- In some cases, functional MRI and EEG can now discern which behaviorally unresponsive patients have residual consciousness
- This ability has led to efforts to update diagnosis codes and guidelines for the care of patients with disorders of consciousness
- Important questions remain about how signals of neural activity correspond to different forms of subjective experience and processing of stimuli and the role of the emerging neurotechnologies in prognostication
- The new uses of these technologies create important ethical dilemmas, and explicit guidance is needed for clinicians, researchers, families and surrogate decision-makers
Traditionally, both normal and pathological states of the brain have been described with respect to two elements of consciousness—wakefulness and awareness. The first is assessed as a level of arousal (e.g., eye-opening) and the other by looking for intentional behavioral responses to external stimuli.
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In 2006 a case report published in Science sparked a paradigm shift in how disorders of consciousness (DoC) are conceptualized and researched. Through the use of functional MRI, a young woman diagnosed as being in a vegetative state was found to have residual awareness. Signals were detected in her supplementary motor area when she was asked to imagine playing tennis and in brain areas related to navigation when she was asked to imagine walking through her house.
Michael J. Young, MD, MPhil, associate director of the NeuroRecovery Clinic at Massachusetts General Hospital, Brian L. Edlow, MD, associate director of the Center for Neurotechnology and Neurorecovery in the Department of Neurology and a faculty member in the Athinoula A. Martinos Center for Biomedical Imaging, and colleagues published in Brain a detailed history of the neuroethics of DoC.
This partial summary briefly reviews advances in detecting consciousness with greater precision and some of the ethical implications.
Overview of Research
By 2015 a meta-analysis of 37 published studies, reported in the Journal of Neurology, Neurosurgery and Psychiatry, showed that 32% of patients with a diagnosis of minimally conscious state and 14% of those with a diagnosis of vegetative state responded to commands on fMRI or EEG.
In many cases, the results of this testing indicate only a binary state of awareness—the upper limit of cognitive assessment consists of asking yes/no questions and can't obtain information about the patient's subjective state. However, the absence of demonstrable brain activity in response to task-based assessments doesn't necessarily mean the relevant cognitive abilities are also absent.
Covert brain activation on EEG has been linked to substantially improved outcomes for patients who are behaviorally unresponsive after acute injury, which suggests the advanced neurotechnologies have potential to aid in prognostication.
These innovations are particularly exciting because they come just as methods to promote neurorecovery in DoC are being identified, including certain medications, music, focused ultrasound pulsation, transcranial stimulation, deep brain stimulation, vagal nerve stimulation, vestibular stimulation and brain–computer interfaces.
Changes in Guidelines
In 2020 the International Federation of Clinical Neurophysiology outlined a stepwise procedure, from standard EEG to paired EEG and transcranial magnetic stimulation, for neurophysiological assessment of patients with prolonged DoC. Its proposal appears in Clinical Neurophysiology.
Current guidelines on DoC from the American Academy of Neurology and European Academy of Neurology advise multimodal evaluations for avoiding misdiagnosis but don't say when and how they should be used in decision-making.
The EAN does recommend that when different modalities have discordant results, the patient should be diagnosed with the highest level of consciousness suggested by any of them. This implies that if fMRI or EEG measures have not been obtained, the workup remains incomplete—an ethical concern in itself.
Meanwhile, there's a move to revise diagnostic categories to reflect the more granular information available. The ICD-10 contains codes for locked-in syndrome, persistent vegetative state and coma but not for minimally conscious state or cognitive motor dissociation (covert consciousness).
Novel neuroimaging and electrophysiological tools for detecting covert consciousness raise a challenging set of ethical questions, including:
- Is the state of consciousness itself intrinsically valuable?
- What is the phenomenological significance of the data the novel technologies provide?
- How should that data be used, considering that keeping additional neurocritically ill patients on prolonged life support strains the already limited supply of ICU beds?
- fMRI and advanced EEG are available at only a few centers; how can access to them be made equitable?
- How can new DoC guidelines be implemented while protecting patients and families from increased suffering in situations where meaningful recovery is unlikely yet possible?
- How should results be conveyed and explained to surrogate decision makers in cases of uncertainty?
A related challenge is the potential need to ensure post-acute care and rehabilitation systems for patients with DoC over the long term.
To address these and other challenges related to DoC, the authors and colleagues recently launched a study supported by the NIH BRAIN Initiative—DECODE (Data-driven neuroEthics for COnsciousness DEtection)—with the goal of developing a framework for responsible clinical translation of these neurotechnologies.
Learn more about the Coma Recovery Lab
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