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Implications of Recent Neuroscientific Findings in Patients with Disorders of Consciousness

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Abstract

A pressing issue in neuroscience is the high rate of misdiagnosis of disorders of consciousness. As new research on patients with disorders of consciousness has revealed surprising and previously unknown cognitive capacities, the need to develop better and more reliable methods of diagnosing these disorders becomes more urgent. So too the need to expand our ethical and social frameworks for thinking about these patients, to accommodate new concerns that will accompany new revelations. A recent study on trace conditioning and learning in vegetative and minimally conscious patients shows promise as a potential diagnostic and prognostic tool, both for differentiating between states of diminished consciousness, and for predicting patient outcomes, but it also generates fresh concerns about quality of life in patients previously thought to be completely unaware. Optimism about progress in diagnosing and treating disorders of consciousness must be tempered by the understanding that not all progress will necessarily be good for all patients. The prognosis for most patients remains bleak, and we must remain vigilant to acute questions and concerns about welfare and quality of life.

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Notes

  1. See Racine et al. [1] for an interesting analysis of media coverage of the Schiavo case.

  2. Exact numbers for the population of VS patients are hard to come by owing to several factors, including worldwide variations in diagnostic criteria, the wide distribution of patients in different kinds of institutions (from acute to chronic care) [2], and a lack of official national statistics [3]. Estimates for the US put the number of adult VS patients at 40–168 per million population, but precise figures are not available [3].

  3. This paper will primarily address the problem of distinguishing between two disorders of consciousness: vegetative states, and minimally conscious states.

  4. Alva Noë recounts the disquieting case of a Belgian woman who was misdiagnosed in a persistent vegetative state, until it was discovered that the stroke that caused her brain injury had damaged a cranial nerve, preventing her from opening her eyes. In fact, she had been fully conscious since soon after her stroke, and overheard bedside conversations debating whether or not to keep her alive ([12] p14). The widely reported case of Rom Houben, a Belgian man with locked-in syndrome who was misdiagnosed as vegetative for 23 years, is an extreme example of misdiagnosis [13]. Houben may have been conscious for decades, after emerging from a coma following a near-fatal car accident.

  5. Trace conditioning is a form of Pavlovian conditioning in which there is a stimulus-free time interval (the “trace interval”) between the conditioned stimulus and the unconditioned stimulus. There is extensive research demonstrating that in trace conditioning, learning is dependent on the hippocampus, an area of the brain implicated in memory (see [30]).

  6. It is a matter of some debate whether learning through trace conditioning requires consciousness or self-awareness. The presence of a conditioned response is not, to be sure, conclusive evidence of conscious awareness, nor is learning equivalent to being self-aware.

  7. The predictive capability of the learning data was evaluated retrospectively, with the researchers comparing learning data to subsequent clinical assessments of the same patients. All of the patients who subsequently exhibited some recovery (i.e. evolved from VS to MCS or severely disabled, or from MCS to severely disabled, or showed improved scores on the Coma Recovery Scale) showed learning. Only 2 out of 10 patients who failed to recover or improve showed any learning. An important difference between the learners and nonlearners was the etiology of their brain injuries. Learners all suffered traumatic brain injury, while nonlearners generally suffered non-traumatic brain injury. This is consistent with previous findings that there is greater likelihood of recovery in patients who suffer traumatic brain injuries than in patients with non-traumatic injuries.

  8. Other studies have found similarly provocative evidence of possible consciousness in VS patients. Owen et al. [25] performed fMRI scans on a behaviorally confirmed VS patient who, as demonstrated by brain activity, was able to follow verbal commands to visualize playing a game of tennis and walking through her home [25]. Her neural responses were consistent with those of healthy control subjects. She subsequently progressed to MCS, and was likely already transitioning from VS to MCS at the time of the study [7].

  9. A case study by Wilson et al [40] documented the anger, frustration, fear, and physical anguish of a patient who recovered from a persistent VS. She described being treated as if she were “stupid,” adding “I thought they were laughing at me I found it very offensive” [40]. The same patient recalled the severe pain she experienced—but could not express because she could not speak—from having her tracheotomy suctioned, and from physical therapy. The patient recovered to normal cognitive function after a brain infection, but remained severely physically disabled, and was unable to speak. She communicated by pointing to letters on a board.

  10. A longitudinal neuroimaging study of permanent VS patients with heterogeneous brain injury revealed a negative and progressive impact of long-lasting permanent VS on the structural, metabolic and functional status of the brain [27].

  11. See [48–51] for case studies of recovery from permanent VS. Many case studies of recovery from permanent VS predate the identification and development of diagnostic criteria for MCS in 2002 (see [3]), or involve patients who were diagnosed prior to the recognition of MCS, making it likely such patients were not vegetative, but had previously evolved to a MCS.

  12. There is some ethical debate about the authority of advance directives for dementia patients who are conscious but incompetent. Concerns arise in the context of potential conflicts between advance directives and the occurrent interests of demented patients (who may, for example, be happy and have an interest in treatment that would prolong life, despite an advance directive that limits treatment, or conversely, may not have foreseen the prolongation of misery that would result from a directive that requests aggressive treatment). One argument against the authority of advance directives questions whether a demented person can be identical with the person who drafted the advance directive. There is no principled reason why there should not be similar concerns about MCS patients with advance directives, which would further undermine the ability of patients to prospectively direct their own care.

  13. In a remarkable 2006 court case, a judge in England rejected a family’s right-to-die plea on behalf of a woman in VS, and ordered treatment with zolpidem, after media reports that zolpidem was a “miracle drug” that could bring patients out of a permanent VS. The family objected that treatment would be “unbearably cruel” and that the patient “would not want to live with severe disabilities while being aware of her condition.” After the treatment produced no effect, the court authorized withdrawal of artificial nutrition and hydration [65, 66].

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Acknowledgments

The author wishes to thank Francoise Baylis and the Novel Tech Ethics team for invaluable commentary on earlier drafts of this paper, and an anonymous reviewer for helpful remarks.

Research funded by Canadian Institutes of Health Research, MOP 77670, Therapeutic Hopes and ethical concerns: Clinical research in the neurosciences, and by NNF 80045, States of Mind: Emerging Issues in Neuroethics.

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Johnson, L.S.M. Implications of Recent Neuroscientific Findings in Patients with Disorders of Consciousness. Neuroethics 3, 185–196 (2010). https://doi.org/10.1007/s12152-010-9073-5

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