The brains of people in vegetative, partially conscious, or fully conscious states have differing profiles of activity as revealed by functional magnetic resonance imaging (fMRI), according to a report today (February 6) in Science Advances. The results of the study indicate that, compared with patients lacking consciousness, the brains of healthy individuals exhibit highly dynamic and complex connectivity.
“This new study provides a substantial advance in characterizing the ‘fingerprints’ of consciousness in the brain” Anil Seth, a neuroscientist at the University of Sussex, UK, who was not involved in the project, writes in an email to The Scientist. “It opens new doors to determining conscious states—or their absence—in a range of different conditions.”
A person can lose consciousness temporarily, such as during sleep or anesthesia, or more permanently as is the case with certain brain injuries. But while unconsciousness manifests behaviorally as a failure to respond to stimuli, such behavior is not necessarily the result of unconsciousness.
Some seemingly unresponsive patients, for example, can display brain activities similar to those of fully conscious individuals when asked to imagine performing a physical task such as playing tennis. Such a mental response in the absence of physical feedback is a condition known as cognitive-motor dissociation.
Researchers are therefore attempting to build a better picture of what is happening in the human brain during consciousness and unconsciousness. In some studies, electroencephalography (EEG) recordings of the brain’s electrical activities during sleep, under anesthesia, or after brain injury have revealed patterns of brain waves associated with consciousness. But, says Jacobo Sitt of the Institute of Brain and Spinal Cord in Paris, such measurements do not provide good spatial information about brain activity. With fMRI, on the other hand, “we know where the activity is coming from.”
Sitt and colleagues performed fMRI brain scans on a total of 47 healthy individuals and 78 patients who either had unresponsive wakefulness syndrome (UWS)—a vegetative state in which the patient’s eyes open, but they never exhibit voluntary movement—or were in a minimally conscious state (MCS)—having more complex behaviors, such as the ability to follow an object with their eyes, but remaining unable to communicate thoughts or feelings. The scans were performed by an international team of collaborators at three different facilities in Paris, New York, and Liège, Belgium.
Data from the fMRI scans, which generated roughly 400 images in approximately 20 minutes for each patient, was computationally analyzed for identifiable patterns of activity. Four patterns were reproducibly detected within the data from each facility. And, for two of these patterns, the likelihood of their occurrence in a given individual’s scan depended on diagnosis.
Healthy individuals, for example, were more likely than patients to display pattern 1—characterized by high spatial complexity and interregional connectivity indicating brain-wide coordination. Patients with UWS, on the other hand, rarely displayed pattern 1, most often displaying pattern 4—characterized by low complexity and reduced interregional connectivity. Generally speaking, MCS patients fell somewhere between. The occurrence of patterns 2 and 3 were equally likely across all groups.
The team went on to analyze a second set of 11 patients at a facility in Ontario, Canada. Again the four distinct patterns were detected within the fMRI images. Six of these patients had UWS and predominantly displayed pattern 4, while the remaining five, who had cognitive-motor dissociation, had higher rates of pattern 1, supporting previous evidence for consciousness in these patients.
With such a mix of patients, facilities, scanners, and researchers, the study “had every possibility of failing,” says neuroscientist Tristan Bekinschtein of the University of Cambridge, UK, who did not participate in the research. However, the results were “brutally consistent,” he says.
Having identifiable signatures of consciousness and unconsciousness might ultimately help doctors and families make difficult decisions about continuing life support for vegetative patients, says anesthesiology researcher Anthony Hudetz of the University of Michigan who was not involved with the work. It might also provide insight into whether particular rehabilitation methods or other treatments are working.
“All that hinges on a better understanding of what goes on in the brains of these patients versus healthy or aware [people],” Hudetz says. To that end, this paper “makes a major step forward.”
A. Demertzi et al., “Human consciousness is supported by dynamic complex patterns of brain signal coordination,” Sci Adv, 5: eaat7603, 2019.