On Aug. 14, 2024, a study co-led by Mass General Brigham found that one in four patients with severe brain injury who appeared unresponsive responded to instructions covertly. Understanding this phenomenon can help guide decisions about life-sustaining treatment, goals of care, and clinical management, according to the authors.

In the study, 241 participants with severe brain injury who do not respond when given a simple instruction were assessed with functional MRI (fMRI), electroencephalography (EEG), or both tests. The fMRI and EEG brain responses showed that 60 (25 percent) of participants repeatedly followed this instruction covertly over minutes. The study results were published in the New England Journal of Medicine, patients who demonstrate this phenomenon, called cognitive motor dissociation, understand language, remember instructions and can sustain attention, even though they appear unresponsive. For these patients, cognitive (i.e., thinking) abilities exceed, and are therefore dissociated from, motor abilities.

Following a significant brain injury, individuals may have a disorder of consciousness, which can include coma, a vegetative state or minimally conscious state. Since the first study demonstrating cognitive motor dissociation in individuals with disorders of consciousness was published nearly two decades ago, centers around the world have found that this condition occurs in approximately 15 to 20 percent of unresponsive patients. However, the current study suggests it could be present in 25 percent of patients, or even more. Cognitive motor dissociation was most common in participants assessed with fMRI and EEG, suggesting that multiple tests, using different approaches, may be required to ensure consciousness is not missed.

This study included participant data from six different sites spanning the United States, United Kingdom, and Europe collected over approximately 15 years. Each site developed and rigorously tested their methods for detecting cognitive motor dissociation to minimize the possibility that a positive result was obtained spuriously. Some sites recruited participants from the intensive care unit just days after they sustained a severe brain injury, often from a trauma such as a car accident, a stroke or cardiac arrest. Other sites included participants who were months to years after their injury or illness and 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 bedside. This latter group would be expected to perform well on the fMRI and EEG tests, but, in 62 percent of those participants, 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.