A large study has revealed that up to one in four brain injury patients in a coma or vegetative state showed cognitive responses on electroencephalography (EEG) readouts or functional magnetic resonance imaging (fMRI) scans.
These patients are unresponsive to bedside commands, and yet fMRI and EEG shows they may perform cognitive tasks. Known as cognitive motor dissociation or “locked in syndrome”, the international study is the largest investigation of this phenomenon to date.
For the study, researchers at six international centres collected clinical, behavioural, and task-based fMRI and EEG data from 353 adults with disorders of consciousness and assessed the response to commands on task-based fMRI or EEG in participants without an observable response to verbal commands, as well as in participants with an observable response to verbal commands.
Weill Cornell University reports that for the study, researchers repeatedly asked each patient to perform a series of continuous motor tasks, as well as motor-related cognitive tasks for multiple bouts of 15 to 30 seconds of performance separated by equal length rest periods.
The team found that 25% of the patients were able to perform the cognitive tasks.
Further, the university reports that while 38% of the patients who demonstrated motor response to spoken commands at the bedside performed these cognitive tasks, the majority of these patient controls did not demonstrate the cognitive performance, emphasising that the fMRI and EEG mental imagery tasks demand the sustained use of several cognitive resources, such as short-term memory, that are not required for following bedside commands or even simple communication.
The fact that one quarter of the motor-unresponsive patients with cognitive-motor dissociation successfully performed the tasks suggests that many seemingly unconscious patients may be aware and capable of cognition, reports Weill Cornell.
“We find that this kind of sharp dissociation of retained cognitive capabilities and no behavioural evidence of them is not uncommon. I think we now have an ethical obligation to engage with these patients, to try to help them connect to the world,” said study corresponding author Dr. Nicholas Schiff, Professor of Neurology and Neuroscience in the Feil Family Brain and Mind Research Institute at Weill Cornell Medicine, in a statement from the University.
“Just knowing that a patient has this ability to respond cognitively can be a game-changer in terms of life-support decisions and the degree of engagement of caregivers and family members.”
“Some patients with severe brain injury do not appear to be processing their external world. However, when they are assessed with advanced techniques such as task-based fMRI and EEG, we can detect brain activity that suggests otherwise,” added lead study author Dr. Yelena Bodien, an investigator for the Spaulding-Harvard Traumatic Brain Injury Model Systems and Massachusetts General Hospital’s Center for Neurotechnology and Neurorecovery.
“These results bring up critical ethical, clinical and scientific questions – such as, how can we harness that unseen cognitive capacity to establish a system of communication and promote further recovery?”
According to the researchers, the results may pave the way for new research and investigations into methods for detecting locked in syndrome, understanding the clinical value of detection, as prior studies suggest that patients with this condition may have a greater chance of recovery compared with those who cannot perform cognitive tasks, as well as studies of specific interventions such as brain-computer interfaces.
“What we need here is what we in our consortium have been trying to get started for 20 years: a sustained effort to benefit patients who have disorders of consciousness with systematic medical research, technology development and better clinical infrastructure,” Schiff added.
The study has been published in The New England Journal of Medicine.
