Patients with disorders of consciousness have a reduced level of awareness, categorised as coma, vegetative state, or minimally conscious state based on their observable responses. Although some patients appear unresponsive, their brains may show activity on functional magnetic resonance imaging (fMRI) or electroencephalography (EEG) when asked to perform cognitive tasks—a phenomenon known as cognitive motor dissociation. Improving the detection of this condition is crucial, as it is associated with better outcomes one year after brain injury.
What you need to know
In this prospective study, six international centres brought together the first large cohort of 353 patients with disorders of consciousness. The researchers collected clinical, behavioural, and task-based fMRI and EEG data to study cognitive motor dissociation. Simple commands like “imagine playing tennis” or “open and close your hand” reflect language comprehension, short-term memory, attention, and persistence that could be detected on fMRI, EEG, or both.
Trained study staff used the Coma Recovery Scale-Revised (CRS-R) to assess patients’ level of consciousness. Patients underwent task-based fMRI, EEG or both within seven days before or after their CRS-R evaluation. Processing and interpreting fMRI and EEG findings were automated, while study staff who were unaware of the behavioural assessment findings removed artefacts from the EEG data. If participants underwent fMRI or EEG across several days, the best response on the first day was selected for further analysis. Only patients diagnosed with coma, vegetative state, or minimally conscious state-minus, and with at least one interpretable fMRI or EEG session, were included in the study. In parallel, a group of healthy controls performed the task-based fMRI and EEG to ensure that responses on imaging were detectable in persons with intact brain processing and observable responses.
What the data revealed
Results in healthy controls showed that the methodological approach with fMRI and EEG gives many false negatives. In other words, fMRI or EEG can fail to detect brain activation in healthy individuals with an observable response to verbal commands. However, even in this setting, about one in four patients who seemed unable to follow commands showed signs of brain activity during task-based fMRI or EEG, compared to one in three patients who could.
fMRI and EEG imaging improve the detection of cognitive motor dissociation, and the combination of both appears to be more sensitive. The proportion of patients with cognitive motor dissociation was much higher than previously published in the literature. In contrast to previous studies, cognitive motor dissociation was also diagnosed in patients with non-traumatic brain injuries, such as strokes or cardiac arrests. In this cohort, cognitive motor dissociation was linked to younger age, longer time since injury, and brain trauma as the underlying cause.
Not so fast
These results may be limited by survival bias, as patients with chronic brain injuries are likely to have higher cognitive resilience. Secondly, different data collection and patient recruitment methods across the six study sites may have led to variations in cognitive motor dissociation detection rates. Therefore, the main findings may not be generalisable across all centres. Thirdly, the specialised and highly qualified personnel required are only available at a few academic centres, which limits the broader use of this approach to detect cognitive motor dissociation. Finally, standardisation, validation, and simplification of fMRI and EEG procedures are necessary for wider clinical adoption.
Why does it matter?
Recognising that patients who appear to be unconscious may still think and process information could impact decisions, including withdrawal of life-sustaining treatment and clinical management. It may also reduce emotional distress, as it helps medical teams and families treat these patients with more awareness and understanding. Also, improved detection of cognitive motor dissociation results in better recovery outcomes one year after injury. More importantly, standardisation in cognitive motor dissociation diagnosis may open new avenues for communication with these patients.
Take home messages
1. One in four patients who appear unresponsive after a brain injury shows signs of hidden consciousness on fMRI and/or EEG, highlighting that cognitive motor dissociation is more common than previously thoughts.
2. Improved identification of cognitive motor dissociation could leave to better clinical decisions and outcomes one year after brain injury.
3. Standardising the diagnosis of cognitive motor dissociation may create new opportunities for communicating with these patients.
Guest author: Solène Grosdidier, PharmD, PhD
This article was written as part of a series of ‘journal club’ summaries for Scientific Writers Ltd and is based on the following publication.
Title: Cognitive Motor Dissociation in Disorders of Consciousness
First Author: Bodien YG, et al.
Journal: The New England Journal Of Medicine
Date online: 14 August 2024
