Functional MRI can measure patterns of connectivity to determine levels of consciousness in nonresponsive patients with brain injury, according to results from a multicenter, cross-sectional, observational study.
E. Tagliazucchi & A. Demertzi
In consciousness, brain regions communicate with a rich temperament, showing both positive and negative connections (coherence, C; red and blue color respectively), facilitating the exchange of information efficiently. In unconsciousness, brain regions become "idle" and do not connect with each other (coherence around zero, green color).
Blood oxygen level–dependent (BOLD) fMRI showed that brain-wide coordination patterns of high complexity became increasingly common moving from unresponsive patients to those with minimal consciousness to healthy individuals, reported lead author Athena Demertzi, PhD, of GIGA Research Institute at the University of Liège in Belgium, and her colleagues.
“Finding reliable markers indicating the presence or absence of consciousness represents an outstanding open problem for science,” the investigators wrote in Science Advances.
In medicine, an fMRI-based measure of consciousness could supplement behavioral assessments of awareness and guide therapeutic strategies; more broadly, image-based markers could help elucidate the nature of consciousness itself.
“We postulate that consciousness has specific characteristics that are based on the temporal dynamics of ongoing brain activity and its coordination over distant cortical regions,” the investigators wrote. “Our hypothesis stems from the common stance of various contemporary theories which propose that consciousness relates to a dynamic process of self-sustained, coordinated brain-scale activity assisting the tuning to a constantly evolving environment, rather than in static descriptions of brain function.”
There is a need for a reliable way of distinguishing consciousness from unconscious states, the investigators said. “Given that nonresponsiveness can be associated with a variety of brain lesions, varying levels of vigilance, and covert cognition, we highlight the need to determine a common set of features capable of accounting for the capacity to sustain conscious experience.”
To search for patterns of brain signal coordination that correlate with consciousness, four independent research centers performed BOLD fMRI scans of participants at rest or under anesthesia with propofol. Of 159 total participants, 47 were healthy individuals and 112 were patients in a vegetative state/with unresponsive wakefulness syndrome (UWS) or in a minimally conscious state (MCS), based on standardized behavioral assessments. The main data analysis, which included 125 participants, assessed BOLD fMRI signal coordination between six brain networks known to have roles in cognitive and functional processes.
The researchers’ analysis revealed four distinct and recurring brain-wide coordination patterns ranging on a scale from highest activity (pattern 1) to lowest activity (pattern 4). Pattern 1, which exhibited most long-distance edges, spatial complexity, efficiency, and community structure, became increasingly common when moving from UWS patients to MCS patients to healthy control individuals (UWS < MCS < HC, rho = 0.7, Spearman rank correlation between rate and group, P less than 1 x 10-16).
In contrast, pattern 4, characterized by low interareal coordination, showed an inverse trend; it became less common when moving from vegetative patients to healthy individuals (UWS > MCS > HC, Spearman rank correlation between rate and group, rho = –0.6, P less than 1 x 10-11). Although patterns 2 and 3 occurred with equal frequency across all groups, the investigators noted that switching between patterns was most common and predictably sequential in healthy individuals, versus patients with UWS, who were least likely to switch patterns. A total of 23 patients who were scanned under propofol anesthesia were equally likely to exhibit pattern 4, regardless of health status, suggesting that pattern 4 depends upon fixed anatomical pathways. Results were not affected by scanning site or other patient characteristics, such as age, gender, etiology, or chronicity.
“We conclude that these patterns of transient brain signal coordination are characteristic of conscious and unconscious brain states,” the investigators wrote, “warranting future research concerning their relationship to ongoing conscious content, and the possibility of modifying their prevalence by external perturbations, both in healthy and pathological individuals, as well as across species.”
The study was funded by a James S. McDonnell Foundation Collaborative Activity Award, INSERM, the Belgian National Funds for Scientific Research, the Canada Excellence Research Chairs program, and others. The authors declared having no conflicts of interest.
SOURCE: Demertzi A et al. Sci Adv. 2019 Feb 6. doi: 10.1126/sciadv.aat7603.