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BOSTON — For years, families of brain-injured patients have insisted their unresponsive loved ones were still “in there.” Now, a groundbreaking study on consciousness suggests they may have been right all along.
Researchers have discovered that approximately one in four patients who appear completely unresponsive may actually be conscious and aware but physically unable to show it. This phenomenon, known as cognitive motor dissociation, challenges long-held assumptions about disorders of consciousness and could have profound implications for how we assess and care for brain-injured patients.
The study, published in the New England Journal of Medicine, represents the largest and most comprehensive investigation of cognitive motor dissociation to date. An international team of researchers used advanced brain imaging and electrophysiological techniques to detect signs of consciousness in patients who seemed entirely unresponsive based on standard behavioral assessments.
The findings suggest that cognitive motor dissociation is far more common than previously thought. This has major implications for clinical care, end-of-life decision-making, and our fundamental understanding of consciousness itself.
The study examined 353 adult patients with disorders of consciousness resulting from various types of brain injuries. These conditions exist on a spectrum, ranging from coma (where patients are completely unresponsive and show no signs of awareness) to the vegetative state (where patients may open their eyes and have sleep-wake cycles but show no signs of awareness) to the minimally conscious state (where patients show some inconsistent but reproducible signs of awareness).
Traditionally, doctors have relied on bedside behavioral assessments to diagnose a patient’s level of consciousness. However, this approach assumes that if a patient can’t physically respond to commands or stimuli, they must not be aware. The new study challenges this assumption, revealing signs of consciousness that may not be outwardly visible.
The researchers used two main techniques to probe for hidden consciousness:
- Functional magnetic resonance imaging (fMRI): This technique measures brain activity by detecting changes in blood flow. Patients were asked to imagine performing specific tasks, like playing tennis or navigating their home, while in the scanner. If the appropriate brain areas activated in response to these commands, it suggested the patient could understand and follow instructions, even if they couldn’t physically respond.
- Electroencephalography (EEG): This technique measures electrical activity in the brain using electrodes placed on the scalp. Patients were given similar mental tasks, and their brain wave patterns were analyzed for signs of intentional responses.
Strikingly, the study found that 25% of patients who showed no behavioral signs of consciousness demonstrated brain activity consistent with awareness and the ability to follow commands. In other words, one in four patients who appeared to be in a vegetative state or minimally conscious state without command-following ability were actually conscious and able to understand and respond mentally to instructions.
“Some patients with severe brain injury do not appear to be processing their external world. However, when they are assessed with advanced techniques such as task-based fMRI and EEG, we can detect brain activity that suggests otherwise,” says lead study author Yelena Bodien, PhD, in a statement.
Bodien is an investigator for the Spaulding-Harvard Traumatic Brain Injury Model Systems and Massachusetts General Hospital’s Center for Neurotechnology and Neurorecovery.
“These results bring up critical ethical, clinical, and scientific questions – such as how can we harness that unseen cognitive capacity to establish a system of communication and promote further recovery?”
The study also found that cognitive motor dissociation was more common in younger patients, those with traumatic brain injuries, and those who were assessed later after their initial injury. This suggests that some patients may recover cognitive abilities over time, even if they remain unable to communicate behaviorally.
Interestingly, even among patients who could follow commands behaviorally, more than 60% did not show responses on the brain imaging tests. This highlights the complex nature of consciousness and the limitations of current detection methods.
The findings raise challenging questions about how we diagnose disorders of consciousness, make end-of-life decisions, and allocate resources for long-term care and rehabilitation. It also opens up new avenues for potential therapies aimed at restoring communication in these patients.
While the study represents a significant advance, the authors caution that the techniques used are not yet widely available and require further refinement before they can be routinely used in clinical practice.
“To continue our progress in this field, we need to validate our tools and to develop approaches for systematically and pragmatically assessing unresponsive patients so that the testing is more accessible,” adds Bodien. “We know that cognitive motor dissociation is not uncommon, but resources and infrastructure are required to optimize detection of this condition and provide adequate support to patients and their families.”
As this research continues to evolve, it holds the promise of giving voice to the voiceless and bringing hope to families grappling with the aftermath of severe brain injuries. It’s a powerful reminder of how much we still have to learn about the human brain and the nature of consciousness.
Paper Summary
Methodology
The researchers used a standardized behavioral assessment tool called the Coma Recovery Scale-Revised (CRS-R) to categorize patients’ level of consciousness based on their observable responses. They then used fMRI and EEG to look for hidden signs of awareness. In the fMRI tests, patients were asked to imagine doing specific activities, like playing tennis. If the brain areas associated with those activities lit up, it suggested the patient was following commands mentally.
For EEG, patients were given similar mental tasks, and their brain wave patterns were analyzed for signs of intentional responses. The researchers compared the results of these brain-based tests to the behavioral assessments to identify cases of cognitive motor dissociation.
Results Breakdown
Out of 241 patients who showed no behavioral signs of following commands, 60 (25%) demonstrated the ability to follow commands on either fMRI or EEG. This group was considered to have cognitive motor dissociation. These patients tended to be younger, were more likely to have traumatic brain injuries, and were assessed later after their initial injury compared to those without cognitive motor dissociation. Interestingly, among 112 patients who could follow commands behaviorally, only 43 (38%) showed responses on fMRI or EEG, highlighting the complexity of consciousness detection.
Study Limitations
The study had several limitations. The patient sample was not fully representative, as it included many chronic patients who had survived their initial injury and had access to advanced imaging facilities. This could have led to an overestimation of the prevalence of cognitive motor dissociation. The methods for acquiring and analyzing data varied across study sites, which could have influenced the results. Additionally, the study was descriptive and couldn’t determine causal relationships between factors like age or time since injury and the presence of cognitive motor dissociation.
Discussion & Takeaways
The study suggests that cognitive motor dissociation is more common than previously thought, occurring in about one in four patients who appear unresponsive. This has significant implications for clinical care, ethical decision-making, and our understanding of consciousness.
The findings highlight the need for more sophisticated consciousness assessment tools in clinical practice and suggest that some patients may retain or recover cognitive abilities over time, even without showing behavioral improvements. The research also underscores the complex nature of consciousness and the limitations of current detection methods.
Funding & Disclosures
The study was primarily funded by the James S. McDonnell Foundation, with additional support from various national and international research organizations. The authors disclosed no relevant conflicts of interest. It’s worth noting that while some of the brain imaging equipment used in the study was manufactured by private companies, these companies had no role in the study design, data collection, analysis, or reporting of results.
—-Shocking brain scans reveal active consciousness among ‘vegetative’ patients
Please no:
—-Brain scans reveal active consciousness among patients with persisting coma
The use of the term ‘vegetative’ is unethical, dehumanizing, depersonalizing.
Harold A Maio, retired mental health editor