medwireNews: Around one in four patients with brain injury who are unresponsive to verbal commands perform cognitive tasks detectable on functional magnetic resonance imaging (fMRI) and/or electroencephalography (EEG), suggests a prospective cohort study.
This is “higher than previous estimates,” say Nicholas Schiff (Fiel Family Brain and Mind Research Institute, New York, USA) and colleagues, and suggests that “the use of task-based fMRI and EEG can improve detection.”
They studied clinical, behavioral, and task-based fMRI and EEG data, gathered from six international centers between 2006 to 2023, to explore the phenomenon known as cognitive motor dissociation in 353 patients with disorders of consciousness from brain injury.
Cognitive motor dissociation was defined as “a lack of responses to commands and a lack of intelligible speech as assessed with the CRS-R [Coma Recovery Scale-Revised],” the researchers explain.
Among 353 brain injury patients (median age 37.9 years; 64% men) who had undergone at least one assessment for an observable response to commands using the CRS-R, and had interpretable data from at least one fMRI or EEG (65%) or both (35%).
The predominant etiologic factor among the patients was brain trauma, in 50%, and the most common diagnosis made based on the CRS-R was coma or vegetative state in 40%, followed by minimally conscious state–minus in 29%, minimally conscious state–plus in 22%, and emerged from a minimally conscious state in 10%.
In all, 241 patients in a coma or vegetative state (unconscious) or with minimally conscious state–minus (presence or signs of conscious awareness or intelligible verbal output) did not respond to commands on the CRS-R when tested a median 6.3 years after injury.
However, 25% of these individuals showed cognitive motor dissociation, in that they did respond to commands such as “imagine playing tennis” and “imagine opening and closing your hand,” on task-based fMRI (n=11), task-based EEG (n=13), or both (n=36), when assessed within 7 days before or after the CRS-R assessment.
Schiff and team comment that “[t]he percentage of participants with cognitive motor dissociation is 5 to 10 percentage points higher in our study than in previous studies,” which may be due to the use of multi-modal assessment, whereby the responses of patients assessed with both fMRI and EEG were based on results for either technique.
In addition, while previous studies have shown that cognitive motor dissociation is more common in patients with traumatic brain injury, the investigators also observed the phenomenon in patients with nontraumatic brain injury, such as following stroke or cardiac arrest. However, the percentage of patients with traumatic brain injury was higher among those with cognitive motor dissociation, compared with individuals who did not respond to commands on the CRS-R or imaging (65% vs 38%).
The team notes that the cognitive motor dissociation cohort was younger than the group who did not respond to imaging commands (median 30.5 years vs 45.3 years) and was assessed later after injury (median 10.7 months vs 4.3 months).
The investigators highlight that “[a]lthough standardized behavioral evaluation remains the reference standard for detecting a response to commands at the bedside, the use of task-based fMRI and EEG can improve detection, and the use of both imaging techniques appears to be a more sensitive approach than the use of one of the techniques alone.”
They add that cognitive motor dissociation may have been underestimated in this and previous studies because task-based imaging draws on more cognitive resources, such as short-term memory, selective attention, and mental persistence, than typically measured in command-following tasks assessed at the bedside, a hypothesis backed up by the comparatively low 38% of 112 patients who responded to both CRS-R and imaging commands.
Schiff and team write in The New England Journal of Medicine that their results “indicate that cognitive motor dissociation is more common than previously realized.”
They acknowledge that “task-based fMRI and EEG are not yet widely available for the clinical assessment of disorders of consciousness,” but believe that “the standardization, validation, and simplification of task-based fMRI and EEG methods that are used to detect cognitive motor dissociation are needed to prompt widespread clinical integration of these techniques and investigation of the bioethical implications of the findings.”
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