New research co-led by Mass General Brigham experts has found that brain scans can detect consciousness in some unresponsive brain-injured patients.
In the study, 241 severely brain-injured participants who were unresponsive when given a simple instruction were tested with functional magnetic resonance imaging (fMRI), electroencephalography (EEG), or both. During these tests, participants heard instructions, such as “imagine opening and closing your hand” followed, 15-30 seconds later, by “stop imagining opening and closing your hand.” The fMRI and EEG brain responses showed that 60 (25 percent) of the participants repeatedly followed this instruction covertly for minutes. According to the authors of the study, published August 15 in the journal New England Journal of Medicine, Patients with this phenomenon, called cognitive-motor dissociation, understand language, remember instructions, and can maintain attention, even though they appear unresponsive. In these patients, cognitive (i.e., thinking) abilities outweigh motor abilities and are therefore dissociated from them.
“Some severely brain-injured patients don’t seem to process their external world. However, when assessed with advanced techniques such as task-based functional MRI and EEG, we can detect brain activity that suggests otherwise,” said study senior author Dr. Yelena Bodien, a researcher at the Spaulding-Harvard Traumatic Brain Injury Model System and the Center for Neurotechnology and Neurorecovery at Massachusetts General Hospital. “These results raise critical ethical, clinical and scientific questions, such as how can we harness this invisible cognitive ability to establish a system of communication and promote greater recovery?”
Following a major brain injury, people may suffer from a disorder of consciousness, which can include coma, vegetative state, or minimally conscious state. Since the first study demonstrating cognitive-motor dissociation in people with disorders of consciousness was published nearly two decades ago, centers around the world have found that this condition occurs in about 15 to 20 percent of unresponsive patients. However, the current study suggests that it might be present in 25 percent of patients, or even more. Cognitive-motor dissociation was more common in participants assessed with fMRI and EEG, suggesting that multiple tests, using different approaches, may be necessary to ensure that consciousness is not missed.
This study included data from participants at six different sites in the United States, the United Kingdom, and Europe collected over approximately 15 years. Each site developed and rigorously tested its methods for detecting cognitive-motor dissociation to minimize the possibility of a false-positive result. Some sites recruited participants from the intensive care unit just days after they had suffered a severe brain injury, often due to trauma such as a car accident, stroke, or cardiac arrest. Other sites included participants who were months or years removed from their injury or illness and who were living in nursing facilities or at home.
In addition to studying the 241 participants who did not respond to simple instructions, the research included 112 participants who did respond to simple instructions at the patient’s bedside. This latter group would be expected to perform well on fMRI and EEG tests, but in 62 percent of those participants, the researchers did not detect brain responses suggesting they were covertly following instructions. The authors note that this finding may reflect the complexity of the fMRI and EEG tasks and underscores the high level of thinking skills required to perform them.
Simply knowing that someone is cognitively aware and more capable than they appear at first glance can substantially alter their clinical care. “Families have told us that once a positive result revealing cognitive motor dissociation is shared with the patient’s clinical team, it can change the way the team interacts with their loved one,” Bodien said. “Suddenly, the team pays more attention to subtle behavioral signs that might be under voluntary control, such as talking to the patient or playing music in the room. On the other hand, failing to detect cognitive motor dissociation can have serious consequences, including premature withdrawal of life support, lack of signs of consciousness, and lack of access to intensive rehabilitation.”
“We’ve found that this kind of acute dissociation of retained cognitive abilities and the absence of behavioral evidence of them is not uncommon. I think we now have an ethical obligation to work with these patients, to try to help them connect with the world,” said senior author Dr. Nicholas Schiff, the Jerold B. Katz Professor of Neurology and Neuroscience in the Feil Family Brain and Mind Research Institute at Weill Cornell Medicine and administrative director of the consortium. “What we need here is what we in our consortium have been trying to put in place for 20 years: a sustained effort to benefit patients with disorders of consciousness with systematic medical research, technological development and improved clinical infrastructure.
A limitation of the study was that the tests were not standardized; each of the study centers assessed patients in their own way, which created variability within the data. In addition, many participants were enrolled because family members learned about the study and contacted the researchers. This recruitment approach limits the researchers’ ability to determine the global prevalence of cognitive motor dissociation. There are no professional guidelines stipulating how cognitive motor dissociation should be assessed, and most centers are unable to provide these tests; clinical translation will need to be a focal point for future research.
“To continue our progress in this field, we need to validate our tools and develop approaches to systematically and pragmatically screen non-responders so that testing becomes more accessible,” Bodien said. “The Massachusetts General Hospital Emerging Awareness Program offers these clinical assessments, however, in other settings, a patient may have to enroll in a research study to be tested. We know that cognitive motor dissociation is not uncommon, but resources and infrastructure are required to optimize screening for this condition and provide appropriate support to patients and their families.”
The researchers added that the findings could spur research into specific interventions to foster effective communication, including brain-computer interfaces.