When people suffer severe brain damage – from vehicle accidents, for example, or falls or aneurysms – they may slip into a coma for weeks, even years, with their eyes closed and their bodies unresponsive. However, a recent study suggests that even if they can’t communicate, they might still be aware.
Some of these patients recover, but others enter a mysterious state with their eyes open, yet without clear signs of consciousness. They may survive for decades without regaining a connection to the outside world.
These patients pose an agonising mystery both for their families and for the medical professionals who care for them, and who always wonder: if they can’t communicate, might they still be aware?
A large study published recently suggests that at least a quarter of them are, reports The New York Times.
Teams of neurologists at six research centres asked 241 unresponsive patients to spend several minutes at a time doing complex cognitive tasks, such as imagining themselves playing tennis.
Twenty-five percent of them responded with the same patterns of brain activity seen in healthy people, suggesting that they were able to think and were at least somewhat aware.
Dr Nicholas Schiff, a neurologist at Weill Cornell Medicine and an author of the study, said their findings show that up to 100 000 patients in the United States alone might have some level of consciousness despite their devastating injuries.
The results should lead to more sophisticated exams of people with so-called disorders of consciousness, and to more research into how these patients might communicate with the outside world, he said: “It’s not ok to know this and to do nothing.”
When people lose consciousness after a brain injury, neurologists traditionally diagnose them with a bedside exam. They may ask patients to say something, to look to their left or right, or to give a thumbs-up.
A patient who doesn’t respond at all might be diagnosed as being in a vegetative state. A patient who produces only fleeting responses might be diagnosed as minimally conscious.
Starting in the late 1990s, Schiff and his colleagues took detailed scans of the brains of some patients with disorders of consciousness. While many of them turned out to have massive damage, others had surprisingly large swaths of intact tissue.
The neurologists wondered if at least some of the patients were still “in there”, and just couldn’t let anyone know.
A few teams of researchers began probing for signs of awareness. They first used a technique called functional magnetic resonance imaging to track the flow of blood through the brain.
In a 2006 study, Adrian Owen, then at the Medical Research Council Cognition and Brain Sciences Unit in Cambridge, England, and his colleagues asked a woman diagnosed as being in a vegetative state to imagine playing tennis.
Regions of her brain became active in response, imaging scans showed. They were the same regions that become active in undamaged brains.
The early studies left neurologists wondering whether such a condition – which Schiff calls cognitive motor dissociation – was rare. The only way to find out was to run a large survey.
Six groups of experts, including Owen’s and Schiff’s teams, began collaborating on this in 2008. To accelerate it, they figured out how to record brain activity in patients with an electrode-covered cap. It’s much easier to use electrodes to test patients at their bedside than to wheel them into a brain scanner.
Despite these advances, the work crept forward slowly. The researchers had to get permission from the families of patients to examine them, and then they had to carry out a standardised set of tests.
To make sure false signals did not fool them, the researchers tried to get the patients to perform cognitive tasks over the course of several minutes.
They tested 241 patients who did not respond to commands during a traditional exam. They also had healthy volunteers perform the same tasks. The researchers then handed the data to a team of statisticians at the Icahn School of Medicine at Mount Sinai. The team performed the analysis without knowing which results came from which research group.
Their analysis revealed that 60 patients showed signs of awareness on the functional MRI scans, electrode recordings, or both. The results were published in The New England Journal of Medicine.
Schiff said that the results may be biased by the fact that he and his colleagues examined the patients eight months on average after their injuries. The people who managed to survive that long might be more resilient than those who died sooner. And that resilience might have made them more likely to remain aware.
On the other hand, Schiff argued, the tests were so demanding that some patients with some awareness probably did not score positive results. “We are likely to be missing people,” he said.
Dr James Bernat, a neurologist at the Geisel School of Medicine at Dartmouth who was not involved in the study, said that it offered a definitive look at cognitive motor dissociation.
“This is, without a doubt, the largest study that’s ever been done of these patients,” he said. “It’s done by the best people at the best places, so we’re not going to be seeing a better one coming down the pike in a long, long time.”
It’s possible that people with disorders of consciousness may one day take advantage of brain implants that have been developed to help those with other conditions to communicate.
Recently, another team of researchers reported that a patient paralysed by amyotrophic lateral sclerosis, or Lou Gehrig’s disease, was able to communicate through a brain implant after just 30 minutes of training.
Schiff suspects that some people with cognitive motor dissociation will probably be able to master these implants.
“We have tens of thousands of people like that,” he said. “We should do something about it.”
Study details
Cognitive Motor Dissociation in Disorders of Consciousness
Yelena Bodien, Judith Allanson, Nicholas Schiff et al.
Published in The New England Journal of Medicine on 14 August 2024
Abstract
Background
Patients with brain injury who are unresponsive to commands may perform cognitive tasks that are detected on functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). This phenomenon, known as cognitive motor dissociation, has not been systematically studied in a large cohort of persons with disorders of consciousness.
Methods
In this prospective cohort study conducted at six international centers, we collected clinical, behavioural, and task-based fMRI and EEG data from a convenience sample of 353 adults with disorders of consciousness. We assessed the response to commands on task-based fMRI or EEG in participants without an observable response to verbal commands (i.e., those with a behavioral diagnosis of coma, vegetative state, or minimally conscious state–minus) and in participants with an observable response to verbal commands. The presence or absence of an observable response to commands was assessed with the use of the Coma Recovery Scale–Revised (CRS-R).
Results
Data from fMRI only or EEG only were available for 65% of the participants, and data from both fMRI and EEG were available for 35%. The median age of the participants was 37.9 years, the median time between brain injury and assessment with the CRS-R was 7.9 months (25% of the participants were assessed with the CRS-R within 28 days after injury), and brain trauma was an etiologic factor in 50%. We detected cognitive motor dissociation in 60 of the 241 participants (25%) without an observable response to commands, of whom 11 had been assessed with the use of fMRI only, 13 with the use of EEG only, and 36 with the use of both techniques. Cognitive motor dissociation was associated with younger age, longer time since injury, and brain trauma as an etiologic factor. In contrast, responses on task-based fMRI or EEG occurred in 43 of 112 participants (38%) with an observable response to verbal commands.
Conclusions
Approximately one in four participants without an observable response to commands performed a cognitive task on fMRI or EEG as compared with one in three participants with an observable response to commands.
NEJM article – Cognitive Motor Dissociation in Disorders of Consciousness (Open access)
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