nutrition and hydration even more complicated. In a personal communication with Dr. Owen, he mentioned that one such patient was asked whether he wished to continue living. He responded: “yes”. This is exciting news in the context of legal decision-making; perhaps we could simply ask the fMRI-responsive patients to decide their own fate.
But what can be said for the remaining 83% of patients? Can we conclude that they are simply not conscious, and thus truly fit their derogatory label of “vegetative”? The problem with such a conclusion is one of false negatives. When someone consistently “responds” to high-level questions with their brain activity, we can be sure of their consciousness – arguably to the same extent as someone who is saying “yes” and “no” in plain English (or French).
However, when a vegetative patient fails to show any meaningful fMRI responses, we cannot be certain that they are not conscious. Consider, for example, patients that have lost function in their auditory cortex and thus cannot hear the task instruction nor questions – not to mention many more nuanced neural complications that may prevent successful performance despite consciousness.
Legal Applications for Neuroscience Data
Dr. Owen's work has received enormous media attention and, most relevant to the legal context, Dr. Owen recently submitted an affidavit that was admitted into evidence by the Supreme Court of British Columbia (BC) in
In a personal communication with Dr. Owen, he mentioned that one such patient was asked whether he wished to continue living. He responded: “yes”.