An international study launched in 2008 by Dr. Nicholas Schiff (Weill Cornell Medicine), Steven Laureys (University of Liège), and Adrian Owen (University of Cambridge, currently at the University of Western Ontario) shows that patients suffering from severe brain injuries can exhibit clear signs of consciousness when examined through brain imaging and asked to perform a complex mental task, even if they are unable to move or speak.
The study, published in the New England Journal of Medicine, is the largest ever conducted on the prevalence of this state, called cognitive-motor dissociation. Clinical teams observed that among 241 patients in a coma or in unresponsive wakefulness (formerly called vegetative state), who could not visibly respond to commands given at their bedside, a quarter of them showed cognitive responses, as indicated by electroencephalography (EEG) readings or functional magnetic resonance imaging (fMRI) scans. The patients were included from six university medical centers, the largest being the Brain Center at the CHU de Liège, founded by Professor Laureys.
The results confirm what the Liège team has demonstrated over the past two decades: some patients who survive a coma retain a form of consciousness.
“We find that this clear dissociation between preserved cognitive abilities and the absence of behavioral evidence is not rare,” said Dr. Nicholas Schiff, neurologist at Weill Cornell Medical Center. “We now have an ethical obligation to engage with these patients and try to help them interact with their environment.”
The patients in the study were assessed at Weill Cornell Medical Center, CHU de Liège, University of Cambridge, Massachusetts General Hospital, Columbia University Irving Medical Center, Rockefeller University Hospital, as well as Pitié-Salpêtrière Hospital in Paris.
Cognitive-motor dissociation is considered close to the locked-in syndrome, which isolates an intact brain, generally as a result of a stroke or degeneration of motor neurons in amyotrophic lateral sclerosis. However, it is also observed in patients with more extensive brain injuries who otherwise appear little or not at all aware of their surroundings.
For the study, researchers recruited a total of 353 adults suffering from disorders of consciousness, usually due to severe traumatic brain injuries or interruptions in the oxygen supply to the brain following a stroke or heart attack. The majority of them were cared for at home or in long-term care facilities, and the median time elapsed since the brain injury was about eight months.
Researchers asked each patient to perform a series of motor tasks (e.g., “open and close your hand”) as well as cognitive tasks related to motor function (“imagine opening and closing your hand”) for several periods of 15 to 30 seconds, interspersed with rest periods of the same duration. These tasks were carried out using rigorous protocols that the researchers had designed and validated to avoid false positives.
Of the 241 patients who were unable to follow bedside commands, 25% were able to perform these cognitive tasks, as evidenced by brain activity patterns measured by EEG and/or fMRI, comparable to those observed in control subjects.
Among the 112 patients who demonstrated a motor response to verbal commands at the bedside, only 38% were able to carry out these cognitive tasks. This dissociation underscores that the mental imagery tasks in fMRI and EEG require sustained use of several cognitive resources, such as short-term memory, which are not necessary for responding to simple commands or for communication.
According to the researchers, the fact that a quarter of motor-unresponsive patients presenting cognitive-motor dissociation were able to execute these tasks suggests that many apparently unconscious patients may actually be conscious and possess cognitive faculties.
“Some patients with severe brain injuries seem to not process their external environment. However, when evaluated using advanced techniques such as fMRI and EEG, we can detect brain activity suggesting otherwise,” said Dr. Yelena Bodien, the lead author of the study. “These results raise crucial ethical, clinical, and scientific questions: how to leverage this invisible cognitive ability to establish a communication system and promote recovery?”
The findings of the study should lead to new research avenues, including the development of more accessible methods to detect this dissociation, methods that, unlike task-based fMRI and EEG, could be used in a greater number of clinical centers.
“New brain-computer interface technologies will allow for more democratic use by clinicians and offer patients the possibility to respond to questions regarding their quality of life,” commented Professor Steven Laureys, FNRS Research Director and founder of the Coma Science Group and the Brain Center.
“What we need is what our consortium has been striving to implement for 20 years: a sustained effort for patients with disorders of consciousness, through systematic medical research, technology development, and better clinical infrastructure,” said Dr. Schiff.
As Dr. Olivia Gosseries, FNRS Researcher and co-director of the Coma Science Group notes, “this study is an important step as it shows that the absence of response is not synonymous with unconsciousness and is much more common than we initially thought. Some patients seem unconscious and yet, through brain imaging, we find that they retain their cognitive abilities. This changes the game for the treatment of patients with disorders of consciousness.”
Source
Cognitive Motor Dissociation in Disorders of Consciousness.
Bodien YG, Allanson J, Cardone P, Bonhomme A, Carmona J, Chatelle C, Chennu S, Conte M, Dehaene S, Finoia P, Heinonen G, Hersh JE, Kamau E, Lawrence PK, Lupson VC, Meydan A, Rohaut B, Sanders WR, Sitt JD, Soddu A, Valente M, Velazquez A, Voss HU, Vrosgou A, Claassen J, Edlow BL, Fins JJ, Gosseries O, Laureys S, Menon D, Naccache L, Owen AM, Pickard J, Stamatakis EA, Thibaut A, Victor JD, Giacino JT, Bagiella E, Schiff ND.
N Engl J Med. 2024 Aug 15;391(7):598-608. doi: 10.1056/NEJMoa2400645.
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Olivia Gosseries
Exploring the Future of Consciousness Research and Patient Care
Recent breakthroughs in consciousness research, particularly highlighted by an international study led by renowned neurologists, have unveiled the possibility that patients with severe brain injuries may retain cognitive abilities even when they appear unresponsive. This phenomenon, known as cognitive motor dissociation, has broad implications for how we understand consciousness and approach the treatment and rehabilitation of affected individuals.
Emerging technologies, such as brain-computer interfaces (BCIs), are at the forefront of this evolving landscape. These innovative tools promise to provide new ways for clinicians to interact with patients diagnosed with disorders of consciousness. BCIs could facilitate communication by translating brain activity into actionable signals, potentially allowing these patients to express their needs and thoughts, which might significantly contribute to their quality of life.
While traditional imaging techniques like EEG and functional MRI have shown that a notable percentage of so-called unresponsive patients can process information cognitively, the challenge remains in making these assessments routine and accessible. This gap in detection can lead to an underestimation of a patient’s cognitive state and may hinder the development of personalized rehabilitation strategies.
Researchers are advocating for a paradigm shift in how medical professionals assess consciousness. By expanding the tools available for diagnosis and treatment—ranging from advanced neuroimaging to simpler, more portable devices—the healthcare community could better understand patient states and enhance therapeutic interventions. This shift not only has the potential to transform patient care but also necessitates new ethical considerations regarding patient autonomy and the importance of informed decision-making in treatment plans.
As the field of neuroscience continues to evolve, interdisciplinary collaboration will be crucial. Beyond advancements in technology, integrating insights from cognitive psychology, rehabilitation science, and even philosophy will enrich our understanding of consciousness. This holistic approach may foster innovative care models that respect the agency of patients while supporting their rehabilitation.
The findings from the recent study underscore the necessity of developing effective communication strategies for patients who may be cognitive but unable to move or speak. This focus on patient agency will likely shape future research and clinical practices, paving the way for more humane and informed care for those affected by disorders of consciousness.