Researchers at Columbia University have identified brain injuries that may be at the root of hidden consciousness, a perplexing phenomenon in which brain-injured patients are unable to respond to simple commands, making them appear unconscious despite having some level of awareness.
The observational study findings could aid physicians in identifying brain-injured patients who may have hidden consciousness and in predicting which patients are more likely to recover after rehabilitation.
Hidden consciousness, also known as cognitive motor dissociation (CMD), occurs in 15 to 25 percent of patients with brain injuries resulting from head trauma, brain hemorrhage, or cardiac arrest.
“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,”
said study leader Jan Claassen, MD, associate professor of neurology at Columbia University Vagelos College of Physicians and Surgeons.
Motor Command Analysis
Claassen and colleagues discovered in prior research that the most accurate predictor of cognitive motor dissociation and eventual recovery in unresponsive brain-injured patients is the application of machine learning to EEG data collected during motor command presentation in unresponsive patients.
However, the precise brain pathways that are disrupted in this condition remain unknown.
The researchers examined 107 brain injury patients using EEG in the new study. The technique can detect when patients are attempting but failing to respond to commands like “keep opening and closing your left hand.”
Twenty-one patients had CMD, as determined by the analysis.
The researchers subsequently analyzed structural lesion patterns using MRI scans of each patient.
“Using a technique we developed called bi-clustering analysis, we were able to identify patterns of brain injury that are shared among patients with CMD and contrast to those without CMD,”
said co-lead author Qi Shen, PhD, an expert in machine learning, signal processing, and biostatistics and an associate research scientist in the Claassen lab.
All CMD patients were found to have intact brain structures related to arousal and command comprehension, supporting the theory that they heard and understood the commands but could not carry them out.
A group of cognitive motor dissociation patients had similar lesion patterns in the globus pallidus and putamen. Such patterns have been linked to the anterior forebrain mesocircuit in patients with reversible consciousness disorders.
“We saw that all of the CMD patients had deficits in brain regions responsible for integrating comprehended motor commands with motor output, preventing CMD patients from acting on verbal commands,”
Hidden Consciousness Detection
Researchers may better understand which brain injury patients have cognitive motor dissociation as a result of the findings, which will be useful for clinical trials that support consciousness recovery. More research is needed before these approaches can be used in clinical practice.
However, the study shows that it may be possible to screen for hidden consciousness using widely available structural brain imaging, bringing hidden consciousness detection one step closer to widespread clinical use.
“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,”
- Eva Franzova, et al. Injury patterns associated with cognitive motor dissociation. Brain, 2023; awad197