Home Human communication Hunting for hidden signs of consciousness in inaccessible patients

Hunting for hidden signs of consciousness in inaccessible patients


Emery Brown, a neuroscientist and anesthesiologist who is the director of the Harvard-MIT program in health sciences and technology, is reserving judgment, waiting for more evidence to arrive. He is wary of letting “theory guide analysis”. Still, Brown admires Massimini for his experiments, his careful analysis of the data, and posting the results for everyone to see.

“What I love about it, when I hear Marcello talk about it, is that he’s a total empiricist,” Brown told me. “He has shown empirically that when brain networks are closed by anesthesia, sleep, or brain injury, you have different complexity patterns than when someone is awake.”

And this empiricism is a compelling argument when PCI values ​​are calculated in real human beings.

Nice consistency

The power of Massimini’s approach is perhaps best represented in a beautifully cohesive graphic drawn from years of testing the technology.

On the graph, PCI values ​​calculated from people known to be conscious or not are recorded as dots separated by a dotted line at the threshold of 0.31. In each case, the maximum PCI scores recorded in dreamless sleep, or under the influence of one of three different anesthetic drugs, are below the line. And for the same people, each of the maximum scores while awake, the dream sleep experience of REM sleep, or under the influence of ketamine (which in anesthetic doses induces a dream state) is above line.

The same is true of almost all of the maximum scores for patients with lock-in syndrome and stroke, who at the time of the study were able to prove their conscience by communicating. Notably, 36 of 38 minimally conscious patients showed high complexity, demonstrating the unprecedented sensitivity of PCI as an objective marker of consciousness.

brain activity
Live TMS-EEG recordings from the brain of the control subject during the experiment.


But nine of the 43 patients previously considered totally unconscious also scored above the line. This raises difficult questions. With no other way to prove their conscience and no way to communicate, these patients represent either PCI’s failure or its horrific promise. Their zap-ZIP responses were similar in quality to people with minimal consciousness, as well as people who are conscious when awake, dreaming, or on ketamine. And in fact, six months after the test, six of those patients improved to the point that they were classified as having low awareness. Someone, it seems, was there after all.

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