A study published this week could help doctors to identify patients with brain injuries, in seemingly unresponsive states, who are more likely to recover.
In the study, published in the journal Brain on Monday, researchers identified what may be the source of a curious phenomenon known as “hidden consciousness” or cognitive motor dissociation (CMD).
Hidden consciousness is seen in patients with acute brain injury who appear to be in a coma or other unresponsive state.
Patients with CMD seem to be able to hear and comprehend verbal commands even though they cannot carry out those instructions because the body does not respond, study author Jan Claassen, a researcher at Columbia University and critical care neurologist at New York-Presbyterian/Columbia University Irving Medical Center, said in a statement.
The CMD phenomenon has only been identified in the past few years and is still poorly understood.
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Methods have been developed to detect CMD in unresponsive patients. These include analyzing changes in electrical activity or cerebral blood flow recorded by an electroencephalogram (EEG) or functional magnetic resonance imaging (fMRI) respectively. But both of these methods currently have their limitations.
Nevertheless, it is thought that around 15 to 20 percent of patients who appear to be in a coma or another unresponsive state display signs of CMD when evaluated with such methods, Claassen told Newsweek. The detection of CMD is reshaping our understanding of patients in comatose or other unresponsive states.
Associated With Recovery of Consciousness
Clinicians define when a patient is in a “coma” purely based on the clinical examination, Claassen said. They apply this label to patients who display a complete absence of arousal (for example, eye opening) and awareness.
Patients with CMD do not seem to be able to follow commands and may in clinical examination appear to be in a coma.
But an analysis of EEG or functional MRI, recorded while patients are given verbal commands, reveals that the brains of these unresponsive patients are being activated in a similar way to conscious patients, Claassen said. This supports the interpretation that patients with CMD are to some degree conscious.
Identifying patients with CMD has important clinical implications for interactions, communication with families and the guidance of therapeutic decisions, according to the study.
Importantly, in prior research, Claassen and colleagues have been able to associate CMD with the recovery of consciousness and long-term recovery of independence in brain-damaged patients.
Researchers have been trying to develop more effective screening methods to identify which patients are likely to be in a state of hidden consciousness. But progress has been hampered by the fact that the brain mechanisms underlying the phenomenon have remained a mystery. This is where the latest study comes in.
In previous research, Claassen and colleagues found that subtle brainwaves detectable with EEG are the strongest predictor of hidden consciousness and eventual recovery for patients with brain injuries.
Many Patients With Hidden Consciousness Remain Undiagnosed.
For the latest study, the scientists used EEG to examine 107 unresponsive patients with acute brain injury. Almost half of the patients appeared comatose, while one quarter were in a vegetative state—i.e. their eyes were open but they could not follow commands.
The remaining patents were in a minimally conscious state—meaning they could track an examiner with their eyes or look at them but were not able to follow any commands.
Using the EEG, scientists can identify when patients are trying, but are unable, to respond to a command such as “keep opening and closing your right hand.”
This method detected CMD in 21 of the patients. The scientists then analyzed structural MRI brains scans from all the patients.
Using a special analysis technique, the team were able to identify patterns of brain injury that the patients with CMD shared and contrast those to the individuals who did not display signs of hidden consciousness.
The researchers found that all of the CMD patients had intact brain structures related to arousal and command comprehension. This supports the idea that they were able to hear and understand the verbal commands.
But they also found that the CMD patients had damage to brain regions responsible for integrating and carrying out motor commands, which is why they were unable to take action.
“Our study suggests that patients with hidden consciousness can hear and comprehend verbal commands, but they cannot carry out those commands because of injuries in brain circuits that relay instructions from the brain to the muscles,” Claassen said in the statement.
The findings could lead to more frequent and earlier diagnosis of CMD. This, in turn, could help better predict which brain-injured individuals are more likely to recover with rehabilitation, according to the scientists.
More research is required before the approaches documented in the study can be applied to clinical practice. But the latest study shows that it may be possible to screen for CMD using widely available structural brain-imaging techniques.
Due to the technical complexity of CMD detection, at this time it is only available in a few academic centers. As a result, the vast majority of patients with hidden consciousness in the United States and around the world remain undiagnosed.
“Not every critical care unit may have resources and staff that is trained in using EEG to detect hidden consciousness, so MRI may offer a simple way to identify patients who require further screening and diagnosis,” Claassen said in the statement.